Ocean-sourced Carbonate Production

Abstract

Globally, atmospheric carbon dioxide (CO2) is exchanged with the surface ocean through a gas exchange mechanism which is driven by the partial pressure differences in carbon dioxide between the air and the sea (Ciais and others, 2013). Once in the ocean, the production of carbonates is a process that is governed by a series of chemical reactions as described by Doney and others (2009). Carbon dioxide dissolves in sea water (H2 O) to form carbonic acid (H2 CO3). This then dissociates to form bicarbonate ions (HCO3), hydrogen ions (H+) and carbonate ions (CO3). These reactions are reversible and are in an equilibrium state in seawater which has a pH of around 8.1 (Doney and others, 2009). At this pH, approximately 90 per cent of the inorganic carbon is in the form of bicarbonate, 9 per cent exists as carbonate and 1 per cent is in the form of dissolved carbon dioxide (Doney and others, 2009). Calcification is the process in which calcium (Ca) combines with carbonate ions to form the mineral calcium carbonate (CaCO3) (Andersson and Gledhill 2013). Most of the calcium carbonate production in the sea is attributed to corals, calcifying algae, foraminifera, echinoderms, molluscs and bryozoans (Andersson and Gledhill 2013) and in these organisms the calcification process involves the formation of calcium carbonate deposits in shells and other skeletal parts (Doney and others, 2009, Lobban and Harrison 1994). scopic foraminifera (microscopic animals) and coccolithophores (microscopic algae) which are carried around in the oceanic systems and once they die their calcareous skeletons sink to the bottom of the ocean and form part of the oceanic bed (Langer 2008, Shutler and others, 2013).