Alexandrea Arnold1,3*, John Mering4,
Lauren Santi2-4, Cristian
Román-Palacios3, Huashu Li5,
Victoria Petryshyn6, Bryce
Mitsunaga4, Ben Elliott4, John
Wilson4, Jamie Lucarelli3-4, Ronny
Boch7, Daniel Ibarra8, Lin
Li11, Majie Fan9, Darrell
Kaufman10, Andrew Cohen11, Rob
Dunbar12, James Russell8, Stefan
Lalonde13, Priyadarsi D. Roy14,
Martin Dietzel7, Xingqi Liu5,
Fengming Chang15, Robert A.
Eagle1,3,13,16, and Aradhna
Tripati1-4,13,16
1Department of Atmospheric and Oceanic Sciences,
University of California, Los Angeles, California, USA, Math Science
Building, 520 Portola Plaza, Los Angeles, CA 90024, USA
2Institute of the Environment and Sustainability,
University of California, Los Angeles, LaKretz Hall, 619 Charles E Young
Dr E #300, Los Angeles, CA 90024, USA
3Center for Diverse Leadership in Science, University
of California, Los Angeles, California, USA, 595 Charles E Young Dr E,
Los Angeles, CA 90024, USA
4Department of Earth, Planetary, and Space Sciences,
University of California, Los Angeles, 595 Charles E Young Dr E, Los
Angeles, CA 90024, USA
5College of Resource Environment & Tourism, Capital
Normal University, Beijing 100048, China
6Environmental Studies Program, University of Southern
California, Los Angeles, CA, 3454 Trousdale Pkwy CAS 106, Los Angeles,
CA 90089-0740
7Institut für Angewandte Geowissenschaften, Technische
Universität Graz, Rechbauerstraße 12, 8010 Graz, Austria
8Earth, Environmental, and Planetary Sciences, Brown
University, 324 Brook Street, Providence, RI, 02906
9Department of Earth and Environmental Sciences,
University of Texas at Arlington, Arlington, Texas 76019, USA
10School of Earth and Sustainability, Northern Arizona
University, S San Francisco St, Flagstaff, AZ 86011
11Department of Geosciences, University of Arizona,
1040 E. 4th Street Tucson, AZ 85721
12Department of Earth System Science, Stanford
University, 473 Via Ortega, Building Y2E2, Stanford, CA 94305, USA
13University of Brest, Brest, France, UMR 6538
Laboratoire Géosciences Océan, Institut Universitaire Européen de la
Mer, Technopôle Brest-Iroise, Place Nicolas Copernic, Plouzané 29280,
Brest, France
14Instituto de Geología, Universidad Nacional Autónoma
de México (UNAM), Ciudad Universitaria, 04510 Ciudad de México, México
15Key Laboratory of Marine Geology and Environment,
Institute of Oceanology, Chinese Academy of Sciences, Qingdao 266071,
China
16School of Earth Sciences, School of Geographical
Sciences, University of Bristol, Bristol, BS8 1QU, United Kingdom
Corresponding author: Alexandrea Arnold (ajarnold1@g.ucla.edu) and
Aradhna Tripati (atripati@g.ucla.edu)
Key Points:
- Δ47 calibration dataset for 135 freshwater carbonate
samples shows evidence for material-specificity in
Δ47-temperature dependence.
- Δ47-derived estimates of source water
δ18O usually within 2‰ of modern values.
- We evaluate the impact of calibrations and predictions on
paleotemperature reconstructions.
Abstract
Lacustrine, riverine, and spring carbonates are archives of terrestrial
climate change and are extensively used to study paleoenvironments.
Clumped isotope thermometry has been applied to freshwater carbonates to
reconstruct temperatures, however, limited work has been done to
evaluate comparative relationships between clumped isotopes and
temperature in different types of modern freshwater carbonates.
Therefore, in this study, we assemble an extensive calibration dataset
with 135 samples of modern lacustrine, fluvial, and spring carbonates
from 96 sites and constrain the relationship between independent
observations of water temperature and the clumped isotopic composition
of carbonates (denoted by Δ47). We restandardize and
synthesize published data and report 159 new measurements of 25 samples.
