Biology Reference
In-Depth Information
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Determine past temperatures in tropical lowlands from the solubility
of noble gases (argon, helium, krypton, neon, radon, xenon) in radio-
metrically dated groundwater. The solubility of these stable and inert
gases varies with temperature, and amounts of He
in groundwater from
Brazil indicate temperatures were cooler by an unexpected 5°C at the Last
Glacial Maximum (LGM) at 21-18 kyr.
Trace precipitation patterns from the titanium content in marine basins.
As noted, titanium is a terrestrial mineral, so its abundance in an ocean
core is a function of precipitation. Sequences from offshore Venezuela
reveal wet and dry periods in the Amazon Basin during the Quaternary,
and some of these coincide with the rise and fall of the great ceremonial
centers in ancient Latin America.
Estimate changes in atmospheric CO
2
from stomatal density on the lower
surface of leaves. Stomata are openings that allow the intake of CO
2
for
photosynthesis and the outfl ow of water that constitutes the transpiration
stream emitted from vegetation. Their number varies with the amount of
CO
2
in the atmosphere (increasing stomata over time means decreasing
CO
2
). Since CO
2
is a greenhouse gas, relative changes in stomatal density
in sequences of fossil fl oras indicate trends in temperature through
time. The changes can be calibrated to actual temperatures by measur-
ing stomatal density from old to recent leaf collections at sites with long
meteorological records.
Estimate paleotemperatures from the percentage of entire-margined
leaves prominent in tropical environments compared to the lobate or
toothed-margined leaves of temperate environments. The percentage is
primarily a refl ection of MAT, while other features of leaf physiognomy
such as large size, thin texture, and drip tips correlate generally with
high MAP.
Track the migration patterns of seed-distributing birds from the occur-
rence of isotopes in their feathers. The abundance of
2
H (deuterium)
in rainfall has a characteristic geographic signal that is deposited in the
feathers. Most migratory birds grow new feathers before each migra-
tion, so the approximate latitudinal starting point can be determined
from the
2
H/normal H ratio. When this technique is applied to potential
seed-dispersing black-throated blue warblers (
Dendroica coerulescens
), for
example, it documents that “Warblers wintering in the western Caribbean
islands migrate from the northern United States, whereas those wintering
in the eastern Caribbean islands arrive from the southern United States”
(Hobson 2002; Rubenstein et al. 2002).
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