GAO YI 2001 GRL

Abstract. Among the factors affecting the photosynthetic rate of marine phytoplankton, aeolian iron (Fe) fluxes appear to be critical in several large regions of the global ocean. Here we present an analysis of in situ aerosol iron data obtained from a wide variety of marine locations to quantify the seasonal Fe inputs to the global ocean. When extrapolated to the global ocean, our results indicate strong seasonal
Samoa(14øS,171øW)in the Pacific. Thesesitesprovidelongterm recordsof seasonalpatterns of dustin vast areas of the
2. Method
2.1. Iron Data Base
The predominant fractionof the Fe inputs enters the oceansin the NorthernHemisphere,with the summerflux rates ca. twice those of winter. The high Fe fluxes in the Northern Hemisphereare concentrated in low and mid-latitudes. With the promising new datafrom MODIS aboardthe Terra satellite, the linkage between Fe fluxes and phytoplanktonbiomass and productivitymay be soonfurther quantified.
GEOPHYSICAL RESEARCH LETTERS, VOL. 28, NO. 1, PAGES 29-32, JANUARY 1,2001
Seasonal
Global
Distributions
Ocean
of Aeolian
Iron
Fluxes
to he
Y. Gao, •'2 Y. J. Kaufman, 3D. Tanr•,4 D. Kolber, • andP. G. Falkowski •
1. Introduction
John Martin and colleagues (Martin and Gordon, 1988) hypothesizedthat in certain oceanic regions (high-nitrate, low chlorophyll - HNLC regions), the micronutrient, Fe, regulates phytoplankton growth. Fe fertilization experiments in the equatorialPacific (Coale et al., 1996) and Southern Ocean(Boyd et al., 2000) providedunequivocal supportof the Fe hypothesis.The resultsfrom these experimentsalso led to the suggestionthat Fe fertilization could affect the cycles of other nutrients,especially nitrogen (Falkowski, 1997), which may further affect nitrogen fixing bacteria such as Trichodesmium (Caponeet al., 1997) and the biomass specific rate of photosynthesis (Behrenfeld et al., 1996). Thus the deliveryof iron to the oceanmay causechangesin the global carbon cycles, in particular atmospheric CO2. Indeed, the -420 kyr ice core recordfrom Vostok reveals a strong inverse relationship between dust loading (e.g., aeolian Fe) and atmosphericCO2 (Petit et al., 1999). Fe-inducedCO2 uptake by oceanicbiosphere may well interactwith global climate on geologicaltime scales(Broeckerand Henderson,1998). The major sourceof Fe in the surfacewaters of the open ocean is aeolian dust delivered through long-range transport from arid continental regions (Duce et al., 1980). Model
and CoastalSciences,RutgersUniversity, New Brunswick, NJ 08901. (email: falko@, yuangao@) Y. J. Kaufman, NASA Goddard Space Flight, Center, Greenbelt, MD 20771. (email: kaufman@) D. Tanr6, Laboratoired'OptiqueAtmosph6rique, Villeneuve d'Ascq, France. (email: Didier. Tanre@univ-lillel.fr)
globalocean to be 32 x 10•2g yr-•. Although thesestudies
demonstrate the importance of Fe inputs,a detailed coupling
of aeolianFe fluxesand biologicalresponses remainsunclear. Since many biological processes are seasonallydependent, quantification of the total aeolianFe depositionon a seasonal basisis needed to characterize the linkage. As the first stepto examiningthe seasonal linkage between aeolianFe and phytoplankton productivity,we applied limited in situ aerosol data obtained in the marine boundary layer (MBL) to quantify seasonal Fe fluxes. Our goal was to establish the seasonal climatological distributions of Fe fluxes on a global scale. The preliminary results from this work will further support the exploration of the Fe input oceanicbiomassrelationship and the developmentof oceanic biogeochemicalmodels. Inevitably, however, this approach will always undersample the global ocean. To address this deficiency, we examined the potentialapplication of remotely sensed dust detectedby a Moderate Resolution Imaging Spectroradiometer(MODIS) onboard the Terra spacecraft
P. G. Falkowski, Y. Gao, and D. Kolber, Institute of Marine
Seasonal
Fe fluxes
to the oceans
were
derived
from
a
compilation of aerosol Fe or dust concentrations obtained
(Kaufman et al., 1997; Tanr6 et al, 1997). Since dust absorption relates to its Fe content, the results can, in principle, be used to assist in real-time retrieval of dust propertiesfrom satellitesto improve the Fe flux estimates.
variations in aeolian Fe fluxes in different oceanic basins.