Were short warm periods typical for transitions between interglacial and glacial epochs?

Russian and German researchers took sediment probes of four silted up lakes in Central and Eastern Europe in order to reconstruct the climate of the Eemian Interglacial 115,000 years ago. At this time the Eemian Interglacial ended and was followed by the Weichselian Glacial which ended 15,000 years ago. -  Frank W. Junge/SAW
Russian and German researchers took sediment probes of four silted up lakes in Central and Eastern Europe in order to reconstruct the climate of the Eemian Interglacial 115,000 years ago. At this time the Eemian Interglacial ended and was followed by the Weichselian Glacial which ended 15,000 years ago. – Frank W. Junge/SAW

At the end of the last interglacial epoch, around 115,000 years ago, there were significant climate fluctuations. In Central and Eastern Europe, the slow transition from the Eemian Interglacial to the Weichselian Glacial was marked by a growing instability in vegetation trends with possibly at least two warming events. This is the finding of German and Russian climate researchers who have evaluated geochemical and pollen analysis of lake sediments in Saxony-Anhalt, Brandenburg and Russia. Writing in Quaternary International, scientists from the Helmholtz Centre for Environmental Research (UFZ), the Saxon Academy of Sciences (SAW) in Leipzig and the Russian Academy of Sciences say that a short warming event at the very end of the last interglacial period marked the final transition to the ice age.

The Eemian Interglacial was the last interglacial epoch before the current one, the Holocene. It began around 126,000 years ago, ended around 115,000 years ago and is named after the river Eem in the Netherlands. The followed Weichselian Glacial ended around 15,000 years ago is the most recent glacial epoch named after the Polish river Weichsel. At its peak around 21,000 years ago, the glaciers stretched as far as the south of Berlin (Brandenburg Stadium).

The researchers studied lake sediments to reconstruct the climate history of the Eemian Interglacial, since deposits on river and lake beds can build up a climate archive over the years. The sediment samples came from lakes that existed at the time, but which have since silted up and been uncovered in the former open cast mines at Gröbern near Bitterfeld, Neumark-Nord in the Geiseltal valley near Merseburg, and Klinge near Cottbus and at Ples on the upper reaches of the Volga, around 400 kilometres north-east of Moscow. Gröbern in Saxony-Anhalt is now seen by experts as one of the most studied places for Eemian Interglacial climate history in Germany. As well as pollen concentrations, the researchers analyzed the level and ratios of stable carbon (13C/12C) and oxygen isotopes (18O/16O) in carbonates and organic matter from sediment layers, since these provide information about the vegetation development and an indication of the climate.

The results show a relatively stable climate over most of the time, but with instabilities at the beginning and end of the Eemian Interglacial. “The observed instability with the proven occurrence of short warming events during the transition from the last interglacial to the last glacial epoch could be, when viewed carefully, a general, naturally occurring characteristic of such transition phases,” concludes Dr Tatjana Boettger of the UFZ, who analyzed the sediment profiles at the UFZ’s isotope laboratory in Halle. “Detailed studies of these phenomena are important for understanding the current controversial discussed climate trend so that we can assess the human contribution to climate change with more certainty,” explains Dr Frank W. Junge of the SAW.

From reconstructions of climate history, we know that in the Earth’s recent history, interglacial epochs occurred only once every 100,000 years or so and lasted for an average of around 10,000 years. The current interglacial epoch – the Holocene – has already lasted more than 10,000 years and reached its highest point so far around 6000 years ago. From a climate history perspective, we are currently at the end of the Holocene and could therefore expect to see a cooling-down in a few thousand years if there had been no human influence on the atmosphere and the resulting global warming.

Top scientists to discuss global changes at arctic conference in Miami

Hundreds of the world’s top scientists and policymakers are expected to attend the State of the Arctic conference at the Miami Hyatt Regency from March 16 – 19, 2010. Speakers will include Arden Bement, director of the National Science Foundation (NSF), Jane Lubchenko, administrator of the National Oceanographic and Atmospheric Administration (NOAA), and Wendy Watson-Wright, assistant director-general of the United Nations Educational, Scientific and Cultural Organization (UNESCO).

The conference will review our understanding of the arctic system in a time of rapid environmental change and will include some of the latest research results from the world’s leading polar scientists.

Specific topics to be addressed include historical and future perspectives on current warming and predictions of future climate; the changing carbon cycle of the Arctic; and the future of sea ice loss, its impact and links to changes on land. For a copy of the current program, go to http://soa.arcus.org/program.

Who: Major funding provided by the National Science Foundation along with 14 additional sponsors and partners. For a list of cooperating organizations, see http://soa.arcus.org/about/sponsors.

