Environmental Engineering Reference
In-Depth Information
up to 750 ppm for the year 2100 implicate a decrease in pH of 0.3 units,
which falls in a potential scenario outside the natural range over the past
20 million years (IPCC 2007).
Global warming and rising ocean temperature
Global air and sea temperatures have risen in the past century by 0.4-0.8°C.
Global circulation models predict warmer conditions of additional
ca
. 3°C in
some areas of the global ocean by the end of the 21st century, from a mean
sea surface temperature (SST) of 18°C today to 21.5°C (McNeil and Matear
2006, IPCC 2007). Rising SST enhances the water column stratifi cation and
decreases nutrient supply in the euphotic zone (Behrenfeld et al. 2006,
Doney 2006). It further induces alterations in the underwater light regime
(Sarmiento et al. 2004). Along with the growing temperatures, global
circulation models forecast a potential freshening of mean sea surface
salinity, presumably as a result of increased precipitation and ice-melt in
the poles offsetting increased evaporation from the surface of ocean in low
latitudes (McNeil and Matear 2006).
Additional abiotic consequences of climate warming are the thermal
expansion of the world ocean, which coupled with freshwater input from
ice-melt causes sea level rise (IPCC 2007). Thermal expansion enhances
water column stratifi cation and a deepening of the thermocline preventing
cool, nutrient-rich waters from being upwelled (Roemmich and Mc
Gowan 1995). Owing to the fundamental importance of upwelling in the
productivity of coastal marine systems, further elucidation of the linkage
between these events and climate is a high research priority (Harley et al.
2006). In a more local scale, changes in atmospheric circulation also affect
storm frequency and wind and precipitation patterns, which eventually may
yield changes in coastal salinity, turbidity, light attenuation and inputs of
terrestrial and bottom sediments-derived nutrients and pollutants (Nixon
et al. 2009, Noyes et al. 2009, Wetz et al. 2011).
Overall, the main modifi cations that result from rising atmospheric
CO
2
and global warming in the physical and chemical nature of pelagic
environments can be synthesized by 1) carbon enrichment and acidifi cation
and 2) thermal stratifi cation and associated changes in nutrient and light
regimes. These changes shape seawater chemical speciation, nutrient
supply and biogeochemical cycles, and ultimately structure of ecosystems.
In the following sections we assess the implications of such climate-
related modifi cations on phytoplankton ecological performance and the
repercussion on pelagic food webs.
