BAS Research - Launching a weather balloon
Home » BAS Research » Our Research Programmes » Previous Research » Global Science in an Antarctic Context » Research outputs and impacts » Major discoveries - GSAC »
Summary of major discoveries and key references from BAS research programme Global Science in an Antarctic Context (GSAC):
Over the last ~1 million years, Earth has regularly warmed to conditions like the present, and cooled to give large ice sheets on the northern continents. Although it is understood that they are controlled by the changing parameters of Earth’s orbit, the detail of the triggers and amplifiers leading to these huge climate swings has remained elusive.
BAS has played a major role within the European Project for Ice Coring in Antarctica (EPICA) in publishing new ice core data covering the last 800,000 years that show how different parts of the Earth System reacted during these changes. The new records have provided the data with which theories about causes can be generated and tested quantitatively. This has spawned a new generation of modelling studies, data syntheses and hypotheses, many of which BAS is contributing to.
For some years, it has been realised that the lowest layers of the Arctic and Antarctic atmosphere have some unusual chemistry, that might be related to the production of halogen (especially bromine) compounds. However, there has been no clear understanding of how the micro and macroscale properties of sea ice might control this chemistry.
Using year-round measurements at Halley, we have been able to show that halogens affect many different aspects of atmospheric chemistry there, including the partitioning of nitrogen oxides. And using combinations of in situ data, satellite and meteorological observations, we have shown how sea ice and meteorology together create the conditions under which vast clouds of halogen compounds can form. This work provides a basis for modelling the influence of the polar regions on the global atmosphere, and the likely changes we can expect as sea ice diminishes in response to climate change.
Antarctica is important to assessments of future climate change and their global impacts since it is a key regulator of factors such as ice-sheet mass balance, sea level and ocean circulation. Improved projections of Antarctic climate change were produced by weighting the output from climate models based on their ability to reproduce the climate of the late 20th century. Output from 19 of the 24 coupled ocean-atmosphere models submitted to the Intergovernmental Panel on Climate Change (IPCC) Assessment Report 4 (AR4) were used in this study.
Over the 21st century, projections show a widespread surface warming across high southern latitudes, with peaks on the Antarctic plateau and in the sea ice zone during winter of 0.3–0.5 °C per decade. The weighting gives a temperature increase that is 20% larger in the sea ice zone than the unweighted trend. The warming over the Southern Ocean results in a loss of approximately 33% of the sea ice area by 2100, which may affect the production of Antarctic Bottom Water, and therefore the global theremohaline circulation, as well as the biodiversity.
Coastal polynyas — areas of open water around the coasts of Antarctica, kept open by the action of persistent offshore winds — are sites of intense ocean-to-atmosphere heat fluxes. As sites of rapid sea ice production, they play an important role in controlling Antarctic sea ice extent and dense water formation. However, the regions in which they form are difficult to access with ships, so few
in situ
observations of air-sea interaction in these regions exist.
The first airborne observations of the atmosphere over an Antarctic coastal polynya were made using a BAS instrumented Twin Otter aircraft. These observations revealed that only a relatively small fraction of the polynya was truly open water, with much of the remainder covered by thin ice which significantly modified ocean-atmosphere heat exchange. These measurements have improved understanding of the processes at work in Antarctic coastal polynyas and will lead to their improved representation in large-scale atmosphere-ice-ocean models.
The strong westerly winds that blow over the Southern Ocean are important in driving the world’s largest ocean current system, the Antarctic Circumpolar Current (ACC). These winds have been dramatically increasing in strength during recent decades. BAS research, based on satellite measurements of the ocean surface and computer modelling, indicates that the ACC only shows a slight acceleration but instead the ACC shows a large increase in ocean eddy activity. These eddies play a key role in moving heat southward toward the Antarctic continent and need to be included in climate models to improve their accuracy.
A four-year study by scientists from the University of East Anglia (UEA), British Antarctic Survey (BAS) and the Max-Planck Institute for Biogeochemistry reveals that an increase in winds over the Southern Ocean, caused by greenhouse gases and ozone depletion, has led to a release of stored CO
2
into the atmosphere and is preventing further absorption of the greenhouse gas.
The saturation of the Southern Ocean was revealed by scrutinising observations of atmospheric CO 2 from 40 stations around the world. Since 1981 the Southern Ocean sink ceased to increase, whereas CO 2 emissions increased by 40%. The possibility that in a warmer world the Southern Ocean — the strongest ocean sink — is weakening is of major importance and a cause for concern.