What: The State of the Arctic Conference. The conference’s main goal is to review our understanding of the arctic system in a time of rapid environmental change and recommendations on what can be done to address areas of concern. It will provide an open international forum for discussion of future research directions aimed toward a better understanding of the arctic system and its trajectory. Topics will range from basic understanding of the Arctic and system-wide change to developing response strategies to adapt and mitigate change.

When: March 16-19, 2010

Where: Hyatt Regency Miami, 400 Southeast 2nd Avenue, in Miami, Florida

The Arctic Research Consortium of the U.S. (ARCUS) is organizing the conference on behalf of the arctic community and sponsoring organizations.

Tides, Earth’s rotation among sources of giant underwater waves

Scientists at the University of Rhode Island are gaining new insight into the mechanisms that generate huge, steep underwater waves that occur between layers of warm and cold water in coastal regions of the world’s oceans.

David Farmer, a physical oceanographer and dean of the URI Graduate School of Oceanography, together with student Qiang Li, said that large amplitude, nonlinear internal waves can reach heights of 150 meters or more in the South China Sea, and the effects they have on surface wave fields ensure that they are readily observable from space.

Farmer and Li will report results of their research at the Ocean Sciences Meeting of the American Geophysical Union in Portland, Ore., on February 25.

“The large waves in the South China Sea have attracted a fair bit of attention in recent years,” Farmer said, “but much of this has been directed at the interaction of the waves with the sloping continental shelf of mainland China where they break, overturn and produce intense mixing. Our focus is on the way in which they are generated in Luzon Strait, between Taiwan and the Philippines, and the way they evolve as they propagate westwards across the deep ocean basin of the South China Sea.”

Farmer and Li studied the evolution of large internal waves occurring at tidal periods generated by currents traversing submarine ridges in Luzon Strait. As these waves travel west through the South China Sea, they steepen and evolve into packets of steep, energetic waves occurring at periods of 20-30 minutes. It is these energetic short period waves that modulate the ocean surface roughness, making their presence observable from satellites in space.

The URI scientists’ observations showed that the Earth’s rotation modifies internal waves as they travel cross the deep basin. This effect mainly influences the internal waves that form on the 24-hour period of diurnal tides, dispersing the energy and inhibiting the steepening process. Internal waves that form on the semi-diurnal tides are not affected in this way, are more readily steepened and then break into the energetic, short period waves.

Farmer and Li studied internal waves in the South China Sea using pressure equipped inverted echo-sounders, instruments developed by scientists at the University of Rhode Island. From the seafloor, the device transmits an acoustic pulse and then listens for the echo from the sea surface. Sound travels faster through warm water than it does through cold water, so changes in the echo delay allow measurement of the thickness of the warm surface layer, enabling the shape and size of passing internal waves to be recorded.

According to Farmer, nonlinear internal waves impact the ocean in many ways: stirring up sediment on the sea floor, creating hazards to offshore engineering structures, interfering with submarine navigation, and greatly affecting propagation of underwater sound. Internal waves also appear to have significant, if not fully understood, biological impacts, and in shallow water environments they can mix water masses and modify coastal circulation.

Chile quake occurred in zone of ‘increased stress’

The incredible geology of Chile, such as found in Torres Del Paine, does not stop at the ocean's edge. As we explore four sites along the Chilean coast we will study how the exceptional geologic structures fuel a unique suite of species. Photo courtesy of INSPIRE: Chile Margin 2010.
The incredible geology of Chile, such as found in Torres Del Paine, does not stop at the ocean’s edge. As we explore four sites along the Chilean coast we will study how the exceptional geologic structures fuel a unique suite of species. Photo courtesy of INSPIRE: Chile Margin 2010.

The massive, 8.8-magnitude earthquake that struck Chile Feb. 27 occurred in an offshore zone that was under increased stress caused by a 1960 quake of magnitude 9.5, according to geologist Jian Lin of the Woods Hole Oceanographic Institution (WHOI).

The earthquake, some 300-500 times more powerful than the magnitude 7.0 quake in Haiti Jan. 12, ruptured at the boundary between the Nazca and South American tectonic plates. The temblor was triggered when the “subducting” Nazca plate was thrust under the South American plate, uplifting a large patch of the seafloor and prompting tsunami warnings throughout the Pacific Ocean. The two plates are converging at a rate of 80 mm per year, says Lin, “which is one of the fastest rates on Earth.”

Lin and colleague Ross S. Stein of the U.S. Geological Survey in Menlo Park, Ca., have studied the region extensively, and alerted the scientific community to a build up of stress along the interface of the two plates in a 2004 paper in the Journal of Geophysical Research.

