Environmental Drivers of Biogeochemical Variability in the Southern Ross Sea: Results from a 1D Modeling Study

Ross Sea phytoplankton, generally dominated by diatoms and Phaeocystis antarctica, play an essential biogeochemical role in this highly biologically productive Southern Ocean region. Although associations between these phytoplankton and environmental factors such as temperature, vertical mixing, and irradiance have been documented, the causal mechanisms among these interactions and extent to which they are modified by altered climatic conditions are poorly understood. To investigate these relationships, data from a 2012 glider deployment are analyzed in conjunction with model experiments performed using a modified version of the multi-component Model of Ecosystem Dynamics, nutrient Utilisation, Sequestration and Acidification (MEDUSA) run within the Marine Model Optimization Testbed (MarMOT), a one-dimensional data assimilative analysis framework. Specifically, MEDUSA has been adapted for the Ross Sea by including both solitary and colonial forms of P. antarctica and irradiance-Fe interactions. After evaluating model performance with glider observations of chlorophyll and particulate organic carbon, scenario experiments are conducted investigating how the magnitude and phenology of spring and summer phytoplankton are likely to be modified by a future altered climate. In particular, the relative impacts of potential increased water temperatures on phytoplankton productivity will be assessed, through differences in biological rates, increased iron and light availability from melting ice, and increased stratification. Variability in phytoplankton productivity resulting from these effects of warming temperatures are analyzed individually and in combination to evaluate the relative importance of these drivers of change in the biogeochemical environment of the Ross Sea.