A document by Sanjit Kumar Jena. Click on the document to view its contents.

Paleosalinity reconstructions of the subsurface Equatorial Indian Ocean (EIO) has been carried out using the Mg/Ca and δ 18 O records of sub Mixed Layer (ML) dwelling planktonic foraminifera T. sacculifer (w/s) from a sediment core SK-312/12 spanning over the last 44 kyr. An assessment of temporal variability in the Arabian Sea High Salinity Water (ASHSW) influx into the EIO during the last glacial-interglacial transition has been obtained. The results provide clear evidence of increased ASHSW influx during the cold glacial period caused by its enhanced formation over the northern AS as a result of intensified NorthEast Monsoon (NEM) activity. Conversely, a decrease in the ASHSW influx during the warm interglacial period took place as a result of reduced ASHSW production, following an intensification in the SouthWest Monsoon (SWM) activity. The Heinrich events (H2 and H3) mark distinct signatures of North Atlantic tele-climatic variability resulted by concurrent increases in the NEM activity. The present study is thus unique to report a maiden record of the Indian Monsoon and the North Atlantic tele-climatic controls upon the temporal production and equatorward distribution of ASHSW during the past geologic time periods. The study also acknowledges the ASHSW as an additional marker of the North Atlanctic tele-climatic influence over the tropical Indian Oceanic paleoclimate as a maiden historic report.

The US Northeast continental shelf “cold pool” comprises winter-cooled Shelf Water that is trapped below the warm surface layer during the stratified season. The regional ecosystem relies on the preservation of winter conditions within the cold pool throughout the year. Here, we present first evidence of a significant increase in the cold pool’s salt content throughout the stratified season, revealed by sustained multi-year observations from the Ocean Observatories Initiative (OOI) Coastal Pioneer Array (2015-2022) and high-resolution realistic regional model output. Cold pool salinification rates of $0.17\,\mbox{PSU/month}$ remain steady throughout the stratified season, leading to salinity differences of over $1\,\mbox{PSU}$ between March and October. The seasonal onshore movement of the US Northeast shelfbreak front cannot explain the salinity increase since seasonal frontal oscillations are too small and not in phase with the salinification signal. Instead, a cold-pool salinity budget reveals that the observed salinification is caused by an imbalance between cross-shelf salt fluxes, which deposit salt into the cold pool at all times of year, and the strong seasonal cycle of vertical mixing. During the stratified season, vertical mixing shuts down and no longer opposes the cross-shelf flux, leading to net salinification of the cold pool over the summer. Along-shelf freshwater advection from upstream contributes little and is only present in the fall. The strong relationship between the seasonal cycle of cold pool salinification and seasonal stratification points toward the importance of the timing of spring re- and fall de-stratification on near-bottom continental shelf conditions.

The long-term North Atlantic Cold Anomaly (Cold Blob) was largely the consequence of three major episodes of low sea surface temperature (SST) in the subpolar North Atlantic in 1972-74, 1984-85 and 1991-94. Each of these episodes correlated with unusually low SST at Flemish Cap (a subsurface island of the Canadian continental shelf 600km east of Newfoundland) and with periods of high sea-ice cover over the deep basin of the Labrador Sea a year earlier. These cold periods at Flemish Cap and the Cold Blob were associated with the advance of sea-ice and icebergs to Flemish Cap, high iceberg counts off the coast of Newfoundland and the appearance of icebergs along the path of the North Atlantic Current (NAC) east of Flemish Cap. Studies of SST anomalies provided evidence for surface connections between Flemish Cap and the CB which utilize part of the NAC pathway. We propose that in the cold periods, residual meltwater from sea-ice and icebergs conveyed in the Labrador Current to Flemish Cap was relayed via the NAC to the subpolar North Atlantic to form the Cold Blob. After 1995, anomalous ice expansion in the Labrador Sea basin greatly diminished, sea-ice and icebergs did not reach Flemish Cap and cold meltwater was no longer transmitted to the subpolar North Atlantic to sustain the Cold Blob. This improved understanding of 20th century meltwater pathways in the North Atlantic may relate to changes in the Atlantic Meridional Overturning Circulation and associated impacts on regional climate in the 21st century.

