Polynyas, or recurring areas of seasonally open water surrounded by sea ice, are foci for energy and material transfer between the atmosphere and the polar ocean. They are also climate sensitive, with both sea ice extent and glacial melt influencing their productivity. The Amundsen Sea Polynya (ASP) is the greenest polynya in the Southern Ocean, with summertime chlorophyll a concentrations exceeding 20 µg L−1. During the Amundsen Sea Polynya International Research Expedition (ASPIRE) in austral summer 2010–11, we aimed to determine the fate of this high algal productivity. We collected water column profiles for total dissolved inorganic carbon (DIC) and nutrients, particulate and dissolved organic matter, chlorophyll a, mesozooplankton, and microbial biomass to make a carbon budget for this ecosystem. We also measured primary and secondary production, community respiration rates, vertical particle flux and fecal pellet production and grazing. With observations arranged along a gradient of increasing integrated dissolved inorganic nitrogen drawdown (ΔDIN; 0.027–0.74 mol N m−2), changes in DIC in the upper water column (ranging from 0.2 to 4.7 mol C m−2) and gas exchange (0–1.7 mol C m−2) were combined to estimate early season net community production (sNCP; 0.2–5.9 mol C m−2) and then compared to organic matter inventories to estimate export. From a phytoplankton bloom dominated by Phaeocystis antarctica, a high fraction (up to ∼60%) of sNCP was exported to sub-euphotic depths. Microbial respiration remineralized much of this export in the mid waters. Comparisons to short-term (2–3 days) drifting traps and a year-long moored sediment trap capturing the downward flux confirmed that a relatively high fraction (3–6%) of the export from ∼100 m made it through the mid waters to depth. We discuss the climate-sensitive nature of these carbon fluxes, in light of the changing sea ice cover and melting ice sheets in the region.

Partial pressure of CO 2 (pCO 2 ) 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 pCO 2 in the central polynya was as low as 130 µatm, mainly due to strong net primary production. Comparing saturation states of pCO 2 and DO distinguished dominant factors (biological activity, temperature, upwelling, and ice melt) controlling pCO 2 across regions. Air-sea CO 2 flux, estimated using average shipboard winds, showed high spatial variability (-52 , 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 km 2 ) accounted for 85% of the CO 2 uptake for the entire open water area. Margins with lower algal biomass accounted for ∼ 15% of regional carbon uptake, likely resulting from pCO 2 reductions by sea ice melt. During ASPIRE we also observed pCO 2 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 CO 2 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 CO 2 by the Southern Ocean. Since the region has experienced a significant increase in open water duration , we speculate about whether this CO 2 sink will increase with future climate-driven change.

The partial pressure of carbon dioxide (pCO2) was surveyed across the Amazon River plume and the surrounding western tropical North Atlantic Ocean (15–0°N, 43–60°W) during three oceanic expeditions (May–June 2010, September–October 2011, and July 2012). The survey timing was chosen according to previously described temporal variability in plume behavior due to changing river discharge and winds. In situ sea surface pCO2 and air‐sea CO2 flux exhibited robust linear relationships with sea surface salinity (SSS; 15 < SSS < 35), although the relationships differed among the surveys. Regional distributions of pCO2 and CO2 flux were estimated using SSS maps from high‐resolution ocean color satellite‐derived (MODIS‐Aqua) diffuse attenuation coefficient at 490 nm (Kd490) during the periods of study. Results confirmed that the plume is a net CO2 sink with distinctive temporal variability: the strongest drawdown occurred during the spring flood (−2.39 ± 1.29 mmol m−2 d−1 in June 2010), while moderate drawdown with relatively greater spatial variability was observed during the transitional stages of declining river discharge (−0.42 ± 0.76 mmol m−2 d−1 in September–October 2011). The region turned into a weak source in July 2012 (0.26 ± 0.62 mmol m−2 d−1) when strong CO2 uptake in the mid‐plume was overwhelmed by weak CO2 outgassing over a larger area in the outer plume. Outgassing near the mouth of the river was observed in July 2012. Our observations draw attention to the importance of assessing the variable impacts of biological activity, export, and air‐sea gas exchange before estimating regional CO2 fluxes from salinity distributions alone.

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