Alexander van Geen

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[1] Arsenic concentrations measured by graphite furnace atomic absorption range from < 5 to 900 mg/L in groundwater pumped from 6000 wells within a 25 km area of Bangladesh. The proportion of wells that exceed the Bangladesh standard for drinking water of 50 mg/L arsenic increases with depth from 25% between 8 and 10 m to 75% between 15 and 30 m, then(More)
[1] Water column depth profiles along the North Pacific margin from Point Conception to the tip of Baja California indicate elevation of nitrate (NO3 ) N/N and O/O associated with denitrification in the oxygen-deficient thermocline waters of the eastern tropical North Pacific. The increase in dO is up to 3% greater than in dN, whereas our experiments with(More)
Detailed hydrochemical measurements, SSO4 and H analyses were performed on 37 groundwater samples collected during February 1999, January and March 2000 from 6 locations in eastern and southeastern Bangladesh to examine redox processes that lead to As mobilization in groundwater. The study sites were chosen based on available nation-wide As surveys to span(More)
We study how effectively information induces Bangladeshi households to avoid a health risk. The response to information is large and rapid; knowing that the household’s well water has an unsafe concentration of arsenic raises the probability that the household changes to another well within one year by 0.37. Households who change wells increase the time(More)
Sediment cores of known chronology from Richardson and San Pablo Bays in San Francisco Bay. CA, were analyzed for a suite of chlorinated hydrocarbon pesticides and polychlorinated biphenyls to reconstruct a historic record of inputs. Total DDTs (DDT = 2,4'and 4,4'-dichlorodiphenylmchloroethane and the metabolites, 2.4'and 4,4'-DDE, -DDD) range in(More)
[1] Below its sill depth, the Santa Barbara Basin (SBB) is commonly suboxic ([O2] 3 mM), with only brief periods of ventilation. Associated with development of suboxia, the concentration of nitrate decreases with depth into the basin without an associated decrease in phosphate, indicating that a substantial fraction of the nitrate supplied to the basin is(More)
Studies of the Santa Barbara Basin off the coast of California have linked changes in its bottom-water oxygen content to millennial-scale climate changes as recorded by the oxygen isotope composition of Greenland ice. Through the use of detailed records from a sediment core collected off the Magdalena Margin of Baja California, Mexico, we demonstrate that(More)
[1] Warren’s [1983] ‘‘Why is no deep water formed in the North Pacific’’ is revisited. His box model of the northern North Pacific is used with updated estimates of oceanic volume transports and boundary freshwater fluxes derived from the most recent data sets, using diverse methods. Estimates of the reliability of the result and its sensitivity to error in(More)
Lamont-Doherty Earth Observatory of Columbia University, Palisades, New York 10964, USA e-mail: avangeen@ldeo.columbia.edu, Phone: (845) 365 8644, Fax: (845) 365 8154. Queens College, City University of New York, Flushing, New York 11367, USA Idaho National Environmental and Engineering Laboratory, Idaho Falls, ID 83404, USA Barnard College, New York, New(More)
When normalized per unit of surface area, the quantity of arsenic adsorbed at the maghemite surface remains constant for particles between 300 and 20 nm. However, nanoparticles smaller than 20 nm exhibit enhanced adsorption capacity. The origin of this observed size-dependence for adsorption or "nano effect" is unclear. Arsenic was chosen as a probe of the(More)