Oxygen production and respiration in the Antarctic Polar Front region during the austral spring and summer

Gross and net O2 production and dark community respiration rates were measured during austral spring and summer from 53°S to 70°S along 170°W across the Antarctic Polar Front (APF). Integrated production and respiration rates were compared for stations north of the APF (53–59°S), within the front (59–61.5°S) and south of the APF (61.5–71°S). Production and respiration rates in the spring were highest north of the polar front and at the seasonal ice-edge (∼65°S) during a phytoplankton bloom. Depth-integrated rates of gross C, net C production and community respiration across the region were 155, 84 and –71 mmol C m−2 d−1, respectively. During the austral summer integrated gross O2 production rates remained high north of the APF and were similar to rates measured there in the spring, but decreased within the front and south of it. Production exceeded respiration north of the APF, but net heterotrophic conditions were observed within and south of the front. Depth-integrated rates of gross C, net C production and community respiration for the transect were 87, 5 and –37 mmol C m−2 d−1. Higher rates of oxygen consumption in the light suggest that phytoplankton respiration may have been a significant sink for gross production in the summer. Net O2 production estimated from mixed-layer O2 saturation levels was about a factor of two lower than in vitro bottle incubations and confirmed that respiration slightly exceeded production over much of the region in the summer.