Emilia Salgueiro

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.

Influence of dominant wind patterns in a distal region of the NW Iberian Margin during the last glaciation

This work combines planktonic foraminiferal assemblages, stable isotope, transfer function estimated sea surface paleotemperatures (SST) and export productivity (Pexp) with sedimentological records from the PC7 core to document paleoclimatic and paleoceanographic changes on a distal region of the NW Iberian Margin since the last glaciation (<≈68 ka). Neodymium and strontium isotope data are also used to identify the provenance of ice rafted debris (IRD) during Heinrich event 5 (H5). Our results are compared and combined with previously published records and evidence that melt water and icebergs from the Canada, Greenland, Iceland and Europe ice sheets arrived to the NW Iberian Margin causing a significant decrease of SST during the last six Heinrich Stadials (HS) and some Dansgaard–Oeschger (D-O) stadial events. εNd and 87Sr/86Sr indicate that the studied locality mostly received sediments from European Ice Sheets (EIS) during H5. During the HS and D–O stadial events, SSTs were in general higher than in other cores collected in inner areas of the NW Iberian Margin. The presence and intensification of Portugal Current probably induced heat transfer to this distal region of the Iberian Margin. Our results also suggest the occurrence of high variability in the intensity and wind patterns during the last glaciation. In some periods, the intensity of northerly winds could have been very strong and contributed to a significant stimulation of ocean productivity in this distal area through the intensification of upwelling. In general, oceanic productivity decreased during the HS and D–O as the presence of cold and less saline water prevented nutrient rich waters from deep levels reaching the surface. The high productivity events were bracketed by periods characterized by the highest influence of the Azores Current eastern branch during which northerly winds and the oceanic productivity should have been weakened. Supplementary material: Geochemical and foraminiferal data analysed in this work as well as Pearson Correlations between the analysed data are available at https://doi.org/10.6084/m9.figshare.c.3931813

Diversity of planktonic foraminifer fauna found in 18 deep-sea cores from the North Atlantic

Greenland stadial/interstadial cycles are known to affect the North Atlantics hydrography and overturning circulation and to cause ecological changes on land (e.g., vegetation). Hardly any information, directly expressed as diversity indices, however, exists on the impacts of these millennial-scale variations on the marine flora and fauna. We calculated three diversity indices (species richness, Shannon diversity index, Hurlberts probability of interspecific encounter) for the planktonic foraminifer fauna found in 18 deep-sea cores covering a time span back to 60 ka. Clear differences in diversity response to the abrupt climate change can be observed and some records can be grouped accordingly. Core SO82-05 from the southern section of the subpolar gyre, the cores along the British margin and core MD04-2845 in the Bay of Biscay show two modes of diversity distribution, with reduced diversity (uneven fauna) during cold phases and the reverse (even fauna) during warm phases. Along the Iberian margin high species diversity prevailed throughout most of the glacial period. The exceptions were the Heinrich stadials when the fauna abruptly shifted from an even to an uneven or less even fauna. Diversity changes were often abrupt, but revealed a high resilience of the planktonic foraminifer faunas. The subtropical gyre waters seem to buffer the climatic effects of the Heinrich events and Greenland Stadials allowing for a quick recovery of the fauna after such an event. The current work clearly shows that planktonic foraminifer faunas quickly adapt to climate change, albeit with a reduced diversity.