AWA: Academic Writing at Auckland

Despite its isolation, climate change is affecting Antarctica through warming and increased salinity, sea ice decrease, ice shelf disintegration, glacial retreat. Particularly, the effects of sea temperature rise are seen in marine ecosystems due to the loss of habitat for under-ice organisms like algae, which has affected all trophic levels due to the subsequent decline of Antarctic krill (Euphausia superba). The understanding of the effects of ocean acidification on present ecosystems is not well known, but it is likely to have a dramatic future impact. Other future impacts on Antarctic ecosystems are likely to include invasion of alien species, domination of salps, increased ice scouring and ecosystem-wide interaction changes.

Marine systems such as that of the Southern Ocean surrounding Antarctica were once thought to be relatively immune from human influence (Aronson, Thatje, McClintock, & Hughes, 2011, p. 82). In fact, the Western Antarctic Peninsula (WAP) is the most rapidly warming region in the Southern Hemisphere (Vaughan, n.d.). While conditions have been much more variable in other areas of the Antarctic, several effects of global warming can still be observed (Turner et al., 2005, p. 279). Generally, there has been an increase in the mean annual air temperature particularly in the WAP region, of 3Ëš Celsius since 1951 (Meredith & King, 2005, p. 1). This warming has resulted in decreased seasonal snow cover, as well as increased breakup of ice shelves (Vaughan, n.d.).  The majority of Antarctic glaciers are retreating, and the retreat rates are accelerating (Meredith & King, 2005, p. 1). This acceleration is due to increased meltwater making surfaces more fluid (Vaughan, n.d.).  The combined factors of shelf disintegrations and glacier melt have contributed as much as 0.16 ± 0.06 mm to global sea level rise already (Vaughan, n.d.). Unfortunately, this process is also sustaining and amplifying itself; warmer temperatures prevent sea ice formation and increase disintegration of existing ice, meaning less albedo and more absorbed energy, increasing the warming. Decreased sea ice formation has also led to increased ocean salinity (Meredith & King, 2005, p. 4). These effects have the potential to affect all trophic levels of marine ecosystems.

In fact, because marine organisms in the Antarctic are often ‘stenotherms’, meaning they cannot tolerate a sustained change from the narrow temperature range of Antarctic waters, they are especially vulnerable (Aronson, et al., 2011, p. 97). Sea temperature rise in particular is already having an effect. The temperature rise does not yet appear to be at a level where it is compromising the physiological functions of organisms, but sea ice decrease as a consequence of temperature rise is having many effects. Sea ice is critical in helping to ‘structure’ Antarctic ecosystems. Each year’s spring melt has a major role in determining phytoplankton blooms, and thus influences entire food webs (Hoegh-Guldberg & Bruno, 2010, p. 1526). Phytoplankton blooms now occur earlier and further south, which indicates that warming can actually favour some species (Barnes & Clarke, 2011, p. R455). However, decreased sea ice reduces the habitat for organisms like sea ice algae. The breakup of sea ice each year provides the Antarctic benthos with a carbon flux that generally accounts for most of its energy input for the year (Aronson, et al., 2011, p. 84; McMinn, 2011, p. 48). During the (up to) nine colder months of the year, sea ice algae is the only source of primary production available, and any organism that must survive the colder months is forced to either rely on consuming sea ice algae, or on other organisms that consume it (McMinn, 2011, p. 45).

Antarctic krill in particular are subject to this; juvenile krill cannot survive starvation and are therefore dependent on sea ice algae (McMinn, 2011, p. 49). Much has been made in the literature of the “order of magnitude” decrease in krill over the past 25 years (Hays, Richardson, & Robinson, 2005, p. 338).  This has been linked to sea temperature rise and subsequent loss of sea ice cover (Aronson, et al., 2011, p. 94; Hays, et al., 2005, p. 338; Meredith & King, 2005, p. 4). This is a particularly important change for marine ecosystems (and terrestrial) because krill are often the main food source for many higher predators, like penguins or baleen whales (Barnes & Clarke, 2011, p. R453). The decrease in krill has led to a concurrent increase in salps, another type of zooplankton grazer that dominates warmer waters freer of sea ice (Aronson, et al., 2011, p. 94; McMinn, 2011, p. 49). However, salps are thought to be of little nutritional value to predators, and few species are known to prey on them (McMinn, 2011, p. 49). Sea temperature rise has also potentially had another effect: it has decreased the physical barriers (mainly cold) to colonization by non-native species. Lithodid king crabs are already being found on the peninsula (Aronson, et al., 2011, p. 98). Sea temperature rise is thus already having cascade effects on Antarctic marine ecosystems.

