Award: OPP-1643845

Phytoplankton are microscopic algae that form large blooms along portions of Antarctica’s coastlines and in the Southern Ocean during the southern hemisphere’s spring and summer seasons. These blooms can play a significant role in removing atmospheric carbon dioxide due to their high rates of marine photosynthesis and associated sinking of organic matter. Phytoplankton species composition is important as rates of carbon fixed vary among different species. In the Amundsen Sea region of western Antarctica, recent increases in the rate of glacial ice melt has resulted in enhanced fresh water and trace metal additions such as iron to the coastal environment. Iron is a nutrient that can stimulate large phytoplankton blooms in Antarctic coastal waters. Most broadly, this project focused on understanding iron and other trace element impacts on coastal Antarctic productivity with a view towards predicting future marine conditions as Antarctic glacial ice continues to melt. We previously published data suggesting that both iron and vitamin B12 may play a role in stimulating phytoplankton growth in the Ross Sea. This study investigated the potential for both iron and zinc additions from the glacial melt water and vitamin B12 (cobalamin) additions from coastal bacterial populations to stimulate phytoplankton growth and influence species composition in the Amundsen and Ross Seas. It is becoming clear that bacterial-algal interactions are important in structuring the microbial community composition as well as primary production in Antarctic coastal waters. It is also known that phytoplankton species composition can be a major factor determining the role of the Southern Ocean on impacting carbon uptake by algal communities. We observed that the growth of diatom populations was preferentially limited by iron and vitamin B12 compared to the predominantly iron-limited growth of Phaeocystis antarctica, another important phytoplankton species in the Southern Ocean. Additional experiments showed that dissolved Zn can also be co-limiting with Fe and Cobalamin. Taken together, the data suggested that from a biogeochemical and nutrient supply point of view, increased melting of Antarctica’s ice sheet may foster increased levels of primary production by algae in coastal waters. The Stanford University portion of the overall project involved conducting carbon concentration analyses of newly formed particulate materials in all experiments, as well as dissolved carbon contents and particulate carbon contents of the water column along the cruise track. Stanford group participants also collected water samples for diatom community structure analysis as well as seawater delta 18O values. Stanford led the hydrographic program and performed all initial quality-control data processing. Stanford scientists measured salinity on nearly 700 bottle samples during the cruise, to better calibrate the shipboard and deployable instrument salinity sensors. During the expedition we collected hydrographic data along the western Antarctic coastline. Some of this data was published in the journal Nature in a collaborative effort with Italian physical oceanography researchers. The project fostered international collaborations between Italian students, post-docs and researchers from the University of Napoli and Stazione Zoologica Dohrn with USA students and researchers. Specifically, Italian post-doctoral associate (Pasquale Castagno) and Ph.D. student (Francesco Bolinesi) participated on the expedition (at no cost to NSF) and interacted with graduate students and technicians from the College of Charleston, Stanford University, Rutgers University, Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution. Additionally, University of Otago (New Zealand) graduate student Michael Bollen participated on the expedition (at no cost to NSF) and interacted with the full shipboard scientific party. Michael is now pursuing Ph.D. Research in Switzerland. Last Modified: 05/18/2023 Submitted by: Robert B Dunbar