When we think of Antarctica, an expansive, frozen wasteland is usually what comes to mind. Perhaps this image is justified; Antarctica is an ice-covered continent, spanning 14,200,000 km2 with average temperatures ranging from -10 °C to -60 °C from the coastline inwards. Antarctica holds the record for the lowest temperature ever recorded on Earth at -89.2 °C.
Despite the apparent hostility, Antarctica is home to 235 animals: all of which rely on the marine habitat at some point in their life history.
Other forms of life found in Antarctica include algae (most of which are phytoplankton), fungi, and plant species. The true extent of Antarctic wildlife is largely determined by temperature and light availability, both of which are determined by season.
The Polar Seasons
Seasons in the south pole work rather differently to typical seasons seen in temperate-tropical regions. Much like its northern counterpart, Antarctica experiences a phenomenon known as the polar cycle, which consists of the polar night and day.
In contrast to the typical amount of daylight that we experience at lower latitudes, Antarctica experiences more than 24 hours of darkness in winter months. This phenomenon is called the polar night and only occurs within the polar circles.
In the winter, this darkness extends throughout the entire season and naturally, exerts tremendous pressures on Antarctic ecosystem, which is sustained by photosynthesising plankton.
The polar night is a result of the Earth’s axial tilt relative to the position of the sun. This tilt is roughly 23.5° and as such, both the Arctic and Antarctica undergo periods of prolonged daylight and darkness.
Thus, without even considering the unbearable temperatures and harsh icy desert, Antarctic life is fighting an uphill battle to survive. To understand how this is possible, first we must delve beneath the ice, and explore Antarctica’s tenacious ecosystem.
The Antarctic Food Web
As with most marine food webs, that of Antarctica begins at the surface. This is where light is readily available, and phytoplankton can convert sunlight into organic compounds. Antarctica has a huge variety of phytoplankton species; most of which belong to either the diatom or dinoflagellate group.
These organisms are the primary food source for all of the world’s oceans and facilitate life across the entire planet.
Antarctic krill are just one organism that feeds on primary producers. However, the contribution of these unsuspecting creatures is perhaps even larger than that of phytoplankton. In fact, Antarctic krill are considered the keystone species of the entire Southern Ocean.
By congregating in large schools, krill provide food for whales, seals, squid, icefish, and a variety of seabirds. In addition to the obvious benefits of having huge schools of krill in the ecosystem, these animals also contribute to vital biogeochemical cycles.
By having the largest biomass in the Southern Ocean and undergoing daily vertical migrations, Antarctic krill play a key role in transporting nutrients essential for life down to the seabed. This in turns supports a vast array of benthic life.
This is an example of ‘pelagic-benthic coupling’, the exchange of energy, mass, or nutrients from the pelagic realm to the benthic habitat.
Albeit the greatest life support for benthic life, Antarctic Krill are not the only organisms responsible for sustaining life at the seafloor.
Phytoplankton, whale faeces, and other dead/dying animals are just some of the constituents of marine snow that is found in all of the world’s oceans.
Due to the significant seasonality characteristic of Antarctica, there is a large disparity between the amount of food matter that falls down to the sea floor between summer and winter months. This difference is yet another pressure that Antarctic organisms have adapted to cope with.
It was long believed that there was no way that benthic organisms could live through the polar night. The dwindling sunlight as winter comes reduces the available light for phytoplankton. This in turn reduces the amount of organic matter (and food) being produced until the supply is essentially depleted. And thus, the already extreme conditions of Antarctic waters become a little more so.
It is easy to see why scientists thought it impossible for the seafloor community to operate as usual in summer months.
However, this is no longer the case.
The FOODBANCS (Food for Benthos along the Antarctic Continental Shelf) project was designed to study the true effects of the summer phytoplankton blooms on the West Antarctic Peninsula (WAP) benthos.
The hypothesis was as follows:
Sea ice retreat and intense summer phytoplankton blooms yield substantial summer deposition of algal detritus onto the WAP shelf floor; deposited bloom material then provides a substantial source of labile particulate organic carbon (i.e., a “food bank”) for benthic detritivores during winter months.
Roughly translated, scientists thought that the sheer amount of organic materials being produced in the Antarctic summer could leave enough food behind to sustain life throughout the long winter and thus serving as a “food bank”.
Beginning in December 1999, the team set out a series of sediment traps 150-170 m above the seafloor, which were then recovered and redeployed every 3-4 months.
A seafloor timelapse camera was also deployed along the study site so as to monitor the accumulation of biological material on the seabed.
As expected, POC fluxes displayed seasonal variability; average summer deposits were often double or even triple that of winter months. Inter-annual variability was even greater. The summer seasons of 1999-2000 and 2000-2001 had a 4-10-fold difference in the amount of organic carbon deposited. These results were consistent with the typical pattern of Antarctic shelf deposits over a decadal time scale.
The most significant result of the study was the confirmation of the hypothesis; the intense seasonality of the Antarctic primary production does indeed create a substantial food bank that sustains the benthic community over winter months.
The success of the FOODBANCS project paved the way for FOODBANCS II, in which the team would study the benthic response to the latitudinal sea ice gradient. This would give an insight into some of the potential consequences of a retreating ice sheet due to global warming.
The results were a somewhat mixed bag, with some important benthic ecosystem processes showing resilience to climate change, and others suffering greatly. One unexpected finding was the invasion of predacious king crabs, facilitated by rising temperatures. As with many non-native species, these organisms have the potential to wreak havoc on the Antarctic benthos and are one of many visible effects of global warming.
The Antarctic Outlook
Antarctica is truly one of Earth’s most compelling curiosities. The biting cold waters and extreme seasonality has given rise to some of the finest examples of evolution and bonds seen in nature. Pelagic-benthic coupling is just one process which keeps the Antarctic ecosystem going strong all through the year.
However, the pressures of global warming may hold significant consequences for Antarctic life. Sea ice retreat and warming temperatures hold an array of negative consequences for the benthic and pelagic communities alike.
The FOODBANCS projects have only scratched the surface of uncovering the impacts of global warming on the Antarctic ecosystem. Future studies investigating the nonlinearities, community mechanisms, and effect of invasive species may equip us with the knowledge we need to tackle climate change and preserve this iconic community.
But by then, it may already be too late.
Written by Lucas King