This is an important result of the US GEOTRACES East Pacific Zonal Transect (EPZT) cruise (GP16) discussed by Hawco and his co-workers (2016, see reference below). The distribution of dissolved cobalt and labile cobalt along this section is closely tied to the oxygen minimum zone. This work also shows that (1) elevated concentrations of labile cobalt are generated by input from coastal sources and reduced scavenging at low oxygen; (2) atmospheric deposition and hydrothermal vents along the East Pacific Rise are contrastingly minor sources of cobalt; (3) high cobalt waters are further upwelled and advected offshore and; (4) phytoplankton export returns cobalt to low-oxygen water masses underneath. These processes result in covariation of dissolved cobalt with oxygen and phosphates, schematically represented in the Figure below.
Hawco, N. J., Ohnemus, D. C., Resing, J. A., Twining, B. S., & Saito, M. A. (2016). A dissolved cobalt plume in the oxygen minimum zone of the eastern tropical South Pacific. Biogeosciences, 13(20), 5697–5717. DOI: 10.5194/bg-13-5697-2016