Sabina Brütsch

A high‐resolution air chemistry record from an Alpine ice core: Fiescherhorn glacier, Swiss Alps

Glaciochemical studies at midlatitudes promise to contribute significantly to the understanding of the atmospheric cycling of species with short atmospheric lifetimes. Here we present results of chemical analyses of environmentally relevant species performed on an ice core from Fiescherhorn glacier, Swiss Alps (3890 m above sea level). This glacier site is unique since it is located near the high-alpine research station Jungfraujoch. There long-term meteorological and air quality measurements exist, which were used to calibrate the paleodata. The 77-m-long ice core was dated by annual layer counting using the seasonally varying signals of tritium and δ18O. It covers the time period 1946–1988 and shows a high net accumulation of water of 1.4 m yr−1 allowing for the reconstruction of high-resolution environmental records. Chemical composition was dominated by secondary aerosol constituents as well as mineral dust components, characterizing the Fiescherhorn site as a relatively unpolluted continental site. Concentrations of species like ammonium, nitrate, and sulfate showed an increasing trend from 1946 until about 1975, reflecting anthropogenic emission trends in western Europe. For mineral dust tracers, no trends were obvious, whereas chloride and sodium showed slightly higher levels from 1965 until 1988, indicating a change in the strength of sea-salt transport. Good agreement between the sulfate paleorecord with direct atmospheric measurements was found (correlation coefficient r2 = 0.41). Thus a “calibration” of the paleorecord over a significant period of time could be conducted, revealing an average scavenging ratio of 180 for sulfate.

Ammonium concentration in ice cores: A new proxy for regional temperature reconstruction?

[1] We present a reconstruction of tropical South American temperature anomalies over the last ∼1600 years. The reconstruction is based on a highly resolved and carefully dated ammonium record from an ice core that was drilled in 1999 on Nevado Illimani in the eastern Bolivian Andes. Concerning the relevant processes governing the observed correlation between ammonium concentrations and temperature anomalies, we discuss anthropogenic emissions, biomass burning, and precipitation changes but clearly favor a temperature‐dependent source strength of the vegetation in the Amazon Basin. That given, the reconstruction reveals that Medieval Warm Period– and Little Ice Age–type episodes are distinguishable in tropical South America, a region for which until now only very limited temperature proxy data have been available. For the time period from about 1050 to 1300 AD, our reconstruction shows relatively warm conditions that are followed by cooler conditions from the 15th to the 18th century, when temperatures dropped by up to 0.6°C below the 1961–1990 average. The last decades of the past millennium are characterized again by warm temperatures that seem to be unprecedented in the context of the last ∼1600 years.

A potential high-elevation ice-core site at Hielo Patagonico Sur

Abstract The Patagonia icefields constitute a unique location in the Southern Hemisphere for obtaining non-polar paleo-records from ice cores south of 45°S. Nevertheless, no ice-core record with meaningful paleoclimate information has yet been obtained from Patagonia. This deficiency is due to extremely harsh field conditions, and to the fact that the main plateaus of both Hielo Patagónico Norte (HPN; northern Patagonia icefield) and Hielo Patagónico Sur (HPS; southern Patagonia icefield) are strongly affected by meltwater percolation. In order to explore the suitability of high-elevation glacier sites at HPS as paleoclimate archives, three shallow firn cores were retrieved covering the altitude range 1543−2300 ma.s.l. The glaciochemical records from the two lower sites confirm the presence of superimposed ice, a clear sign of meltwater formation and percolation. In the core from 2300 m, the glaciochemical signature appears to be preserved, indicating that no significant melting occurred. Although there might be problems associated with wind erosion and extreme melt events, there is good potential for well-preserved paleo-records within glaciers in the Patagonia icefields located higher than 2300 m.

Ion fractionation in young sea ice from Kongsfjorden, Svalbard

Abstract The fractionation of major sea-water ions, or deviation in their relative concentrations from Standard Mean Ocean Water ratios, has been frequently observed in sea ice. It is generally thought to be associated with precipitation of solid salts at certain eutectic temperatures. the variability found in bulk sea-ice samples indicates that the fractionation of ions depends on the often unknown thermal history of sea ice, which affects the structure of pore networks and fate of solid salts within them. Here we investigate the distribution of ions in Arctic sea ice that is a few weeks old with a reconstructible thermal history. We separate the centrifugable (interconnected) and entrapped (likely disconnected) contributions to the ice salinity and determine their ion fractionation signatures. the results indicate that differential diffusion of ions, rather than eutectic precipitation of cryohydrates, has led to significant ion fractionation. the finding emphasizes the role of coupled diffusive–convective salt transport through complex pore networks in shaping the biogeochemistry of sea ice.