Deep-ocean ecosystems in the stranglehold of climate change
The deep ocean and its ecosystems are vastly affected by climate change, a new study now published in Proceedings of the National Academy of Sciences (PNAS) confirms. The UK-US team of researchers points out that the food supply found several thousand metres under the water surface is likely to be subject to large variation due to global warming. The scientists base their statement on data collected at two stations off the coast of southwest Ireland (Porcupine Abyssal Plain Observatory) and off the central California coast (Station M). The Porcupine Abyssal Plain Observatory, situated at a depth of nearly 5,000 metres in the northeast Atlantic several hundred kilometres off the Irish coast, is supported by the EU-funded Networks of Excellence MARBEF ('Marine biodiversity and ecosystem functioning') and ESONET ('European seas observatory network'), which both received funding under the 'Sustainable development, global change and ecosystems' Thematic area of the EU's Sixth Framework Programme (FP6). 'Climate-driven variation affects oceanic communities from surface water to the much-overlooked deep sea and will have impacts on the global carbon cycle,' the paper reads. 'Data from these two widely separated areas of the deep ocean provide compelling evidence that changes in climate can readily influence deep-sea processes. However, the limited geographic coverage of ... existing ... studies stresses the importance of developing a more global effort to monitor deep-sea ecosystems under modern conditions of rapidly changing climate.' The analysis of the data indicates that the food supply to the deep sea - even though already dependent on seasonal influences - could be affected by climate change through its impact on ocean processes that normally foster the transport of nutrients to the depth of the ocean. These include wind-driven upwelling, the depth of mixing of the surface waters, and the delivery of nutrients to surface waters via dust storms. 'Changes in upper ocean temperature influence stratification and can affect the availability of nutrients for phytoplankton production,' the paper explains. 'Global warming has been predicted to intensify stratification and reduce vertical mixing.' Due to this reduction of exchange between individual ocean layers, the organic matter that is the food of deep-sea organisms will not sink to the ocean floor to the same extent as before. The results can be drastic. For instance, the researchers collaborating with lead author Dr Ken Smith of the Monterey Bay Aquarium Research Institute (MBARI) in the US discovered that the population of grenadiers, one of the most important groups of fish on the deep seafloor, at Californian Station M doubled between 1989 and 2004. They attribute this substantial increase to climate change and commercial fishing. In much the same way, a previously common species of sea cucumber virtually disappeared after 1998 - an event likely tied to the El Niño phenomenon. The researchers were able to observe similar fluctuations at Porcupine Abyssal Plain, all linked to the quantity and type of food reaching the seafloor. Many of these processes and interdependencies are still not very well understood, the scientists argue. Therefore, more research is needed. At the same time, findings such as theirs should be better integrated into the discussion on climate change. 'Processes over the greatest area of the Earth's surface are very poorly constrained in most carbon cycle models and rarely considered in discussions of global climate variation,' the paper warns. 'This out-of-sight, out-of-mind mentality in ignoring the vast expanse of the deep ocean needs to be reversed in light of long-term datasets from two major ocean basins showing that the deep sea is strongly impacted by climate variation over a range of time scales.'
Countries
United Kingdom, United States