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DOI: 10.1126/science.1185198, 1512 (2010);328 ScienceScott C. DoneyBiogeochemistryThe Growing Human Footprint on Coastal and Open-Ocean This copy is for your personal, non-commercial use only. clicking here.colleagues, clients, or customers by , you can order high-quality copies for yourIf you wish to distribute this article to others here.following the guidelines can be obtained byPermission to republish or repurpose articles or portions of articles ): January 6, 2011 www.sciencemag.org (this infomation is current as ofThe following resources related to this article are available online at http://www.sciencemag.org/content/328/5985/1512.full.htmlversion of this article at: including high-resolution figures, can be found in the onlineUpdated information and services, http://www.sciencemag.org/content/328/5985/1512.full.html#ref-list-1, 11 of which can be accessed free:cites 53 articlesThis article http://www.sciencemag.org/cgi/collection/oceansOceanographysubject collections:This article appears in the following registered trademark of AAAS. is aScience2010 by the American Association for the Advancement of Science; all rights reserved. The title CopyrightAmerican Association for the Advancement of Science, 1200 New York Avenue NW, Washington, DC 20005. (print ISSN 0036-8075; online ISSN 1095-9203) is published weekly, except the last week in December, by theScience on January 6, 2011www.sciencemag.orgDownloaded fromREVIEWThe Growing Human Footprint on Coastaland Open-Ocean BiogeochemistryScott C. DoneyClimate change, rising atmospheric carbon dioxide, excess nutrient inputs, and pollution in its manyforms are fundamentally altering the chemistry oftheocean,oftenonaglobalscaleand,insomecases, at rates greatly exceeding those in the historical and recent geological record. Major observedtrends include a shift in the acid-base chemistry of seawater, reduced subsurface oxygen both in near-shore coastal water and in the open ocean, rising coastal nitrogen levels, and widespread increasein mercury and persistent organic pollutants. Most of these perturbations, tied either directly orindirectly to human fossil fuel combustion, fertilizer use, and industri al activity, are projected to grow incoming decades, resulting in increasing negative impacts on ocean biota and marine resources.The ocean plays a pivotal role in the globalbiogeochemical cycles of carbon, nitro-gen, phosphorus, silicon, and a variety ofother biologically active elements and chemicalcompounds (1, 2). Human fossil-fuel combustion,agriculture, and climate change have a growinginfluence on ocean chemistry , both regionally incoastal waters and globally in the open ocean (3–5)(Fig. 1). Some of the largest anthropogenic im-pacts are on inorganic carbon (6), nutrients (4, 7),and dissolved oxygen (8, 9), which are linkedthrough and affect biological productivity. Sea-water chemistry is also altered, some times quitestrongly, by the industrial production, transport,and environmental release of a host of persistentorganic chemicals (10) and trace metals, in par-ticular mercury (11), lead (12), and perhaps iron(13).Marine biogeochemical dynamics is increas-ingly relevant to discussions of ecosystem health,climate impacts and mitigation strategies, andplanetary sustainability. Human-driven chemicalperturbations overlay substantial natural biogeo-chemical cycling and variability . Key scientificchallenges involve the detection and attributionof decadal and longer trends in ocean chemistryas well as more definitive assessments of theresulting implications for ocean life and marineresources.The biogeochemical state of the sea reflectsboth cycling and transformations within the ocean,much of which are governed by biological dy-namics, and fluxes across the ocean boundarieswith the land, atmosphere, and sea floor (2, 14).For most chemical species, seawater concentra-tions are governed more by kinetics—the rates ofnet formation and transport processes—than bychemical equilibrium with particles and sedi-ments. Clear exceptions ar e dissolved gases suchas carbon dioxide (CO2) and oxygen (O2), whichare driven to solubility equilibrium with the partialpressure of gases in the atmosphere in the surfaceocean by air-sea gas exchange.Phytoplankton in the ocean surface plays acrucial biogeochemical role, converting CO2andnutrients into particulate organic and inorganicmatter via photosynthesis and releasing O2in theprocess. The rate of marine primary productionis governed by temperature, light (strongly in-fluenced by surface tur bulent mixing depths), andlimiting nutrients, most notably nitrogen, phos-phorus, iron, an d silicon for some plankton. Somefraction of the biologically produced particulatematter subsequently sinks into the subsurfaceocean and is consumed by microbes and macro-fauna, releasing CO2and nutrients and con-suming subsurface O2. Export production thusmaintains strong vertical gradients in biogeo-chemical tracers over the water column.The global biologically driven export flux of~10PgofCyear−1must be balanced by a supplyof “new” nutrients brought up from below byocean circulation, input by rivers, or depositedfrom the atmosphere. With sufficient iron and phos-phorus, some diazotrophic microbes can produce“new” nitrogen in situ through nitrogen fixationthat converts inert nitrogen gas into biologicalreactive nitrogen. Marine microbes produce andconsume a number of trace gases that can in-fluence climate, for example CO2, nitrous oxide(N2O), methane (CH4), and dimethylsulfide(DMS).Ocean upwelling and mixing bring water withelevated CO2and nutrients to the surface andreplenish subsurface O2, with ventilation timescales of years to a few decades in the mainthermocline (upper 1 km of the water column ) andmany centuries for deep waters. Natural ocean-atmosphere climate modes (e.g., El Nino–SouthernOscillation and Pacific Decadal Oscillation) gen-erate substantial interannual to interdecadal var-iability in ocean biogeochemistry. The majorexternal source terms to the ocean are typicallyriver inputs and atmospheric deposition of dust,Marine Chemistry and Geochemistry Department, WoodsHole Oceanographic Institution, Woods Hole, MA 02543,USA. E-mail: [email protected] dioxideOrganic pollutants and trace metalsReactivenitrogenNutrientsDeforestation AgricultureFossil fuelsand industryCoastal eutrophicationand hypoxiaAltered primaryproductionOcean uptakeand acidificationLow O2


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