Oceanic contributions to theatmospheric N2O budget

An analysis of nitrous oxide (N2O)isotopomers—isotope-containingmolecules—in the western North Pa-cific Ocean has led Japanese scientiststo conclude that the ocean is a signif-icant source of N2O, second only toN2O terrestrial production sources.N2O’s known sources are mainly

microbial production in soils andwater, and human activities, such asfossil fuel combustion. There is stillsignificant uncertainty concerningthe estimated magnitude of N2Osources and sinks.Isotopic signatures of N2O are a

useful tool for inferring the mole-cule’s production mechanism and itsglobal budget, say Sakae Toyoda andco-workers at the Tokyo Institute ofTechnology, the National Institute forEnvironmental Studies, and theNational Institute of AdvancedIndustrial Science and Technology,all in Japan.For the first time, the researchers

measured the intramolecular 15N dis-tribution and nitrogen/oxygen iso-tope ratios in the western NorthPacific Ocean, revealing that the sitepreference (14N15N16O versus15N14N16O) for the intramolecular 15Ndistribution varies widely with oceandepth. This, they say, indicates thatthere is oceanic subsurface and deep-source mixing of chemical speciesrelevant to the occurrence of N2O iso-topomers. Because N2O isotopomers“contain” biogeochemical informa-tion about the molecule’s production,consumption, and transportation,they also provide clues about the na-ture of the N2O production mecha-nism in the ocean.Further isotopomer investigations,

the researchers say, should help re-fine assessments of the sources andsinks of this important greenhousegas, which is one of the six gases ad-dressed in the Kyoto Protocol. (Geo-phys. Res. Lett. 2002, 29 (3), 10.1029/2001GL014311)

Uncovering hazardous wastelandfill threats

Children born to mothers living nearhazardous waste landfills are 40%more likely to develop chromosomalabnormalities, such as those associat-ed with Down’s syndrome, accordingto a recent European study. Previous-ly, the study team reported that thereis a 33% higher risk of nonchromoso-mal abnormalities, such as cleftpalate.

The team from the London Schoolof Hygiene and Tropical Medicine stud-ied 245 cases of chromosomal anom-alies and 2412 healthy individuals (thecontrol group) who lived near 23 land-fill sites in Denmark, France, Italy,England, and Belgium. After adjustingfor maternal age and socioeconomicstatus, they found that the risk associ-ated with chromosomal anomalieswas 40% higher in those born within 3km of a site compared with those born3–7 km away. The study looked atbirths between 1986 and 1994.Team leader Martine Vrijheid ad-

mits that it remains unclear whetherthese increased risks result from liv-ing near a hazardous waste landfillsite or from other factors. Most im-portantly, she says, it is not knownhow much, if any, exposure mothershad to chemicals from the landfills.Dirk Hazell, chief executive of the

United Kingdom’s EnvironmentalServices Association, questions therelevancy of the study, adding thatthere are superior pools of more re-cent data from other studies(Environ. Sci. Technol. 2001, 35,438A–439A). And he stresses that theresearch, which included eight sitesin the United Kingdom, do notdemonstrate causality.

The environmental group Friendsof the Earth used the study to reiter-ate its calls for immediate govern-ment action to reduce landfilling ofhazardous wastes by increasing land-fill tax rates and setting statutory tar-gets. (Lancet 2002, 359, 320–322)

Ocean circulation slowdownwarms waters, slows CO2-to-airinputsTwo U.S. scientists report that theyhave detected a decades-long slow-down in Pacific Ocean currents. Thechange, they say, affects surface watertemperatures and the release of CO2from seawater, while also having a sig-nificant effect on marine ecosystems.Researchers Michael McPhaden of

the National Oceanic and AtmosphericAdministration’s Pacific Marine Envi-ronmental Laboratory in Seattle,Wash.,and Dongxiao Zhang of the UniversityofWashington, also in Seattle, exam-ined water circulation records for thepast 50 years. The data indicate thatsince the mid-1970s, sea surface tem-peratures in the tropical Pacific haverisen about 0.8 °C, and seawater circu-lation has decreased about 25% from47� 106 to 35� 106 m3/s.The researchers suggest that the

circulation changes may be associatedwith the naturally occurring PacificDecadal Oscillation and also may beinfluenced by greenhouse gas buildup.Although available data do not clearlyindicate the effect of the latter, what isperhaps of greater interest is under-standing the extent to which the circu-lation changes affect Pacific fisheries.McPhaden and Zhang say it is difficultto assess whether the supply of nutri-ents to the surface layer of the oceanhas decreased from the 1970s to the1990s, because of a lack of data.The circulation-associated slow-

down in CO2 release from ocean wateris significant, as the equatorial Pacificis the largest oceanic source of CO2 tothe atmosphere. (Nature 2002, 415,603–608)

Research�Watch

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