Pa-Pm

Pacific-Antarctic Basin

One of three major basins in the Southern Ocean. It extends from its western border with the Australian-Antarctic Basin at the longitude of Tasmania (about 145$^\circ$ E) to its eastern border with the Atlantic-Indian Basin at the Scotia Ridge and Drake Passage (about 70$^\circ$ W). It consists of the Amundsen, Bellingshausen, and Mornington Abyssal Plains and is separated from the basins further north in the Pacific by the Pacific-Antarctic Ridge and the East Pacific Rise in the east and by the Chile rise in the east.

Pacific Basin Extended Climate Study (PBECS)

A proposed CLIVAR program to put in place in the Pacific Ocean a long-term process experiment to test and improve dynamical models of the ocean processes that participate in climate variability. Specific program objectives are:

• to obtain a quantitative description of the low-frequency, three-dimensional circulation and associated thermohaline structure of the upper Pacific Ocean with sufficient accuracy to measure advective fluxes and their divergences;
• to test models of this circulation and its intrinsic modes of variability as well as those due to coupling with the atmosphere; and
• to understand the processes that couple the tropical and subtropical Pacific oceanic gyres on climatic time scales and to test hypotheses about the role of the ocean in basin-scale variability on a broad range of climate time scales.

[http://www.usclivar.org/publications.html]
[http://www.soest.hawaii.edu/~rlukas/PBECS/pbecs_v3.1.html]

Pacific Decadal Oscillation (PDO)

A long-lived El Niño-like pattern of Pacific climate variability. The PDO is distinguished from El Niño by two characteristics:

• 20th century PDO events have persisted for 20 to 30 years, while typical ENSO events persist for 6 to 19 months; and
• the fingerprints of the PDO are most visible in the North Pacific and North American sector, with secondary signatures in the tropics, while the opposite is true for ENSO events.

Two full PDO cycles have been identified for the 20th century. Cool regimes prevailed from 1890-1924 and again from 1947-1976, while warm regimes domained from 1925-1946 and from 1977 through at least the mid-1990s. PDO fluctuations are most energetic in the 15-25 year and 50-70 year bands. The PDO Index is defined as the leading principal component of North Pacific monthly sea surface temperature variability (poleward of 20$^\circ$N for the 1900-1993 period).

Large changes in Northeast Pacific ecosystems have been correlated with PDO phase changes. Warm eras are characterized by increased coastal ocean productivity in Alaska and inhibited productivity off the coast of the contiguous U.S., while cold eras show the opposite behavior. See Zhang et al. (1996) and Mantua et al. (1997).

[http://tao.atmos.washington.edu/pdo/]

Pacific Deep Water (PDW)

In physical oceanography, a water mass 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$^\circ$ C. It is also has an oxygen minimum and a silica maximum, with the latter's lateral origin in the northeastern Pacific. This is separated from the bottom AABW by a benthic front in the southern and western North Pacific. 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$^\circ$ 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$^\circ$ N and 140$^\circ$ W in winter. It moves northwestward to about 40$^\circ$ N and 150$^\circ$ W and intensifies in the summer and effectively fills in the Aleutian Low. See Angell and Korshover (1974).

Pacific Marine Environmental Laboratory (PMEL)

A part of the NOAA ERL network the carries out interdisciplinary scientific investigations in oceanography, marine meteorology, and related subjects. See the PMEL Web site.

Pacific Ocean

The largest and probably least understood of the world oceans. Early attempts at synthesizing and charting the currents of the Pacific are summarized in Peterson et al. (1996). Wüst published the first modern (i.e. using his core layer method) treatise on the deep circulation of the Pacific in 1929. This treatise, published four years before his better known work on the Atlantic, outlined the basics of the deep circulation reasonably well given the poor database with which he worked. More recent summaries by Reid (1965), Reid (1981), Reid (1986), and Talley (1995) have provided a much more detailed look at the circulation at all depths, the variability, and the water masses of the Pacific Ocean.

The surface current structure of the Pacific consists of (from north to south) a cyclonic subpolar gyre, an anticyclonic North Pacific subtropical gyre, a cyclonic and very narrow northern tropical cell including the North Equatorial Countercurrent (NECC), the westward flowing South Equatorial Current (SEC) at and to the south of the equator, an anticyclonic subtropical gyre in the South Pacific, and the Antarctic Circumpolar Current (ACC). The subropical gyre circulations shrink poleward with increasing depth in the North and South Pacific. The western parts of these gyres are C-shaped wherein the western boundary current has a westward and equatorward recirculation just equatorward of and east of the boundary current and its eastward flowing separated extension. This recirculation reconnects to the eastward flow of the gyre at a lower latitude.

