Digital Database of Modern Evaporites and their Predicted Distribution Based on Results...
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and was 11.3° in the Northern Hemisphere and 7° in the Southern Hemisphere.
The mean latitude of Northern Hemisphere evaporites is 3.4° north of 30° Nand
the Southern Hemisphere evaporites are 2.4° north of300S latitude. The fact that
these are not centered on 30° latitude probably reflects the annual average northward shift of the meteorological "thermal" equator (e.g. Barry and Chorley
1992).
It is apparent from any map of the Earth, that the majority of present -day land
area is in the Northern Hemisphere. This is shown graphically in Fig. 3B. The
distribution of land area explains to a first approximation, the larger observed
area of evaporites in the Northern Hemisphere (Fig. 3A). When we divide the
area covered by evaporites by the total land area, we can plot the percent of total
land area covered by evaporites (Fig. 3C). This suggests that if the land were
more evenly distributed between the Northern and Southern Hemispheres, then
the evaporites would also be more evenly distributed.
At the latitudes where evaporites occur, they typically occupy about 1 % of the
land area (Fig. 3C). In the Southern Hemisphere evaporites reach more than 1 %
of land area near 40°,30°, and 20 0 S latitude. In the Northern Hemisphere evaporites peak over 1 % at ISO, 2So, 3So, 40°, and 46°N latitude. The differences between the left and right sides of Fig. 3C are due to differences in climate, the
land-sea distribution, and the availability of closed drainage basins or land areas
with no surface runoff.
The majority of Phanerozoic evaporites were formed in basins along continental margins with restricted marine connections. Examples include the Late
Miocene Mediterranean, Aptian South Atlantic, Jurassic Gulf of Mexico and
North Atlantic, Permian Zechstein, and Silurian Michigan Basins. It is interesting to note that based on the geologic record, the present-day evaporites most
likely to be preserved millions of years from now are the marginal marine salinas
and sabkhas and that these are centered near 30 0 N and 30 0 S latitude (Fig. 1D).
Although the marginal marine evaporites (Fig. 1D) represent a very small portion of modern evaporites (Fig. 1A), they do closely approximate the mean latitudes (33SN and 27.6°S) of evaporite distribution at the present time.
4
The GENESIS AGCM
The GENESIS (Global ENvironmental and Ecological Simulation of Interactive
Systems) version 2.0 AGCM was developed at the National Center for Atmospheric Research (NCAR; Pollard and Thompson 1995; Thompson and Pollard
1995a; b). GENESIS (2.0) includes an AGCM derived from GENESIS version
1.02b that was a highly modified version of the NCAR Community Climate Model version 1 (CCMI). The AGCM includes a diurnal cycle with solar-radiation
calculations every 1.S h and uses multi-layer randomly overlapped clouds. The
infrared radiative effects of CO 2 , CH 4 , N 2 0, and chlorofluorocarbons are all
treated explicitly. The AGCM resolutions are a horizontal grid of 3.7S0 x 3.7So,
and 18 levels in the vertical. GENESIS (2.0) also has a Land-Surface-Transfer
155
and was 11.3° in the Northern Hemisphere and 7° in the Southern Hemisphere.
The mean latitude of Northern Hemisphere evaporites is 3.4° north of 30° Nand
the Southern Hemisphere evaporites are 2.4° north of300S latitude. The fact that
these are not centered on 30° latitude probably reflects the annual average northward shift of the meteorological "thermal" equator (e.g. Barry and Chorley
1992).
It is apparent from any map of the Earth, that the majority of present -day land
area is in the Northern Hemisphere. This is shown graphically in Fig. 3B. The
distribution of land area explains to a first approximation, the larger observed
area of evaporites in the Northern Hemisphere (Fig. 3A). When we divide the
area covered by evaporites by the total land area, we can plot the percent of total
land area covered by evaporites (Fig. 3C). This suggests that if the land were
more evenly distributed between the Northern and Southern Hemispheres, then
the evaporites would also be more evenly distributed.
At the latitudes where evaporites occur, they typically occupy about 1 % of the
land area (Fig. 3C). In the Southern Hemisphere evaporites reach more than 1 %
of land area near 40°,30°, and 20 0 S latitude. In the Northern Hemisphere evaporites peak over 1 % at ISO, 2So, 3So, 40°, and 46°N latitude. The differences between the left and right sides of Fig. 3C are due to differences in climate, the
land-sea distribution, and the availability of closed drainage basins or land areas
with no surface runoff.
The majority of Phanerozoic evaporites were formed in basins along continental margins with restricted marine connections. Examples include the Late
Miocene Mediterranean, Aptian South Atlantic, Jurassic Gulf of Mexico and
North Atlantic, Permian Zechstein, and Silurian Michigan Basins. It is interesting to note that based on the geologic record, the present-day evaporites most
likely to be preserved millions of years from now are the marginal marine salinas
and sabkhas and that these are centered near 30 0 N and 30 0 S latitude (Fig. 1D).
Although the marginal marine evaporites (Fig. 1D) represent a very small portion of modern evaporites (Fig. 1A), they do closely approximate the mean latitudes (33SN and 27.6°S) of evaporite distribution at the present time.
4
The GENESIS AGCM
The GENESIS (Global ENvironmental and Ecological Simulation of Interactive
Systems) version 2.0 AGCM was developed at the National Center for Atmospheric Research (NCAR; Pollard and Thompson 1995; Thompson and Pollard
1995a; b). GENESIS (2.0) includes an AGCM derived from GENESIS version
1.02b that was a highly modified version of the NCAR Community Climate Model version 1 (CCMI). The AGCM includes a diurnal cycle with solar-radiation
calculations every 1.S h and uses multi-layer randomly overlapped clouds. The
infrared radiative effects of CO 2 , CH 4 , N 2 0, and chlorofluorocarbons are all
treated explicitly. The AGCM resolutions are a horizontal grid of 3.7S0 x 3.7So,
and 18 levels in the vertical. GENESIS (2.0) also has a Land-Surface-Transfer