It is well known that changes in total solar irradiance and solar UV have an effect on atmospheric temperatures. However, by analysing more than 40 years of atmospheric data BAS has found evidence that the temperature of the Earth’s troposphere and stratosphere are not only related to changes in solar radiation, but also to changes in the geomagnetic field driven disturbances originating on the Sun. Furthermore, these solar driven changes are systematically modulated by other internal oscillations in the atmosphere, such as the quasi-biennial oscillation (QBO) and the northern annular mode (NAM).
Periods when the solar wind pressure, the outward flow of electrically charged particles from the Sun, is high correlates with a positive NAM; these conditions are linked to wetter, stormier, winters in the UK. Under similar conditions, some parts of the Arctic showed anomalies in surface air temperature of up to 4K. The mechanism for these changes remains elusive.
The Earth’s Van Allen radiation belts consist of very energetic electrons and protons trapped inside the Earth’s magnetic field and which drift around the Earth on a timescale of tens of minutes. They are important since they cause damage to satellites, and since they provide a link to climate via their effects on the atmosphere.
Conclusive evidence has been found as to the mechanism responsible for accelerating the particles to very high energies, namely whistler-mode waves. The theory has also been shown to work equally effectively on Jupiter, a very rigorous test in a completely different geophysical environment. These studies have resolved an outstanding issue since the Van Allen radiation belts were first identified in 1957.
Changes in the volume of ice contained in the Antarctic and Greenland ice sheets directly affect global sea level. Accelerating ice loss has been reported from a growing number of glaciers along the Greenland and Antarctic ice-sheet margins.
BAS has developed a new technique to use high-resolution data acquired by satellite (43 million satellite measurements of the Antarctic and seven million of Greenland), which reveals recent change in unprecedented detail over the entire coastal margin of both ice sheets. The results show that the most profound changes occur as glaciers, which drain the ice sheets from the high plateaux down to the coast, transmit any coastal changes back up into the ice sheets.
Retreating ice shelves and accelerating glaciers cause ice-sheet thinning, which now reaches all latitudes in Greenland and has intensified around some key parts of Antarctica. Around the Antarctic Peninsula, where ice shelves have been retreating due to climate change, ice-sheet thinning still persists decades after ice-shelf collapse. While the current contribution to sea-level rise along the Greenland and Antarctic ice-sheet margins is ~1.8mm per year, our findings indicate that this could grow rapidly in the coming decades.
The northern Antarctic Peninsula is unlike the rest of the Antarctic continent — it is warmer, has high rates of snowfall, is drained by hundreds of glaciers, and has been subject to rapid rates of atmospheric warming (around 3°C in the last 50 years). Compared with the rest of the Antarctic ice sheet, the Antarctic Peninsula could make a contribution to sea-level rise out of proportion to its size.
By tracking glacial features in 75 pairs of satellite images, BAS measured the change in speed in over 300 glaciers. The results reveal the effect of climate warming — a 12% increase in glacier speed from 1993 to 2003.
The study allows the first assessment of how much the northern Antarctic Peninsula contributes to a rise in sea level (0.16 ± 0.06mm per year in 2000), which is similar to that of glaciers in Alaska. The research also provides new insight into how sub-polar glacier systems respond to climate change, such as those in Greenland, Alaska and Svalbard glaciers which have been shortening and accelerating in recent years.
Although the East Antarctic Ice Sheet is considered to be stable, recent satellite observations have detected changes, in particular over George V Land, where the Wilkes Subglacial Basin lies. BAS and the Italian Antarctic programme targeted this largely unknown region with a major aerogeophysical survey.
Aeromagnetic and aerogravity data imaged sub-ice geology, while radar imaged ice layers, ice thickness, bedrock topography and subglacial lakes. A new sub-ice topography map radically changed existing views of the region. Deep subglacial trenches flanked by mountain blocks and plateaux were revealed, with striking similarity to the topography underlying dynamic and potentially unstable parts of the West Antarctic Ice Sheet.
Understanding past climate, especially during periods when atmospheric carbon dioxide concentrations were similar to today, can provide new insight into how the planet operates. An important constituent is the link between climate and vegetation.
