Column Actions

The purpose of this indicator is to measure average marine acidity.

Ocean acidification is the reduction in the pH of the ocean over an extended period, typically of decades or longer, which is caused primarily by the uptake of carbon dioxide from the atmosphere. This indicator is based on observations that constrain the ocean carbon system and which are required to describe the variability of ocean acidity. The carbon system in this context mainly refers to the four measurable parameters: pH (the concentration of hydrogen ions on a logarithmic scale), DIC (CT; total dissolved inorganic carbon), pCO² (carbon dioxide partial pressure), and TA (AT, total alkalinity). Average, as used here, is the equally weighed annual mean. An agreed suite of representative sampling stations are sites that:

1. have a measurement frequency adequate to describe variability and trends in carbonate chemistry to deliver critical information on the exposure of and impacts on marine systems to ocean acidification,
2.  provide data of sufficient quality and with comprehensive metadata information to enable integration with data from other sites in the country.

Coastal Zone Management Authority and Institute (CZMAI)

Department of Environment (DOE)

Department of Environment (DOE)

Annual

pH on total scale, and/or pCO² [µatm or ppt], CT [µmol kg^-1 ], AT [µmol kg^-1 ]

The ocean absorbs around 30% of anthropogenic carbon from the atmosphere annually. This carbon dioxide (CO2) reacts with the seawater, changing its chemical composition and progressively acidifying the ocean. The observed decrease in seawater pH has been shown to affect a range of organisms and ecosystems, biodiversity and food security. Fisheries and aquaculture can be negatively affected, as can other services provided by the ocean, including tourism, transportation and coastal protection. Observations from the last 20 – 30 years have shown a clear trend of ocean acidification (decreasing pH) in open ocean locations. For coastal areas, however, the pattern is often confounded by natural processes like freshwater input, coastal upwelling, biological activities and temperature changes, among others. These factors complicate the prediction of and possible management responses to ocean acidification in the highly dynamic and productive coastal areas.

Ocean acidification is caused by an increase in the amount of dissolved atmospheric CO² in the seawater. The average marine acidity is expressed as pH, the concentration of hydrogen ions on a logarithmic scale. In order to be able to constrain the carbonate chemistry of seawater, it is necessary to measure at least two of the four parameters, i.e. pH, pCO², DIC (CT), and TA (AT).  pH (the concentration of hydrogen ions on a logarithmic scale, expressed on total scale), DIC (total dissolved inorganic carbon, in μmol kg^-1), pCO² (carbon dioxide partial pressure, in ppt or μatm), and TA (AT, total alkalinity, in μmol kg^-1).

N/A

This indicator calls for the collection of multiple observations, in the form of individual data points, to capture the variability in ocean acidity. Individual data points for pH either are measured directly or can be calculated based on data for two of the other carbonate chemistry parameters, these being TA (AT), DIC (CT) and pCO².  Calculation tools developed by experts in the field are freely available, and they are introduced and linked in the methodology. Average pH is defined as the annual equally weighed mean of multiple data points at representative sampling stations. The exact number of samples and data points depends on the level of variability of ocean acidity at the site in question. The minimum number of samples should enable the characterisation of a seasonal cycle at the site. Detailed guidelines on the minimum number of observations required are provided in the Methodology. In addition to the data value, standard deviation and the total range (minimum and maximum values measured), as well as underlying data used to provide traceability and transparency (metadata information) should be reported. If historical data is available, this should be released to enable calculations about the rate of change and to compare natural variability and anthropogenic effects.

Department of Environment can utilize this indicator to help monitor ecosystems in coastal areas.

N/A

All the metadata shown in this document was gathered from United Nation Statistics Division. The metadata was extracted from https://unstats.un.org/sdgs/metadata/.