AAAS at the BA: Whale food, winners and losers in Antarctica and solar insights

Climate clues from the Earth’s poles – swarming whale food, winners and losers in Antarctic waters, and solar insights at the BA 2002 Annual Meeting

The latest thinking on the chances of extinction for Antarctic animals in seas and lakes, whale food hiding beneath sea ice, and new insights on the Sun’s spin are among the hot topics slated for discussion at today’s Frontiers of Polar Science panel, organized by the American Association for the Advancement of Science (AAAS), through its journal Science.

Clues from the planet’s coldest regions were the focus of work by panelists Lloyd S. Peck of the British Antarctic Survey (BAS), Andrew S. Brierley of the University of St. Andrews, and Michael E. McIntyre of the University of Cambridge. The researchers presented their latest findings as part of the 2002 Annual Meeting of the prestigious British Association for the Advancement of Science.

“The icy fastnesses of the polar regions are revealing the secrets of the Earth’s recent climatic history,” said Andrew M. Sugden, international managing editor for Science’s Cambridge office, who planned the Frontiers of Polar Science panel. “At the same time, a new understanding of their sensitive ecosystems and atmospheric chemistry is warning us about the impacts of humans on the climate and biosphere of today and tomorrow.”

At the AAAS panel, Peck discusses the latest thinking on the chances of survival or extinction for Antarctic animals by comparing results from fast-changing lakes with observations of the Antarctic marine environment – possibly the most constant temperature regime on Earth.

In the 25 January issue of Science, researchers from the British Antarctic Survey showed that the environmental and ecological characteristics of lakes on Signy Island in the Antarctic were changing as fast, if not faster than any site on earth.

Peck and colleagues reported that Signy Island’s winter lake temperatures rose by 1.3 degrees Celsius between 1980 and 1995. While the shift doesn’t sound dramatic, it set off rapid changes in the lakes’ ecologies, making them more nutrient-rich, increasing the number of sun-dependent plankton and extending the open water periods for 4 weeks.

Warming of Signy Island lakes was found to be three times greater than warming of the local air temperature during the same period. These trends show that “local climate change has been translated into extreme ecological change,” Peck reported.

Species living in Antarctic lakes have great biological flexibility with some being able to survive temperatures down to -25°C as eggs in winter and up to +25°C as adults in summer. However these animals do face a problem in a changing environment, not from the environmental change itself, but in surviving competition from invasions by alien species from lower latitudes.

Marine species, in contrast, appear highly fragile in the face of predicted environmental temperature change and may be amongst the most vulnerable on earth because of their poor physiological capacities to cope with rising temperature.

In the icy waters surrounding Antarctica, even fluctuations in the abundance of tiny, shrimp-like crustaceans called krill, a staple food source for fish and sea mammals such as whales, may trigger major ecosystem impacts. Brierley’s research on the distribution of krill under ice has shown how possible climate related changes in ice extent may impact krill.

“Krill are at the hub of the food web in the Southern Ocean. If you remove krill, the whole ecosystem will collapse,” Brierley said. The first direct comparisons of krill population densities in open-water and under-ice environments were described in the 8 March 2002 issue of Science by Brierley and colleagues. Krill swarm sizes under ice, as compared with swarms in the adjacent ice environment, and relationships between krill distribution and sea ice thickness are now a focus of his research.

Does the thickness of polar sea-ice directly relate to the number of krill swarming beneath these hiding spots? Clearly, Brierly noted: “If krill prefer to locate beneath thick, multi-year ice floes, and the incidence of these floes were to diminish following climate change, then the distribution of krill may change too. There could be knock-on effects for predators who depend on krill as a food source.”

Using an echosounder attached to an unmanned submersible the length of a school bus-Autosub-2-Brierley’s research team measured concentrations of krill five times higher in near-ice environments than in open waters. This near-ice dwelling place is created during the summers when sea ice breaks off and melts, kicking off a phytoplankton bloom that serves as food for krill. Whales then feed on the krill.

Brierley’s discovery of dense aggregations of the shrimp-like creatures, within a 1-13 kilometer-thick band under the sea ice, suggested that survival for krill may be all about location: They seem to seek a compromise between proximity to food-the ice edge-and spots offering refuge from air-breathing predators unable to dive through ice.

High above the polar ice and krill, Michael McIntyre points to recent progress in understanding the ozone hole, and a new — totally unexpected, he said — application of that understanding: making sense of the way the Sun spins.

McIntyre’s work has also settled one of the questions about possible causes of solar variability, and its consequences for the Earth’s climate. “Sometimes in science the best results are not the ones you are looking for, as when Fleming discovered penicillin,” said McIntyre. “We were studying the fluid dynamics of the ozone hole, and entirely by chance made a breakthrough towards understanding the Sun’s rotation.”

Using knowledge of the ozone hole and related patterns of motion in the Earth’s stratosphere, McIntyre said, he and Douglas Gough have found “the first credible explanation of the observed pattern of spin, why some parts of the Sun spin faster than others.”

The Sun spins once on its axis every 27 days or so, on average, with the equatorial regions spinning faster than the polar regions of the visible surface. A few years ago, when helioseismology began to reveal the internal pattern of spin, big surprises emerged — the pattern didn’t conform to any previous expectations.

The new insights into the Sun are based on today’s understanding of motion in the Earth’s stratosphere. That in turn depends on an older but nevertheless dramatic “paradigm change” in fundamental theories of atmospheric motion. “Turbulent eddy viscosity,” an old theoretical idea implying that a turbulent fluid behaves like a very viscous fluid, is still used in solar physics but has had to be thrown out in the atmospheric case because observations show it to be wrong. The theoretical reasons are now well understood. The eddy viscosity idea is still accepted in the literature on the solar case, but McIntyre argues that it will have to be thrown out in that case too, for fundamentally similar reasons.

If the idea of eddy viscosity were correct, he said, then the fluid system, left to itself, would tend to settle down to a state of rigid rotation, just like a balloon full of treacle in space. But it has been known for some time, he said, that “the chaotic eddying motions in the real atmosphere often do the opposite thing. They drive the fluid system away from solid rotation. This is sometimes called “negative friction”, or “anti-friction”.

It is intimately part of today’s understanding of the ozone hole, and of how global circulation patterns move greenhouse gases around the Earth and into polar regions. McIntyre claims that the same ideas must apply to the Sun’s interior, whose fluid dynamics is similar in key respects.

McIntyre is a Fellow of the Royal Society and a recipient of the Rossby Medal of the American Meteorological Society, and the Julius Bartels Medal of the European Geophysical Society, for his work on understanding stratospheric circulations and the exchange of greenhouse gases between stratosphere and troposphere.