- Pacific Deep Water
In physical oceanography, a water mass type
found in the Pacific Ocean in the depth range
from 1000-3000 m. It does not participate much in the overall
circulation and as such its properties are determined mostly by
slow mixing processes. It is composed of a mixture of
AABW, NADW and
AAIW, and has a characteristic salinity
from 34.60-34.65 and a temperature around 2 deg. C.
See Tomczak and Godfrey (1994), p. 159.
- Pacific Equatorial Water
In physical oceanography, the water mass that
occupies the largest volume of the Pacific thermocline waters.
The NPEW and the SPEW are
two varieties of this separated, as one might guess, by the Equator.
They differ in T-S properties above 8 deg. C but merge into a single
curve below this, which reaches T-S combinations showing high salinities
indicative of mixing with deep water.
See Tomczak and Godfrey (1994).
- Pacific High
A center of action centered off the
coast of Baja, California at about 30 deg. N and 140 deg. W in winter.
It moves northwestward to about 40 deg. N and 150 deg. W and intensifies
in the summer and effectively fills in the Aleutian Low.
See Angell and Korshover (1974).
Acronym for PanAmerican Climate Studies, a proposed program in the
1995-2004 time frame directed toward the goal of improving the skill
of operational seasonal-to-interannual climate prediction (with
emphasis on precipitation) over the Americas. It is a sequel to
the NOAA EPOCS program. Further
information can be found at the
PACS Web site.
the retention of ancestral juvenile characters by
descendant adults. Paedomorphosis is if the rate of shape change
is reduced or the period of operation is contracted such that
a descendant adult passes through fewer growth changes and as
such resembles a juvenile stage of its ancestor.
This can occur by progenesis,
neoteny, or post-displacement.
This was coined by W. Garstang in the 1920s
as part of the reaction to the Biogenetic Law
when he recognized that ontogeny did not always recapitulate
phylogeny but sometimes created it. The Biogenetic Law has been
somewhat superseded by the concept of
Both processes are now
recognized to play important roles in evolution. See
Gould (1977) and McKinney and McNamara (1991).
Acronym for Past Global Changes, an
IGBP Core Project charged with providing
a quantitative understanding of the Earth's past environment
and defining the envelope of natural climate variability within
which we can assess anthropogenic impact on the Earth's biosphere,
geosphere, and atmosphere. PAGES seeks the integration and
intercomparison of ice, ocean, and terrestrial paleorecords and
encourages the creation of consistent analytical and database
methodologies within the paleosciences.
More information can be found at the
PAGES Web site.
Acronym for Paleoclimate of Arctic Lakes and Estuaries, an
NSF/ARCSS and PAGES initiative to study the
paleoclimate of arctic lakes and estuaries. The goal is to reconstruct
Arctic climate variations over the past 150,000, 20,000 and 2,000 years
and understand its interation with the global climate. More
information can be found at the
PALE Web site.
The study of the spatial distribution of ancient organisms, including
analysis of the ecological and historical factors governing this
distribution. In contrast to paleoecology,
most paleobiogeographical studies have dealt with distributions of
individual taxa or with questions of global or
regional provincialism. See Briggs and Crowther (1990), pp. 452-460.
The science dealing with the fields of evolution, ecology and
the subsequent taphonomy of extinct
animals and plants. See Briggs and Crowther (1990).
- paleocalibration method
A method for calculating the relationship between paleoclimates and
the future climate. For a given time interval, one obtains both
the difference from present-day globally averaged surface temperature
(DT) and the difference from the present-day globally averaged radiative
forcing (DQ). DT is obtained from whatever geologic proxies
are available. DQ is obtained by calculating or estimating the
total effect of the heat trapped by greenhouse gases and the changes
in absorption of solar radiation due to changes in solar luminosity,
surface albedo and atmospheric aerosol content. Finally, the ratio
DT/DQ is defined as the climate sensitivity, i.e. the global
temperature response to the radiative forcing.
See Covey et al. (1996).
The first of five epochs in
the Tertiary period, lasting from 66.4 to 57.8 Ma.
It is preceded by the Late epoch of the Cretaceous
period and followed by the Eocene epoch.
The branch of science that
deals with the ecology of extinct and fossil plants and animals.
A time interval of the
Cenozoic era, lasting from 66.4 to 23.7 Ma
and incorporating the Paleocene (66.4-57.8 Ma), Eocene (57.8-36.6 Ma),
and Oligocene (36.6-23.7 Ma) epochs.
