In biology, the origin and development of the individual organism,
as opposed to phylogeny.
See also Biogenetic Law.
- Oort Cloud
A spherical zone surrounding and bound to the solar system between
20,000 and 100,000 AU from the Sun. It is hypothesized to contain
10**12 comets whose orbits, perturbed by passing
stars or molecular clouds, can occasionally reach to within
Jupiter's orbit. The existence of the Oort Cloud is a key
element of the Nemesis theory.
Acronym for Observatoire Permanent de l'Atlantique Tropical.
- Operation Cabot
A multiple-ship cruise to survey the Gulf Stream in 1950.
See Fuglister and Worthington (1951) and
- operator splitting
In numerical ocean circulation modeling this is a technique
for splitting the fast and slow dynamics into separate subproblems.
When the partial differential equations governing large-scale
ocean dynamics are discretized to achieve numerical solutions,
dynamical phenomena with many temporal and spatial scales are
usually included in the discretized equations. Most prominent
in discretizations of the
primitive equations are
external and internal gravity waves, where the characteristic
wave speeds are, respectively, 200 m/s and 1-2 m/s.
The size of the discrete time step used to integrate the
equations is limited by the fastest motion that has to be
resolved, in this case the external gravity waves. One way
to get around this limitation is to separate the fast and slow
motions into separate subproblems. The fast external motions are
essentially 2-D due to approximate independence from depth, which
leads to the common option of obtaining the 2-D velocity field
from a vertical average of the horizontal velocity field in the
original 3-D equations.
This procedure can give rise to computational instabilities
since the operator splitting method is inexact except for the
case of a linearized flow with a horizontal bottom and a
In this case one solution is exactly independent of depth and
the horizontal velocity field obtained
corresponds exactly to the vertically averaged velocity.
However, if any of the restrictions are relaxed the fast and
slow motions can be mixed by variable bottom topography or
nonlinearities and can result in numerical instabilities if
an explicit method with a long time step is used to advance
the slow motion component in time. See
Higdon and Bennett (1996).
A class of marine invertebrates in the phylum
The more than 1600 species of these are commonly
known as brittle stars.
Introduction to the Ophiuroidea
U.C. Museum of Paleontology.
In tidal mechanics,
that instant when the Earth-centered longitude of the Moon
differs from that of the Sun by 180 degrees. This is also
the time of the full moon and
of one of two monthly spring tides.
See also conjunction.
- optical depth
See optical thickness.
- optical oceanography
- optical thickness
A measure of the attenuation of solar radiation by the atmosphere
that allows the convenience of considering as a single unit the losses
due to scattering and
absorption processes. The greater
the thickness, the greater the attenuation of incoming
This is also referred to
as the optical depth.
Acronym for Ocean Prediction Through Observation, Modeling, and
Analysis, a program that consisted of a lengthy set of surveys
of the eddy field in the
See Rienecker et al. (1985).
Acronym for Organization of Persistent Upwelling Structures, a
program taking place in 1983 that studied the inner part of
a filament near Point Conception, California.
See Atkinson et al. (1986).
Abbreviation for an isopycnic ocean
circulation model developed and used
at the DKRZ.
- orbital elements
The six pieces of mathematical data needed to completely determine
a planet's orbit and its position in that orbit. These data are:
(1) longitude of the ascending node, (2)
inclination of the orbit, (3) longitude of
(4) semi-axis major, (5) eccentricity, (6) epoch, or date of planet's
passing perihelion. Analogous elements are used for satellites.
Acronym for Oceanographic Remotely Controlled Automaton, a diesel
powered semi-submersible designed to survey water depths from 10 to
300 meters. This instrument was designed for the cost effective
collection of hydrographic and oceanographic data.
ORCA Web site.
The second period of the
Paleozoic era, lasting from 505 to 438 Ma.
It precedes the Silurian period and
follows the Cambrian period, and is comprised of
the Early (505-478 Ma), Middle (478-458 Ma), and Late (458-438 Ma) epochs.
Named after the Ordovices, an ancient Celtic tribe in Central Wales.
Widespread volcanic activity and the vast mountain-building
movement known as the Caledonian Orogeny
took place during this era.
- organic matter pump
Then name given to the cycle of organic matter and nutrients in
the ocean. Since
exceeds respiration only in the
there is a net sink of CO2, phosphate and nitrate in the
euphotic zone and a net source in the
aphotic zone. Thus a downward
flux of organic matter and an upward flux of nutrients connects
the euphotic zone sink and the aphotic zone source of nutrients.
