Paleoceanology of the North Atlantic and initiation of the Great Ocean Conveyor based on foraminifera data

Category Climate system
Group GSI.IR
Location International Geological Congress,oslo 2008
Source www.۳۳
Holding Date 18 August 2008

Paleoceanology of the North Atlantic and initiation of the Great Ocean Conveyor based on foraminifera data

Lukashina, Lukashina
Atlantic Branch of Shirshov Institute of Oceanology, RAS, Russian Federation

An interaction between the warm surface and cold deep pars of the global thermohaline circulation in the North Atlantic determines the Earth's modern climate. Foraminifera research is one of the methods, which allows us to reconstruct the time of the appearance of the Great Ocean Conveyor and its variations in the past. Thanks to planktonic foraminifera the upper circulation of the World Ocean was studied in detail. All-round studying of benthonic foraminifera allows to understand the processes in the near-bottom layers of oceans. Recent assemblage C. laevigata with thermophilic planktonic foraminifera from the North Atlantic allows to look over pathway of the North Atlantic Upper water (NAUW) — warm part of the Conveyor. Assemblage G.praeggeri is indicator of the Mediterranean Intermediate water (MIW).

North Atlantic Deep water (NADW) associates with assemblage P. wuellerstorfi/H.elegans. Assemblage E.exigua/O.umbonatus is indicator of Labrador Bottom water (LBW). NADW and LBW flow southward and form cold deep part of the Great Ocean Conveyor in the Atlantic Generation of NADW began in the Middle Eocene. In the beginning of the Middle Miocene in the North-West Atlantic became to form NAUW. Its penetration to Norwegian Sea resulted in forming of present NADW — basal deep component of the recent thermohaline Conveyor from the end of Middle Miocene. Bottom water from Labrador Sea, a second component of deep part of the Conveyor, formed from the end of Paleocene. Activity of the Conveyor increased after final closing of

Panama Sea Way
in the Middle Pliocene.

Glaciations of the Quaternary Period began from the end of Pliocene but more strong fluctuations of climate began from the middle of Pleistocen. The circulation of the water masses in the interglacial periods of the Late Pleistocene was like Holocene in generally but warm strong saline MIW more affected on the nature of the NAUW and Great Ocean Conveyor was more intensive.

The circulation of the water masses in principal differed from Present during the glacial periods. Inflow of MIW to the North Atlantic decreased a lot. It decreased of temperature and salinity of NAUW and reduced its penetration to the Norwegian Sea. Penetration of the NAUW there decreased quite in the result of the year-around freezing of the surface of the Norwegian Sea.

In result decreased or stopped forming of the NADW in the North Atlantic. Deep structure zone in the North Atlantic was occupied by water like recent Circumantarctic Intermediate water.
In summary, only LBW took part in forming of the North Atlantic deep part of the Great Thermohaline Conveyor in the glacial periods of Late Pleistocene, and in the result circulation of the water masses was not so strong.