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- Title
Alkyl Lipid Distributions and Compound‐Specific <sup>14</sup>C Isotope Compositions in Diverse Sedimentary Archives in Sub‐Antarctic South Georgia: Deconvolving (Past and Present) Marine and Terrestrial Sources and Revealing Localized Export Dynamics in Response to Environmental Change
- Authors
Berg, S.; Kusch, S.; Jivcov, S.
- Abstract
Alkyl lipid distributions in terrestrial, lacustrine and marine sedimentary archives on sub‐Antarctic South Georgia are investigated to identify source endmembers and evaluate their variation in response to Holocene environmental changes. To understand organic matter exchange processes along the land‐ocean continuum, we combine lipid compositional data with compound‐specific 14C data in representative sedimentary records. These data provide additional source information and temporal constraints on exchange processes that operate at the landscape level. The alkane, alkanoic acid and alkanol distributions are distinct between terrestrial and marine sources, between vascular and primarily non‐vascular plants, and according to the level of degradation. Compound‐specific 14C ages of alkanes, alkanoic acids and alkanols reveal the complexity of the carbon pools associated with these carbon sources. We find that terrigenous compounds in lacustrine and marine sediments are generally older than those produced by aquatic sources, reflecting intermediate storage in peat/soil prior to deposition. Nonetheless, the pre‐depositional age of terrigenous alkyl lipids differs in the different settings although they are located in close proximity under the same climatic conditions. Overall, the 14C data reflect changes in the balance of accumulation and erosion of organic matter in the terrestrial catchments of the investigated sites in response to prevailing environmental conditions. Petrogenic OC ranges from 0% to 7% and 4%–37% in catchments with minor glacier presence and to up to 67%–76% in the large tidewater glacier catchment. Long‐term biospheric OC turnover seems to have been remarkably constant throughout most of the Holocene and higher than in analog settings in the northern hemisphere. Plain Language Summary: We investigate the distribution of plant lipids found in sedimentary records of South Georgia, an island in the sub‐Antarctic region. This study aims to discern the origin of these compounds and assess how they have varied over time due to environmental changes such as glacier advances and retreats during the Holocene period. By analyzing the composition of these plant lipids and their radiocarbon ages, we aim to gain insights into the processes influencing the exchange of organic matter between land and aquatic environments. Different types of plant lipids exhibit distinct patterns between terrestrial and marine sources, revealing differences in plant types and the level of organic matter degradation. Our findings suggest that organic compounds originating from land tend to be older than those produced within lakes or fjords, indicating a period of storage in soil or peat before deposition. The radiocarbon data further indicate fluctuations in the accumulation and erosion of organic matter on land in response to changing environmental conditions, notably glacier dynamics. Despite these fluctuations, the long‐term turnover of plant lipids appears to have remained relatively stable for much of the Holocene. Key Points: Alkyl lipid 14C ages imply efficient turnover/erosion of shallow peat and soil as well as localized source effectsLocalized glacier activity controls biospheric and petrogenic organic matter input in lakes and fjordsEnvironmental reconstructions may be biased by point‐source interpretations when using alkyl lipids to infer vegetation/catchment evolution
- Subjects
SOUTH Georgia &; South Sandwich Islands; PLANT lipids; HOLOCENE Epoch; PEAT soils; LIPIDS; MARINE sediments; GLACIERS; PEAT bogs
- Publication
Journal of Geophysical Research. Biogeosciences, 2024, Vol 129, Issue 5, p1
- ISSN
2169-8953
- Publication type
Article
- DOI
10.1029/2024JG008001