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\begin{document}

\title{Peak glacial-to-Heinrich-1 changes in Denmark Strait Overflow and
seawater stratification in the Nordic Seas, a switchboard of changes in
Atlantic Meridional Overturning Circulation and the 'Nordic Heat Pump'}



\author[1]{Michael Sarnthein}%
\author[1]{Patrick Blaser}%
\affil[1]{Affiliation not available}%


\vspace{-1em}



  
  \date{May 24, 2024}


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Peak glacial-to-Heinrich-1 changes in Denmark Strait Overflow and
seawater stratification in the Nordic Seas, a switchboard of changes in
Atlantic Meridional Overturning Circulation and the 'Nordic Heat Pump'

Michael Sarnthein\textsuperscript{1)} and Patrick
Blaser\textsuperscript{2)}

\textsuperscript{1)} Institut f\selectlanguage{ngerman}ür Geowissenschaften, University of Kiel,
D-24118 Kiel, Germany

\emph{\textless{}michael.sarnthein@ifg.uni-kiel.de\textgreater{}}

\textsuperscript{2)} ISTE, University of Lausanne, CH-1015 Lausanne,
Switzerland

\emph{\textless{}patrick.blaser@unil.ch\textgreater{}}

ABSTRACT (246 w.)

Today, the sub-surface Denmark Strait Overflow (DSO) and the Iceland
Scotland Overflow form the starting points of Atlantic Meridional
Overturning Circulation and compensate for the poleward flowing
Norwegian and Irminger branches of the North Atlantic surface current
that drive the 'Nordic Heat Pump'. During peak glacial and early
deglacial times, ice sheets on Iceland and Greenland, and ice-induced
isostatic and eustatic sea-level changes reduced the Denmark Strait
aperture and DSO. Nonetheless, extremely high benthic stable carbon and
oxygen isotope values together with very high ventilation ages of bottom
waters reflect a north-south density gradient of intermediate-waters and
persistent flow of partially Arctic-sourced waters through both the
Denmark Strait and the Faeroe Channel, similar to today. The first
arrival of Heinrich -1 meltwaters northwest of Iceland, arriving from
the southwest around 18.4 cal ka, accompanied a tipping point in DSO
circulation, documented by reduced ventilation and ventilation ages, a
3°C warming, and increased radiogenic Nd isotope signatures in sediments
at luff-side Site PS2644. These records suggest a sudden subsurface
incursion of Atlantic intermediate waters across basaltic sediments from
S.E. of Iceland. Deep-water convection off Norway then was replaced by
weak brine water formation, coeval with a breakdown of the 'Nordic Heat
Pump' evidenced by a temperature drop on Greenland. After 16.2 cal. ka,
a major meltwater outbreak from the Barents ice shelf led to modified
Heinrich-1-style circulation until \textasciitilde{}15.1 cal ka.
Vice-versa, the DSO intensified during interstadial and Holocene times,
then causing sediment hiatuses at site PS2644.

KEY WORDS:

Nordic Seas, Deep-water formation, Denmark Strait Overflow, Age control
of Heinrich stadial 1, Nordic Heat Pump, Atlantic Meridional Overturning
Circulation

KEY POINTS:

The Overflow of Nordic Sea's deep waters forms the onset of Atlantic
Meridional Overturning Circulation being enhanced at interstadial times

Sediments off N. Iceland show a joint onset of deglacial meltwater
dilution and 3-degree warming of the Denmark Strait Overflow 18400 yr
ago

Deglacial changes in circulation caused Heinrich Stadial 1, a temporary
end of heat advection to European high latitudes 18400--15000 yr ago

PLAIN LANGUAGE SUMMARY (200 w.)

Differences in salt content of North Atlantic surface waters drive
variations in Nordic Seas' overturning circulation. These form a
switchboard for changes in the oceanic heat transport to North European
high latitudes, the 'Nordic Heat Pump', and for Atlantic Meridional
Overturning Circulation (AMOC). We deduced changes in the Nordic Seas'
overturning circulation during the peak last glacial and early deglacial
from two high-resolution marine sediment cores with centennial-scale age
resolution based on the technique of radiocarbon plateau tuning (22-15
cal. ka). Sediment data suggest that the salinity of surface water,
advected from the North Atlantic, started to drop about 18 400 years
ago. This drop accompanied a 3°C rise in temperature and a drop in
ventilation and radiocarbon ventilation age of Denmark Strait Overflow
waters feeding the AMOC. Also, it paralleled a massive rise in the
radiocarbon reservoir age of surface waters up to 2000 yr and an abrupt
breakdown of Nordic Seas' deep-water convection off Norway. Accordingly,
Atlantic waters were replaced by less saline polar waters, marking a
breakdown of the Nordic Heat Pump and start of 'Heinrich Stadial 1' as
reflected by a coeval cooling documented on top of the Greenland ice
sheet, lasting until \textasciitilde{}15.1 cal. ka.

INTRODUCTION

The Denmark Strait Overflow (DSO; Fig. 1) with its exceptionally high
density plays a key role for \textasciitilde{}50\% of the Atlantic
meridional overturning circulation (AMOC) and thereby, for global
deep-ocean circulation. The DSO is closely associated with the ''Nordic
Heat Pump'', and any changes therefore have major implications for
northern hemispheric climate, moreover, it is crucial for deep-ocean
ventilation and radiocarbon uptake. Today, the flux of DSO is long-term
fairly stable with \textgreater{}3 Sv entering from the southern
Greenland Sea and Arctic Ocean (Brakstad et al., 2023). Further 5 Sv are
entrained into DSO during its overflow in the Irminger Sea to the south
of the Denmark Strait, where a 2.5 km deep descend acts in stabilizing
the DSO (data of Biastoch et al., 2003 and 2021; Kösters, 2004, Kösters
et al., 2005; Kaese \& Oschlies, 2000, Kaese et al. 2003 and refs.
therein)

East of Faroe the DSO is paralleled by the Iceland-Scotland Overflow
Water (ISO), also enfolding \textasciitilde{}1.4--2.4 Sv, being supplied
to the N.E. North Atlantic and subsequently, after having passed the
Charlie Gibbs Fracture Zone, into the AMOC in the western Atlantic
(Hansen et al., 2000; Sessford et al., 2019; Biastoch et al., 2021).

Important characteristics of modern DSO waters are low bottom water
temperatures near -1°C, high bottom water salinities of 34.9 psu, and
densities (\selectlanguage{greek}σ\selectlanguage{english}) of 27.8-28.05 kg/m\textsuperscript{3} for Theta=2\selectlanguage{ngerman}°C at the
bottle neck of the Denmark Strait (Whitehead et al., 1974; Macrander and
Käse, 2007; Haine, 2021). A slight but persistent north-south density
gradient is indicated for the Last Glacial Maximum (LGM, 19--23 thousand
calibrated yr before present; cal. ka) by \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O records
of single specimens of epibenthic foraminifera (Millo et al., 2006) and
confirmed by the distribution pattern of \selectlanguage{greek}ε\selectlanguage{english}\textsubscript{Nd} isotopes, a
tracer of dominantly continental or basaltic sediments overflown by
bottom waters (Larkin et al., 2022; Blaser et al., 2020).

To monitor short-term variations in the DSO over peak glacial-to-early
deglacial climate change (22 - 15 cal. ka; here 'ka' is used for 'kilo
yr ago' in the sense of BP = Before Present = 1950 yr AD) we now employ,
partly refine, and supplement published centennial-scale proxy records
obtained from sediment Core PS2644, a site that marks the southern
margin of the Blosseville Basin, that is the northern funnel to the
Denmark Strait north of westernmost Iceland (Fig. 1; Voelker, 1999;
Millo et al., 2006). We compare the effect and origin of long-term
climate trends and intermittent short, centennial-to-millennial-scale
episodes of major cold spells with episodes of fast climate warming,
regimes in part lasting until today. The very last major Greenland
stadial we redefined as Heinrich Stadial 1a and b (HS-1a and b), in
contrast to a redefinition of stadials proposed by Andrews and Voelker
(2018). On the basis of advanced age control (details are given below)
our definition of HS-1 differs strongly from that previously given by
Hodell et al. (2017) based on sediments from the southern subpolar North
Atlantic.

Moreover, we compare our records with proxy data and circulation models
of stadial and interstadial analogue variations over Marine Isotope
Stage 3 (MIS3) near to the northern entrance of the Denmark Strait as
proposed by Hagen and Hald (2002), Sadatzki et al. (2020), and Sessford
et al. (2018, 2019). The latter authors report on distinct changes in
MIS3 bottom water temperature, which we now try to reproduce for late
MIS2. Sessford et al. (2019) proposed pathways of brine water-induced
intermediate waters that finally might have been funneled into the DSO,
assuming a water column homogenous in the Nordic Seas down to 1500 m.

We test this model by means of a number of multiproxy records from Site
PS2644, compared to pertinent records obtained from outside on the basis
of centennial-scale age resolution (Sarnthein et al., 2020): (i) We
employ records from two neighbor sites at the western margin of the
V\selectlanguage{ngerman}øring Plateau in the eastern Nordic Seas (Fig. 1; GIK23074 and
MD95-211), where brine water formation is widely accepted to have
occurred during HS-1 (Meland et al., 2008; Waelbroeck et al., 2011).
(ii) We compare coeval paleoceanographic records obtained south of
Iceland in the northern North Atlantic (Thornalley et al., 2011; Millo
et al., 2006; Sarnthein et al., 1994).

In this way we focus on minor and major changes in the origin of early
deglacial DSO waters and related changes in the flow geometry of the
eastern Nordic Seas and of North Atlantic intermediate- and deep-water
circulation. Changes in flow geometry were possibly linked to crucial
tipping points in the composition of DSO waters, items to be constrained
in this study. The origin of these changes appears highly important for
a better understanding of past and future trends of the ''Nordic Heat
Pump'' and European climate change (\emph{sensu} Jansen et al., 2020;
Ditlevsen and Ditlevsen, 2023).

OCEANOGRAPHIC WATCHDOG POSITIONS of SITES PS2644 AND GIK23074

Bathymetry and modern patterns of surface and bottom water circulation
in the Denmark Strait (Fig. 1; today: \textasciitilde{}630 m w.d.) are
detailed by Kösters et al. (2004). Macrander et al. (2007) present
details of the modern DSO structure being ruled by geostrophic forcing.
Sediment Core PS2644 lies within the lower portion of the modern plume
funneled into the DSO (Käse et al., 2003). Prior to entering the Denmark
Strait, Norwegian Sea Deep Water (NSDW) today is entrained from both the
Greenland Basin and Arctic Ocean (Brakstad etal., 2023), a scenario to
be traced back over last glacial and early deglacial times 22--15 cal.
ka.

Sediments of Core PS2644 are well suited to monitor past
glacial-to-early deglacial variations in the flow of surface and
deep-water masses since the site lies close to the Polar Front, that is
the mean position of the border of perennial sea ice, the boundary
between the East Iceland Current (EIC) and the nearshore North Iceland
Irminger Current (NIIC) (Fig. 1; Voelker, 1999), while not lying too
close to the Denmark Strait where extreme winnowing due to strong bottom
currents largely prevents any sediment deposition. To achieve an
undisturbed and largely continuous sediment record of past changes in
the geometry of ocean water masses, Site PS2644 at 777 m water depth on
top of a narrow hemipelagic sediment ridge was chosen after careful
selection by means of a high-resolution PARASOUND parametric echosounder
system (Hubberten et al., 1995). As detailed in Voelker (1999) the site
shows a sediment drift free from lateral near-bottom sediment input like
sediment slumps and/or turbidity currents (Fig. 2a; Fig. S1).

