Evolution and Climate Change in the Oceans
Salinity refers to the dissolved salt content of a body of water. Salinity can have a great impact on the type of organisms that live in a body of water, as examined in the case studies below. Additionally, salinity plays a critical role in the water cycle and ocean circulation. The exact influence of salinity on these two phenomenons is explained in this video by NASA.
A Change in the Freshwater Balance of the Atlantic Ocean over the Past Four Decades
The
salinity of oceans, particularly the Atlantic, has changed over the past four
decades. When researchers measured the change in salinity levels of a “long
transect (50° S
to 60° N) through the western basins of the Atlantic
Ocean” (Ruth, 2003). They found that the oceans freshened in areas north of 40° N
and south of 25° S. The region between 35° N and 25° S, on the other hand,
experienced an increase in salinity. The freshening of the ocean can be
attributed to “enhanced wind-driven exports of ice or fresh water from the
Arctic, increased net precipitation rates, and/or elevated volumes of continental
runoff from melting ice” (Ruth, 2003). Conversely, the increase of salinity levels could be
the result of altered circulation between surrounding waters, intensified trade
winds and/or higher evaporation rates due to warmer ocean surfaces. Salt cannot
be gained nor lost through the atmosphere, so an increase in salinity can only
occur via (1) a transfer of additional salt from surrounding waters or (2) the
removal of fresh water. Because surrounding waters do not exhibit the
corresponding decrease in salinity, the increase in salinity levels must be due
to higher evaporation rates.
The Impact of Climate Change on the Adaptation of Fish in the Baltic Sea
Climate change has influenced the development and evolution of marine species in the Baltic Sea since the last glaciation. The distribution and abundance of marine fish in this area is heavily dependent on the salinity, temperature, and oxygen content of the different water layers. The salinity and oxygen content of the Baltic Sea are determined by the intensity of water exchange between it and the North Sea. Water exchange, in turn, is controlled by meteorological processes which could change along with the climate. Because salinity and oxygen content can vary significantly from year to year, successful establishment of the Baltic Sea by marine species is difficult. For instance, “of about 120 marine fish species in the North Sea, fewer than 30 occur permanently and can reproduce in [the Baltic Sea]” (Ojaveer, 2005). These numbers are quiet alarming since they show that less than one quarter of marine species in the vicinity of the Baltic Sea have been able to adapt to the salinity levels which are constantly changing as a result of climate change. The adaptations employed by the few marine species that have been able to establish themselves in the Baltic Sea are very interesting. Species with floating eggs have altered their specific gravity/egg diameter ratios effectively changing the density of their eggs. The spawning period of some species in the Baltic Sea starts earlier and lasts longer than that of their counterparts in the west. Additionally, these species mature faster and exhibit higher reproductive ability. The few marine species that have been able to adapt may soon see those adaptations become obsolete as the salinity levels change beyond the normal year-to-year range. This is a great case study of how climate change may semi-directly affect marine species in the Baltic Sea.
Include interesting or additional articles here.
Curry, Ruth, Bob Dickson, and Igor Yashayaev. "A Change in the Freshwater Balance of the Atlantic Ocean over the past Four Decades." Nature 426.6968 (2003): 826-29. Web.
Ojaveer, E., and M. Kalejs. "The Impact of Climate Change on the Adaptation of Marine Fish in the Baltic Sea." ICES Journal of Marine Science 62.7 (2005): 1492-500. Web.
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