Work package POL 2: Southern Ocean climate and ecosystem
The overarching goal of the proposed research is to deliver improved scientific
understanding of climate change that could result inter alia from anthropogenic CO2
emissions. Knowledge of the processes governing the recurring patterns of CO2 variations
in the past is a prerequisite to forecasting future climate development. The research effort
will focus on the poorly explored Southern Ocean because of its crucial role in the global
climate machinery.
A major feature of the Southern Ocean is the broad ring of cold water - the Antarctic
Circumpolar Current (ACC) - which encircles Antarctica and isolates its ice cap from
warming. The ACC connects all the other oceans and thus plays an important role in the
global heat and freshwater transports and ocean-wide biogeochemical cycles. It harbours a
series of unique and distinct ecosystems along concentric, zonal bands that displace each
other with changing climate regimes as indicated in the sedimentary record. Due to the
upwelling of deep water masses from all ocean basins in the Antarctic Divergence the plant
nutrient concentrations are the highest worldwide in the surface open ocean. These
concentrations could support much higher phytoplankton primary production and hence CO2
uptake than observed. The paradoxically low rates of primary production have been
attributed to insufficient light availability due to wind-driven deep mixing, limiting
concentrations of trace nutrients such as dissolved iron, or heavy grazing by zooplankton.
Recently, a series of open ocean experiments have demonstrated that addition of small
quantities of dissolved iron results in dramatic phytoplankton biomass build-up. Since the
glacial CO2 minima correlate well with aeolian deposition of iron-rich dust on the ACC, a
strong case has been made that phytoplankton blooms represent a significant sink of
atmospheric CO2 during glacial periods. However, since the fate of biomass produced by
iron fertilization has not yet been documented, the role of the ACC as a potential sink of
CO2 has yet to be demonstrated.
The complexity of interacting processes, which determine the internal and external forcing
and amplification mechanisms of climate change, shall be elucidated by integrating
physical, chemical, biological and geological disciplines of the ocean sciences and by
coordinating field observations, experiments and modelling exercises.