Potential Effects of Climate Changes on the Marine Ecosystem Stability: Assessment of the Water Quality

Abstract

A huge amount of carbon is being annually released into the Earth?s atmosphere, reaching levels of gigatonnes (Jongen et al. 2011, Zhang et al. 2012). These accumulative post-industrial emissions have caused different effects, including increasing global temperature, rising sea level, changes in regional weather patterns, acidifi cation of oceans, variations in nutrient loads or alteration in ocean circulation (Brierley and Kingsford 2009). All these changes and others that may be occurring, affect biological processes taking place in the ocean at all levels, from the molecular to the ecosystemic one (Drinkwater et al. 2010). There is broad consensus that contemporary global climate change is a reality, and that much of the ongoing change is a direct result of human activity (IPCC 2007a). In particular, burning fossil fuels, making cement and changing land use have driven atmospheric carbon dioxide concentrations up from a pre-industrial value of about 280 ppm to 385 ppm in 2008 (Meure et al. 2006) (Fig. 1). Annual increases are now exceeding 2 ppm, an emission trend that exceeds the worst case scenario discussed at the Intergovernmental Panel on Climate Change (IPCC 2007b). There is a direct link between global temperature and CO2 concentration (IPCC 2007a). The increased heating in the lower atmosphere/ Earth?s surface (radiative forcing) resulting from the ?greenhouse? effect caused by increasing atmospheric CO2, methane and other gases (at a value of about 3 W.m?2, following IPCC 2007c) is unprecedented in at least the last 22,000 years (Joos and Spahni 2008) and has already had direct physical consequences for the marine environment and organisms living there. These include increases in mean global sea surface temperature by 0.13ºC per decade since 1979, and ocean interior temperature by >0.1ºC since 1961, increasing wind velocity and storm frequency, changes in ocean circulation, vertical structure and nutrient loads (IPCC 2007c), as well as rising sea level by more than 15 cm in the last century (Rahmstorf 2007)(Fig. 1), and presently by a mean of about 3.3 mm per year. Because the oceanic and atmospheric gas concentrations tend towards equilibrium, increasing CO2 pressure drives more CO2 into the ocean, where it dissolves forming carbonic acid (H2CO3) and thus increases ocean acidity; ocean pH has dropped by 0.1 (a 30% increase in H+ ion concentration) in the last 200 years (The Royal Society 2005) (Fig. 1).