Spatial variability of surface pCO2 and air-sea CO2 flux in the Amundsen Sea Polynya, Antarctica

Abstract

Abstract Partial pressure of CO2 (pCO2) and dissolved oxygen (DO) in the surface waters of the Amundsen Sea Polynya (ASP) were measured during austral summer 2010–2011 on the Amundsen Sea Polynya International Research Expedition (ASPIRE). Surface pCO2 in the central polynya was as low as 130 µatm, mainly due to strong net primary production. Comparing saturation states of pCO2 and DO distinguished dominant factors (biological activity, temperature, upwelling, and ice melt) controlling pCO2 across regions. Air-sea CO2 flux, estimated using average shipboard winds, showed high spatial variability (-52 to 25 mmol C m-2 d-1) related to these factors. The central region exhibited a high flux of -36 ± 8.4 mmol C m-2 d-1, which is ∼ 50% larger than that reported for the peak of the bloom in the well-studied Ross Sea, comparable to high rates reported for the Chukchi Sea, and significantly higher than reported for most continental shelves around the world. This central region (∼ 20,000 km2) accounted for 85% of the CO2 uptake for the entire open water area. Margins with lower algal biomass accounted for ∼ 15% of regional carbon uptake, likely resulting from pCO2 reductions by sea ice melt. During ASPIRE we also observed pCO2 up to 490 µatm in a small region near the Dotson Ice Shelf with an efflux of 11 ± 5.4 mmol C m-2 d-1 that offset about 3% of the uptake in the much larger central region. Overall, the 2010–2011 ASP was a large net sink for atmospheric CO2 with a spatially averaged flux density of -18 ± 14 mmol C m-2 d-1. This high flux suggests a disproportionate influence on the uptake of CO2 by the Southern Ocean. Since the region has experienced a significant increase in open water duration (1979–2013), we speculate about whether this CO2 sink will increase with future climate-driven change.