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a Salinity (in parts per thousand, %) is defined as 1.80655 times the chlorinity (in parts per thousand, %), where chlorinity represents the concentration of chloride and other halogen ions (i.e., bromine, iodine, and fluorine). Adapted from Thurman (1978).

a Salinity (in parts per thousand, %) is defined as 1.80655 times the chlorinity (in parts per thousand, %), where chlorinity represents the concentration of chloride and other halogen ions (i.e., bromine, iodine, and fluorine). Adapted from Thurman (1978).

How does Antarctica influence global climate conditions through the oceans and atmosphere?

Around Antarctica, surface water masses are the coldest in the ocean, with temperatures approaching -2°C. Antarctica also has a relatively narrow and deep continental shelf, which further facilitates the exchange of water masses between the sea surface and deep sea (Fig. 7.8). Together these oceanographic features enable extremely cold dense water masses to sink into the deep sea from the Weddell and Ross Sea basins—forming Antarctic Bottom Water as the primary source of the abyssal circulation in the ocean.

As we move northward between 60° and 50° south latitude, sea surface temperatures sharply warm 2 to 3°C. In this region, Antarctic Surface Waters down-well with warmer Sub-Antarctic Surface Water to form the Antarctic Convergence (Fig. 7.8). These surface water masses produce Antarctic IntermediateWater, which can be recognized throughout much of the ocean as a tongue of relatively low salinity and high oxygen content at around 1500 meters depth. This Antarctic Polar Front Zone is the northern boundary of the Antarctic marine ecosystem (Chapter 9: Living Planet).

Sea-surface temperatures suddenly increase an additional 4°C around 40° south latitude, with consequent downwelling at the Subtropical Convergence. This Sub-Antarctic Front Zone is the northern boundary of the Southern Ocean.

Between the Antarctic Intermediate Water and Antarctic Bottom Water, there is a relatively warm and salty water mass that originates in the North Atlantic. Sinking of this dense North Atlantic Deep Water, primarily in the Norwegian Sea region, is influenced by cooling and evaporation of warm Gulf Stream surface waters flowing northward from the tropics. Arriving in the Antarctic region—long after

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