Former group member Haidi Chen and Professor McKinley illustrate that isopycnal displacement in the subtropics drives high oxygen, high organic carbon, low nutrient waters to depth over the summer. These waters are pushed down along isopycnals as the season progresses. The organic carbon is remineralized along the way, and thus, there is net remineralization occurring at the same time that a positive tendency of oxygen appears along a fixed depth.
Read the paper: Chen, H.C. and G.A. McKinley (2019) Isopycnal processes allow for summertime heterotrophy despite net oxygen accumulation in the lower-euphotic zone of the western North Atlantic subtropical gyre, Global Biogeochemical Cycles, doi:10.1029/2018GB006094