We derive a composite freshwater calibration and also evaluate
differences in the Δ47-temperature dependence for
different types of materials to examine whether material-specific
calibrations may be justified. When material type is considered, there
is a convergence of slopes between biological carbonates (freshwater
gastropods and bivalves), micrite, biologically-mediated carbonates
(microbialites and tufas), travertines, and other recently published
syntheses, but statistically significant differences in intercepts
between some materials, possibly due to seasonal biases, kinetic isotope
effects, and/or varying degrees of biological influence.
Δ47-based reconstructions of water
δ18O generally yield values within 2‰ of measured
water δ18O when using a material-specific calibration.
We explore the implications of applying these new calibrations in
reconstructing temperature in three case studies.
1 Introduction
Paleoenvironmental reconstructions from freshwater sediments can be used
to enhance our understanding of ecosystem and climate change both within
the aquatic systems and their proximal terrestrial environments (e.g.,
Brenner et al., 1999; Xu et al., 2006)). Carbonate-bearing sediments
deposited in freshwater systems are widespread and are sensitive to
changes in the local environment, tectonic setting, and hydrological
conditions, and thus provide a promising archive of continental
paleoclimatic information (Arenas-Abad et al., 2010;
Gierlowski-Kordesch, 2010; Hren & Sheldon, 2012). However, quantitative
terrestrial temperature proxies that can be applied to carbonate
sediments are relatively scarce. Of the multiple proxies that have been
used to estimate terrestrial temperatures with varying degrees of
uncertainty, including soil carbonates, speleothems, fracture veins,
ostracods, trace element ratios in lacustrine sediments, tree rings,
leaf margin analysis, pollen, biomarkers, and noble gasses in
groundwater (Boch et al., 2019; Esper et al., 2018; Gallagher &
Sheldon, 2013; Kaufman et al., 2020; Meckler et al., 2021; Powers et
al., 2010; Stute & Schlosser, 2000; Wilf, 1997; Wrozyna et al., 2022),
only the first five types of proxies are carbonate-associated.
However, work has shown that multiply-substituted carbonate “clumped”
isotope thermometry presents a promising proxy for reconstructing
temperature, based on the thermodynamic exchange of isotopes between
isotopologues of carbonate-containing groups (Ghosh, Adkins, et al.,
2006; Hill et al., 2014; Schauble et al., 2006; Tripati et al., 2015)
with widespread applicability in paleoclimatic, paleohydrological, and
paleoelevation contexts (e.g. Csank et al., 2011; Eagle et al., 2013;
Hren et al., 2013; Huntington et al., 2010, 2015; Huntington & Lechler,
2015; Santi et al., 2020; Tripati et al., 2010, 2014). Theoretical
calculations indicate that measurements of clumped isotopes can be used
for paleothermometery because at equilibrium, the abundance of the
multiply-substituted isotopologue13C18O16O2in carbonates is related solely to the formation temperature of the
mineral (Ghosh, Adkins, et al., 2006; Hill et al., 2014; Schauble et
al., 2006; Tripati et al., 2015), with cooler temperatures favoring
enhanced “clumping” of heavy isotopes within the mineral lattice
(e.g., the forward reaction in Equation 1).
Ca12C18O16O2+ Ca13C16O3 →
Ca13C18O16O2+ Ca12C16O3 (1)
We report the abundance of mass-47 CO2 liberated from
carbonate minerals digested in phosphoric acid (δ47)
compared to a randomized (stochastic) distribution of clumping in a
sample. This excess of13C18O16O is
denoted as Δ47 in Equation 2, where Ri= (mass i/mass 44):
Δ47 (‰) =
[(R47/(R47stochastic)
- 1) -
(R46/(R46stochastic)
- 1) -
(R45/(R45stochastic)
- 1)] × 1000 (2)
An advantage of carbonate clumped isotope derived temperature estimates
is that they are independent of the18O/16O ratio
(δ18O) of the precipitating fluid, as the relevant
isotope exchange reaction (Equation 1) takes place within a single
phase. Carbonate δ18O ratios are simultaneously
measured during clumped isotope analysis and can be combined with
temperature estimates obtained from Δ47 analysis to
calculate δ18O values of water at the time of
carbonate formation (Epstein et al., 1953; Urey, 1947; Vasconcelos et
al., 2005).
