Marine Atlas: Maximizing Benefits for Kiribati

TURNING SOUR: OCEAN ACIDITY Climate change is not only causing sea temperatures and levels to rise but also its acidity, which causes serious problems for many marine organisms.

Seawater acidity can be measured using the pH, a numeric scale to specify the acidity or basicity of a solution; a pH of 7 is neutral—neither acidic nor basic. A decrease in pH by one means a solution is twice as acidic, whereas an increase by one means a solution twice as basic (see graphic). The pH of the global oceans ranges from around 7.5 to 8.4. Kiribati’s waters are at the higher end of this range, with pH between 8.26 and 8.30. Increas- ing CO 2 in the surface water leads to increased acidification (lower pH). Already, CO 2 emissions have resulted in a 26 per

cent increase in the acid content in the ocean (see small map).

How does acidification affect calcite levels? Firstly, CO 2 in the water transforms into carbonic acid and the carbonate saturation decreases. This is problematic for all animals that use marine carbonate to make their shells, such as mussels, snails, corals and sea urchins, among many others (see also chapter “Travellers or homebodies”). The less car- bonate there is in the water, the more difficult it is for them to make suitable shells. The effects can already be seen among foraminifera: tiny calcifying creatures that make up an important part of the plankton. The shell-thickness of animals in the Southern Ocean has noticeably

In this context, it is important to look at cal- cite, which is another vital element found in seawater (see map on the right), as calcium carbonate is a building block of the skele- tons of most marine organisms, including corals. Globally, calcite concentrations are highest in the high latitudes and in coastal areas. The calcite concentrations in Kiriba- ti’s oceanic waters are low, with the coastal areas around the islands having a higher concentration (see calcite map).

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Ocean acidification Kiribati is suffering the effects of global warming, with greenhouse gas emissions not only heating the nation’s sea, but also ending up in it. In fact, worldwide the oceans have absorbed about one third of the carbon dioxide (CO 2 ) produced by human activities since 1800 and about

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Kiribati Provisional EEZ Boundary

half of the CO 2 produced by burning fossil fuels (Sabine et al., 2004). As CO 2 in the ocean increases, ocean pH decreas- es, resulting in the water becoming more acidic. This is called ocean acidification, the “evil twin” of sea temperature and sea level rise, described in the previous maps.

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Copyright © MACBIO Map produced by GRID-Arendal Sources : Becker et al, 2009; Claus et al, 2016; IHO-IOC GEBCO, 2017; Smith and Sandwell, 1997.

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CLIMATE CHANGE THREATS MAXIMIZING BENEFITS FOR KIRIBATI

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