| Summary: | 8 pages, 3 figures, 2 tables. We present the elemental composition (Al, Cd, Co, Cu, Fe, Mn, Mo, Ni, V, Zn, and P) of field-collected Trichodesmiumpo pulations. To distinguisht he effects of river discharges( Amazon and Niger Rivers) and Saharand ust deposition on metal concentrationsi n the colonies, samplesw ere collected both in the western (February 2001, July-August 2001, and April-May 2003) and eastern (May-June 2003) basins of the North Atlantic.M etalc omposition( mediansn ormalizedt o P) in Trichodesmiurma ngedf rom 0.011 mmol mol- for Co to 39 mmol mol-l for Fe and varied over an order of magnitude among different locations. A comparison of metal ratios measuredi n the Trichodesmiumco loniesw ith ratios reportedf or the potentials ourcess uggestst hat the most importants ourceso f tracem etalst o the tropicala nd subtropicaAl tlanticd uringo ur samplingw eret he Amazon and Niger Rivers, rather than dust deposition from the Sahara. This work was supported by funds from the NOAA Carbon Sequestration Program (award NA040AR4310097) and NSF (OCE 9912333) to S.A.S.-W. and by Spanish "Plan Nacional de I+D" CICYT (REN-2000-1471-C02)t o S.A. A fellowship from the Spanish Ramon y Cajal Programme supported A.T.-S. Peer reviewed
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