June 2008 Geology and GSA Today media highlights

J. Halfar et al., Dept. of Chemical and Physical Sciences, University of Toronto at Mississauga, 3359 Mississauga Rd. N, South Building, Room 3006, Mississauga, Ontario L5L 1C6, Canada. Pages 463-466.

Assessing human impact on climate and ecosystems and predicting future climate evolution require knowledge of climates from past centuries. While we have achieved a good understanding of century-scale climate change in mid- and high-latitude terrestrial areas (mainly through the analysis of tree-ring records), such data are incomplete in many extratropical marine regions, due to a lack of appropriate climate archives. Halfar et al. have investigated the potential of long-lived marine algae as recorders of past climates. Coralline red algae, which live in many coastal regions worldwide, produce a skeleton made up of calcium carbonate. Individual calcified plants exhibit annual growth bands, very similar to tree rings, and can live continuously for several centuries in temperate and subarctic oceans. By monitoring coralline red algae of the genus Clathromorphum for a one-year period in the gulf of Maine, United States, Halfar et al. were subsequently able to relate geochemical information contained in the calcified algal growth bands to locally measured ocean temperatures, thus highlighting the suitability of coralline red algae as extratropical climate archives. By applying the results of the monitoring experiment to a 30-year coralline-algal oxygen isotope record, they demonstrated that the algae archived past water temperatures. In addition, the specimen contained a record of past variations of the Labrador ocean current and related climate oscillations in the northwestern Atlantic—a key region in Earth's oceans where poorly understood climate and oceanographic changes have recently had a dramatic impact on ecosystems and fishery yields.

Influence of precipitation phase on the form of mountain ranges

Alison M. Anders et al., Dept. of Geology, University of Illinois at Urbana-Champaign, NHB 245, 1301 W. Green St., Urbana, Illinois 61801, USA. Pages 479-482.

Mountainous topography influences the spatial distribution of rain and snowfall. Precipitation, in turn, shapes mountain ranges through erosion. Using a coupled numerical model, Anders et al. explore the interrelationship between precipitation and mountain evolution. This model suggests profound differences between rain- and snow-dominated mountain ranges. If most precipitation falls as rain, modeled mountain ranges tend to be steep and narrow with deeply set river valleys in the center of the range and low-relief range shoulders. In contrast, if most precipitation falls as snow, modeled mountain ranges are broader, less high and steep, and the relief between river valleys and ridges is uniform from foothills through the center of the range. These results suggest that complex relationships between climate and topography may be present in the natural system, and indicate an increased efficiency of erosion in snow-dominated climates.

Extreme storm events, landscape denudation, and carbon sequestration: Typhoon Mindulle, Choshui River, Taiwan