The Arctic Ocean is a key region in global climate for various reasons including the vast amount of organic carbon and methane stored there as well as the role it plays in contributing fresh water to the Atlantic meridional overturning circulation. This high latitude region is particularly sensitive to impacts of climate change: studies of chemical distributions in the Arctic Ocean can provide insight into changes both in water masses/water sources as well as into the biogeochemistry and biology of the Arctic Ocean. Trace elements are important because some can be trace nutrients affecting productivity (e.g., iron), some are potentially toxic indicators of human impacts (e.g., mercury), and some are indicators of various input and removal processes (e.g., vanadium).

We proposed studies of selected dissolved trace elements along with dissolved methane in association with the 2015 US GEOTRACES Arctic section, which went from the Aleutians to the North Pole and back. This cruise offered a unique opportunity to collect samples through the western Arctic and participate in related studies of chemical fluxes in this important environment. We also obtained similar sets of samples collected in 2015 Canadian and European scientists to get a broader representation of Arctic Ocean geochemistry. Barents Sea samples were also obtained from Russian colleagues. Figure 1 shows sample locations.

Besides trace elements, we also examined the distribution of dissolve methane. Methane is a greenhouse gas responsible for ~20% of anthropogenic warming; it also plays an important role in atmospheric chemistry. Within the Arctic, there is particular interest in the effects of climate warming on methane reservoirs including those in permafrost and shelf sediment hydrates. The economic costs of the release of methane from these stored reservoirs could be staggering due to its impact on global warming and ultimately sea level rise.

Our research revealed a number of important and useful findings:

1. We contributed to two research papers involving multiple groups of investigators examining the impact of atmospheric input on trace element distributions on Arctic Ocean waters. This is important because some trace nutrients and contaminants are primarily delivered to the ocean from the atmosphere. As the extent and timing of ice cover on the Arctic Ocean changes, the timing of the input of these atmospheric materials...and their impact on biological processes...will change.

2. We found that dissolved gallium (Ga) concentrations help distinguish waters derived from the Atlantic Ocean versus the Pacific Ocean. Unraveling these contributions is important because the inflowing Atlantic waters have a greater potential for global change effects (such as release of trapped sedimentary methane) than Pacific waters. Our data show a more realistic separation of Atlantic and Pacific waters than had previously been estimated from nutrient distributions. In particular, our results indicate a greater contribution of Pacific water in the western Arctic Ocean compared to estimates from previous methods.

3. We found that processes on the margins of the Arctic Ocean basin, particularly the shallow shelf areas, can strongly affect the distributions of certain trace elements. The exchange of material between the shelves and open waters is an important process that can affect biological productivity. We demonstrated that dissolved vanadium (V) gets removed over the continental shelves by particle scavenging coupled with reducing conditions. Because of this, low dissolved V concentrations in the central Arctic Ocean basins are indicative of shelf exposure.

4. Dissolved barium (Ba) has previously been applied in the Arctic Ocean as a tracer of river waters, and it has also been noted that Ba concentrations tend to be lowest in Atlantic-derived waters. We see similar trends: concentrations are highest in surface waters and Pacific-derived water types and lowest in deeper, Atlantic-derived waters.

5. Dissolved methane concentrations in our section are highest over the continental shelves and slope, which supports our understanding of the major sources of methane (i.e., from microbes in oxygen limited sediments, from gas seeps, and from gas-hydrates). Current-induced resuspension of seafloor sediments at the shelf break may release greater amounts of methane to the water column than regions without mixing at the seafloor. Additionally, our data suggests a lower release of this greenhouse gas from shelf sediments than indicated by previous work on the Siberian Shelf.

Beyond the increased scientific understanding of Arctic Ocean chemical distributions, this project has had other broader impacts. A graduate student, who should defend her dissertation later this year, was trained as part of the project. Additionally, an undergraduate honors student trained in our lab. Results of the work have been or will be disseminated publication in peer-reviewed journals. The increased knowledge of Arctic Ocean processes gained in this work will benefit other Arctic Ocean researchers and those trying to understand the relationship of the Arctic Ocean to ongoing global change.

Last Modified: 05/17/2019
Modified by: Alan M Shiller