Eddy-driven oxygen supply to the eastern tropical North Atlantic oxygen minimum zone

• Main Authors: Hahn, Johannes, Brandt, Peter, Kemme, Jöran
• Format: Conference Object
• Language: English
• Published: 2018
• Subjects: North Atlantic
• Online Access: https://oceanrep.geomar.de/id/eprint/45082/; https://oceanrep.geomar.de/id/eprint/45082/1/20181023_PIRATA23meeting_Hahn_et_al.pptx

Shipboard oxygen observations from the last decade (2006-2015) reveal substantial oxygen changes in the eastern tropical North Atlantic (ETNA) oxygen minimum zone (OMZ) with a strong oxygen decrease at depth of the deep oxycline (200-400m) and oxygen increase below (400-1000m). This pronounced pattern is superimposed on the weaker but large-scale multi-decadal deoxygenation. Opposing both trends in a time-varying oxygen budget of the OMZ shows that, qualitatively, variations in the zonal current field are most likely responsible for the observed ten-year oxygen change pattern. Though, other processes might play a role as well. Here, we use a combined set of satellite altimetry and in situ moored and shipboard data to investigate the potential of a temporally varying mesoscale eddy field in driving interannual to decadal variations of the oxygen supply to and the associated oxygen inventory of the ETNA OMZ. By assuming an idealized vertical structure of the mesoscale eddy activity as was recently formulated, satellite observations are used to parameterize the subsurface eddy kinetic energy and eddy diffusivity for the period 1993-2017. The eddy-driven oxygen flux time series, which is derived by combining eddy diffusivity and horizontal oxygen gradients, is then compared, in the overlapping period, with a multi-year oxygen flux time series derived from moored velocity and oxygen observations to test the plausibility of both methods. Eventually, the relative importance of eddy fluxes in the time-varying oxygen budget and in driving interannual to decadal oxygen changes is discussed.