Summer Carbonate Chemistry in the Dalton Polynya, East Antarctica

Abstract

The carbonate chemistry in the Dalton Polynya in East Antarctica (115°–123°E) was investigated in summer 2014/2015 using high‐frequency underway measurements of CO2 fugacity (fCO2) and discrete water column measurements of total dissolved inorganic carbon (TCO2) and total alkalinity. Air‐sea CO2 fluxes indicate this region was a weak net source of CO2 to the atmosphere (0.7 ± 0.9 mmol C m−2 day−1) during the period of observation, with the largest degree of surface water supersaturation (ΔfCO2 = +45 μatm) in ice‐covered waters near the Totten Ice Shelf (TIS) as compared to the ice‐free surface waters in the Dalton Polynya. The seasonal depletion of mixed‐layer TCO2 (6 to 51 μmol/kg) in ice‐free regions was primarily driven by sea ice melt and biological CO2 uptake. Estimates of net community production (NCP) reveal net autotrophy in the ice‐free Dalton Polynya (NCP = 5–20 mmol C m−2 day−1) and weakly heterotrophic waters near the ice‐covered TIS (NCP = −4–0 mmol C m−2 day−1). Satellite‐derived estimates of chlorophyll a (Chl a) and sea ice coverage suggest that the early summer season in 2014/2015 was anomalous relative to the long‐term (1997–2017) record, with lower surface Chl a concentrations and a greater degree of sea ice cover during the period of observation; the implications for seasonal primary production and air‐sea CO2 exchange are discussed. This study highlights the importance of both physical and biological processes in controlling air‐sea CO2 fluxes and the significant interannual variability of the CO2 system in Antarctic coastal regions.

A Continental Shelf Pump for CO2 on the Adélie Land Coast, East Antarctica

“…The inferred winter TCO 2 was therefore defined as the average value at 150 m depth in the combined AU1402 and AU1602 data sets (TCO 2 winter = 2,230 μmol kg −1 ; standard deviation = 4 μmol kg −1 ; n = 33). This approach in determining winter TCO 2 follows previous studies in East Antarctic polynyas (e.g., Arroyo et al, 2019;Shadwick et al, 2014) as the temperature minimum on the shelf was not clearly defined and influenced by the presence of Ice Shelf Water (ISW).…”

The influence of tides on the marine carbonate chemistry of a coastal polynya in the south-eastern Weddell Sea

“…The prolonged ice-free conditions also potentially allow enough time for the polynya to take up as much CO 2 as is necessary to reach equilibrium with the atmosphere (Hoppema and Anderson, 2007). However, biological productivity is found to be variable among Antarctic coastal polynyas (Arrigo et al, 2015), and in some cases it is not sufficient to keep a polynya from outgassing CO 2 (Arroyo et al, 2019). Tides can displace water on short timescales (Skogseth et al, 2013;Llanillo et al, 2019) and modify the water column structure through enhanced mixing (Padman et al, 2009).…”

“…The effects of tides on the marine carbonate chemistry of these biogeochemically impactful regions along the Antarctic coastline remain largely unexplored. Understanding the tidal influence may help us to quantify some of the variability observed among Antarctic polynyas, such as the variability in the biological productivity (Arrigo et al, 2015) as well as the capacity of coastal polynyas to absorb or release atmospheric CO 2 (Arroyo et al, 2019). Practically, this improved understanding can help develop more reliable sampling activities that consider the timing and strength of tidal currents, thereby obtaining representative data of a highly dynamic system.…”

Seasonal Variations and Drivers of Surface Ocean pCO2 in the Seasonal Ice Zone of the Eastern Indian Sector, Southern Ocean

“…Surface CO 2 flux is proportional to the downgradient of pCO 2 in the atmosphere and ocean (R. Wanninkhof, 2014). The surface ocean pCO 2 is affected by CO 2 production/consumption due to biological activities, dilution by sea ice/glacial meltwaters, temperature changes, and mixing with ambient water masses (Arroyo et al., 2019; Legge et al., 2017; Shadwick et al., 2017). The decrease of the solubility of CO 2 with increasing water temperature and salinity, in turn, increases pCO 2 in the ocean.…”

“…In the Southern Ocean, as sea surface temperature increases from winter to summer, primary production increases, and salinity decrease because of the inflow of freshwater from melting sea ice and glacial ice. Several previous studies have pointed out these seasonal effects (Arroyo et al, 2019;Kiuchi et al, 2021;Legge, 2017;Nakaoka et al, 2009;Nomura, 2014;Shadwick et al, 2017). For example, Nakaoka et al (2009) indicated that water column stratification and biology influence oceanic pCO 2 .…”