AGU Journal Highlights -- Aug. 14, 2007

1. Concurrent arrival of the 2004 Sumatra tsunami and storm-generated waves on North America's Atlantic coast

The Sumatra-Andaman earthquake generated a catastrophic tsunami that caused heavy damage and fatalities in coastal areas around the Indian Ocean. The tsunami, which struck on 26 December 2004, also propagated throughout the world's oceans, making it the first such event to be scrutinized with continuous observations of widespread oceanic monitoring networks. Thomson et al. analyze more than 100 tide gauge records from the Atlantic coast of North America and find that the tsunami was identified in most outer tide gauges from Florida to Nova Scotia. Maximum heights for northern regions were between 32 and 39 centimeters (1.0 and 1.3 feet), while southern regions experienced wave heights between 15 and 33 centimeters (0.49 and 1.1 feet). However, along the shores of Maine and Nova Scotia, the arrival of the tsunami coincided with the presence of tsunami-like waves generated by a major storm tracking northward along the U.S. eastern seaboard. The combined waves reached heights in excess of 1 meter (3.3 feet). The authors warn that, although the northern Atlantic Ocean has low tsunami hazards, tsunamis from distant seismic events could threaten coastal infrastructure and habitat when the waves coincide with winter storm waves.

Title: Double jeopardy: Concurrent arrival of the 2004 Sumatra tsunami and storm-generated waves on the Atlantic coast of the United States and Canada

Authors: Richard E. Thomson: Institute of Ocean Sciences, Sidney, British Columbia, Canada;

Alexander B. Rabinovich: Institute of Ocean Sciences, Sidney, British Columbia, Canada; also at P.P. Shirshov Institute of Oceanology, Moscow, Russia;

Maxim V. Krassovski: School of Earth and Ocean Sciences, University of Victoria, Victoria, British Columbia, Canada.

Source: Geophysical Research Letters (GRL) paper 10.1029/2007GL030685, 2007

2. Antarctic Bottom Water has warmed within recent decades

The western South Atlantic’s coldest, deepest layer, called the Antarctic Bottom Water, originates in the waters surrounding Antarctica. In the subtropics, most of this current joins water in the Brazil Basin through the Vema Channel, a narrow gorge on the seafloor about 1000 kilometers (600 miles) southeast of Rio de Janeiro. Zenk and other researchers have made measurements of water temperatures and other parameters of the flow through the Vema Channel during the past 35 years. In this new analysis, he and Morozov find that temperatures in this channel were fairly level before 1992, but that the next 15 years were marked by a warming trend that raised temperatures about 0.0028ºC (0.005 ºF) each year. Although this trend is seen, the flow's properties through the Vema Channel were highly variable. Nonetheless, the authors use this long record to conjecture that the Antarctic Bottom Water also has undergone slight freshening. They note that additional long-term studies on deep circulation and water mass properties may help reveal whether abyssal oceans are warming at locations other than choke points such as the Vema Channel.

Title: Decadal warming of the coldest Antarctic Bottom Water flow through the Vema Channel