Abstract. Mediterranean–Atlantic exchange through the Strait of Gibraltar plays a
significant role in the global ocean–climate dynamics in two ways. On one
side, the injection of the saline and warm Mediterranean Outflow Water (MOW)
contributes to North Atlantic deep-water formation. In return, the Atlantic
inflow is considered a sink of less saline water for the North Atlantic
Ocean. However, while the history of MOW is the focus of numerous studies,
the Pliocene Atlantic inflow has received little attention so far. The
present study provides an assessment of the Mediterranean–Atlantic exchange
with a focus on the Atlantic inflow strength and its response to regional and
global climate from 3.33 to 2.60 Ma. This time interval comprises the
mid-Pliocene warm period (MPWP; 3.29–2.97 Ma) and the onset of the Northern
Hemisphere glaciation (NHG). For this purpose, gradients in surface
δ18O records of the planktonic foraminifer Globigerinoides ruber between the Integrated Ocean Drilling Program (IODP) Hole U1389E (Gulf
of Cádiz) and Ocean Drilling Program (ODP) Hole 978A (Alboran Sea) have
been evaluated. Interglacial stages and warm glacials of the MPWP revealed
steep and reversed (relative to the present) W–E δ18O gradients
suggesting a weakening of Mediterranean–Atlantic exchange likely caused by
high levels of relative humidity in the Mediterranean region. In contrast,
periods of stronger inflow are indicated by flat δ18O gradients due
to more intense arid conditions during the severe glacial Marine Isotope
Stage (MIS) M2 and the initiation of NHG (MIS G22, G14, G6–104). Intensified
Mediterranean–Atlantic exchange in cold periods is linked to the occurrence
of ice-rafted debris (IRD) at low latitudes and a weakening of the Atlantic
Meridional Overturning Circulation (AMOC). Our results thus suggest the
development of a negative feedback between AMOC and exchange rates at the
Strait of Gibraltar in the latest Pliocene as it has been proposed for the
late Quaternary.
Mud Volcanism on the Mediterranean Ridge
