The following highlights summarize research papers in
Geophysical Research Letters (GL), Journal of Geophysical
Research - Solid Earth (JB), Journal of Geophysical Research -
Oceans (JC), Global Biogeochemical Cycles (GB), and Water
Resources Research (WR). The papers related to these
Highlights are printed in the next paper issue of the journal
following their electronic publication.

1. New isoprene estimates can revise emissions models
2. Aerosol haze likely source of sulfate in ancient volcanic ash bed
3. Guadalupe Island tracks Pacific plate motion
4. Measuring seasonal cloud particle size changes
5. Height of Tibetan plateau influences global atmospheric
circulation
6. Reinterpreting conductivity estimates along San Andreas fault
7. Global warming increases salt content in soil
8. Seismic waves change distant groundwater flow after earthquake
9. Improved method to map global oceanic nitrate
10. Finding the cause of unusual decadal ocean surface warming
11. Modeling the concentrations of pathogens in natural waters

Newly available satellite measurements of North American
isoprene levels can help revise existing models that track the
quantity and variability of the climate-influencing natural
compound. Abbot et al. report seven years of data from the Global
Ozone Monitoring Experiment and analyze the levels and patterns
of the natural hydrocarbon over North America during all seasons.
Isoprene is emitted from natural vegetation growth and has a large
effect on atmospheric chemistry, including the oxidizing potential
of the troposphere and ozone production. The authors offer a new
observation method to estimate isoprene emissions and find
significant regional discrepancies between their observations and
the levels reported in existing global atmospheric chemistry
models.

Title: Seasonal and interannual variability of North American
isoprene emissions as determined by formaldehyde column
measurements from space

Authors:
Dorian S. Abbot, Paul, I. Palmer, Daniel J. Jacob, Harvard
University, Cambridge, Massachusetts;
Randall V. Martin, Kelly V. Chance, Harvard-Smithsonian Center
for Astrophysics, Cambridge, Massachusetts;
Alex Guenther, National Center for Atmospheric Research,
Boulder, Colorado.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL017336, 2003

A thick blanket of volcanic aerosol haze may have provided a huge
amount of sulfur to a North American basin during the Cenozoic
era. Bao et al. report high concentrations of an unusual sulfate in
the mid-Gering volcanic ash bed from approximately 28 million
years ago. The authors suggest that sulfur gas emitted from
volcanoes formed a thick blanket of pollution in the atmosphere
that eventually settled in the volcanic ash. The researchers also
analyzed the composition of newly collected ash from recent
volcanic eruptions around the world and determined that sulfate
from the ancient ash had a different isotopic signature than the
current samples, which they attribute to oxidation of sulfur gases
that produced an aerosol haze. They conclude that sulfate haze
from volcanic eruptions might provide a viable explanation for the
sulfur content found in ash beds globally and could help refine
global climate models.

Title: Widespread sulfate oxygen-17 anomaly in Cenozoic ash beds
in mid-North America: Was it the dry fogs?

Authors:
Huiming Bao, Louisiana State University, Baton Rouge, Louisiana;
Mark H. Theimens, University of San Diego, San Diego,
California;
David B. Loope, University of Nebraska, Lincoln, Nebraska;
Xun-Lai Yuan, Nanjing Institute of Geology and Paleontology,
Academia Sinica, Nanjing, People's Republic of China.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL016869, 2003

New research suggests that Mexico's Guadalupe Island, off the
Baja Peninsula, is part of the Pacific tectonic plate and can be used
as an above-water measure to estimate the plate's movement.
Gonzalez-Garcia et al. confirmed that the island was located on
the plate by comparing Global Positioning System data from the island
to other sites known to be on the Pacific plate. Most of the plate is
located underwater, which has complicated efforts to measure its
motion and rigidity. The authors suggest that other offshore islands
in the California region are located in the plate boundary zone
between the Pacific and North America plates and are not suitable
for determining Pacific plate motion. They suggest that since
Guadalupe Island is not volcanically active and is not affected by
seismic activity in the region, it can serve as an important station to
accurately monitor the plate's motion.

