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Assessment of geochemical and micropaleontological sedimentary parameters as proxies of surface water properties in the Canary Islands region

Abstract The Canary Islands region occupies a key position with respect to biogeochemical cycles, with the zonal transition from oligotrophic to nutrient-rich waters and the contribution of Saharan dust to the particle flux. We present the distribution of geochemical proxies (TOC, carbonate, δ15N, δ13Corg, C/N-ratio) and micropaleontological parameters (diatoms, dinoflagellates, foraminifera, pteropods), in 80 surface-sediment samples in order to characterise the influence of coastally upwelled water on the domain of the subtropical gyre. Results of the surface-sediment analyses confirmed the high biomass gradient from the coast to the open ocean inferred from satellite data of surface chlorophyll or SST. The distribution of total dinoflagellate cysts, the planktic foraminifera species Globigerina bulloides, the diatom resting spore Chaetoceros spp., and TOC concentration coincided well with the areas of strong filament production off Cape Ghir and Cape Yubi. The warm-water planktic foraminifera Globigerinoides ruber (white), the diatom Nitzschia spp., and the δ15N-values showed the opposite trend with high values in the open ocean. Factor analyses on the planktic foraminifera species distribution indicated three major assemblages in the Canary Islands region that represent the present surface-water conditions from the upwelling influenced region via a mixing area towards the subtropical gyre.

Productivity response in the North Canary Basin to climate changes during the last 250 000 yr: a multi-proxy approach

We present results from the investigation of the primary productivity record over the last 250 kyr in the North Canary Basin (30°N) off Northwest Africa. Two distinct productive systems interfere in this area: the oligotrophic open ocean and the upwelling filament off Cape Ghir, that occasionally carries offshore cool nutrient-rich waters. The following geochemical and micropaleontological paleoproductivity proxies have been used in our study: calcium carbonate, barium excess (Baexcess), total organic carbon (TOC) and diatoms. Time series analysis of these proxies indicates that paleoproductivity in the North Canary Basin underwent important changes following precession and eccentricity cycles. While the precessional signal appears to be mainly related to trade wind strength, superimposed peaks in Baexcess, TOC and diatom records point to large productivity events at Terminations I, II and III. Lowering of the North Atlantic sea surface temperatures by melt water discharges which in turn strengthened the Azores high-pressure center and increased trade wind velocities is postulated as the mechanism to explain the enhancement of the coastal upwelling and associated filaments at terminations. Additionally, the Canary Current may play a role in transmitting cold melt waters and nutrients from higher latitudes to the North Canary Basin.

Siliceous sedimentary record of the last 280 kyr in the Canary basin (NW Africa)

Abstract Siliceous microfossils were quantified in four sedimentary sequences off Northwest Africa in order to disclose the productivity story of the last 280 kyr. Three sediment cores retrieved along an E–W profile, at about 29°N (GeoB4240, GeoB4241 and GeoB4242), and one core (GeoB4216) from the highly productive area off Cape Ghir in the Canary Island region. At 29°N, along all but the most offshore sequences (GeoB4242), coincidence of high diatom accumulation rates (DAR) and high abundances of Chaetoceros spores, the upwelling-related species, indicate glacial stages (isotope stages (IS) 4 and 2) as more productive than the interglacial intervals (IS5 and Holocene). The DAR in the coastal area of the Canary basin during IS2 is of the same order of magnitude (108 valves cm−2 kyr−1) reported for Cape Blanc and one order of magnitude higher than reported for the Iberian margin. The deviation observed between the offshore (higher DAR at IS3 and 6) and the coastal diatom records (higher DAR at IS2 and 4) may be a reflection of local productivity generated by wind input of nutrients and advection from coastal sources. The occurrence of DAR spikes at the timing of some Heinrich events seems to support the hypothesis of productivity maxima associated with the presence of meltwater off NW Africa, as previously proposed by other authors.

High-resolution geological cartography and coastal evolution assessment at Armação de Pêra – Galé sector: a prototype for a national coastal mapping

Portuguese coastal areas are of current major concern due to the continuous expansion of a strong urbanization, accentuated development of economic activities, resilient land use and general population growth. A particular attention has been given to the shoreline evolution, pointing out evidences of critical coastal sectors that are prone to suffer adverse consequences of climate changes direct impacts. Areas where climate change and sea-level rise effects will be stronger include, among others, coastal sectors associated to soft rocky or mobile substrate shores and/or low morphological shores with recognized marked erosion trend. Within this context, the knowledge of the geological setting is imperative as different lithologies have distinct resistance and behavior against marine erosion. The available digital geological Portuguese cartography at 1:25000 scale is not suitable to well characterize the geology within the context of small geographic areas or within the perspective of costal management. Hence, the National Laboratory of Energy and Geology (LNEG) developed a prototype to evaluate the potential of the integrated “geological and coastal hazard mapping” at a 1:3000 resolution scale. The combination of detailed geology and historical coastline displacement information, in a single map, constitute a new and valuable cartographic product to support coastal managers and general users of littoral regions. The application of the prototype to the entire Portuguese coastal areas will be carried out by LNEG and digital information will be available at LNEG GeoPortal (http://geoportal.lneg.pt/).