The Loop Current and Its Effect on the Gulf of Mexico - Assignment Example

Organization Conference December 14, 2005 The Loop Current and its Effect on the Gulf of Mexico When studying the various reasons why hurricanes are especially strong when they hit the coast within the Gulf of Mexico, it is necessary to understand the unique conditions that exist in and around that body of water. The gulf itself is bordered by the United States to the north (Florida, Alabama, Mississippi, Texas, Louisiana), five Mexican states (Tamaulipas, Veracruz, Tabasco, Campeche and Yucatan) to the west and Cuba to the south. According to Nipper, Chavez and Tunnell, the marine shoreline of the gulf “from Cape Sable, Florida to the tip of the Yucatan peninsula extends approximately 5,700 kilometers (3,541 miles), with another 380 kilometers (236 miles) of shore on the northwest tip of Cuba. If bays and other inland waters are included, the total shoreline increases to more than 27,000 kilometers (16,777 miles) in the United States alone” (Nipper, 2005). Further, the gulf has a surface area of approximately 1.5 million square kilometers that is affected by coastal winds and weather patterns. It holds 2,434,000 cubic kilometers, or 643 quadrillion gallons, of water, of which approximately 38 percent is comprised of shallow and intertidal areas, 22 percent is continental shelf, 20 percent is continental shelf and the remaining 20 percent is abyssal areas (Nipper, Chavez, Tunnell, 2005). Much of what happens in this area, both in and on the water as well as along the vast coastlines, is greatly affected by something called the Loop Current. This is a current that begins when the Caribbean Current merges with the North Equatorial Current just south of Cuba, becoming the Yucatan Current. This current then enters the Gulf of Mexico, forming the large looping action from which it received its name (Gyory, Mariano, Ryan., n.d.). The current is a clockwise, or anticyclonic, flow that extends northward into the Gulf of Mexico often as far north as the United States coastline. Eventually, the current joins with the Florida Current to exit the gulf, forming part of the Gulf Stream in the process. The Gulf Stream is one of the most powerful currents within the world’s oceans, transporting warm water from the Gulf of Mexico to western Europe and affecting climate there enough to make the landmasses there hospitable at latitudes that are not conducive to life further inland (Day, 1999). This major current typically travels approximately 2.5-4.5 miles per hour transporting about 30 billion gallons of water every second, a staggering number that surpasses that of all the rivers in all the world (Day, 1999). This velocity contributes to the strength of the Loop Current as it constantly demands feeding. As the Loop Current develops through its cycle, the current naturally forms large eddies within the gulf that spin in both anticyclonic and cyclonic directions depending upon when and where they are formed. These eddies further help to distribute warmer water to other portions of the gulf and function to create nutrient-rich upwellings that facilitate fishing and other industries. Although its exact position fluctuates with the season and other variables, the loop has been known to often reach as far north as the Mississippi Delta and the Florida continental shelf (Gyory, Mariano, Ryan., n.d.). It is the main circulation channel for the entire gulf and occupies a large role in the gulf’s ecology, fishing, offshore drilling industry, shipping and weather patterns of this region of the United States and Mexico. It is when the Loop Current is in its long phase, stretching from the Yucatan up into the gulf as far as the Mississippi that eddies begin to be formed. 1 2 3 Source: Nipper, Chavez, Tunnell, 2005 Much like the formation of oxbow lakes along inland riverways, eddies are created when the loop of the current is long and waters at the narrow neck of the loop begin to take the shortcut (figure 1), effectively cutting off the longer portion of the loop (figure 2). As shown in the example provided (figure 3), this remnant portion of the loop, still containing expendable energy and motion, closes together to form a circular eddy that normally rotates in the same clockwise, or anticyclonic, direction as it’s parent current. These areas of circular eddies, still rotating around a pocket of warm water, then drift westward toward the Mexican border and western portions of the United States border (Biggs, Wormuth, 1998). These spinning bubbles of warm water can continue to drift through the gulf for several months, affecting everything that happens within these waters, including oil drilling and fishing; therefore, sailors and rig operators must remain aware of these strong variable currents. Although the example shows the formation of only one eddy, at any given time, there can be several eddies circulating through the western gulf simultaneously, each at its own velocity, temperature, drift speed and depth. At the same time, counterclockwise, or cyclonic, eddies are formed in the eastern