Giuseppe Siani

A HIGH-RESOLUTION RECORD OF THE LAST DEGLACIATION IN THE CENTRAL MEDITERRANEAN SEA: PALAEOVEGETATION AND PALAEOHYDROLOGICAL EVOLUTION

Abstract A high-resolution palynological and stratigraphical record of a marine deep-sea core in the Adriatic sea documents marine and continental palaeoenvironmental changes in the basin during the last deglaciation and early Holocene. A chronology is derived from the oxygen isotope stratigraphy. Three periods of aridity, marked by the development of a semi-desert rich in Artemisia , occurred between 18.5 and 16xa0kyr, between 14.4 and 12.7xa0kyr and between 11.1 and 9.7xa0kyr, consistent with the Last Glacial Maximum, the Oldest Dryas and the Younger Dryas. They are correlated with increases in productivity and intensification of the Levantine water formation in the Eastern Mediterranean basin. During the warmer Bolling/Allerod (12.7–11.1xa0kyr), the presence of the cold temperate dinocyst Bitectatodinium tepikiense is interpreted as indicating the establishment of a strong seasonal thermal gradient, probably linked to seasonal cold freshwater runoff from the Po river, attested by the unique presence of pollen of freshwater plants. The expansion of forest and the development of the warmer dinocysts start with Termination IB. During the Holocene, three tree phases are recognized and are contemporaneous with the Preboreal, Boreal and Atlantic chronozones of Europe. The two phases of sapropel deposition are marked by higher pollen and dinocyst concentrations and a high representation of Brigantedinium spp which indicate higher preservation of organic material and/or freshwater runoff of the Po River.

Enhanced ocean-atmosphere carbon partitioning via the carbonate counter pump during the last deglacial

Several synergistic mechanisms were likely involved in the last deglacial atmospheric pCO2 rise. Leading hypotheses invoke a release of deep-ocean carbon through enhanced convection in the Southern Ocean (SO) and concomitant decreased efficiency of the global soft-tissue pump (STP). However, the temporal evolution of both the STP and the carbonate counter pump (CCP) remains unclear, thus preventing the evaluation of their contributions to the pCO2 rise. Here we present sedimentary coccolith records combined with export production reconstructions from the Subantarctic Pacific to document the leverage the SO biological carbon pump (BCP) has imposed on deglacial pCO2. Our data suggest a weakening of BCP during the phases of carbon outgassing, due in part to an increased CCP along with higher surface ocean fertility and elevated [CO2aq]. We propose that reduced BCP efficiency combined with enhanced SO ventilation played a major role in propelling the Earth out of the last ice age.The contribution of the carbonate counter pump (CCP) to the last deglacial atmospheric CO2 rise has yet been largely ignored. Here, the authors show that an increased CCP in the Subantarctic Pacific along with high surface ocean fertility and [CO2aq], contributed in propelling the Earth out of the last ice age.