Resumen del producto

Biogeochemical cycles of elements in the ocean lie at the center of our understanding of the functioning of ecosystems on different scales, whether global or regional. Some major, trace elements and lanthanides are known to be useful indicators of the origin of settling particulate matter and marine sediments, especially in contrasting environments with distinctive features such as active tectonics or environmental pollution. The objective of this study is to characterize shale-normalized lanthanide patterns as well as trace element composition of settling particulate matter (SPM) and marine sediments of the Alfonso Basin, southwestern Gulf of California. The SPM was collected with an automated sediment trap during 2002-2010 with a periodicity of 7-15 days near the bottom of Alfonso Basin. A recent sediment core was obtained with a box corer near the trap location. The major, trace element and lanthanide contents were determined using instrumental neutron activation analysis, aided with suitable standard reference materials. The core was dated using the Pb-210 method. The trap material composition and sediment core analyses helped establishing fluvial supply, mostly during tropical cyclones (Sc and Fe), biogenic contribution (Ca, Ba and U), aeolian effect (Sc, Fe and As) and authigenic particle formation due to suboxic conditions of the water columna or associated to organic matter (U and As). The shale-normalized patterns in SPM show an alternation between light and heavy lanthanides, as well as a typical negative Eu anomaly, which becomes positive during some events. The light/heavy (normalized La/Yb ratio) in the core, representing the time span between 1850 and 2008, showed the same alternation as the settling particles. Mostly the core has a negative Eu anomaly with rare positive Eu prominent peaks. The positive Eu anomaly in both cases is presumably related to hydrothermal activity of Gulf of California tectonics. Calcium values in the sediment core show an increase tendency after the year 1950 which seem to coincide with a superficial temperature reconstruction (NOAA ERSST v3b).

Palabras clave: La Paz Bay; Lanthanides; sediments; Alfonso Basin; settling matter

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