Rao, Alexandra M. F., Polerecky, Lubos, Ionescu, Danny, Meysman, Filip J. R. and de Beer, Dirk (2012) The influence of pore-water advection, benthic photosynthesis, and respiration on calcium carbonate dynamics in reef sands. Limnology and Oceanography, 57 (3). pp. 809-825. DOI 10.4319/lo.2012.57.3.0809.

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Abstract

To investigate diel calcium carbonate (CaCO3) dynamics in permeable coral reef sands, we measured pore-water profiles and fluxes of oxygen (O2), nutrients, pH, calcium (Ca2+), and alkalinity (TA) across the sediment-water interface in sands of different permeability at Heron Reef, Australia. Background flushing rates were high, most likely as a result of infaunal burrow irrigation, but flux chamber stirring enhanced pore-water exchange. Light and pore-water advection fueled high rates of benthic primary production and calcification in sunlit surface sediments. In the light, benthic photosynthesis and calcification induced surface minima in Ca2+ and TA and peaks in pH and O2. Oxygen penetration depth in coarse sands decreased from ∼ 1.2 cm during the day to ∼ 0.6 cm at night. Total oxygen uptake (TOU) in dark chambers was three to fourteen times greater than diffusive uptake and showed a direct effect of pore-water advection. Greater sediment oxygen consumption rates were observed in higher permeability sands. In the dark, TA release was not stimulated by increasing TOU because of a damping effect of pore-water advection on metabolic CaCO3 dissolution efficiency. On a daily basis, CaCO3 undergoes net dissolution in Heron Reef sands. However, pore-water advection can reverse the CaCO3 budget and promote CaCO3 preservation under the most energetic conditions.

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