Core GIK23074 was retrieved from the western margin of the Vøring
Plateau right below the North Atlantic Current (NAC), but far away from
the Norwegian margin (Fig. 1; Voelker, 1999). The site is marked by
exceptionally high, yet undisturbed hemipelagic sedimentation rates
(25-60 cm /ky; Fig. 2b), thus providing a unique high-resolution (17-50
yr per cm sediment depth) record of ocean history in the eastern Nordic
Seas at 1157 m water depth.

AGE CONTROL and PALEOCEANOGRAPHIC PROXIES

\textbf{Precise age control} of marine sediment records PS2644 and
GIK23074 is essential for constraining the objectives of this study. Age
control has been based on various conventional, correlation-based age
tie points by Voelker (1999) and Voelker et al. (1998 and 2000).
Finally, however, we based our age model on the technique
of\textsuperscript{14}C plateau tuning (Figs. 2a and b) (Sarnthein et
al., 2020 and 2023). The different approaches are listed below:

\selectlanguage{english}* Distinct features in the planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O records were
correlated to apparently analogous age-calibrated \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O
oscillations in ice core records GISP2 and NGRIP, where ages are based
on incremental time scales (Grootes and Stuiver, 1997; Svensson et al.,
2008) (Fig. S1; Voelker, 1999).

* Likewise, distinct variations in \% \emph{Neogloboquadrina
pachyderma}sin (Nps; in ''old'' teminology) served as tracer of
short-term SST changes that were used as stratigraphic markers by
comparison to temperature variations dated in Greenland ice core
records.

* The Vedde volcanic ash layer was used as tracer dated by land plants
at \textasciitilde{}10.31\selectlanguage{ngerman}±50 yr \textsuperscript{14}C ka (= 12.1 cal.
ka) on the basis of ambient plant macrofossils (age revised by Birks et
al., 2017; Bronk Ramsey et al., 2020).

\selectlanguage{english}* Initial age control was established by means of a high-resolution
suite of planktic \textsuperscript{14}C ages in Core PS2644, using the
general assignment of a hypothetical Marine Reservoir Age (MRA) of 400
yr (Voelker, 1999; Voelker et al., 1998). This assumption, however, has
now been subject to major revision (Sarnthein et al., 2015 and 2020) as
shown below.

\selectlanguage{english}* On top of a simple conventional stratigraphic alignment of
planktic\textsuperscript{14}C ages, we further refined the age control
by defining local planktic \textsuperscript{14}C age plateaus and
plateau boundaries that were tuned as cal. age tie points to pertinent
age-calibrated structures in the atmospheric \textsuperscript{14}C
record of Lake Suigetsu (Table 1; Sarnthein et al., 2023). In turn,
Suigetsu age control is based on U/Th-based model ages of Bronk Ramsey
et al., 2020 (details of age derivation in Sarnthein et al., 2020 and
2023) (Figs. 2a and b). We are aware that our approach is in conflict
with allegations of Bard and Heaton (2021) claiming that the approach is
flawed. However, we trust in \textsuperscript{14}C plateau tuning for
various crucial reasons: (i) Different from Bard and Heaton (op. cit.)
we have clearly shown that past centennial to millennial-scale
fluctuations of the atmospheric \textsuperscript{14}C record have been
authentic (Sarnthein et al. (2023). (ii) Our technique of plateau tuning
solely relies on the tuning of a whole suite of \textsuperscript{14}C
plateaus in the atmosphere and a sediment core each (Figs. 2a+b), thus
can clearly distinguish and/or exclude potential fake plateaus in a
sediment core, such as given for Core GIK23074 for the top portion of
HS-1 (Fig. 2b). (iii) Our text (Figs. 4 and 5) is demonstrating two
prominent cases of abrupt deglacial climate change during Heinrich
stadial 1 at 18.4 and 16.2 cal. ka, where the \textsuperscript{14}C
plateau-based age estimates precisely match pertinent estimates based on
the incremental age scale of the North GRIP ice core with less than 100
years deviation, results that are far from incidental and \emph{would
not be revealed} by any other stratigraphic method. (iv) On the basis of
numerous details, we have refuted one-by-one the allegations of Bard and
Heaton (op.cit.), as published in the discussion section of their
article (Grootes and Sarnthein, 2021; Sarnthein and Grootes, 2021),
though ignored by Bard and Heaton.

Calendar-age uncertainties of the atmospheric \textsuperscript{14}C
plateau boundaries employed for our tuning approach hardly exceed
\textasciitilde{}50 to \textasciitilde{}100 yr each. Local MRA of
planktic foraminifers and surface waters were derived from the age
difference between the average \textsuperscript{14}C age estimated for
paired, that is, coeval atmospheric and marine plateaus based
on\textsuperscript{14}C plateau tuning (Sarnthein et al., 2020, and
references therein).

\selectlanguage{english}* In addition, a single U/Th-based cal. age was obtained from a solitary
coral in Core MD95-2011. This age was compared with
the\textsuperscript{14}C ages of paired planktic and benthic
foraminifera specimens (Fig. 3), thereby largely confirming the paired
age estimates and MRA derived on the basis of \textsuperscript{14}C
plateau tuning of the planktic \textsuperscript{14}C record (unpubl.
comm. of Dreger, 2000; thorium/uranium data of Lomitschka and Mangini
{[}1999{]}. The ratio of thorium to uranium in each sample, which yield
the calendar age of the coral, were measured by thermal ionisation mass
spectrometry (TIMS) at the Heidelberger Akademie der Wissenschaften
(Heidelberg, Germany) according to the method outlined by Bollhofer et
al. (1996) and Neff et al. (1999).

\selectlanguage{english}* Sedimentation rates with multi-centennial time resolution were derived
from the age interpolation of sediment sections using the cal. age of
planktic \textsuperscript{14}C plateau boundaries (Fig. 2a and b). The
estimates were widely supported by means of ages independent
of\textsuperscript{14}C plateau tuning such as the linear age
interpolation between conventional age tie points to pertinent ages of
ice core record GISP2 (Voelker, 1999; Fig. S1).

\selectlanguage{english}* To a large extent, Site \textbf{PS2644 lacks modern and Holocene
reference values} for most proxy records employed in this study. Except
for a few cm thick \textsuperscript{14}C-dated sediment layer that forms
the actual core top, a strong DSO flow has hindered any Holocene
sediment deposition and/or led to sediment erosion prevalent over most
of the last \textasciitilde{}15 cal. ka (Voelker, 1999; Kuijpers et al.,
2003).

\selectlanguage{english}* The derivation and constraints of various paleoceanographic proxy
values employed in this study are given in Supplementary Text no. 1.

PS2644: FOUR STRATIGRAPHIC TIME SEGMENTS \textasciitilde{}22--15 cal. ka

The PS2644 sediment section representing LGM and HS-1 times starts and
ends with major \textbf{stratigraphic gaps} prior to
\textasciitilde{}21.9 cal. ka and subsequent to \textasciitilde{}15.1
cal. ka (Fig. 2a). The gaps occur near the end of Greenland Interstadial
(GI) 2 and close to the end of HS1, shortly prior to the Bolling-Allerod
(B/A) interstadial that is lost by erosion or non-deposition (Fig. S1;
Voelker, 1999, and Voelker et al., 2000). This sediment gap is
documented by X-ray radiography as distinct unconformity at 54-53 cm
composite core depth, right below the Vedde Ash layer, 12.6 cal. ka
(\emph{sensu} Voelker, 1999, and Voelker and Haflidason, 2015). The
stratigraphic gaps probably result from enhanced sediment winnowing due
to the constriction of an enhanced inflow to the Denmark Strait near to
its northern entrance.

This peak-glacial-to-early-deglacial sediment record of PS2644 for MIS2
is partitioned into four stratigraphic time segments I through IV that
lasted from 21.8--19.8, 19.8--18.4, 18.4--17.2, and
17.2--\textasciitilde{}15.1 cal. ka, based on epibenthic ventilation
ages, changes in the stable C and O isotope composition of planktic and
epibenthic foraminifera (Nps and mainly \emph{Cibicidoides lobatulus} ),
and less distinct, planktic MRA. The partitioning is also reflected by
the \selectlanguage{greek}ε\selectlanguage{english}\textsubscript{Nd} and Pb isotope records, moreover, by distinct
changes in sedimentation rate (Fig. 4). It is important to note that the
time segments apply to the suite of structures in the proxy records of
both the cores PS2644 near Iceland and GIK23074 from the eastern Nordic
Seas.

\textbf{Time segment (I), 21.8--19.8 cal. ka,} in PS22644 covers the top
portion of the Last Glacial Maximum (LGM; as defined by Mix et al.,
2001), while \textbf{time} \textbf{segment (II) 19.8--18.4 cal.
ka}already reflects the end of the LGM, as suggested by a first major
deglacial rise in eustatic sea level starting at 19.4 cal. ka (based on
purely atmospheric \textsuperscript{14}C ages of Hanebuth et al., 2009).
During segments I and II, sea ice-covered subsurface waters of the East
Greenland Current (EGC) at PS2644 (Sadatzki et al., 2020) are marked by
minimum temperature and peak salinity values as reflected by fairly
persistent planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values of 4.5 %0 and minimum
SST of 3.7\selectlanguage{ngerman}°C based on census counts of planktic foraminifera species
(Pflaumann et al., 2003; Millo et al., 2006). Time segment I shows a
maximum MRA near 2200 yr, that slightly dropped to \textasciitilde{}1900
yr after 19.8 cal. ka (Fig. 4).

During time segment I, bottom waters at PS2644 were marked by a
bipartite population of epibenthic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values. One of
them presents the highest \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values and, despite all
processes of ocean mixing, the highest deep-water ventilation recorded
in the global ocean (Millo et al., 2006; Duplessy et al., 2002), clearly
predominant over 21.8--20.3 cal. ka, when bottom water ventilation ages
reached up to 2500 \textsuperscript{14}C yr.

Radiogenic isotopes in the detrital sediment fraction indicate a mixture
of Arctic and European sources of the sediment, with a reduced
contribution from nearby Iceland (Fig. 4 and 5; Struve et al., 2019;
Larkin et al., 2021; Blaser et al., 2020). We hypothesize that this
could have been caused by the complete glaciation of Iceland and/or a
change in ocean currents shielding the site from Icelandic input.
Interestingly, the authigenic sediment fraction exhibited significantly
more radiogenic signatures in both Nd and Pb. A similar effect has been
observed in front of the Barents Shelf (Struve et al. 2019) and in the
eastern subpolar North Atlantic (ODP980; Crocket et al. 2013) and
attributed to the glacial erosion of terrestrial metal oxides in
Northwest Europe and their supply to the ocean.

During \textbf{time segment} II, after 19.8 cal. ka, the antecedent high
in bottom water ventilation age was short-term replaced by very low ages
of 100-400 yr. North of Iceland they mark an early deglacial incursion
of waters reflecting a direct contact with the atmosphere nearby,
closely resembling ages that already marked the end of GI 2, and more
important, LGM bottom water ages found at Site GIK23074 in the eastern
Nordic Seas. Moreover, we find a distinct rise in radiogenic \selectlanguage{greek}ε\selectlanguage{english}Nd values
of the detritus up to -5, which traces an increased contribution by
Icelandic basalts passed by DSO waters prior to reaching Site PS2644
(Fig. 4), or increased supply through an early deglaciation of parts of
Iceland (\emph{sensu} Crocket et al., 2012).

