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Aa-Am

AABW
Abbreviation for Antarctic Bottom Water.

AACW
Abbreviation for Antarctic Circumpolar Water.

AAIW
Abbreviation for Antarctic Intermediate Water.

AASW
Abbreviation for Antarctic Surface Water.

AATE
Abbreviation for Arctic Acoustic Transmission Experiment, a project of the APL at the University of Washington School of Oceanography.

Abiki
An instance of the meteorological tsunami phenomenon in Nagasaki Bay. See Hibaya and Kajiura (1982).

ABF
Abbreviation for Angola-Benguela Front.

ABL
1. Abbreviation for atmospheric boundary layer. 2. Abbreviation for airborne backscatter lidar.

ABP
Abbreviation for Acoustic Backscatter Probes.

absolute humidity
The ratio of the mass of water vapor in a sample of moist air to a unit volume of the sample. It is expressed in grams per cubic meter and also called the vapor concentration.

absolute vorticity
The sum of the relative vorticity ($ \zeta$) and the planetary vorticity, i.e. $ \zeta\,+\,f$. More later.

absorptance
In radiation transfer, the fraction of incoming radiation that is absorbed by a medium. The sum of this, the transmittance, and the reflectance must equal unity.

absorption
A process by which incident radiation is taken into a body and retained without reflection or transmission. It increases either the internal or the kinetic energy of the molecules or atoms composing the absorbing medium.

absorption band
In atmospheric radiative transfer, a collection of absorption lines in a particular frequency interval.

absorption line
In atmospheric radiative transfer, a discrete frequency at which an energy transition of an atmospheric gas occurs due to the absorption of incident solar radiation. The line width depends on broadening processes, the most important of which are natural, pressure (also known as collision), and Doppler broadening.

ABW
See Arctic Bottom Water.

abyssal hill
Small hills found only in the deep sea which rise from the ocean basin floor with heights ranging from 10 to over 500 feet and widths from a few hundred feet to a few miles. They are found along the seaward margin of most abyssal plains and originate from the spreading of mid-ocean ridges. As such, they usually form two strips parallel to mid-ocean ridges. They generally decrease in height as one traverses away from the ridges as they gradually become covered with sediment and are replaced by abyssal plains. See Fairbridge (1966).

abyssal plain
Flat areas of the ocean basin floor which slope less than 1 part in 1000. These were formed by turbidity currents which covered the preexisting topography. Most abyssal plains are located between the base of the continental rise and the abyssal hills. The remainder are trench abyssal plains that lie in the bottom of deep-sea trenches. This latter type traps all sediment from turbidity currents and prevents abyssal plains from forming further seaward, e.g. much of the Pacific Ocean floor. See Fairbridge (1966).

abyssal zone
This originally meant (before the mid-1800s) the entire depth area beyond the reach of fisherman, but later investigations led to its use being restricted to the deepest regions with a uniform fauna and low temperatures. Thus it was distinguished from the overlying bathyal or archibenthal zone with more varied fauna and higher temperatures. Eventually an underlying hadal zone was defined for areas in trenches and deeps below 6000-7000 m depth. The upper boundary of the abyssal zone ranges between 1000-3000 m, with the position of the 4$ ^\circ$ C isotherm generally considered the demarcation line. It is the world's largest ecological unit, with depths exceeding 2000 m comprising over three-quarters of the world ocean. See Fairbridge (1966).

abyssopelagic zone
One of five vertical ecological zones into which the deep sea is sometimes divided. There is a pronounced drop in the number of species and the quantity of animals as one passes into this zone. It is separated from the overlying bathypelagic zone by the 4$ ^\circ$ C isotherm and from the underlying hadopelagic zone at about 6000 meters. The distinction between pelagic and benthic species can be difficult to ascertain in this zone. See Bruun (1957).

a-c meter
An instrument used to perform in-situ measurements of the amount of chlorophyll in water. It does this by pulling water into two tubes, one measuring light absorption and the other attenuation. A beam of light with a wavelength rotating among three values is projected into each tube. The attenuation tube determines light absorption and scattering by measuring how much of the original light beam remains after it passes through the water inside the blackened tube. The absorption tube determines only how much light is absorbed by particles by measuring how much light is left of the original beam including that which has bounded off particles. This tube is lined with a quartz mirror which, in contrast to the absorbing black surface in the attenuation tube, reflects scattered light toward the detector. Chlorophyll causes a large change in the attenuation of light with a wavelength of about 676 nanometers, so a measurement of attenuation at the appropriate wavelength is a proxy measurement of chlorophyll concentration to first order. A fluorometer can also be used to measure chlorophyll.

ACC
1. Abbreviation for the Antarctic Circumpolar Current. 2. Abbreviation for the Alaskan Coastal Current.

ACCE
Abbreviation for Atlantic Climate Change Experiment, a joint program between WOCE and NOAA's ACCP designed to increase understanding of the meridional overturning circulation (MOC) of the Atlantic Ocean and the overlying atmosphere at interannual and longer time scales. The goals of ACCE were: See WOCE (1995).

[http://www.aoml.noaa.gov/phod/acce/]
[http://www-ocean.tamu.edu/WOCE97/Future/acce.html]

ACCIS
Acronym for Austral Chilean Coast and Inland Sea project, a program to facilitate the development of an interdisciplinary and multi-institutional program focused on ecological and socio-econonomic-human health issues in the temperate waters of the Austral Chilean Coast and Inland Sea.

[http://www.ccpo.odu.edu/~atkinson/ACCIS/accis.html]

ACCLAIM
Acronym for the Antarctic Circumpolar Current Levels by Altimetry and Island Measurements program in the South Atlantic and Southern Oceans. It consists of measurements from coastal tide gauges and bottom pressure stations, along with an ongoing research program in satellite altimetry. ACCLAIM was the Proudman Oceanographic Laboratory's main contribution to WOCE and now provides data for CLIVAR, GLOSS and PSMSL.

