Evolution of the tropical Pacific oxygen minimum zone during the Miocene-Pliocene from model simulations: A role of the Panama Isthmus closure 

Abstract

<p>The world’s largest oxygen minimum zone (OMZ) resides in the eastern tropical Pacific where a poor oceanic ventilation and high biological production are both favourable for ocean oxygen deficiency in this area. The modern continental configuration with the Panamanian isthmus prevents the Pacific-Atlantic water mass exchange, shaping the climate and marine biogeochemistry features in this region. Therefore, a tectonic transition from the open to closed Central American Seaway (CAS) during the middle Miocene to middle Pliocene (~16-3 Ma BP) can be considered as a key time interval for the development of the tropical Pacific OMZ. This study aims at investigating an impact of the Pliocene CAS closure on a large-scale ocean circulation and its role for emergence of the modern tropical Pacific OMZ. To this end, we employ the global climate model KCM in combination with biogeochemical model PISCES.</p> <p>According to our experiments, the Pliocene CAS closure has led to a termination of fresh-water supply from the Pacific to the North Atlantic and therefore to intensification of Atlantic Meridional Overturning Circulation. This result is supported by many previous modelling studies. It was also found that the open CAS is associated with large-scale eastward subsurface flow in the eastern tropical Pacific thereby enhancing water mass ventilation in this area. This, in turn, leads to an increase in marine oxygen concentration in the eastern tropical Pacific during the Miocene.</p> <p>A biological production is another important factor affecting the OMZ maintenance. Here we show that the CAS opening is associated with the export of nutrients from the Pacific towards the Atlantic. This, in turn, leads to a reduced net primary production (NPP) in the eastern tropical Pacific and, therefore, to lower oxygen consumption in this region. Both altered NPP and ocean ventilation contribute effectively to the OMZ development in the eastern tropical Pacific for the modern continental configuration.</p>