Title: Guadalupe Island, Mexico as a new constraint for Pacific
plate motion

Authors:
J. Javier Gonzalez-Garcia, Center for Scientific Investigation and
Higher Education, Baja California, Mexico;
L. Prawirodirdjo, Y. Bock, D. Agnew, Scripps Institution of
Oceanography, La Jolla, California.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL017732, 2003

A long-term seasonal cloud analysis suggests that cloud droplets
decreased in size between 1985 and 1994, a finding that could
affect Earth's climate and hydrological systems. Kawamoto and
Nakajima performed the first long-term global study of particle
size and density within low-lying water clouds observed by the
Advanced Very High Resolution Radiometer. The researchers
documented a steep trend toward smaller particle sizes over time
but were unable to speculate whether the cause was from seasonal
variation or a shift in the satellite's orbit. The NOAA satellite
changed the angle of its orbit in 1989 and may have observed
diurnal cloud variations, creating a potential bias in its readings.
The authors conclude that their results, if accurate, could help
scientists estimate seasonal shifts in cloud particle sizes and the
resulting impact on precipitation worldwide.

Title: Seasonal variation of cloud particle size as derived from
AVHRR remote sensing

Authors:
Kazuaki Kawamoto, Research Institute for Humanity and Nature,
Kyoto, Japan;
Teruyuki Nakajima, University of Tokyo, Tokyo, Japan.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL017437, 2003

Changes in the altitude of the "Earth's roof" may affect how
strongly Asian monsoons respond to changes in solar radiation,
according to Liu et al. The researchers used climate model
experiments to show that when the Tibetan Plateau is high, the
summer monsoon precipitation and winds in East Asia exhibit a
greater range of variability than when it is low. Their study of the
Chinese plateau's geological records confirms an increase in
monsoon variability over the past several million years, which they
suggest is in response to changes in the Earth's axial tilt and the
resulting redistribution of solar rays. Previous reports have noted
the sensitivity of such orbital changes to the plateau, which spans
the world's highest mountain range including Mount Everest, on
the Indian monsoon but the current study concludes that the East
Asian climates may also be significantly affected.

Title: The Tibetan Plateau as amplifier of orbital-scale variability
of the East Asian monsoon

Authors:
Xiaodong Liu, Zhisheng An, Li Li, Institute of Earth Environment,
Chinese Academy of Sciences, Xi'an, China;
John E. Kutzbach, Zhengyu Liu, University of Wisconsin,
Madison, Wisconsin.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL017510, 2003

A stretch of anomalous conductivity along the San Andreas fault is
probably caused by an unusual rock formation, rather than by
fractured rocks. Park and Roberts present a different interpretation
of magnetic maps near the San Andreas fault used to indicate
potential earthquakes. The authors analysis shows a narrow
conductive zone adjacent to the well-known fault line that they
suggest is caused by "folded" sediment. They tested rock samples
from the sediments and found that its electrical and porosity
characteristics matched those from a region identified as
fault-damaged rock. Instead, they propose that a known section of
folded sediment is responsible for the properties observed near
Parkfield, California. Some previous analyses estimated that loose
rock would be under greater pressure and strain than the folded
formation, which could have a significant effect of fault modeling
and predicting the fault's behavior.

Title: Conductivity structure of the San Andreas fault, Parkfield,
revisited

Authors:
Stephen K. Park, Institute of Geophysics and Planetary Physics,
University of California, Riverside, California;
Jeffery J. Roberts, Lawrence Livermore National Laboratory,
Livermore, California.

Source: Geophysical Research Letters (GL) paper
10.1029/2003GL017689, 2003

Soils in several parts of the world are likely at risk of accumulating
potentially harmful quantities of salt in the future because of
predicted climate warming. Schofield and Kirkby suggest a
significant correlation between warmer environmental conditions
and increased salt content in the ground. The authors propose that
existing land areas with high salinization may grow and new areas
could form during the next century. Currently, approximately 10
percent of the world's land surface is adversely affected by salt
naturally found in water, soil and rocks. The authors propose that
the salt easily migrates through soil via water transport and tends to
settle in low-lying areas. Using existing global climate model
estimates, they conclude that agricultural areas in Australia, Europe
and the Americas may be most affected by increased salt levels.

Title: Application of salinization indicators and initial development
of potential global soil salinization scenario under climatic change

Authors:
R. V. Schofield, M. J. Kirkby, University of Leeds, Leeds, UK.

Source: Global Biogeochemical Cycles (GB) paper
10.1029/2002GB001935, 2003

A newly proposed model may allow researchers to predict the
previously enigmatic groundwater behavior after earthquakes that
can alter the land surface and perhaps even trigger new quakes.
Brodsky et al. used detailed historical data from an Oregon well to
advance their theory that seismic waves from an earthquake can
suddenly change the underground pressure and influence the flow
of aquifers. Previous research had shown that earthquakes caused
unexpectedly large water level changes in distant wells but could
not pinpoint a cause for the fluctuations. The authors analyzed the
effects on the Oregon well from a quake in Mexico and propose
that sustained water level changes were caused by seismic waves
that altered the water pressure in the aquifer. Their model suggests
that seismic waves remove a barrier of sediment or solid material
to generate water level changes.