portion of the gulf, the largest being primarily around the area of the Florida Keys. According to the National Oceanic and Atmospheric Administration, there is a counterclockwise eddy just south of the Keys that is so persistent it is known as the Portales Gyre. Although it isn’t uncommon for people who work in and around the gulf to name the various eddies as they are formed, this one has proven so consistent as to find its way into the oceanography books on the subject. This eddy has also shown researchers how animal and plant life circulate within the gulf and provides them with the ways and means of measuring these societies for greater protection efforts (2005). Other cold water, counterclockwise eddies can be formed within the gulf when the loop meanders just slightly off the straight and narrow. If the current drifts slightly to the right of a cooler area and then back again, that loop can also be cut off in a spinning eddy of cold water in much the same way that the warm water eddies are formed. These eddies also tend to drift along with the warm water eddies toward the western portion of the gulf. Other cold water eddies are formed by the physical properties of water shear working along the outside edges of both the loop itself and the warm water eddies that it casts off. As the loop makes its way northward through the existing water patterns of the gulf, this existing water is dragged along with it for a ways. Like children riding on the outside edges of a merry-go-round, these colder waters tend to shear off when the loop makes any kind of meander in its path, often moving in the opposite direction at a much higher rate of speed than the water its entering. The force of this motion causes the sheared water to also close around itself, often encircling the colder waters of the gulf and rotating in a counterclockwise rotation as would be expected. Waters added to the gulf from surrounding rivers can also have an effect on the formation of cold water eddies as they interrupt or contribute to their natural circular motion. Whether the eddy is warm or cold, the fact that it spun from the deep Loop Current means it doesn’t operate only on the surface layers of the ocean. These eddies are subject to the same laws of nature as the larger gyres within the world’s oceans. As the warm water cools, it begins to sink further into the depths, gaining salinity as it goes. As the cooler water warms, it rises and loses salinity (Loop Current, 2005). Where the warm water is concentrated, the water level of that eddy rises, while the cooler water sinks below the surface level of the surrounding water, each creating observable ‘lakes’ within the confines of the Gulf of Mexico that can be measured and studied, anticipated and forecast for when they will begin to dissipate or potentially have an influence on weather patterns (Dorics, n.d.). This lateral movement in the water helps to facilitate the circulation of nutrients, plant life and animal life within the gulf waters, contributing to unique ecosystems on and around the gulf floor (National Oceanic and Atmospheric Administration, 2005). Eddies spun off from the great Gulf Stream itself, near the intersection with the Labrador Current have shown similar characteristics. In the case of the Gulf Stream, eddies formed on the north side of this intersection enclose the warm waters of the Sargasso Sea, that portion of the Atlantic Ocean that exists within the circular movements of the greater gyre (the big brother of an eddy) formed by the Gulf Stream, Canary Current and North Equatorial Current (Day, 1999). Eddies formed on the south side of the Gulf Stream rotate counterclockwise and contain the colder waters brought in by the Labrador Current. Because they exist on a larger, more stable scale, scientists have been able to discover several key characteristics of these eddies. According to Day (1999), the warm water eddies cast off by the Gulf Stream tend to dissipate relatively quickly and are re-absorbed by the quickly moving waters of the Gulf Stream. The cold water eddies, however, can remain in existence for several years. “In fact, cold-water eddies tend to draw nutrient-rich water from the depths so that productivity tends to be higher within such eddies” (Day, 1999). In addition to the lateral movement of the water within the eddies, additional water entering the gulf from the Mississippi and other rivers on the American continent contribute their portion of non-saline, usually cold water to the general mix. As the Mississippi in particular releases its load into the gulf, these waters begin to drift westward along the Louisiana coast toward Texas until it hits the Loop Current, at which point it is thrown back eastward in a current all its own known as the Texas Current, because this reversal in directions typically happens somewhere around the city of Corpus Christi in Texas (National Oceanic and Atmospheric Administration, 2005). This clearwater current contributes to the confusion of differing salinities, temperatures and flow directions already present in the gulf and possibly