Isthmus of Tehuantepec

The Isthmus of Tehuantepec, a region located in the south of Mexico, is the narrowest area between the Atlantic and Pacific oceans in the whole country. Only 220 kilometers separate the two oceans between the gulfs of Mexico and Tehuantepec. During the first half of the sixteenth century, it seemed as if nature could not withstand the strenuous effort of the Spanish conquistadores to find, within the tropics, a strait connecting the two oceans.[4] This meant that in the conquest explorations during the sixteenth century, this region was used as an interoceanic passage. The exploration of this region between the ‘North Sea’ and the ‘South Sea’ was, since the conquest of Mesoamerica, a fixed idea of the Spanish monarchy and its representatives. Carlos V made this project one of the priority missions of the explorers whose objective was to put the kingdom of New Spain in communication with that of Peru.[5] Hernán Cortés, in 1520, used this route to transport equipment and supplies across the isthmus from the Gulf of Mexico to his shipyard located on the Pacific coast, near the town of Santo Domingo de Tehuantepec. The advantage lay in the ability to make a good part of the journey by river.[6] Approximately two-thirds of the Isthmus is crossed by the Coatzacoalcos River, which is navigable for approximately 200 kilometers. Cortés saw this river as a means of fluvial communication across the Isthmus itself. During the last third of the sixteenth century, Spanish expeditions arrived at the port of Veracruz, in the Gulf of Mexico, and from there they moved by boat to the mouth of the Coatzacoalcos River. The material necessary to build ships (supplies and tools or provisions) in the shipyards located along the Pacific coast, together with the artillery, were loaded into shallow canoes to navigate upstream, and subsequently transported, on the backs of the indigenous people, from the sources of the Coatzacoalcos River to the Pacific coast, in the Gulf of Tehuantepec.1 Many of these expeditions later moved along the coast to the port of Acapulco, from where they sailed along the western coast of North America, and then set off westwards, seeking a passage to the Philippines and southern China. The advantages of this itinerary would lead to the proposal, as early as the sixteenth century, of an interoceanic canal. However, a series of difficulties caused the most feasible option, Panama, to eclipse Tehuantepec as an interoceanic passage.[7]

Location of the Province of Coatzacoalcos in a modern satellite image. This indicates the settlements of Coatzacoalcos and Tehuantepec, where Gali also made a map for the Relaciónes Geográficas. Image prepared by Morato-Moreno, M.

The Isthmus of Tehuantepec, a valley otherwise surrounded by montane habitats, has also been noted as an important biogeographical barrier among montane taxa, such as Mexican birds.[8][9] Population diversification has been observed among not only avian fauna, but other organisms as well, including toads[10] and the Central American river turtle.[11] As a result, the Isthmus presents a case of allopatric speciation wherein a geographic divide gives rise to population divergence and a significant decrease in gene flow.

The predominant climates in the region are tropical savanna (primarily in the south) and tropical monsoon (primarily in the north). There are also small central areas with a temperate climate due to elevation. The annual rainfall on the Atlantic or northern slope is 3,960 mm (156 in) and the maximum temperature about 35 °C (95 °F) in the shade. The Pacific slope has a light rainfall and dryer climate.[1]

External image
Oaxaca Wind Resource Map

The narrowness of the isthmus, and the gap in the Sierra Madre, allow the trade winds from the Gulf of Mexico to blow through to the Pacific. Normally, these winds are not particularly strong, but periodically, a surge of denser air originating from the North American continent will send strong winds through the Chivela Pass and out over the Gulf of Tehuantepec on the Pacific coast. This wind is known as the Tehuano. The region has one of the best wind resources in Mexico, with several wind farms.[12][13]

The cuisine of the region is based upon traditional foods and ingredients. Dishes may range from simple to elaborate; most dishes incorporate maize and moles. Common items include tamales made with iguana, chicken, beef or armadillo; guetabingui (fried balls of rice and shrimp); garnachas topped with dried queso Oaxaca; and pozol, a maize-based drink.[15][16]

The Tehuantepec railway (now the Ferrocarril Transístmico ("Trans-Isthmic Railroad")), is 308 km (191 mi) long, running from the port of Coatzacoalcos on the Gulf of Mexico to Salina Cruz in Oaxaca on the Pacific coast, with a branch of 29 km (18 mi) between Juile and San Juan Evangelista. The minimum depth at low water in both ports is 10 m (33 ft). An extensive system of quays and railway tracks at both terminals affords ample facilities for the expeditious handling of heavy cargoes. The general offices and repair shops of the original Tehuantepec Railway were located at Rincón Antonio, at the entrance to the Chivela Pass.[1] At Santa Lucrecia, 175 km (109 mi) from Salina Cruz, connection was made with the Veracruz & Pacific Railway, 343 km (213 mi) to Córdoba, Veracruz, and 500 km (310 mi) to Mexico City. Those connecting lines are now owned and operated by Ferrosur, a company that also operates along the Ferroistmo-owned Tuehantepec line.

Several proposals have been made for modernizing the inter-ocean rail connection.[20] In 2019, as part of the Isthmus of Tehuantepec Development Plan, a project has been taking place since June of that year to create a communication like between the Pacific and Atlantic Oceans through the Tehuantepec Railway and the ports of Salina Cruz and Coatzacoalcos, known as the Interoceanic Corridor of the Isthmus of Tehuantepec.[26] Recent reports state that this corridor will be fully operational by December 2023.[27]