Mediterranean isolation preconditioning the Earth System for late Miocene climate cooling

Walter Capella,F Javier Hernández-Molina,Rachel Flecker,Paul Th Meijer,Francisco J Sierro,Wout Krijgsman,Dirk Simon,Mike Rogerson

doi:10.1038/s41598-019-40208-2

Abstract

A global Neogene cooling trend culminated ~7 million years ago with the onset of Greenland glaciation. Increased ocean-atmosphere interaction and low- to high-latitude circulation are thought to be key factors in reorganizing late Miocene global temperature and precipitation patterns, but the drivers of this reorganization have yet to be identified. Here, we present new information about the evolution of the Atlantic-Mediterranean gateway that generated Mediterranean overflow. We use sedimentary and palaeogeographic evidence to constrain the timing and dimensions of this gateway and document the initiation of a saline plume of water within the North Atlantic. Today, this saline jet entrains and transports Eastern North Atlantic water and its dissolved inorganic carbon into the interior of the ocean, contributing to the drawdown of CO2 and the sensitivity of the ocean to atmospheric changes. We show that during the Miocene this transport emerged simultaneously with gateway restriction and propose that the resulting interaction of ocean-surface and ocean-interior carbon inventories would have greatly enhanced ocean-atmosphere exchange, preconditioning the Earth System for late Miocene cooling.

Highlights

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We show that during the Miocene this transport emerged simultaneously with gateway restriction and propose that the resulting interaction of ocean-surface and ocean-interior carbon inventories would have greatly enhanced ocean-atmosphere exchange, preconditioning the Earth System for late Miocene cooling
Significant deep-sea water cooling occurred around 12–15 Ma, after the Middle Miocene Climatic Optimum[3] and remained rather constant during the late Miocene (Fig. 1b)

Summary

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We explore the impact of restricting the Atlantic-Mediterranean gateway and initiating Mediterranean overflow This late Miocene oceanographic change may have had far-reaching implications, not just for sea-surface temperature changes, and for CO2 exchange between the ocean and atmosphere. Progressive isolation of the Mediterranean from the Atlantic occurred throughout the Miocene, driven by Africa-Eurasia convergence coupled with the westward drift of the Alboran Plate[39] This restriction replaced a wide gateway (Fig. 2) floored with oceanic crust[40] with narrower, shallower connections: the Rifian and Betic corridors[41,42], through which Atlantic-Mediterranean exchange was funnelled (Fig. 2). The late Miocene Betic[41] and Rifian[13] corridors both contain Miocene contourites (i.e. sediments deposited by bottom-currents) formed by Mediterranean water overflowing into the Atlantic, at flow-velocities greater than 0.5–1 m/s.

The link between sedimentary evidence and overflow behaviour

Mediterranean overflow velocity and Atlantic water entrainment

Methods

Additional Information