\textbf{Time segment III, 18.4--17.2 cal. ka,} reflects a phase of
transition, when planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values at PS2644 show a
marked gradual drop by more than 1.5 per mil (Fig. 4). The drop
primarily reflects a drop in sea surface salinity induced by a lateral
advection of meltwaters from southwest, from the Irminger Sea, and thus
records the onset of HS-1. Also, foraminifera census counts reflect a
slight SST rise up to 4\selectlanguage{ngerman}°C (Sarnthein et al., 2001). Over this time,
local MRA dropped to 1670-1780 yr, a value slightly lower than before,
but still reflecting a reduced carbon exchange of sub-surface waters
with the atmosphere, impeded by ongoing perennial sea ice cover. At the
eastern Site GIK23074 MRAs at the onset of time segment III showed an
impressive sudden rise from 1175 yr up to 1900 yr, a level equating that
found at the western Site PS2644 (Figs. 2b and 3).

Like surface waters, bottom waters document a major change near 18.4
cal. ka: The maxima of benthic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values measured on
single epibenthic specimens reveal a rapid,
centennial-scale\textsuperscript{18}O depletion by 0.8 %0, equivalent to
a rise in bottom water temperature of up to 3.4\selectlanguage{ngerman}°C (Fig. 4). At this
time, the data population with extremely high epibenthic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values has disappeared in favor of medium high
values, coeval with a renewed short-term reduction of bottom water
ventilation ages down to 750 yr near 17.5 cal. ka. Once more, \selectlanguage{greek}ε\selectlanguage{english}Nd
signatures in both the detrital and authigenic fractions have increased,
indicating an elevated supply of Icelandic volcanogenic material
overflown by DSO waters prior to reaching Site PS2644 (Fig. 4) or
delivered to the site directly by surface currents such as the North
Iceland Irminger Current (Fig. 1). The contemporaneous
authigenic\textsuperscript{206}Pb/\textsuperscript{204}Pb -based ratios
show a pronounced short-lasting maximum (Fig. 5), which could result
from an increased delivery of Pb glacially eroded from Northwest Europe
18.4-17.0 cal. ka.

\textbf{Time segment IV, 17.2--15.1 cal. ka} (i.e., until the onset of a
major hiatus), presents the full maturation of the HS-1 sub-ice
meltwater regime as reflected by a persistent minimum in planktic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O. Near the very onset, this interval was marked by
a short-term SST peak of 7.5\selectlanguage{ngerman}°C (census counts of planktic foraminifera
species; Fig. 15c of Voelker, 1999). As in antecedent periods, MRA of
1900 years continued. By contrast, paired bottom water ages were as low
as 1100 to 1550 \textsuperscript{14}C years, significantly lower than
during the LGM. As in time segment III, epibenthic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values of bottom water ventilation were modestly
high (0.6-1.4 %0).

The onset of time segment IV shows a remarkable sudden rise in bulk
sedimentation rates at PS2644, almost by a factor of three, with
sediments marked by a high in the concentration of ice-rafted
hematite-stained quartz grains originating from (North-) East Greenland
(Voelker, 1999). At the same time,
detrital\textsuperscript{206}Pb/\textsuperscript{204}Pb ratios decreased
while \selectlanguage{greek}ε\selectlanguage{english}Nd became more radiogenic (Fig. 4), which would agree with an
increased delivery of Tertiary basalt sediment. On the expense of the
''European'' source (Fig. 5) the basalt signal then may have come from
the nearby Iceland-Scotland Ridge east of Iceland, overflown by the
North Iceland Jet, when heading west for Site PS2644. Also, Fig. 5 may
suggest an input of basalt debris from major basalt sources in East
Greenland south of 70\selectlanguage{ngerman}°N. Conversely, however, we regard this east-west
sediment transport as unlikely, since it would need to cross the
(sea-ice covered) frontal systems of the East Greenland Current flowing
toward southwest (Fig. 1).

Altogether, MRAs and bottom water ventilation ages at \textbf{Site
GIK23074} (Fig. 3) reveal a suite of changes in differential
stratification of the eastern Nordic Seas contemporary with that in the
west, at PS2644 (Fig. 1). In addition, however, time segment IV has been
dissected near 16.15 cal. ka by a subsequent major drop in both MRA and
bottom water ventilation age (Fig. 2b and 3). The drops are tied to the
great late-deglacial meltwater outbreak from the Barents Shelf as
documented by a short-term extreme low in planktic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values extending south to the Faeroe Isles
(Weinelt et al, 1991; Voelker, 1999).

DISCUSSION -- LINKAGES BETWEEN CHANGING SOURCES OF DSO WATERS AND
SHORT-TERM CHANGES IN SEA SURFACE SALINITY AND CLIMATE

\emph{In search of differential sources of DSO waters}

Today, DSO source waters are intermediate and deep waters of the
Icelandic and Greenland Seas, that means, convection-induced waters of
North Atlantic sources (NAC), Arctic Ocean waters, and the subsurface
North Iceland Jet (NIJ) (Fig. 1). The isotope composition and
ventilation age of waters feeding the DSO as recorded at Site PS2644
(and by fragmentary records from the southern exit of the Denmark
Strait; Millo et al., 2006) document a number of short-term
millennial-scale changes in circulation geometry (Fig. 4) to be compared
with the modern regime of the overflow. Differential ventilation ages
suggest a distinction of three different modes of DSO water: (1)
Extremely low ages mark the DSO mode 1, both at the very end of GI 2 at
21.8 cal. ka (GICC05 record of Wolff et al., 2010) and at the end of the
LGM between \textasciitilde{}19.5 and 18.7 cal. ka (Mix et al., 2001),
the center of time segment II (Fig. 4). (2) Most of LGM time segment I
displays DSO mode 2 marked by a stable high ventilation age of 2200-2500
years, almost recurring near 18.7--18.4 cal. ka. (3) Finally, time
segments III and IV show DSO mode 3 with an intermediate ventilation age
of 1100-1600 years. Near 17.6--17.3 cal. ka, mode 3 starts with an age
minimum of \textasciitilde{}700-960 years similar to DSO mode 1.
Finally, this mode continued until about 15.1 cal. ka (Fig. 2a), the
base of a sedimentation gap (Voelker 1999).

DSO modes 1 and 2 are paired with two separate, but coeval populations
of epibenthic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values measured on single
foraminifera specimens in each sediment sample, one with 0.8--1.4 %0, one
with 1.4--1.7 %0 (encircled in Fig. 4), an absolute extreme in the
estimates of global ocean ventilation (Millo et al., 2006). In part,
these extreme populations may just represent the product of seasonal to
decadal variability. The highest values suggest that DSO mode-2 waters
then have been entrained from polar regions (Brakstad et al., 2023; in
harmony with a model of Haine, 2021) that are largely bare of any
organic carbon production. Based on data of single foraminifera
specimens, maximum \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values of 5.5 %0 likewise
record extremely low intermediate-water temperatures typical of an
Arctic source (Waelbroeck et al., 2011). Conversely, briefly
intercalated ventilation age minima of DSO mode 1 indicate that a major
portion of these waters then may have originated nearby, likely from
convection in the eastern Nordic Seas, near Site GIK23074, as discussed
below (Fig. 3).

Nd and Pb radiogenic isotope signatures suggest the sediment related to
DSO modes 1 and 2 was largely sourced from northern Europe, Iceland, and
probably, basaltic sediments on the Iceland-Scotland Ridge overflown by
the North Iceland Jet (Figs. 1, 4, and 5). Altogether, DSO modes 1 and 2
may have come close to patterns of modern circulation geometry. The flow
strength of mode 2, however, was probably reduced as suggested by medium
high sedimentation rates at PS2644 (Fig. 4). Conversely, the flow of
mode 1 was probably much stronger. At \textgreater{}21.8 cal. ka, it
resulted in a sedimentation gap and erosional hiatus at Site PS2644,
where the inflow to the DK Strait was constricted like in a funnel. The
enhanced current regime is also documented at the end of GI 2, during
the B/A, and major parts of the Holocene, by contrast to today, where a
thin layer of few cm modern sediment is still preserved
and\textsuperscript{14}C dated (Voelker, 1999).

During time segment 4, features of DSO mode 3 were fundamentally
different from LGM DSO modes 1 and 2. Apart from just medium high
ventilation ages mode 3 shows a broad range of intermediate epibenthic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values (0.6--1.4 %0) that record an attenuated
source water ventilation, possibly due to a modest HS-1 input of
remineralized organic carbon. DSO mode 3 starts with a significant,
almost abrupt 0.8 %0 drop of maximum \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values,
equivalent to a 3.4\selectlanguage{ngerman}°C rise in minimum bottom water temperature, that
occurred near the actual end of a last high in bottom water ventilation
age (Fig. 4). The diverse range of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O data of
epibenthic single species could reflect a broad array of bottom water
temperatures for each sediment sample extending over 1.5--2.0 %0, equal
to about 8\selectlanguage{ngerman}°C. Since this range appears unlikely, it probably includes an
imprint of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O signatures of waters from different
seasons and short-term changing source waters.

Per analogy to the records of PS2644, Sessford et al. (2018) report on
Mg/Ca-based bottom water temperatures for stadial and interstadial
periods over MIS3, analyzed in twin sediment core GS15-198-36CC. Here,
minimum values of 1\selectlanguage{ngerman}° to -1.5°C mark Greenland Interstadials (GI) 5, 6,
7, and GI 8, when bottom waters were formed by convection in the Nordic
Seas, whereas warm temperatures of 2°--4°/ 5°C marked Greenland Stadials
(GS) 4, 5, 7, 8, and the very onset of GI 8. Temperature anomalies
reached up to 6°C and provide crucial evidence for short-term
substantial changes in the origin and circulation geometry of DSO waters
during MIS3, similar to those deduced in our study.

Last but not least, DSO mode 3 goes along with a significant rise in \selectlanguage{greek}ε\selectlanguage{english}Nd
and drop in \textsuperscript{206}Pb/\textsuperscript{204}Pb isotope
ratios, in particular during time segment IV (Figs. 4 and 5). The
proxies form an important tracer of basaltic sediments from Iceland
and/or the Iceland-Scotland Ridge, predominantly passed by mode-3 waters
prior to reaching Site PS2644 (\textasciitilde{}68\selectlanguage{ngerman}°N) at the northern
entrance of the Denmark Strait, similar to the modern track of the
''North Iceland Jet'' (Våge et al., 2011). Less likely, the isotope
ratios may trace East Greenland basalts (S of 70°N) (Peate and Stecher,
2003), since the EGC acts as interjacent barrier (Fig. 1).

During time segment III, the flow strength of DSO mode 3 may have been
similar to that of the preceding mode 2. During time segment IV,
however, it may have decreased significantly or may have even been
negligible, when meltwater advection reached a final maximum and
hemipelagic bulk sedimentation rates at Site PS2644 displayed an abrupt
rise by a factor of 3 to 5 (Fig. 4). The high sedimentation rates were
paired with abundant ice-rafted debris (IRD) rich in hematite-stained
red quartz grains that depict an ongoing flux of Devonian 'Old Red'
sediments picked up by icebergs along the N.E. Greenland margin (N of
72°30'N), hence reflect a continued afflux of the EGC (Voelker, 1999).

