Continental boundary currents

As in Eurasia, the southern boundary of the Tundra ecosystems in North America deviates considerably from strictly latitudinal direction. In Labrador, cooled by the cold current, and on the shores of cold Hudson Bay, the Tundra ecosystems penetrate south to 54° N. To the west of Hudson Bay, with the increasing continentality of the climate, the boundary between Tundra and Boreal Taiga Forest ecosystems is... 

Temperature and pressure both increase with depth in the Earth and control the composition and properties of the material present at various depths. The Earth comprises a number of layers, the boundaries between which are marked by relatively abrupt compositional and density changes (Fig. 1.1). The inner core is an iron-nickel alloy, which is solid under the prevailing pressure and temperature ranges. In contrast, the outer core is molten and comprises an iron alloy, the convection currents within which are believed to drive the Earth s magnetic field. The core-mantle boundary lies at c. 2900km depth and marks the transition to rocky material above. The mantle can be divided into upper and lower parts, although the boundary is quite a broad transitional zone (c.lOOCM-OOkm depth). It behaves in a plastic, ductile fashion and supports convection cells. The upper mantle layer from c.100 to 400 km depth is called the asthenosphere, and its convection system carries the drifting continental plates. 

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