The coastal tide gauge portion of ACCLAIM took place in two phases. In Phase I from 1983, measurements at coastal tide gauge sites were sub-surface pressure (SSP) measurements rather than sea level (where SSP is defined as the total, measured pressure recorded by a sub-surface pressure transducer, a measurement including the atmospheric as well as the water column pressure). These data were acquired with different sensors and with different pressre integration periods. Phase II, which started in early 1993, involved replacing the gauges at several sites with `B gauges' that recorded SSP, air pressure and sea level. These gauges have precise datum control and are used to provide long term sea level change data to the PSMSL. See Spencer et al. (1993).

[http://www.pol.ac.uk/psmsl/programmes/acclaim.info.html]

ACCP
Abbreviation for the Atlantic Climate Change Program, a NOAA research initiative for understanding the decadal-scale interactions of deep circulation in the Atlantic and how it influences the overlying atmosphere. The goals of ACCP are:

[http://www.aoml.noaa.gov/phod/accp/]

accuracy
The degree of freedom from error. The total error compared to a theoretically true value. Contrast with and see precision for an example.

ACE
Abbreviation for Antarctic Current Experiment, a GARP project.

ACE
Acronym for Australian Coastal Experiment, an investigation whose primary goal was to identify continental shelf waves (CSW). It was carried out off the coast of New South Wales (eastern Australia) between Cape Howe and Newcastle from September 1983 to March 1984. The experiment included an array of current meters with three main lines with five moorings each, repeated CTD and XBT surveys, meteorological measurements from moored buoys and coastal stations, sea level measurements at coastal tide gauges, and bottom pressure measurements at a few sites. Each of the three mooring lines was arranged perpendicular to the local coastline, were nominally identical, and consisted of 15 Aanderaa current meters on 5 moorings.

A free wave analysis of the data gathered demonstrated that waves passed through the experimental array and exhibited dispersion characteristics strongly indicative of coastal trapped waves. The measured pattern speed was between those predicted for free and forced waves. There was some predictive skill using a trapped wave model. Although the model predictions only accounted for a maximum of 40% of the observed variance, the best statistical predictor could only account for 50%. This led to the conclusion that not all of the energy in the weather forcing band was described by coastal trapped waves. See Freeland et al. (1986) and Church and Freeland (1987).

ACME
Abbreviation for Advisory Committee on the Marine Environment, an ICES committee.

ACMP
Abbreviation for Advisory Committee on Marine Pollution, an ICES committee.

ACMRR
Abbreviation for Advisory Committee of Experts on Marine Resources Research, a FAO committee.

ACOMR
Abbreviation for Advisory Committee on Oceanic Meteorological Research, an WMO committee.

ACOPS
Abbreviation for Advisory Committee on Protection of the Sea.

ACOUS
Acronym for Arctic Climate Observations using Underwater Sound, a joint U.S. and Russian program started in 1995. The main objective of ACOUS is to establish a long-term, real-time Arctic Ocean observing system using cabled moorings that integrate point measurements with acoustic remote sensing measurements. The remote sensing is used to monitor basin-scale changes in the ocean temperature and the thickness of the Arctic ice cover. See Mikhalevsky et al. (1999).

acoustic signature
A set of characteristics used to describe a sound signal. This may include sound echos from targets, radiated and ambient noise, with salient echo characteristics including target strength, spectral reflectivity versus frequency, doppler shift, doppler spread and target range extent.

acoustic tomography
The inference of the state of the ocean from precise measurements of the properties of sound waves passing through it. This technique takes advantage of the facts that the properties of sound in the ocean are functions of temperature, water velocity and other salient oceanographic properties and that the ocean is nearly transparent to low-frequency sound waves. These felicitous circumstances combine to allow signals transmitted over hundreds to thousands of kilometers to be processed with inverse methods to obtain estimates of large-scale fields of ocean properties. An especially advantageous feature of this method is that, given the 3000 knot speed of sound in the ocean, reasonably synoptic fields can be constructed. The chief problems presently encountered in this field are those related to engineering sufficiently accurate transmitters and receivers for the task. See Munk et al. (1995).

acoustical oceanography
The study of sound propagation in the ocean and its underlying sediments. This ranges from the earliest use of depth soundings to chart the ocean floor to the use of SONAR to locate schools of fish, underwater vehicles and ocean drifters to the most recent applications of acoustic tomography to infer large-scale properties of the ocean and the ocean floor.

ACSYS
Abbreviation for the Arctic Climate System Study, a WCRP program whose goal to to ascertain the role of the Arctic in global climate. The primary scientific objectives are:

The components of ACSYS include:

[http://acsys.npolar.no/]

adaptive mesh refinement
A method for locally refining grids in finite difference ocean models. The basic idea behind the method is to attain a given accuracy for a minimum amount of work. This is done by computing estimates of the truncation error, and creating refined grids (or removing existing ones) where and when it is necessary. The approach is also recursive so that fine grids can contain even finer grids. See Blayo and Debreu (1999) for an initial application of this method to ocean circulation models.

ADCP
Abbreviation for Acoustic Doppler Current Profiler, an instrument used to measure ocean currents. It transmits high frequency acoustic signals which are backscattered from plankton, suspended sediment, and bubbles, all of which are assumed to be traveling with the mean speed of the water. The ADCP estimates horizontal and vertical velocity as a function of depth by using the Doppler effect to measure the radial relative velocity between the instrument and scatterers in the ocean.

