Biogeochemical Properties and Transports in the North East Atlantic

The eastern subpolar North Atlantic is a source of nutrients to the Northwest European Shelf and Arctic; however, biogeochemical transports in this important region are unknown. We examine variability in nutrients and carbon at the eastern boundary of the subpolar North Atlantic between 2017 and 2020, and calculate their transport by a branch of the North Atlantic Current and the European Slope Current. By combining observations from moorings and ship-based surveys, we derive novel biogeochemical property transports at high temporal resolution. Data from 63 m provide new evidence of a strong seasonal signal with silicate declining between April and May (-2.3 mu mol kg-1) and a concurrent increase in pH (0.04) and oxygen saturation (3.5%). Additionally, pH and oxygen saturation show a secondary peak in October during the autumn bloom. Biogeochemical transports are northwards and highly variable with volume transport dominating the variability over a multi-annual timescale. However, historical data suggests that nitrate and phosphate transports were 15% and 19% lower respectively in the late 2000s when the subpolar gyre circulation was weaker and lower nutrient source waters were dominant. These changes may have been amplified by concurrent reductions in volume transport. Changes in carbon and nutrient transports in the eastern subpolar North Atlantic may propagate downstream with potential effects on the Northwest European Shelf and Eurasian Arctic. Water flowing northward in the eastern subpolar North Atlantic transports nutrients onto the Northwest European Shelf and to the Arctic Ocean. However, biogeochemical transports through the region remain unknown. We examine variability in nutrients and carbon at the eastern boundary of the subpolar North Atlantic and calculate their transport by two important northward flowing currents. We use observations from ship-based surveys and instruments that recorded conditions in the ocean over 3 years to derive biogeochemical transports every 12 hr between May 2017 and October 2020. Transports of nutrients and carbon in the eastern subpolar North Atlantic are northwards although the transport is highly variable. Historical data suggests that when circulation around the subpolar North Atlantic is weaker, nutrient transports are around 15%-20% lower due to changes in the water nutrient concentrations. These changes may be amplified by concurrent reductions in current strength and volume transport. Changes in carbon and nutrient transports in the eastern subpolar North Atlantic may propagate downstream with potential effects on the Northwest European Shelf and Arctic Ocean. Silicate decreases and pH and oxygen increase from April to May with oxygen and pH showing a secondary peak in October Nutrient and carbon transports through the eastern boundary of the subpolar North Atlantic are northward and highly variable Biogeochemical transport magnitude may vary on multi-annual timescales and have downstream impacts