160
C. N. Wold· G. J. Schwartz· C. Morrill
Southern Hemisphere summer occurs over southwest Africa where saline pans
and marginal marine sabkhas and salinas occur, and over western and central
Australia where all types of modern evaporites occur. All of the evaporites in Africa were predicted by the PFM driven by 12-month forcing (Fig. 4A).
The PFM for evaporites initialized for halite (S=385) presents a more focused
picture of E-P than when the model is initialized for gypsum. This is because it
takes more energy to evaporate a brine to the point where halite will start to precipitate than it does for gypsum. The result in the PFM prediction is that the geographic distribution of positive E-P contours will focus more on those regions
having the very highest (climatic) potential for evaporite formation (Fig. 5A).
The PFM for evaporites initialized for halite and run for the Northern Hemisphere summer (Fig. 5B) predicts a smaller region of potential evaporite formation than the PFM did when initialized for gypsum (Fig. 4B) and the pattern of
E-P contours more closely matches the observed evaporite distribution. Saline
lakes in west central North America (Nevada and Utah, USA) and on the Himalayan Plateau are not predicted, again due to incomplete resolution of mountain
ranges by the AGCM.
6
Discussion
The new database significantly expands the regions covered by GGHYDRO (Cogley 1991). This is primarily due to the different method that we used to compile
the new database. Cogley (1991) used a 1° x 1° overlay with 100 points within
each 1 ° x 1 ° grid cell. To calculate the percent coverage of salt, Cogley (1991)
counted only those features that were located directly below one of the 100
points. Thus, smaller salt-accumulating bodies that were located between adjacent points were not counted 0. G. Cogley 1995; pers. comm.). In the present
compilation, however, all salt -accumulating bodies that could be identified on
the 1:1,000,000 scale maps (AMS 1934-1965) were digitized. The result is a much
broader distribution of present-day evaporites (Fig. 1). The Cogley (1991) data
(Fig. 6) is primarily a subset of the new database.
To compare the new evaporite database (Fig. 1) with GGHYDRO (Fig. 6), we
plotted the SFLT field, and filtered the SLTW field to exclude coastal points and
oceans. The most notable locations where GGHYDRO indicated evaporites and
the new database did not, were in Brazil, South Africa, central North Africa, and
near the Black Sea. Some of the differences could be because SLTW, may refer to
any water that is more saline than freshwater, but is not necessarily precipitating
evaporites. The Brazilian locations between 15°N and 15°S latitude in Fig. 2 can
be thrown out because these are covered by the Amazon rainforest. There are a
few grid cells in South Africa, central North Africa and around the Black Sea
(Fig. 6) that were not included in the new database. We searched the AMS (19341965) maps for these locations, but found no indication of evaporites. Otherwise, the Cogley (1991) database representing salt fiats (SFLT) and salt water on
land (subset of SLTW) is a subset of the new database.
C. N. Wold· G. J. Schwartz· C. Morrill
Southern Hemisphere summer occurs over southwest Africa where saline pans
and marginal marine sabkhas and salinas occur, and over western and central
Australia where all types of modern evaporites occur. All of the evaporites in Africa were predicted by the PFM driven by 12-month forcing (Fig. 4A).
The PFM for evaporites initialized for halite (S=385) presents a more focused
picture of E-P than when the model is initialized for gypsum. This is because it
takes more energy to evaporate a brine to the point where halite will start to precipitate than it does for gypsum. The result in the PFM prediction is that the geographic distribution of positive E-P contours will focus more on those regions
having the very highest (climatic) potential for evaporite formation (Fig. 5A).
The PFM for evaporites initialized for halite and run for the Northern Hemisphere summer (Fig. 5B) predicts a smaller region of potential evaporite formation than the PFM did when initialized for gypsum (Fig. 4B) and the pattern of
E-P contours more closely matches the observed evaporite distribution. Saline
lakes in west central North America (Nevada and Utah, USA) and on the Himalayan Plateau are not predicted, again due to incomplete resolution of mountain
ranges by the AGCM.
6
Discussion
The new database significantly expands the regions covered by GGHYDRO (Cogley 1991). This is primarily due to the different method that we used to compile
the new database. Cogley (1991) used a 1° x 1° overlay with 100 points within
each 1 ° x 1 ° grid cell. To calculate the percent coverage of salt, Cogley (1991)
counted only those features that were located directly below one of the 100
points. Thus, smaller salt-accumulating bodies that were located between adjacent points were not counted 0. G. Cogley 1995; pers. comm.). In the present
compilation, however, all salt -accumulating bodies that could be identified on
the 1:1,000,000 scale maps (AMS 1934-1965) were digitized. The result is a much
broader distribution of present-day evaporites (Fig. 1). The Cogley (1991) data
(Fig. 6) is primarily a subset of the new database.
To compare the new evaporite database (Fig. 1) with GGHYDRO (Fig. 6), we
plotted the SFLT field, and filtered the SLTW field to exclude coastal points and
oceans. The most notable locations where GGHYDRO indicated evaporites and
the new database did not, were in Brazil, South Africa, central North Africa, and
near the Black Sea. Some of the differences could be because SLTW, may refer to
any water that is more saline than freshwater, but is not necessarily precipitating
evaporites. The Brazilian locations between 15°N and 15°S latitude in Fig. 2 can
be thrown out because these are covered by the Amazon rainforest. There are a
few grid cells in South Africa, central North Africa and around the Black Sea
(Fig. 6) that were not included in the new database. We searched the AMS (19341965) maps for these locations, but found no indication of evaporites. Otherwise, the Cogley (1991) database representing salt fiats (SFLT) and salt water on
land (subset of SLTW) is a subset of the new database.