Weathering, atmosphere and sea-ice: The cycling of aluminium in coastal Antarctica
Abstract
Aluminium (Al) is the third most abundant element in crustal materials, and is released into seawater mainly from terrestrial weathering, via fluvial and glacial runoff, dust and aerosols. However, concentrations of dissolved Al in seawater are disproportionately low as a result of rapid scavenging and uptake by particles. Quantifying the geochemical behaviour of Al in seawater is important for our understanding of the biogeochemical cycling of other elements, such as iron, which share common input and output processes. In particular, further understanding is required of the relative importance of, and geographical variations in, different inputs and outputs of Al to the oceans, and how perturbations related to human activity may impact these processes. Here, we investigate the behaviour of Al in seawater, sea-ice, meteoric water and sediments collected from a region of high biological productivity in coastal Antarctica from 2005-2006. Dissolved Al concentrations at the chlorophyll maximum showed systematic variation, with a peak between two phytoplankton blooms. We find that, even in a coastal setting, upwelling deep-waters are the dominant source of dissolved Al to the surface waters, probably due to release from sediments or brine rejection, the latter of which appears to be common to both northern and southern high latitudes. Glacial, snow and sea-ice melt contributes secondarily to the supply of Al to surface waters. Total particulate Al increases with meteoric input towards the end of the summer, indicating an increase in lithogenic particles sourced from glacial runoff. The normalised Al content of opal, (Al/Si)opal, does not vary significantly throughout the year, also consistent with input of Al from upwelling waters, as opposed to atmospheric or melt-water sources. The (Al/Si)opal of core top material is considerably higher than water column opal, indicative of a diagenetic overprint and incorporation of Al at the sediment-water interface. Dissolution of this biogenic opal could be a source of Al to pore fluids, which could then diffuse into the overlying water column. Conversely, the opal that remains undissolved in the sediment could represent a significant sink of Al from seawater.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFMPP23A1372H
- Keywords:
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- 0461 BIOGEOSCIENCES / Metals;
- 0750 CRYOSPHERE / Sea ice;
- 4207 OCEANOGRAPHY: GENERAL / Arctic and Antarctic oceanography;
- 4924 PALEOCEANOGRAPHY / Geochemical tracers