Pedro M. S. Monteiro

Intraseasonal variability linked to sampling alias in air‐sea CO2 fluxes in the Southern Ocean

The Southern Ocean (SO) contributes most of the uncertainty in contemporary estimates of the mean annual flux of carbon dioxide CO2 between the ocean and the atmosphere. Attempts to reduce this uncertainty have aimed at resolving the seasonal cycle of the fugacity of CO2 (fCO2). We use hourly CO2 flux and driver observations collected by the combined deployment of ocean gliders to show that resolving the seasonal cycle is not sufficient to reduce the uncertainty of the flux of CO2 to below the threshold required to reveal climatic trends in CO2 fluxes. This was done by iteratively subsampling the hourly CO2 data set at various time intervals. We show that because of storm-linked intraseasonal variability in the spring-late summer, sampling intervals longer than 2 days alias the seasonal mean flux estimate above the required threshold. Moreover, the regional nature and long-term trends in storm characteristics may be an important influence in the future role of the SO in the carbon-climate system.

Investigation into the impact of storms on sustaining summer primary productivity in the Sub‐Antarctic Ocean

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 intra-seasonal 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.