Award: OCE-1433349

The purpose of this research project was the measure the isotopic composition of dissolved carbon dioxide (CO2) in the Arctic Ocean. The isotopic composition refers to the ratio of carbon-13 to carbon-12 (i.e. 13C/12C). The importance of the 13C/12C is two-fold. First, the 13C/12C composition of CO2 in the ocean changes as the ocean adsorbs CO2 emitted from a specific source, in this case, the burning of fossil fuels. Second, by measuring the 13C/12C of carbonate shells originally produced by phytoplankton in the surface ocean and currently buried in sediments, one can attempt to reconstruct the concentrations of CO2 in the ocean back through time. We collected ~500 samples of seawater from the Arctic Ocean during an oceanographic research cruise during fall of 2015 (Figure 1). These samples were analyzed for the 13C/12C of CO2 in our laboratory at the University of Washington. The 13C/12C of CO2 in the upper 2000m of the Arctic Ocean clearly showed the increase in CO2 concentration due to absorption of CO2 produced during fossil fuel burning (Figure 2). This means that the levels of CO2 in the Arctic Ocean have increased significantly during the last ~150 years (i.e., the industrial era). This is an important observation because it verifies earlier claims that the Arctic Ocean is becoming more acidic, which is referred to as Ocean Acidification, as a result of accumulation of CO2 produced by fossil fuel burning. We made another important observation about the change in the 13C/12C of CO2 in the seawater of the Arctic Ocean. We determined that the change was the result primarily of CO2 that was carried into the Arctic Ocean by ocean currents entering from the Atlantic and Pacific Oceans. This is important because it means that the acidification of the Arctic Ocean is driven mainly by ocean circulation rather than by the uptake of CO2 within the Arctic Ocean basin itself. Furthermore, we determined that chemical compounds necessary for photosynthesis by phytoplankton, like nitrate and phosphate, were added primarily by ocean currents just like for CO2. This is important because it means that the rate of photosynthesis in the Arctic Ocean is, in part, tied to the supply of nutrients from the Atlantic and Pacific Oceans. This observation also suggests that changes in photosynthesis rates in the Arctic Ocean during the past, as recorded by the 13C/12C of carbonate shells in ocean sediments, are partially the results of changes in the supply of nutrients via ocean currents. From a broader impact perspective, the 13C/12C measurements on CO2 that we made during the 2015 cruise provide an important benchmark for future cruises. We expect the 13C/12C of CO2 to continue to change as the Arctic Ocean continues to accumulate CO2 in the future. By comparing the 13C/12C of CO2 measured on future cruises to the Arctic Ocean to the measurements we made in 2015 we will be able to calculate the rate at which CO2 produced by fossil fuel burning has been accumulating in the seawater and, as a result, the increase rate in ocean acidification. Determining the rate of ocean acidification in the Arctic Ocean will be an important factor impacting the future populations of many shellfish (specifically crabs and clams) which are important commercial fisheries in this region. Last Modified: 01/03/2019 Submitted by: Paul D Quay