BIOPOLE in the Western Arctic Ocean

Polar oceans export nutrients to the lower latitudes where this export flux can be an important regulator of lower latitude productivity.  In the Arctic Ocean careful analysis of nutrient inputs and outputs suggests that the Arctic is a net exporter of phosphorous and silicate to the North Atlantic but intriguingly not nitrogen with nitrogen inputs to, and outputs from, the Arctic seemingly balanced. The result is a characteristic change to the nitrogen to phosphorous (N:P) ratio found in seawater which gradually increases as ocean waters flow from the Pacific through the Arctic and eventually out into the Atlantic Ocean. Despite considerable uncertainties and limitations of existing datasets nitrogen loss processes occurring in the Western Arctic, particularly within the sediments of the shallow Bering and Chukchi Seas, are known to contribute to the removal of nitrogen and enrichment of phosphorous reported in seawater nutrient measurements. However, the magnitude of this sedimentary nitrogen removal process is insufficient to account for the observed shift in seawater N:P ratios, with several competing explanations presented in the literature as to why this may be. One interesting possibility, and a target of BIOPOLE Work Package 2 (WP2) activities in the western Arctic, is the presence of an additional nitrogen sink operating within the water column.

To address this possibility BIOPOLE WP2 was tasked with measuring bacterial denitrification rates, collecting eDNA/eRNA samples to probe the makeup and function of bacterial communities present in seawater, and to deploy an automated water sampler to collect an annual cycle of seawater nutrient concentrations in water flowing across the remote and seasonally icebound northern Chukchi Shelf. These activities will contribute to wider programme efforts investigating how ecosystem processes can change elemental balances in the northern polar region and to project Milestones i and ii (new observations in polar environments and obtainment of seasonal measurements via autonomous technologies).

Access to the Western Arctic (from the UK at least) is non-trivial but through the supporting efforts of project partners based at the University of Maryland and the University of Alaska, Fairbanks, a single berth was secured on the 2023 autumn Arctic ecosystem survey aboard the R.V. Sikuliaq, an ice-class research vessel operated by the University of Alaska, Fairbanks. Demand for berths was high and the cruise itself was a consortium effort supporting NOAA’s EcoFOCI program (Ecosystems and Fisheries Oceanography) and the NOAA Marine Mammal Lab,  the Distributed Biological Observatory (DBO) programme run from the University of Maryland (project partner), and the Arctic Marine Biodiversity Observation Network (AMBON) and Chukchi Ecosystem Observatory (CEO) projects both run from the University of Alaska Fairbanks (project partner).

The result was an enjoyable cruise with diverse scientific activities ranging from benthic trawls, benthic landers, water sampling, mooring recoveries/deployments, sea-bird and marine mammal observations, and detailed chemical and physical observations across this key Arctic region. Results from BIOPOLE activities will be made available in due course once samples have returned to the UK and have been analysed, but which is expected to be within 6-12 months.

Map of the survey region and sampling locations

Stuart Painter from the National Oceanography Centre