Dissolved gallium in the Beaufort Sea of the Western Arctic Ocean: A GEOTRACES cruise in the International Polar Year

Dissolved gallium (Ga) concentrations are presented from the Beaufort Sea, representing the first reported values of Ga in the Arctic Ocean. Profiles of dissolved Ga in this region reflect Pacific and Atlantic Oceans source waters. Dissolved Ga concentrations of 4-6 pmol kg− 1 at depths < ~ 150 m are characteristic of dissolved Ga in the North Pacific, and at depths > ~ 350 m concentrations of 25-28 pmol kg− 1 are indicative of Atlantic waters. A smooth gradient of increasing dissolved Ga concentrations is observed through the thermocline, consistent with mixing of cool Pacific waters of low Ga concentration and relatively warm Atlantic waters of higher Ga concentration. Dissolved Ga is shown here to represent a complimentary tracer of Pacific inputs to the Western Arctic Ocean, as seasonal processes influencing temperature and Nitrate:Phosphate of Pacific Water entering the Arctic are not apparent in dissolved Ga profiles. Observed phosphate deficiency within nitrate deplete waters in the upper ~ 70 m is interpreted to result from nitrogen fixation in Pacific waters stored within the anticyclonic Beaufort Gyre. Conservative behavior of dissolved Ga within Pacific waters supports the interpretation here that nitrogen fixation rates calculated in this work are associated with Pacific source waters, as opposed to freshwater sources associated with the Mackenzie River or sea ice melt. Storage of phosphate deficient Pacific waters in the Beaufort Gyre followed by release and transport to the North Atlantic would result in pulses of phosphate deplete waters from the Arctic, impacting nitrogen fixation in the Atlantic Ocean. Sampling at one shelf station revealed local impacts on dissolved Ga concentrations, including high concentrations at shallow depths, interpreted to represent fresh waters inputs from the Mackenzie River or sea ice melt, while a restricted increase in Ga concentrations associated with the thermocline is suggested to result from increased scavenging rates within shelf environments due to increased particle abundance. Finally, first reports here of dissolved Ga in the Arctic allow comparison with profiles of dissolved Al. Distinct profiles of these two similar elements in the Arctic Ocean are interpreted to result from differential scavenging rates and vertical transport of dissolved Ga and Al within Atlantic sourced waters and deep basin waters.