Award: PLR-1304563

The long-standing paradigm of the Arctic Ocean is one in which phytoplankton (single-celled plant-like organisms) do not begin to grow until the winter sea ice begins to melt in the late spring, exposing surface waters to the light from the sun. Phytoplankton then proliferate at the ice edge (called the marginal ice zone or MIZ), supplying a substantial fraction of the food that feeds the rest of the Arctic marine ecosystem. However, data from the SUBICE (Study of Under-ice Blooms In the Chukchi Ecosystem) project suggest that this paradigm needs to be revised for areas of the Arctic Ocean like the Chukchi Sea, where phytoplankton have been shown to thrive in the relatively low light environment that exists beneath the extensive sea ice cover. Phytoplankton growth under the ice in the nutrient-rich Chukchi Sea likely begins soon after the snow cover melts, surface melt ponds form, and light transmission through the ice to the water column increases. Whether this early stage of the phytoplankton bloom is initiated by the release of algae from the sea ice is not known. As phytoplankton continue to grow under the ice, they consume nutrients at the ocean surface. Eventually, a subsurface layer of phytoplankton develops as nutrients are consumed in the upper water column beneath the ice. When the sea ice finally melts, nutrient-poor surface waters become isolated from nutrient-rich waters below, preventing the development of the classic MIZ bloom that has been observed so frequently in the past. Because the phytoplankton growing in the subsurface layer beneath the sea ice are already accustomed to low light conditions, they grow very rapidly once the sea ice retreats. Thus, phytoplankton blooms beneath the Arctic ice pack transform the MIZ from a highly productive surface environment to one where nutrients have been exhausted weeks earlier and the bulk of the algal biomass is located 20-30 m below the surface. In addition, Arctic sea ice is retreating 2.4 days earlier each year, accelerating the development of open water phytoplankton blooms. The implications of this marked shift in the timing and location of peak biological productivity in Arctic waters are unclear but potentially profound. Many organisms time their migrations and reproduction cycle to coincide with peak phytoplankton abundance in the Arctic so altering the location and timing of the spring bloom could disrupt life cycle strategies that have evolved over millenia. Furthermore, because these under-ice blooms develop in such cold water, zooplankton grazers cannot grow fast enough to keep pace. As a result, much of the phytoplankton under the ice go uneaten, ultimately sinking to the bottom in a region already distinguished by tremendous concentrations of bottom-dwelling animals while at the same time decreasing the food available to fish, birds, and mammals that feed in the water column. The SUBICE project supported the training and intellectual development of five female Ph.D. students. The project also provided underrepresented undergraduates from different US universities and diverse cultural backgrounds the opportunity to spend a summer doing a research project at Stanford. This was facilitated through the SURGE (Stanford's Summer Undergraduate Research in Geoscience and Engineering) program, which also included workshops on preparing for the GRE, applying to graduate school, and understanding geoscience and engineering careers. The Arrigo lab hosted two students in the summer of 2015 as part of this program, one from University of Miami and one from California State Monterey Bay. Both worked on different aspects of the Arctic nitrogen cycle and presented their summer research at the 2016 Ocean Sciences meeting in New Orleans. Last Modified: 09/06/2017 Submitted by: Kevin R Arrigo