Combined Impacts of Ocean Acidification and Climate Change

Changes in climate resulting from anthropogenic influences will synchronously alter environmental conditions such as temperature, pH, salinity, wind strength and oxygen levels [7]. While seawater pH is sensitive to temperature, it is only a small contributing factor such that the predicted range for future temperatures will not make a significant difference to the pH decline [8]. However, organisms' responses may be different with increasing temperature depending on the level at which they adapted [9]. pH is also sensitive to changes in salinity, as a result of changes in total alkalinity and dissolved inorganic carbon, so organisms in coastal waters with riverine input, can experience larger variability in pH than in open oceans [10]. Both increasing temperature and decreasing salinity will also act to increase ocean stratification, which in turn will alter the nutrient supply that fuels primary production. A change in wind strength is also an important consideration for ocean acidification for two reasons. Firstly, wind strength determines the flux of CO2 between the ocean and the atmosphere, so may reduce the ocean CO2 sinks [11]. Secondly, wind strength drives ocean currents, mixes nutrients into the productive upper ocean and is particularly important for generating upwelling areas [12]. Upwell-ing areas, although rich in nutrients, are also rich in CO2 and are therefore areas of natural low pH [13]. A reduction in oxygen (O2), hypoxia, within the oceans occurs largely as a result of increased nutrient or organic matter input (e.g. caused by increased land-run off). An increase in nutrient load can substantially increase biological productivity and subsequent microbial decomposition of this excess productivity consumes large amounts of O2 and releases CO2 through respiration, causing hypoxia and low pH.

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