The dominant water masses consist of (proceeding from the surface downward): an upper ocean with alternating bands of fresh and saline water directly influenced by surface exchanges, relatively fresh intermediate layers in the Antarctic and North Pacific, Pacific Deep Water (PDW) formed in the north via upwelling and diffusion which intrudes southward, Circumpolar Water (CW) intruding northward, and Antarctic Bottom Water (AABW) intruding northward. The northward spreading CW and AABW are separated from the overlying PDW by a jump in temperature around 1-2$^\circ$ C associated with a vertical stability maximum.

PACS

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. PACS includes the process studies EPIC, NAME and MESA.

[http://tao.atmos.washington.edu/pacs/]

PAGES

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.

[http://www.pages.unibe.ch/]

PALACE

Acronym for Profiling ALACE float, a float with all of the capabilities of an ALACE float as well as a longer lifetime and a CTD profiler to obtain vertical temperature and salinity profiles. See Davis et al. (2001).

PALE

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. PALE ended circa 2001 and was expanded to become PARCS.

paleobiogeography

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.

paleobiology

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).

paleolimnology

The branch of limnology that studies of past fresh water, saline and brackish environments. This is done in large part by taking cores from a limnological sediment system and examining the geological, biological and chemical components preserved in the core.

paleothermometry

The use of various paleoclimate proxy data to attempt to gauge paleotemperatures.

paleotide

The theories of the tidal evolution of the Earth-Moon system show that the effects of tidal friction are such that the Moon's motion and the Earth's rotation can drastically change on geologic time scales. The theories gained empirical support from the paleontological studies of skeletal growth increments in fossil marine invertebrates by Wells (1963) showing an increasing number of days per year, days per lunar month, and lunar months per year going back through the Phanerozoic. Models of the evolution of the Earth-Moon system show the Earth and Moon to have been much closer together in the distant past with the separation increasing with time.

The first models of the Earth as a phase lagged ellipsoid with a constant phase lag angle showed the Earth and Moon to have been close enough together at some point in the past 2.5 billion years (b.y.) to result in tides 1 km high with tidal energy sufficient to not only boil off the oceans but also to melt a part of the Earth and the lunar mantle. It would also have increased the surface air temperature to 1700 K (via an increased greenhouse effect due to increased water vapor in the atmosphere) and eliminated life on Earth. The complete absence of physical evidence for such an event led to relaxing the assumption of a constant phase lag via the incorporation of the effects of continental drift, i.e. a change in continental configuration will change the resonance properties of the ocean and the tides and tidal dissipation therein and therefore the evolution of the Earth-Moon system. Numerical modeling studies have shown the consolidation of continents to attenuate/amplify semidiurnal/diurnal oscillations and the dispersal of continents to have the opposite effect. The inclusion of this effect leads to a more reasonable scenario for the Earth-Moon tidal evolution history. See Kagan and Sündermann (1996).

paleowind

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 ().

PAN

Acronym for Peroxyacetyl Nitrate.

PANASH

Acronym for Paleoclimates of the Northern and Southern Hemispheres program, a proposed project of PAGES.

Panthalassa

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).

PAR

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

$$PAR(z)\,=\,{1 \over {N_0}} {\int^{700}_{400}} {E_{\lambda 0}}(z)\,(\lambda/hc)\,d\lambda$$

where $N_0$ is Avagadro's constant, $h$ is Planck's constant, $c$ the speed of light, $\lambda$ 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.

parabolic approximation

See Mei (1990).

paradox of the plankton

The long-term coexistence of plankton species that might be expected to compete. This is due to the degree to which chance encounters dictate the degree to which intra- or interspecific competition occurs. This, in turn, is due to plankton be unusually dependent on their physical environment for support, transport and food. See Rigby and Milsom (2000).

Parallel Community Climate Model (PCCM)

A parallel version of the NCAR Community Climate Model (CCM2) implemented for MIMD massively parallel computers using the message passing programming paradigm. It can be implemented on a massively parallel machine supporting message passing or across a network of machines with the PVM software package. See the PCCM Web site.

parameterization

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 eddy viscosity 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).

The processes that must be parameterized in ocean circulation models, as summarized by James McWilliams at the APROPOS meeting in 1998, include:

• effects of surface gravity waves on currents (vortex forces and mean Lagrangian transport);
• turbulent transports within the planetary boundary layers and entrainment/detrainment at their interior edges (convective plumes, shear vortices, Langmuir cells);
• interior diapycnal mixing processes (gravity waves, Kelvin-Helmholtz vortices, double diffusion);
• topographic roughness effects (form stress, gravity wave generation, local secondary circulations);
• mesocale eddy transports of momentum and tracers, including potential vorticity (isentropic mixing and mean Lagrangian transport);
• topographic barriers (sills and straits);
• effects of deep convection and its preconditioning (in shallow seas, over topographic features, in interior regions); and
• transports by gravity currents over sills and off of continental shelves.

