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Some micronutrients and chalcophylic elements are enriched in settling particulate matter of a time series (January 2002 - December 2005), especially in some periods. The average enrichment factors (EFs) of elements, calculated using Sc as normalizer (Salomons and Förstner, 1984), display the next sequence in a decreasing order:Normal years (2003-2005) Se (117-927) > Sb (10-53) > Cd (17-41) > As (14-19) > Pb (3-36) > Sr (3-10) > U (2-6) > Cs (5-5.6) > Ca (3-5) = Zn (3-5) > Cu (1.3-5.4) > Ba(1.8-4.3) > Mo (2-2.8) > Co (1.0-3.6) > Mn (1.4-2.1) > Ni (1-2) > Rb(1-1.2) > Fe (1) >Al (0.8-0.9) > Cr (0.9-1) > V (0.6-1) Anomalous year (2002) Se (1488) > Sb (470) > As (239) > U (61) > Cd (35) > Sr (31) > Mo (26) > Zn (15) = Pb (15) > Ca (11) > Cs (9) > Rb (6,.5) > Co (4.8) > Ba (4) = Cu (4) > Ni (3) > Cr (2.4) > Al (1.4)= Mn (1.4) >Fe (1.2) > V (1)The highest values of EFs of As, Cd, Mo and U were observed mainly in late spring – early summer of the year 2002, when the waters from the Pacific Ocean presumably enter into the La Paz Bay, carrying less oxygen, less terrigenous particles and bringing tropical and subtropical plankton species. During that time, the winds become of SE direction, decreasing the continental aerosol input. The Oxygen Minimum Zone can make slower the remineralization rate of sedimenting biogenic particles, also favouring the formation of insoluble Cd, Cu and Zn sulphides, as well as the reduction of Mo and U which can be easily scavenged by particles in a lower oxidation state (+4).

Palabras clave: serie de tiempo; materia particulada ren hundimiento; biogeoquimica; Ciclo biogeoquímico del carbono

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