Distributions of bacterial and archaeal membrane lipids in surface sediments reflect differences in input and loss of terrestrial organic carbon along a cross-shelf Arctic transect

Ayça Doğrul Selver,Robert B Sparkes,Juliane Bischoff,Helen M Talbot,Örjan Gustafsson,Igor P Semiletov,Oleg V Dudarev,Stephen Boult,Bart E Van Dongen

doi:10.1016/j.orggeochem.2015.01.005

Abstract

Enhanced climate warming affecting the Arctic region could have a dramatic impact on the terrigenous organic carbon (terrOC) stored in the Eurasian permafrost and could increase the amount of OC remobilized to the Arctic shelves. An improved understanding of the fate of this remobilized soil OC is essential for better understanding of the consequences for the Arctic and global carbon cycle. In this study, glycerol dialkyl glycerol tetraethers (GDGTs) and bacteriohopanepolyols (BHPs) in surface sediments along a 500km cross shelf transect from the mouth of the Kolyma River to the middle of the vast East Siberian Sea were analysed to assess their potential and that of the associated branched and isoprenoid tetraether (BIT) and R′soil indices for tracing terrOC in Arctic systems. Both BHP and GDGT contributions indicated the greatest contribution of terrOC close to the river mouth, while the associated indices showed declining trends in an offshore direction, supporting an increasing marine OC input and/or a decrease in terrOC. However, while the BHPs indicated a dominance of terrOC at the start of the transect, the GDGTs suggested a much larger, almost 50%, marine OC input at this point. In addition, the BIT index displayed an exponential decline, controlled mainly by a substantial contribution of marine GDGTs, while R′soil revealed a linear trend governed primarily by the removal of soil marker BHPs.These field results suggest that both biomarker approaches could be used to trace terrigenous derived OC in the Arctic environment. However, using a single proxy approach is not recommended and may lead to an under or over estimation of the relative importance of terrOC. Using a multi-proxy approach is valuable for fully understanding the fate of terrigenous derived OC along Arctic land-ocean transects.

Highlights

The Arctic terrestrial regions contain approximately half of all global soil organic carbon (OC; Tarnocai et al, 2009), locked primarily in the first few metres of pan-Arctic permafrost
Along the transect, summed glycerol dialkyl glycerol tetraether (GDGT) concentration showed a general increase from 62 lg/g OC in samples from station YS-34B to 1413 lg/g OC in those from station YS-40 (Table 2 and Fig. 2a)
With the exception of YS-35, all distributions were dominated by GDGT-0, with a concentration between 25 lg/g OC in the sediment from YS-34B and 774 lg/g OC for YS-40, making up between 38% and 57% of the summed GDGT concentration (Table 2 and Fig. 2a)

Summary

Introduction

The Arctic terrestrial regions contain approximately half of all global soil organic carbon (OC; Tarnocai et al, 2009), locked primarily in the first few metres of pan-Arctic permafrost. The widespread extent of the permafrost currently limits the exchange between this large OC reservoir with other more active carbon pools, including the atmosphere. Of terrigenous OC (terrOC) are expected to occur, including an increase in the amount transported to the Arctic shelf seas. There is a requirement to better understand the fate of this remobilized OC on the Arctic shelf (AMAP, 2012; Vonk and Gustafsson, 2013).

Objectives

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Results

Conclusion