Oceanography (Sep 2011)
Sea Ice Biogeochemistry and Material Transport Across the Frozen Interface
Abstract
The porous nature of sea ice not only provides a habitat for ice algae but also opens a pathway for exchanges of organic matter, nutrients, and gases with the seawater below and the atmosphere above. These constituents permeate the ice cover through air-ice gas exchange, brine drainage, seawater entrainment into the ice, and air-sea gas exchange within leads and polynyas. The central goal in sea ice biogeochemistry since the 1980s has been to discover the physical, biological, and chemical rates and pathways by which sea ice affects the distribution and storage of biogenic gases (namely CO2, O2, and dimethyl sulfide) between the ocean and the atmosphere. Historically, sea ice held the fascination of scientists for its role in the ocean heat budget, and the resulting view of sea ice as a barrier to heat and mass transport became its canonical representation. However, the recognition that sea ice contains a vibrant community of ice-tolerant organisms and strategic reserves of carbon has brought forward a more nuanced view of the "barrier" as an active participant in polar biogeochemical cycles. In this context, the organisms and their habitat of brine and salt crystals drive material fluxes into and out of the ice, regulated by liquid and gas permeability. Today, scientists who study sea ice are acutely focused on determining the flux pathways of inorganic carbon, particulate organics, climate-active gases, excess carbonate alkalinity, and ultimately, the role of all of these constituents in the climate system. Thomas and Dieckmann (2010) recently reviewed sea ice biogeochemistry, and so we do not attempt a comprehensive review here. Instead, our goal is to provide a historical perspective, along with some recent discoveries and observations to highlight the most outstanding questions and possibly useful avenues for future research.
