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

摘要

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 (Ba_(excess)), 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 Ba_(excess), 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.