In search for a hypothetical ultimate source of DSO mode 3 waters during
HS-1, sediment proxies provide several independent lines of evidence for
a link to the topmost intermediate and/or subsurface waters in the (then
possibly sea-ice covered) Atlantic south and southeast of Iceland: (i)
Their dominant minimum epibenthic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values of
0.6-0.9 %0 reflect bottom waters far less ventilated during HS-1 than the
output of peak glacial DSO modes 1 and 2. However, they largely resemble
the low \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values of 0.2 - 0.9 %0 for the coeval DSO
output south of the Denmark Strait (at \textasciitilde{}2000 m w. d.
during late HS-1, in addition to some rare \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C
outliers of single specimens that record local brine water formation in
the Irminger Sea (-0.2 to -1.5 %0; Millo et al., 2006; Hagen and Hald,
2002; Sarnthein et al., 1994). (ii) The ventilation age range recorded
for DSO mode 3 during time segments III and IV (Fig. 4) matches closely
that reported for subsurface and intermediate waters south of Iceland
(Thornalley et al., 2011). (iii) Though \emph{per se} largely unknown,
the minimum temperatures of topmost Atlantic Intermediate Waters (that,
as we surmise, crossed the western Iceland-Scotland Ridge with the NIJ
at depths of \textless{}200 m w. d.) have definitely been much higher
than those of polar waters probably entrained at Site PS2644 along with
LGM DSO modes 1 and 2 (e.g., coeval abrupt 1-%0 drop of HS-1 benthic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values at Site SO82-5 south of Iceland,
\textasciitilde{}1400 m w.d.; van Kreveld et al., 2000) and per analogy
to today. (iv) As outlined above, the highly radiogenic \selectlanguage{greek}ε\selectlanguage{english}Nd values of
DSO mode 3 could mean an antecedent passage over basaltic sediments as
found on the Iceland-Faeroe Ridge and northern slope of Iceland, defined
as ''North Iceland Jet'' by V\selectlanguage{ngerman}åge et al. (2011), which today supplies
almost half of the total DSO flow rate (Figs. 1 and 6).

\emph{Variable DSO modes linked to short-term changes in surface water
composition}

On centennial timescales, the immense shift from peak glacial DSO modes
1 and 2 to deglacial mode 3 was directly paired with the distinct onset
of a \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O depletion of (sub-) surface waters at
PS2644. It started right at the base of deglacial time segment III, 18.4
cal. ka, subsequent to a long-term constant LGM \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O
maximum near \textasciitilde{}4.5 %0 that had prevailed since
\textasciitilde{}22.0 cal. ka (Fig. 4). The start of a gradual decrease
in planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O by up to 1.5 %0 displays the onset of
both warmer and meltwater-diluted surface waters advected through the
Denmark Strait, a precursor of the North Iceland branch of the Irminger
Current. After 17.2 cal. ka, the shift resulted in an SST rise by
2\selectlanguage{ngerman}°--4°C during time segment IV (based on census counts of planktic
foraminifera of Voelker, 1999; Pflaumann in Sarnthein et al., 2001;
Hagen and Hald, 2002). The rise was paired with a meltwater-induced
salinity reduction that necessarily led to continued sea ice cover (You
et al., 2023; Sadatzki et al., 2020). Thus, any local
CO\textsubscript{2} and \textsuperscript{14}C exchange between
atmosphere and surface waters off East Greenland was continuously
suppressed until \textasciitilde{}15.1 cal. ka (Fig. 2a).

\emph{Changing surface waters and deep-water formation in the eastern
Nordic Seas}

In the eastern Nordic Seas, by comparison, planktic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values of 4.6--4.8 %0 did not show any substantial
HS-1 meltwater signal over the LGM and most of HS-1, from 18.4--16.3
cal. ka, except for a minor \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O low
\textasciitilde{}17.6--17.2 cal. ka (by \selectlanguage{greek}Δδ\selectlanguage{english}\textsuperscript{18}\selectlanguage{greek}Ο \selectlanguage{english}= 0.3 %0;
Fig. 2b). Figs. 2b and 3, however, display an almost sudden 2-%0 drop in
the planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O record, that clearly document --
after the first incursion of meltwaters at PS2644 in the west -- a
second major ice and meltwater outbreak during the last 1000 yr of HS-1a
starting at 16.3-16.0 cal. ka (as with the onset of HS-1b, precisely
coeval with a second major HS-1 cooling depicted in Greenland ice cores
GRIP2 and NGRIP). The meltwater signal started from the Barents shelf,
spread south down to Faeroe (Sarnthein et al., 2001). The ice breakout
obviously induced a turbulent mixing down to intermediate waters at Site
GIK23074 at 1157 m w. d. (Fig. 3), and lasted until
\textasciitilde{}14.7 cal. ka. This age estimate on top of HS-1a fits
precisely a \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O depletion found in Greenland records
NGRIP and GISP2 (e.g., Grootes and Stuiver, 1997).

Over time segments I and II, \textbf{eastern surface waters} showed
fairly \textbf{low MRA} of \textasciitilde{}500 to 800 and 1200 yr
(Figs. 2b and 3 that closely resemble MRA values recorded for the very
early LGM by Simon et al. (2023). However, they differed strongly from
the high MRA of 1900-2200 yr obtained from Site PS2644 in the west (Fig.
2a). Starting at 18.4 cal. ka, however, eastern MRA depict a fast rise
to 1730 yr and 2000 yr, rapidly reaching a close match with the MRA
found at western Site PS2644 over time segment III and early segment IV
(Fig. 2b). Accordingly, the differential sense of eastern and western
surface water circulation of time segments I and II ended and was
briefly replaced by a close match during time segments III and IV, when
'old' surface waters with an Arctic origin similar to those of the EGC
had started also to cover the eastern Nordic Seas. Per analogy, we infer
that this advection dominated until \textasciitilde{}16 cal. ka.

During time segment I, extremely \textbf{low bottom water
ventilation}ages at Site GIK 23074 attest lively intermediate-water
convection somewhere close to the site in the eastern Nordic Sea at
least down to \textasciitilde{}1200 m w.d. (Figs. 3 and 6; in harmony
with Meland et al., 2008; Thornalley et al., 2015). In contrast, the
regime at Site PS2644 was stratified. Occasionally, extremely young
intermediate waters of Site GIK23074 found their way from the east up to
the west, at Site PS2644 forming DSO mode 1 during time segment II (Fig.
4), where local deep-water convection continued in the eastern Nordic
Seas, though somewhat attenuated (Fig. 3).

\textbf{After 18.4 cal.} \textbf{ka,} with the start of time segment
III, the circulation geometry of the eastern Nordic Seas was strongly
modified (Fig. 6; modified after Thornalley et al., 2015).
The\textbf{inflow of NAC} stopp\textbf{ed} . It was r eplaced by surface
waters with high and very high MRA at Site GIK23074 / MD95-2311 (1157
m), that closely equate the MRA at Site PS2644 reflecting the EGC.
Hence, the waters were probably Arctic-sourced. Their arrival was
precisely coeval with the start of meltwater incursion through the
Denmark Strait (Figs. 3, 4). Local intermediate and deep-water
convection (\emph{sensu} Siedler et al., 2001) then was replaced by
stable stratification and dominantly seasonal, probably fairly modest
volumes of brine-enhanced shelf waters leading to modest deep-water
formation (Bauch and Bauch 2001; Waelbroeck et al., 2011; Thornalley et
al., 2015). This shift is reflected by a local abrupt rise in bottom
water ventilation ages from \textless{}1000 yr up to 2100-2200 yr, ages
that slightly exceed the paired, likewise strongly raised MRA of surface
waters reaching 1900-2100 yr (Fig. 3). In turn, the great iceberg and
meltwater outbreak from the Barents Sea after 16.3 cal. ka obviously
resulted in local stirring and an immediate overturning and renewed
local ventilation of intermediate waters in the eastern Nordic Seas
(Fig. 3).

Different from a model of Sessford et al. (2019), the brine
water-induced intermediate waters of the eastern Nordic Seas during time
segments III and IV apparently did never spread up to the westernmost
Nordic Seas to replace DSO waters at Site PS2644. Our benthic
ventilation ages and other proxy data suggest that the circulation
geometry of the west was different from today being dominated by the
North Iceland Jet (\emph{sensu} V\selectlanguage{ngerman}åge et al., 2011) that entrained DSO
mode-3 waters from the east along the northern slope of Iceland and
ultimately, from upper North Atlantic Intermediate Waters to the south
and southeast of Iceland.

\emph{Differential DSO modes and Nordic Sea stratification --
Implications for short-term glacial-to-deglacial climate change in the
northern hemisphere}

After \textasciitilde{}18.4 cal. ka (note: before 1950 AD) (Figs. 2a,
4), intermediate waters ultimately derived from upper intermediate
and/or subsurface waters in the North Atlantic started to dominate DSO
mode 3 at Site PS2644 north of Iceland below a layer of highly aged,
less saline, and southward flowing Arctic surface waters. This switch in
bottom water circulation in the Icelandic Sea was precisely coeval (i)
with a very first incursion of meltwaters through the Denmark Strait and
(ii) with a pertinent switch in the geometry of surface and
intermediate-water circulation in the Norwegian Sea, that is, coeval
within the error range of the \textsuperscript{14}C plateau tuning
technique (Figs. 4 and 5) (Sarnthein et al., 2020).

The overall switch from an anti-estuarine to a weakened anti-estuarine
flow regime was almost instantaneous, taking from 18.7-18.39 cal. ka. It
presented a tipping point in circulation geometry of the complete Nordic
Seas, and in turn, of AMOC (e.g., major abrupt rise of MRA near to the
Azores Islands; Balmer and Sarnthein, 2018). Accordingly, the switch
triggered a prompt breakdown of the poleward advection of warm Atlantic
surface waters, that previously had driven the ''Nordic Heat Pump'' up
to northern Norway and Svalbard over peak glacial time segments I and II
per analogy to today, though with somewhat lower SST (based on \% Nps
and Artificial Neural Network = ANN records of Weinelt et al., 2003). We
are confronted with a tipping point in North Atlantic circulation
geometry and climate, that marked already the onset of the HS-1b cold
spell at a very early tie point in deglacial time. Below, the age and
potential time span covered by the oceanographic shift itself are
compared with the climate history constrained by temperature records on
Greenland in ice cores, independently dated with an incremental time
scale based on annual-layer counts.

Based on the NGRIP \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O record (GICC05; Wolf et al.,
2010), the temperatures in North Greenland reflect an overall trend of
gradual deglacial warming from 22 to \textasciitilde{}17 cal. ka (Figs.
4 and 5). The trend, however, was interrupted by a significant first
deglacial breakdown in the advection of warm atmospheric moisture, an
event here named 'HS-1b' that started between 18,500 and 18,380 cal. yr
ago (before 2k). The event was less distinct in ice core GISP2, here
depicted between 18,630 and 18,430 cal. yr b2k (Grootes and Stuiver,
1997). This age range matches within the range of a century the great
switch in seawater stratification of Nordic Sea circulation
independently measured at two different marine sediment records at the
base of time segment III, when dated by means of \textsuperscript{14}C
plateau tuning. \emph{Per se} , the age match may form a proof for the
robustness of \textsuperscript{14}C plateau-based age estimates. Also,
the event is reflected directly by a short
atmospheric\textsuperscript{14}C plateau named '4a' lasting from
\textasciitilde{}18.6 to \textasciitilde{}18.4 cal. kyr before 1950 AD
(Figs. 2a and b; Sarnthein et al., 2023). Based on GICC05 ages, the
fundamental switch in seawater stratification and the resulting drop of
the Nordic heat pump may have taken no longer than 80--100 yr.

