The distribution of dissolved and total dissolvable aluminum in the Beaufort Sea and Canada Basin region of the Arctic Ocean

Abstract

Vertical profiles of the concentrations of dissolved Al [D‐Al] and total dissolvable Al [T‐Al] are reported from a transect extending from the continental shelf of the Beaufort Sea into the Canada Basin in the Arctic Ocean. Sampling was performed in late summer and early autumn 2007, a year of historically extensive sea‐ice melt. Vertical profiles of [D‐Al] displayed surface maxima (1–3 nmol kg−1), subsurface minima (<1 nmol kg−1) in the upper halocline layer (Upper HL; 50–200 m), and a general increase in concentration with depth to values of ∼5–10 nmol kg−1. Near surface maxima at this time were associated with relatively fresh surface waters (26–30) resulting from sea‐ice melt in the region. This observation supports sea ice with entrained sediments and surface deposition of aerosols as important mechanisms for the delivery of Al to surface waters of the Canada Basin. No correlation between D‐Al and silicic acid was observed and low D‐Al:Si ratios in waters >300 m depth suggest that Al is likely lost through particle scavenging in the interior of the Canada Basin. Concentrations of T‐Al show that particulate Al (>0.2 µm) is the dominant form of Al in the water column except at greater depths at the most offshore stations. Lateral transport of D‐Al and T‐Al off the shelf likely results from the offshore progression of cyclonic eddies spawned inshore, oscillating upwelling and downwelling favorable winds, and brine rejection during sea‐ice formation that can drive currents sufficiently energetic to resuspend shelf sediments.