An oceanic box model of the Miocene Mediterranean Sea with emphasis on the effects of closure of the eastern gateway

Abstract

The early Miocene Mediterranean Sea had two gateways toward the open ocean: the Indian Ocean in the east and the Atlantic Ocean in the west. Closure of the eastern connection during the middle Miocene had important effects on the water properties and circulation of the Mediterranean Sea. To gain insight into the circulation of the Mediterranean Sea during the Miocene and the effects of closure, we apply a box model. The model has three boxes representing the Atlantic Ocean, the Mediterranean Sea, and the Indian Ocean. The boxes exchange water, heat, and salt through surface and deep flow. The deep flow is driven by the density contrast between the boxes. We analyze the variation of (1) temperature, salinity, and residence time and (2) magnitude and configuration of the gateway flows in response to changes in the gateways and in atmospheric forcing (freshwater and heat fluxes). The analysis is presented in three parts: preclosure, closure, and postclosure. Model results are compared with observations reported in literature. The model analysis indicates that (1) prior to closure of the eastern gateway, deep flow was most likely west to east in both gateways provided the density of the Indian Ocean was relatively low, (2) the preclosure system was not very sensitive to freshwater and heat flux, (3) the response of the Mediterranean water properties and flow to gradual closure is nonlinear, (4) closure probably resulted in cooling and a rise of salinity and residence time of the Mediterranean Sea if evaporation exceeded freshwater input, and (5) multiple equilibrium states are possible (i.e., different surface and deep flow for the same value of freshwater flux) in the case of two gateways. In addition, we tentatively propose a best-fit scenario for the history of closure, linking the available data and our model results