Sources and characteristics of terrestrial carbon in Holocene-scale sediments of the East Siberian Sea

Kirsi Keskitalo,Lisa Bröder,Igor P Semiletov,Tommaso Tesi,August Andersson,Oleg V Dudarev,Christof Pearce,Martin Sköld,Örjan Gustafsson

doi:10.5194/cp-13-1213-2017

Abstract

Abstract. Thawing of permafrost carbon (PF-C) due to climate warming can remobilise considerable amounts of terrestrial carbon from its long-term storage to the marine environment. PF-C can be then be buried in sediments or remineralised to CO2 with implications for the carbon–climate feedback. Studying historical sediment records during past natural climate changes can help us to understand the response of permafrost to current climate warming. In this study, two sediment cores collected from the East Siberian Sea were used to study terrestrial organic carbon sources, composition and degradation during the past ∼ 9500 cal yrs BP. CuO-derived lignin and cutin products (i.e., compounds solely biosynthesised in terrestrial plants) combined with δ13C suggest that there was a higher input of terrestrial organic carbon to the East Siberian Sea between ∼ 9500 and 8200 cal yrs BP than in all later periods. This high input was likely caused by marine transgression and permafrost destabilisation in the early Holocene climatic optimum. Based on source apportionment modelling using dual-carbon isotope (Δ14C, δ13C) data, coastal erosion releasing old Pleistocene permafrost carbon was identified as a significant source of organic matter translocated to the East Siberian Sea during the Holocene.

Highlights

The amount of organic carbon (OC) stored in the northern circumpolar permafrost (PF) amounts to ∼ 1300 Pg OC of which ∼ 800 Pg OC is perennially frozen
Our results suggest a high input of terrestrial organic carbon to the East Siberian Sea (ESS) during the last glacial–interglacial period caused by permafrost destabilisation
This material was mainly characterised as relict Pleistocene permafrost released via coastal erosion as a result of the sea level ingression

Summary

Introduction

The amount of organic carbon (OC) stored in the northern circumpolar permafrost (PF) amounts to ∼ 1300 Pg OC of which ∼ 800 Pg OC is perennially frozen (the remaining 500 Pg is non-permafrost, seasonally thawing active-layer permafrost or talik; Hugelius et al, 2014). Northern Hemisphere circumpolar soils thereby hold roughly half of the global soil OC pool (Tamocai et al, 2009). Modelled future climate scenarios predict continued amplified warming in the Arctic for the coming 100 years (IPCC, 2013). This will further destabilise permafrost, leading to increased delivery of terrestrial OC to the Arctic Ocean. The potential decomposition of this relict permafrost carbon (PF-C) and its subsequent release to the atmosphere as CO2 or CH4 constitutes a positive feedback to global warming (IPCC, 2013; Koven et al, 2011; Schuur et al, 2015; Vonk and Gustafsson, 2013). Considering the size of the Arctic PF-C pool it is important to better understand the dynamics and extent of its vulnerability to remobilisation in response to climate warming

Methods

Results

Conclusion