If the Tertiary is designated as an era, then the
Paleogene and the Neogene are its two
The branch of science that
deals with discovering and analyzing biological patterns in the
history of lineages and biotas over long periods of time, as well
as their relationship to their environments and chronology of
The branch of paleontology dealing with cataloging and illustrating
pathological conditions. Paleopathological indicators includes
such things as shell injury and repair, evidence of parasitic
worm infections, regenerated arms, and dwarfism. See
Moodie (1923) and Tasnadi-Kubacska (1962).
A buried soil horizon of the geologic past.
See Sellwood and Price (1994).
The use of various paleoclimate proxy data
to attempt to gauge paleotemperatures.
A wind of the geological past. The practical geological indicators
of paleowind are several scalar properties (bed thickness, grain size
and sorting, mineral proportions) and directional structures
(dune forms, yardangs
and wind furrows, dune cross-bedding,
windblown trees, wind ripples, adhesion ripples, flues and grooves).
Such an indicator can be an effective paleoclimatic tool only if
it is reasonably common, of high geological preservation potential,
easily recognized and measured, and capable of unique or at least
statistical interpretation. See Allen (1994).
The earliest of three eras of the
Phanerozoic eon, lasting from 570 to 245 Ma.
It is preceded by the Precambrian interval
and followed by the Mesozoic era, and consists of
the Cambrian, Ordovician,
A name given in Argentina and Uruguay to a severe storm of wind,
sometimes accompanied by rain, thunder and lightning.
Acronym for Peroxyacetyl Nitrate.
A supercontinent that existed
from about 200 to 300 Ma
before breaking up into
two smaller supercontinents called
This term was coined by Alfred Wegener.
The Early Mesozoic world ocean.
It was a single ocean reaching from pole to pole, probably
consisting of single southern and northern gyres, deep water
formation at both poles, and slothlike deep-water circulation.
See Bowen (1991).
Abbreviation for Photosynthetically Available Radiation,
a quantity used in studies of photosynthesis as a measure of
total available light. It is defined as a flux of quanta
rather than energy and is usually considered to be the
total photon flux between 400 and 700 nm (with the lower
limit sometimes moved to 350 nm). This is around
38% of the total extraterrestrial solar irradiance.
PAR is defined, as a function of depth, by
where is Avagadro's constant, h is Planck's
constant, c the speed of light, the wavelength,
and E the irradiance. The units
of PAR are einsteins
per square meter per second, and it is
measured underwater using a device called
a quantum meter.
- parameter aggregation
An averaging procedure used in some
SVAT models wherein the value of
a parameter, e.g. the albedo, in a grid box is calculated
by linearly averaging (although the averaging can be more
the range of albedo exhibited by various
plant and soil types within the box.
This is necessitated by the spatial inhomegenity of
the land surface characteristics within individual
grid boxes. Contrast with
See Houghton and Filho (1995).
In numerical modeling, the method of incorporating a process by
representation as a simplified function of some other fully resolved
variables without explicitly considering the details of the
process. The classic example is the representation of
sub-grid scale turbulence as the product of a function of the
velocities at the local grid points and an empirically derived
coefficient (in analogy to the molecular viscosity
coefficient). This analogy has been known to fail. See, for
example, the classic (and wonderfully titled)
monograph of Starr (1968).
Acronym for Paleoclimate in the Southern Hemisphere, an
to investigate the paleoclimates of the Southern Hemisphere.
Its main scope is to correlate Africa, South America and
Planetary Boundary Layer,
a generic term for either OBL or ABL.
These layers are fundamentally turbulent and extend from near the
surface to the boundary layer depth, a limit to which boundary layer
eddies can penetrate in the vertical.
This is a collection of programs that deal with data pertaining to
the PBL. See the
PBL-LIB Web site.
In meteorological and climate modeling, an Abbreviation for
Abbreviation for principal component analysis, usually used
synonymously with EOF.
Abbreviation for Pacific Climate Information System, a comprehensive
information system containing statistical information on rainfall
clmiatology and variation with the ENSO cycle for almost 300 Pacific
islands. See the
PCIS Web site.
Abbreviation for the Program for Climate Model Diagnosis and
Intercomparison, whose mission is to develop improved methods
and tools for the diagnosis, validation and intercomparison of
global climate models. See the
PCMDI Web site.
The equilibrium partial pressure of CO2.
Abbreviation for the Planetary Coral Reef Foundation, whose aim is
to further knowledge about the world's coral reefs by studying
reefs in a global context, to provide new ideas for ecological
management of marine wilderness areas, and to provide hands-on
experience in expeditions and coral reef research. See the
PCRF Web site.
probability density function.