Unfortunately, it is widely impossible to compare this narrow age range
with any of the numerous IRD and SST records published for the onset of
HS-1 from the North Atlantic ''Heinrich-1 IRD Belt''. Except for some
sporadic and wide-spaced single age tie points (Hodell et al., 2017, and
refs. therein), local MRA levels and even more so, the precise timing of
their short-term variations are largely unknown due to a lack of
sediment records with absolute datings such as
high-resolution\textsuperscript{14}C plateau tuning. By comparison to
pertinent changes recovered in the Nordic Seas over HS-1 (Figs. 2a and
b) local MRAs may actually have shown short-term variations between 200
and 2000 yr. Also, the age range of meltwater advection and ice-rafted
debris input was subject to major regional variations, while winds and
currents were driving icebergs over vast sea regions. Off southwestern
Portugal, for example, sediment record SHAK06-5K the ages of which were
calibrated by\textsuperscript{14}C plateau tuning (Ausin et al., 2021)
show a \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O-based local meltwater incursion and an IRD
input not starting prior to 17.8/17.9 cal. ka, that is 500-600 yr after
the start of HS-1b, as defined in our Nordic Seas cores. -- During the
Alpine Late Glacial, the HS-1 cold spell is reflected by the well-dated
''Gschnitz Stadial'' that showed temperatures and aridity closely
similar to those estimated for the LGM (Ivy-Ochs et al., 2023).

CONCLUSIONS

* On the basis of the \textsuperscript{14}C PT technique we define a
suite of four peak glacial to early-deglacial time segments from 22-15
cal. ka, that show differential MRAs and bottom water ventilation ages
at two core sites in the western and eastern Nordic Seas.

* On the basis of sediment-based quantitative proxy-data we distinguish
three glacial-to-deglacial modes of Denmark Strait Overflow (DSO), each
of them revealing differences in source region, formation mode, and/or
in flow intensity.

* The proxy records suggest that waters of DSO modes 1 and 2 were
largely fed by a mix of Arctic intermediate waters and deep-water
convection in the eastern Nordic Seas, either reflecting a weaker (mode
2) or stronger and even erosive (mode 1) anti-estuarine flow geometry at
the northern entrance to the Denmark Strait, similar to today.

* Starting at 18.4 cal. ka, the proxy records of time-segments III and
IV show a meltwater-diluted Irminger Current that entered the Denmark
Strait from southwest. It induced an immediate switch to DSO mode 3,
then dominated - as we hypothesize - by subsurface and upper
intermediate waters advected from the northern North Atlantic southeast
of Iceland, hence suggesting a strongly weakened anti-estuarine flow
geometry.

* Near 18.4 cal. ka, the climate tipping point between DSO modes 2 to 3
is marking the onset of Heinrich stadial 1b. This switch in ocean flow
geometry caused a temporary end of the Nordic Heat Pump. The switches
took hardly more than a century, a time span independently confirmed by
incremental age estimates obtained from the Greenland temperature
records of GISP2 and NGRIP.

* The fundamental switch in Nordic Seas flow geometry
\textasciitilde{}18.6--18.4 cal. ka is also reflected by a special
atmospheric \textsuperscript{14}C plateau, by \textsuperscript{14}C
plateau 4a.

* After 16.3 cal. ka, a subsequent meltwater outbreak from the Barents
shelf (Weinelt et al., 1991) caused a major prolongation of the HS-1
flow geometry in the Nordic Seas and further cooling of HS-1, then named
Heinrich stadial 1a until Dansgaard-Oeschger Event 1, independently
documented in Greenland ice core records (\textasciitilde{}16.1 -- 14.7
cal. kyr b2k).

IMPLICATIONS

The onset of cold spell HS-1b forms a scenario enticing to speculate
about potential trends found today and in the near future (e.g., in view
of models of Ditlevsen and Ditlevsen, 2023; Jansen et al., 2020; Caesar
et al., 2018) on the basis of following boundary conditions: (i) Within
few decades the onset of the cold spell near 18.4 cal. ka was found
coeval at two records from Greenland ice cores and two marine sediment
records that showed a fundamental switch from anti-estuarine to modified
sources of anti-estuarine flow geometry in the western and a switch to
weak anti-estuarine in the eastern Nordic Seas and accordingly, also in
AMOC. (ii) The tipping point of seawater stratification was met as soon
as first meltwaters had arrived through the Denmark Strait. (iii) The
switch to estuarine and/or weak anti-estuarine flow geometry in the
Nordic Seas and consequentially, the breakdown of Nordic Heat Pump took
probably less than 100 yr.

In turn, however, we don't have any evidence for the actual source of
these meltwaters somewhere in the Irminger and Labrador Seas. Even less,
we can quantify the past meltwater fluxes needed to trigger the almost
abrupt onset of HS-1b by comparison to meltwater fluxes from Western
Greenland and Baffin Island, that today are admixed to the North
Atlantic Drift and finally may serve as potential origin of a future
tipping point in AMOC geometry. Thus, the analog of the start of HS-1 is
left with open questions.

Data availability

All primary radiocarbon data and cal. ages assigned are stored at
PANGAEA.de\selectlanguage{ngerman}® under ''still to be processed''.

,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,,

ACKNOWLEDGMENTS

We thank Pieter M. Grootes, Kiel, and Antje Voelker, Lisboa, for
substantial critical comments on our manuscript and for references to
recent publications. In particular we thank A. Biastoch, Kiel, for his
advice in potential questions of physical oceanography. We gratefully
acknowledge the help of Ralf Tiedemann, AWI Bremerhaven, with the
acquisition of special additional sediment samples from Core PS2644,
John Southon, Irvine CA, and Gesine Mollenhauer, AWI Bremerhaven, for
analyzing \textsuperscript{14}C ages of benthic foraminifera samples of
Core GIK23074, and Michael Bollen for help with the analysis of Nd and
Pb isotope data at the University of Lausanne. Sebastian Beil, Kiel, and
Hugo Ortner, Innsbruck, kindly helped us with software problems. P.B.
acknowledges funding from the European Union's Horizon 2020 research and
innovation program (grant agreements No 101065424, project OxyQuant).

FIGURE CAPTIONS

Figure 1. Location of twin sites PS2644 and GS15-198-36GC in the
Icelandic Sea (67°52'N, 21°46'W, 777 m w.d.) and twin sites GIK23074 and
MD95-2311 in the Norwegian Sea (66°40'N, 4°54'E, 1157 m w.d.). Yellow
arrows mark warm surface water currents entering the Nordic Seas (NAC:
North Atlantic Current, NIIC: North Iceland Irminger Current), green
arrow shows the EGC. Arrows on top of broken lines depict
intermediate-water currents such as the Denmark Strait Overflow (DSO),
the North Iceland Jet (NIJ), and the Iceland Scotland Overflow Water
(ISO). Bathymetry based on Ocean Data View (Schlitzer, 2002),
highlighted by faint 250-m isoline.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image1/image1}

\end{center}
\end{figure}

Figures 2a and b. Planktic 14C records of sediment cores PS2644 and
GIK232074 plotted vs. core depth; for core locations see Fig. 1.
Planktic 14C plateaus (horizontal boxes) are compared to atmospheric
(atm) 14C plateau suite of Lake Suigetsu (Bronk Ramsey et al., 2020),
where calendar ages of plateau boundaries (and average atmospheric 14C
ages) are given below in cal. ka BP (before 1950 AD). Atmospheric
plateau 4a directly reflects the switch in Nordic Seas flow geometry
\textasciitilde{}18.6--18.4 cal. ka (before 1950 AD). Local planktic
reservoir ages (in blue) result from the difference between the average
raw 14C age of planktic 14C plateaus measured in the core and the 14C
age of equivalent atmospheric \textsuperscript{14}C plateaus numbered 1
-- 6 (numbers in brackets). Top panel shows units of the 1st derivative
(14C yr per m core depth) and 1-\selectlanguage{greek}σ \selectlanguage{english}uncertainty range, with high values
indicating 14C jumps and 14C plateaus (numbered in red) constrained at
'half-height' by asterisks (as defined in Sarnthein et al. 2015). Green
dots display paired benthic \textsuperscript{14}C ages. B/A =
B\selectlanguage{ngerman}ølling-Allerød; HS-1a+b = Heinrich Stadial 1 a and b; LGM = Last
Glacial Maximum. Sedimentation rates are based on cal. ages of 14C
plateau boundaries. Red dotted line in Fig. 2b shows local planktic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O record of \emph{N. pachyderma} sin. (Voelker,
1999)\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image2/image2}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image3/image3}

\end{center}
\end{figure}

Figure 3. Top panel: NGRIP \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O record vs. cal. ka b2k
(GICC05, Wolff et al., 2010) as reference to centennial-scale climate
changes in the northern hemisphere. Second panel: Prominent late-HS-1
minimum in planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O record of Core GIK23074
records meltwater breakout from Barents Shelf ice, also reflected by a
distinct cooling of HS-1a (topmost panel). Third panel: Planktic
reservoir ages (''MRAs''; blue) and benthic ventilation age records
(red) of sediment core GIK23074 document peak glacial-to-deglacial
changes in surface and bottom water oceanography in the Norwegian Sea 23
-- 13 cal. ka (before 1950 AD). Benthic \textsuperscript{14}C ages are
based on specimens of \emph{Cribrononion teretis} only. Blue and red
asterisks mark two cal. age estimates of planktic and benthic
foraminifera based on paired U/Th ages of a solitary coral (Dreger,
1999, plus unpubl. written comm. 2000). Lowermost panel: Planktic
reservoir ages (''MRAs''; blue) and benthic ventilation age records
(red) of sediment core PD2644 document peak glacial-to-deglacial changes
in surface and bottom water oceanography in the Icelandic Sea 22 -- 15
cal. ka (before 1950 AD). Benthic \textsuperscript{14}C ages are based
on specimens of epibenthic\emph{Cibicidoides lobatulus} . ---- Roman
numbers show time segments I to IV. Note, age scales of GIK 23074 and
PS2644 records have not been aligned to the age scale of NGRIP but are
independently based on atmospheric \textsuperscript{14}C plateau tuning.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image4/image4}

\end{center}
\end{figure}

Figure 4. Comparison of various proxy records from sediment core PS2644
that document peak glacial-to-deglacial changes in surface and bottom
water oceanography at the northern entrance of the Denmark Strait 22 --
15 cal. ka (before 1950 AD). Age control based on \textsuperscript{14}C
plateau tuning technique. Top panel shows NGRIP \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O
record of Greenland vs. cal. ka b2k (GICC05; Wolff et al., 2010) as
reference to coeval changes in northern hemisphere climate plotted vs.
planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O record of SST rise and meltwater
dilution of NIIC waters (Voelker, 1999). Roman numbers indicate time
segments I to IV. Panel 2 shows planktic reservoir ages (i.e., MRA; red
broken line), prominent changes in benthic ventilation age (blue line;
Sarnthein et al., 2020), and two separate populations of epibenthic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values obtained from single foraminifera tests
(Voelker, 1999). Panel 3 depicts epibenthic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O
values of single foraminifera tests (Voelker, 1999), where a 0.8 shift
in maximum \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O reflects an abrupt 3.4\selectlanguage{ngerman}°C rise in
minimum bottom water temperature near 18.4 cal. ka. Panel 4 shows
gradual rise in the radiogenic \selectlanguage{greek}ε\selectlanguage{english}\textsubscript{Nd} portion of Nd
isotopes of authigenic and detrital sediment fractions as compared to
modern and mid-Holocene (''Oetzi time'' \textasciitilde{}5.7 cal. ka)
values (Kutschera, 2002). Panel 5 shows variations in authigenic and
detrital Pb206/Pb204 ratios. Panel 6 gives changes in bulk sedimentation
rate (cm/kyr) as derived from cal. ages obtained by means of
the\textsuperscript{14}C plateau tuning technique (Sarnthein et al.,
2020).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image5/image5}

