An-Az

Anadyr Current

A surface current that flows along the northwestern side of the Bering Sea and on through the Bering Strait. It is mostly seasonally invariant with a velocity of about 0.3 m/s. See Tomczak and Godfrey (1994).

analog

In signal processing this refers to a continuous physical variable which bears a direct relationship to another variable so that one is proportional to the other. An example would be the mercury level in a thermometer and its relation to the temperature, both of which vary continuously on the macroscopic level. Contrast with digital.

Andaman Sea

A body of water in the northeastern corner of the Indian Ocean that lies to the west of the Malay Peninsula, the north of Sumatra, the east of the Andaman Islands, and the south of the Irrawaddy Delta in Burma. It stretches about 650 km from west to east and 1200 km from north to south. The Andaman communicates with the westward lying Bay of Bengal through several channels between the chain of islands that stretches along 93$^\circ$ E., including the Preparis (200 m deep), Ten Degree (800 m deep) and Great (1800 m deep) Channels. It is connected with the Australasian Mediterranean Sea via the Malacca Strait between Thailand and Sumatra. It has been variously estimated to have an area of 600,000 to 800,000 km2 and an average and maximum depth of, respectively, 870-1100 m and 4200 m.

The temperature of the surface waters fluctuates mildly from a monthly average of about 30$^\circ$ C in the summer months to one of about 27.5 in the winter months. They drop off with depth to about 5$^\circ$ C and 2000 m. The surface salinities exhibit strong seasonal variations due to an extremely large freshwater influx from the Irrawaddy and Salween rivers during monsoon season. In the northern part the salinities range from about 20 during the monsoon months from June to November to about 32 from Demember to May. These grade to a fairly constant 33.5 in the southwest end and to a maximum of about 35 near 1500 m depth.

The steadiest current is the inflow through the Malacca Straits, averaging around 1/3-2 knots through the year. The monsoons controls the currents elswhere, driving inflow waters from the Bay of Bengal through the western channels from June to August during the southwest monsoon. This also pushes the Malaccan inflow against the Sumatran coast and forces some Andaman sea water through the Straits. When these winds die southwestward currents gradually form that are maintained and enhanced by the northeast monsoon from December through February. A more sudden shift is seen from March through May when the southwest monsoons begins anew. See Fairbridge (1966).

anelastic approximation

A filtering approximation for the equations of motion that eliminates sound waves by assuming that the flow has velocities and phase speeds much smaller than the speed of sound. In its purest form, it requires that the reference state be isentropic as well as hydrostatic, although in practice the reference state is often taken to be nonisentropic which can have deleterious effects on the energy conservation properties of the full set of equations. The anelastic approximation is one of the set of approximations used for the somewhat similar Boussinesq approximation. See Ogura and Phillips (1962), Durran (1989), and Houze (1993), pp. 35-37.

Angola Basin

An ocean basin located to the west of Africa at about 15$^\circ$ S in the south-central Atlantic Ocean. It is demarcated to the north by the Guinea Ridge, south of which lies the Angola Abyssal Plain which is fed by the Congo Canyon, the largest in the eastern Atlantic. This has also been known as the Buchanan Deep. See Fairbridge (1966).

Angola-Benguela Front

A front, often abbreviated as ABF, caused by the confluence of the southward flowing Angola Current and the northward flowing Benguela Current near 16$^\circ$ S off the African coast. This can be identified in the temperature of the upper 50 m and in the salinity to at least 200 m. See Tomczak and Godfrey (1994) and Lass et al. (2000).

Angola Current

The eastern part of a cyclonic gyre centered around 13$^\circ$ S and 4$^\circ$ E that is driven by the South Equatorial Countercurrent in the Atlantic Ocean. This subsurface circulation gyre extends from just below the surface to around 300 m depth with velocities of about 0.5 m/s in the section nearest the African coast. The confluence between this southward flowing current and the northward flowing Benguela Current near 16$^\circ$ S off the African coast is called the Angola-Benguela Front. See Tomczak and Godfrey (1994).

