Publication Date:
2015-06-17
Description:
We present measurements of p CO 2 , O 2 concentration, biological oxygen saturation (ΔO 2 /Ar) and N 2 saturation (ΔN 2 ) 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. p CO 2 and ΔO 2 /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 O 2 accumulation to dissolved inorganic carbon (DIC) drawdown was significantly lower than expected from photosynthetic stoichiometry, reflecting the differential time-scales of O 2 and CO 2 air-sea equilibration. We measured significant oceanic CO 2 uptake, with a mean air-sea flux (~ −10 mmol m −2 d −1 ) that significantly exceeded regional climatological values. N 2 was mostly supersaturated in surface waters (mean ΔN 2 of +2.5 %), while physical processes resulted in both supersaturation and undersaturation of mixed layer O 2 (mean ΔO 2phys = 2.1 %). Box model calculations were able to reproduce much of the spatial variability of ΔN 2 and ΔO 2phys 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 ΔO 2 /Ar data, ranged from ~ −40 to 〉 300 mmol O 2 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 stratified regions of sea-ice melt, reflecting physical controls on surface water light fields and nutrient availability.
Print ISSN:
0886-6236
Electronic ISSN:
1944-9224
Topics:
Biology
,
Chemistry and Pharmacology
,
Geography
,
Geosciences
,
Physics
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