\end{center}
\end{figure}

Figure 5. Authigenic and
detrital\textsuperscript{206}Pb/\textsuperscript{20}4\selectlanguage{english}Pb ratios vs. eNd
at Site PS2644 and potential sediment sources. PS2644 data are symbols
indicate different time segments as described in the text. The Holocene
sample was derived from a combination of eNd data at the core top and Pb
isotope data from an ash layer at 18 cm depth, since the core top
appeared to be contaminated by strongly unradiogenic anthropogenic lead.
Potential end members are indicated as shaded areas (Crocker et al.,
2016; Crocket et al., 2012; Eisenhauer et al., 1999; Fagel et al., 2002;
Farmer et al., 2003; Haley et al., 2008; Kempton et al., 2000; Peate and
Stecher, 2003; Struve et al., 2019). Data from ODP Site 980 in the
Northeast Atlantic are from authigenic sediment fractions only.
Greenland isotopic ratios span large ranges outside the limits of the
figure.\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image6/image6}

\end{center}
\end{figure}

Figure 6. Scheme showing vertical transects of hypothetical circulation
geometry across the western and eastern Nordic Seas between North
Atlantic, Greenland-Island (GI) / Island-Scotland (I-S) Ridge, and Fram
Strait (schemes modified from Thornalley et al., 2015), showing deep-
and intermediate-water convection separately for the eastern (lower
panel) and western (upper panel) Nordic Seas. Grey arrow colors indicate
brine water-induced intermediate waters and weak anti-estuarine
overflow. Transect (A) for LGM, transect (B) for HS-1 times starting at
18.4 cal. ka. Red asterisks: Core sites PS2644 and 23074. Red numbers
give prime evidence, the range of local planktic reservoir ages (MRA)
and benthic ventilation ages. Pertinent MRA and bottom water ventilation
ages for core sites RAPID-10-1P and RAPID-17-5P south of the
Iceland-Scotland Ridge are from Thornalley et al. (2011). SSDW =
Southern Source Deep Water, GA SSW = Glacial Atlantic Southern Source
Waters, NIJ = North Iceland Jet, DSO = Denmark Strait Overflow, ISO =
Iceland Strait Overflow, EGC = East Greenland Current. Estimates of full
and partial sea ice cover for LGM and Heinrich transects are based on
Sadatzki et al. (2019), and Sessford et al. (2019).

Note, in our view, MRAs and benthic ventilation ages listed by
Thornalley et al. (2011 and 2015) and in part incorporated in Fig. 6B
may not reflect true past values (1) because of a lack of precise atm.
age calibration (leading to little evidenced MRAs), (2) since a majority
of age samples were based on \emph{Pyrgo} , etc. species which are
strongly subject to the bias of ''old'' pore waters in the ambient
sediment (Magana et al., 2010).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image7/image7}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image8/image8}

\end{center}
\end{figure}

Figure S1. Stratigraphic alignment of structures in planktic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O record and various further proxy records of
PS2644, correlated for detailed age derivation to \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O
record of GISP2 dated on the basis of annual-layer counts (copy of
Voelker, 1999).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image9/image9}

\end{center}
\end{figure}

TABLES

Table 1: Listing of planktic and benthic \textsuperscript{14}C ages, age
tie points derived from \textsuperscript{14}C plateau tuning, MRA, and
benthic ventilation ages deduced for sediment cores Core PS2644 (Table
1a) and Core GIK23074 (Table 1b).\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image10/image10}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image11/image11}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image12/image12}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image13/image13}

\end{center}
\end{figure}\selectlanguage{english}
\begin{figure}[H]
\begin{center}
\includegraphics[width=0.70\columnwidth]{figures/image14/image14}

\end{center}
\end{figure}

Table 2: Detrital and authigenic data of radiogenic \selectlanguage{greek}ε\selectlanguage{english}Nd and Pb isotopes
in Core PS2644

(see xlsx-Table 2)

===========================================================

\emph{}

Supplementary Text no.1

\textbf{Derivation of paleoceanographic proxy values}

\textbf{* Reduced sea surface salinity and meltwater dilution} of local
surface and subsurface waters are inferred from strongly reduced
planktic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values of \emph{Neogloboquadrina pachyd}
e\emph{rma} sin. (Nps) that in part also serve as tracer of increased
sea surface temperature (SST) both below an ongoing sea ice cover in the
Icelandic Sea and in the eastern Nordic Seas (Voelker, 1999; van Kreveld
et al., 2000; Sarnthein et al., 2001; Simstich et al., 2003; Sadatzki et
al., 2020).

* \textbf{Straight estimates of SST} are derived from census counts of
planktic foraminiferal species (Pflaumann et al., 2003; Sarnthein et
al., 2001; Voelker, 1999).

* \textbf{The particular minimum of bottom water temperature} (BWT) at
Site PS2644 has been deduced from maximum epibenthic
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values measured on single specimens of
epibenthic\emph{Cibicides lobatulus} and \emph{C. wuellerstorfi} (suppl.
by 0.64 %0 for each value; data of Voelker, 1999). Actually,
interpretation of this record is complex, since each sediment sample is
providing a 1--2 %0 broad array of isotope values as result of seasonal
and/or interannual temperature oscillations, if we assume a widely
constant bottom water salinity. For the interval 22--18.4 cal. ka,
however, the maximum value of each \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O array is
strictly confined to 5.6 %0 per mil, in contrast to the time span
18.4--15.1 cal. ka, where maximum \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values are
confined to 4.8 %0 (Fig. 4). The outlined difference by 0.8-%0 may serve
to constrain a short-term major shift in minimum bottom water
temperature corresponding to \textasciitilde{}3.4\selectlanguage{ngerman}°C (following the
conversion of \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values by Shackleton, 1974;
Ganssen, 1983).

* \textbf{Short-term} \textbf{oscillations} \textbf{of BWT} were also
derived from Mg/Ca ratios of \emph{C. neoteretis} at neighbor Site
GS15-198-36CC for stadials GS4 to GS9 and interstadials GI5-GI8 during
MIS3 (Sessford et al., 2018). The latter temperature record forms a
valuable analog to identify potential differential bottom water sources
assumed for the interstadial scenario of late LGM and the onset and
culmination of stadial HS1.

* \textbf{Different levels of bottom water ventilation} and their
seasonal and/or interannual variability at PS2644 are traced by means of
epibenthic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{13}C values of single specimens of
epibenthic \emph{C. lobatulus} (Fig. 4). Analytical details of measuring
stable C and C isotope data of single specimens are given in Voelker
(1999\emph{).}

* \textbf{Spatial and temporal MRA variations of subsurface
waters}(Table 1) are deduced by means of \textsuperscript{14}C plateau
tuning outlined in the main text and presented in \textsuperscript{14}C
yr (details in Sarnthein et al., 2020). Low MRA serve as tracer of open,
high MRA as tracer of impeded CO\textsubscript{2} exchange surface
waters with the atmosphere. At Site PS2644 the exchange was blocked by
long-term predominant sea ice cover (per analogy to MIS3; Sadatzki et
al., 2020) and by Arctic sourced waters of the EGC (Fig. 2a). Likewise,
MRA at Site GIK23074 are temporarily very high (\textasciitilde{}2000 yr
and more), hence also suggesting a lid of Arctic sourced surface waters
(Fig. 2b).

* \textbf{(Raw, i.e., uncorrected)} \textbf{estimates of ventilation
ages of bottom waters} (Table 1) record their last contact with the
atmosphere and form a robust tracer of deep-water masses since their
last contact with the atmosphere (Matsumoto, 2007). The short-term age
variations are simply deduced from the age difference between paired
epibenthic and planktic \textsuperscript{14}C ages in addition to the
paired planktic MRA (following rules defined by Cook and Keigwin, 2015,
and Sarnthein et al., 2020). Temporal and spatial differences in benthic
ventilation age serve as tracer of a differential origin of bottom
waters either in the Nordic Seas and/or the North Atlantic. Brine
water-derived bottom waters are earmarked by the close affinity of their
ventilation age to paired high planktic MRA and by 'aberrant' light
benthic \selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O values that closely reflect the
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O level of nearby of surface waters freezing during
late summer (Bauch and Bauch, 2001).

* \textbf{The geometry of past bottom water circulation} is further
constrained by authigenic and detrital Nd and Pb isotopes at Site
PS2644. We use both isotope systems together in order to constrain the
provenance of sediment and deep-water currents. However, it is well
established that the authigenic sediment fraction in regions of volcanic
input can be overprinted in situ by detrital contributions of radiogenic
Nd; accordingly, the authigenic Nd isotope data must be interpreted with
caution (Elmore et al., 2011, Blaser et al., 2016). We thus largely
constrain out interpretations on the radiogenic isotope data of the
detrital sediment fraction (see also Struve et al., 2019).

Nd and Pb isotope data were analysed from the same solutions. Sediments
were leached with a weak acid-reductive solution as described by Blaser
et al. (2020) and Blaser et al. (2016). Afterwards the remaining
sediment was digested with an automated micro wave system employing a
mixture of HNO\textsubscript{3} and HBF\textsubscript{4} under high
pressure and temperature. The sample solutions were purified with
established column chromatography methods (Blaser et al. (2016), Gutjahr
et al. (2007)) and their isotopic ratios measured with a Neptune Plus
MC-ICP-MS at the University of Lausanne.

For Nd isotopes, instrument-induced mass fractionation was corrected to
a \textsuperscript{146}Nd/\textsuperscript{144}Nd value of 0.7219. The
corrected \textsuperscript{143}Nd/\textsuperscript{144}Nd ratios were
then normalised to the accepted value of 0.512115 based on repeatedly
measured JNdi-1 standard solutions (Tanaka et al., 2000). Nd isotope
signatures are reported as \selectlanguage{greek}ε\selectlanguage{english}Nd =
({[}(\textsuperscript{143}Nd/\textsuperscript{144}Nd)\textsubscript{sample}/
(\textsuperscript{143}Nd/\textsuperscript{144}Nd)\textsubscript{CHUR}{]}
- 1) * 10,000, where (\textsuperscript{143}Nd/\textsuperscript{144}
Nd)\textsubscript{CHUR} = 0.512638 (Jacobsen and Wasserburg, 1980). The
reproducibility was determined via in-house standard solutions to be 0.3
\selectlanguage{greek}ε\selectlanguage{english}Nd units (2 standard deviations).

Pb isotopes were measured with a Tl-doping technique for exponential
mass bias correction and all three isotopic ratios were normalised to
SRM NBS 981 (Gutjahr et al., 2007, Galer and Abouchami, 1998).
Reproducibilities of \textsuperscript{206}Pb/\textsuperscript{204}Pb
varied between 0.3 and 4.3 * 10\textsuperscript{-3}, which is far
smaller than the variation observed in sediments of Site PS2644 or the
regional end members.

=============================================================

REFERENCES

Andrews, J.T., Voelker, A.H.L. 2018: ''Heinrich events'' (\& sediments):
A history of terminology and recommendations for future
usage.\emph{Quaternary Science Reviews} 187, 31-40.

Ausin, B., Sarnthein, M., Haghipour, N., 2021. Glacial-to-deglacial
reservoir and ventilation ages on the southwest Iberian continental
margin. \emph{Quaternary Science Reviews} , 255, 106818 (1-12 pp.),

Balmer, S., Sarnthein, M. 2018: Glacial-to deglacial changes in North
Atlantic meltwater advection and deep-water formation --
Centennial-to-millennial-scale \textsuperscript{14}C records from the
Azores Plateau. \emph{Geochimica Cosmochimica Acta} , 236, 399-415,
https://doi.org/10.1016/j.gca.2018.03.001.

Bauch, D., Bauch, H. 2001: Last glacial benthic foraminiferal
\selectlanguage{greek}δ\selectlanguage{english}\textsuperscript{18}O anomalies in the polar North Atlantic: A modern
analogue evaluation. \emph{Journal of Geophysical Research} 106 (C5),
9135-9143.