Reconstructing atmospheric CO2 concentration in the Late Miocene is crucial for understanding the relationship between greenhouse gas concentrations and climate change in a warmer-than-modern world. Both δ11B-based and alkenone-ep-based CO2 estimates feature uncertainties due to poorly constrained past seawater chemistry, and algal physiological processes, respectively. Additionally, both proxies estimate CO2[aq], so they require reliable surface ocean temperatures to calculate solubility and atmospheric CO2. To evaluate proxy coherence, in this study we generate new records of alkenone ep and δ11B, from the western Tropical Atlantic ODP Site 926 during the Late Miocene. We provide surface ocean temperature estimates from coccolith clumped isotope thermometry, alkenone undersaturation ratios, and planktonic foraminiferal Mg/Ca ratios. The warm temperatures estimated from our new clumped isotope records, together with alkenone temperatures >29°C, confirm warm tropics, and provide constraints on the assumptions of seawater Mg/Ca and dissolution corrections for foraminiferal Mg/Ca SST estimates. The new alkenone ep CO2 estimates at 926 yield generally similar CO2 as the new and published δ11B-based CO2 records for the site, and are similar to published alkenone ep CO2 records from the South Atlantic ODP Site 1088. However, over the 7.3 to 7.8 Ma interval, the CO2 values from ep are lower than other records. We evaluate which proxy indicators can best predict variations in algal physiology which may bias the ep-based CO2 reconstructions in this interval at Site 926.

Lakes are sources of nitrous oxide (N2O). However, labor-intensive gas analysis has confined evaluations of temporal variability in lakes to the seasonal time scale. We used a state-of-the-art laser-based N2O analyzer combined with a floating chamber to examine sub-daily variations in N2O emissions from a shallow eutrophic lake in Japan. We conducted intense daytime field campaigns during different seasons to reveal differences in sub-daily variations in N2O emissions from the water surface in conjunction with the dynamics of dissolved N2O concentrations in the lake water. The study revealed that N2O fluxes varied within a day: emissions increased in response to increased wind speeds. Variations in surface dissolved N2O concentrations caused by water mixing were also important during the summer, when accumulation of N2O initially occurred in the lake bottom layer during stably stratified conditions. During winter, the lake water was well mixed and dissolved N2O concentrations were uniform throughout the water column; thus, wind speed was the only factor controlling the diurnal variations in N2O emissions. These findings demonstrate the need to consider diurnal variability when estimating cumulative N2O emissions accurately over long periods.

Climate change is affecting ocean temperature, acidity, currents, and primary production, causing shifts in species distributions, marine ecosystems, and ultimately fisheries. Earth system models simulate climate change impacts on physical and biogeochemical properties of future oceans under varying emissions scenarios. Coupling these simulations with an ensemble of global marine ecosystem models indicates decreasing global fish biomass with warming. However, regional projections of these impacts remain much more uncertain. Here, we employ CMIP5 and CMIP6 climate change impact projections using two Earth system models coupled with four regional and nine global marine ecosystem models in ten ocean regions to evaluate model agreement at regional scales. We find that models developed at different scales can lead to stark differences in biomass projections. On average, global models projected greater biomass declines by the end of the 21st century than regional models. For both global and regional models, greater biomass declines were projected using CMIP6 than CMIP5 simulations. Global models projected biomass declines in 86% of CMIP5 simulations for ocean regions compared to 50% for regional models in the same ocean regions. In CMIP6 simulations, all global model simulations projected biomass declines in ocean regions by 2100, while regional models projected biomass declines in 67% of the ocean region simulations. Our analysis suggests that improved understanding of the causes of differences between global and regional marine ecosystem model climate change projections is needed, alongside observational evaluation of modelled responses.

High-resolution water budget estimates benefit from modeling of human water management and satellite data assimilation (DA) in river basins with a large human footprint. Utilizing the Noah-MP land surface model, in combination with an irrigation module, Sentinel-1 backscatter and snow depth observations, we produce a set of 0.7-km$^2$ digital water budget replicas of the Po river basin (Italy) for 2015-2023. The results demonstrate that irrigation modeling consistently improves the seasonal soil moisture variation and summer streamflow at all gauges in the valley after withdrawal of irrigation water from the streamflow (12\% error reduction relative to observed low summer streamflow), even if the basin-wide irrigation amount is underestimated. Sentinel-1 backscatter DA for soil moisture updating strongly interacts with irrigation modeling: when both are activated, the soil moisture updates are limited, and the simulated irrigation amounts are reduced. Backscatter DA systematically reduces soil moisture in the spring, which improves downstream spring streamflow. Assimilating Sentinel-1 snow depth retrievals over the surrounding Alps and Apennines further improves spring streamflow in a complementary way (2\% error reduction relative to observed high spring streamflow). Despite the seasonal improvements, irrigation modeling and Sentinel-1 backscatter DA cannot significantly improve short-term or interannual variations in soil moisture, irrigation results in a systematically prolonged high vegetation productivity, and snow depth DA only impacts the deep snowpacks. These findings help to advance the design and production of digital water budget replicas for river basins.

