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Antarctic meltdown: The knock-on effects of climate change in the Western Antarctica Peninsula
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I know what you’re thinking… how could she use such a clichéd phrase, “meltdown”, for describing the effects of global warming in Antarctica?
Well, I cringed using it at first too, but when I looked up the definition of the word “meltdown” given by Collins English Dictionary (Complete and Unabridged), I decided it was quite possibly the most appropriate phrase to use. According to Collins, the informal definition of the word “meltdown” is “the process or state of irreversible breakdown or decline”.
Much like other parts of Antarctica, the Western Antarctic Peninsula (WAP) supports teeming life from phytoplankton and krill through to penguins, seals and whales. Unlike the rest of Antarctica, however, this prolific region is one of a few globally that are experiencing the greatest warming on the entire planet. With an increase in winter air temperatures of 6°C in the last 50 years, and consequently a significant decline in winter sea ice, this change is having dramatic and dire knock-on effects in the pelagic ecosystem, from primary producers right the way up to the top predators.
The US Palmer Antarctica Long Term Ecological Research (LTER) project has been at the forefront of long-term research in this pristine environment, making substantial and ground-breaking contributions to our understanding of how climate change is affecting the Western Antarctic Peninsula.
The Western Antarctic Peninsula: A region of extreme climate change
On top of the effects of an increase in temperature, La Niña events and positive phases of the Southern Annular Mode (SAM) seem to be exacerbating the situation. It appears that the regional warming occurring in the WAP is being intensified by an increase in ocean heat content as a result of more frequent occurrences of upwelling-favourable winds and a shift towards more positive phases of the SAM, both of which contribute to elevated upwelling of the warmer Upper Circumpolar Deep Water (UCDW).
During El Niño years, when south-westerly winds dominate in the region, winter ice formation is good and the mixed layer depth becomes shallower in the spring, which is more favourable for phytoplankton production. This results in the formation of diatom blooms which support the large krill populations and ensure greater larval krill survival rates. The onset of these blooms during El Niño years coincides with the penguin chick rearing season, resulting in greater chick weights.
However, during a La Niña year north-westerly winds dominate, resulting in a deeper mixed layer depth and poor winter sea ice conditions, related to the timing of the advance and retreat of the sea ice. During La Niña periods the Antarctic Circumpolar Current meanders more, bringing it and the warmer UCDW water closer to the WAP shelf. A poor sea ice year will typically result in lower primary production, dominated largely by small phytoplankton cells. This translates into less food for larval krill and consequently a reduction in larval krill survival rates. Penguin chicks are significantly lighter during La Niña years as a result of a reduction in available food.
Shifting ecosystems
It is now clear that a climate shift is occurring in the WAP, with greater warming and sea ice reduction occurring in the northern and mid-Peninsula regions, and less noticeable changes in the south. Essentially, the northern part of the WAP is becoming more sub-Antarctic, which is suitable for sub-Antarctic species, but not for the true Antarctic species, which are effectively being displaced.
The Palmer Antarctica LTER project has noted significant changes in the WAP marine ecosystem in response to regional warming and changes in sea ice dynamics. These changes have been observed on all trophic (the position an organism occupies on the food chain) levels. At the base of the food chain, cryptophytes (small phytoplankton) are replacing the previously abundant diatoms (larger phytoplankton) in the nearshore regions.
Phytoplankton productivity and community structure in the WAP is complex and highly variable. Diatom blooms typically start offshore and move towards the coast following the retreating ice. This large annual bloom of diatoms has recently disappeared from the northern parts of the WAP.
Such changes in the community structure and overall productivity of phytoplankton are having subsidiary effects further up the food chain. For instance, Antarctic zooplankton that rely heavily on sea ice for reproductive success, such as Antarctic krill (Euphausia superba), are being replaced by more oceanic species, such as salps (Salpa thompsoni) and pteropods (Limacina helicina). True Antarctic ice species, such as the Antarctic silverfish (Pleurogramma antarcticum) and the ice krill (Euphausia crystallorophias) appear to have disappeared almost entirely from the northern WAP as a result of the decrease in sea ice in that region.
At the top of the WAP food chain, Adélie penguins (Pygoscelis adelaie) that rely heavily on sea ice dynamics as well as abundant krill and silverfish stocks for their breeding success have declined dramatically and are being replaced by chinstrap (Pygoscelis antarctica) and gentoo penguins (Pygoscelis papua).
The value of long-term ecological research in understanding climate change
Much of what we now know to be occurring in the WAP region is largely due to the concerted efforts of a diverse team of researchers working through the Palmer Antarctica LTER (PAL) project, currently led by Dr Hugh Ducklow of the Marine Biological Laboratory, Woods Hole, USA.
The PAL project is an excellent example of what can be achieved through well thought out and coordinated long-term research. The project was officially added to the LTER network in 1990 and in 1993 the first of the annual PAL summer surveys to the WAP was conducted. Since then, a summer survey has been conducted every year and as such the PAL project now has 18 years worth of biological, chemical and physical oceanographic data for the region. The project is now in its fourth cycle of funding, through the National Science Foundation (NSF) Office1 of Polar Programs Antarctic Ecosystems and Organisms Program.
Having spent the last three years at the SAEON Elwandle Node as part of the team developing and coordinating SAEON’s first coastal ecosystem level long-term monitoring and research programme in South Africa2, my experience with the Palmer Antarctica LTER has afforded me the opportunity to really envisage what SAEON is capable of and what it will achieve in the not-so-distant future.
We cannot afford to underestimate the great value of the information that long-term research and monitoring will ultimately reap.
Acknowledgements
I would like to thank those people and organisations that made this experience possible for me: Dr Debbie Steinberg (Virginia Institute of Marine Science, VA); Dr Hugh Ducklow (Marine Biological Laboratory, MA); Dr Oscar Schofield (Rutgers University, NJ); the National Science Foundation (NSF) and the Gordon & Betty Moore Foundation (for funding); participants in the LMG10-01 research cruise, including scientists, students, Raytheon Polar Services support personnel and officers and crew of the Antarctic Research Support Vessel (ARSV) Laurence M Gould.
For more information on the programme, go to http://pal.lternet.edu/
1 NSF grant number #OPP-08-23101.
2 The Algoa Bay Long Term Monitoring and Research Programme is officially registered with the International Long Term Ecological Research, I-LTER, Network.
