Orbital-scale variability in primary productivity off the Portuguese margin over the last 1.3 Myr: benthic foraminiferal evidence
Description
This dataset includes stable oxygen and carbon isotopes of planktonic foraminifera Globigerina bulloides, benthic foraminfieral census data, Q-mode factor loadings based on benthic foraminiferal percentage data, and the sediment redness a* from the upper 415 m-long composite section of IODP Site U1391. The planktonic oxygen isotope record documents 19 glacial/interglacial cycles from MIS 1 to MIS 40 (0-1.3 Ma). The benthic foraminiferal fauna is grouped into four assemblages based on the Q-mode factor analysis. Species in the S. bulloides assemblage have high positive scores of Factor 1, consisting of S. bulloides, agglutinated taxa and Lenticulina as major components. Cibicidoides robertsonianus, P. ariminensis and U. peregrina parva are subsidiary species of this assemblage. In the C. pachyderma-dominated assemblage, C. wuellerstorfi and B. mexicana are important accessory species, which have distinct negative scores of Factor 2. Miliolids and B. mexicana are dominant in the miliolids assemblage with distint negative scores of Factor 3. U. mediterranea is the important associated species of this assemblage. The P. ovata assemblage is represented by P. ovata which has a high positive score of Factor 4, along with G. affinis, M. pompiloides, M. barleeanum and U. peregrina parva as important accessory species. The relation between the benthic foraminiferal assemblages and surface primary productivity was obtained according to their dependency on organic matter flux in the study area and the adjacent areas. The S. bulloides assemblage indicates enhanced organic matter flux to the sea floor and represents the highest level of primary productivity. The miliolids assemblage represents the lowest level of primary productivity. the P. ovata assemblage indicates a moderate decrease in primary productivity relative to the S. bulloides assemblage and represents a medium level of primary productivity or slightly above. The C. pachyderma assemblage points to significantly reduced primary productivity between levels indicated by the P. ovata assemblage and the miliolids assemblage. High productivity characterized by the dominance of the S. bulloides assemblage with subsidiary P. ovata assemblage mainly occurred during the interglacial stages, and low productivity marked by the miliolids assemblage and the C. pachyderma assemblage occurred during the glacial stages. Benthic foraminiferal records suggest there is also a long-term decreasing trend in primary productivity, supported by the long-term indecreasing trend in the sediment redness a* which is mainly controlled by the organic matter flux.