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The salinity of the North Atlantic Ocean and the next glaciation
QUATERNARY
RESEARCH
The
2, 399~~
Salinity
(1972)
of
the
North
Next
Atlantic
Ocean
and
the
Glaciation
PETER
K. WEYL
Received
June
’
10, 1972
A reduction in the surface salinity of the North Atlantic, by causing an extension of sea ice, could initiate the next Glacial period. Such a salinity reduction could be the result of a slight persistent change in surface pressure in the Caribbean area, that reduces the transfer of water vapor from the Atlantic to the Pacific across the Isthmus of Panama.
In a previous publication (Weyl, 1968), I suggested that the surface salinity of the North Atlantic Ocean, by controlling the extent of sea ice, can have a marked effect on the global climate. The purpose of the present note is to suggest how the salinitysea ice-climate mechanism could &ad to a termination of the present interglacial interval. For details and geological confirmation, the reader is referred to the previous publication (Weyl, 1968). The formation of sea ice in the Greenland-Norwegian Sea is primarily controlled by the vertical salinity distribution. In the west, the existence of a shallow layer of low salinity surface water leads to extensive sea ice formation. Toward the east, the sea water is essentially isohaline from the surface to the bottom and therefore thermal convection inhibits sea ice formation. Ice could not form until the entire water column has been cooled to the freezing point. In contrast, in the west, thermal convection is limted to the shallow layer of less saline water and therefore little cooling is required before sea ice formation commences. ___1 Marine Sciences Research Center, State versity of New York, Stony Brook 11790. Present address: The Hebrew University, salem, Israel.
UniJeru-
399 Copyright All rights
0 1972 by Academic Press, of reproduction in any form
Inc. reserved
If the advection of saline water from the south is reduced, the area of low surface salinity can expand, leading to an expansion of the sea ice. Expansion of sea ice will lead to cooling because of an increase in albedo and because the ice cover insulates the atmosphere from the water column and so inhibits the northward transport of heat by ocean currents. The cooling in the North Atlantic will have the tendency to expand the polar high pressure zone and push the Icelandic Low to the south. The southward displacement of the Icelandic Low alters the ocean circulation in the North Atlantic in such a way, as to reduce the northward advection of warm saline water from the extension of the Gulf Stream. If the Icelandic Low is pushed about 10” of latitude south of its present position, to a position comparable to the Aleutian Low in the North Pacific, the circulation in the North Atlantic is drastically altered to one like the North Pacific. This would result in formation of a North Atlantic Subarctic Gyre north of 40”N, having low surface salinity. By analogy with the Pacific. this would lead to a winter sea ice limit at about 60”N in the North Atlantic, resulting in extensive cooling due to the increased albedo and the lack of heat advection by ocean currents.
400
WEYL
Meteorological model studies are needed to determine if such an expansion of sea ice could lead to the pattern of glaciation recorded during the Pleistocene. To set the mechanism in motion requires a decrease in the surface salinity of the North Atlantic, which currently is significantly more saline than the North Pacific. Such a change could be brought about by reducing the transport of atmospheric moisture from the Atlantic to the Pacific. A significant portion of that transport is carried across the Isthmus of Panama and that transport has a large annual variation, being large in winter and small in summer. A persistent climatic change that resulted in a more summer-like pressure distribution over the Caribbean Sea would lead to reduced export of moisture from the Atlantic and so to a reduction in its surface salinity. A small atmospheric change in this region, if it persists for the order of a thousand years, could lead to a sufficient salinity reduction in the North Atlantic surface waters,
to initiate the mechanism proposed and so bring on the next glaciation. For details and references, the reader should consult the previous detailed paper (\Veyl, 1968). NOTE
BY EDITOR
The short article by Weyl is especially interesting in the context with the new findings from deep-sea cores in the North Atlantic and the Gulf of Mexico, reported in this volume by McIntyre and Ruddiman, Sancetta et al., and Kennett and Huddlestun, and with the fast drop in apparent temperatures in Greenland observed by Dansgaard et al. There should be mentioned perhaps, that the salinity decrease of North Atlantic could result not only from the reduced moisture transport to the Pacific, but from various other mechanismsas well, REFERENCE WEYL,
P. K. (1968).
The role of the oceans in
climatic change,a theory of the Ice Ages. Meteorological
Monographs
8, (No. 30) 37-62.
