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

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.

Automated summary

The burial of organic material in marine sediments is a dominant natural mechanism of long-term carbon sequestration globally, but critical aspects of this carbon sink remain unresolved. By analyzing the chemical composition of sediments and pore waters from four locations in the Barents Sea, it was found that the carbon-iron coupling persists below the uppermost, oxygenated sediment layer over thousands of years.