This paper addresses the critical aspect of water conservation in public buildings within the context of sustainable urban water resources management. While conventional approaches rely on pricing controls and water-saving appliances, this research emphasizes the key consideration of psychological factors influencing users' willingness to conserve water. Through a survey involving 1,206 volunteers, an expanded theory of planned behavior model is constructed and analyzed to evaluate the impact of water-saving attitudes, subjective norms, self-efficacy, and perceived behavioral control on individuals' water-saving behavior. Intervention experiments conducted in three types of public buildings equipped with smart water meters unveil the nuanced dynamics of real-time water-saving behavior and its responsiveness to external interventions. Findings underscore the collective influence of subjective norms, water-saving attitudes, self-efficacy, and perceived behavioral control on individuals' intentions and behaviors. Noteworthy is the observed time lag and diminishing impact of external interventions, where economic, feedback, and subjective norms interventions prove more effective. This study not only contributes a theoretical framework but also provides practical insights, emphasizing the need for consistent and targeted external interventions. Practitioners, decision-makers, and stakeholders are urged to recognize the profound impact of users' psychological factors on public water-saving behavior and strategically employ interventions for sustained positive outcomes.

The occurrence of cold spells over different regions of North America has been linked to windy extremes over western Europe. These events – termed pan-Atlantic extremes – are mediated by an anomalous state of the North Atlantic storm track. While it is known that the occurrence of European windstorms is modulated by the state of the storm track, the relative contribution of the North American cold spells to European wind extremes is not easy to quantify. In this study, cold spells over two regions of North America are clustered with respect to the evolution of the large-scale circulation over the North Atlantic. The contribution of cold spells to the European wind extremes is then ascertained using circulation analogs, so that different states of the North Atlantic storm track can be compared for days with and without cold spells. Consistent with previous work, two main pathways emerge from the analysis, called “zonal” and “wavy” for simplicity. For a wavy pathway, North American cold spell occurrence is associated with more frequent European wind extremes than expected from the state of the North Atlantic storm track. For the other pathways, on the other hand, the anomalous state of the storm track was able to account alone for the more frequent wind extremes than climatology observed across Europe, with no or little ascertainable contribution from the cold spells. This analysis clarifies the causality of wintertime pan-Atlantic extremes and how these link to different atmospheric dynamical pathways.

Vertical motions associated with mesoscale ocean eddies modulate the light and nutrient environment, stimulating phytoplankton biomass and chlorophyll anomalies. Populations within eddies may be trapped by the horizontal circulation or laterally diluted by mixing with surrounding waters. Conventionally, eddy boundaries are determined using Eulerian methods from daily satellite sea level anomaly fields. However, Eulerian methods do not delineate the bounds of trapped water masses, which is an important consideration when interpreting eddy-induced changes in chlorophyll concentration. Integrated Lagrangian particle tracking methods, on the other hand, more accurately identify coherent structure boundaries that trap fluid masses for time scales relevant to phytoplankton bloom evolution. From two decades of remote sensing observations in the North Pacific Subtropical Gyre, we compared coincident Eulerian and Lagrangian eddy atlases to assess the impact of eddy trapping on chlorophyll concentration. We found more positive chlorophyll anomalies within Lagrangian coherent vortices than in Eulerian eddy boundaries and outside-eddy waters. Yet, there are striking differences seasonally and regionally within the gyre. Chlorophyll is most enriched within coherent boundaries of the Hawaiian Lee eddies and in the region southeast of the Islands in fall and winter. Our results suggest that typical Eulerian analyses underestimate the role of mesoscale eddies in enhancing chlorophyll by not accounting for lateral mixing. Consequently, quantifying the contribution of mesoscale eddies toward open ocean primary production is more complex than previously assumed.

Joanne S. Boden1*, Sanjoy M. Som2,5, William J. Brazelton2,4, Rika E. Anderson3, Eva E. Stüeken11 School of Earth and Environmental Sciences, University of St. Andrews, Bute Building, Queen’s terrace, St. Andrews, Fife, KY16 9TS, United Kingdom2 Blue Marble Space Institute of Science, Seattle, WA, USA3 Department of Biology, Carleton College, Northfield, MN, USA4 School of Biological Sciences, University of Utah, Salt Lake City, Utah, USA5 Space Science and Astrobiology Division, Exobiology Branch, NASA Ames Research Center, Moffett Field, Mountain View, CA, USA* Corresponding author ([email protected])Key Words: Phosphite, serpentinization, hydrothermal vent, metagenomics, Archean, phosphorus, geothermal

