The Arctic Ocean is uniquely influenced by biogeochemical processes on continental shelves, which underlie more than half the ocean’s area. Shelf-derived nutrients and carbon are rapidly transported across the central ocean basin—from the East Siberian and Laptev Seas toward the Fram Strait between Greenland and Svalbard—by a surface current known as the Transpolar Drift (TPD) on timescales of 1–3 years.
The TPD carries clues to how climate change is reshaping the Arctic, the fastest warming region on Earth. During the peak of summertime melt in 2018, the discharge rate of the largest Arctic rivers was 20% higher than in the 1980s. As temperatures rise, increasing discharge from rivers and melting permafrost could have an impact on primary production across the basin. But there is a dearth of data on the transport of trace elements and carbon in the remote region, where icebreakers are a critical component of any sampling expedition.
Charette et al. took advantage of data collected by the GEOTRACES program during a pan-Arctic survey in 2015. The research cruises crossed the TPD twice, measuring concentrations of nutrients, trace elements, and carbon concentrations along the way. In the new study, the researchers used radionuclide tracers and ice flow models to infer the mass transport rate for the TPD and to estimate trace element fluxes from the shelves to the central Arctic Ocean, with the goal of better understanding how climate change will affect Arctic basin ecosystems.
Isotopic ratios of radium—which is not biologically important itself but acts as a tracer for other elements—indicated that continental shelf sediments were the dominant source of the element in the TPD. Concentrations of some dissolved trace elements—notably, iron, cobalt, nickel, copper, mercury, neodymium, and thorium—were higher than expected within the TPD. Concentrations of aluminum, vanadium, gallium, and lead, meanwhile, were lower. The observed trace metal enrichments resulted in large part from the elements binding to dissolved organic matter sourced from Arctic rivers and permafrost thaw.
As both temperatures and freshwater inputs to the Arctic Ocean increase in the future, researchers expect Arctic waters to become increasingly stratified, which will affect nutrient availability and could mean that the TPD will become even more important in primary productivity in the Arctic Ocean and beyond. Understanding the elemental “fingerprint” of the TPD could help researchers track flows and uptake of nutrients and elements into other ocean basins, and in the increasingly ice-free Arctic. (Journal of Geophysical Research: Oceans, https://doi.org/10.1029/2019JC015920, 2020)
—Kate Wheeling, Freelance Writer