Geochemistry, Geophysics, Geosystems

Dissolved gallium in the northwest Pacific and the south and central Atlantic Oceans: Implications for aeolian Fe input and a reconsideration of profiles

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Abstract

The distribution of dissolved gallium, a less-reactive analogue of aluminum, has the potential to reveal information about the averaged dust input to the surface ocean and to complement studies using aluminum as a tracer. New data are presented here on the distribution of dissolved Ga, including six profiles in the south and central Atlantic as well as seven shallow and two deep profiles from the northwest Pacific. The Atlantic data allow for an estimate of Ga in Antarctic Bottom Water (∼25–30 pmol kg−1) and show reasonably conservative behavior in deep waters. In the northwest Pacific, surface water Ga/Al ratios correlate with chlorophyll concentrations, probably reflecting the biogenic removal of dissolved Al and suggesting a possible means for estimating variation in surface water Al removal times. Also in the northwest Pacific, low surface water Ga in subpolar surface waters suggests low dust input, thereby providing an explanation for the high nutrient–low chlorophyll behavior of this environment. This low Ga subpolar water implies that North Pacific Intermediate Water is low in Ga and thus provides an advective explanation for the intermediate water Ga minimum observed in the temperate North Pacific. Surprisingly, the deepest waters sampled in the North Pacific have Ga concentrations similar to that estimated for circumpolar waters, thus indicating minimal reactivity of Ga in its northward transit in the deep Pacific.

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