Influence of microbial community composition and metabolism on air-sea ΔpCO2 variation off the western Antarctic Peninsula

We studied CO2 and O-2 dynamics in the western Antarctic Peninsula (WAP) waters in relation to (1) phytoplankton biomass, (2) microbial community primary production and respiration, and (3), for the first time, phytoplankton composition, during summer and fall in 3 consecutive years (2002, 2003 and 2004). The areal average of Delta pCO(2) (the difference between surface seawater and atmospheric partial pressure of CO2) for the 3 yr was significantly negative (-20.04 +/- 44.3 mu atm, p < 0.01) during the summer to fall period in the region, possibly indicating a CO2 sink. In the southern WAP (i.e. south of Anvers Island), Delta pCO(2) was significantly negative (-43.60 +/- 39.06 mu atm) during fall. In the northern WA? (north of Anvers Island), Delta pCO(2) values showed a more complex distribution during summer and fall (-4.96 +/- 37.6 and 21.71 +/- 22.39 mu atm, respectively). Chlorophyll a (chl a) concentration averaged 1.03 +/- 0.25 mu g l(-1) and was higher in the south of the peninsula. Phytoplankton composition influenced chl a concentration with higher and lower va:Lues for diatom- and phytoflagellate-dominated communities, respectively. A significant negative correlation existed between chl a and Delta pCO(2). From incubation experiments performed in the northern WAP, respiration was low (averaging 5 1 mmol O-2 m(-3) d(-1)), and the net community production (NCP) correlated negatively with Delta pCO(2) and positively with %O-2 saturation. However, despite the high NCP values measured, Delta pCO(2) was significantly positive in the northern WAP during the summer to fall period. Strong mixing and lower chl a concentration may explain this result. In contrast, Delta pCO(2) was significantly negative in the southern WAP, possibly because of high surface water chl a concentration.