New evidence for preservation of contemporary marine organic carbon by iron in Arctic shelf sediments

Abstract

The protection of organic carbon through association with iron minerals (Fe _R ) is an important factor in its stabilisation, long-term storage, and burial efficiency in marine sediments. However, large uncertainties still exist concerning the sources, lability, age, and composition of the organic matter associated with Fe _R in natural sediments. Therefore, the timing and environmental setting of the carbon-iron bonding process remain elusive. Here we use radiocarbon (Δ ^14 C) and stable isotopes (δ ^13 C) of downcore bulk sedimentary organic matter, benthic foraminifera and the organic carbon fraction bound to Fe _R to interrogate the source and age of the organic carbon pool associated with Fe _R in Arctic marine sediments. In the Barents Sea, we find that the organic carbon associated with Fe _R is younger overall than the bulk organic matter and is probably marine derived. The comparison to other investigations of OC-Fe _R origins reveals that in large parts of Arctic shelf regions Fe _R associated organic carbon is radiocarbon enriched and has a higher δ ^13 C _org value compared to the bulk sediment, irrespective of sediment depth/age. Our findings suggest a rapid and preferential binding of fresh and marine organic matter with Fe _R . Hence, labile organic matter prone to decomposition is protected and stabilised, underlining the potential of the organic carbon–iron association as an efficient carbon burial mechanism.

Keywords

• Barents Sea
• OC-Fe
• marine shelf sediments
• radiocarbon
• carbon isotopes
• carbon sequestration