Ocean acidification, on the other hand, is a by-product of COâ‚‚ emissions where the effects on Antarctic marine ecosystems are, for the moment, mostly projected rather than current. Ocean acidification refers to oceans becoming undersaturated first in aragonite, and then in calcite (Barnes & Clarke, 2011, p. R455). This is predicted to be a particularly costly effect of climate change on Antarctic marine ecosystems, because many planktonic organisms with calcareous shells and skeletal elements already live to the limit of their ability to form these elements (Aronson, et al., 2011, pp. 84-85).  Ocean acidification can suppress the ability of organisms to secrete their calcified shells and other skeletal elements, and can also affect processes like reproduction, development, respiration, and photosynthesis (Aronson, et al., 2011, p. 100; Hofmann et al., 2010, p. 128). Currently, many studies show that the ability of Antarctic organisms to tolerate pH changes is very limited (Aronson, et al., 2011, p. 100) However, ocean acidification knowledge at present mainly consists of short term studies conducted in experimental laboratory conditions (Hofmann, et al., 2010, p. 128). It is therefore difficult to understand the relevance of these studies and their implications for long term responses, especially since tolerance is not the only response available (migration is another) (Barnes & Clarke, 2011, p. R455). Aronson et al. (2011, p. 101) state that currently, “our understanding of the prospective impacts of ocean acidification on Antarctic marine life is in its infancy.”

Nonetheless, given present rates of COâ‚‚ emissions, ocean acidification will be a major future consequence of global climate change, and the effects on marine organisms are expected to be dramatic (Aronson, et al., 2011, p. 100; Hofmann, et al., 2010, p. 128). Higher trophic levels that depend on calcifying organisms will also be affected (Aronson, et al., 2011, pp. 84-85). Unchecked, pH levels are expected to change by levels greater than any in the last 300 million years (Hays, et al., 2005, p. 341). In the future, continuing warming is likely to result in pelagic ecosystems being dominated by salps instead of krill, resulting in a decline in those species dependent on krill (McMinn, 2011, p. 49). The ability of Antarctic organisms to respond to higher temperatures is limited by their stenothermal physiologies, and thus it has been suggested that many benthic organisms could be at risk of extinction from only a 1-2Ëš increase in summer ocean temperature (Meredith & King, 2005, p. 4). Communities in the shallows will also be further vulnerable to ice scouring from increased ice movement (Barnes & Clarke, 2011, p. R455). The likelihood of alien species invasions will increase, and given that many of the potential re-invaders are generalists, this could come at a great cost to Antarctic biodiversity (Aronson et al., 2007, p. 130). Ultimately, predictions of future impacts of climate change are complicated. This is because the most likely effects of climate change will be altered interactions within ecosystems, but these are very difficult to measure and model (Barnes & Clarke, 2011, p. R455). However, it is safe to argue that global climate change, continued at its present rate, will have far-reaching consequences on all trophic levels of Antarctic ecosystems, and extinctions are highly likely.

The general effects of global climate change on Antarctica are warming, sea ice decrease, ice shelf disintegration and glacial retreat, and increased salinity. The effects of sea temperature rise are particularly seen in marine ecosystems due to the loss of habitat for under-ice organisms like algae, which has affected all trophic levels due to the consequent decline of Antarctic krill. Current understandings of the effects of ocean acidification are mostly future projections rather than present observations, but it is likely to have a dramatic future impact on ecosystems, along with other effects like, increased ice scouring, invasion of alien species, domination of salps, and ecosystem-wide interaction changes.

References Cited

Aronson, R., Thatje, S., Clarke, A., Peck, L., Blake, D., Wilga, C., & Seibel, B. (2007). Climate Change and Invasibility of the Antarctic Benthos. Annu. Rev. Ecol. Evol. Syst, 38, 129-154.

Aronson, R., Thatje, S., McClintock, B., & Hughes, K. (2011). Anthropogenic impacts on marine ecosystems in Antarctica. Annals of the New York Academy of Sciences, 1223, 82-107.

Barnes, D., & Clarke, A. (2011). Antarctic Marine Biology. Current Biology, 21(12), R451-R457.

Hays, G., Richardson, A., & Robinson, C. (2005). Climate change and marine plankton. Trends in Ecology and Evolution, 20(6), 337-344.

Hoegh-Guldberg, O., & Bruno, J. (2010). The Impact of Climate Change on the World's Marine Ecosystems. Science, 328, 1523-1528.

Hofmann, G. E., Barry, J., Edmunds, P., Gates, R., Hutchins, D., Klinger, T., & Sewell, M. (2010). The Effect of Ocean Acidification on Calcifying Organisms in Marine Ecosystems: An Organism to Ecosystem Perspective. Annu. Rev. Ecol. Evol. Syst, 41(127-47).

McMinn, A. (2011). Climate Change in Polar Marine Ecosystems. Journal of Tropical Marine Ecosystem, 1, 44-50.

Meredith, M., & King, J. (2005). Rapid climate change warming in the ocean west of the Antarctic Peninsula. Geophysical Research Letters, 32, 1-5.

Turner, J., Colwell, S., Marshall, G., Lachlan-Cope, T., Carleton, A., Jones, P., . . . Iagovkin, S. (2005). Antarctic Climate Change During the Last 50 Years. International Journal of Climatology, 25, 279-294.

Vaughan, D. (n.d.). Antarctic Peninsula: Rapid Warming  Retrieved August 28th, 2011, from http://www.antarctica.ac.uk/bas_research/science/climate/antarctic_peninsula.php