71. The Role of Planktonic Foraminifers as Driver of Carbonate Export in the Scotia Sea (Southern Ocean)

Meltem Ok (1,2)*, Gabriele Stowasser (1), Sophie Fielding (1), Geraint Tarling (1) and Clara Manno (1)

1 British Antarctic Survey, Cambridge, Cambridgeshire, CB3 0ET, United Kingdom
2 Middle East Technical University, Institute of Marine Sciences, 33731, Erdemli, Mersin, Turkey

Background
In the Southern Ocean the 20% of the global carbon uptake takes place. The amount of carbon dioxide transferred to the deep ocean is regulated by the carbon (promoting CO2 sink by photosynthesis) and carbonate (producing CO2 source by calcification) pump. Planktonic foraminifers (carbonate producers), contribute up to 50 % of the total carbonate export in the ocean and in the Southern Ocean can represent a dominant component of carbonate flux. Therefore the understanding of foraminifera population dynamic and their response to the forecasted anthropogenic stressors (i.e. Ocean Acidification) is a critical issue.

Methods
Foraminifera samples were collected by deep sediment traps (2000m) deployed at two sites with contrasting ocean productivity regimes (P3, naturally iron-fertilized, and P2, iron-limited). We investigated the seasonal and interannual variability in foraminifera relative abundance. Since global models suggested that iron fertilization could accelerate Ocean Acidification to the deep water, we focus our study on the variability in shell degradation/dissolution between the two sites.

Findings
Despite, foraminifera seasonal trend was similar at both sites with a peak occurring in late summer-early autumn, foraminifera flux was 1 order of magnitude higher at P2 than at P3. The contribution of foraminifera to the carbonate flux was also significantly higher at P2 than P3 (up to 67% and 34% of the total carbonate flux respectively). Preliminary results suggested a higher level of shell degradation at the iron fertilized region compare to the iron-limited ones.

Conclusions
This is the first study showing the important role of foraminifera as driver of the carbonate export in the Scotia Sea. However iron supply does not seems to promote carbonate export by foraminifera precipitation. The understanding of how a decrease in foraminifera population, due to environmental anthropogenic stressors, could impact the balance between carbonate and carbon pump requires further investigation.