Abstract

In the Sub-Antarctic Ocean elevated phytoplankton biomass persists through summer at a time when productivity is expected to be low due to iron limitation. Biological iron recycling has been shown to support summer biomass. In addition, we investigate an iron supply mechanism previously unaccounted for in iron budget studies. Using a 1-D biogeochemical model, we show how storm-driven mixing provides relief from phytoplankton iron limitation through the entrainment of iron beneath the productive layer. This effect is significant when a mixing transition layer of strong diffusivities (kz > 10−4 m2 s−1) is present beneath the surface-mixing layer. Such subsurface mixing has been shown to arise from interactions between turbulent ocean dynamics and storm-driven inertial motions. The addition of intraseasonal mixing yielded increases of up to 60% in summer primary production. These results stress the need to acquire observations of subsurface mixing and to develop the appropriate parameterizations of such phenomena for ocean-biogeochemical models.

Link to Full Article
Comparisons of (a and b) primary production, (c and d) DFe, and (e and f) integrated PP, surface PP*64, MLD, and surface DFe between the 'SXLD surface mixed-layer deepening' and the 'subsurface mixing run'.

Comparisons of (a and b) primary production, (c and d) DFe, and (e and f) integrated PP, surface PP*64, MLD, and surface DFe between the ‘SXLD surface mixed-layer deepening’ and the ‘subsurface mixing run’.

'