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Leatherback turtles can easily maintain deep body temperatures at least 18 degrees higher than the ambient temperature of cold water (Frair et al., 1972). Some of the mechanisms that underly this amazing temperature differential are metabolic heat combined with a thick layer of subepidermal insulation, a large body mass which has high thermal inertia, and counter current heat exchangers in their front and rear flippers which heat cool venous blood entering the body so that the core can be kept warm.

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Most all birds and mammals have evolved counter current heat exchangers to help them retain body heat and generate a temperature differental between their core body and extremeties. Leatherbacks are one of the few species of reptile that have also adapted these circulatory capabilites, allowing it to be very successful in dispersing all over the world. In arctic waters that are approaching freezing, leatherbacks can contain the heat generated by their muscles and stabalize their deep body temperature at 20 degrees Celcius and above, even though the ends of their flippers are also approaching freezing. Counter current heat exchangers are able to create this striking temperature differential through cappilary beds that lie near the junction of the body in each of the flippers (Greer et al., 1973). These capillary beds which consist of a huge bundle of closely packed veins and arteries, are sometimes referred to as rete mirable or 'miraculous net'. Rete mirable make continuous heat exchange between the cool venous blood and the warm arterial blood very easy, because there is a lot of surface area for heat exchange to occur. Arteries bringing blood to the flippers break up over a very short distance into hundereds of smaller vessels, which are closely associated with hundereds of small veins. Histological sections of a leatherback flipper show that the average ratio of veins to arteries is 3 to 1, helping to increase the surface area that the arteries have to supply heat to the surrounding veins (Greer et al., 1973). Also, because the blood in veins and arteries is always moving in opposing directions, there is a constant heat gradient allowing the heat to continually move from the warm arteries to the cool veins before the blood is allowed to enter the body core.

Counter current heat exchangers are extremely affective in retaining heat and creating temperature gradients when the environment is cold, but they can also be used to offload heat to keep nesting leatherbacks from overheating (Frair et al., 1972). On the beach, leatherbacks heat up very quickly because they have very a lot of surface area exposed to the sun. To keep from overheating they can shunt blood away from their core and out toward their surface and extremeties allowing them to heat up and decrease radiative heat transfer from the environment (Frair et al., 1972). Using the convective properties of heat transfer, leatherbakcs can gently fan their flippers and offload a lot of heat to the surrounding environment to cool the blood in their flippers before it returns to their body core. Therefore, due to incredible circulatory adaptations and counter current heat exchangers, leatherbacks can essentially change the thickness of their insulating layer and efficeintly maintain their core body temperature regardless of environmental conditions.