Hypersensitivity of Southern Ocean air-sea carbon fluxes to background
turbulent diapycnal mixing
The Southern Ocean (SO) is the worlds largest high nutrient low
chlorophyll region and has a plentiful supply of underutilised
macronutrients due to light and iron limitation. These macronutrients
supply the rest of the neighboring ocean basins, and are hugely
important for global productivity and ocean carbon sequestration.
Vertical mixing rates in the SO are known to vary by an order of
magnitude temporally and spatially, however there is great uncertainty
in the parameterization of this mixing, including in the specification
of a background mixing value in coarse resolutation Earth System Models.
Using a biogeochemical-ocean model we show that SO biomass is highly
sensitive to altering the background diapycnal mixing over short
timescales. Increasing mixing enhances biomass by altering key
biogeochemical and physical parameters. An increased surface supply of
iron is responsible for biomass increases in most areas, demonstrating
the importance of year round diapycnal fluxes of iron to SO surface
waters. These changes to SO biomass could potentially alter atmospheric
CO2 concentration over longer timescales, demonstrating the importance
of accurate representation of diapycnal mixing in climate models.