Abbreviation for Precision Depth Recorder.
Abbreviation for the Palmer drought severity index, an index used
for assessment of long-term drought conditions in the U.S. It
categorizes moisture conditions in increasing order of intensity
as near normal, mild to moderate, severe, or extreme for
drought or wetness. It is affected by both long-term moisture
shortages and excesses and by variability of temperature-driven
evaporation from soils and transpiration from plants. Similar
climate indexes are the CEI and the
See Karl (1986).
See Pacific Deep Water.
Abbreviation for primitive equations.
Acronym for Pacific ENSO Applications Center,
a NOAA project established to conduct
research and produce information products on climate variability
related to the ENSO climate cycle in the U.S.-affiliated
PEAC Web site.
A current profiling system.
Acronym for the Pacific Equatorial Dynamics Experiment.
An unconsolidated deposit of semi-carbonized plant remains in
a water saturated environment. It has a persistently high moisture
content (at least 75%) and is considered an early stage in the
development of coal. Its carbon content is about 60% and
it forms via plant decomposition in stagnant water with
small amounts of oxygen.
A wetland that accumulates more than 30 cm (40 cm in Canada) of highly
organic peat. These originate in two major ways: by the filling in
of shallow water bodies and their invasion by semiaquatic peat-forming
plants, or by the swamping and waterlogging (paludification) of
unsaturated mineral soils in upland situations, with the latter
being areally more important than the former.
See Gorham (1995).
- Peclet number
A dimensionless number expressing the ratio of
advection to thermal diffusion.
It is expressed by
where U is a velocity scale, L a horizontal length scale,
Molecular diffusion of heat is negligible when .
In practice, the Peclet number is almost always large except for
extremely small-scale phenomena with low velocities.
This is similar to the Reynolds number
except that the kinematic viscosity
has been replaced by the
thermal diffusivity .
See Kraus and Businger (1994), p. 32.
The soil-bearing or solid portion of the Earth's surface.
Descriptive of organisms that inhabit open water, as opposed
In heterochrony, this is the process
whereby if the rate of shape change of an organism is increased,
or its period of operation is extended, the descendant adult
passes morphologically beyond the ancestor.
This can occur by hypermorphosis,
The concept of peramorphosis somewhat
equates and supersedes the Biogenetic Law.
Compare to paedomorphosis.
See Briggs and Crowther (1990), pp. 111-119.
- percolation zone
One of five glacier zones defined
in terms of the ice temperature and the amount of melting.
This is a zone in which some surface melting occurs, which
can percolate a short distance into lower layers before it
refreezes. If it encounters an impermeable layer it will
spread laterally and freeze into an ice layer or lens.
Vertical water channels can also freeze into pipe-like
structures called ice glands. The latent heat released by
the refreezing process raises successively deeper snow layers
to the melting point, and there exists a point where, by the
end of the present summer, all the snow deposited since the
end of the previous summer has been raised to the melting
temperature. This is called the saturation line and forms
the boundary between this zone and the lower
soaked zone. The upper limit
to the percolation zone, which separates it from the
dry snow zone, is called the
dry snow line.
The nearest point to Earth in the orbit of a satellite, artificial
The climatic and geomorphological zone peripheral to the ice sheets
and glaciers at high latitudes, and occupying nonglacial environments
at high latitudes.
The point in a satellite's orbit at which it is nearest to the Sun.
- peristaltic pumping velocity
See eddy-induced transport velocity.
- permanent thermocline
A relatively sharp change in temperature (and therefore density)
beneath the seasonal thermocline
maintained by a balance between downward diffusion of heat and
the gradual upwelling of deep, cool water.
The final period of the
Paleozoic era, lasting from 286 to 245 Ma.
It precedes the Triassic period of
the Mesozoic era and
follows the Carboniferous period, and is
comprised of the Early (286-258 Ma) and Late (258-245 Ma) epochs.
It is named from the province of Perm in Russia and characterized
by vulcanicity, an on-going mountain-building movement called
the Variscan (Appalachian in North America), and the end of
the Southern Hemisphere glaciation.
