Modelling global-scale climate impacts of the late Miocene Messinian Salinity Crisis

Abstract

Abstract. Late Miocene tectonic changes in MediterraneanAtlantic connectivity and climatic changes caused Mediterranean salinity to fluctuate dramatically, including a tenfold increase and near-freshening. Recent proxy-and modelbased evidence suggests that at times during this Messinian Salinity Crisis (MSC, 5.96-5.33 Ma), highly saline and highly fresh Mediterranean water flowed into the North Atlantic Ocean, whilst at others, no Mediterranean Outflow Water (MOW) reached the Atlantic. By running extreme, sensitivity-type experiments with a fully coupled oceanatmosphere general circulation model, we investigate the potential of these various MSC MOW scenarios to impact global-scale climate.The simulations suggest that although the effect remains relatively small, MOW had a greater influence on North Atlantic Ocean circulation and climate than it does today. We also find that depending on the presence, strength and salinity of MOW, the MSC could have been capable of cooling mid-high northern latitudes by a few degrees, with the greatest cooling taking place in the Labrador, Greenland-IcelandNorwegian and Barents seas. With hypersaline MOW, a component of North Atlantic Deep Water formation shifts to the Mediterranean, strengthening the Atlantic Meridional Overturning Circulation (AMOC) south of 35 • N by 1.5-6 Sv. With hyposaline MOW, AMOC completely shuts down, inducing a bipolar climate anomaly with strong cooling in the north (mainly −1 to −3 • C, but up to −8 • C) and weaker warming in the south (up to +0.5 to +2.7 • C).These simulations identify key target regions and climate variables for future proxy reconstructions to provide the best and most robust test cases for (a) assessing Messinian model performance, (b) evaluating Mediterranean-Atlantic connectivity during the MSC and (c) establishing whether or not the MSC could ever have affected global-scale climate.

Holocene lowering of the Laurentide ice sheet affects North Atlantic gyre circulation and climate

“…This model has been extensively used to model past climates (e.g. Lunt et al 2008;Roberts et al 2014;Ivanovic et al 2014Ivanovic et al , 2017Singarayer et al 2011;Valdes et al 2017). and performs well with respect to mean climate (Flato et al 2013), capturing the key features of the mid-latitude atmospheric circulation, including planetary waves and storm tracks .…”

Miocene–Pliocene stepwise intensification of the Benguela upwelling over the Walvis Ridge off Namibia

“…The Mediterranean begun to desiccate shortly before 6.2 Ma, creating salty and dense waters flowing into the Atlantic and contributing to NADW formation until 6.0 Ma (Pérez-Asensio et al, 2012). Further restriction of the Mediterranean Outflow Water between 6.0 and 5.5 Ma weakened the AMOC, although the effects of the Mediterranean Outflow Water on the AMOC strongly 5 depend on the salinity of the Outflow Water (Ivanovic et al, 2014). An earlier salinity crisis in the Mediterranean occurred during the Tortonian between 7.8 and 7.6 Ma (Kouwenhoven et al, 2003).…”

Orbital control on late Miocene climate and the North African monsoon: insight from an ensemble of sub-precessional simulations

“…The model has also been used in several other pre-Quaternary palaeoclimate studies, both for the late Miocene (Bradshaw et al, 2012a(Bradshaw et al, , 2015 and Eocene (Loptson et al, 2014;Lunt et al, 2010;Tindall et al, 2010). Other late Miocene simulations have also been carried out running the higher-resolution-ocean (1.25 • latitude and longitude) version of the model (Ivanovic et al, 2013(Ivanovic et al, , 2014a. However, here we used the lower-resolution and more computationally efficient HadCM3L because of the availability of an existing 2000-year spin-up, for consistency with the Bradshaw et al (2012a) study, and because of the number of simulations conducted in the ensemble.…”

“…For the presentation of our results we use a modern-day calendar. This does not take into account the changes in the length of the seasons determined by variations in the date of perihelion along a precession cycle (Kutzbach and Gallimore, 1988;Joussaume and Braconnot, 1997). This socalled "calendar effect" has the potential to introduce biases in the seasonal interpretation of the analysed variables.…”