Fluxes of dissolved aluminum and manganese to the Weddell Sea and indications for manganese co‐limitation

Abstract

The trace metals aluminum (Al) and manganese (Mn) were studied in the Weddell Sea in March 2008. Concentrations of dissolved Al ([Al]) were slightly elevated (0.23–0.35 nmol L−1) in the surface layer compared to the subsurface minimum (0.07–0.21 nmol L−1) observed in the winter water. Atmospheric deposition is the main source of Al to the central Weddell Sea (22 µmol m−2 yr−1), and the residence time of dissolved Al in the upper mixed layer is ∼ 0.8 yr. The flux from the shelf and slope regions equals about 50% of the atmospheric input of Al to the western Weddell Sea. The highest [Al] in the Weddell Sea bottom water (WSBW) is related to the formation of deep water, and the associated downward flux is in the range of 3–10 µmol Al m−2 yr−1. The concentrations of dissolved Mn ([Mn]) were depleted in the surface layer, likely as a result of biological uptake, as indicated by the correlation among Mn, major nutrients, and fluorescence. The significant negative relation between the ΔMn : ΔP ratio and the ambient concentration of dissolved iron indicates iron‐Mn co‐limitation. The flux of Mn from the continental margin is about 2.2 times greater than atmospheric input (1.1 µmol m−2 yr−1). The flux of both Al and Mn from the continental margin indicates melting of continental ice (icebergs) or direct continental runoff. The slightly elevated [Mn] in the WSBW is due to a relatively small flux of 1 µmol Mn m−2 yr−1 associated with WSBW formation.