Acidification of the Barrier Reef.

By Dave Armstrong - 07 Mar 2016 7:30:0 GMT
Acidification of the Barrier Reef.

The residents of the GBR include Acropora and other stony corals, all the soft corals, more fish than you can guess at, even here, many more invertebrates such as these sea cucumbers and Homo scubaensis. Together, they form one of the most diverse ecosystems imaginable. Those corals are declining, as they bleach and die in many reefs around the earth, so we lose the fish, the variety, the tourism and our climate control.

Great Barrier Reef image; Credit: © Shutterstock

Coral build reefs such as the GBR. They take calcium carbonate from normal sea water and form it into aragonite, which is simply the common anhydrous form. With increasing ocean acidification, the dissolution of calcium carbonate is likely to exceed this removal by the animals from solution by precipitation. The aragonite saturation state of seawater varies according to local acidity (largely cause by CO2), so each reef should be assessed if we are going to counter this chemistry.

An estimated 3,581 reefs form the Australian Great Barrier Reef, first seen, and felt, by Captain Cook. Freshwater from the neighbouring coastal river plumes feeds both minerals and pollution into the marine environment. Measurements of total alkalinity, dissolved carbon, salinity and temperature were us to estimate the saturation levels of aragonite (Ca 2+ and CO32-) using models. Preliminary results for this novel approach seem to indicate quite precise levels and interestingly large gradients along and across the reefs as well as 22 coastal observation sites.

Driving the saturation levels of calcium salts were the freshwater fluxes and hydrological cycles, the calcification levels and gas exchange including photosynthetic and respiration exchanges:

(1) freshwater and hydrological influence was mostly limited. The southern Swain Reefs experienced the largest fluxes.

(2) photosynthesis/respiration balance was a very negative influence on saturation, as respiration usually exceeded photosynthesis and CO2 influx from the air sea interface was considerable. However, the outer reefs were better situated as photosynthesis there seemed to exceed respiration.

(3) net calcification was negative over the whole of the Barrier Reef, with the outer reefs best suited with the relatively high levels found in the nearby Coral Sea.

The open ocean has higher levels of saturation compared with these low levels of aragonite in solution., with predicted levels for the GBH likely to be lower. These figures indicate more acidification than other recent reports, which says to us that the models may be better here. They also provide an insight into future change as thermal stress and acidification combine to reduce coral activity even more. In this region, the open ocean and the Coral Sea in particular are great providers of the required calcium salts. Central inter-reef areas seem very low in saturation levels. Their dissolution levels and all the factors affecting it are difficult to estimate for the future.

• Management of these sensitive areas and the measurement of these deficient central reef areas as they are becoming larger is an obvious follow-up. Mathieu Mongin and others from CSIRO in Hobart, Tasmania and many colleagues from the Antarctic Climate and Ecosystems Co-operative Research Centre, the Red Sea Research Center in the Kingdom of Saudi Arabia and the University of Technology, Sydney, labelled their report, The exposure of the Great Barrier Reef to ocean acidification and publish it in Nature Communications.

Going light, we previewed a wonderful panorama of coral reefs provided by Google way back in 2012. Try clicking on our steals from them or go to the site concerned, directly from our story at Panoramic Reef Photography.