Title: A mechanism for sustained groundwater pressure changes
induced by distant earthquakes

Authors:
Emily E. Brodsky, University of California, Los Angeles,
California;
Evelyn Roeloffs, U. S. Geological Survey, Vancouver,
Washington,
Douglas Woodcock, Oregon Water Resources Department, Salem,
Oregon;
Ivan Gall, Oregon Water Resources Department, Grants Pass,
Oregon;
Michael Manga, University of California, Berkeley, California.

Source: Journal of Geophysical Research-Solid Earth (JB) paper
10.1029/2002JB002321, 2003

Satellite observations of sea surface temperatures can be used to
map oceanic nitrogen levels and help determine the global
movement of nitrate. Switzer et al. found that estimating the
difference between oceanic temperatures lowered by increased
nitrogen concentrations and the surrounding sea surface
temperatures can produce an accurate nitrate map. Nitrate limits
the growth of phytoplankton, which absorbs atmospheric carbon
dioxide, and affects water temperatures and marine life. The
authors applied their temperature difference method to a 10-year
record of satellite ocean temperature observations and suggest that
their findings produced a nitrate map similar to those using more
complex measurements. They conclude that the remote sensing
technique can provide regularly updated nitrate maps reporting the
growth and spread of oxidized nitrogen more efficiently than
currently used water and coastal monitors.

Title: Mapping nitrate in the global ocean using remotely sensed
sea surface temperature

Authors:
Anna C. Switzer, Daniel Kamykowski, Sara-Joan Zentara, North
Carolina State University, Raleigh, North Carolina.

Source: Journal of Geophysical Research-Oceans (JC) paper
10.1029/2000JC000444, 2003

Global warming has been observed fluctuating nearly every decade
in the upper layer of the global ocean concurrently with the Sun's
11-year cycle of solar irradiance during the 20th century. White et
al. found that the approximately 11-year cycles of warming and
cooling of the Earth's upper ocean raised (and lowered) the upper
ocean temperatures by nearly one-tenth degree Celsius [two-tenths
degree Fahrenheit]. The authors found that the fluctuations are
driven by air temperatures in the lower atmosphere, which are
warmer and more humid than in the upper ocean. The authors
studied an approximately 25-year inventory of potential heat
sources affecting the upper ocean and suggest that the
quasi-decadal variation in ocean surface temperatures is not
directly associated with influences like the Sun and its warming
radiation. They instead point to ultraviolet heating, which is
absorbed by stratospheric ozone that is prevalent at the sea surface.

Title: Sources of global warming of the upper ocean on decadal period scales

Authors:
Warren B. White, Scripps Institution of Oceanography, La Jolla,
California;
Michael D. Dettinger, Daniel R. Cayan, U. S. Geological Survey,
San Diego, California.

Source: Journal of Geophysical Research-Oceans (JC) paper
10.1029/2002JC001396, 2003

11. Modeling the concentrations of pathogens in natural waters

New statistical methods can be used to describe pathogen
concentrations in natural waters and help manage the health risks
from hazardous waterborne microorganisms. Crainiceanu et al.
developed statistical methods for monitoring the concentrations of
dangerous waterborne pathogens, including cyptosporidium and
giardia, which can cause sickness or death if ingested. The authors
suggest that their study can be used to issue alerts of a pathogen's
presence or to help water utilities determine the appropriate
treatment technologies. Currently, the two organisms can be
filtered out during water treatment, although cryptosporidium is
resistant to chlorination. The researchers suggest that current
methods to measure the microorganisms are hindered by the
relative rarity of the pathogens in the environment and are
complicated by the difficulty collecting appropriate samples from a
region. They conclude that their methods will likely allow
scientists to better understand the regional distribution of
microorganisms in natural waters.

Title: Modeling the U.S. national distribution of waterborne
pathogen concentrations with application to Cryptosporidium parvum

Authors:
Ciprian M. Crainiceanu, Jery R. Stedinger, David Ruppert, Cornell
University, Ithaca, New York;
Christopher T. Behr, eDesign Dynamics LLC, West New York,
New Jersey.

Source: Water Resources Research (WR) paper
10.1029/2002WR001664, 2003

*****
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American Geophysical Union
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