The primary objective of the ocean acidification program is to describe spatial, seasonal and interannual variability in the marine carbon cycle to assess the extent and potential impacts of ocean acidification. Secondarily, data are obtained via CTD (conductivity-temperature-depth) casts that will better characterize how much of a sink the Chukchi Sea provides for atmospheric CO2. This data will be critical to long-term projections of how the Arctic Ocean will respond under future climate scenarios.
Samples were collected and analyzed for dissolved inorganic carbon and total alkalinity
in August, September, and October in the Berger, Klondike, and Statoil lease sites in the eastern
Chukchi Sea. These samples where used to calculate the pH, partial pressure of CO2, and
carbonate mineral saturation states for calcite and aragonite in the water column. The data was
consistent with recent studies in the region that showed that phytoplankton primary production in
late spring significantly alters the carbon biogeochemistry of the water column throughout the
year. Early in the ice-free period, primary production consumes DIC in the euphotic zone
causing pH and carbonate mineral saturation states to increase. However, much of the organic
matter that is produced is exported from the surface making the eastern Chukchi Sea a strong
sink for atmospheric CO2. As the organic matter settles near the bottom and is broken down by
bacteria, DIC concentrations increase sharply, particularly later in the year, driving down pH and
suppressing the concentrations of important carbonate minerals that are necessary for shell
growth in benthic calcifying organisms. The data from 2010 shows a definitive seasonal
progression of this process with aragonite becoming partially undersaturated along the bottom in
September, and broadly undersaturated in October. While carbonate saturation states would
naturally be suppressed by the high rates of export production, the penetration of anthropogenic
CO2 into water column (ocean acidification) has caused the observed undersaturations and these
will likely expand as CO2 levels in the atmosphere continue to rise in the coming decades. It is
unclear at this time what the implications to the benthic calcifying ecosystem will be due to
ocean acidification.