This has also been called the soft tissue pump, but the present
name was suggested in recognition of the possible role of dissolved
organic species in the transport cycle.
See Najjar (1991).
Abbreviation for Oak Ridge National Laboratory.
Mountain building when a belt of the Earth's crust is compressed by
lateral forces to form a chain of mountains.
Abbreviation for Ocean Surface Current Radar, a measuring system
that uses high frequency radio pulses to probe the ocean surface
to deduce near-surface currents. The shore-based system consists
of two units which are deployed several kilometers apart. Each
unit makes independent measurements of current speed along radials
emanating from its phased-array antennae system. The data are
then combined via UHF or telephone communication to produce
accurate vector currents, store them to disk, and display them
in near real time. Measurements can be made simultaneously at
up to 700 grid points at either 1 km or 250 m resolution. The
OSCR samples for about 10 minutes and then processes radar returns
for about 10 minutes to create a quasi-synoptic surface current
map every 20 minutes.
OSCR Web site.
Abbreviation for Intergovernmental Committee for Ocean Science
and Living Resources, an IOC committee.
Acronym for Ocean Thermal Energy Conversion, the use of the
temperature difference between surface and deep sea water to
generate electric power. This is done by taking a working
fluid with a low boiling point, turning it to vapor by heating
it up or depressurizing it, and then using the pressure of
the expanding vapor to turn a turbine. The liquid used may
be either the sea water or ammonia. The OTEC is called
open-cycle if the ocean water itself functions as the
refrigerant, transferring heat energy by changing between
the liquid and gaseous phases. It is called closed-cycle
if ammonia is used.
The idea was first propounded by a French engineer named
Jacques D'Arsonval in 1881, although it was a student of his
named Georges Claude who first tested the idea. Claude
used warm seawater to create a low pressure vacuum system,
i.e. an open-cycle system. D'Arsonval's original idea was to
use another fluid such as ammonia, i.e. a closed-cycle system.
At present the only operating OTEC plant is at the Natural
Energy Laboratory of Hawaii.
Abbreviation for over-the-horizon radar, a type of radar
originally developed to detect military targets far beyond the
optical horizon. Radio waves in the 5 to 28 MHz range are reflected
from the ionosphere and reach up to 3500 km in one hop. Properties
of the ocean surface are extracted from the energy backscattered
from the ocean surface. Properties that can be measured
include surface wind direction, radial surface currents,
sea state, surface wind speed, and more.
OTH Web site.
A research project whose goal is to improve the knowledge about
the hydrodynamics of the Straits of Otranto and the evaluate the
water and particulate fluxes across this strait at synoptic,
seasonal, and interannual time scales. This
MTP Core Project took place from Dec. 1993 to
OTRANTO Web site.
Acronym for the Oregon Transect Ecosystem Research Project,
a study of a climatic and elevational gradient extending from the
Pacific coast 200 kilometers to the east. See the
OTTER Web site.
- otter trawl
A device used in biological oceanography to trawl for
pelagic organisms. As opposed to the
beam trawl, the opening to this
is kept open not by a rigid rectangular frame but rather by
otter boards attached to either side of the net opening.
These boards are forced apart by the force of the water when
the trawl is towed and close when it is not being towed, an
eventuality convenient for retaining the organisms caught.
The open may be 20 to 26 m wide and the net up to 40 m in
See Sverdrup et al. (1942).
Abbreviation for operational taxonomic units.
See numerical taxonomy.
- outer sublittoral zone
See circalittoral zone.
- overall Richardson number
A dimensionless number expressing the ratio of the removal of energy
by buoyancy forces to its production by the shear in a flow. It
is expressed by
where g' is the reduced gravity and
L and U are, respectively, length and velocity scales imposed
by the boundary conditions of the problem. The name comes from the
fact that this is an overall parameter describing a whole flow as
opposed to the gradient and
flux Richardson numbers.
See Turner (1973).
- OVERFLOW '60
An ICES investigation of cold, sub-arctic,
deep water overspill into the North Atlantic Ocean from the
Iceland-Faroe Ridge. It was carried out from May 30 to
June 18 in 1960 under the leadership of J. B. Tait and
was an optimal coordination of 9 research ships in a small
region to reach a maximum of synoptic work. This experiment
is considered to be the starting point of current
measurements in deep water by self-recording anchored
instruments. The data collected in the experiment is
available at the
OVERFLOW '60 Web site.
- OVERFLOW '73
An ICES expedition whose core period
of observation was between August 15 and September 15 in 1973.
