Bounding cross-shelf transport time and degradation in Siberian-Arctic land-ocean carbon transfer

Lisa Bröder,Igor Semiletov,August Andersson,Tommaso Tesi,Örjan Gustafsson

doi:10.1038/s41467-018-03192-1

Abstract

The burial of terrestrial organic carbon (terrOC) in marine sediments contributes to the regulation of atmospheric CO2 on geological timescales and may mitigate positive feedback to present-day climate warming. However, the fate of terrOC in marine settings is debated, with uncertainties regarding its degradation during transport. Here, we employ compound-specific radiocarbon analyses of terrestrial biomarkers to determine cross-shelf transport times. For the World’s largest marginal sea, the East Siberian Arctic shelf, transport requires 3600 ± 300 years for the 600 km from the Lena River to the Laptev Sea shelf edge. TerrOC was reduced by ~85% during transit resulting in a degradation rate constant of 2.4 ± 0.6 kyr−1. Hence, terrOC degradation during cross-shelf transport constitutes a carbon source to the atmosphere over millennial time. For the contemporary carbon cycle on the other hand, slow terrOC degradation brings considerable attenuation of the decadal-centennial permafrost carbon-climate feedback caused by global warming.

Highlights

The burial of terrestrial organic carbon in marine sediments contributes to the regulation of atmospheric CO2 on geological timescales and may mitigate positive feedback to present-day climate warming
We obtained a quantitative estimate of 3600 ± 300 years for the transport of sedimentary terrestrial organic carbon (terrOC) across the 600 km-wide Laptev Sea shelf upon supply from the Lena river
The time spent during lateral transport, likely characterized by recurrent oxic-suboxic cycles driven by resuspension events, appears to be the regulatory parameter for sedimentary terrOC degradation as shown by the exponential decrease of bulk terrOC and terrestrial biomarker loadings with increasing transport times

Summary

Introduction

The burial of terrestrial organic carbon (terrOC) in marine sediments contributes to the regulation of atmospheric CO2 on geological timescales and may mitigate positive feedback to present-day climate warming. In highlatitude regions, increasing soil permafrost thaw[3], accelerating coastal and sea floor erosion[4,5], and rising fluvial sediment discharge[6] are expected to amplify the delivery of terrestrial organic carbon (terrOC) to the Arctic Ocean. To what extent this dislocated material undergoes remineralization during transport and upon discharge, determines the intensity of this positive feedback mechanism to climate change, yet the fundamental processes are still insufficiently understood[2,7]. The East Siberian Arctic Shelf is the widest ocean margin on Earth and, provides an extraordinary natural laboratory to constrain the age and fate of terrOC during its cross-shelf transport

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Conclusion