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Biological and physical controls on N 2 , O 2 , and CO 2 distributions in contrasting Southern Ocean surface waters
Author(s) -
Tortell Philippe D.,
Bittig Henry C.,
Körtzinger Arne,
Jones Elizabeth M.,
Hoppema Mario
Publication year - 2015
Publication title -
global biogeochemical cycles
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.512
H-Index - 187
eISSN - 1944-9224
pISSN - 0886-6236
DOI - 10.1002/2014gb004975
Subject(s) - phytoplankton , saturation (graph theory) , mixed layer , hydrography , dissolved organic carbon , redfield ratio , entrainment (biomusicology) , supersaturation , flux (metallurgy) , atmospheric sciences , chemistry , oceanography , environmental chemistry , geology , nutrient , philosophy , mathematics , organic chemistry , combinatorics , rhythm , aesthetics
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 (Chl a ) 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 covaried strongly with Chl a . 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.