- Peru Current
A component of the eastern limb of the
counterclockwise-flowing southern subtropical
gyre in the Pacific Ocean. The flow rate has been estimated
at around 15 Sv, although variations from this can be
considerable. This current is part of the most impressive
upwelling system in the oceans,
with the upwelling driven by prevailing winds from the east
that push the surface water westward, allowing the cold, nutrient-rich
water beneath to well to the surface. Without the upwelling, this
current lowers the temperatures along South America several
degrees belows the zonal average, and the upwelling serves to
lower the temperatures without about 100 km of the coast another
2 to 4 deg. C. The nutrient content of the upwelled water makes
this region the most productive upwelling region in the world
ocean, although a combination of overfishing and the effects of
the El Nino phenomenon put an end to
what was the largest fishery in the world before 1973.
The southern part of the Peru Current is sometimes called the
Chile Current, and both were originally known as the
See Tomczak and Godfrey (1994).
- Peterson grab
A type of bottom sampler used in biological oceanography to
for the quantitative investigation of
benthic organisms in relatively
shallow waters. It comprises a set of heavy hinged jaws
that are held open during descent but are released when
the device hits bottom. The jaws close on an area of
benthic material (usually around 0.1 m2) when the cable
is drawn tight and the device returned to the surface.
The organisms thus caught are screened from the bottom
sediments, classifed and counted to develop statistics for
organisms per square meter in the study area.
See Sverdrup et al. (1942).
Polar Frontal Zone.
Descriptive of a heterotrophic
phytoplankton species that feeds
on phytoplankton or detritus.
An eon comprising the whole of geologic
time since the end of the Precambrian
era, as opposed to Cryptozoic before that.
It is comprised of the Paleozoic,
Mesozoic, and Cenozoic eras and
represented by rocks in which the evidence for life is abundant.
It means ``obvious life''.
Abbreviation for the Palmer Hydrological Drought Index, a drought
index designed using the principles of balance between moisture
supply and demand.
See Rind et al. (1990).
One of two major types of dendrograms,
a tree-like diagram used to show similarity (or otherwise)
among specimens or groups of specimens. It is based only
on similarities in phenotypes.
The study of cyclic and seasonal
natural phenomena, especially in relation to climate and plant and
animal life. Phenological data would refer to phenomena such as
flowering times of trees, harvest times, and migration dates of
biota. Not to be confused with the slightly knottier science
- photic zone
See euphotic zone.
The process in plants by which carbon dioxide
is converted into organic compounds using the energy of light
absorbed by chlorophyll, which in all plants except some bacteria
involves the production of oxygen from water.
The movement of a motile organism
in response to stimulation by a light source. It is called
negative phototaxis when it moves away from and positive phototaxis
when it moves toward the source.
a phytoplankton species that lives
primarily by photosynthesis.
In biology, the evolutionary development of a species or other group
of organisms through a succession of forms. This can also refer to
the evolutionary development of a particular feature of any organism.
Compare to ontogeny.
See also Biogenetic Law.
- physical oceanography
The study of physical conditions and physical processes within the
ocean, especially the motions and physical properties of the ocean.
This is usually further divided into the activities of
descriptive and theoretical oceanography, the former being
concerned with observing the oceans to prepare
maps of the spatial and temporal variations of its properties,
and the latter with constructing theoretical models to attempt
to explain the observations. As in most natural sciences, most
significant advances are the result of the interaction between
theory and observation.
Physical oceanography is not a pure but an applied science in which
the knowledge of many disciplines is relevant,
e.g. fluid mechanics,
optics (optical oceanography),
acoustics (acoustical oceanography),
thermodynamics and, especially in the age of satellites,
This is one of four sub-fields into which the general field
has been divided, the others
A phytogeographic term used as
the unit of flora, i.e. a floristic unit. The plural
is phytochoria. The top phytochoric level or realm is that of
floral region, with floral province and flora district
following in the hierarchy.
See Collinson (1988).
The branch of biogeography dealing with
the geographic distribution of plants.
Free-floating microscopic plants which, having little mobility,
are distributed by ocean currents.
Most marine phytoplankton
are found in one of five Phyla:
See Riley and Chester (1971).
The study of plant communities.
See McIntosh (1978).
The second of two ages in the
Pliocene epoch (coincidental with the
Late Pliocene), lasting from 3.4 to 1.6 Ma. It is preceded by
the Zanclean age and followed by
the Calabrian age of the
Abbreviation for particulate inorganic carbon.
Abbreviation for North Pacific Marine Science Organization, whose
purpose is to promote and coordinate marine scientific research in
order to advance scientific knowledge of the living resources in
the North Pacific. It was founded in 1992 and the members now
include Canada, Japan, the People's Republic of China, the USA,
the Russian Federation and the Republic of Korea. This is sort
of a version of the ICES but for the
North Pacific rather than the North Atlantic.
PICES Web site.