PARCS

Acronym for Paleoenvironmental ARCtic Science, a part of ARCSS program. The theme is to explore the importance of land-ocean interactions and the variation in freshwater and chemical fluxes within the total arctic system.

[http://www.ngdc.noaa.gov/paleo/parcs/]

Particle and Optics Profiling System (POPS)

An assembly of instruments designed to count and measure particles and to determine optical and environmental properties of water as a function of depth. The main part of the POPS system is the Large Aggregate Profiling System (LAPS) package used to measure particles ranging from 250 microns to several millimeters in diameter. It also usually carries an LISST which measures smaller particles ranging from one to 250 microns in diameter. Other instruments found on POPS include a CTD, a transmissometer (for measuring particles less than 20 microns in diameter), a fluorometer and an a-c meter (for measuring chlorophyll), LSS (for measuring particle abundance).

particulate matter

The suspended particle load that controls the chemistry of the oceans. The physical and chemical properties of the particles control how rapidly a chemical species is removed from solution and incorporated in sediment. The four main sources of this in the oceans are: (1) fluvial input of terrigenic material; (2) aeolian input from wind erosion of continental masses, volcanism and anthropogenic sources; (3) resuspension of sedimentary material by current erosion, earthquakes and slumping; and (4) authigenic production by biota, submarine volcanism and the precipitation of inorganic minerals. See Simpson (1982).

PATCHEX

Acronym for the Patches Experiment, which took place off the California coast in October 1986. See Brainerd and Gregg (1993).

PATHS

Acronym for Pacific Transport of Heat and Salt, a joint program among Canada, Japan and the U.S. See WMO (1983).

PBECS

Acronym for Pacific Basin Extended Climate Study.

PBL

Abbreviation for planetary boundary layer.

PBL-LIB

This is a collection of programs that deal with data pertaining to the PBL. See the PBL-LIB Web site.

PCA

Abbreviation for principal component analysis, usually used synonymously with EOF.

PCCM

Abbreviation for Parallel Community Climate Model.

PCIS

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.

[http://lumahai.soest.hawaii.edu/Enso/pcis/pcis.html]

PCMDI

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.

[http://www-pcmdi.llnl.gov/]

pCO2

The equilibrium partial pressure of CO2.

PCSP

Abbreviation for Polar Continental Shelf Project, a Canadian program.

[http://polar.nrcan.gc.ca/]

PDO

Abbreviation for Pacific Decadal Oscillation.

PDR

Abbreviation for Precision Depth Recorder.

PDW

See Pacific Deep Water.

PE

Abbreviation for primitive equations.

PEAC

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 Pacific Island. See the PEAC Web site.

PECHORA

Acronym for Paleo Environment and Climate History of the Russian Arctic, a project whose main purpose is to increase the understanding of climate changes and the impact these changes have on the environment in arctic Russian during the last interglacial-glacial cycle. The goals are:

• reconstruction of the Barents and Kara Ice Sheets through time;
• reconstruction of fauna, vegetation and climate history; and
• reconstruction of the history of human settlement.

[http://www.geomar.de/~hbauch/king/html/Svend.htm]

PEGASUS

An acoustically tracked velocity profiler. See Spain et al. (1981).

PEQUOD

Acronym for the Pacific Equatorial Dynamics Experiment. See Eriksen (1987).

Peclet number

A dimensionless number expressing the ratio of advection to thermal diffusion. It is expressed by

$$Pe\,=\,{UL\over{\kappa}}$$

where $U$ is a velocity scale, $L$ a horizontal length scale, and $\kappa$ the thermal diffusivity. Molecular diffusion of heat is negligible when $Pe\,\gg\,1$. 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 $\nu$ has been replaced by the thermal diffusivity $\kappa$. See Kraus and Businger (1994), p. 32.

pelagic

Descriptive of organisms that inhabit open water, as opposed to benthic. This is sometimes divided into five separate ecological zones which are, proceeding from the surface to the bottom, the epipelagic, mesopelagic, bathypelagic, abyssopelagic and hadopelagic zones. See Bruun (1957).

Pelagic Fisheries Research Program (PFRP)

A research program established in 1992 to provide scientific information on pelagic fisheries to the Western Pacific Regional Fishery Management Council (WPRFMC) after the Magnuson Fishery Conservation and Management Act of 1976 was amended to include highly migratory fish. It is located at JIMAR at the University of Hawaii.

