Boron to salinity ratios for Atlantic, Arctic and Polar Waters: A view from downstream

Discharges of freshwater into the Arctic Ocean from rivers in Eurasia and North America account for approximately 11% of the global riverine freshwater input, and contain weathering products including dissolved continental boron. Much of this freshwater flows into the North Atlantic Ocean, primarily via the East Greenland Current carrying the Polar Water with salinity <34.4. As a result, the input of boron-containing freshwater could cause the boron content in low salinity water to deviate from predictions based on the open ocean ratio for boron to salinity. Significant deviations from predictions would affect carbonate system calculations for seawater in the Arctic. We analysed the boron concentrations and salinity for seawater samples (n = 249; salinity = 30–35) collected primarily from the areas of the East Greenland Current downstream of the influence of freshwater inputs, and from northward flowing Atlantic Water in the vicinity of Iceland. Unexpectedly, the mean boron to salinity ratio of 0.1324 ± 0.0008 mg kg⁻¹‰⁻¹ was similar to the ratio for the open ocean (0.1336 mg kg⁻¹‰⁻¹). The absence of anomalies in the boron to salinity ratio measured for our samples provides compelling evidence that continental freshwater flowing into the Arctic Ocean probably contains little dissolved boron, and hence has a negligible effect on the boron to salinity ratio in the Arctic Ocean. Our results also indicate that known deviations in the polar water alkalinity from predictions based on the open ocean alkalinity-salinity relationship stem largely from other sources, primarily inputs of carbonate-rich freshwater.