Three acoustic beams in different directions are the minimum number required for measuring the three velocity components, with a fourth adding redundancy and an error estimate. A ping is transmitted from each transducer about once per second, with the echo returning over an extended period. Echos from shallow depths return before those from greater depths. Profiles are produced by range-gating the echo signal, i.e. breaking the echo into successive segments called depth bins corresponding to successively deeper depth ranges. The noisy velocity estimates from each ping are vector-averaged into 1- to 10-minute ensembles, and the resulting relative velocities are rotated from the transducer's to the earth's reference frame using the ship's gyrocompass.

A navigation calculation is performed to obtain absolute currents, which are obtained by subtracting the average of the ship velocity relative to a reference layer (i.e. ADCP velocities) from the absolute ship velocity over the ground (from GPS navigation). The raw absolute current velocities relative to the reference layer are then smoothed to reduce the effect of noise in the position fixes, and combined with the navigation data to obtain the best estimates of ship positions and velocities. Thus, absolute currents at any depth can be determined from the ship navigation data and the relative ADCP measurements.

The ADCP measures the ocean current velocity continuously over the upper 300 m of the water column, usually in 8 m depth increments. It is also used to estimate the abundance and distribution of biological scatterers over the same depth range and in the same depth increments.

ADCP data collection requires that four instruments work together. These are the ADCP itself, the ship's gyrocompass, a GPS receiver, and a GPS Attitude Determination Unit (ADU).

[http://ilikai.soest.hawaii.edu/sadcp/]

adiabatic
Involving or allowing neither gain nor loss of heat.

adiabatic compressibility
A quantity arising from taking derivatives of the density in the $ (p, \theta , S)$ representation of the equation of state. It is defined by

$\displaystyle \kappa\,=\,{1\over\rho} {{\left({ {\partial\rho} \over {\partial p} }\right)}_{\theta, S}}$

where $ \rho$ is the fluid density, $ p$ the pressure, $ \theta$ the potential temperature, and $ S$ the salinity. See Muller (1995), McDougall et al. (1987) and the related saline contraction coefficient and thermal expansion coefficient.

ADIOS
Acronym for Asian Dust Input to the Oceanic System. See Betzer et al. (1988).

adjustment time
A time scale characterizing the decay of an instantaneous input pulse into a reservoir. It is also used to characterize the adjustment of the mass of a reservoir following a change in the source strength.

Adriatic Bottom Water (ABW)
A water mass - also known as Adriatic Deep Water - formed in the southern Adriatic Sea that exits into the Ionian Sea via Otranto Strait. The temperature and salinity of ABW are 13$ ^\circ$C and 38.6 psu, respectively. There are a couple of competing conjectures as to the origin of the ABW: Either way, most studies confirm that ABW represents the most important component of the bottom water of the entire Eastern Mediterranean. See Artegiani et al. (1993).

Adriatic Deep Water (ADW)
Another name for Adriatic Bottom Water (ABW).

Adriatic Sea
A part of the eastern basin of the Mediterranean Sea located between Italy and the Balkan Peninsula. It is landlocked on the north, east and west, and is linked with the Mediterranean through the Otranto Strait to the south. The Adriatic is a rectangular basin oriented in a NW-SE direction with a length of about 800 km and a width of about 200 km. It can be divided into three sub-basins: The bottom rises toward the Strait of Otranto past the southern basin, with the strait having a maximum depth of 780 m, and average depth of 325 m, and a width of about 75 km.

The meteorological forcing has been summarized by Artegiani et al. (1993) as:

Mainly during the winter, the Adriatic Sea region is under a continuous influence of passing mid-latitude meteorological perturbations and of the wind systems associated with them. The two main wind systems are the bora and the scirocco. The bora is a dry and cold wind blowing in an offshore direction from the eastern coast. The scirocco blows from the southeast (i.e. along the longitudinal axis of the basin) bringing rather humid and relatively warm air into the region. In particular, the bora produces appreciable buoyancy fluxes through evaporative and sensible heat loss, induces both wind-driven and thermohaline circulation, and, most importantly, is responsible for deep water formation processes.
This is one of the two regions within the Mediterranean where freshwater input exceeds evaporation (the other being the Black Sea). This is due mostly to outflow from the Po River in the north, which accounts for 1700 m$ ^3$ s$ ^{-1}$ of the 4000 m$ ^3$ s$ ^{-1}$ total river discharge in the Adriatic.

The flow between the Adriatic and the greater Mediterranean through the Otranto Strait is that of a typical dilution basin wherein low salinity water exits near the surface and high salinity water enters at depth. The Mediterranean inflow is of surface Ionian water and, in a deeper layer from 200-300 m, of Modified Levantine Intermediate Water (MLIW). This inflow occurs over a wide area along the eastern shore of the strait, with near-surface outflow concentrated in a thin layer along the western coast. The latter consists of relatively fresh water originating mostly from the northern Adriatic. The remainder of the outflow consists of Adriatic Bottom Water (ABW), a water mass formed in the southern basin that flows over the sill of the Otranto Strait into the Ionian Sea.

The mean basin-wide circulation is generally a cyclonic pattern with several smaller, more or less permanent gyres embedded therein. A topographically controlled cyclonic gyre sitting over the South Adriatic Pit partially isolates the northern Adriatic from Mediterranean influence. This gyre causes a bifurcation of the incoming MLIW, with part of it entering the northern basins over the Palagruza Sill, while the rest is entrained into the South Adriatic cyclonic circulation cell. The circulation regime varies seasonally and interannually in response to changes in the heating and wind regimes. Seasonally, the winter circulation is characterized by a prevalence of warmer Mediterranean inflow reinforced by southerly winds. In summer, there is a stronger outflow of fresher and warmer Adriatic water along the western coast supported by the Etesian winds. See Buljan and Zore-Armanda (1976), Orlic et al. (1992), Artegiani et al. (1993), Tomczak and Godfrey (1994), Artegiani et al. (1997a), Artegiani et al. (1997b) and Poulain (2001).