RESEARCH
The
2, 399~~
Salinity
(1972)
of
the
North
Next
Atlantic
Ocean
and
the
Glaciation
PETER
K. WEYL
Received
June
’
10, 1972
A reduction in the surface salinity of the North Atlantic, by causing an extension of sea ice, could initiate the next Glacial period. Such a salinity reduction could be the result of a slight persistent change in surface pressure in the Caribbean area, that reduces the transfer of water vapor from the Atlantic to the Pacific across the Isthmus of Panama.
In a previous publication (Weyl, 1968), I suggested that the surface salinity of the North Atlantic Ocean, by controlling the extent of sea ice, can have a marked effect on the global climate. The purpose of the present note is to suggest how the salinitysea ice-climate mechanism could &ad to a termination of the present interglacial interval. For details and geological confirmation, the reader is referred to the previous publication (Weyl, 1968). The formation of sea ice in the Greenland-Norwegian Sea is primarily controlled by the vertical salinity distribution. In the west, the existence of a shallow layer of low salinity surface water leads to extensive sea ice formation. Toward the east, the sea water is essentially isohaline from the surface to the bottom and therefore thermal convection inhibits sea ice formation. Ice could not form until the entire water column has been cooled to the freezing point. In contrast, in the west, thermal convection is limted to the shallow layer of less saline water and therefore little cooling is required before sea ice formation commences. ___1 Marine Sciences Research Center, State versity of New York, Stony Brook 11790. Present address: The Hebrew University, salem, Israel.
UniJeru-
399 Copyright All rights
0 1972 by Academic Press, of reproduction in any form
Inc. reserved
If the advection of saline water from the south is reduced, the area of low surface salinity can expand, leading to an expansion of the sea ice. Expansion of sea ice will lead to cooling because of an increase in albedo and because the ice cover insulates the atmosphere from the water column and so inhibits the northward transport of heat by ocean currents. The cooling in the North Atlantic will have the tendency to expand the polar high pressure zone and push the Icelandic Low to the south. The southward displacement of the Icelandic Low alters the ocean circulation in the North Atlantic in such a way, as to reduce the northward advection of warm saline water from the extension of the Gulf Stream. If the Icelandic Low is pushed about 10” of latitude south of its present position, to a position comparable to the Aleutian Low in the North Pacific, the circulation in the North Atlantic is drastically altered to one like the North Pacific. This would result in formation of a North Atlantic Subarctic Gyre north of 40”N, having low surface salinity. By analogy with the Pacific. this would lead to a winter sea ice limit at about 60”N in the North Atlantic, resulting in extensive cooling due to the increased albedo and the lack of heat advection by ocean currents.
400
WEYL
Meteorological model studies are needed to determine if such an expansion of sea ice could lead to the pattern of glaciation recorded during the Pleistocene. To set the mechanism in motion requires a decrease in the surface salinity of the North Atlantic, which currently is significantly more saline than the North Pacific. Such a change could be brought about by reducing the transport of atmospheric moisture from the Atlantic to the Pacific. A significant portion of that transport is carried across the Isthmus of Panama and that transport has a large annual variation, being large in winter and small in summer. A persistent climatic change that resulted in a more summer-like pressure distribution over the Caribbean Sea would lead to reduced export of moisture from the Atlantic and so to a reduction in its surface salinity. A small atmospheric change in this region, if it persists for the order of a thousand years, could lead to a sufficient salinity reduction in the North Atlantic surface waters,
to initiate the mechanism proposed and so bring on the next glaciation. For details and references, the reader should consult the previous detailed paper (\Veyl, 1968). NOTE
BY EDITOR
The short article by Weyl is especially interesting in the context with the new findings from deep-sea cores in the North Atlantic and the Gulf of Mexico, reported in this volume by McIntyre and Ruddiman, Sancetta et al., and Kennett and Huddlestun, and with the fast drop in apparent temperatures in Greenland observed by Dansgaard et al. There should be mentioned perhaps, that the salinity decrease of North Atlantic could result not only from the reduced moisture transport to the Pacific, but from various other mechanismsas well, REFERENCE WEYL,
P. K. (1968).
The role of the oceans in
climatic change,a theory of the Ice Ages. Meteorological
Monographs
8, (No. 30) 37-62.