The circumpolar Southern Ocean connects the major ocean basins, returning carbon (and nutrients) to the surface ocean via the upwelling branch of the overturning circulation, and transporting heat and carbon to the ocean interior via the downwelling branch. Understanding the Southern Ocean response to both natural and anthropogenic changes is critical to understanding changing global biogoechemical cycles. However, major uncertainties persist in our knowledge of the Southern Ocean carbon budget due in part to unresolved variability at the seasonal scale, and in part to a significant lack of observations in coastal regions.
Figure 1: Laurence M Gould in Punta Arenas May 2006
Our understanding of Antarctic coastal systems is heavily biased by observations restricted to the summer where open water primary production dominates CO2 system variability. Changes in the physical and biogeochemical state of coastal Antarctic waters are already underway: warming, freshening and onshore intrusion of carbon-rich circumpolar deep water are all processes with associated feedbacks to the CO2 system that are expected to influence contemporary rates of air-sea CO2 exchange. Resolving the dominant drivers of variability and predicting the evolution of these systems in the context of future change requires sustained observations. Given the challenges of working in remote Antarctic coastal waters, acquiring observations outside of the summer season necessitates the use of autonomous platforms.
This 3-year project funded by the US National Science Foundation’s Division of Polar Programs will make an essential contribution to our understanding of coastal Southern Ocean CO2 system variability by delivering new autonomous observations that will allow the full CO2 system seasonality to be resolved. Using a moored observing system (to measure pH, CO2 partial pressure, temperature, salinity and dissolved oxygen with 3-hour frequency) on the West Antarctic Peninsula continental shelf, we will characterise diurnal and seasonal variability, and identify the dominant physical and biological controls on the seasonal variations in the CO2 system and the net annual air-sea exchange. By expanding our observational records beyond the summer season, when pH and carbonate saturation state are at the annual maxima (due to inorganic carbon drawdown by open water primary production), a more realistic projection of the evolution of the carbonate system in response to increasing atmospheric CO2 will be possible.
Figure 2: Schematic diagram of the mooring
Given the rapid environmental change occurring in the West Antarctic Peninsula, which is warming faster than any other region globally, an improved understanding of natural CO2 system variability and feedbacks to the carbonate system will additionally provide insight for the evolution of other coastal Antarctic systems not currently impacted by the same magnitude of change.