What are the science objectives of CORSACS, and why is the project important? Those two questions are fundamental to any project and need to be clearly stated and addressed.

The earth's atmosphere is changing, with increased carbon dioxide concentrations occurring throughout. As a result, CO2 levels are also increasing in the ocean's surface layer. In the past most oceanographers did not worry about the slight increase, because carbon dioxide was not considered to limit phytoplankton growth in any way.

However, because different species have different carbon dioxide uptake systems and different preferences for the various inorganic forms of carbon present in seawater, researchers tested the effects of increased levels of CO2 on phytoplankton growth and composition. They found that elevated CO2 greatly altered the composition of phytoplankton, likely through changing the competitive advantages of those groups that use CO2 instead of bicarbonate (the most common form of inorganic C in the ocean).

At high CO2 levels a type of algae called Phaeocystis dominated, whereas at lower CO2 levels diatoms grew best. These experiments were conducted in coastal waters, but not in polar regions. The CORSACS group proposed to test this hypothesis in the Ross Sea, a region where both diatoms and Phaeocystis occur. The logo of the project (designed at Woods Hole Oceanographic) depicts these goals.

Last year's cruise concentrated on diatoms, and this year's will concentrate on Phaeocystis. We hypothesize that there is an interaction among light, iron, and CO2 that controls species composition, and will conduct large-volume experimental manipulations using trace-metal clean techniques to test this. We will sample water and then vary the light, iron and CO2 levels; these experiments will last approximately 20 days, and at the end we will see if these factors generate a change in composition among various phytoplankton groups.

The VIMS group is an essential part of this test, as we are in charge of assessing the response to light using various assays of photosynthesis. The group will also make many measurements at various locations, and will construct an in situ depiction of light, iron, and CO2 so that we can compare our experimental results with the field situation.

Many additional "sub-projects" occur within CORSACS as well. For example, a number of us are also testing the effects of temperature and the interaction with light and iron. The sum of all of this work will allow us to better predict the impacts of the global increases in atmospheric CO2 on the marine biota.