Environmental Engineering Reference
In-Depth Information
scenarios. According to the review by Brierley and Kingsford (2009) the
following parameters must be kept in mind:
- Temperature (seawater, air, ocean—atmosphere boundary layer)
- Salinity
- CO
2
concentration and partial pressure
- pH and alkalinity
- Dissolved oxygen concentration
- Sea level rise
- Timing of plankton blooms
- Strengthened stratifi cation/mixed layer depth
In this sense it might be included several brief comments might be
included which could help to enlighten these points. For example, CO
2
and
ocean pH represent a great threat to many marine organisms and ecosystems
(Doney et al. 2009). Over the past 200 years, the oceans have absorbed
approximately half of the anthropogenically-generated CO
2
and at present a
further approximately 1 million tonnes of CO
2
diffuses into the world ocean
per hour (Joos and Spahni 2008). The rate of decreasing pH, 0.1 units in the
last 200 years and an expected drop of 0.3 to 0.5 units by 2100, is more than
100 times as rapid as at any time over the past hundreds of millennia (IPCC
2007c). Rates of oceanic CO
2
absorption vary regionally as a function of wind
strength and temperature. Colder waters can accommodate more dissolved
CO
2
than warm waters and are, therefore, more prone to acidifi cation
(Guinotte and Fabry 2008). One of the main impacts of ocean acidifi cation
on marine life arises because of interactions between acidity and carbonate
availability. A taxonomically diverse array of marine organisms, including
tiny coccolithophores (a type of phytoplankton), pelagic and benthic
mollusks, fi st-sized starfi sh and urchins, as well as massive corals, require
calcium carbonate for their skeletons, and others have key carbonate rich
structures (e.g., fi sh otoliths). All of these are likely to suffer as increasing
acidity reduces carbonate availability, and impacts at the species level may
cascade through to widespread community change (Hoegh-Guldberg 1999).
At present, shallow waters are generally saturated with carbonate ions, but
dissolution increases with depth (Orr et al. 2005).
Another well known confl ictive scenario in the marine environment
is the occurrence of a
reducing dissolved oxygen concentration
one. Low
oxygen concentrations transform compartments of the world ocean in
inadequate habitats for most of the marine organisms. Oxygen solubility
in seawater is a function of temperature, and O
2
availability in the world
ocean has been declining since the 1950s (García et al. 2005) as the ocean
has warmed. Over a range from 0 to 15ºC, dissolved oxygen concentration
in seawater is related approximately linearly to temperature, and will
decline by about 6% per one degree rise (Brierley and Kingsford 2009).
