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The creation of biogeochemical cycles in the marine environment requires the quantification of vertical fluxes of settling particulate matter and the particulate elements transported to the bottom. These fluxes depend on the composition and amount of sedimentary particles, formed in the upper layer of the aqueous reservoir, their transformations in the water column, as well as their final deposition at the bottom. The objective of this work is to study the settling particle composition and the particulate element fluxes to the Alfonso Basin (410 m deep), La Paz Bay (southern part of the Baja California Peninsula) and try to find their possible contribution sources. An important characteristic of this area is the desertic arid climate with very low precipitation (< 200 mm/yr), occurring mainly during the passage of tropical cyclones, as well as a high probability of dust storms. Settling particulate matter was collected by an automated sediment trap during 2002-2009 with a periodicity of 7-15 days. Major and trace elements, including lanthanides, were determined using instrumental neutron activation analysis. The present study also partially includes the 2002-2005 database (Rodríguez Castañeda, 2008). At the actual moment we can conclude that the total mass flux, composition and different particulate element fluxes show a high variability and do not exactly coincide with each other. However, some element behavior seems to be influenced by different extraordinary events. Tropical cyclone effect on settling particulate matter, specially noted for ?Ignacio? (22-27 August, 2003), ?Marty? (18-14 September, 2003) and ?Henriette? (30 August - 6 September, 2007) hurricanes, was found for Sc and Fe, representing the fluvial terrigenous input. Reported planktonic blooms for the study area, especially on June and July of 2002 and December of 2007, were affecting Ca, Ba and U contents, as well as their fluxes, defining the marine biogenic supply. Dust storm effect was found for Sc, Fe and As, being related to aeolian input due to strong northeast winds, acting mostly on fall-winter in the study area. And finally, suboxic conditions of the water column of the La Paz Bay could be creating authigenic particles, due to reduction of some redox-sensitive elements, transferring them from the dissolved to particulate phase, as could be the case for U and As. Shale-normalized lanthanide patterns revealed strong terrigenous influence, with a negative Eu anomaly, prevailing during all the time span, as well as on extraordinary events. A dilution effect was present (lower values) for the high biogenic flux periods, however the same shale-normalize pattern remained. Some elements did not show a relation to only one phenomena, but to a variety of them. So in consequence these might be controlled by a combination of processes and interactions.

Palabras clave: Settling particulate matter composition; La Paz Bay; Settling particulate matter composition; Evtraordinary event

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