ABW
Abbreviation for Adriatic Bottom Water.

ADW
Abbreviation for Adriatic Deep Water.

Aegean Deep Water
See POEM Group (1992).

Aegean Sea
A marginal sea in the eastern Mediterranean Sea centered at approximately 25$ ^\circ$ E and 38$ ^\circ$ N. It is located between the Greek coast to the west, the Turkish coast to the east, and the islands of Crete and Rhodes to the south. It contains more than 2000 islands forming small basins and narrow passages with very irregular coastline and topography. The northern part of the Aegean is also known as the Thracian Sea, and the southern part between the Cretan Arc and the Kiklades Plateau (defined as the 400 m isobath) as the Cretan Sea. It contains an extended plateau (Thermaikos, Samothraki, Limnos and Kyklades) as well as the deep basins the North Aegean Trough (1600 m maximum depth), the Chios Basin (1160 m) and the Cretan Sea (two depressions in the east 2561 m and 2295 m deep). It covers an area of 20,105 km$ ^2$, has a volume of 74,000 km$ ^3$, and a maximum depth of 2500 m.

It is connected to the Levantine Sea to the southeast via the Cassos or Kasos Strait (67 km wide, 1000 m deep) between Crete and Karpathos, the Karpathos strait (43 km wide, 850 m deep) between Karpathos and Rhodes, and the Rodos or Rhodos Strait (17 km wide, 350 m deep) between Rhodes and Turkey. It joins the Ionian Sea and Cretan Sea to the southwest through the Antikithira Strait between Crete and Antikithira (32 km wide, 700 m deep), the Kithira Strait between Antikithira and Kithira (33 km wide, 160 m deep), and the Elafonissos Strait between Kithira and Peloponnese (11 km wide and 180 m deep). There is considerable and complicated interchange of water with the eastern Mediterranean through these passages. The Strait of Dardanelles (55 m deep, 0.45-7.4 km wide) provides a northern link to the Black Sea from which the Aegean receives around 190 km$ ^3$ per year of water.

The climate in the Aegean Sea area is characterized by the presence of two distinct periods, summer and winter, with spring and autumn relatively short and transitional. The topography and continual alternation of land and sea make the climate highly variable. Annual river runoff averages about 18,800 $ \times\,{10^6}$ m$ ^3$, and evaporation exceeds precipitation and river runoff. The most prominent wind pattern is the Etesian winds, which are persistent, northerly, cold and dry winds that often reach gale force in July and August. When this wind approaches the southern Aegean is bifurcates, becoming northeasterly over the Kitherian Straits and northwesterly-westerly over the southeastern Aegean. The Etesians vanish in late autumn to be replaced by violent cyclonic storms and highly variable prevailing winds.

The surface circulation is most affected by the summer Etesian winds and the low salinity inflow from the Black Sea. The winds cause upwelling along the western coasts of the islands in the eastern Aegean, and a accompanying cold surface zone with temperatures 2-3$ ^\circ$C lower than in the northern and western Aegean. During the summer, this colder water is present in the eastern Aegean from Rodos Island up to the Limnos Plateau. In winter, the warmer waters of Levantine origin are found in the same area, while the cold waters arriving from the Strait of Dardanelles spread over the Samothraki Plateau and follow the general cyclonic circulation of the north Aegean. In addition to the overall cyclonic circulation, there is also a Samothraki anticyclonic gyre located in the northeastern part of the North Aegean, a semi-permanent feature that can be detected through most of the year, and an anticyclone near Athos.

The surface flow in the south is into the Aegean between Kithira and Crete, Crete and Karpathos, Karpathos and Rhodes, and Rhodes and Turkey, and into the Mediterranean between Kithira and the Peloponnese coast. There is systematic wind-driven upwelling along the northern coasts of the Patraikos and Korinthiakos Gulfs.

The main water masses found in the Aegean are (from shallowest to deepest):

The BSW enters from the Strait of Dardanelles, producing a pronounced halocline in the norther Aegean with a maximum depth from 20-80 m. It moves southward and westward, following the general cyclonic circulation, and can be detected by a surface salinity minimum as far south as the Kithira Straits. LIW is the saltiest water mass of the eastern Mediterranean. It is generated in the Levantine and southern Aegean Seas in February and March. It flows eastwards and westwards from the Aegean, and also flows into the Aegean via the eastern straits of the Cretan Arc. It predominates in the subsurface layers of the Cretan Sea as well as in the eastern parts of the Aegean as far north as the southern boundary of the Limnos Plateau, and is easily identified by its salinity maximum. The modified AW enters the Aegean through the straits of the Cretan Arc and is identifed in several regions as a subsurface (30-200 m) salinity maximum. The Aegean deep water mass extends from about 400-500 m to the bottom, with temperatures ranging from 12-14.5$ ^\circ$C and salinities from 38.68-38.9. See POEM Group (1992), Stergiou et al. (1997) and Balopoulos et al. (1999).

AEROCE
Acronym for Atmosphere/Ocean Chemistry Experiment, a multi-disciplinary and -institutional program focusing on a number of aspects of the atmospheric chemistry over the North Atlantic Ocean. The objectives of AEROCE are:

The program officially started in 1987 with coordinate measurements from four stations, i.e. Barbados, West Indies; Bermuda; Izaña, Tenerife, Canary Islands; and Mace Head Ireland. Five more stations were added in June 1995 to give greater geographical coverage of continuous measurements of bulk aerosol chemical composition and condensation nuclei.

[http://web.mit.edu/igac/www/newsletter/highlights/old/AEROCE.html]

AESOP
Acronym for Alaska Environmental Satellite Oceanography Project, a collection of remote sensing experiments and projects being performed at the Institute of Marine Sciences at the University of Alaska Fairbanks. This seems to have been mothballed as of 2001. This is part of the larger SEA Project.