Biastoch, A., Kaese, R.H., Stammer, D.B. 2003: The sensitivity of the
Greenland-Scotland Ridge Overflow to forcing changes. \emph{Journal of
Physical Oceanography} 33, 2307-2319.

Biastoch, A., Schwarzkopf, F.U., Getzlaff, K., R\selectlanguage{ngerman}ühs, S., Martin, T.,
Scheinert, M. Schulzki, T., Handmann, P., Hummels, R., Böning, W.C.
2021: Regional imprints of changes in the Atlantic Meridional
Overturning Circulation in the eddy-rich ocean model
VIKING20X.\emph{Ocean Science} 17, 1177-1211.

Birks, H.H., Gulliksen, S., Haflidason, H., Mangerud, J., Possnert, G.
1996: New radiocarbon dates for the Vedde Ash and Saksunavatn Ash from
western Norway. \emph{Quaternary Research} 45, 119-127.

Blaser, P., Gutjahr, M., Pöppelmeier, F., Frank, M., Kaboth-Bahr, S.,
Lippold, J. 2020: Labrador Sea bottom water provenance and REE exchange
during the past 35,000 years. \emph{Earth and Planetary Science
Letters}542, 116299, 1-12.

Blaser, P., Lippold, J., Gutjahr, M., Frank, N., Link, J.M., Frank, M.,
2016. Extracting foraminiferal seawater Nd isotope signatures from bulk
deep-sea sediment by chemical leaching. \emph{Chemical Geology} 439,
189--204. https://doi.org/10.1016/j.chemgeo.2016.06.024

Bollho\selectlanguage{english}ffer, A., Eisenhauer, A., Frank, N., Pech, D., Mangini, A. 1996:
Thorium and uranium isotopes in a manganese nodule from the Peru basin
determined by alpha spectrometry and thermal ionization mass
spectrometry (TIMS): Are manganese supply and growth
related?\emph{Geologische Rundschau} 85, 577-585.

Brakstad, A, Gebbie, G., V\selectlanguage{ngerman}åge, K., Jeansson, E., Olafsdottir S.R. 2023:
Formation and pathways of dense water in the Nordic Seas based on a
regional inversion. \emph{Progress in Oceanography} 212, 102.981.
doi.org/10.21335/NMDC-1271328906,

Bronk Ramsey, C., Heaton, T.J., Schlolaut, G., Staff, R.A., Bryant,
C.L., Lamb, H.F., Marshall, M.H., Nakagawa, T. 2020: Reanalysis of the
atmospheric radiocarbon calibration record from Lake Suigetsu,
Japan.\emph{Radiocarbon} , doi.org/10.1017/RDC2020/18.

Caesar, L., Rahmstorf, S., Robinson, A., Feulner, G., Saba, V., 2018:
Observed fingerprint of a weakening Atlantic Ocean overturning
circulation. \emph{Nature} 556, 191-196.

Cook M.S. and Keigwin L.D. 2015: Radiocarbon profiles of the NW Pacific
from the LGM and deglaciation: Evaluating ventilation metrics and the
effect of uncertain surface reservoir ages. \emph{Paleoceanography} 30,
174--195.

Crocker, A.J., Chalk, T.B., Bailey, I., Spencer, M.R., Gutjahr, M.,
Foster, G.L., Wilson, P.A., 2016. Geochemical response of the mid-depth
Northeast Atlantic Ocean to freshwater input during Heinrich events 1 to
4. \emph{Quaternary Science Reviews} 151, 236--254.
https://doi.org/10.1016/j.quascirev.2016.08.035

Crocket, K.C., Vance, D., Foster, G.L., Richards, D.A., Tranter, M.,
2012. Continental weathering fluxes during the last glacial/interglacial
cycle: insights from the marine sedimentary Pb isotope record at Orphan
Knoll, NW Atlantic. \emph{Quaternary Science Reviews} 38, 89--99.
https://doi.org/10.1016/j.quascirev.2012.02.004

Ditlevsen, P. and Ditlevsen, S., 2023: Warning of forthcoming collapse
of the Atlantic meridional overturning circulation. \emph{Nature
communications} 14, article no. 4254.

Dreger, D. 2000: Decadal-to-centennial-scale sediment records of ice
advance on the Barents shelf and melt- water discharge into the
north-eastern Norwegian Sea over the last 40 kyr, \emph{D.Sc. Thesis,
Univ. of Ki} el, Kiel, pp. 1--79.

Duplessy, J.-C., Labeyrie, L., Waelbroeck, C. 2002: Constraints on the
ocean oxygen isotopic enrichment between the Last Glacial Maximum and
the Holocene: Paleoceanographic implications. \emph{Quaternary Science
Reviews} 21, 315/330

Eisenhauer, A., Meyer, H., Rachold, V., Tu\selectlanguage{english}tken, T., Wiegand, B., Hansen,
B.T., Spielhagen, R.F., Lindemann, F., Kassens, H., 1999. Grain size
separation and sediment mixing in Arctic Ocean sediments: evidence from
the strontium isotope systematic. \emph{Chemical Geology} 158, 173--188.
https://doi.org/10.1016/S0009-2541(99)00026-1

Elmore, A.C., Piotrowski, A.M., Wright, J.D., Scrivner, A.E., 2011.
Testing the extraction of past seawater Nd isotopic composition from
North Atlantic deep-sea sediments and foraminifera. \emph{Geochemistry,
Geophysics, Geosystems} 12. https://doi.org/10.1029/2011GC003741

\emph{Fagel, N., Innocent, C., Gariepy, C., Hillaire-Marcel, C., 2002.
Sources of Labrador Sea sediments since the last glacial maximum
inferred from Nd-Pb isotopes. Geochimica et Cosmochimica Acta 66,
2569--2581.}

Farmer, G.L., Barber, D., Andrews, J., 2003. Provenance of Late
Quaternary ice-proximal sediments in the North Atlantic: Nd, Sr and Pb
isotopic evidence. Earth and Planetary Science Letters 209, 227--243.
https://doi.org/10.1016/S0012-821X(03)00068-2

Galer, S.J.G., Abouchami, W., 1998. Practical application of lead triple
spiking for correction of instrumental mass discrimination.
Mineralogical Magazine 62 A, 491--492.

Ganssen, G. 1983: Dokumentation von k\selectlanguage{ngerman}üstennahem Auftrieb anhand stabiler
Isotope in rezenten Foraminiferen vor Nordwest
Afrika,\emph{Meteor-Forschungsergebnisse} C37, 1--46.

Grootes, P.M., Stuiver, M.
1997:\textsuperscript{18}O/\textsuperscript{16}O variability in snow and
ice with 10\textsuperscript{-3} to 10\textsuperscript{-5} year time
resolution. \emph{Journal of Geophysical Research} 102 (C12),
26,455-26,470.

Hagen, S. and Hald, M. 2002. Variation in surface and deep-water
circulation in the Denmark Strait, North Atlantic, during marine isotope
stages 3 and 2. \emph{Paleoceanography} 17 (4):13-1 -- 13-16.

Haine, T.W.N. 2021. A conceptual model of polar overturning
circulations. \emph{J. Physical Oceanography} 51, 727-744.

Haley, B.A., Frank, M., Spielhagen, R.F., Fietzke, J., 2008. Radiogenic
isotope record of Arctic Ocean circulation and weathering inputs of the
past 15 million years. \emph{Paleoceanography} 23.
https://doi.org/10.1029/2007PA001486

Hanebuth, T. J. J., Stattegger, K., Bojanowski, A., 2009: Termination of
the Last Glacial Maximum sea-level low-stand: The Sunda-Shelf data
revisited. \emph{Global and Planetary Change} 66, 76-84.

Hansen, B., Østerhus, S. 2000: North Atlantic-Nordic Seas
exchange.\emph{Progress Oceanography} 45, 109-208,
doi.org/10.1016/S0079-6611(99)00052-X

Hodell, D.A., Nicholl, J.A., Bontognali, T.R.R., plus 9 coauthors 2017:
Anatomy of Heinrich Layer 1 and its role in the last
deglaciation.\emph{Paleoceanography} 32, 284-303,
doi:10.1002/2016PA00302.

Hubberten, H.-W. (edit.) 1995: Die Expedition Arktis-X2 mit FS
''Polarstern'' in 1994. \emph{Berichte zur Polarforschung} 174: 186 pp.

Ivy-Ochs, S. (2015): Glacier variations in the European Alps at the end
of the last glaciation. -- \emph{Cuadernos de Investigación Geográfica}
, 41: 295--315.

Jacobsen, S.B., Wasserburg, G.J., 1980. Sm-Nd isotopic evolution of
chondrites. \emph{Earth and Planetary Science Letters} 50, 139--155.

Jansen, E., Hesselberg Christensen, J., Dokken, T., et al., 2020: Past
perspectives on the present era of abrupt Arctic climate
change.\emph{Nature Climate Change} 10, 714-721.

\emph{doi.org/101038/s41558-020-0860-7.}

Kaese, R.H., Oschlies, A. 2000: Flow through Denmark Strait. \emph{J.
Geophysical Research} 105 (28):527,528,546.

Kaese, R.H., Girton, J.B., Sanford, T.B. 2003: Structure and variability
of the Denmark Strait Overflow: Model and observations. \emph{J.
Geophysical Research, Oceans} 108 (C6).

\emph{https://doi.org/10.1029/2002JC001548}

Kempton, P.D., Fitton, J.G., Saunders, A.D., Nowell, G.M., Taylor, R.N.,
Hardarson, B.S., Pearson, G., 2000. The Iceland plume in space and time:
a Sr--Nd--Pb--Hf study of the North Atlantic rifted margin. \emph{Earth
and Planetary Science Letters} 177, 255--271.
https://doi.org/10.1016/S0012-821X(00)00047-9

Kösters, F. 2004. Denmark Strait overflow: comparing model results and
hydraulic transport estimates. \emph{J. Geophysical Research}109:C10011,
DOI 10.1029/2004JC002297

Kösters, F., Käse, R.H., Schmittner, A., Herrmann, P. 2005: The effect
of Denmark Strait overflow on the Atlantic Meridional Overturning
Circulation. \emph{Geophysical Research Letters} 32, L04602,
doi:10.1029/2004GL022112.

Kuijpers, A., Troelstra, S.R., Prins, M.A., et al. 2003: Late Quaternary
sedimentary processes and ocean circulation changes at the southeast
Greenland margin. \emph{Marine Geology} 195: 109-129,

Kutschera, W., Müller, W. 2003: ''Isotope language'' of the Alpine
Iceman investigated with AMS and MS. \emph{Nuclear Instruments and
Methods in Physics Research} B204, 705-719.

Labeyrie, L. D., Duplessy, J.C., Blanc, P.L. 1987: Variations in mode of
formation and temperature of oceanic deep waters over the past 125,000
years, \emph{Nature} 327, 477--482.

Larkin, C.S., M. M. Ezat, R. Spielhagen, H. Bauch, R. Noormets, L.
Polyak, S. Moreton, N.L. Roberts, T. L. Rasmussen, M. Sarnthein, E. T.
Tipper, A. M. Piotrowski, 2022. Resolving Nordic Seas deep-water
formation during the last glacial maximum. -- \emph{Nature geoscience} ,
15, 1-7. doi.org/10.1038/s41561-022-01050-w

Lomitschka, M., Mangini, A. 1999: Precise Th/U-dating of small and
heavily coated samples of deep-sea corals, \emph{Earth and Planetary
Science Letters} 170, 391-401.

Macrander, A., Käse, R.H., Send, U., Valdimarsson, H., Jónsson, S.,
2007: Spatial and temporal structure of the Denmark Strait Overflow
revealed by acoustic observations. \emph{Ocean Dynamics} 57:75-89.

