Carbonate Sands Biogeochemistry

Unravelling the synergistic effect of ocean acidification and porewater advection on carbonate sediment dissolution: A global source of alkalinity and a sink for CO2?

Funding: ARC Discovery (2011 to 2013)

Investigators: Bradley Eyre, Isaac Santos, Ronnie Glud

Background/Summary

The advective transport of porewater in permeable sediments is widespread and has been increasingly recognized to play a major role in C, N, and P global biogeochemical cycles. The entire ocean volume is filtered by permeable continental shelf sands every ~10,000 years. This process is at least 4-fold faster than the global water cycle between the atmosphere, continents, and the ocean and is driven primarily by current- and topography-induced recirculation and tidal pumping.As a result of high microbial activities and deep oxygen penetration in permeable sediments, seawater Particulate Organic Matter (POM) and Dissolved Organic Carbon (DOC) are rapidly degraded in carbonate sands, releasing large amounts of nutrients and CO2 to porewaters. When combined with the anthropogenic CO2 that is invading the oceans and causing acidification, the metabolic CO2 in porewaters can fuel carbonate (CaCO3) sediment dissolution. The dissolution of marine carbonate sediments consumes CO2 and releases Ca2+ and HCO3-:

CaCO3+CO2(aq)+H2O ↔Ca2++2HCO3-

In this project, we will quantify the release of Ca2+ and alkalinity (as HCO3-) to the overlying water as a function of porewater advection. This unaccounted for mechanism may lead to an additional uptake of atmospheric CO2 into the global ocean and partially counteract ocean acidification. Our preliminary investigations revealed a dramatic diel pH variability in coral reefs that could be partially (at night) explained by porewater advection in carbonate sands.

Relevant Publications

Santos, I. R., Glud, R. N., Maher, D. and Eyre, B. D. 2011. Diel coral reef acidification driven by pore water advection in permeable carbonate sands, Heron Island, Great Barrier Reef. Geophysical Research Letters 38, L03604, doi:10.1029/2010GL046053. JIF= 2.959; (ERA Rank *A)

Updated: 08 October 2012