On using Si to unravel potential sources of dissolved Al to the deep Arctic

The initial observation of a correlation between dissolved Si and Al within the water column of the Mediterranean was invoked to imply vertical transport and remineralisation of a biogenic Si phase to explain observed deep water enrichments of dissolved Al. However, the development of more extended data sets of dissolved Al and Si from a greater number of oceanic regions has shown that this relationship is either highly variable or non-existent in many places, calling into question the significance of this mechanism. This is particularly true in the Arctic Ocean, which shows one of the most elevated deep-water enrichments of dissolved Al of any ocean basin, but as a result of its perennial ice cover has one of the lowest vertical fluxes of biogenic particles. While it seems unlikely that this vertical mechanism can be important in the Arctic, the extent and magnitude of both the dissolved Si and Al concentrations provides clues to their sources. We will show that the Si:Al ratio in the deep waters are inconsistent with upper water column sources, but are consistent with resuspension and dissolution of sedimentary material and release of associated pore waters. In addition, the Si:Al ratios suggest that it is the dissolution of aluminosilicate material of continental origin that is providing these enhancements, not from biogenic material. Thus the distribution of dissolved Al in the deep water of the Arctic, and other basins appears to be tracing direct continental inputs to the deep ocean in much the same manner that surface water values reflect the input of wind-blown continental materials to the surface ocean.