Magana, A.L., Southon, J.R., Kennett, J.P., Brendan Roark E., Sarnthein,
M., Stott, L.D. 2010: Resolving the cause of large differences between
deglacial benthic fauna radiocarbon measurements in the Santa Barbara
Basin. \emph{Paleoceanography} , 25,
PA4102.doi:10.1029/2010PA002011,2010.

Matsumoto, K. 2007: Radiocarbon-based circulation age of the world
oceans, \emph{J. Geophysical Research: Oceans} 112(C9), C09004.
https://doi.org/10.1029/2007JC004095.

Meland, M.Y., Dokken, T.M., Jansen, E., Hevrøy, K., 2008. Water mass
properties and exchange between the Nordic seas and the northern North
Atlantic during the period 23--6 ka: Benthic oxygen isotopic
evidence.\emph{Paleoceanography} 23, doi: 10.1029/2007PA001416.

Millo, C., Ms. Sarnthein, H. Erlenkeuser, 2006: Variability of the
Denmark Strait Overflow during the Last Glacial Maximum.
\emph{Boreas,}35, 50-60.

Mix, A.C., Bard, E. and Schneider, R. 2001: Environmental processes of
the Ice age: Land, oceans, glaciers (EPILOG), \emph{Quaternary Science
Rev} iews 20, 627-658.

Neff, U., Bollho\selectlanguage{english}ffer, A., Frank, A., Mangini, A. 1999: Explaining
discrepant depth profiles of 234U/238U and 230Th\textsubscript{exec} in
Mn-crusts, \emph{Geochemica et Cosmochimica Ac} ta.

Peate, D.W., Stecher, O. 2003. Pb isotope evidence for contributions
from different Iceland mantle components to Palaeogene East Greenland
flood basalts. \emph{Lithos} 67, 39--52.
doi.org/10.1016/S0024-4937(02)00250-5

Pflaumann, U., Sarnthein, M., Chapman, M., d'Abreu, L., plus 10
coauthors 2003: Glacial North Atlantic: Sea-surface conditions
reconstructed by GLAMAP 2000. \emph{Paleoceanography} 18 (3), 1065.

\emph{doi:10.1029/2002PA000774}

Sadatzki, H., Maffezzoli, N., Dokken, T.M., plus 9 coauthors 2020: Rapid
reductions and millennial-scale variability in Nordic Seas' sea ice
cover during abrupt glacial climate changes. \emph{PNAS} 117 (47),
29478-29486.

Sarnthein, M., Winn, K., Jung, S.J., Duplessy, J.C., Labeyrie, L.,
Erlenkeuser, H., Ganssen, G. 1994: Changes in east Atlantic deep-water
circulation over the last 30,000 years: Eight time slice
reconstructions. \emph{Paleoceanography} 9(2), 209--267.

Sarnthein, M., K. Stattegger, D. Dreger, H. Erlenkeuser, P. Grootes, B.
Haupt, S. Jung, T. Kiefer, W. Kuhnt, U. Pflaumann, C. Sch\selectlanguage{ngerman}äfer-Neth, H.
Schulz, M. Schulz, D. Seidov, J. Simstich, S. van Kreveld-Alfane, E.
Vogelsang, A. Völker, M. Weinelt, 2001: Fundamental modes and abrupt
changes in North Atlantic circulation and climate over the last 60 ky -
Concepts, reconstruction, and numerical modelling. - In: P. Schäfer et
al. (eds): \emph{The northern North Atlantic: A changing
environment}(Springer Verlag) 365-410.

Sarnthein, M., Balmer, S., Grootes, P.M., Mudelsee, M. 2015: Planktic
and benthic \textsuperscript{14}C reservoir ages for three ocean basins,
calibrated by a suite of \textsuperscript{14}C plateaus in the
glacial-to-deglacial Suigetsu atmospheric \textsuperscript{14}C
record.\emph{Radiocarbon} 57, 129-151.

Sarnthein, M., Küssner, K., Grootes, P.M., Ausin, B., Eglinton, T.,
Muglia, J., Muscheler, R., Schlolaut, G. 2020. Plateaus and jumps in the
atmospheric radiocarbon record -- Potential origin and value as global
age markers for glacial-to-deglacial paleoceanography, a
synthesis.\emph{Climate of the Past} 16, 2547--2571. URL: doi:
10.5194/cp-16-2547-2020.

Sarnthein, M., Grootes, P.M., Mudelsee, M. 2023. Centennial to
millennial-sale fluctuations of the Lake Suigetsu
atmopsheric\textsuperscript{14}C record represent real
\textsuperscript{14}C features over last glacial-to-deglacial times.
\emph{Radiocarbon} 65 (4), DOI:10.1017/RDC.2023.47.

Schlitzer, R. 2002: Interactive analysis and visualization of geoscience
data

with Ocean Data View, \emph{Comput. Geoscience} 28, 1211-1218.

Sessford, E.G., Tisserand, A.A., Risebrobakken, B., Andersson. C.,
Dokken, T., and Jansen E. 2018: High-resolution benthic Mg/Ca
temperature record of the intermediate water in the Denmark Strait
across D-O stadial-interstadial cycles. \emph{Paleoceanography and
Paleoclimatology} 33, 1169-1185. doi.org/10.1029/2018PA003370

Sessford, E.G., Jensen, M.F., Tisserand, A.A., Muschitiello, F., Dokken,
T., Nisancioglu, K.H., and Jansen, E., 2019: Consistent fluctuations on
intermediate water temperature off the coast off Greenland and Norway
during Dansgaard-Oeschger events, \emph{Quaternary Science Reviews} 223,
105887, 1-17.

Shackleton, N.J., 1974: Attainment of isotopic equilibrium between ocean
water and the benthonic foraminifera genus \emph{Uvigerina} : Isotopic
change in the ocean during the last Glacial, \emph{Colloques
Internationaux du C.N.R.S} . 219: 203-209.

Siedler, G., Church, J., Gould, J. (eds.) 2001: \emph{Ocean circulation
and climate. Observing and modelling the global ocean.} Academic Press
San Diego - New York, 1-715.

Simon, M.H., Rutledal, S., Menviel, L., Zolles, T., Haflidason, H.,
Born, A., Berben, S.M., Dokken, T.M. 2023: Atlantic inflow and low
sea-ice cover in the Nordic Seas promotes Fennoscandian Ice Sheet growth
during the Last Glacial Maximum. \emph{Communications Earth and
Environment} 4, 385, doi.org/10.1038/s43247-0223-01032-9.

Struve, T., Roberts, N.L., Frank, M., Piotrowski, A.M., Spielhagen,
R.F., Gutjahr, M., Teschner, C., Bauch, H.A. 2019: Ice-sheet-driven
weathering input and water mass mixing in the Nordic Seas during the
last 25,000 years. \emph{Earth and Planetary Science Letters} 514,
108-118.

Svensson, A., Andersen, K.K., Bigler, M., Clausen, H.B., Dahl-Jensen,
D., Davies, S.M., Johnsen, S.J., Muscheler, R., Parrenin, F., Rasmussen,
S.O., Röthlisberger, R., Seierstad, I., Steffensen, J.P., and Vinther,
B.M. 2008: A 60,000-year Greenland stratigraphic ice core
chronology,\emph{Climate of the Past} 4, 47--57.

Tanaka, T., Togashi, S., Kamioka, H., Amakawa, H., Kagami, H., Hamamoto,
T., Yuhara, M., Orihashi, Y., Yoneda, S., Shimizu, H., Kunimaru, T.,
Takahashi, K., Yanagi, T., Nakano, T., Fujimaki, H., Shinjo, R.,
Asahara, Y., Tanimizu, M., Dragusanu, C., 2000. JNdi-1: a neodymium
isotopic reference in consistency with LaJolla neodymium. Chemical
Geology 168, 279--281. https://doi.org/10.1016/S0009-2541(00)00198-4

Thornalley, D.J.R., Barker, S., Broecker, W.S., Elderfield, H. and
McCave, I.N. 2011. The deglacial evolution of the North Atlantic deep
convection. \emph{Science} \textbf{331} , 202-205.

Våge, K., Pickart, R.S., Spall, M.A., et al. s2011: Significant role of
the North Iceland Jet in the formation of Denmark Strait overflow
water.\emph{Nature geoscience} 4, \emph{DOI: 10.1038/NGEO1234}

Van Kreveld, S., M. Sarnthein, H. Erlenkeuser, P. Grootes, S. Jung, M.J.
Nadeau, U. Pflaumann, and A. Voelker, 2000: Potential links between
surging ice sheets, circulation changes, and the Dansgaard-Oeschger
cycles in the Irminger Sea. \emph{Paleoceanography} 15: 425-442.

Voelker, A. 1999: Dansgaard-Oeschger events in ultra-high resolution
sediment records from the Nordic Seas. \emph{Berichte-Reports Institut
für Geowissenschaften} , University of Kiel, 9, pp. 1-278.

Voelker, A.H.L., P.M. Grootes, M.J. Nadeau, \& M. Sarnthein, 2000: 14C
levels in the Iceland Sea from 25-53 kyr and their link to the Earth's
magnetic field intensity. - \emph{Radiocarbon} 42 (3):437-452.

Voelker, A.H.L., Haflidason, H., 2015: Refining the Icelandic
tephrachronology of the last glacial period -- The deep-sea core PS2644
record from the southern Greenland Sea. \emph{Global and Planetary
Change} 131, 32-62.

Voelker, A., M. Sarnthein, P.M. Grootes, H. Erlenkeuser, C. Laj, A.
Mazaud, M. Nadeau, and M. Schleicher, 1998: Correlation of marine 14C
ages from the Nordic Seas with the GISP2 Isotope record: Implications
for radiocarbon calibration beyond 25 kyr. \emph{Radiocarbon} 40,
517-534.

Waelbroeck, C., Skinner, L.C., Labeyrie, L., Duplessy, J.-C., Michel,
E., Riveiros, N.V., Gherardi, J.-M., and Dewilde, F. 2011: The timing of
deglacial circulation changes in the Atlantic.
\emph{Paleoceanography}26, PA3213, https://doi.org/10.1029/2010PA002007.

Weinelt, M., Sarnthein, M., Vogelsang, E., and Erlenkeuser, H. 1991:
Early decay of the Barents Shelf ice shelf -- Spread of stable isotope
signals across the eastern Norwegian Sea. \emph{Norsk Geologisk
Tidsskift} 71, 137-140.

Weinelt, M., Vogelsang, E., Kucera, M., Pflaumann, U., Sarnthein, M.,
Voelker, A., Erlenkeuser, H., Malmgren, B.A. 2003: Variability of North
Atlantic heat transfer during MIS 2. \emph{Paleoceanograph} y 18, 1-16,
doi:10.1029/2002PA000772

Whitehead, J. A., Leetmaa, A., Knox, R. A. 1974: Rotating hydraulics of
strait and sill flows. \emph{Geophysical Fluid Dynamics} 6, 101--125.

Wolff, E.W., Chappelaz, J., Blunier,T., Rasmussen, S.O., Svensson, A.
2010: Millennial-scale variability during the last glacial: The ice core
record. \emph{Quaternary Science Reviews} 29, 2828-2838.

\emph{doi.org/10.1016/j.quascirev.2009.10.013}

You, D., Stein, R., Fahl, K., Williams, M.C., Schmidt, D.N., McCave,
I.N., Barker, S., Schefuß, Niu, L., Kuhn, G., Niessen, F. 2023: Last
deglacial abrupt climate changes caused by meltwater pulses in the
Labrador Sea. \emph{Communications Earth \& Environment} 4:81.

\emph{doi.org/10.1038/s43247-023-00743-3}

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