High-magnesium calcite dissolution in tropical continental shelf sediments controlled by ocean acidification  

Authors / CoAuthors

Haese, R.R. | Smith, J. | Weber, R. | Trafford, J.M.

Abstract

Increases in atmospheric CO¬2 cause the oceanic surface water to continuously acidify, which has multiple and profound impacts on coastal and continental shelf environments. Here we present the carbonate mineral composition in surface sediments from a range of continental shelf seabed environments and their current and predicted stability under ocean acidifying conditions. Samples come from the following four tropical Australian regions. 1. Capricorn Reef (southern end of the Great Barrier Reef). 2. The Great Barrier Reef Lagoon. 3. Torres Strait. 4. The eastern Joseph Bonaparte Gulf. Outside of the near-shore zone, these regions typically have a carbonate content in surface sediments of 80 wt% or more. The abundance of high magnesium-calcites (HMC) dominates over aragonite (Arag) and low magnesium-calcite (LMC) and makes up between 36 and 50% of all carbonate. HMC is significantly more soluble than Arag and LMC and the solubility of HMC positively correlates with its magnesium concentration. Using the solubility data by Plummer and Mackenzie (1974) (1), 96% of HMC in the four regions is presently in thermodynamic equilibrium or slightly supersaturated relative to global mean tropical sea surface water. When the modelled saturation state for aragonite in equatorial areas for this century (2) is converted into HMC saturation state curves, HMC is predicted to become undersaturated in the four regions between 2040 to 2080 AD with typical HMC decline rates between 2 and 5% per year. The range of respective estimated carbonate dissolution rates is expected to exceed current continental shelf carbonate accumulation rates leading to net dissolution of carbonate during the period of HMC decline. In a geological context, the decline in HMC is a global event in tropical continental shelf environments triggered by reaching below-equilibrium conditions. The characteristic change in carbonate mineral composition in continental shelf sediments will serve as a geological marker for the proposed Anthropocene Epoch.

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nonGeographicDataset

eCat Id

79278

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Keywords

• External PublicationScientific Journal Paper

( Theme )

• continental shelf

( Theme )

• geochemistry

( Theme )

• minerals

( Theme )

• seabed

( Theme )

• marine

• QLDNT

Australian and New Zealand Standard Research Classification (ANZSRC)

• Earth Sciences

• Published_Internal

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2014-01-01T00:00:00

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Australian Government Security ClassificationSystem    

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Creative Commons Attribution 4.0 International Licence    

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geoscientificInformation

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Unknown

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[-25.0, 0.0, 125.0, 160.0]

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