Ventilation History of the Tropical Atlantic Thermocline: New Insights From the Sensitivity of Foraminifera to Water Mass Nutrient Concentrations
Abstract
The sensitivity of certain species of foraminifera to nutrient distributions throughout today's oceans highlights their potential for reconstructing water mass nutrient distributions in the past. Applying these new insights to reconstructed abundances of several key species during the last glacial, we find that thermocline waters throughout the entire tropical Atlantic were better ventilated than today. These findings are in line with independent evidence for stronger intermediate-depth ventilation driven by widespread Glacial North Atlantic Intermediate Water (GNAIW), supporting the validity of our new approach. Our results also suggest that well- ventilated GNAIW penetrated at least as far as 25 degrees South, thereby confining the northernmost glacial limits of poorly ventilated Antarctic Intermediate Water (AAIW) to the southernmost Atlantic. We show that the glacial Atlantic thermocline switched to its modern, more poorly ventilated state (probably indicative of a return of AAIW dominance) in a two-step process: a transient reduction in ventilation during the Bolling/Allerod, with the definitive switch to a regime of poor thermocline ventilation occurring at the close of the Younger Dryas. Furthermore, longer-term reconstructions of past distributions of these several key foraminiferal species suggest that a major and enduring impact of glacial-interglacial cycles on Atlantic hydrography has been this vacillating behaviour in tropical thermocline ventilation.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2008
- Bibcode:
- 2008AGUFMPP11A1364S
- Keywords:
-
- 4845 Nutrients and nutrient cycling (0470;
- 1050);
- 4926 Glacial;
- 4944 Micropaleontology (0459;
- 3030);
- 4962 Thermohaline