Case Study: Miocene Tectonics, the Gulf Stream, Runaway Global Cooling and Sea Level Change

Post-Miocene Climate Change: Was Tectonics and the Panamanian Isthmus Responsible for Global Cooling in the Plio-Pliestocene Interval?

As mentioned, tectonism creates substantial changes in the ways that oceans circulate, and, hence the way that heat and moisture is exchanged between low and high-latitude areas. With the development of the Isthmus of Panama between North and South America, the Pacific-Atlantic equatorial seaway no longer connected the two oceans. Warm water, instead of flowing into the Pacific from the Caribbean and Atlantic, flowed northward and formed the Gulf Stream. Therefore, there was no Gulf Stream before the Pliocene like there is today. The Gulf Stream is responsible for the relatively warm (but generally moist) climates of northwestern Europe (i.e., the British Isles).

In Figure 4.25, notice the red and orange-colored (warm) surface waters that flow from the Gulf of Mexico toward the northeastern part of the Atlantic Ocean. Prior to the development of the isthmus, water exchanged freely between the Pacific and Atlantic Oceans. This kept Caribbean waters a bit cooler than they are today, and North Atlantic Ocean waters were also cooler, so little atmospheric moisture could contribute to glacial ice development. With closure of the isthmus, residence time of waters in the Caribbean and Gulf of Mexico increased, and waters are now warmed significantly more than they were prior to the land bridge being established between North and South America.

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Figure 4.25: Emanating from the Gulf of Mexico, the Gulf Stream, pictured here in red, moves northward along the southeastern coast of the United States and begins to flow northeasterly across the Atlantic Ocean where it eventually reaches the coast of northern Europe.

Credit: NASA Visible Earth: RO: Data are from May 8, 2000 taken from the Terra MODIS satellite

As a result, hyper-warming of water in the Gulf of Mexico produces warm water currents that carry energy out of the Gulf of Mexico and into the Atlantic. These warm surface waters (as shown in Figure 4.25), are extremely fast flowing and carry significant quantities of heat northward from the equator. These currents produce water vapor that is released into the atmosphere as it travels. In the North Atlantic, it can cool and can contribute to dense fog and various forms of precipitation, including snowfall. When the snow falls on land, or sea-ice, the white, snow-covered surface reflects incoming solar radiation (insolation) and results in intensified albedo impacts.

In Europe, between 30 and 60 degrees north, winds from the west, aka the "westerlies" blow water vapor into highlands in the Alps, across Scandinavia, and other areas of Europe where large alpine glaciers developed after moist air masses cooled and precipitation occurred.

In the polar easterlies zone north of 60 degrees latitude, winds blew across the remnants of the Gulf Stream and water vapor was moved westward (as today) across Iceland, Greenland, and Arctic Canada where still larger continental ice sheets developed.

Collectively, as most of the Earth's landmasses are located in the northern hemisphere, the sum total of glacial ice in Europe, Iceland, Greenland, and Arctic Canada helped to initiate increased rates of albedo as insolation was reflected back into the atmosphere. The result was runaway cooling during the Plio-Pleistocene precipitation events, which led to successive cooling and sea level fall. This is shown in the data in Figure 4.24 on the previous page.

Geoscientists refer to these additive or compounding impacts as positive feedback systems. In this case, a positive feedback loop was initiated when initial snow fall contributed to cooler and cooler climates, which produced more snowfall, more albedo, cooler climates, etc. Likely, the process initiated in the Pliocene, but maximum extent of ice (and significantly lower sea levels) didn't occur until the Pleistocene. In systems terminology, this time delay is known as a lag time.

If you don't yet know, the Pleistocene is known for significant development of glacial ice sheets, including the large Laurentide Ice Sheet that advanced and retreated several times producing many of the features of the North American landscape, including the Great Lakes; the Finger Lakes of central New York; Long Island, New York; Cape Cod; the Hudson River Canyon; erosional scenery of the western U.S.; the great fjords of Scandinavia; and more. The end result was therefore lower and lower sea levels as water was locked up more and more on land in the form of glacial ice.

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