Intact Polar brGDGTs in Arctic Lake Catchments: Implications for Lipid Sources and Paleoclimate Applications. Issue 10 (27th September 2022)

• Record Type: Journal Article
• Authors: Raberg, Jonathan H.; Flores, Edgart; Crump, Sarah E.; de Wet, Greg; Dildar, Nadia; Miller, Gifford H.; Geirsdóttir, Áslaug; Sepúlveda, Julio
• Is Part Of: Journal of geophysical research. Volume 127:Issue 10(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-27
• Subjects: brGDGT -- intact polar lipid -- paleoclimate -- Arctic -- lake sediment -- biomarker; Geobiology -- Periodicals; Biogeochemistry -- Periodicals; Biotic communities -- Periodicals; Geophysics -- Periodicals; 577.14
• DOI: 10.1029/2022JG006969
• Languages: English
• ISSNs: 2169-8953

Abstract

Abstract: Paleotemperature histories derived from lake sediment archives provide valuable context for modern and future climate changes. Branched glycerol dialkyl glycerol tetraether (brGDGT) lipids are a valuable tool in such pursuits due to their empirical correlation with temperature and near ubiquity in nature. However, the relative contributions of terrestrial and lacustrine sources of brGDGTs to lake sediments is site‐dependent and difficult to constrain. Here, we explored the potential for intact brGDGTs—the complete lipids with polar head groups (HGs) still attached—to provide insight into the sources of brGDGTs on the landscape and their contributions to the sedimentary record in a set of Arctic lakes. We measured core and intact brGDGTs in soils, surface and downcore sediments, water filtrates, and sediment traps across five lake catchments in the Eastern Canadian Arctic, with an emphasis on Lake Qaupat (QPT), Baffin Island. Soils were dominated by brGDGTs with a monoglycosyl (1G) HG, while lacustrine samples contained more phosphohexose (PH) brGDGTs, providing evidence for in situ brGDGT production in both settings. Core‐ and PH‐brGDGT‐IIIa were more abundant in sediments than in the soils or water column, implying an additional post‐depositional source of brGDGTs. A hierarchical clustering analysis indicated that core brGDGTs in Lake QPT sediments were largely lacustrine in origin, while 1G‐brGDGTs were primarily soil‐derived. Additionally, we found evidence for preservation of intact brGDGTs—especially 1G‐brGDGTs—downcore on thousand‐year timespans, though in situ production deeper in the sediment column cannot be ruled out. Finally, we explored the possibility of reconstructing 1G‐brGDGT‐derived soil temperatures and core‐brGDGT‐derived lake temperatures in tandem from sedimentary archives. Plain Language Summary: Bacteria can record aspects of their environment, such as temperature, via the composition of their lipid membranes. These lipids and the environmental information they contain can then be preserved in natural archives such as lake sediments, allowing for temperatures to be reconstructed deep into the past. Branched glycerol dialkyl glycerol tetraether (brGDGTs) lipids are one such type of lipid that which have become popular due to their ubiquity in nature and resistance to degradation. However, it can be challenging to figure out where the brGDGTs in a lake sedimentary archive originated. They could have been produced in the lake, washed in from surrounding soils or an inflow stream, or even been generated in the sediment itself. Here, we looked at a less commonly measured form of brGDGTs called intact polar lipids to address this question. We found that these intact lipids looked strikingly different in the soils and the lakes across five Arctic sites. We then examined one lake in further detail and found that some of the intact brGDGTs in the lake appeared to be coming from the soil. These observations could allow researchers to track changes in both soil and lake environments from lake sedimentary archives at the same time. Key Points: Intact polar branched glycerol dialkyl glycerol tetraether (brGDGT) lipids in soils were distinct from those in lakes In lake sediments, core brGDGTs were lacustrine in origin, and intact monoglycosyl‐brGDGTs were soil derived Distinct intact brGDGTs could serve as proxies for both soil and lake temperatures in lake sediment archives