Investigating wind-driven surface currents in the Rheic Ocean through modelling

Abstract

The Rheic Ocean was one of the most important oceans of the Paleozoic, evidenced by remnants that can be found across present-day Central America, North America, Europe, and Northern Africa. Its closure led to the formation of Pangea and has been attributed to the abrupt change in climate and mass extinctions that occurred at the end of the Devonian. Although geological evidence of the shallow environments of the Rheic Ocean can be found at its former margin edges, subduction of the ocean and subsequent destruction of its lithosphere leaves no direct evidence of its deep-sea environment. Inferences of the mid-Paleozoic oceanic surface circulation within the Rheic Ocean have thus far been made through the application of general oceanic theory in schematic reconstructions. This study was aimed at testing several published schematic reconstructions through numerical modelling, thereby increasing the understanding of the Rheic Ocean surface circulation. A numerical ocean model was constructing with the Princeton Ocean Model (POM). An additional aim of this study involved determining whether the model could be used to infer the position of peri-Gondwanan terranes and the paleoposition of Gondwana in the mid-Paleozoic. Experiments were carried out to test various aspects of three known controls on surface circulation, namely the paleogeography, wind stress, and Coriolis force. The experiments showed that the model was sensitive to wind stress, throughflow and bathymetry in particular. The resulting circulation patterns justify the depiction of certain oceanographic phenomena in the schematic reconstructions, such as a Western Boundary Current (WBC) and gyres. Higher velocities gave some indication of the position of Gondwana as well as the peri-Gondwanan terranes. The sensitivity of the model to bathymetry, however, makes it difficult to make directly correlate terrane orientation and Gondwanan paleoposition to an increase in velocity. We propose the model be further improved by expanding it to a three-dimensional model and by refining the bathymetry. This can be achieved by focusing on smaller basins and obtaining a more detailed bathymetry from published research. Another option would be to use the knowledge obtained in this study in combination with an approximated tectonic model to create a global circulation model. This global model could then be used to gain a better understanding of the dynamics between ocean closure, climate change and extinction that took place in the Devonian.