[http://www.soest.hawaii.edu/PFRP/pfrp1.html]

PELAGOS

Greek acronym for 'Hydrodynamics and Biogeochemical Fluxes in the Straits of the Cretan Arc', a project designed to research the hydrodynamics of the South Aegean Sea and the southeastern Ionian and northwestern Levantine Seas, with the aim of investigating biogeochemical fluxes through the Straits of the Cretan Arc. The project was launched within the framework of the Mediterranean Targeted Project (MTP) of the Marine Science and Technology Programme (MAST) of the European Union (EU), and included scientists from Greek, British and French institutions. The National Centre for Marine Research (NCMR) in Athens coordinated the program during its contracted duration from September 1993 to March 1996. The study area originally covered the Straits of the Cretan Arc (Eastern Mediterranean Basin), but was eventually extended further, first into the South Aegean Sea, and then to the southeastern Ionian Sea and the northwestern Levantine Sea.

The field programme of PELAGOS lasted from March 1994 to June 1995, during which time four major synoptic surveys were undertaken in the Cretan Sea, the Straits of the Cretan Arc and adjacent seas (northwestern Levantine and southeastern Ionian). In addition, four seasonal surveys (for the investigation of specific variables) were undertaken along a west-east section of the Cretan Sea. Finally, several short cruises were undertaken in connection with current meter and sediment trap deployments, recoveries, and re-deployments. The synoptic cruises were carried out on board R/V Aegaio for hydrographic, chemical (nutrients, dissolved oxygen) and biological (phytoplankton, chlorophyll-a, zooplankton) sampling. The other surveys were directed mainly towards biological and geochemical sampling, undertaking ADCP measurements, and the deployment/recovery of current meters and sediment trap moorings.

The primary tasks were the measurement of various physical, chemical, biological and geochemical parameters; together with the water circulation controlling their basin-wide distribution and disposition. Particular emphasis was placed upon the processes across the Straits of the Cretan Arc and their seasonal time-scales. Hence, expanded horizontal coverage and dense vertical sampling/measurement of temperature and salinity was established. Concurrently, data on nutrients, dissolved oxygen, trace elements dissolved in seawater and the geochemical characteristics of suspended particulate matter (SPM) were collected at selected depths, to enable their subsequent vertical and horizontal integration with the various water exchanges. The chemical analyses of dissolved trace elements, together with SPM trace and major elements, were related mainly to the Straits of the Cretan Arc and along an east-west section of the Cretan Sea. Self-recording current meters were deployed within the Straits of the Cretan Arc for a year. These deployments improved the understanding of the prevailing flow patterns and controlling mechanisms, together with their variability; similarly, they permitted the estimation of fluxes of water and associated (dissolved or suspended) material through the various Straits. At the same time, moored sediment traps provided independent (time-series) assessments of the vertical flux of settling particles and the nature of material deposited in the western Straits (Antikithira Strait). Size-fractionated chlorophyll-a and primary production determinations were undertaken, to estimate productivity. In addition, phytoplankton and zooplankton sampling was performed, to obtain qualitative and quantitative estimations of the aforementioned parameters and their variability.

See Balopoulos and Collins (2000) and the other papers in Volume 44 of "Progress in Oceanography" for further details. Project data and results are archived at the HNODC.

PEP

Acronym for Pole-Equator-Pole, a PAGES sponsored inter-American paleoenvironmental research program focuses on the dynamics of transequatorial atmospheric and ocean linkages.

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.

Persey Current

See Pfirman et al. (1994).

Persian Gulf

A marginal sea of the Indian Ocean centered at approximately 52$^\circ$ E and 27$^\circ$ N. It is surrounded by Iran to the north, Kuwait, Saudi Arabia, Qatar, and the United Arab Emirates to the east and south, and connects with the Gulf of Oman (and on into the Arabian Sea) through the Strait of Hormuz to the east. It has a length of 990 km, ranges in width from 56 to 338 km, covers an area of 241,000 km$^2$, occupies a volume of 10,000 km$^3$, has a mean depth of 40 m, and a maximum depth of about 170 m.

The circulation features have been well summarized in RSMAS (2000) as:

The basic features of the Arabian (or Persian) Gulf can be divided into a northern and southern or eastern regime. The northern regime is dominated by wind forcing to the south along the axis of the Gulf and the riverine input at the Gulf's head. The wind-driven response of the Gulf appears to be the typical adjustment of the pressure field such as to produce a down-wind flow, i.e. there is downwelling on the western coast and upwelling on the coast of Iran, and evidence for a southeastward flowing coastal current along both the northern and southern coasts (Reynolds (1993)). The flow along the Kuwait and Saudi coast is augmented by the freshwater input from the north which forms a riverine plume. The river inflows are approximately split between the flow out of the Shalat Ariabi (Tigris and Euphrates) and rivers flowing out of the highland of Iran (the Hendijan, Hilleh, and Mand). In current times the flow of the Shalat Ariabi is much smaller than it once was because of massive dam projects in Turkey. It is not clear what changes this decline in freshwater input has made. The center of the northern Gulf appears to be fairly stagnant (Reynolds (1993)). The southern end of this regime corresponds roughly to the longitude of Qatar and Bahrain, although the termination of the northern circulation is poorly understood. The flow along the Iran coast seems to continue into the southeastern basin as a tightly trapped coastal current extending perhaps as far as the Strait of Hormuz. This flow becomes very complex in proximity to the island of Jazareh in the northern portion of the Strait.

