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The North Water Polynya (NOW, Greenlandic Inuit: Pikialasorsuaq), Baffin Bay, is the largest polynya and one of the most productive regions in the Arctic. This area of thin to absent sea ice is a critical moisture source for local ice sheet sustenance and coupled with the inflow of nutrient-rich Arctic Surface Water, supports a diverse community of Arctic fauna and indigenous people. Although paleoceanographic records can provide critical insight into the NOW’s past behavior, it is critical that we better understand the modern functionality of paleoceanographic proxies. In this study, we analyzed lipid biomarkers, including algal highly-branched isoprenoids and sterols for sea ice extent and pelagic productivity, and archaeal GDGTs for ocean temperature, in a suite of modern surface sediment samples from within and around the NOW. Our data show that all highly-branched isoprenoids exhibit strong correlations with each other and show highest concentrations within the NOW, which suggests a spring/autumn sea ice diatom source rather than a combination of sea ice and open water diatoms as seen elsewhere in the Arctic. Sterols are also highly concentrated in the NOW and exhibit an order of magnitude higher concentration here compared to sites south of the NOW, consistent with the order of magnitude higher primary productivity observed within the NOW relative to surrounding waters in spring/summer months. Finally, our temperature calibrations for GDGTs and OH-GDGTs reduce the uncertainty present in global temperature calibrations, but also identify some additional variables that may be important in controlling their local distribution, such as nutrient availability and dissolved oxygen. Collectively, our datasets provide new insight into the utility of these lipid biomarker proxies in high-latitude settings and will help provide a refined perspective on the Holocene development of the NOW with their application in downcore reconstructions. [ABSTRACT FROM AUTHOR]

Paleo water isotope records can elucidate how the Arctic water cycle responded to past climate changes. We analyze the hydrogen isotope composition (δ2H) of plant‐derived n‐alkanoic acids (waxes) from Lake Qaupat, Baffin Island, Nunavut, Canada, to assess moisture sources and seasonality during the past 5.8 ka. We compare this record to a sedimentary ancient DNA (sedaDNA)‐inferred vascular plant record from the same lake, aiming to overcome the uncertainty of plant community impacts on leaf waxes. As the sedaDNA record reveals a stable plant community after the colonization of Betula sp. at 6.1 ka, we interpret plant wax δ2H values to reflect climate, specifically mean annual precipitation δ2H. However, the distributions of n‐alkanoic acid homologs suggest that aquatic mosses, which are not represented in the sedaDNA record, may become more abundant towards the present. Therefore, we cannot exclude the possibility that changes in the plant community cause changes in the plant wax δ2H record, particularly long‐chain waxes, which become less abundant through this record. We find that Lake Qaupat mid‐chain plant wax δ2H is enriched coincident with high Labrador Sea summer surface temperature, which suggests that local moisture sources in summer and early autumn have the greatest impact on precipitation isotopes in this region. [ABSTRACT FROM AUTHOR]

Elevated concentrations of organic matter are found in sediments of hadal trenches relative to those found in the abyssal seabed, but the origin of such biological material remains elusive. Here, we report the composition and distribution of cell membrane intact polar lipids (IPLs) in surface sediments around the deepest points of the Atacama Trench and adjacent bathyal depths to assess and constrain the sources of labile organic matter in the hadal seabed. Multiscale bootstrap resampling of IPLs' structural diversity and abundance indicates distinct lipid signatures in the sediments of the Atacama Trench that are more closely related to those found in bathyal sediments than to those previously reported for the upper ocean water column in the region. While the overall number of unique IPL structures in hadal sediments is limited and they contribute a small fraction of the total IPL pool, they include a high contribution of phospholipids with mono- and di-unsaturated fatty acids that are not associated with photoautotrophic sources. The diversity of labile IPLs in hadal sediments of the Atacama Trench suggests the presence of in situ microbial production and biomass that resembles traits of physiological adaptation to high pressure and low temperature, and/or the transport of labile organic matter from shallower sediment. We argue that the export of the most labile lipid component of the organic matter pool from the euphotic zone and the overlying oxygen minimum zone into the hadal sediments is neglectable. Our results contribute to the understanding of the mechanisms that control the delivery of labile organic matter to this extreme deep-sea ecosystem, whereas they provide insights into some potential physiological adaptation of the in situ microbial community to high pressure and low temperature through lipid remodeling. [ABSTRACT FROM AUTHOR]

The North Water Polynya (NOW, Greenlandic Inuit: Pikialasorsuaq), Baffin Bay, is the largest polynya and one of the most productive regions in the Arctic. This area of thin to absent sea ice is a critical moisture source for local ice sheet sustenance and coupled with the inflow of nutrient-rich Arctic Surface Water, supports a diverse community of Arctic fauna and indigenous people. Although paleoceanographic records can provide critical insight into the NOW's past behavior, it is critical that we fully understand the modern functionality of the paleoceanographic proxies beforehand. In this study, we analyzed lipid biomarkers, including algal highly-branched isoprenoids and sterols for sea ice extent and pelagic productivity, and algal alkenones and archaeal GDGTs for ocean temperature, in a suite of modern surface sediment samples from within and around the NOW. Our data show that all highly-branched isoprenoids exhibit strong correlations with each other and show highest concentrations within the NOW, which suggests a spring/autumn sea ice diatom source rather than a combination of sea ice and open water diatoms as seen elsewhere in the Arctic. Sterols are also highly concentrated in the NOW and exhibit an order of magnitude higher concentration here compared to sites south of the NOW, consistent with the order of magnitude higher primary productivity observed within the NOW relative to surrounding waters in spring/summer months. Finally, our temperature calibrations for alkenones, GDGTs and OH-GDGTs reduce the uncertainty present in global temperature calibrations, but also identify some additional variables that may be important in controlling their local distribution, such as salinity, nutrients, and dissolved oxygen. Collectively, our datasets provide new insight into the utility of these lipid biomarker proxies in high-latitude settings and will help provide a refined perspective on the Holocene development of the NOW with their application in downcore reconstructions. [ABSTRACT FROM AUTHOR]