[http://murre.ims.uaf.edu/]

AESOP
Acronym for Antarctic Environment and Southern Ocean Process Study, also known as the U.S. Southern Ocean Joint Global Ocean Flux Study (JGOFS). AESOP involved studies of two different and distinct regions. The first was the Ross Sea continental shelf, where a series of six cruises (on the R.V.I.B. Nathaniel B. Palmer) collected data from October 1996 through February 1998. The second was the southwest Pacific sector of the Southern Ocean spanning the Antarctic Circumpolar Current (ACC) at 170$ ^\circ$W, where data were collected during five cruises (on the R.V. Roger Revelle) from September 1996 through March 1998, as well as during selected transits between New Zealand and the Ross Sea.

The objectives of the project were to:

The findings of AESOPS include:

See Smith et al. (2000) and other papers therein.

[http://usjgofs.whoi.edu/research/aesops.html]

AFZ
Abbreviation for Arctic Frontal Zone.

AGDW
Abbreviation for Aegean Deep Water.

age of tide
The delay, usually a day or two, between full and new moons (when the equilibrium semi-diurnal tide is maximum) and the following spring tides. This terminology was first used to refer to this phenomenon by Whewell in 1883, although Defant referred to it as ``spring retardation'' in 1961 and Wood later (in 1978) used the terms ``age of the phase inequality'' and ``age of the diurnal equality'' to refer to, respectively, the ages of the semi-diurnal and diurnal tides. This delay is caused by frictional energy dissipation in coastal seas, although a localized increase in the age of tide is also a good indication of resonances at that location. See Murty and El-Sabh (1985).

age of water
The elapsed time since a given water mass was last at the sea surface. See Groves and Hunt (1980).

agger
See double tide.

aggregation
A process that significantly alters the sizes, characteristics and abundances of suspended particles in the ocean. There are two major mechanisms for aggregation:

The impacts of aggregation on marine ecosystems include:

See Alldredge and Jackson (1995).

aguaje
A condition observed annually in the coast water off Peru in which the water is discolored red or yellow and there is a significant loss of marine life. It typically occurs from April through June and is probably caused by an increase in water temperatures via the importation of warmer waters by ocean currents. This causes the death of temperature sensitive marine organisms such as dinoflagellates, which may in turn kill other organisms via the release of toxins. The annual nature of this phenomenon makes it distinct from the El Nino phenomenon occurring in the same region. This is also known as salgaso or aqua enferma.

Agulas Basin
An ocean basin located off the southern tip of Africa at about 43$ ^\circ$ S in the South Atlantic Ocean. It includes the Agulhas Abyssal Plain. See Fairbridge (1966).

Agulhas Current
The western boundary current in the Indian Ocean south of 30$ ^\circ$ S. The southern Agulhas Current flows southwestward as a narrow jet along a steep continental slope, and is normally pinned to within 10-15 km of its mean position at latitudes 28.5-34$ ^\circ$S. Large meanders - called the Natal pulse - can sometimes occur within this region. These extend an average of 170 km offshore with downstream propagation rates of about 21 cm s$ ^{-1}$, with the rates decreasing to 5 cm s$ ^{-1}$ as the continental shelf broadens near 34$ ^\circ$S. At this point the current separates from the coast and continues southwestward along the Agulhas Bank, where many meanders, plumes and eddies exist. The maximum transport of the Agulhas occurs in the vicinity of Agulhas Bank, where transport estimates range from 95 to 136 Sv. The core of the current has been defined as where surface velocities exceed 100 cm s$ ^{-1}$, with the core averaging about 34 km wide with a mean peak speed of 136 cm s$ ^{-1}$ (with a greatest peak speed of 245 cm s$ ^{-1}$).

At around 36$ ^\circ$S the Agulhas leaves the continental shelf and develops oscillations of increasing amplitude, eventually retroflecting back toward the Indian Ocean in the region of 16-20$ ^\circ$E as the Agulhas Return Current. The retroflection loop usually encloses a pool of Indian Ocean surface water south of Africa whose temperature is more than 5$ ^\circ$ warmer than South Atlantic surface water at similar latitudes. The core of the Return Current infrequently passes over the Agulhas Plateau. See Lutjeharms and van Ballegooyen (1988) and Peterson and Stramma (1991).

Agulhas Front (AF)
A strong subsurface to intermediate depth front beneath the upper 100-150 m that originates at around 20$ ^\circ$-25$ ^\circ$ E below the southern tip of Africa. It extends to between 65$ ^\circ$-90$ ^\circ$ E where it merges with the Southern Subtropical Front in the Indian Ocean sector of the ACC. The chief identification criterion is usually the depth range of the 10$ ^\circ$ isotherm, about 300-800 m south of Africa at 16$ ^\circ$-27$ ^\circ$ E. This range shrinks to about 400-650 m to the east in the Kerguelan-Amsterdam passage, indicating the gradual weakening of the AF. A thermostad on the warm side of the AF in the 150-300 m layer is another useful identification criterion. This thermostad cools and freshens to east, ranging from 17$ ^\circ$-18$ ^\circ$ C/35.5-35.6 at 20$ ^\circ$ E to 12$ ^\circ$-14$ ^\circ$ C/35.2-35.4 at 70$ ^\circ$ E. See Belkin and Gordon (1996).

Agulhas Retroflection
See Peterson and Stramma (1991) and Lutjeharms et al. (1992).

Agulhas Return Current
See Agulhas Current and Peterson and Stramma (1991).

Agulhas Undercurrent
A current flowing beneath the Agulhas Current. LADCP measurements indicate the core is centered around 1200 m, against the continental slope and directly below the surface core of the southwestward flowing Agulhas Current. Maximum velocities of 30 cm/s to the northeast are observed in the undercurrent, and its volume transport is 6 Sv, about a tenth that of the overlying Agulhas. See Beal and Bryden (1997).

