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Into The Seas
And Oceans |
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The early flush of spring melt water
from the land generates a surge of cold water from the land surrounding
the Arctic Ocean. Annually about 4000 cubic kilometers of water
flows from the rivers. This is only about 2% of the water coming
into the Ocean from the Atlantic and, to a much lesser extent, from
the Bering Sea, but it is a high proportion compared with other
oceans. It carries with it nutrients and sediment ground from the
rocks by the glaciers. The coarser sediments are deposited as the
flow rate decreases, especially over flat ground, but enormous amounts
of fine silt are transported to the estuaries and seas. |
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The Yenisey River passes about 6 million
tonnes of sediment into the shallow Kara Sea each year, carried
by the 600 cubic kilometers of water. In contrast, the Mackenzie
River brings 7x more sediment to the Beaufort Sea although the water
volume is only about half that of the Yenisey. The reason for the
difference is that the Yenisey crosses flat frozen tundra while
the catchment of the Mackenzie is shorter, steeper, with less permafrost
and much exposed soil and rock. (see figure
11). |
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The estuaries and deltas act as a major sediment trap, followed
by the extensive continental shelf which extends up to 900km off
Siberia. (see figure 12). Only 10-20%
of particles from the Ob and.
Yenisey Rivers are transported beyond the borders of the deltas
and the Kara Sea shelf. The Mackenzie Delta accumulates several
centimeters of sediment through the year. Some of the sediment
flows over the sea ice in spring, later it extends as a plume
into the sea and flocculation continues the deposition process.
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The shape of the sea bottom, distance
from shore, and ice cover determine the physical characteristics
and processes over the continental shelf (see
figure 13a and figure 13b). The water
from the rivers and from sea ice cools the sea water over the shelf
but the summer sun raises the shallow water temperatures up to 4-5°C
in summer. The surface waters and the sea ice circulate in the Beaufort
Gyre and generally move westwards from the eastern Arctic towards
the Fram Strait where they exit into the North Atlantic. |
Sea ice extent in September and March and the major surface currents
governing the transport of sea ice. The numbered lines show the
expected time in years for the ice at that location to exit the
Arctic Ocean through the Fram Strait. |
It takes only 5-6 years for sea ice to move from the Chukchi
Sea off Alaska to the Fram Strait although the general pattern
masks many more localised movements (see
figure 13). The warm waters influence temperatures on land
and one useful consequences of the circulation pattern is that
the temperature on Iceland is similar to that on Svalbard - but
delayed by about 2 years!
As the cool surface water (near 0°C) with low salinity exits
the Fram Strait it meets and overlaps with the warm (3.5- 6°C)
water from the Atlantic. The warm water brings heat from the southern
oceans of the World and is responsible for the Gulf Stream. It
is the reason that Svalbard, Iceland and Western Europe have warmer
climates than comparable latitudes in North America and Russia.
As this warm, salty water reaches the Arctic and meets the cool
waters escaping through the Fram Strait it becomes denser as it
cools and sinks to deeper layers. This is a slow process but every
winter several million cubic kilometers of water sink to deeper
layers and move south on the bottom of the Atlantic. This is the
'Ocean Conveyer Belt' - the thermohaline circulation - that moves
heat around the globe.
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