contributes to the formation of cold water eddies in the northern section. It also facilitates upwelling within the gulf, creating greater vertical mixing of the various temperatures of water already existing and forcing nutrients and planktonic individuals toward the surface, contributing to the rich diversity of life found in this unique environment. “Upwelling” is the term used to describe this type of vertical movement of cold, dense waters from the bottom of the ocean to the upper surfaces. Downwelling is its direct opposite being used to describe the way in which warm waters are forced to the lower layers of the body of water (Day, 1999). While upwelling serves to enrich the upper layers of the ocean, downwelling serves to bring these same nutrients and life forms to the bottom layers, therefore contributing to the formation of coral reefs such as the Meso-American Barrier Reef. As these pockets of warm and cold water become highly significant factors to consider when larger storms approach the gulf areas, scientists have worked to develop a means of predicting when the loop will shed a new eddy and how large the eddy might become. In recent studies conducted by Hyun-Chul Lee and Lie-Yauw Oey, oceanographers at Princeton University, using computer generated models, it was discovered that under average conditions of water temperature and salinity, with no interference from wind patterns or already existing eddies, the computer generated loop shed a new eddy every nine months (Perkins, 2003). While seasonal changes in temperature and salinity didn’t seem to have any effect on this phenomena, wind patterns brought the average down to a new eddy forming approximately every four to nine months, while existing eddies in the gulf increased the time between new eddy formation to as long as 15 months (Perkins, 2003). Another computer modeled study created by Jorge Zavala-Hidalgo, an oceanographer at Florida State University in Tallahassee, showed that large cold water eddies sometimes form in the northern portions of the gulf and function to hinder the northward expansion of the loop, thereby preventing it from creating warm water eddies. Instead, Zavala-Hidalgo claims the loop will be forced to continue to shear off several smaller cold-water eddies until the larger northern one dissipates (Perkins, 2003). Knowing the frequency of eddy formation can help weather forecasters better predict weather conditions for coastal regions by providing much needed clues as to water temperature-generated variabilities. Although colder water tends to stabilize weather patterns, warm water eddies have been proven to actually intensify the severity of storms coming into the gulf coast areas. Tropical storms or hurricanes passing over cold water eddies have a tendency to be reduced in intensity. In order to form, these types of storms depend on ocean water temperatures that are at least 80 degrees F to a depth of at least 164 feet below the surface (“Hurricanes”, n.d.). They also require a lot of warm, moist air in the upper levels of the atmosphere. Because cold water eddies bring colder water to the surface layers, storms such as these cannot pull more energy from the water itself and must sustain their own energy until they have returned again to warmer water. They are also bereft of the necessary warm, moist air required to maintain the circular movement that provides their intensity. Because tropical storms depend upon heat and warm water to form, colder temperatures and colder water tends to draw some of the energy away from them, thereby reducing the severity of the storm and decreasing the potential damaging effects (“Hurricanes”, n.d.). Therefore, cold water eddies created as shear eddies or as inverse loops in the Loop Current can serve to help the gulf coastal areas by significantly reducing the severity of storms entering the gulf during hurricane season. Examples of storms that have been reduced in scale upon entering the gulf include Francis in 2004 and Isadore in 2002. Francis existed as a hurricane while it was crossing over the Florida panhandle, but the effects of the landmass plus a cold water eddy encountered upon reaching the gulf guaranteed the storm’s loss of intensity by the time it re-entered Florida around the Pensacola area. Isadore, which only existed as a hurricane briefly when it made landfall in Cancun, was reduced again to a tropical storm upon its journey across the gulf to Louisiana, again perhaps because of an encounter with one of the cold water eddies as Zavala-Hidalgo describes. However, when these storms pass over the warm water eddies, which provide not only a swirling mass of warm water from which to draw, but warm and moist atmospheric conditions above, tropical storms can quickly escalate into major hurricanes causing uncountable damage to coastal regions. Because stronger storms have a tendency to pull water up from deep below the surface of the ocean, it isn’t only surface temperatures that have a factor, but the underlying water temperature. Because the Gulf Stream and its associated contributing currents like the Loop