Exchange processes and watermass modifications along the subarctic front in the North Pacific: Oxygen consumption rates and net carbon flux

Exchange processes along the subarctic front and the modification of subpolar water in the North Pacific are investigated using tracer data from World Ocean Circulation Experiment P14N and P17N lines. The North Pacific Current transports water on both sides of the subarctic front from the western to eastern North Pacific. During this transport, subpolar water from the western subpolar gyre becomes warmer and saltier through the main thermocline via isopycnal mixing with subtropical water. It is shown that this modified subpolar water of western origin is the primary source of well-ventilated water to the eastern subpolar gyre. The isopycnal mixing along the subarctic front is quantified with a two end-member linear mixing analysis using potential temperature, which allowed estimates of oxygen consumption and nitrate remineralization on intermediate layers. Based on the oxygen consumption estimates and temporal information from transient tracers, the vertically integrated oxygen consumption rate is calculated to be 2.1 ± 0.4 M m^-2y^-1 in the 132-706 m depth range. This implies a net carbon flux of approximately 19 ± 4 gC m^-2y^-1 out of the euphotic zone.