Characterization of Organic Matter of the Laptev Sea Eroded Coastal Sediments: A Case Study from the Cape Muostakh, Bykovsky Peninsula

Andrey A Grinko,Natalia E Shakhova,Elena V Gershelis,Michail V Shaldybin,Alexey K Mazurov,Alexey S Ruban,Oleg V Dudarev,Nikolay V Oblasov,Ivan V Goncharov,Alexey G Zarubin,Maxim A Veklich,Igor P Semiletov

doi:10.3390/geosciences11020083

Abstract

The article provides new data about characteristics of the organic matter and mineralogical composition of the Cape Muostakh sediments related to intense permafrost degradation (thermoerosion processes). The sedimentary material has been investigated by X-ray diffraction, GC-MS, IRM-GC-MS, pyrolysis–gas chromatography–mass spectrometry (Py–GC–MS), and Rock-Eval pyrolysis. Variable distribution of the total organic carbon content over the coast cliff is established. The minimum content of the organic carbon occurs at the cliff level of 5 m above sea level, and the maximum is located on the top of the cape cliff. The practical absence of unsaturated compounds indicates the intense destruction of the ice complex deposits that occurred at the level of 5 m of the Cape Muostakh cliff. The minimum organic carbon, aliphatic compounds, and the increase of the δ13C indicates the loss of hydrogen-enriched organic matter, while condensed carbon structures remain in sediment. Aromatic compounds of both plant and petroleum origin were identified in all sediments, except in the sediment sample collected at the cliff level of 5 m. Unsaturated fatty acids were detected only in the sediments of the upper cliff levels. The novel hopenes and hopane were detected and they predominantly occur in the upper layers of the cape cliff.

Highlights

Northern circumpolar soils store huge amounts of global soil organic carbon (∼1300 Pg) with its greater part being perennially frozen (∼800 Pg) [1]
Massive release of remobilized carbon from the Yedoma Ice Complex is considered as a major source (>57 ± 2%, r ∼44 ± 10 Tg C y−1 ) of terrigenous carbon (terrOC) on the East Siberian Arctic shelf (ESAS) already exceeding marine and top-soil terrestrial contributions [7],Yedoma Ice Complex is considered as a major source and this process is expected to further increase due to accelerating coastal retreat rates [8,12,13,14]
To better understand how the organic matter (OM) frozen in Yedoma deposits will contribute to the Arctic carbon cycle, it is necessary to provide deeper insights into the molecular composition of Yedoma OM accumulated during the late Pleistocene and Holocene and to recognize its geochemical evolution during the past

Summary

Introduction

Northern circumpolar soils store huge amounts of global soil organic carbon (∼1300 Pg) with its greater part being perennially frozen (∼800 Pg) [1]. With amplified global warming these vast carbon reservoirs become increasingly susceptible and heavily affect the modern biogeochemical cycle. This remobilized material can be buried in shelf sediments, transported towards deeper basins, or degraded providing a potential positive feedback to climate warming and causing severe ocean acidification [2]. Vulnerable to thaw remobilization are the late-Pleistocene ice-rich coastal deposits known as the Yedoma Ice Complex that extend for ~7000 km along the East. To better understand how the organic matter (OM) frozen in Yedoma deposits will contribute to the Arctic carbon cycle, it is necessary to provide deeper insights into the molecular composition of Yedoma OM accumulated during the late Pleistocene and Holocene and to recognize its geochemical evolution during the past. Major progress has been made in constraining OM composition stored in permafrost at the molecular level using lipid biomarker analysis [15,16,17], humic substances analysis performed by 13 C-NMR spectroscopy method [18,19,20], and characterization of water-extractable organic matter [21]

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Results

Conclusion