Articles | Volume 13, issue 4
Clim. Past, 13, 333–344, 2017
Clim. Past, 13, 333–344, 2017

Research article 10 Apr 2017

Research article | 10 Apr 2017

Holocene evolution of the North Atlantic subsurface transport

Janne Repschläger1,a, Dieter Garbe-Schönberg1, Mara Weinelt2, and Ralph Schneider1 Janne Repschläger et al.
  • 1Institute of Geosciences, Kiel University, 24118 Kiel, Germany
  • 2Institute of Prehistoric and Protohistoric Archaeology, Kiel University, 24118 Kiel, Germany
  • anow at: Climate Geochemistry Department, Max Planck Institute for Chemistry, 55128 Mainz, Germany

Abstract. Previous studies suggested that short-term freshening events in the subpolar gyre can be counterbalanced by advection of saline waters from the subtropical gyre and thus stabilize the Atlantic Meridional Overturning Circulation (AMOC). However, little is known about the inter-gyre transport pathways. Here, we infer changes in surface and subsurface transport between the subtropical and polar North Atlantic during the last 11 000 years, by combining new temperature and salinity reconstructions obtained from combined δ18O and Mg ∕ Ca measurements on surface and subsurface dwelling foraminifera with published foraminiferal abundance data from the subtropical North Atlantic, and with salinity and temperature data from the tropical and subpolar North Atlantic. This compilation implies an overall stable subtropical warm surface water transport since 10 ka BP. In contrast, subsurface warm water transport started at about 8 ka but still with subsurface heat storage in the subtropical gyre. The full strength of intergyre exchange was probably reached only after the onset of northward transport of warm saline subsurface waters at about 7 ka BP, associated with the onset of the modern AMOC mode. A critical evaluation of different potential forcing mechanisms leads to the assumption that freshwater supply from the Laurentide Ice Sheet was the main control on subtropical to subpolar ocean transport at surface and subsurface levels.

Short summary
We reconstruct changes in the warm water transport from the subtropical to the subpolar North Atlantic over the last 10 000 years. We use stable isotope and Mg / Ca ratios measured on surface and subsurface dwelling foraminifera. Results indicate an overall stable warm water transport at surface. The northward transport at subsurface evolves stepwise and stabilizes at 7 ka BP on the modern mode. These ocean transport changes seem to be controlled by the meltwater inflow into the North Atlantic.