Environmental Engineering Reference
In-Depth Information
Marine Zooplankton and Global Warming
Global warming and increase in sea surface water temperature
The increase in production of greenhouse gases has contributed to the
observed warming of the atmosphere and the oceans in the last decades.
Rising atmospheric concentrations have increased global mean sea-surface
temperature by approximately 0.2°C per decade over the past 30 years
(Guldberg and Bruno 2010). Consequently, the heat content of the upper 700
m of the global ocean has increased by 14 x 10
22
J since 1975 (Guldberg and
Bruno 2010), resulting in many cascading environmental changes (Fig. 1).
The warming of the upper layers as well as mid- to high-latitude
freshening (Doney et al. 2012) promotes greater stratification of the
water column, reducing mixing of the ocean and consequently affecting
nutrient cycling and primary production. The relationship between nitrate
concentrations and sea-surface temperature suggests that global nitrate
supply to the surface might have decreased in the 20th
century as a result of
climate-driven changes in ocean stratifi cation and circulation (Kamykowski
and Zentara 2005). The decrease in surface nitrate as a result of water
stratifi cation, however, does not consider anthropogenic changes in riverine
nutrient inputs, which might also affect global ocean uptake of atmospheric
CO
2
(Schultz 2008). Recent observations indicate that ocean warming and
increased stratifi cation also entails serious consequences on dissolved
oxygen concentrations (O
2
) (Keeling et al. 2012). Systematic deoxygenation
of the ocean will have dramatic implication for ocean productivity since
O
2
saturation affects the functioning of marine ecosystems as it drives the
biogeochemical cycles of most seawater constituent and determines the
fate of all aerobic marine life (Keeling et al. 2012).
As a consequence of increasing temperatures in high latitudes, which
are rising faster than the global temperature average, sea-ice extent has
declined dramatically in the Arctic (7.4% per decade since 1978) (Bindoff
et al. 2007) and along the western Antarctic Peninsula (Stammerjohn et al.
2008). Thermal expansions of the oceans as well as increased meltwater and
discharged ice from terrestrial glaciers and ice sheets have increased ocean
volume and hence, sea level (Guldberg and Bruno 2010). Climate warming
affects regional wind patterns and thus ocean circulation in multiple
dimensions (Doney et al. 2012). A shift in the balance between evaporation
and precipitation regime has led to an increase of sea-surface salinity in
low latitude regions, while high latitude waters have become fresher due
to both increased precipitation and melting of the ice (Bindoff et al. 2007).
Warmer oceans also drive more intense storm systems and other changes
in the hydrological cycle, increasing the vulnerability of coastal habitats.