AIDJEX
Acronym for Arctic Ice Dynamics Joint Experiment, a collaborative program between the U.S., Canada and Japan that took place in two phases in 1975-1976. In summer 1975 four manned camps were maintained on ice floes in the Arctic Ocean to measure surface and geostrophic winds, ocean current velocities, and ice floe position. In April of 1976 the submarine USS Gurnard traversed 777 nautical miles along three tracklines in the Beaufort Sea, collecting ice thickness data from upward-looking acoustical soundings. See Trowbridge (1976).

air-sea interaction
The processes that involve the transfer of energy, matter, and momentum between the atmosphere and the ocean. The is one of the least well understood areas of physical oceanography, with the theory inadequate and the data sparse. Specific areas with glaring gaps include the interaction of the wind and surface waves, the parameterization of subgrid scale processes in large-scale circulation models, and the transfer of gases across the air-sea interfaces. See Donelan (1990), Geernaert (1990), Kraus and Businger (1994) and Rogers (1995).

[http://earth.agu.org/revgeophys/rogers01/rogers01.html]

AIRES
Acronym for Automatic Recording Inverted Echo Sounder.

Airy wave
A theory of waves of small amplitude in water of arbitrary depth that is also known as linear wave theory. The derivation of the theory, given the assumptions of small wave slope ( $ H/L\,\ll\,1$) and a depth much greater than the wave height ( $ h/H\,\gg\,1$), gives the expression for the water surface elevation

$\displaystyle \eta (x,t)\,=\,{H\over 2}\,\cos(kx\,-\,\sigma t)$

where $ H$ is the wave height, $ k$ the wave number, and $ \sigma$ the wave frequency. An expression for the wave length has also been developed, although it must be solved iteratively.

Simpler expressions are available for the limiting cases of deep and shallow water, with deep water being the case where $ h/{L_\infty}\,>\,1/4$ (where $ h$ is the depth and $ {L_\infty}$ the deep water wavelength) and shallow water the case where $ h/{L_\infty}\,<\,1/20$. The particles move generally in closed elliptical orbits that decrease in diameter with depth, reducing to limiting cases of circles and straight lines in, respectively, deep and shallow water. See Kinsman (1984), LeMehaute (1976) and Komar (1976).

AITMP
Abbreviation for Arctic Ice Thickness Monitoring Project.

AIW
Abbreviation for Arctic Intermediate Water.

AIWEX
Acronym for Arctic Internal Wave Experiment, a project of the APL at the University of Washington that took place in 1985. See also LEADEX. See Levine (1990).

Ajax Expedition
An oceanographic research expedition from 1983-1984.

ALACE
Acronym for Autonomous Lagrangian Circulation Explorer float, an instrument that can be programmed to cycle up and down through the water column at predetermined intervals to provide vertical profiles of temperature and salinity. ALACE floats have been used to track currents down to 1.5 km. In operation, the float sinks to its neutral buoyancy depth, drifts with the current, and after a programmed time (5-30 days) increases its buoyancy by pumping oil into an external bladder to rise to the surface. It then transmits data to Service Argos satellites over a 24 hour period, returns the oil to the internal bladder, and sinks again to its neutral buoyancy depth. The cycling continues until the battery energy is depleted after around 100 cycles, or until the float fails for some other reason. See Davis et al. (1992).

Aland Sea
A part of the Baltic Sea bordered by the Gulf of Bothnia to the north, the Gulf of Finland to the east, and the man part of the Baltic Sea to the south.

Alaska Coastal Current
A narrow, high-speed, westward flow which extends for more than 1000 km along the coast of Alaska. This is a separate feature from the offshore, deepwater Alaskan Stream. It was not recognized as such up until the mid-1970s when a series of hydrocast surveys in the area was begun which led to its identification as a distinct circulation feature. The ACC is driven by freshwater discharge from the mountainous and coastal regions around the Gulf of Alaska and the consequent nearshore confinement of this low-salinity water by westward winds. It is typically narrow ($ <$ 50 km), shallow ($ <$ 150 m) and partially baroclinic. It flows most intensely between 145 and 155$ ^\circ$ W through the Shelikov Strait between the Alaskan Peninsula and Kodiak and Afognak Islands, but extends recognizably along the Peninsula as far as 165$ ^\circ$ W.

The baroclinic speeds and transports have been estimated as typically $ <$30 cm s$ ^{-1}$ and 0.4 Sv, respectively, in the winter, spring and summer. In the fall, when the freshwater influx leads to the spin-up of the ACC, the speeds and transports have been estimated as 89-133 cm s$ ^{-1}$ and 1.0-1.2 Sv, respectively. Current mooring measurements have yielded estimates of six-month mean total transports ranging from 0.85 Sv at 151$ ^\circ$ W to 0.64 Sv at 155$ ^\circ$ in Shelikof Strait, with daily means as high as 2.5 Sv and marked variability from day to day. This variability is thought to be mainly due to variations in wind-forcing caused by the passage of large-scale storms along the coast. The mean baroclinic transport as estimated from the same measurements was found to be about 75% of the total. See Stabeno et al. (1995).

Alaska Current
The eastern limb of the counterclockwise-flowing subpolar gyre in the North Pacific. This current is concentrated on the shelf region by the freshwater input from Alaskan rivers which enhances the pressure gradient across it. It is strongest in winter with current speeds around 0.3 m/s and weakest in July and August when prevailing winds tend to oppose its flow. This current may or may not be distinguished from a western boundary current flowing along the Aleutian Islands and called the Alaskan Stream. Both have previously gone by the name of Aleutian Current. Whether or not the nomenclature makes a distinction, the Alaskan Stream and Current do have distinguishing characteristics. The Current is shallow and highly variable while the Stream is steadier and reaches to the ocean floor. The more barotropic nature of the latter is evidence that it is indeed a product of western boundary current dynamics while the former is in an eastern boundary regime. See Thomson (1972). Tomczak and Godfrey (1994).

