Page 395 - Earth's Climate Past and Future

GLOSSARY 371

productivity The amount of organic matter synthesized by Scandinavian ice sheet An ice sheet that covered most of
organisms from inorganic substances per unit of area per unit Norway and Sweden as well as the northern part of Germany
of time. and France during orbital-scale glaciation cycles.
proglacial lake A short-lived lake that develops after the seafloor spreading The mechanism by which new seafloor is
retreat of an ice sheet in the bedrock depression left by the created at an ocean ridge as the adjacent plates move away
weight of the ice. from the ridge crest at a rate of centimeters per year.
sediment drift A lens-shaped pile of fine sediment (clay and
radiation Electromagnetic energy that drives Earth’s climate silt) picked up in a region where bottom currents move swiftly
system. Ultraviolet and visible radiation emitted by the Sun and then deposited in a region of the seafloor where currents
affect climate on Earth, which emits infrared back radiation to slow.
space. sensible heat Heat energy carried by water or air in a form that
radiative forcing The effect of greenhouse gases in trapping can be easily felt or sensed, rather than hidden in latent form.
(or blocking) solar radiation, expressed in the same units as sensitivity test A simulation run with a climate model in
those of solar energy: watts per square meter (W/m2). which one boundary condition is altered from the (modern)
radiocarbon dating Dating of relatively young carbon-bear- control case to test its effect on climate.
ing geologic materials by means of 14C, a radioactive isotope shortwave radiation Electromagnetic energy emitted by the
that decays with a half-life of 5700 years. Sun in visible and ultraviolet wavelengths that deliver heat to
radiolaria Sand-sized organisms that live in surface waters Earth’s climate system.
and form shells of opal (SiO ·H O).
2 2 silicate minerals Minerals rich in silicon and oxygen and
radiometric dating Determining the ages of rocks or sedi- accounting for most of the rocks in Earth’s crust and mantle.
ments by measuring the amount of naturally occurring radioac- sine wave A perfectly regular wave form in which successive
tive parent isotopes and their nonradioactive daughter products. peaks and troughs are evenly spaced, with each peak reaching
reconstruction A simulation run with a climate model by a value of +1 and each trough a value of –1.
altering of several boundary conditions in an effort to repro- sintering The process by which bubbles of air become sealed
duce a climate that existed at some time in the past. off and preserved as snow turns to ice at depths of 50 to 100 m
red beds Sediments or rocks with a red color caused by the within an ice sheet.
oxidation of iron (similar to rust). snowball Earth hypothesis The hypothesis that Earth was
regressions Relative motions of the ocean down and off the frozen even in the tropics sometime in the interval between
margins of the land. 850 and 550 Myr ago.
reservoir A place of residence for an element or isotope solstices The times during Earth’s yearly revolution around
that moves in a cycle. the Sun when the days are longest (summer solstice) and
shortest (winter solstice).
residence time The average amount of time a tracer of any
substance spends in a reservoir. southern oscillation Naturally occurring fluctuations in
which changes in lower atmospheric surface pressure in the
resolution The degree of detail detected in a climate signal far western Pacific, near northern Australia, are opposite in
by sampling at a particular interval.
sense to those in the south-central Pacific, near Tahiti.
resonant response A strong cyclic response of the climate specific heat The amount of heat required to raise the tem-
system to perturbations occurring at the same or other cycles.
perature of 1 gram of a substance by 1°C.
response Any change in the climate system caused by a
spectral analysis A numerical technique for detecting and
change in climate forcing.
quantifying the distribution of regular (periodic) behavior in a
response time The time required for a climatic response to complex signal.
move a defined fraction of the way from its existing value to speleothems Cave deposits made of CaCO containing cli-
the value it would hold at its full equilibrium response. 3
matic signals.
Sporer sunspot minimum An interval between 1460 and
salinity A measure of the salt content of seawater in parts per 1550 A.D. when very few sunspots were observed on the Sun’s
thousand (‰).
surface.
salt rejection The salt left in seawater when sea ice forms on
stratosphere The stable layer of the atmosphere lying
the ocean.
between 10 and 50 km above Earth’s surface and containing
sapropels Black organic-rich muds deposited on the most of Earth’s ozone.
Mediterranean seafloor as a result of strong inflow from the subduction The slow downward sinking of an ocean plate
Nile River, which stifles delivery of oxygen to the deep parts beneath a continent or an island arc as a result of plate tec-
of the basin. tonic processes.
saturation vapor density The maximum amount of water sulfate aerosols Fine particles produced in the atmosphere
vapor that air can hold at a given temperature. from SO gas emitted by volcanoes or by industrial smoke-
2
savanna A semi-arid region of grasses and scattered trees. stacks. These particles can block incoming solar radiation.