Acronym for the Potsdam Institute for Climate Impact Research, whose
mission is to investigate the consequences of global climate change
as a paradigm for the unfolding fundamental crisis between the
ecosphere and humanity. More information can be found at the
PIK Web site.
Acronym for Project for Intercomparison of Landsurface Parameterization
Schemes, a joint research activity sponsored by GEWEX
and WGNE of WCRP project. See
Henderson-Sellers and Dickinson (1992),
Henderson-Sellers et al. (1993) and
Henderson-Sellers et al. (1995) as well as the
PILPS Web page for further information.
Abbreviation for Particulate Inorganic Matter.
- Piora oscillation
This refers to an advance of glaciers in Europe in the last 500 years
or so of the Atlantic period. It was
a sharper oscillation twards cold climate conditions than any for
several thousand years previously.
See Lamb (1985), p. 372.
Abbreviation for principal interaction patterns, a method of
reducing the complexity of a full covariance matrix by combining
an EOF-type pattern expansion in the spatial domain with an
ARMA-type dynamical modeling approach in the time domain.
This technique is useful for constructing simple dynamical
models for forecasting or diagnostic purposes and as an
approximate multivariate spectral compression technique.
See Hasselmann (1988) and Hasselmann (1993).
Acronym for Program for International Polar Oceans Research.
- piston velocity
The velocity with which gas diffuses across the air-sea interface
stagnant film model.
It is proportional to the molecular diffusivity of the gas in
sea water and inversely proportional to the thickness of the
stagnant film across which it travels.
The piston velocity has been found to be a function of the
Schmidt number, with different
dependencies at high and low wind speeds. The velocity
is also a function of wind speed, increasing
nonlinearly with wind speed and having a greater sensitivity to wind
changes at higher wind speeds, with the change in sensivity occurring
fairly abruptly at around 10 m/s. Due to the variability of real
winds and this variable sensitivity, the piston velocity at the
average wind speed will be lower than the average piston velocity.
The general functional form of the piston velocity is usually taken
where Sc is the Schmidt number and V the wind speed.
This is also occasionally known as the transfer velocity.
See Najjar (1991).
Abbrevation for the International Paleoclimate Database (Internationale
Palao Klima-Daten Bank, located at the Institut fur Botanik at
the Universitat Hohenheim in Stuttgart. See the
PKDB Web site (in German).
- Planck function
The amount of radiation emitted by a body at a given temperature
as a function of the wavelength of the radiation.
- plane-parallel assumption
An assumption made in the study of atmospheric radiation
transfer where variations in radiation
intensity and atmospheric parameters are permitted only in
the vertical direction, at least in localized areas.
Absorption and emission processes are symmetrical with
respect to the zenith angle when this assumption is made,
and consequently the intensity is a function of only
the vertical position and zenith angle.
See Liou (1992).
An assumption made when modeling the radiative effects of clouds
where the distribution of clouds is assumed to be uniform and infinite in the
horizontal rather than its actual patchy nature.
- planetary vorticity
An asteroid, comet or meteorite.
Small aquatic organisms (animals and plants) that, generally having no
locomotive organs, drift with water movements as opposed to
nekton. The animals in this category include
small crustaceans, and the larval stages of larger
organisms while plant forms are mainly diatoms.
- plant succession model
A model to designate the ways in which plant communities develop
from initial colonization to climax vegetation. The two main
types are conceptual and mathematical. The conceptual models
can be divided into four main types:
(1) initial floristic composition,
and (4) inhibition models.
The mathematical models are significantly more varied and
trusted slightly less.
See Collinson (1988).
The earliest epoch of the
Quaternary period, lasting from 1.6 Ma to
The final of five epochs in
the Tertiary period, lasting from 5.3 to 1.6 Ma.
It is preceded by the Miocene epoch
and followed by the Pleistocene epoch
of the Quaternary period.
Observational evidence shows this to be perhaps the last time when
global temperatures were significantly warmer than at present
These observations indicate that:
(1) global sea level was probably 20-30 m higher, implying
a significant reduction in the Antarctic ice sheet; (2) there
was a significant northward migration of the freezing line in
winter Thompson (1991),
and (3) tropical sea surface temperatures may have been
similar to present Dowsett et al. (1991).
Abbreviation for Pacific Marine Environmental Laboratory, a laboratory
under the auspices of NOAA that conducts scientific
investigations in physical oceanography, marine meteorology,
geochemistry, and related subjects. For more information see the
PMEL Web site.
Abbrevation of Palaeoclimate Model Inter-comparison Project, a