Underway measurements of dissolved gases along POLARSTERN cruise track ANT-XXVII/2

• Main Authors: Bittig, Henry, Körtzinger, Arne
• Format: Dataset
• Language: English
• Published: PANGAEA 2015
• Subjects: ANT-XXVII/2; CT; DATE/TIME; DEPTH; water; derived; Gas Tension Device; LATITUDE; LONGITUDE; Nitrogen; partial pressure; total dissolved; Nitrogen saturation; OCEANET; Oxygen; Oxygen optode; Aanderaa; type 3830; Oxygen saturation; Polarstern; Pressure; atmospheric; total; dissolved gases; PS77; PS77/2-track; Salinity; Ships weather station; South Atlantic Ocean; Temperature; Thermosalinograph; TSG; Underway cruise track measurements; Southern Ocean; Austral; Sea ice
• Online Access: https://doi.pangaea.de/10.1594/PANGAEA.848615; https://doi.org/10.1594/PANGAEA.848615

We present measurements of pCO2, O2 concentration, biological oxygen saturation (Delta O2/Ar) and N2 saturation (Delta N2) in Southern Ocean surface waters during austral summer, 2010-2011. Phytoplankton biomass varied strongly across distinct hydrographic zones, with high chlorophyll a (Chla) concentrations in regions of frontal mixing and sea-ice melt. pCO2 and Delta O2 /Ar exhibited large spatial gradients (range 90 to 450 µatm and -10 to 60%, respectively) and co-varied strongly with Chla. However, the ratio of biological O2 accumulation to dissolved inorganic carbon (DIC) drawdown was significantly lower than expected from photosynthetic stoichiometry, reflecting the differential time-scales of O2 and CO2 air-sea equilibration. We measured significant oceanic CO2 uptake, with a mean air-sea flux (~ -20 mmol m-2 d-1) that significantly exceeded regional climatological values. N2 was mostly supersaturated in surface waters (mean Delta N2 of +2.5 %), while physical processes resulted in both supersaturation and undersaturation of mixed layer O2 (mean Delta O2phys = 2.1 %). Box model calculations were able to reproduce much of the spatial variability of Delta N2 and Delta O2phys along the cruise track, demonstrating significant effects of air-sea exchange processes (e.g. atmospheric pressure changes and bubble injection) and mixed layer entrainment on surface gas disequilibria. Net community production (NCP) derived from entrainment-corrected surface Delta O2 /Ar data, ranged from ~ -40 to > 300 mmol O2 m-2 d-1 and showed good coherence with independent NCP estimates based on seasonal mixed layer DIC deficits. Elevated NCP was observed in hydrographic frontal zones and regions of sea-ice melt with shallow mixed layer depths, reflecting the importance of mixing in controlling surface water light and nutrient availability.