Nathan Garcia

I am a Master’s candidate in the College of Charleston’s Marine Biology Program where I am studying an Antarctic species of phytoplankton, Phaeocystis antarctica (Prymnesiophyceae).  In the Austral summer P. antarctica blooms in the South Central Ross Sea (located South of New Zealand) and is the largest source of primary productivity in the entire southern ocean.

This bloom is important to the global climate for two reasons: 1) when the bloom dies, comparatively high amounts of carbon (initially attained from the atmosphere) are drawn down to the sea floor; and 2) the bloom produces a high amount of a radiatively important gas, dimethylsulfide (DMS).  Dimethylsulfide comprises approximately 50% of atmospheric sulfur and is able to reflect sunlight off the earth’s atmosphere, ultimately decreasing the amount of light reaching the earth’s surface.  Furthermore, water condenses on the DMS molecule ultimately forming clouds.  Therefore, the production of DMS can be viewed as a reflective sunglasses effect and has major implications for predicting future global climate change with the onset of global warming.  Some data support the claim that DMS is produced in high amounts when exposed to high irradiance levels from the sun.  The production of DMS can be viewed as a feedback mechanism that ultimately provides protection from the sun.

Currently, the physiological purpose for the production of the precursor to DMS, dimethylsulfoniopropionate (DMSP) is poorly understood.  The goal of our project is to investigate a physiological protective mechanism of DMS.  Recently, DMS has been hypothesized to function as an anti-oxidant to scavenge free radicals produced in the cell when exposed to high irradiance levels.  Furthermore high amounts of free radicals may be generated under iron limitation.  Nanomolar and sub-nanomolar concentrations of iron have been well documented in many regions of the Southern Ocean including the Ross Sea.  We will examine sulfur production in response to oxidative stress induced by high light and iron limitation in Phaeocystis antarctica.

Data support the hypothesis that global warming is shifting species compositions in sensitive regions (such as ice forming regions) that contribute to high primary production.  Future global warming will most likely result in a species shift in the South Central Ross Sea ultimately producing changes in the sulfur cycle and changes in carbon drawdown from the atmosphere to the sea floor.  Future models attempting to predict changes in the global climate must understand the ramifications of such species shift.  Our study will contribute to understanding these ramifications.