Upwelling dominated oceanographic periods in the Ria de Vigo during the late Holocene

Abstract

Different oceanographic regimes were identified at millennial scale in the last 3 ka cal BP in a sedimentary sequence from the outer sector of Ria de Vigo (NW Spain) based on a multi-proxy approach (textural, mineralogical, geochemical and benthic foraminifera data). The prevalence of stronger wave climate linked with a developed downwelling regime and a more efficient erosion phase, allowed the deposition of coarser sediments, enriched in geogenic (Si/Al and Zr/Al) and biogenic chemical elements (Ca/Al and Sr/Al), coarse detrital minerals (quartz and feldspars) and carbonates during the periods ≈2.9-2.3 ka cal BP and ≈1.5-0.6 ka cal BP. However the prevalence of soother wave climate regime, linked with reinforced upwelling events, could have occurred between ≈2.5–1.5 ka cal BP and ≈0.5–0 ka cal BP, giving origin to a finer sedimentation enriched in organic matter and phyllosilicates. In these muddy events the consumption of oxygen during aerobic organic matter degradation caused suboxic/anoxic conditions in the sediments, which induced higher early diagenetic changes with pyrite formation in anoxic environments. When the sediments became again oxic/suboxic precipitation of redox, sensitive elements such as Fe and Ni could have arisen.