Palaeoproductivity changes and upwelling variability in the Galicia Mud Patch during the last 5000 years: geochemical and microfloral evidence

Abstract

The Holocene paleoclimatic history of the Galician continental shelf (NW Spain) has been investigated through the analyses of diatom remains, as well as geochemical and sedimentological parameters. Diatoms, other siliceous compounds, and biogenic silica (BSi) and metals content were analysed from a gravity core recovered from the Galicia Mud Patch, NW Iberian Peninsula, covering the last 5000 years. Results were integrated together in a multiproxy study in order to determine the climatic and the oceanographic influence on the paleoproductivity conditions that have occurred in the region. Downcore changes in diatom assemblages composition and abundance reflect changes in diatom production related to long/short-term variations in climate, regional oceanography, upwelling strength, and river influx off the coast of Galicia and Portugal. As displayed by the diatom taxa record, paleoclimatic variability was related to different atmospheric conditions, particularly the relative strengths and position of the Azores High and Iceland Low pressure cells. Metals and microflora fluctuations are interpreted as changes in the riverine influence and upwelling intensity paced by oceanographic, atmospheric and climatic changes. Lack of diatoms between 4700-3300 and 1800-1200 cal. yr BP could be linked to early diagenetic processes taking place in the sediment after burial. All tracers considered, biogenic barium (Ba excess), metals and diatom assemblages, show consistent profiles displaying a general increase of the marine productivity for the last 1200 cal. yr BP. River runoff due to high precipitation conditions in the catchment area is an additional important source of nutrients to the surface waters promoting diatom production. In this way, 3 microflora indicates that during and 500 cal. yr BP high production is triggered by influx of river-derived nutrients under conditions of SW winds and storms due to a NAO negative-like phase. The biosiliceous and geochemical signatures of sediments from the last 500 cal. yr BP indicate conditions of enhanced upwelling and increased phytoplanktonic production associated to the intensification of northerly winds. Upwelling strengthening in this area, attributed to recent global warming, could provoke an increase in phytoplankton biomass and the consequent biological, climatological and socioeconomical impacts. The imprint of the anthropic activities has been recorded by the increasing Pb/Al ratios for the last 400 cal. yr BP. The oceanographic changes recorded in Galician shelf are correlative with other marine and terrestrial paleoenvironmental records in the NW Iberian Peninsula.

Marsh benthic Foraminifera response to estuarine hydrological balance driven by climate variability over the last 2000 yr (Minho estuary, NW Portugal)

“…Therefore, as a response to reduced solar activity, European midlatitudes experienced colder temperatures and increased humidity. The palaeoclimatic records of the Iberian Peninsula continental shelf reveal increased river discharge during periods of NAO-negative (Álvarez et al, 2005;Lebreiro et al, 2006;Bernárdez et al, 2008b;Abrantes et al, 2011;González-Álvarez, 2013) and the instrumental data show good correlations between negative phases of NAO index and winter precipitation and river flow in NW Iberia, namely in Minho river basin (e.g., Trigo et al, 2004;DeCastro et al, 2006;Fatela et al, 2013). The hydrological balance recorded by the Caminha marsh foraminifera and sedimentological proxies is controlled by the atmospherical modes, reflecting the NE Atlantic climate dynamic, namely from LIA to present.…”

Centennial-scale variations in diatom productivity off Peru over the last 3000 years

“…Diatoms are a major biogenic component of coastal upwelling sediments and have been largely used to derive information on paleoproductivity variations and, hence, on upwelling activity variations on tectonic, orbital, and millennial timescales (e.g. Abrantes, 1991a, 1991b, 2000; Bernárdez et al, 2008; Lange et al, 1998; Romero et al, 2006). Off Peru, only a few studies have focused on diatom assemblages and mostly at low temporal resolution for the last climatic cycles (De Vries and Schrader, 1981; Schrader, 1992; Schrader and Sorknes, 1990, 1991).…”

Environmental change in theRía deVigo,NW Iberia, since the mid‐Holocene: new palaeoecological and seismic evidence

“…Bernárdez et al . (, b) reconstructed two strong river flow events that reached the Galician continental shelf: the younger dated at 800–500 cal. a BP and linked to a pervasive negative NAO period; and the second around 2000–1800 cal.…”