Millennial scale persistence of organic carbon bound to iron in Arctic marine sediments

Johan C Faust,Katherine A Doyle,Christian März,Sonia Papadaki,Allyson Tessin,Ben J Fisher,Katharine R Hendry,Mark Zindorf

doi:10.1038/s41467-020-20550-0

Johan C Faust, Katherine A Doyle + Show 6 more

Open Access

https://doi.org/10.1038/s41467-020-20550-0

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Abstract

Burial of organic material in marine sediments represents a dominant natural mechanism of long-term carbon sequestration globally, but critical aspects of this carbon sink remain unresolved. Investigation of surface sediments led to the proposition that on average 10-20% of sedimentary organic carbon is stabilised and physically protected against microbial degradation through binding to reactive metal (e.g. iron and manganese) oxides. Here we examine the long-term efficiency of this rusty carbon sink by analysing the chemical composition of sediments and pore waters from four locations in the Barents Sea. Our findings show that the carbon-iron coupling persists below the uppermost, oxygenated sediment layer over thousands of years. We further propose that authigenic coprecipitation is not the dominant factor of the carbon-iron bounding in these Arctic shelf sediments and that a substantial fraction of the organic carbon is already bound to reactive iron prior deposition on the seafloor.

Highlights

Burial of organic material in marine sediments represents a dominant natural mechanism of long-term carbon sequestration globally, but critical aspects of this carbon sink remain unresolved
Organic carbon (OC) burial in shelf sediments plays an important role in the global carbon cycle as ∼87% of the estimated 169 × 106 tons of OC deposited at the seafloor were buried in these shallow parts of the ocean each year[1]
Reactive iron phases may serve as an efficient shuttle to promote carbon burial as OC associated with these Fe(III) phases should be protected against microbial degradation, allowing it to bypass the efficient early diagenetic degradation regime[18] and to be buried into anoxic sediments, where the OC preservation potential is much higher

Summary

Introduction

Burial of organic material in marine sediments represents a dominant natural mechanism of long-term carbon sequestration globally, but critical aspects of this carbon sink remain unresolved. To better understand the effect of sedimentary degradation processes on the formation and stability of the OC-FeR and OCMnR association over long (millennial) timescales, we chemically analysed pore water and sediment samples retrieved at four coring sites along a south-north transect across the Arctic Barents Sea shelf area (Fig. 1).

Results

Conclusion