The northern Gulf is separated from the southern regime by a front that typically is found off Qatar. This front is most intense in summer and weakest, at least in sea surface temperature, in the late winter and spring. The location of this front appears in both climatological hydrographic data and remotely sensed SST to be tied to the penetration of fresh inflow into the Gulf from the Strait of Hormuz. The available data suggests that much of this inflow may terminate in a counter-clockwise, cyclonic flow to the east of the mid-Gulf front. This cyclone appears in circulation climatologies and appears as a coherent SST anomaly in satellite imagery. East of this front the available data suggest a flow out of the Gulf around the tip of the Musandem peninsula and into the northern Gulf of Oman. The large evaporation over the Gulf leads to an inverse estuarine circulation with the highly saline waters leaving the Gulf through the deep part of the Strait of Hormuz and being replaced by a fresh surface inflow from the Gulf of Aden. The saline bottom waters that flow out through the Strait may originate from several locations in the Gulf. Historical salinity data and SST data implicate a broad region of high salinity waters extending from Qatar eastward along the Emirate coast. Waters in this shallow region can reach very high salinities ($>$42 psu) and appear to form a warm and salty endpoint of the Gulf outflow. The temperature salinity relationships of the observed outflowing waters imply a fairly complicated set of water mass modifications in the Gulf. Colder and somewhat fresher waters are also found in the deep outflow from the Gulf and suggest another source, probably from the northern Gulf. Modeling results suggest that some of the outflow arises from sinking in the shallow high salinity area off the Emirates, but that further sinking occurs in the vicinity of the variable mid-Gulf front.

The deep water arising from these sources exits the Gulf on the southern (deepest) side of the Strait of Hormuz at a maximum depth of $\sim$100 m. Unlike the Mediterranean or Red Sea the Gulf is shallow ($<$100 m) and there is no prominent sill to constrain the outflow. The annual mean outflow of the deep waters and compensating fresh surface inflow is estimated from the Knudsen relations to be approximately 0.2 Sv, assuming a mean evaporation rate of approximately 1.5 m/yr and net freshwater input from rivers of $\sim$0.2 m/yr. Estimates of the exchange rate from available models span a range from 0.1 Sv to nearly 0.4 Sv. Seasonal variability of the deep outflow and surface inflow is not clearly established, although recent measurements suggest that the deep outflow may be fairly steady throughout the year.

See Elliot and Savidge (1990), Reynolds (1993), Flagg and Kim (1998), Bower et al. (2000) and RSMAS (2000).

[http://mpo.rsmas.miami.edu/~zantopp/AMSG-report.html]

Peru-Chile Countercurrent (PCCC)

One of two branches into which the Pacific Equatorial Undercurrent (EUC) splits when it encounters the Galapagos Islands. The Poleward Undercurrent (PUC) is one branch, while the other branch flows to the southeast of the Islands and approaches the coast at about 6-7$^\circ$S to form the Peru-Chile Countercurrent. Tongues of minimum phosphate distributions and surface drifters have been used to identify this current.

According to Strub et al. (1998):

Evidence for the location and variability of the Peru-Chile Countercurrent is less conclusive, especially off Chile. It is better documented off Peru, where it appears 200 m offshore in mean sections at 10$^\circ$S. South of 15$^\circ$S is was originally thought to flow straight south along approximately 75-77$^\circ$W. More recently, three years of satellite altimetry data show a continuous band of poleward currents 100-300 km from the coast that extend from approximately 8-35$^\circ$S, following the coastline. The poleward currents in the altimeter data are maximum in austral spring and minimum in fall.

See Strub et al. (1998).

Peru-Chile Undercurrent

Another name for the Poleward Undercurrent (PUC).

Peru Coastal Current (PCC)

According to Strub et al. (1998) ...