The principal objective of this experiment was to describe
in detail the kinematic and dynamical processes which lead to
the renewal of the sub-Arctic bottom water of the northern
North Atlantic across the Iceland-Faeroe Ridge and the
Denmark Strait. This experiment, a follow-up to
OVERFLOW '60, consisted of
over 1700 hydrographic stations and 52 current meter moorings
as well as numerous XBTs, tide measurements and drogue tracking.
The chief scientist was J. Meincke of the University of Hamburg.
The data collected in this experiment is available at the
OVERFLOW '73 Web site.
A condition that can exist in strongly stratified
estuaries with net circulation out in the upper layer and
net circulation in in the lower layer. This limits the
amount of salt water available for mixing inside the
estuary. This condition begins as mixing proceeds within
the estuary by whatever processes are dominant. The mixing
causes more salt water to be added to the net circulation and
volume flow out of the estuary up to a critical condition
past which any more increased mixing has no further effect
on the discharge flow or the exiting salinity.
See Officer (1976).
The first of three ages in the
Late Jurassic epoch, lasting
from 163 to 156 Ma. It is preceded by
the Callovian age of the
Middle Jurassic epoch and followed by
the Kimmeridgian age.
See Richards (1957).
- oxygen isotope analysis
The use of stable oxygen isotopes to extract paleoclimatic information
from ice cores. The theoretical basis Bradley (1985)
of the method is that two paleoclimatically important
heavy isotopes (one containing deuterium and the other 18O)
have vapor pressures lower than that of pure H20.
Thus, evaporation leads to water vapor depleted in deuterium and
18O as well as a water body enriched in the same.
Further, condensation of the vapor preferentially removes even
more of these heavy isotopes, leaving the vapor even more
depleted in deuterium and 18O. Therefore, to a first approximation
isotopic concentration in the condensate can be considered as a
function of the temperature at which the condensation occurred,
although other considerations come into play.
A major use of this
method is to gauge the waxing and waning of glacial periods since
the deposition of large amounts of water on land in the form of
glaciers leaves the water enriched in and the water depleted of
the heavy isotopes.
- oxygen isotope ratio
The ratio of oxygen-18 to oxygen-16, used as an indicator of
paleotemperatures since it is related to ocean temperature.
- Oyashio Current
The western boundary current
of the subpolar gyre in the
North Pacific Ocean. Divergence in the center
of this gyre causes the Oyashio to carry cold water rich
in upwelled nutrients and full of marine life - hence the
meaning of the name as ``parent current''. The Oyashio is
formed by the confluence of the
Alaskan Stream and
the Kamchatka Current
west of the Kamchatka Peninsula at about 55 N. It flows
southward and splits into two paths called the First and
Second Oyashio Intrusion just south of Hokkaido, after which
the First Intrusion proceeds southward along mainland Japan
(Honshu) where it turns west at about 38 N
to rejoin the First Intrusion, which has proceeded more or
less directly south from the splitting point.
They merge at about 39 N and 145 E where the
southern boundary of the Oyashio defines the Polar Front.
This boundary and the northern edge of the Kuroshio maintain
their identities at least through the
Kuroshio Extension, although
it is not well known how much further east they continue to
be distinguishable and distinct from the broader eastward flow of
the North Pacific Current.
Thus the Oyashio forms the western and part of the southern limb
of the North Pacific subpolar gyre.
See Tomczak and Godfrey (1994).
A marine invertebrate of the phylum Mollusca
and the class Pelecypoda.
Related animals include clams and mussels.
An allotropic form of oxygen, a bluish toxic
gas, O , with
a characteristic sharp odor, produced from molecular oxygen
by electrical discharge and in the upper atmosphere by
ultraviolet light. Ozone is climatically significant for
this ability to absorb ultraviolet light in the
ozonosphere, which is being reduced
by its being broken down by anthropogenic
chlorofluorocarbon in the atmosphere.
Ozonesonde Web site.
- ozone depleting substance
Any compound that contributes to ozone depletion in
These include halons,
- ozone depletion potential (ODP)
A measure of the amount of ozone depletion caused by a substance.
It is the ratio of the impact on ozone of a chemical compared to
the impact of a similar mass of CFC-11, with the ODP of the latter
defined as unity.
- ozone layer
The region of the stratosophere, at an altitude of 10-15 to 40-50 km
(6 to 30 miles), containing significant amounts of ozone, which
aborbs short ultraviolet light. The region of maximum ozone
concentration is between 20 and 25 km (12 and 15 miles).
This is also called the ozone layer.