The Effects of Flowline Length Evolution on Chemistry-Delta O-18 Profiles from Penny Ice Cap, Baffin Island, Canada

The isotopic and chemical signatures for ice-age and Holocene ice from Summit, Greenland and Penny Ice Cap, Baffin Island, Canada, arc compared. The usual pattern of low delta(18)O, high Ca2+ and high Cl- is presented in the Summit records, but Penny Ice Cap has lower than present Cl- in its ice-age ice. A simple extension of the Hansson model (Hansson, 1994) is developed and used to simulate these signatures. The low ice-age Cl- from Penny Ice Cap is explained by having the ice-age ice originating many thousands of km inland near the centre of the Laurentide ice sheet and much further from the marine sources. Summit's flowlines all start close to the present site. The Penny Ice Cap early-Holocene delta(18)O's had to be corrected to offset the Laurentide meltwater distortion. The analysis suggests that presently the Summit and Penny Ice Cap marine impurity originates about,500 km away, and that presently Penny Ice Cap receives a significant amount of local continental impurity.

Landscape Evolution of the Dry Valleys, Transantarctic Mountains: Tectonic Implications

There are different views about the amount and timing of surface uplift in the Transantarctic Mountains and the geophysical mechanisms involved. Our new interpretation of the landscape evolution and tectonic history of the Dry Valleys area of the Transantarctic Mountains is based on geomorphic mapping of an area of 10,000 km(2). The landforms are dated mainly by their association with volcanic ashes and glaciomarine deposits and this permits a reconstruction of the stages and timing of landscape evolution. Following a lowering of base level about 55 m.y. ago, there was a phase of rapid denudation associated with planation and escarpment retreat, probably under semiarid conditions. Eventually, downcutting by rivers, aided in places by glaciers, graded valleys to near present sea level. The main valleys were flooded by the sea in the Miocene during a phase of subsidence before experiencing a final stage of modest upwarping near the coast. There has been remarkably little landform change under the stable, cold, polar conditions of the last 15 m.y. It is difficult to explain the Sirius Group deposits, which occur at high elevations in the area, if they are Pliocene in age. Overall, denudation may have removed a wedge of rock with a thickness of over 4 km at the coast declining to 1 km at a point 75 km inland, which is in good agreement with the results of existing apatite fission track analyses. It is suggested that denudation reflects the differences in base level caused by high elevation at the time of extension due to underplating and the subsequent role of thermal uplift and flexural isostasy. Most crustal uplift (2-4 km) is inferred to have occurred in the early Cenozoic with 400 m of subsidence in the Miocene followed by 300 m of uplift in the Pliocene.

Evolution of 1996-1999 La Niña and El Niño Conditions Off the Western Coast of South America: A Remote Sensing Perspective

We present the evolution of oceanographic conditions off the western coast of South America between 1996 and 1999, including the cold periods of 1996 and 1998-1999 and the 1997-1998 El Niño, using satellite observations of sea level, winds, sea surface temperature (SST), and chlorophyll concentration. Following a period of cold SST and low sea levels in 1996, both were anomalously high between March 1997 and May 1998. The anomalies were greatest between 5 degrees S and 15 degrees S, although they extended beyond 40 degrees S. Two distinct peaks in sea level and SST occurred in June-July 1997 and December 1997 to January 1998, separated by a relaxation period (August-November) of weaker anomalies. Satellite winds were upwelling favorable throughout the time period for most of the region and in fact increased between November 1997 and March 1998 between 5 degrees S and 25 degrees S. Satellite-derived chlorophyll concentrations are available for November 1996 to June 1997 (Ocean Color and Temperature Sensor (OCTS)) and then from October 1997 to present (Sea-viewing Wide Field-of-view Sensor (SeaWiFS)). Near-surface chlorophyll concentrations fell from May to June 1997 and from December 1997 to March 1998. The decrease was more pronounced in northern Chile than off the coast of Peru or central Chile and was stronger for larger cross-shelf averaging bins since nearshore concentrations remained relatively high.