News - The Daily Aztec

Future of Earth's climate depends on the past
By: Maureen Moses, Contributor
Source: The Daily Aztec - Issue date: 3/1/07 - Section: Science & Technology

Scientists at San Diego State are researching an ancient global warming event in hopes of providing information that can help accurately predict modern global warming changes.

Stephen Schellenberg, Ph.D., a professor in the geological sciences department, and the students in his lab are researching previous global warming events to get an idea of how the planet has responded in the past. He's researching an intense warming event that occurred 55 million years ago, known as the Paleocene-Eocene Thermal Maximum. During this event, massive amounts of carbon and other greenhouse gases were released into the atmosphere, causing a rapid increase in global temperature. This increase occurred during the course of thousands of years, and the Earth's climate took tens of thousands of years to recover from the influx of greenhouse gasses.
The information obtained from these experiments about the Earth's climactic history is used to assess how the Earth responds to the influxes of greenhouse gasses. Schellenberg and his team are looking at the PETM event carefully because it is similar to present-day global warming. Both the PETM and today's global warming represent events where massive amounts of greenhouse gases are poured into the atmosphere in a short amount of time. "The PETM represents the best analog in terms of rate, and still, it took thousands of years, and we'll probably reach the same amount of carbon in hundreds of years," Schellenberg said.Schellenberg and one of his graduate students, Elizabeth Landau, are trying to discover more about this event by analyzing fossils recovered from the Ocean Drilling Program, a research cruise that travels the world gathering samples from the seafloor.
Landau's research on the PETM is based on these samples as well as other samples that come from an international archive of sediment cores. She is looking specifically at how organisms called Ostracodes were affected before, during and after the PETM, giving insight to how living organisms changed with respect to their environment. Their research method is two-fold; after obtaining the samples, the tedious process of separating the individual organisms by species from the sediment occurs, and the bodies of the Ostracodes are analyzed by hand. The scientists are looking for evidence of a poor living environment. Then, a chemical analysis will be done. Because the ocean acts like a sponge and absorbs a large portion of what is in the air, the chemistry of the ocean changes. By adding greenhouse gases such as carbon, the ocean becomes more acidic, making survival for any living organism much more difficult. Under the microscope, it's clear that there was degeneration in the Ostracode bodies throughout the PETM. The difficult living environment forced some species to have less robust body physiologies and sent others into extinction. "We can create a baseline of temperature changes based on who's thriving and who's not and by comparing them to modern species," Landau said. The surviving PETM Ostracode species present today have been used to determine the ancient temperatures throughout the PETM, chronicling the changes. The current estimation of the temperature change was about 5 to 7 degrees (Celsius).
The final stage in Landau's graduate research with Schellenberg will be a chemical analysis to determine what PETM-age Ostracodes are made of. Some atoms, although they may have the same names, come in different varieties, such as Carbon-14. This is used to determine the age of ancient artifacts, although the majority of this element is Carbon-12. These atoms are called isotopes and are distinguished by varying weights. When the temperature of the Earth changes, the isotope used in the organism's body changes as well.
The results of this final stage are pending, but based on the overwhelming amount of paleoclimate isotope data, it is unlikely that her research would be inconsistent with past results. Schellenberg is providing detailed pieces of information that describe what happened to the Earth in the past. To better understand the current global warming trends on Earth today, it is imperative to thoroughly assess how the Earth responded to a similar event in the past. By studying organisms' responses to their environment, Schellenberg and his lab can create a timeline of when major changes in Earth's temperature, oceans and ocean circulation patterns occurred and how long it took for Earth to recover. All the climate models in use today take this paleoclimate data into account. Ultimately, one lesson that can be taken away from the PETM is that the Earth is resilient and it recovered from all the greenhouses gases emitted into the atmosphere, but that took a long time. "Eventually, the Earth will reach a stable point," Landau said. "It might not be a place where we can live or where animals can live, but it will recover."

New Publication - Aaron Meltzner & Tom Rockwell

Bulletin of the Seismological Society of America, December 2006, Vol. 96, Issue 6, pp. 2304-2328

Recent and long-term behavior of the Brawley fault zone, Imperial Valley, California; an escalation in slip rate?
Meltzner, Aron J. (San Diego State University, Department of Geological Sciences, San Diego, CA, United States); Rockwell, Thomas K.; Owen, Lewis A.

ABSTRACT

The Brawley fault zone (BFZ) and the Brawley Seismic Zone constitute the principal transfer zone accommodating strain between the San Andreas and Imperial faults in southernmost California. The BFZ ruptured along with the Imperial fault in the 1940 M (sub w) 6.9 and the 1979 M (sub w) 6.4 earthquakes, although in each case only minor slip apparently occurred on the BFZ; several other episodes of slip and creep have been documented on the BFZ historically. Until this study, it has been unclear whether the past few decades reflect average behavior of the fault. Two trenches were opened and a series of auger holes were bored across three strands of the BFZ at Harris Road to compare the amount of slip observed historically with the displacements observed in the paleoseismic record. Evidence is presented, across the westernmost strand of the BFZ and across the entire BFZ at Harris Road, to show that both the average vertical slip rate observed in modern times (since 1970) and the vertical creep rate (excluding coseismic slip) observed during the 1970s are significantly higher than the long-term average. Across the westernmost strand, the long- term vertical rate is 1.2 (+1.5/-0.5) mm/yr, and the average rate since about A.D. 1710 is determined to be no greater than 2.0 mm/yr; in contrast, the average vertical rate between 1970 and 2004 across that strand was at least 4.3 mm/yr, and the 1970s vertical aseismic creep rate was 10 mm/yr. Likewise, across the entire BFZ, the long-term vertical rate is 2.8 (+4.1/-1.4) mm/yr, whereas the rate between 1970 and 2004 was at least 7.2 mm/yr, and the 1970s aseismic creep rate was 10 mm/yr. The long-term strike-slip rate cannot be determined across any strands of the BFZ but may be significant. In contrast to the commonly accepted higher sedimentation rates inferred for the entire Imperial Valley, we find that the average sedimentation rate on the downthrown side of the BFZ adjacent to Mesquite Basin, in the millennium preceding the onset of agricultural influences, was at most 3.5 mm/yr. Finally, a creep event occurred on the BFZ during our study in 2002 and is documented herein.

Southern Salton Trough deltaic system, based on DEM imagery. Color contours indicate elevation; each color band represents a 5- to 10-m change in elevation. Sections of some contours are highlighted with thin black lines for improved visibility. The band labeled “12m” is the contour at an elevation of 12 m above mean sea level, which represents the highstand shoreline of Lake Cahuilla. Note the location of the modern delta, which is interpreted to have formed initially in response to the 1905– 1907 filling of the Salton Sea; slow retreat of the lake combined with regular flow of the New and Alamo Rivers has built this modern delta that is prograding into the Salton Sea. In addition to the modern delta, four prehistoric delta lobes have been interpreted on this DEM: deltas N1 and N2 on the New River, and deltas A1 and A2 on the Alamo River. Main faults are mapped in black. SMF, Superstition Mountain fault; SHF, Superstition Hills fault. Modified from Ragona (2003). ( E A color version of this figure is available in the electronic edition of BSSA.)

Full Text (pdf)

Tidal Bore on the Dordogne River

Alumni Banquet presentation by honoree Dr. Clive Dorman

Video from Clive's trip to France