Vertical profiles of Volcanic Aerosol and Polar Stratospheric Clouds Above Kiruna, Sweden: Winters 1993 and 1995

Vertical profiles of aerosol were measured in February 1993, and January - March 1995 using balloon-borne particle counters released from Kiruna, Sweden. Condensation nuclei (CN) and aerosol with radii 0.15 - 10.0 µm were measured in 8-12 size classes. The three flights in 1993 were within the polar vortex. Temperatures were below polar stratospheric cloud (PSC) threshold temperatures on one flight and a thin PSC was observed. The volcanic aerosol in the 1993 vortex was similar to that in 1992. In 1993, surface areas were 10 - 20 µm2 cm-3 and volumes 1 - 3 µm3 cm-3. In 1995 three of five flights were within the polar vortex. The volcanic aerosol had decreased to 3 - 7 µm2 cm-3 and 0.1 - 0.4 µm3 cm-3. The top of the volcanic aerosol layer in both years was near 500 K potential temperature (~20 km). A thick nitric acid and water PSC was observed in January 1995. In the thickest region of this PSC nearly all CN were observed to be activated, and surface areas of 5 - 10 µm2 cm-3 were calculated. The volumes observed in this PSC were closer to what would be expected for particles composed of nitric acid trihydrate than for ternary solution droplets. In 1993 the opposite was observed, the volumes in the thin PSC were closer to what would be expected for ternary solution droplets.     

Recent rapid salinity rise in three East Antarctic lakes

Research in East Antarctica has shown several recent environmental changes that may be linked to human impacts on climate. In order to detect the influence and context of these changes on coastal aquatic ecosystems we examined lake sediment cores from three lakes in the Windmill Islands, East Antarctica; Beall Lake, Holl Lake and ȁ8Lake Mȁ9. Cores were sectioned at␣2.5 mm intervals. Their diatom species composition was examined to detect changes in lake salinity using a diatom-salinity transfer function, and their algal pigment content was examined to detect photoautotrophic community responses to environmental change. Results showed that Holl Lake originated in a depression exposed by Holocene recession of the continental ice sheet and that Beall Lake and Lake M originated as isolated marine basins formed by changes in relative sea level. A general late Holocene trend of declining lake salinity was evident in all three lakes, interrupted by one short-term high salinity event in Beall Lake. This is consistent with a long-term positive moisture balance. This general decline in salinity has been followed by a remarkable recent rapid increase in salinity in all three lakes in the last few decades. We speculate that this rapid increase in salinity might be linked to changes taking place in the region including feedbacks resulting from decreasing sea ice extent as recorded in the nearby Law Dome ice core, and positive feedbacks in the catchments whereby reduced snow cover has led to decreased albedo, which in turn has caused increased evaporation and sublimation. Collectively these changes have shifted the lakes across a threshold from positive to negative moisture balance. A minor, but not rapid shift in the abundance of diatom pigments relative to pigments from green algae and cyanobacteria was also detected suggesting that some changes in photoautotrophic community composition have occurred. Measurements of modern nutrient levels are also higher than would be expected in Beall Lake and Holl Lake, given the extremely low sediment accumulation rates. This may be associated with a c. 300% increase in the population of Adélie penguins in the Windmill Islands recorded since the 1950s, or may a first signs of a rapid increase in catchment development and associated lake productivity as experienced in Antarctic and Arctic lakes subject to recent rapid regional warming. The most marked feature of the records is the rapid increase in salinity in all three lakes in␣the last few decades, which has occurred in lakes both with and without resident penguin populations.Dominic A. Hodgson and Donna Roberts contributed equally to this work