1. Crust below Nicaraguan slab is wettest ever observed
2. Ancient volcanic eruption released more sulfur than predicted
3. Rain's role in delivering oceanic dissolved iron
4. Clean air "slots" in southern African air pollution
5. Major Southern Hemisphere warming shrinks ozone hole
6. Identifying Pacific Ocean water in the Arctic
7. Combined measures help to predict flood risk
8. Indian Ocean dust sources identified
9. Deforestation has major impact on montane cloud forest
10. Determining the intensity of prehistoric cyclones

Recently analyzed seismic evidence suggests that the crust below a volcanic chain in Nicaragua contains at least twice the water content of any other series of interconnected volcanoes in the world, making it the most hydrated slab ever observed. Such wetness can affect magma flow and the movement of nearby tectonic plates. Abers et al. found that the Nicaragua slab contains nearly five percent of its weight in water, an amount greater than many parts of the ocean floor. The researchers suggest that ocean water contributes significantly to the crustal slab deep beneath the Central American volcanic chain on the Cocos plate, a conclusion
inferred from the geochemistry of the volcano's magma. They propose that the shape of the steeply inclined Nicaraguan slab may facilitate water circulation better than similar subducting plates studied in the Pacific and that extensive faults near the slab may allow a large amount of fluids to penetrate into the crust.

Title: The wet Nicaraguan slab

Authors:
Geoffrey A. Abers, Terry Plank, Boston University, Boston, Massachusetts;
Bradley R. Hacker, University of California, Santa Barbara, California.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL015649, 2003

An ancient eruption may have released more than twice the amount of sulfur than was previously estimated from ice core data. Costa et al. used a petrologic method to estimate that previous projections of the sulfur concentrations were too low to account for the significant global climate change observed after the eruption. Their study suggests much of the sulfur from the eruption, an event associated with the largest temperature change of the past 600 years, did not reach the stratosphere and was not deposited in the ice studied by previous researchers. The researchers compared their estimate from the Huaynaputina eruption with more recent similar eruptions, which led them to conclude that the petrologic method, which studies the composition of rocks, can be applied to establish volcano-climate links beyond the time period covered by ice-core archives.

Title: Massive atmospheric sulfur loading of the AD 1600 Huaynaputina eruption and implications for petrologic sulfur estimates

Authors:
Fidel Costa, Bruno Scaillet, Orleans Institute of Earth Science, Orleans, France;
Alain Gourgaud, Blaise Pascal University, Clermont-Ferrand, France.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016402, 2003

Rains deliver the majority of wind-transported dissolved iron to the ocean, more than three times the amount currently predicted from wind deposition, that helps sustain surface and mid-level sea life. Gao et al. found that such "wet" iron deposition from precipitation provides a larger percentage of more easily absorbed dissolved iron food sources for plankton and similar life forms than windblown "dry" deposits. The researchers suggest that iron-rich dust particles are incorporated into raindrops in clouds and, as the clouds are transported over long distances, the particles chemically break down to form dissolved iron. The authors used a combination of atmospheric model simulations and observations to provide the first global budget of dissolved iron deposition and conclude that wet deposition accounts for up to 60 percent of the total iron content dropped on the open ocean.

Title: Aeolian iron input to the ocean through precipitation scavenging: A modeling perspective and its implication for natural iron fertilization in the ocean

Authors:
Yuan Gao, Song-Miao Fan, Jorge L. Sarmiento, Princeton University, Princeton, New Jersey.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper: 10.1029/2002JD002420, 2003

A researcher has reported an unusual phenomenon of long-lasting clean air "slots" between dense layers of smoke and pollution in southern Africa. Peter V. Hobbs has observed similar layers of narrowly spaced clean and polluted layers of air elsewhere in the world, suggesting that they are not unique to Africa, but his
analysis is the first to attempt to explain the events. Hobbs proposes that the thin layers of clean air have likely originated in the higher reaches of the atmosphere and descended because of gravity and differences between temperature and pressure from the clean and the polluted air. Previous research has indicated that
pollution generally tends to accumulate beneath stable layers, which Hobbs suggests contributes to the clean-polluted sandwiched layers. Under stable conditions, the thin layers of clean air can resist the incursion of polluted air for several days.

Title: Clean air slots amid dense atmospheric pollution in southern Africa

Author:
Peter V. Hobbs, University of Washington, Seattle.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper: 10.1029/2002JD002156, 2003

The first major stratospheric warming ever observed in the Southern Hemisphere led to observations of exceptionally high ozone concentrations in the Antarctic during winter 2002. Hoppel et al. report a marked increase in ozone levels in the lower and middle stratosphere near the southern pole at a time when the
ozone hole is normally reaching its maximum size. The researchers analyzed ozone profiles measured by the Polar Ozone and Aerosol Measurement (POAM) instrument and found that the ozone increases resulted primarily from an unusual stratospheric transport associated with the warming, which brought ozone-rich air from outside the polar vortex to the polar region. They conclude that the warming reduced the typical photochemical ozone loss by approximately 20 percent compared to previous years.

Title: POAM III observations of the anomalous 2002 Antarctic ozone hole

Authors:
Karl Hoppel, Richard Bevilacqua, Douglas Allen, Gerald Nedoluha, Naval Research Laboratory, Washington, DC;
Cora Randall, University of Colorado, Boulder, Colorado.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2003GL016899, 2003

Researchers have differentiated Pacific Ocean water entering the Arctic Ocean using nutrient levels, providing an improved method of identifying the source waters that influence currents and the global ocean circulation. Jones et al. traced the flow of Pacific Ocean water properties using its higher phosphate concentration
and decreased salinity levels to identify its path and mixing through the North Atlantic. The researchers note that Pacific surface waters are fresher than Atlantic waters and combine with other Arctic freshwater sources to affect the deepwater production rate in the North Atlantic and the worldwide thermohaline
(vertical) circulation. The authors conclude that their marker of Pacific source water can help identify salt, heat and freshwater fluxes in the North Atlantic that can change ocean water turnover and influence climactic patterns.

