Contrasting provenance, fluxes and budgets for dissolved aluminium and barium in the Mediterranean; an integrating overview

Abstract

The Mediterranean is a restricted basin considered to be a model-ocean for which sources and sinks of detrital and dissolved material can be effectively studied. The apparent behaviour of dissolved aluminium and barium in the water column appears to be mostly conservative despite their ‘nutrient-like’ profiles. The latter are determined by Atlantic inflowing surface water with low concentrations of Al and Ba, whereas the outflowing intermediate/deep water has much higher concentrations. This results in a major net removal of dissolved Al, Ba from the Mediterranean. In steady state, the large net removal of dissolved Al, Ba must be compensated by external sources. Fractional dissolution from dust for Al derived to be 2.2 ± 0.2% appears to be the main source (92%) for dissolved Al but a minor source (0.5%) for dissolved Ba. For Ba it is not the fractional dissolution from Al-silicates but rather a small barite fraction in dust that contributes substantially (11.5%). In contrast, riverine fluxes appear to be a minor flux for dissolved Al but a pronounced or even dominant source for dissolved Ba (8 vs 40%). The large remaining imbalance for Ba can only be attributed to rivers/groundwater; hence the insufficiently known groundwater/river contributions are likely to contribute not 40 but rather a total of ∼70 ± 15%. Minor contributions for both elements are related to bottom sediments (Al: 0%; Ba: 3%); mud volcanoes and Messinian evaporites (Al,Ba <0.2%), and removal by biogenic carbonates (−0.04%). River- and groundwater-derived dissolved Ba are the major source but with the largest uncertainty, hence requiring additional studies.