Clumped isotopes have been previously used to constrain past lake and
river water temperature (Cheng et al., 2022; Horton et al., 2016; Hudson
et al., 2017; Huntington et al., 2010, 2015; Kele et al., 2015; H. Li et
al., 2021; Petryshyn et al., 2015; L. M. Santi et al., 2020; Wang et
al., 2021). The additional temperature constraint provided from
Δ47 measurements allows for a calculation of the
δ18O of meteoric waters, which can provide constraints
on past hydrology. The Δ47-temperature and
Δ47-derived water δ18O in freshwater
carbonates and other types of terrestrial archives have in turn been
used to evaluate process depiction in climate models (Cheng et al.,
2022; Eagle, Risi, et al., 2013; L. M. Santi et al., 2020; Tripati et
al., 2014), constrain hydrologic parameters (L. M. Santi et al., 2020),
and to constrain paleoaltimetry (e.g., Ghosh, Garzione, et al., 2006;
Huntington et al., 2010, 2015; Ingalls et al., 2017; L. Li et al.,
2019).
However, the accuracy of these reconstructions is fundamentally
underpinned by the calibration(s) used for calculations. The body of
literature for clumped isotope measurements of modern lacustrine and
riverine samples is limited. Only four studies have reported
Δ47-T calibrations (Anderson et al., 2021; Kato et al.,
2019; Kele et al., 2015; H. Li et al., 2021), with three calibrations
being solely derived from freshwater sediments (H. Li et al., 2021:
n=33, Kele et al. 2015: n = 24, Kato et al. 2019: n=33). Most clumped
isotope studies of freshwater carbonates have analyzed a small number of
samples (Anderson et al., 2021; Grauel et al., 2016; Horton et al.,
2016; Hudson et al., 2017; Huntington et al., 2010, 2015; Kato et al.,
2019; Kele et al., 2015; H. Li et al., 2021; Petryshyn et al., 2015; L.
M. Santi et al., 2020; Wang et al., 2021). Of these 11 studies reporting
data for modern freshwater carbonates, five report new data for
<5 samples, while eight have data for <11 samples,
and the remaining four have data consisting of 25-33 samples. The
smaller size of these prior datasets on clumped isotope compositions
means that the community has not been able to explore in detail the
potential for material-specific calibrations, possible influences of
seasonal and temperature bias in carbonate formation, and
non-equilibrium kinetic or pH dependent effects which could
differentially affect different types of carbonates.
Recent work to constrain the Δ47-temperature
relationship has suggested that all carbonates have the same temperature
dependence (i.e., calibration slope), but the calibration intercept may
differ due to mineral-specific phosphoric acid fractionation factors
(Müller et al., 2019; van Dijk et al., 2019). Recent efforts have
advanced practices and improved interlaboratory consistency (Anderson et
al., 2021; Bernasconi et al., 2021; Daëron et al., 2016; Petersen et
al., 2019; Upadhyay et al., 2021), and use of consistent approaches for
standardization and isotope ratio calculations have reduced many offsets
(e.g., Petersen et al., 2019). Petersen et al. (2019) reprocessed 14
calibration studies, encompassing synthetic and natural carbonates,
using updated parameter values for clumped isotope calculations and
found that use of the IUPAC parameters with identical data processing
resulted in increased agreement between calibration lines and a
convergence of slopes within many of the individual studies. From this
synthesis, the authors proposed a ‘universal’, in which one calibration
is derived and applied for all carbonate types. However, it has been
acknowledged that it is uncertain if only one relationship exists, since
despite improvements in data processing and standardization procedures,
differences are still observed (Petersen et al., 2019). Recently, the
“InterCarb” project defined new, community-based standard values for
carbonate clumped isotope standardization, as well as proposed a new
reference frame (I-CDES), which has been shown to help resolve
inter-laboratory differences (Bernasconi et al., 2021). The application
of carbonate standardization and newly defined carbonate standard
values, in concert with developments in data handling procedures
(Daëron, 2021), to reprocessed data from four older calibration studies
has been shown to help resolve the disagreement between their derived
calibration lines (Anderson et al., 2021).