Alaska Gyre
A subpolar cyclonic circulation in the northeast Pacific associated with the Aleutian low. The primary currents consist of a broad eastern boundary current flowing north, condensing into a narrow western boundary flow in the apex of the gyre and proceeding west-southwest along the Aleutian Peninsula as the Alaskan Stream. See Lagerloef (1995).

Alaskan Stream
See Alaska Current.

ALBATROSS
Acronym for Antarctic Largescale Box Analysis and the Role Of the Scotia Sea, a cruise along the rim of the Scotia Sea that took place from March 15 to April 23, 1999 on the RRS James Clark Ross. The aim of the cruise was to study the influence of the Scotia Sea on global ocean circulation by undertaking a detailed hydrographic survey of a box surrounding the Scotia Sea, with CFCs, oxygen isotopes, tritium, helium and nutrients sampled as well as the traditional temperature, salinity and oxygen. The specific goals of ALBATROSS were:

[http://www.mth.uea.ac.uk/ocean/ALBATROSS/]

albedo
The proportion of incident radiation reflected by a surface. About 30% of the incoming solar energy is reflected back to space from the earth, of which 25% is reflected by clouds and 5% by the surface or by atmospheric molecules or suspended particles. The clouds and atmospheric gases and particles absorb 25% of the incident radiation with the remainder absorbed at the surface. See Peixoto and Oort (1992), Ch. 6.

Alboran Sea
A part of the western basin of the Mediterranean Sea that extends from the Gibraltar Strait Alboran Islands covering an area between about 35$ ^\circ$ and 38$ ^\circ$ N and 6$ ^\circ$ N and the Equator. This sea is dominated by a wavelike front with two anticyclonic gyres in the western and eastern parts of the basin, which at times disappear completely. The Algerian Current is closely tied to the dynamics associated with the eastern anticyclonic gyre. It abuts the Balearic Sea to the east. See Va (1984), Fairbridge (1966), Gascard and Richez (1985), Vazquez-Cuervo et al. (1996) and Viúdez et al. (1998).

Alboran gyre
A gyre found in the Alboran Sea. See Speich et al. (1996) and Nof and Pichevin (1999).

ALE
Acronym for Arbitrary Lagrangian Eulerian, a finite element solution technique for fluid flow problems with moving interfaces, e.g. moving walls, free surfaces, etc. In the ALE method, the newly updated free surface is determined purely via the Lagrangian method, i.e. by the velocities of the fluid particles at the free surface. The nodes in the interior of the domain are displaced in an arbitrarily prescribed way to obtain a mesh of proper shape and to avoid mesh crossing.

Aleutian Current
See Alaska Current.

Aleutian low
A center of action centered over the Aleutian Islands between the east coast of the Siberian Kamchatka Peninsula and the Gulf of Alaska at about 50$ ^\circ$ N. It is prominent in the winter and disappears in summer, with the average central pressure below 1000 mb in January. See Angell and Korshover (1974).

ALEX
Acronym for AIDJEX Lead Experiment, which took place Feb. 23 through Apr. 10, 1974 and investigated small-scale meteorological and oceanographic processes associated with leads in pack ice near Barrow, Alaska. The experiment plan called for rapid deployment of five instrumental huts, measuring equipment and personnel by helicopeters and fixed-wing aircraft. The processes of primary interest were sensible, latent, and radiant heat loss to the atmosphere as well as the sinking of convective plumes of saline water formed by freezing and brine rejection at the surface. Logistical problems limited the success of the experiment, with the helicopter range limiting deployment to within 30 miles of Barrow and a dearth of suitable leads in that area. See SMith et al. (1990).

ALFOS
Acronym for Long-life, multi-cycle, pop-up RAFOS floats, i.e. RAFOS floats that surface at regular intervals throughout their lifetime and transmit data via satellite.

Alfred Wegener Institute (AWI)
The German national research center for polar and marine research. The Institute was founded in 1980 and named after the geophysicist and polar researcher Alfred Wegener. The mandate of the AWI includes fundamental scientific research in the polar regions, national coordination of polar research projects, and logistic support of polar expeditions from other German institutes. The Institute uses the RV Polarstern to perform research at sea. See the AWI Web site.

Algerian Current
A current that flows eastward along the Algerian coast in the Mediterranean Sea. It flows as a narrow, easily distinguished current for around 300 km from about 0 to 4$ ^\circ$ E with a width of less than 30 km, average and maximum velocities of 0.4 and 0.8 m/s, respectively, and a tranport of about 0.5 Sv. This is a continuation of the current associated with the Almeria-Oran Front that is itself a continuation of the flow of Atlantic Ocean water entering through the Gibraltar Strait. See Arnone et al. (1990) and Tomczak and Godfrey (1994).

aliasing
A phenomenon encountered when sampling a continuous function to produce values at discrete points. If the sampling frequency isn't high enough to resolve the highest frequency signal present in the continuous function, then the high frequency information above the sampling frequency will appear as a false enhancement of (or, equivalently, be aliased onto) a related lower frequency in the computed power spectrum.

ALIPOR
Acronym for Autonomous Lander Instrumentation Packages for Oceanographic Research, a project funded by MAST III to create a European fleet of lander vehicles that can operate together in joint research projects. Lander vehicles will be built to carry out a variety of experiments ranging from sediment probes to fish tracking. Three facets of lander technology are to be addressed: (1) the development of techniques to launch a fleet of landers from a single ship; (2) the development of new sensors for examining processes in the water of the deep benthic boundary layer at depths ranging from 200 to 5000 meters; and (3) the design and construction of two new types of landers, i.e. one that can carry several sensing devices and another compact one that can be operated from a small vessel. See the ALIPOR Web site.

