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Transport of organic carbon in the Arctic

Climate warming is expected to result in the transport of organic carbon (OC) from the land to the Arctic Ocean, thereby affecting marine geochemistry at high latitudes. An EU-funded project investigated the amount of OC transported and the climate response to this phenomenon.
Transport of organic carbon in the Arctic
In the Arctic, huge quantities of carbon are locked in permanently frozen ground. Its potential release into the atmosphere due to thawing of the permafrost could represent a serious risk for the future climate. Recent studies indicate that a significant fraction of previously frozen soil will be transported across the East Siberian Arctic Shelf (ESAS) because of increased river runoff. However, the fate of this material once it enters the Arctic Ocean is not well understood.

The ARCTIC project addressed this critical knowledge gap. Project partners investigated the composition and physical properties of surface sediments collected from across the ESAS. The consortium also characterised marine and land-derived carbon using a large number of molecular biomarkers.

Biomarkers used included lignin, phenols, cutin-derived products and high-molecular-weight compounds (n-alkanols, n-alkanoic acids and n-alkanes). The analyses focused on differences in density, size and settling fractions to overcome the potential bias due to sorting during transport of the sediment over the ESAS.

Results showed that land-derived OC, referred to as terrigenous organic carbon (TerrOC), can vary greatly across the ESAS. In the inner shelf, a significant fraction of OC is associated with plant debris. However, in the outer-shelf, most of the OC is bound to the mineral matrix, mainly as fine sediment.

The plant debris is retained in the inner shelf because, despite its light density, it is relatively large in size, resulting in a high settling velocity. Therefore, as the sediments move across the ESAS the relative concentration of the different terrigenous biomarkers changes.

Furthermore, by focusing on particular size and density fractions the ARCTIC consortium could measure TerrOC degradation at the macromolecular level along the sediment transport. This showed that both degradation and winnowing of TerrOC significantly affects the composition of the permafrost once it enters the Arctic Ocean.

The ARCTIC project provided valuable data on the sources, transport and degradation of permafrost-derived OC resulting from the warming of the Arctic. This will help scientists to understand how a thawing of the permafrost may contribute to climate change.

Related information

Keywords

Organic carbon, Arctic, climate warming, permafrost, terrigenous
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