Closure of the Panama Seaway during the Pliocene: implications for climate and Northern Hemisphere glaciation

Abstract

The ''Panama Hypothesis'' states that the gradual closure of the Panama Seaway, between 13 million years ago (13 Ma) and 2.6 Ma, led to decreased mixing of Atlantic and Pacific water Masses, the formation of North Atlantic Deep water and strengthening of the Atlantic thermohaline circulation, increased temperatures and evaporation in the North Atlantic, increased precipitation in Northern Hemisphere (NH) high latitudes, culminating in the intensification of Northern Hemisphere Glaciation (NHG) during the Pliocene, 3.2-2.7 Ma. Here we test this hypothesis using a fully coupled, fully dynamic oceanatmosphere general circulation model (GCM) with boundary conditions specific to the Pliocene, and a high resolution dynamic ice sheet model. We carry out two GCM simulations with ''closed'' and ''open'' Panama Seaways, and use the simulated climatologies to force the ice sheet model. We find that the models support the ''Panama Hypothesis'' in as much as the closure of the seaway results in a more intense Atlantic thermohaline circulation, enhanced precipitation over Greenland and North America, and ultimately larger ice sheets. However, the volume difference between the ice sheets in the ''closed'' and ''open'' configurations is small, equivalent to about 5 cm of sea level. We conclude that although the closure of the Panama Seaway may have slightly enhanced or advanced the onset of NHG, it was not a major forcing mechanism. Future work must fully couple the ice sheet model and GCM, and investigate the role of orbital and CO 2 effects in controlling NHG.

The emergence of modern sea ice cover in the Arctic Ocean

“…54). That the closure and associated enhanced MOC is unable to produce large-scale ice sheets in numerical models 55 may be owing to the use of similar to modern boundary conditions (gateways and orography) for the Pliocene. However, adjusting the models for orographic changes over Greenland, and the exposed landmasses of northern Eurasia above a threshold for glacial ice accumulation and massive winter sea ice coverage since ca.…”

Modelling global-scale climate impacts of the late Miocene Messinian Salinity Crisis

“…Details of the PRISM2 Pliocene HadCM3 model setup and modifications to this configuration to include an open CAS are given by Haywood and Valdes (2004) and Lunt et al (2008), respectively. (Note that Lunt et al, 2008, present their findings in the chronological framework of the CAS closing through time.…”

“…Therefore, one change made to the model configuration of Haywood and Valdes (2004) was to open the CAS, as per Lunt et al (2008).…”

Fossil proxies of near-shore sea surface temperatures and seasonality from the late Neogene Antarctic shelf

“…Although many circumstances could have caused cooling between the early and late Pliocene (e.g. Sjunneskog and Winter 2012), it has been shown that the closure of the Panama Seaway during the Pliocene would cool the western Ross Sea region by up to 2°C (Lunt et al 2008). …”