Calcium carbonate corrosivity in an Alaskan inland sea

Abstract

Ocean acidification is the hydrogen ion increase caused by the oceanic uptake of anthropogenic CO₂, and is a focal point in marine biogeochemistry, in part, because this chemical reaction reduces calcium carbonate (CaCO₃) saturation states (&Omega;) to levels that are corrosive (i.e. &Omega; &le; 1) to shell-forming marine organisms. However, other processes can drive CaCO₃ corrosivity; specifically, the addition of tidewater glacial melt. Carbonate system data collected in May and September from 2009 through 2012 in Prince William Sound (PWS), a semi-enclosed inland sea located on the south-central coast of Alaska that is ringed with fjords containing tidewater glaciers, reveal the unique impact of glacial melt on CaCO₃ corrosivity. Initial limited sampling was expanded in September 2011 to span large portions of the western and central sound, and included two fjords proximal to tidewater glaciers: Icy Bay and Columbia Bay. The observed conditions in these fjords affected CaCO₃ corrosivity in the upper water column (<50 m) in PWS in two ways: (1) as spring-time formation sites of mode water with near-corrosive &Omega; levels seen below the mixed layer across the sound, and (2) as point sources for surface plumes of glacial melt with corrosive &Omega; levels (&Omega; for aragonite and calcite down to 0.60 and 1.02, respectively) and carbon dioxide partial pressures (<i>p</i>CO₂) well below atmospheric levels. CaCO₃ corrosivity in glacial melt plumes is poorly reflected by <i>p</i>CO₂ or pH_T, indicating that either one of these carbonate parameters alone would fail to track &Omega; in PWS. The unique &Omega; and <i>p</i>CO₂ conditions in the glacial melt plumes enhances atmospheric CO₂ uptake, which, if not offset by mixing or primary productivity, would rapidly exacerbate CaCO₃ corrosivity in a positive feedback. The cumulative effects of glacial melt and air-sea gas exchange are likely responsible for the seasonal widespread reduction of &Omega; in PWS; making PWS highly sensitive to increasing atmospheric CO₂ and amplified CaCO₃ corrosivity

Effect of glacial drainage water on the CO2 system and ocean acidification state in an Arctic tidewater‐glacier fjord during two contrasting years

“…Similar results of decreased pH and Ω due to the effect of glacial drainage water were found in the sub‐Arctic inland sea of the Prince William Sound in Alaska by Evans et al . [].…”

Tracing sources of freshwater contributions to first-year sea ice in Svalbard fjords

“…The acceleration of glacial retreat ensures that this freshwater source will play a continually larger role in the freshwater flux and carbonate saturation state of the Arctic and subarctic seas in the near future. As regions where glaciers flow into the ocean, Arctic and subarctic fjords are particularly susceptible to increases in both air and seawater temperatures (Hop et al, 2002;Cottier et al, 2005) that melt ice and thereby influence the carbon cycle through impacts on the saturation state of calcium carbonate (Brown, 2002;Sejr et al, 2011;Rysgaard et al, 2012), primary production (Wiktor, 1999;Zajaczkowski, et al, 2010), and the uptake of atmospheric carbon dioxide (Evans et al, 2014).…”

The Importance of Freshwater to Spatial Variability of Aragonite Saturation State in the Gulf of Alaska

“…Recent field observations (Evans et al, ) have shown that the inner and middle shelf of the GOA currently experiences seasonal manifestations of corrosive events (Ω < 1), including decreased pH and suppressed Ω in response to rising CO 2 levels and increased discharge of low‐alkalinity, glacial meltwater (Evans et al, ; Reisdorph & Mathis, ). While the glacial discharge mainly influences water on the inner shelf, upwelling brings nutrient and CO 2 ‐rich waters that are undersaturated in the calcium carbonate mineral aragonite from the deep GOA onto the outer shelf (Evans et al, ).…”

“…A portion of the ACC flows through Prince William Sound (Figure ; Niebauer et al, ; Royer et al, ; Vaughan et al, ) and, thus affects the heat, salt, nutrient, and carbon budgets of the sound and its adjacent bays (Gay & Vaughan, ). This narrow (∼40 km), swift, year‐round flow is maintained by the integrated forcing of winds and freshwater discharge with seasonally high rates of glacier runoff (Evans et al, ). Both the winds and the discharge vary seasonally, although not in‐phase with one another: discharge is a maximum in fall and the westward (downwelling‐favorable) winds are strongest in winter.…”