A few studies have suggested statistically significant differences
between calibrations using different types of carbonates (Davies &
John, 2019; Eagle, Eiler, et al., 2013; Henkes et al., 2013; Kele et
al., 2015; Kimball et al., 2016; Müller et al., 2019). Factors such as
seasonality of carbonate growth, the ecology of shell forming organisms,
and kinetic isotope effects relating to different processes in mineral
formation have been shown to broadly influence empirical relationships
between Δ47 measurements and environmental parameters,
including in corals (eg. Ghosh, Adkins, et al., 2006; Kimball et al.,
2016; Saenger et al., 2012; Spooner et al., 2016), echinoids (Davies &
John, 2019), terrestrial gastropods (eg. Dong et al., 2021; Eagle,
Eiler, et al., 2013; Zaarur et al., 2013), as well as synthetic
carbonates (eg. Tang et al., 2014; Tripati et al., 2015), with studies
of slow growing cave carbonates indicating that many if not most
carbonates could express a degree of kinetic isotope effect (Daëron et
al., 2019; Kluge et al., 2014; Tripati et al., 2015).
In this work, we discuss clumped isotope data from 135 samples collected
from 96 sites in modern lakes, rivers, and springs. At present, due to
limited freshwater calibration data, it is unresolved whether the
differences in calibration relationships between different types of
freshwater carbonate materials exist, and whether synthetically-derived
regression parameters are appropriate to use in freshwater samples that
are field-collected. The recently published syntheses from Petersen et
al. (2019) had no freshwater carbonates, and Anderson et al. (2021) had
16 carbonates (tufas and travertines) of which 7 were between T
< 10 oC, and 6 were T > 30oC. This study augments the literature with 159 new
clumped isotope measurements for 25 sites, and additionally incorporates
measurements from published datasets, including samples from 59 sites
that have been recalculated on the new reference frame (Bernasconi et
al., 2021). It includes pairs of measurements from 12 sites that have
been recently reanalyzed (Anderson et al., 2021) and are recalculated on
the new reference frame.
This dataset allows us to investigate clumped isotope signatures in
travertines, micrites, biotic (freshwater mollusks), and biologically
mediated (tufas and microbialites) phases of freshwater carbonate in
order to provide a foundation for intercomparison and calibration of
carbonate clumped isotope results from freshwater systems. Sample
localities within this study are geographically diverse, and include
equatorial, mid-latitude, and polar sites at a variety of elevations and
climates. We evaluate the seasonality of carbonate formation, and
present a composite freshwater calibration and material-specific
calibrations. We assess the potential of this proxy to robustly
reconstruct water temperature and source water δ18O in
both modern and past contexts.
2 Materials and Methods
2.1 Sample and site selection
Samples included in this study are from modern lakes (including playas),
rivers, and springs, from geographically and climatically diverse
settings (Figure 1; Table 1). Carbonate materials included in this
dataset were selected to represent modern lacustrine surface-water
conditions. For lakes, biogenic and biologically-mediated samples
selected for analysis are types that grow nearshore, or occupy the
photic zone above the thermocline; we also selected endogenic carbonate
because formation occurs in surface waters, where evaporation and
photosynthesis have the strongest effect on water chemistry
(Gierlowski-Kordesch, 2010; Hren & Sheldon, 2012; Platt & Wright,
2009).
For this work, we only included localities where modern surface water
temperatures have been measured (Supplementary Table 1). For sites where
multiple years of hydrographic data are available, we report temperature
variability of one standard deviation of the monthly average
temperatures during the typical season of carbonate formation for each
type of carbonate (see Section 3.1). In sites where the average modern
water temperature during the interval of carbonate growth was limited to
data from a short time interval (i.e., less than one year), given that
there is year-to-year variability in temperatures, we report a
temperature uncertainty of two standard deviations of the available
measurements. Some sites within our study are less studied, and if there
was limited temperature information for the water body, such as a
‘summer’ average, or the site has a measured temperature value but
uncertainty was not reported, we use the average standard deviation for
well constrained sample sites in our study (± 2°C).