BAS developed a comprehensive database of global vegetation data from marine and terrestrial records from 202 mid-Pliocene sites, taken from fossil pollen, leaf or wood, into a consistent biome classification scheme called Tertiary Environment and Vegetation Information System (TEVIS). TEVIS thus provides new boundary conditions for Global Climate Model simulations which indicate that the mid-Pliocene climate was warmer and moister than today. There is a northward shift of temperate and boreal forest, a spread of warm-temperate forests in middle and eastern Europe, and expansion of savannas and woodland at the expense of tropical deserts.
Two or three times every decade large numbers of seabird and seal young die across a large area of the Southern Ocean. Drawing on unique long-term datasets on the breeding success of seals and penguins, alongside detailed observations and experiments from major research cruises and quantitative modelling, the changes in predator breeding performance has been shown to be linked to changes in the dynamics of the krill populations. The krill fluctuations are driven by changes in ocean temperature, circulation and sea-ice conditions, which in turn are driven by Southern Hemisphere-scale changes in atmospheric conditions.
These analyses provide the basis for developing understanding and quantifying how these unique ecosystems respond to the rapid climate-related changes occurring in the environments of the Southern Ocean. They also highlighted the importance of incorporating climate-related impacts in the development of procedures for the sustainable management of marine resources.
Copepods and krill are the main links in the transfer of energy from primary producers to the large predators in the Southern Ocean food web but it is unclear how these invertebrates survive during the winter months when the phytoplankton does not bloom. BAS research has demonstrated that when food is abundant, copepods grow many times faster than krill, but this is reversed when food is scarce. During such periods of low food availability most copepods simply continued their winter hibernation at depth, whereas the krill keep growing as they exploit a number of alternative food sources including microbial organisms, material from the seafloor and even their own moults.
These new findings have resulted in a major reassessment of how the unique marine food web in Antarctica operates and how it will respond to environmental changes.
Mackerel icefish is one of the key species exploited in the Southern Ocean. New analyses both of the occurrence and the length of icefish in predator diets have revealed a clear relationship between sea temperature and the number of young fish entering the population. Identifying such an important relationship provides an excellent way to forecast changes in the population and hence to adjust fishery management strategies accordingly.
Krill are the main prey of many of the marine mammal and seabird species in the Southern Ocean. To study the circumpolar distribution of krill, nations working around Antarctica pooled their regional survey data into a central database spanning 1926–2006. This emphasised the asymmetry in krill distribution, with 70% of their total stock concentrated into just one-quarter of the Southern Ocean from 0°–90°W, and that 87% of the population live over deep oceanic water.
This distribution can be envisaged as a trade-off between occupying risky, food-rich habitats such as shelves; and low-risk, low-food areas over the deep ocean. Through these analyses, in conjunction with detailed studies of krill biology, a quantitative understanding of the controls on the distribution and abundance of this key species is being developed.
Since 1972, BAS scientists have conducted a census of the breeding pairs of wandering albatrosses nesting on Bird Island, South Georgia as part of our long-term monitoring programme. We have documented a very marked decline with the population halving in just 25 years. The breeding success of wandering albatrosses has remained consistently high. The decline is attributed to birds being killed as they scavenged for food behind long-line fishing vessels. Deaths increased in the mid 1990s when long-lining for Patagonian toothfish became established around South Georgia.
BAS scientists have used both the long-term monitoring data and the extensive tracking programme, along with fishers and fisheries managers to implement mitigation measures around South Georgia. This has reduced the level of albatross by-catch from almost 6,000 birds in 1997 to 0 since 2006. Unfortunately tracking non-breeding wandering albatrosses has highlighted areas under the jurisdiction of other commissions, where they are almost certainly still being killed. So the objective now is to demonstrate this success to other fishery management organisations.
The Antarctic Peninsula is warming faster than anywhere in the Southern Hemisphere — temperatures have increased by 3°C in the last 50 years, and the surface waters are rising in temperature too. The critical question is “Will the marine animals there acclimatise to the unprecedented changes?”.
Carefully controlled experiments show that Antarctic marine animals can survive short term increases in temperature (days) but cannot acclimate to longer term increases (months or years). Smaller individuals (juveniles) and more active species, usually predators, cope better with the changes. The effects of temperature change are complex, affecting not only survival rates, but also reproductive capacity and food webs. These are important findings that allow insight into how the biodiversity of the marine Antarctic environment will evolve as the Earth warms.
© NERC-BAS 2007