“In 2004, we calculated that the 1960 magnitude 9.5 earthquake has caused large stress increase on both the northern and southern ends of its rupture,” said Lin. That quake, centered a few hundred kilometers south of Saturday’s earthquake, was the largest instrumentally recorded earthquake in the world. It killed 1,655 people in southern Chile and unleashed a tsunami that crossed the Pacific, killing 61 people in Hawaii and 185 in Japan. Saturday’s “quake picked up where the 1960 rupture ended in the north,” Lin said.

“This story is quite similar to the Dec. 26, 2004 magnitude-9.0 Sumatra earthquake, which was followed by a magnitude 8.7 quake on its southern end on 28 March 2005,” he said. “The only difference is that it took 50 years for the northern neighboring section of the 1960 [Chile] earthquake to rupture, while it took only 3 months for the southern adjacent segment to rupture in Sumatra.

“We do not yet have good enough science to say why one place took only 3 months and another took 50 years. But even 50 years is short enough [to fall within] in a person’s lifetime. Thus, we should consider the earthquake interaction possibilities seriously.”

In Haiti, Lin point out that and others have calculated that the Jan. 12 rupture has heightened stress further east along the Enriquillo Fault, thereby increasing chances of a quake in that region, which “comes within five kilometers of Port-au-Prince,” he said.

The latest Chile quake, which had killed more than 700 people as of Mar. 1, was centered some 65 miles west-southwest of Talca, Chile, about 21.7 miles below the ocean’s surface, “relatively shallow for a subduction quake,” said Lin. It struck about 200 miles southwest of Santiago, the country’s capitol. Saturday’s earthquake had a “much longer” rupture zone-500-600 km-than that of the Haiti quake-35-50 km, Lin said.

“So why was the Haiti quake so much more catastrophic than the Chile quake?” he asked.

“First, as a nation, Chile is much better prepared for earthquakes than Haiti. People in Chile today still remember the pain of the 1960 quake,” Lin said. In addition, coastal Chile has a history of other very large earthquakes. Since 1973, there have been 13 events of magnitude 7.0 or greater. Approximately 870 km to the north of the Feb. 27 earthquake is the source region of the magnitude 8.5 earthquake of November 1922. That great quake significantly killed several hundred people and caused severe property damage. The 1922 quake generated a 9-meter local tsunami that inundated the Chile coast near the town of Coquimbo; the tsunami also crossed the Pacific, washing away boats in Hilo harbor, Hawaii.

“In contrast, the last catastrophic earthquake in Haiti was 240 years ago,” Lin said, “and thus few people were aware of a string of ‘earthquake bombs’ lying next to Port-au-Prince until Jan. 12.

“Second,” he said, “the economy of Chile is much better than that of Haiti. Thus, building codes are better developed and enforced in Chile. The contrasts between the aftermaths of the Chile and Haiti quakes reminded us, once again, that ‘earthquakes do not kill people, buildings do.'”

The Chile temblor dispatched tsunami waves onshore to Chile and across the Pacific Ocean toward Hawaii and the west coast of the US mainland, primarily California, and experts warned that tsunami waves were likely to hit Asian, Australian and New Zealand shores within 24 hours of the earthquake. Waves 6 feet (1.8 meters) above normal hit Talcahuano near Concepcion 23 minutes after the quake, and President Michelle Bachelet said a huge wave swept into a populated area in the Robinson Crusoe Islands, 410 miles (660 kilometers) off the Chilean coast. There were no immediate reports of major damage from the waves.

Since the major earthquake, there have been nearly 200 aftershocks in the area according to this USGS map.
Since the major earthquake, there have been nearly 200 aftershocks in the area according to this USGS map.

Though the predicted tsunami waves did reach Hawaii, California, New Zealand and other Pacific Rim regions, they proved to be relatively small and had minimal impact. “Even though the waves turned out to be not devastating”, Lin said, “it was an important opportunity for communities in coastal regions to improve the preparedness for potential greater tsunamis in the future.”

The WHOI research vessel Atlantis was operating off the coast of northern Chile when the magnitude 8.8 earthquake struck on Saturday. WHOI confirmed that R/V Atlantis and all on board are safe. There were no ill effects to R/V Atlantis or those on board from the quake or the subsequent tsunami.

R/V Atlantis has a scheduled port stop beginning on March 3, 2010, in Arica, Chile, which is on the northern coast of Chile. The WHOI Marine Operations Department is assessing the situation with their port agents to determine how or if that port stop will be affected.

A number of WHOI staff are onboard the R/V Melville, operated by Scripps Institution of Oceanography, which is conducting research at the Chile Triple Junction. WHOI received an email from an employee onboard the ship, and was told that all onboard are fine. The blog associated with this expedition (http://oceanexplorer.noaa.gov/explorations/10chile/) had not been updated on Saturday because, WHOI was told, the ship’s communication capability was being used to communicate by those onboard with family on shore.