Valentí Rull1,2

Analysis of forty years of tide gauge data and reanalysis wind stresses from the Middle Atlantic Bight indicate that along-shelf wind stresses are a dominant driver of coastal dynamic sea level (sea level plus atmospheric pressure) variability at daily to yearly time scales. The sea-level response to along-shelf wind stress varies substantially along the coast and is accurately reproduced by a steady, barotropic, depth-averaged model (Csanady 1978, Arrested Topographic Wave). The model indicates that the sea-level response in the MAB depends primarily on the along-shelf distribution of the along-shelf wind stress, the Coriolis frequency, the bottom drag coefficient, and the cross-shelf bottom slope. The along-shelf wind stress varies along the MAB shelf due primarily to changes in the shelf orientation. The sea-level response depends on both the local and upstream (in the sense of Kelvin wave propagation) along-shelf wind stresses. Consequently, sea-level variability at daily, monthly and yearly time scales along much of the central MAB coast is more strongly driven by upstream winds along the southern New England shelf than by local winds along the central MAB shelf. The residual coastal sea-level variability, after removing the wind-driven response and the trend, is roughly uniform along the MAB coast. The along-coast average of the residual sea level at monthly and yearly time scales is caused by variations in shelf water densities primarily associated with the large annual cycle in water temperature and interannual variations in salinity.

Mesoscale Convective Systems (MCSs) play a critical role in tropical rainfall patterns and circulations. To reduce persistent biases and improve understanding of the climate system, international groups have called for unprecedented investment in global convection-permitting (CP) climate models. It is essential such models accurately represent MCSs, and in particular environmental interactions such as dynamical control by wind shear. We show that in representative current generation CP simulations, MCS updraft entrainment decreases with shear, leading to a realistic increase of extreme rainfall. We find the control of environmental shear extends to mean storm rainfall and anvil heights. The simulation of these effects depends strongly on model physics in both CP and parameterised models. We show that MCS shear response influences the zonal distribution of storm diabatic heating, modifying upscale impacts of convection. Our results demonstrate key tests for focused process-based assessment of CP model fidelity.

Hurricane Nicholas was classified as a Category 1 tropical cyclone (TC) at 0000 UTC on 14 September 2021 and made landfall along the upper Texas Gulf Coast at 0530 UTC with maximum sustained winds of 33 m s-1. Much of the electrical activity during Nicholas was monitored by the Houston Lightning Mapping Array (HLMA) network. Deep convection developed in the rainband at 1700 UTC on 13 September, diminished by 2030 UTC, and re-intensified after 2200 UTC. At 2004 UTC (13 September), a curved megaflash (~220 km) was observed by the HLMA in the stratiform precipitation region of the outer rainband. By 0130 UTC on 14 September 2021, vigorous deep convective cells developed in the eastern eyewall region and propagated cyclonically to the western eyewall region. Several “jet-like” transient luminous events (TLEs) were observed by the HLMA emanating from a deep convective cell in the western eyewall region between 0230-0300 UTC with VHF source points ranging from 30-45 km in altitude. Moreover, the TLEs occurred within a region of strong wind shear, upper-level graupel-ice crystal collisions (~15 km), and strong cloud top divergence. Charge analysis of the deep convection during Nicholas revealed an overall normal dipole structure, while the megaflash and TLE deep convective cases exhibited inverted dipole charge structures. Dissipation of the upper-level screening charge layer resulting from cloud top divergence likely played a role in the observed TLE VHF sources escaping to altitudes exceeding 30 km.

Amidst the time-consuming process of conducting laboratory tests to confirm contamination incidents, utilities must promptly implement measures to mitigate the impact of potential contamination without undue overreaction. This paper proposes a novel approach for mitigating the impact of contamination threats (an unconfirmed contamination event) in smart water networks. By leveraging smart valves, the consumer flows are regulated to create a decreasing pressure gradient from the contamination source to a flushing point, facilitating efficient contamination flushing with minimal consumer inconvenience. The decreasing pressure gradients are formulated as constraints within an online optimization problem. Additionally, two methods for identifying these pressure constraints are presented. To assess the efficacy of the proposed framework, testing is conducted using a realistic water network model.

The X-Ray Sensor (XRS) has been making full-disk observations of the solar soft X-ray irradiance onboard National Oceanic and Atmospheric Administration’s (NOAA) Geostationary Operational Environmental Satellites (GOES) since 1975. XRS provides critical information about the solar activity for space weather operations, and the standard X-ray classification of solar flares is based on its measurements. The GOES-R series of XRS sensors, with the first in the series launched in November 2016, has a completely different instrument design compared to its predecessors, GOES-1 through GOES-15. To provide continuity, the two GOES-R XRS spectral bands remain unchanged providing the solar X-ray irradiance in the 0.05-0.4 nm and 0.1-0.8 nm bands. The changes include using Si photodiodes instead of ionization cells to improve performance, using multiple channels to allow for a wider dynamic range, including quadrant photodiodes for real-time flare location measurements, and providing accurate radiometric calibrations using the National Institute of Standards and Technology (NIST) Synchrotron Ultraviolet Radiation Facility (SURF) in Gaithersburg, Maryland. The design and pre-flight calibration results for this next-generation XRS instrument are presented here in this XRS Paper-1, and in-flight solar X-ray measurements from GOES-16, GOES-17, and GOES-18 are provided in the XRS Paper-2.