... water mass properties suggest that the equatorward surface flow [of the current] is strongest in austral winter, when equatorward winds are maximum. It carries colder and saltier upwelled water to the north in the equatorial cold tongue, characteristic of the South Equatorial Current (SEC). Its confluence with the warm and fresh water moving southward out of the Panama Bight creates the strong Equatorial Front (EF). Low temperatures in the cold tongue are maintained by upwelling along the equator and the extent of the cold tongue is maximum at the end of austral winter (September-October). In austral spring and summer, the cold tongue collapses back toward the coast as the trade winds weaken in the eastern equatorial Pacific. At this time the Equatorial Front is unpredictable, weak or absent and a warm tongue extends southwest along an offshore region from the equator to northern and central Chile, which may be related to the Peru-Chile Countercurrent (PCCC).

This and the Chile Coastal Current (CCC) are together sometimes referred to as the Inshore Peru Current. See Strub et al. (1998).

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$^\circ$ 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. Other names used for the entire current have been Chile-Peru Current, Humboldt Current and Oceanic Peru Current. 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).

Pettersson, Hans

Head of the Swedish Deep Sea Expedition and son of Otto Pettersson. See Guberlet (1964).

Pettersson, Otto

A Swedish chemist and physical oceanographer who organized many of the earliest cooperative cruises in Scandanavian waters and promoted the idea of what would become the ICES. See Schlee (1973) and Pettersson (1894).

PEX

Acronym for Baltic Sea Patchiness Experiment, an ICES investigation which took place in the Gotland Basin during April through May in 1986 under the leadership of B. Dybern. The basic objective of the experiment was to study the heterogeneous and patchiness in the distribution of physical, chemical and biological properties in the region. Almost all of the Baltic Sea countries contributed to a total of 15 research vessels used in this experiment.

[http://www.ices.dk/ocean/project/data/pex86.htm]

PF

Abbreviation for Polar Front.

PFRP

Abbreviation for Pelagic Fisheries Research Program.

PFZ

Abbreviation for Polar Frontal Zone.

phagotrophic

Descriptive of a heterotrophic phytoplankton species that feeds on phytoplankton or detritus.

Philippine Sea

See Qu et al. (1998).

Phleger Bottom Sampler

A bottom sampler used for quantitative studies of foraminifera, designed to take a short core of the upper sediment layers without disturbing the surface layer. This sampler, first used in 1951, is a short weighted tube with a removable lining tube and a replaceable cutting edge. The liner is a clear plastic tube with a diameter of 3.5 cm. It can be operated with a light winch in depths up to 500 m when weighted with 35-40 pounds of molded lead, and to depths of 4600 m in more cohesive sediments. See Hedgpeth (1957b).

phosphorus

Phosphorus is an essential nutrient used by all organisms for energy transport and growth. One of the most important aspects of the phosphorous cycle is its role in governing productivity, thereby acting with the exogenic part of the carbon cycle.

Known P oceanic sources are:

• rivers, the predominant source, with a total estimated flux of 7.4-15.6 $\times\,10^{11}$ mol P yr$^{-1}$;
• aeolian deposition, with an estimated flux of 4.5 $\times\,10^{10}$ mol P yr$^{-1}$; and
• volcanic emissions, a more local and intermittent source.

The known P sinks are:

• biological uptake and incorporation into sinking particulate organic matter, the predominant sink, is estimated to have a total flux of 2.8-3.1 $\times\,10^{11}$ mol P yr$^{-1}$;
• absorption onto the surface of shells via iron oxyhydroxide coatings, estimated to be 4.0-5.3 $\times\,10^{10}$ mol P yr$^{-1}$;
• the burial of phosphorites, estimated to be $>$8 $\times\,10^{10}$ mol P yr$^{-1}$; and
• hydrothermal processes, estimated at 0.65 $\times\,10^{10}$ mol P yr$^{-1}$.

The global marine inventory of dissolved P is about 3.2 $\times\,10^{15}$ mol P, with the residence time relative to the known P sources estimated to be 20,000 to 80,000 years. The residence time relative to the known sinks is thought to be less than 10,000 years, down from previous estimates as high as 80,000 years as the role of coastal regimes and phosphorite deposits as sinks have become better understood. See Föllmi (1996) and Benitez-Nelson (2000).

photic zone

See euphotic zone.

photosynthesis

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.

phototrophic

Descriptive of a phytoplankton species that lives primarily by photosynthesis.

phycology

The study of algae, especially seaweeds. This is also called algology. Professional organizations for phycologists are the Phycological Society of America and the British Phycological Society.

Physical Oceanographic Real-Time System (PORTS)

An information acquisition and dissemination technology developed by the NOS that supports safe adn cost-efficient navigation by providing ship masters and pilots with accurate real-time information required to avoid groundings and collisions. PORTS provides real-time water levels, currents, and other oceanographic and meteorological data from bays and harbors to the maritime user community in a variety of formats. It also provides nowcasts and predictions of these parameters via the use of numerical circulation models.

