Page 394 - Earth's Climate Past and Future

370 GLOSSARY

North Atlantic drift A warm, multipart current flowing peatlands hypothesis The hypothesis that the increase in
northeastward into the high latitudes of the North Atlantic as methane levels between 5000 and 250 years ago was caused by
a continuation of the Gulf Stream. expanded areas of methane-producing bogs in north polar
North Atlantic Oscillation A fluctuation in subtropical and regions.
North Atlantic temperatures that persists for more than a year. perihelion The point in Earth’s slightly eccentric orbit at
which it is closest to the Sun.
ocean carbon pump hypothesis The hypothesis that changes period The time interval between successive peaks or
in the amount of organic carbon taken up by ocean plankton troughs in a series of regular wave forms.
during photosynthesis and exported to the deep ocean after they
peripheral forebulge A region in which the weight of glacial
die control CO levels in the surface ocean and atmosphere.
2 ice sheets caused bedrock to flow out to the ice margins
ocean crust A layer of rock averaging 7 km thick, having the at great depths and produced a broad upward bulge of the land.
average composition of basalt, and comprising the ocean floor.
permafrost A permanently frozen mixture of rocks and soil
ocean heat transport hypothesis The hypothesis that occurring in very cold regions.
changes in the amount of heat transported toward polar
phase lag The amount by which one cyclic signal lags behind
regions by the ocean cause changes in polar climate.
another signal of the same wavelength (or period).
oceanic gateway A narrow passage between continents that
photosynthesis The process by which plants use nutrients
opens or closes and thereby alters ocean circulation.
and solar energy to convert water and CO to plant tissue
orbital monsoon hypothesis The hypothesis that orbitally (carbohydrates) and thereby produce oxygen. 2
controlled changes in summer insolation at low latitudes drive
physical climate model A numerical model that simulates
the strength of the tropical summer monsoon.
Earth’s climate on the basis of physical principles of fluid motion
orbital tuning The process of constructing a time scale by and transfers of radiative heat energy and momentum.
using the link between astronomically dated changes in solar
physical weathering Any mechanical process by which rocks
radiation and the rhythmic climatic responses they cause on
are broken into smaller fragments of the same material.
Earth.
phytoplankton Small floating organisms (usually algae) that
orographic precipitation Precipitation on the upwind side of
use energy from the Sun and nutrients from the water for the
a mountain or plateau caused by the forced ascent of warm air to
process of photosynthesis.
cooler elevations,where the entrained water vapor condenses.
plane of the ecliptic The plane within which Earth revolves
outwash Layered sediments deposited by meltwater streams
around the Sun.
emerging from a glacier.
planktic foraminifera Sand-sized organisms (protozoans) that
overkill hypothesis The hypothesis that the sudden extinc-
live in ocean surface waters and form shells made of CaCO .
tion of many mammals 12,500 years ago resulted from human 3
hunting rather than climatic stress. plankton Organisms that float in the upper layers of oceans
or lakes.
oxidation A chemical reaction in which electrons are lost
from an atom and its charge becomes more positive; also, the plate tectonics Tectonic interactions resulting from the
addition of oxygen to an element. movement of lithospheric plates.
ozone A triple molecule of oxygen (O ) formed by the colli- polar front A sharp boundary zone in a polar ocean between
3
sion of cosmic particles with normal (O ) oxygen. Ozone in the cold, low-salinity waters and warmer, saltier waters; similarly,
2
stratosphere blocks harmful ultraviolet radiation from the Sun. in the atmosphere, a sharp temperature boundary.
ozone hole A region centered over the Antarctic continent polar position hypothesis The hypothesis that ice sheets
in which ozone (O ) levels in the upper atmosphere (stratos- exist during intervals in Earth’s history when landmasses are
3
phere) drop to very low values in the spring. moved into polar regions by plate tectonic processes.
power spectrum A graphic display of the distribution of
Pacific Decadal Oscillation A fluctuation in tropical and power (the square of wave amplitude) against the period (or
North Pacific temperatures that persists for more than a year. frequency) of each cycle present in a signal.
paleomagnetism The study of patterns of ancient magnetism precessional index The mathematical product (esinv) of
recorded in rocks or sediment. Earth’s sine-wave motion (sinv) around the Sun and the
pandemics Diseases that kill many millions of people on sev- eccentricity of its orbit (e)
eral continents. precession of the ellipse The slow turning of Earth’s ellipti-
Pangaea The giant supercontinent that existed between 300 cal orbit in space.
and 175 Myr ago and consisted of all landmasses present on precession of the equinoxes The movement of the solstices
Earth. and equinoxes around Earth’s elliptical orbit over cycles of
parent isotope A radioactive isotope that naturally decays to 23,000 and 19,000 years.
a daughter isotope. preindustrial CO level The concentration of CO in the
2 2
peat A deposit of decayed carbon-rich plant remains in a wet- atmosphere (280 parts per million) that existed for several
land environment with little oxygen. thousand years before the Industrial Revolution.