Evaluating climate change by multivariate statistical techniques on magnetic and chemical properties of marine sediments (Azores region)

Regression models and cluster analyses are used to link magnetic properties of late Pleistocene deep-sea sediments in the Azores area (Mid-Atlantic Ocean) with the chemical element composition. The influence of the volcanic Azores Archipelago on sedimentation is evident in high magnetic mineral concentrations (low-field magnetic susceptibilities between 30 and 250×10−5 SI) and high Ti/Al ratios (>0.1). Variations in magnetic mineral concentration and Ti/Al ratios can be linked to detrital input and coincide with oxygen isotope ratio (δ18O) changes. The highest magnetic mineral concentrations and Ti/Al ratios are found around temperate climate periods, suggesting that detrital input from the Azores Islands is most prominent during these periods. Lower Ti/Al ratios and a slightly different composition of the lithogenic fraction suggests the presence of a second, probably eolian, detrital component during glacial periods. Higher Ba/Al ratios and ‘excess Ba’ estimates suggest higher productivity during the cold climate periods, especially at the end of stages 2 and 6. Temperate climate periods are characterised by a succession of peaks in magnetic mineral concentration and Ti/Al ratios at the beginning of these periods followed by peaks in CaCO3 and Mn/Al toward the end. Cluster analysis shows that the first peaks might be related to volcanic material, which was initially deposited on land during eruptions in glacials and then washed into the sea due to the sea-level rise at the beginning of temperate periods. The latter peaks represent a more biogenic sediment signal, which might be more diagnostic of vegetation changes in the Azores Archipelago due to a warmer climate.