[http://www.co-ops.nos.noaa.gov/d_ports.html]

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, electromagnetics (satellite oceanography). This is one of four sub-fields into which the general field of oceanography has been divided, the others being biological. chemical and geological oceanography.

phytobenthos

That part of the benthos consisting of plant life.

phytoplankton

One of two groups into which plankton are divided, the other being zooplankton. Phytoplankton comprise all the freely floating photosynthetic forms in the oceans, i.e. they are free-floating microscopic plants which, having little mobility, are distributed by ocean currents. Most marine phytoplankton are found in one of five Phyla: Cyanophyta, Chrysophyta, Chlorophyta, Cryptophyta, and Pyrrophyta. See Johnson (1957) and Riley and Chester (1971).

PIC

Abbreviation for particulate inorganic carbon.

PICES

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.

[http://www.pices.int/]

PICOLO

Acronym for Production Induite en Zone de Convergence par les Ondes Longues, a program to attempt to understand how a heavy catch of tun occurs in a region considered biologically poor although prone to tropical instability waves.

PIDCAP

Acronym for Pilot Study for Intensive Data Collection and Analysis of Precipitation, a component study of BALTEX. The objectives are:

• to collection and analyze measured and estimated precipitation from different data sources;
• to compare different precipitation data sets against each other to identify and establish reliable standards for model validation;
• to validate the output of BALTEX Regional Models against such data sets; and
• to deveop, test and establish necessary data management and analysis procedures.

[http://w3.gkss.de/baltex/pidcap.html]

Pierson, Willard

More later.

Pierson-Moskowitz spectrum

A wave spectrum devised for fully developed wind waves in an open sea. This method assumes that both duration and fetch are large enough to permit an equilibrium state between the mean wind, turbulence and waves. If this is true, then all other variables are determined by the wind speed. It can be expressed as

$$\phi (\omega )\,=\,\alpha{g^2}{n^{-5}} {e^{\left[-\beta{{\left({\omega\over{\omega_0}}\right)}^{-4}}\right]}}$$

where $\alpha\,\sim\,0.0081$, $\beta\,\sim\,1.25$, $\omega_0\,=\,g/U$ is the frequency of the spectral peak, $g$ is gravitational acceleration, $U$ the wind speed, and $\omega$ the wave frequency considered. That is, if the spectral peak is known, then the spectrum and the energy content of the wave field are determined. See Pierson and Moskowitz (1964).

PIM

Abbreviation for Particulate Inorganic Matter.

PIP

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).

PIPOR

Acronym for Program for International Polar Oceans Research.

PIPS

Acronym for Polar Ice Prediction System.

PIRATA

Acronym for Pilot Research Moored Array in the Tropical Atlantic, a plan for an observing system to support tropical Atlantic climate studies from 1997-2001. PIRATA will install and maintain an array of 12 moored ATLAS buoys as part of a multinational effort involving Brazil, France and the U.S. It consists of 12 ATLAS moorings spanning along the equator and two meridional lines. This configuration was chosen to provide coverage along the region of regions of strong wind forcing in the western basin and significant seasonal to interannual variability in SST in the central and eastern basin. The meridional arrays cover the regions of high SST variability associated with the SST dipole mode.

The purpose of PIRATA is to remedy the crucial lack of oceanic and atmospheric data in the tropical Atlantic. The scientific goals are:

• to provide an improved description of the seasonal-to-interannual variability in the upper ocean and at the air-sea interface,
• to improve understanding of the relative contributions of the different components of the surface heat flux and ocean dynamics to the seasonal and interannual variability of SST within the tropical Atlantic basin,
• to provide a data set that can be used to develop and improve predictive models of the coupled Atlantic climate system,
• to design, deploy, operate and maintain a pilot array of moored buoys similar to those used during the TOGA program in the tropical Pacific; and
• to collect and transmit via satellite in real-time a set of oceanic and atmospheric data to monitor and study the upper ocean and atmosphere of the tropical Atlantic.

A pilot phase is proposed for 1997-2000 to be followed, if successful, by a long-term operational system to monitor the area maintained by GOOS and GCOS.

[http://www.pmel.noaa.gov/pirata/]
[http://www.ifremer.fr/orstom/pirata/pirataus.html]
[http://www.brest.ird.fr/pirata/pirataus.html]
[http://www.aoml.noaa.gov/phod/COSTA/abstracts/piracosta.html]

piston velocity

The velocity with which gas diffuses across the air-sea interface in the 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 to be

$${k_w}\,\propto \,{{Sc}^{-n}}f(V)$$

where $Sc$ is the Schmidt number and $V$ the wind speed. This is also occasionally known as the transfer velocity. See Najjar (1991).