Title: Tracing Pacific water in the North Atlantic Ocean

Authors:
E. P. Jones, Bedford Institute of Oceanography, Dartmouth, Nova Scotia, Canada;
J. H. Swift, Scripps Institution of Oceanography, University of California-San Diego, La Jolla, California;
L. G. Anderson, Goteborg University, Goteborg, Sweden;
M. Lipizer, G. Civitarese, Talassografico Institute, Trieste, Italy;
K. K. Falkner, Oregon State University, Corvallis, Oregon;
G. Kattner, Alfred Wegener Institute for Polar and Marine Sciences, Bremerhaven, Germany;
F. Mc Laughlin, Institute of Ocean Sciences, Sidney, British Columbia, Canada.

Source: Journal of Geophysical Research-Oceans (JGR-C) paper: 10.1029/2001JC001141, 2003
 

A new method that pairs two existing measures of climate change in the Pacific can help researchers better estimate the flood risk in Australia and may lead to a re-evaluation of flood risk planning worldwide. Kiem et al. used the inter-decadal Pacific oscillation (IPO) along with a measure of surface water temperature change to analyze anomalous warming and cooling in the Pacific Ocean and the resulting effect on rainfall over the past 75 years. By combining the inter-decadal variability with existing estimates of seasonal changes in oceanic surface water temperature trends, the authors suggest that they can predict both the magnitude and frequency of an elevated flood risk with more certainty than before. They report that precipitation and flood risks increase during a negative IPO, which corresponds to the frequent cold events known as La Nina. The researchers concluded that naturally occurring El Nino/La Nina effects dominate the weather conditions in New South Wales over long periods of time, which can help natural resource managers identify periods of heightened flood and drought risks.

Title: Multi-decadal variability of flood risk

Authors:
Anthony S. Kiem, Stewart W. Franks, George Kuczera, University of Newcastle, Callaghan, New South Wales, Australia.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL015992, 2003

A satellite-mounted infrared monitoring system can yield an accurate assessment of dust emissions over land, providing a method to improve existing ground-based observations. A recent adjustment to the orbit of a weather satellite allowed Leon and Legrand to analyze a full year of infrared readings from atmospheric dust near the North Indian Ocean. They suggest that the infrared dust index method, which calculates the dust based on decreases in solar radiation reaching the ground and on the dust's affect on infrared radiation, could provide an improved technique to identify the origin of airborne dust and track its movement worldwide. The researchers' findings confirm the main dust sources to the ocean are from arid and semi-arid regions in the Arabian Peninsula. They also monitored the seasonal variations of dust production and transport, unexpectedly finding that Somalia contributes significantly to the atmospheric dust load, particularly during its dry and windy seasons between May and October.

Title: Mineral dust sources in the surroundings of the north Indian Ocean

Authors:
Jean-Francois Leon, Michel Legrand, Lille University of Science and Technology, Villeneuve-d'Ascq, France.

Source: Geophysical Research Letters (GRL) paper: 10.1029/2002GL016690, 2003

Deforestation upwind of a tropical cloud forest has a significant impact on cloud cover in the sensitive areas, leading researchers to propose that a "buffer area" should be created to protect the forests. Nair et al. analyzed land use changes near the Monteverde Cloud Forest in Costa Rica and found that deforestation leads to reduced cumulus cloud banks, which affects the physical environment, hydrology and conservation efforts in the mountaintop environments. Symptoms from reduced clouds, like dryer and warmer temperatures, may contribute to a reduction in biodiversity and other deleterious environmental effects. Their model simulation, confirmed by satellite imagery, suggests that cloud forests near deforested regions tended to suffer from reduced cloud formation and elevated cloud bases. 

Title: Impact of land use on Costa Rican tropical montane cloud forests: Sensitivity of cumulus cloud field characteristics to lowland deforestation

Authors:
U. S. Nair, R. M. Welch, National Space Science and Technology Center, University of Alabama-Huntsville, Huntsville, Alabama;
R. O. Lawton, University of Alabama-Huntsville, Huntsville, Alabama;
R. A. Pielke, Sr., Colorado State University, Fort Collins, Colorado.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper: 10.1029/2001JD001135, 2003

The first technique to estimate the intensity of prehistoric cyclones will provide a better understanding of their past frequency and may allow for better predictions of the destructive storms. Jonathan F. Nott analyzed the geological evidence left behind from the storm surge of strong cyclones to determine the strength of the cyclone required to do such damage. His method examines the distance traveled and height above sea level the storm surge reached, which allows him to identify the geologic material at the boundary of the surge and then use traditional methods to estimate its age. The estimate is based on the constant sea level in the tropical southwest Pacific, which has remained relatively unchanged for the past 5,000 years. He concludes that the modeling technique can be used worldwide to predict the intensity limits and frequency for storms in the future to estimate planning and emergency services to hazardous areas, and to compare the effect of an enhanced
greenhouse effect on cyclone behavior.

Title: Intensity of prehistoric tropical cyclones

Author:
Jonathan F. Nott, James Cook University, Cairns, Queensland, Australia.

Source: Journal of Geophysical Research-Atmospheres (JGR-D) paper: 10.1029/2002JD002726, 2003

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