Calcium carbonate corrosivity in an Alaskan inland sea

[摘要] Ocean acidification is the hydrogen ion increase caused by the oceanic uptakeof anthropogenic CO₂, and is a focal point in marine biogeochemistry, inpart, because this chemical reaction reduces calcium carbonate (CaCO₃)saturation states (Ω) to levels that are corrosive (i.e.,Ω ≤1) to shell-forming marine organisms. However, other processes can driveCaCO₃ corrosivity; specifically, the addition of tidewater glacial melt.Carbonate system data collected in May and September from 2009 through 2012in Prince William Sound (PWS), a semienclosed inland sea located on thesouth-central coast of Alaska and ringed with fjords containing tidewaterglaciers, reveal the unique impact of glacial melt on CaCO₃ corrosivity.Initial limited sampling was expanded in September 2011 to span largeportions of the western and central sound, and included two fjords proximalto tidewater glaciers: Icy Bay and Columbia Bay. The observed conditions inthese fjords affected CaCO₃ corrosivity in the upper water column(< 50 m) in PWS in two ways: (1) as spring-time formation sites of modewater with near-corrosive Ω levels seen below the mixed layer over aportion of the sound, and (2) as point sources for surface plumes of glacialmelt with corrosive Ω levels (Ω for aragonite and calcitedown to 0.60 and 1.02, respectively) and carbon dioxide partial pressures(pCO₂) well below atmospheric levels. CaCO₃ corrosivity inglacial melt plumes is poorly reflected by pCO₂ or pH_T,indicating that either one of these carbonate parameters alone would fail totrack Ω in PWS. The unique Ω and pCO₂ conditions in theglacial melt plumes enhances atmospheric CO₂ uptake, which, if notoffset by mixing or primary productivity, would rapidly exacerbate CaCO₃corrosivity in a positive feedback. The cumulative effects of glacial meltand air–sea gas exchange are likely responsible for the seasonal reduction ofΩ in PWS, making PWS highly sensitive to increasing atmosphericCO₂ and amplified CaCO₃ corrosivity.

[学科分类] 地球化学与岩石