Biological and physical controls on O 2 /Ar, Ar and pCO 2 variability at the Western Antarctic Peninsula and in the Drake Passage
© 2016 Elsevier Ltd Using simultaneous sub-kilometer resolution underway measurements of surface O 2 /Ar, total O 2 and pCO 2 from annual austral summer surveys in 2012, 2013 and 2014, we explore the impacts of biological and physical processes on the O 2 and pCO 2 system spatial and interannual variability at the Western Antarctic Peninsula (WAP). In the WAP, mean O 2 /Ar supersaturation was (7.6±9.1)% and mean pCO 2 supersaturation was (−28±22)%. We see substantial spatial variability in O 2 and pCO 2 including sub-mesoscale/mesoscale variability with decorrelation length scales of ~4.5 km, consistent with the regional Rossby radius. This variability is embedded within onshore–offshore gradients. O 2 in the LTER grid region is driven primarily by biological processes as seen by the median ratio of the magnitude of biological oxygen (O 2 /Ar) to physical oxygen (Ar) supersaturation anomalies (%) relative to atmospheric equilibrium (2.6), however physical processes have a more pronounced influence in the southern onshore region of the grid where we see active sea-ice melting. Total O 2 measurements should be interpreted with caution in regions of significant sea-ice formation and melt and glacial meltwater input. pCO 2 undersaturation predominantly reflects biological processes in the LTER grid. In contrast we compare these results to the Drake Passage where gas supersaturations vary by smaller magnitudes and decorrelate at length scales of ~12 km, in line with latitudinal changes in the regional Rossby radius. Here biological processes induce smaller O 2 /Ar supersaturations (mean (0.14±1.3)%) and pCO 2 undersaturations (mean (−2.8±3.9)%) than in the WAP, and pressure changes, bubble and gas exchange fluxes drive stable Ar supersaturations.
Eveleth, R; Cassar, N; Doney, SC; Munro, DR; Sweeney, C
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