Geoscience Reference
In-Depth Information
Table 3.6
Examples of estimates of changes in climatic parameters in the southwestern USA, based on lake-basin studies. The
diversity in inferred climatic parameters for each basin illustrates the difficulties of estimating a quantitative value of climatic
change from geomorphic data.
Mean annual
Summer
Annual
Annual
temperature
temperature
precipitation
evaporation
Evaporation
(
◦
C)
(
◦
C)
Location
(mm)
(mm)
(%)
References
Lake Lahontan,
Nevada
+
840
34
Antevs (1952)
Lake Lahontan,
Nevada
−
5
−
5
+
270
−
410
30
Broecker and Orr
(1958)
Lake Lahontan,
Nevada
−
3
−
+
230
−
180
16
Mifflin and Wheat
(1979)
Lake Estancia,
New Mexico
−
6.5
−
9
+
180
−
380
34
Leopold (1951)
Lake Estancia,
New Mexico
−
8
−
8
−
40
−
250
42
Brackenridge (1978)
Lake Estancia,
New Mexico
−
10.5
−
1
−
46
−
510
45
Galloway (1970)
Spring Valley,
Nevada
−
−
7
+
210
−
330
30
Snyder and Langbein
(1962)
Spring Valley,
Nevada
−
8
−
8
0
−
480
43
Brackenridge (1978)
Lake high stands also have associated difficulties of in-
terpretation because increased rainfall and reduced evap-
oration can both contribute to a positive hydrological
balance (Smith and Street-Perrott, 1983; Bradley, 1985)
(see Table 3.6). Various hydrological-balance models have
been produced to try and resolve these issues (see Brack-
enridge, 1978; Street, 1979; Kutzbach, 1980; Bergner,
Trauth and Bookhagen, 2003; Duhnforth, Bergner and
Trauth, 2006). Additionally, beach ridges and terraces can
be constructed and removed at times of stable high lake
levels in response to increases or decreases in the rate
of sediment supply and wind/wave energy. In all cases,
additional biological and geochemical records from the
lake floor deposits can potentially help to resolve these
issues. Lake basins in drylands are, however, often devoid
of surface water for at least part of the year, subjecting
basin-floor sediments to aeolian deflation and highly ox-
idising conditions and resulting in a dearth of organic
preservation. This can render a high-precision multiproxy
approach, common to temperate and tropical lake investi-
gations highly problematic in arid zones.
In the Makgadikgadi Basin, Botswana, budgetary stud-
ies have shown that the highest palaeolake stage cannot be
accounted for in local climatological terms alone (Grove,
studies that have identified links between the palaeolake
and increased fluvial inputs from distant, more tropical,
sources (Shaw and Thomas, 1988; Burrough and Thomas,
2008; Burrough, Thomas and Bailey, 2009) (Figure 3.7).
Where fluvial inputs have clearly made substantial con-
tributions to high lake stages, but the palaeolake tribu-
taries are now dry, as in the case of Lake Bonneville,
it is extremely difficult to quantify their inputs in bud-
getary studies (Smith and Street-Perrott, 1983). This is
further complicated in very large basins such as the Lake
Eyre basin, megalake Chad and megalake Makgadikgadi,
where increases in the surface area of water during lake
high stands may have led to water recycling and signifi-
cantly altered local or regional rainfall patterns that may
have contributed to lake systems becoming partially self-
sustaining beyond the influence of their initial forcing
mechanisms (Coe and Bonan, 1997; Burrough, Thomas
and Singarayer, 2009).
A further complication is that investigations in the east-
ern Kalahari have indicated that some dry valley systems
have evolved through the influence of higher groundwa-
ter tables and spring sapping, with the magnitude of local
humidity increases necessary to account for their develop-
ment being less than once supposed (Shaw and De Vries,
