Arctic cold-water corals record depleted radiocarbon signatures during the Holocene

Changes in atmospheric CO₂ concentrations during the last deglaciation have been attributed to the release of fossil carbon. However, the processes and mechanisms of the various carbon sources that contributed to this change in the carbon cycle are not yet fully understood. Cold-water corals and their ecosystems are considered important carbonate factories in the Arctic and are particularly vulnerable to changes in the carbon cycle and present an unique archive recording such changes.

Here, we present paired ²³⁰Th/U and radiocarbon (¹⁴C) measurements on pristine fragments of the scleractinian cold-water coral Desmophyllum pertusum, combined with measurements of stable carbon isotopes (δ¹³C) on various benthic foraminifera from a sediment core taken from the Lopphavet CWC reef (71°N, 21°E) covering the last 10 kyrs. This combined approach helps to narrow down sources of carbon cycled within this Holocene CWC reef in the Arctic.

Our results show Δ¹⁴C values that are as low as -500 ‰ resulting in extremely high bottom- atmosphere ages of up to 6000 years. Radiocarbon simulations performed with the ¹⁴C-equipped model CLIMBER-X show that such negative Δ¹⁴C values and high ventilation ages cannot be explained by oceanographically controlled changes in the marine radiocarbon cycle of the Arctic Ocean. Furthermore, the δ¹³C values of various benthic foraminifera with different microhabitats show the expected offsets, suggesting that the carbon source does not originate from dissociations of gas-hydrates.

We suggest that a continuous retreat of the ice-sheets has led to an accelerated release of terrestrial organic carbon into the Norwegian Arctic Ocean on which the corals fed on.  

Our results therefore highlight the need for further studies that constrain the mechanism and processes of organic carbon pathways from high-latitude terrestrial regime into the Arctic Ocean, especially in high latitude carbonate factories.