Late Pliocene Decline of Primary Production Late Pliocene Decline of Primary Production in the Northern North Atlantic, 2.73 MA - Links to the Final Closure of Central American

Late Pliocene benthic-foraminifera assemblages and stable-isotope records at ODP Site 984 (North Atlantic) record changes in North Atlantic surface productivity prior and after the final closure of the Central American Seaways (CAS) having induced the two-step onset of Northern Hemisphere Glaciation (2.82-2.95 Ma; 2.73 Ma). The benthic fauna underwent an abrupt and fundamental change at 2.73 Ma (marine isotope stage -MIS- G6) from assemblages marked by species indicative of high-carbon flux, such as Bolivina pacifica, to assemblages marked by feeding opportunists like Cassidulina teretis. Because of pelagic-benthic coupling, this faunal switch suggests a profound reorganization of productivity and benthic nutrient supply in the northern North Atlantic. In harmony with model [B. Schneider & A. Schmittner, Simulating the impact of the Panamanian seaway closure on ocean circulation, marine productivity and nutrient cycling. Earth Planet. Sci. Lett. 246 (2006) 367-380] primary production was high as long as the CAS were open, but declined precisely coeval with an increased in benthic d18O and d13C values of Upper northern North Atlantic Deep Water (UNADW), suggesting an abrupt cooling and further increase in ventilation at intermediate water depths. This covariance suggests a change in marine productivity that resulted from the onset of a glacial thermohaline circulation mode marked by more pronounced surface water stratification and seasonality. Indeed, detailed faunal records of glacial MIS 104 (~2.6 Ma) display remarkable similarities with those of Late Pleistocene MIS 2 and 3. Short-term fluctuations in benthic faunas suggest a response to rapid environmental changes.