PIW

Abbreviation for Polar Intermediate Water.

planetary boundary layer

A generic term for either oceanic boundary layer (OBL) or atmospheric boundary layer (ABL). These layers are fundamentally turbulent and extend from near the surface to the boundary layer depth or height, defined as the limit to which boundary layer eddies can penetrate in the vertical.

planetary geostrophic equations

A set of filtered equations in which the advection of momentum is neglected in the momentum equations, i.e. the inertia-gravity wave modes have been filtered out. Their use in inappropriate for anything but large-scale, i.e. planetary, circulation. Unlike the quasi-geostrophic equations, these do allow large variations in both the Coriolis parameter and layer depth. These were first developed by Robinson and Stommel (1959) and Welander (1959).

They can be expressed in spherical coordinates (following Muller (1995)) as

$$\left({ \partial \over {\partial t} }\,+\, {u \over {{r_0}\cos\theta} } { \partial \over {\partial\phi} }\,\right. + \, \left.{v \over {r_0} } { \partial \over {\partial\theta} }\,+\, w { \partial \over {\partial z} }\right)\rho '\,=\,0$$

$$fv\, = \,{1\over{\rho_*}} {1 \over {{r_0}\cos\theta}} { {\partial p'} \over {\partial\phi} }$$

$$fu\, = \,{1\over{\rho_*}} {1 \over {r_0}} { {\partial p'} \over {\partial\theta} }$$

$${ {\partial p'} \over {\partial z} }\, = \,-\rho 'g$$

$$f{ {\partial w} \over {\partial z} }\, = \,\beta\upsilon$$

where $r_0$ is the mean radius of the Earth, $(\phi , \theta , r)$ are polar coordinates where $\phi$ is longitude, $\theta$ latitude and $r$ radial distance, $\upsilon$ is specific volume, $(u,v,w)$ are the velocity components, $\rho '$ is the variation of the density from a reference state, $\rho_*$ is the reference density, $p'$ is the variation of the pressure from a reference state, $f\,=\,2\Omega\sin\theta$ is the vertical component of the planetary vorticity vector, and $\beta$ is the beta parameter, i.e.

$$\beta\,=\,{1\over{r_0}}{ {\partial f} \over {\partial\theta} }$$

.

The first equation is the density equation, a prognostic equation governing the dynamical evolution of the flow. The other equations are diagnostic relations. Another prognostic equation can be found by first decomposing the pressure

$$p\,=\,{\rho_*}g\xi\,+\,g{\int_z^0}\,dz'\,\rho '$$

where the first part is the barotropic component due to the displacement $\xi$ of the surface, and the second the baroclinic component due to density fluctuations. The evolution of the baroclinic part is governed by the density equation, and the barotropic part by the kinematic surface boundary condition, i.e.

$${\partial \over {\partial t}}\,=\,w$$

at $z\,=\,0$ in the planetary geostrophic limit. This is usually converted to an equation for the mass transport stream function since lateral boundary conditions are simpler for the stream function than for surface displacement.

The planetary geostrophic equations are usually used in their steady-state form to study the thermocline problem. See Hasselmann (1982) and Muller (1995) for further details of the equations and their derivation.

planetary vorticity

See vorticity.

plankton

One of three major ecological groups into which marine organisms are divided, the other two being the nekton and the benthos. Plankton are small aquatic organisms (animals and plants) that, generally having no locomotive organs, drift with the currents. The animals in this category include protozoans, small crustaceans, and the larval stages of larger organisms while plant forms are mainly diatoms.

pleuston

Marine organisms associated with the water surface or the uppermost water layer that possess special adaptations allowing them to passively float there. This term was originally used in freshwater biology to refer to microscopic plants and animals associated with the surface film and supported by surface tension, but it is now also used by marine biologists to describe organisms found in the upper 100 meters of the ocean. Pleuston was historically used especially by Soviet scientists, with their western counterparts more likely to group the pleuston in with the neuston. See Cheng (1975).

plumes

Convective elements that carry fluid particles vertically over distances comparable to the depth of the ocean. The horizontal scale is about 1 km, and they are driven by intense cooling at the sea surface that reaches $\sim$1000 W m$^{-2}$. They are ascending and descending currents that can reach speeds in excess of $\sim$10 cm s$^{-1}$. Plumes penetrate most of the water column and efficiently homogenize its properties, forming deep, cold mixed layers called chimneys. The chimneys are maintained close to neutrality, geostrophically adjust, and break up into fragments called cones on a time scale of a few days. The cones have a spatial scale of several kilometers. See Jones and Marshall (1993).

Plum Island Sound

See Vallino and Hopkinson Jr. (1998).

PMEL

Abbreviation for Pacific Marine Environmental Laboratory.