Alk
Common abbreviation for alkalinity.

alkalinity
A property of sea water operationally defined as the excess positive charge to be balanced by CO$ _3$ and HCO$ _3$ ions. The carbonate ion content of any unit of sea water is equal to its alkalinity (i.e. excess positive charge) minus its total dissolved carbon content. See Broecker and Peng (1982).

Almeria-Oran Front
A front and an associated current that separate the fresher water flowing in from the Atlantic Ocean via the Gibraltar Strait from the saltier Mediterranean Sea water to the west. The incoming water flows eastward as a jet, breaks into one or two large eddies of around 150 km diameter, and then is deflected to the right (the south) by the Coriolis force where it encounters the African coast and continues flowing eastward as the Algerian Current. See Tomczak and Godfrey (1994).

ALT
Acronym for the radar altimeter used on the TOPEX/POSEIDON mission. The ALT was the first spaceborne dual-frequency altimeter and is the primary instrument for the mission. Measurements are made at two frequencies (5.3 and 13.6 GHz) and combined to minimize the errors caused by the presence of ionospheric free electrons, the total content of which is obtained as a by-product of the measurement. This instrument was based on previous Seasat and Geosat altimeters with several improvements including the 5.3 GHz channel for the ionospheric measurement, more precise height measurement, and a longer lifetime. See Hayne et al. (1994).

ALVIN
A deep submersible commissioned on June 5, 1964 at the Woods Hole Oceanographic Institution. It has been used for over a thousand research and rescue missions in the years since it was first launched, most from aboard the tender ship Atlantis II, which was retired from that duty in 1996. See Kaharl (1990).

[http://www.marine.whoi.edu/ships/alvin/alvin.htm]
[http://www.whoi.edu/oceanus/OceanusS95Alvin.html]

AmasSeds
Abbreviation for Amazone Shelf Sediment Study, an international field program designed to investigate the transport of fresh water and suspended sediment from the Amazon River into the Atlantic. See Nittrouer et al. (1991).

Amazon River
More later.

Amazon shelf
See Geyer et al. (1996).

AMO
Abbreviation for Atlantic Multidecadal Oscillation.

AMOC
Acronym for Acoustic Monitoring of the Ocean Climate in the Arctic Ocean, a 1994-1998 program whose overall objective was to develop and design an acoustic system for long-term monitoring of the ocean temperature and ice thickness in the Arctic Ocean, including the Fram Strait, for climate variability studies and global warming detection. The specific objectives included:

[http://www.nrsc.no/~amoc/]

AMODE
Acronym for Acoustic Mid-Ocean Dynamics Experiment, a 1991-1992 experiment involving a tomography array located between Puerto Rico and Bermuda. The width of the array was abouata 670 km and is consisted of six mooring acoustic sources and receivers. The array detected signals of the lowest internal wave modes at diurnal frequencies. See Dushaw and Worcester (1998).

AMODE-MST
Abbreviation for Acoustic Mid-Ocean Dynamics Experiment-Moving Ship Tomography group. See AMODE-MST Group (1994).

amount effect
A term applied to the relationship between isotopic composition and monthly rainfall where months with heavy rainfall show different isotopic concentrations than do months with low rainfall. In high rainfall months, rain frequency is higher which entails a higher relative humidity in sub-cloud air, hence less evaporation from raindrops. Since the rate of evaporation determines the isotopic concentrations (the greater the rate the higher the heavy stable isotope composition), low rainfall months should show a higher heavy stable isotopic composition than high rainfall months.

AMP
Abbreviation for Advanced Microstructure Profiler, an instrument developed at the APL.

amphidrome
A stationary point around which tides rotate in a counterclockwise (clockwise) sense in the northern (southern) hemisphere, i.e. the point about which the cotidal lines radiate. The vertical range of the tide increases with distance away from the amphidrome, with the amphidrome itself the spot where the tide vanishes to zero (or almost zero). This is also called an amphidromic point. See Fairbridge (1966).

amphridomic point
See amphidrome.

AMT
Acronym for Atlantic Meridional Transect programme.

AMTEX
Acronym for the Air Mass Transformation Experiment, conducted near Japan in 1974 and 1975. See Geernaert (1990).

Amundsen Abyssal Plain
One of the three plains that comprise the Pacific-Antarctic Basin (the others being the Bellingshausen and Mornington Abyssal Plains). It is located at around 150$ ^\circ$ W.

Amundsen Sea
A marginal sea of Antarctica centered at about 112$ ^\circ$ W and 73$ ^\circ$ S. It sits between the Bellingshausen Sea to the east and the Ross Sea to the west, with the Antarctic Circle serving as the northern boundary. See Fairbridge (1966) and Grotov et al. (1998).

AMUSE
Acronym for A Mediterranean Undercurrent Seeding Experiment, an experiment taking place from 1993-1995 whose overall objective was to observe directly the spreading pathways by which Mediterranean Water enters the North Atlantic, including the direct observation of Mediterranean eddies, i.e. meddies. The measurements included repeated high resolution XBT section and RAFOS float deployments across the Mediterranean Undercurrent south of Portugal near 8.5$ ^\circ$W.

A total of 49 floats were deployed at the rate of about two floats per week on 23 cruises of the Portuguese vessel Kialoa II and one cruise of the R/V Endeavor. The floats were ballasted for 1100 or 1200 decibars to seed the lower salinity core of the Undercurrent. The objectives of the float study were:

[http://science.whoi.edu/users/abower/AMUSEdr/amdr.htm]

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Manbreaker Crag 2001-08-17