Australia: The Land Where Time Began

A biography of the Australian continent 

Pacific Ocean

The Pacific Ocean is the world's largest ocean, there is a physical boundary to the north that is breached only by the shallow Bering Strait that is about 50 m deep and 82 km wide, that allows a small net flow from the Pacific Ocean north to the Arctic Ocean. The Pacific Ocean is at its widest at the equator with the result that the phenomena propagating in an east-west direction take much longer to cross from one side to the other than in any other ocean. Trenches and ridges rim the Pacific to the north and west, and as these structures are associated with volcanoes, the rim of the Pacific ibeing termed the "Ring of Fire". In the tropical South Pacific the East Pacific Rise, a spreading centre, is a major topographic feature that is part of the global mid-ocean ridge. Some exchange of water can take place between the deep waters either side of the ridge at fracture zones. The eastward Antarctic Circumpolar Current (ACC), is deflected where it meets the ridge.

There are more islands in the Pacific Ocean than any other ocean, most of which are in the western tropical regions. The Hawaiian Islands and the Emperor seamounts, an extension to the northwest of the Hawaiian Islands, have been formed as the Pacific oceanic plate passed across a hotspot, located east of the big island of Hawaii.

There are many marginal seas around the Pacific Ocean, most of which are along the western side. The seas in the North Pacific are the Bering Sea, the Okhotsk Sea, Sea of Japan, Yellow Sea, East China Sea, South China Sea, and in the east the Gulf of California. Marginal seas in the South Pacific are the Coral Sea, the Tasman Sea, as well as many named smaller distinct regions such as the Solomon Sea. The Ross Sea in the southern part of the South Pacific has an input into the bottom waters of the world ocean.

Of the 3 major oceans the The Pacific Ocean is the largest. In the subtropics, tropics and subpolar North Pacific it has a wind-driven circulation system that is well developed. The Pacific Ocean circulation transitions to the Southern Ocean in the south, connecting it to the other oceans. At low latitudes it also connects to the Indian Ocean through the Indonesian Archipelago via gaps between the islands. The very shallow Bering Strait connects it to the Arctic Ocean.

As a result of small differences between the net evaporation/precipitation it is the freshest of the 3 major oceans. The formation of deep water in the Pacific is inhibited by the freshness of the ocean water, intermediate water formation is also inhibited to some extent by the freshness in the Northern Pacific Ocean. The Pacific Ocean is one of the broad regions of deep upwelling where deep waters formed in the other oceans is brought to mid-depths and in some places even to the surface, when viewed on a global scale. Wind-forcing is the dominant effect in the North Pacific's upper ocean circulation as a result of the weakness of the thermohaline circulation.

The interannual climate mode, El Niņo-Southern Oscillation, ENSO,  is centred in the tropical Pacific. According to the authors1 much of the globe is impacted by ENSO through atmospheric "teleconnections". Also observed in the Pacific is important natural climate variability of quasi-decadal timescales.

  • Water is shunted through complicated paths in the Indonesian Archipelago from the tropical Pacific to the tropical Indian Ocean.
  • At the northern end of the Bering Sea water from the Pacific is connected to the Arctic Ocean as a small leakage across the very shallow Bering Strait, and eventually reaches the Atlantic Ocean.
  • The site of formation of the densest water in the North Pacific is the Okhotsk Sea in the northwestern Pacific. The densest water in the Pacific is only dense enough to be situated at intermediate depths, and it is less dense and its impact is smaller than deep water formed in the North Atlantic and Arctic Oceans, centres of formation of the deepest waters of the global ocean, including the Pacific.

Subtropical gyres in the Northern and Southern Hemispheres are part of the surface circulation of the Pacific Ocean. There is also a subpolar gyre in the North Pacific and in the far south, the Antarctic Circumpolar Current. The Kuroshio Current, the western boundary current of the North Pacific subtropical gyre and in the South Pacific the East Australian Current (EAC), the western boundary current of the subtropical gyre. The eastern boundary current of the North Pacific subtropical gyre is the California Current, and in the South Pacific the eastern boundary current of the subtropical gyre is the Peru Current. The Oyashio/East Kamchatka Current (EKC) is the western boundary current of the North Pacific subpolar gyre. There are also low latitude western boundary currents in the tropical circulation, the Mindanao Current and the New Guinea coastal undercurrent (NGCUC). The deep circulation in the Pacific consists of inflow from the Southern Ocean in the form of a Deep Western Boundary Current (DWBC) that flows along the deep plateaus and island chains from New Zealand to the north.

In the South Pacific much of the deep flow passes through the Samoan Passage to enter the deep tropical ocean. In the west deep flow crosses the equator and follows the deep trenches of the western boundary to the north, filling in the deep North pacific. The oldest deep waters in the world lie in the north-eastern Pacific which is the end of the deep water circulation.

The bottom waters that enter the Pacific upwell along the length of the ocean, though mostly in the South Pacific and tropics. The density of the water is modified by the diffusion downward of heat and freshwater, a relatively homogenous large volume of water, the Pacific Deep Water (PDW; or common water) is produced by the upwelling deep waters, that return to the Southern Ocean to join the Indian Deep Water, that was formed in a similar manner, and the North Atlantic Deep Water that was formed by a different mechanism. Upwelling of deep water to shallower layers also occurs in the Pacific Ocean, both intermediate and upper ocean layers, outflow occurring in all directions in different parts of these layers, such as through the Indonesian Archipelago to the In Indian Ocean, southwestward around Australia, north through the Bering Strait and to east through the Drake Passage.

Sources & Further reading

  1. Emery, William J., Pickard, George L., Tally, Lynne D., & Swift, James H., 2011, Descriptive Physical Oceanography, an Introduction, Academic Press.

Links

Website for source 1

 

Author: M. H. Monroe
Email:  admin@austhrutime.com
Last Updated 25/04/2012

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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading