Impact of the Central American and the Indonesian seaways on the ocean circulation and oxygen minimum zone in the tropical Pacific

The tectonic change in geometry of two tropical seaways, the Central American Seaway (CAS) and Indonesian seaway, during the mid-Miocene to mid-Pliocene (~16-3 Ma BP) is thought as a key factor for the development of the present-day tropical Pacific oxygen minimum zone.

The aim of this study is to investigate the dual impact of sill depth changes in the Central American and the Indonesian seaways on the ocean circulation and oxygen minimum zone in the tropical Pacific. To this end, we performed a series of sensitivity experiments with the global climate model KCM where sill depths of both tropical seaways were set at different depths, ranging from shallow to deep levels.

Our results based on a separate effect of CAS changes support previous modelling studies showing that CAS closure have led to an intensification of the Atlantic Meridional Overturning Circulation due to a termination of fresh-water supply from the tropical Pacific to the North Atlantic. The open CAS increases meridional sea surface height gradient in the tropical Pacific which drives eastward subsurface flow in the region. This, in turn, facilitates stronger west-to-east oxygen supply and subsequent overall oxygen enrichment in the subsurface Pacific waters with strongest anomalies observed in the eastern tropical Pacific.

Another important task of this study is to investigate how various sill depths of the Indonesian seaway can additionally adjust an individual effect of open CAS-induced changes for ocean currents in the Pacific and the tropical Pacific oxygen minimum zone.