Current run abnormally deep, the warm water eddies of the Gulf of Mexico have high chances that the required warm water temperatures extend to much greater depths than might otherwise occur, ensuring these storms have ample supplies of energy on which to draw. There are several examples of intense hurricanes that increased in intensity as they crossed the gulf waters throughout storm history. Hurricane Camille in 1969 is the first such example to be directly attributed to the effects of warm water eddies thrown off by the Loop Current. This hurricane developed in a single day over the warm waters of the Caribbean and then traveled directly up the path of the Loop Current on its way to landfall in Mississippi. Throughout this journey, the storm continued to gain in intensity, becoming a category 5 storm by the time it reached the coast. This storm contained winds of up to 190 miles per hour, which is reported as possibly the highest winds ever recorded in a hurricane with its only rival being the recent Hurricane Katrina. Although the storm weakened in intensity upon landfall, it managed to bring record rainfall to areas east of Mississippi on its way to the Atlantic. Upon reaching the warm water of the Gulf Stream, it again increased in intensity to a tropical storm, but quickly died after encountering the colder water further from the coast. (Loop Current, 2005). The effects of the warm waters of the gulf on the formation of hurricanes are perhaps best illustrated, though, by the progress of Hurricane Allen in 1980. Another record-breaking hurricane, Allen also developed quickly into a category 5 hurricane as it moved through the Caribbean, only weakening in strength upon making landfall on the mountains of Haiti and Jamaica. It regained strength a second time upon its journey across the open water, directly over the warm, deep waters of the Loop Current between Cuba and the Yucatan Peninsula. It again weakened upon making land in Mexico, but again regained strength as it crossed over a warm water eddy in the Gulf of Mexico before landing a third time, this time just north of Brownsville, Texas (Loop Current, 2005). Even when the Loop Current isn’t affecting the intensity of hurricane-strength storms, it does have some affect on weather conditions for those areas of land that border it. Colder water mixed with warmer air produces fog and brings additional moisture to the surrounding lands while warmer water can create moist, tropical conditions for the islands and countries that are placed downwind of the gulf. Dry conditions on land can halt the spread of moisture into other areas of land, such as what occurred during the Texas drought of 1980 when the intensity of Hurricane Andrew was reduced upon meeting the desiccated winds that prevailed right up to the coast, but the warm eddies that were present in the gulf when Allen arrived helped propel the weakened storm through the atmospheric barrier and bring relief to the land. Finally, although the Loop Current and its complex system of eddies in the Gulf of Mexico can have profound impacts on the weather systems for the coastal and inland areas of the bordering land masses, it has also had an impact on the development of unique ocean features, providing a rich suboceanic landscape for those who would explore it. Divers off Cancun have discovered sport in “drift diving”, in which divers submerge into the up to 5 knot Loop Current itself and “drift” for long distances before resurfacing, always hoping their boat was able to keep track of them. The cycle of warm eddies and consistent flow of warm tropical waters has also contributed to the development of the Meso-American Barrier Reef System, largely touted as the second largest coral reef system in the world, following the Australian Great Barrier Reef. Because of its proximity to the Loop Current and the influences such proximity affords, it is believed this reef system displays the most diverse collection of underwater plants and animals available anywhere in the northern hemisphere (National Oceanic and Atmospheric Administration, 2005). Works Cited Biggs, Doug and Wormuth, John. “Spin Cycles.” Quarterdeck. May, 1998. Vol. 6, No. 1. Dorics, ENS Theodore G. “The Loop Current.” United States Navy. n.d. Accessed December 13, 2005 from Gyory, Joanna, Arthur Mariano and Edward Ryan. “The Loop Current.” Ocean Surface Currents. n.d. Accessed December 13, 2005 from . “Hurricanes and Tropical Cyclone Life Cycles.” n.d. Accessed December 14, 2005 from < http://meted.ucar.edu/hurrican/strike/text/htc_t3.htm> Loop Current. (2005, December 6). Wikipedia, The Free Encyclopedia. Accessed December 14, 2005 from National Oceanic and Atmospheric Administration. “Liquid Wind.” September 29, 2005. Accessed December 13, 2005 from Nipper, M. J.A. Sánchez Chávez, and J.W. Tunnell, Jr. Eds. “General Facts About the Gulf of Mexico”. GulfBase: Resource Database for Gulf of Mexico Research. 2005. World Wide Web electronic publication. Accessed December 13, 2005 from . Perkins, Sid. “Oceans Aswirl.” June 14, 2003. Science News. Vol. 163, No. 24, p. 375. Read More