Monday, September 3, 2012

The Rising of Panama—The Panama Passage Part II

Was the Isthmus of Panama once submerged and did the Pacific Ocean have a seaway through to the Atlantic Ocean?

A Central American Seaway allowed for a warm, salty water inflow from the Caribbean to the Pacific, and a cool, low-salinity water outflow from the Pacific to the Caribbean

It is claimed by Manuel A. Iturralde-Vinent, of the National Museum of Natural History in Cuba, that in order to summarize the evolution of the Caribbean Seaway, this is presented to illustrate the history of topographic barriers between North and South America, and their bearing on the history of marine flow across the area. This Seaway is here understood as a truly oceanic basin located between the North and South American continental landmasses. This seaway represents a linkage between the Pacific and the Atlantic Oceans.
Also according to Michael Xavier Kirby, of the Center for Tropical Paleoecology and Archaeology, Smithsonian Tropical Research Institute, and Douglas S. Jones and Bruce J. MacFadden of the University of Florida, the palaeogeography of Central America has changed profoundly…from a volcanic arc separated from South America by a wide seaway, to an isthmus that connected North and South America. The formation of the Isthmus of Panama was important because it allowed the mixing of terrestrial faunas between the two continents, as well as physically separating a once continuous marine province into separate and distinct Pacific and Caribbean communities. The formation of the Isthmus of Panama also ultimately led to profound changes in global climate by strengthening the Gulf Stream and thermohaline downwelling in the North Atlantic.

And according to Daniela N. Schmidt of the Department of Geology, Royal Holloway University of London and Department of Earth Sciences, University of Bristol, in her work The closure history of the Central American seaway: evidence from isotopes and fossils to models and molecules, the rise of the Panama Isthmus was the last step in the closure of the circumtropical seaways. The closure of the Panama Isthmus had fundamental consequences for global ocean circulation, evolution of the tropical ecosystems and potentially influenced the switch to the modern ‘cold house’ climate mode. The Atlantic and Pacific marine ecosystems became gradually separated whereas terrestrial organisms suddenly had the means to migrate between North and South America. Combining high-resolution geochemical proxies for the closure history with data on fossil distributions and genetic data provides independent evidence on the closure history. These datasets provide new boundary conditions for Earth System models to simulate the effects of palaeoceanographic change on global climate and allow exploration of hypotheses for the Northern Hemisphere glaciation.

In addition, according to Hermann Duque-Caro, in his 1990 Stratigraphy paleoceanography and paleobiography in northwest South America in the evolution of the Panama Seaway, "Today, the Panama Isthmus blocks the flow of Pacific waters into the Atlantic. When this land bridge was submerged, Central America consisted of a complex island-arc  archipelago peninsula with several marine corridors and basins. During the initial uplift of the Panama sill to upper middle bathyal depths, and subsequent blocking of the deep-water flow through the seaway, changed bottom-water circulation and sedimentation in the coastal areas of Central America as discovered by the deep sea drilling mentioned in the last post.

Map of plate techtonics in the Caribbean Region. Their movement was responsible for the closing of the Central American Seaway

According to Matthew E. Kirby, Department of Geological Sciences, Cal State University, as part of the Central American volcanic arc, the Panama microplate formed through subduction of various oceanic microplates that lie between the Cocos and Nazca plates to the south, the Caribbean plate to the north and the South American plate to the east (note the tectonic plate map above).

The Atrato Seaway between the Pacific Ocean and the Atlantic Ocean through the Panama Canal Basin as described by Kirby and MacFadden, often referred to as the CAS (Central American Seaway), claimed by Duque-Caro to have been at least 500 feet deep

The closing of the Central American Seaway changed the boundary conditions of the oceans and created a state of the oceanic and atmospheric system. With the rising of the isthmus, it blocked the exchange of tropical water masses between the Atlantic and the Pacific and triggered, or strengthened, the North Atlantic deep water production, initiated the Caribbean Current, strengthened the Gulf Stream, and therefore changed the global distribution of deep water masses and heat salinity, which intensified the circulation causing the buildup of sediment drifts in the Caribbean and deepened the Barnes-Apure Basin in the basement of Guiana, along the northern Barinas-Apure Basin of Venezuela, and the Llanos Basin of Colombia, and later in the North Atlantic.

With the closing of the Central American Seaway, there was a cutoff of the inflow and outflow between the two oceans, and a strong northward flow of warm, salty water with more heat released out of the north into the atmosphere

The existence of this Atrato Seaway (Central American Seaway) did not, however, as these studies verify, change the water circulation in the South Pacific and along the South American west coast. Though it likely resulted in the central Pacific counter-current flowing into the Caribbean.

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