Angola Dome

A small cyclonic gyre, centered near 10$^\circ$ S and 9$^\circ$ E, driven by the South Equatorial Undercurrent in the eastern Atlantic Ocean. It is called a dome due to the elevation or doming of the thermocline in the middle of the gyre. This is distinct from the larger gyre that incorporates the Angola Current. See Peterson and Stramma (1991) and Tomczak and Godfrey (1994).

angular frequency

The repetition rate of a cyclic process measured in radians/sec. If the frequency in cycles/sec is f, then the angular frequency $\omega$ = $2\pi$f.

angular momentum

The product of mass times the perpendicular distance from the axis of rotation times the rotation velocity. The angular momentum about the Earth's axis of rotation can be expressed as the sum of the angular momentum of the solid Earth's rotation plus the angular momentum of zonal air motion relative to the surface of the Earth. Were this quantity to be absolutely conserved, a parcel of air with the angular momentum of the Earth's surface at the Equator would have a westerly zonal wind speed of 134 m/s at 30$^\circ$ latitude. See Hartmann (1994).

anisotropic

Descriptor for a physical property (e.g. density, etc.) that varies depending on the direction in which it is measured.

Annual El Niño Current (AENC)

See Cucalón (1987) and Strub et al. (1998).

anomaly of specific volume

Another name for the specific volume anomaly.

Antarctic Bottom Water (AABW)

A type of water in the seas surrounding Antarctica with temperatures ranging from 0 to -0.8$^\circ$ C, salinities from 34.6 to 34.7, and a density near 27.88. ABW is formed in the Weddell and Ross Seas. This is the densest water in the free ocean, with the only denser waters being found in regional sill basins such as the Norwegian Sea or the Mediterranean. It is overlain by Antarctic Circumpolar Water (AACW) at a depth of 1000 to 2000 m [3000 m (Tchernia)] and overlies Weddell Sea Bottom Water (WSBW) in some locations.

The flow of AABW in the tropical Atlantic is described by Rhein et al. (1998) as:

About one-third of the northward flowing AABW at 10$^\circ$S (4.8 Sv) and at 5$^\circ$S (4.7 Sv) west of about 31$^\circ$30'W enters the Guiana Basin, mainly through the southern half of the Equatorial Channel at 35$^\circ$W (1.5-1.8 Sv). The other part recirculates and some of it flows through the Romanche Fracture Zone into the eastern Atlantic. In the Guiana Basin, west of 40$^\circ$W, the sloping topography and the strong, eastward flowing deep western boundary current might prevent the AABW from flowing west: thus it has to turn north at the eastern slope of the Ceara Rise (2.2 Sv). At 44$^\circ$W, north of the Ceara Rise, AABW flows west in the interior of the basin in a main core near 7$^\circ$15'N (1.9 Sv). A net return flow of about 0.5 Sv was found north of 8$^\circ$43'N. A large fraction of the AABW (1.1 Sv) enters the eastern Atlantic through the Vema Fracture Zone, leaving only 0.3 Sv of AABW for the western Atlantic basins.

See Jacobs et al. (1970), Tomczak and Godfrey (1994), Tchernia (1980) and Rhein et al. (1998).

Antarctic Circumpolar Current (ACC)

A major eastward flowing current that circles the globe in the Southern Ocean. It is principally driven by surface wind stress, although there is a significant thermohaline component that is not yet well understood. In the way of vorticity dynamics a simple Sverdrup balance with dissipative mechanisms of form drag by bottom topography and lateral dissipation in western boundary layers has been found consistent with the data. The present best estimates of its transport through Drake Passage give a net mean transport of 125 Sv (with a standard deviation of 10 Sv) above 2500 m.

The transport of the ACC is concentrated in two current cores separated by a transition zone with surface water characteristics intermediate between those found to the south in the Antarctic Zone and to the north in the Subantarctic Zone, with the transition zone being known as the Polar Frontal Zone. The maximum geostrophic surface speeds in these cores have been calculated as 25-45 cm s${^{-1}}$ in Drake Passage.

There is also considerable mesoscale variability in the ACC region due to instabilities causing both cold and warm core rings to be shed. These eddies have been found to have spatial scales varying from 30 to 100 km, surface velocities typically 30 cm s$^{-1}$ or greater, and are vertically coherent from surface to bottom. The regions of highest variability have been found to be correlated with prominent topographic features on the sea floor.

The ACC is a region of complicated and large meridional heat flux, with a mean ocean heat loss to the south estimated at about 0.45 petawatts due to ocean-atmosphere heat exchange and equatorward Ekman transport. This is thought to be balanced by the import of heat via eddy processes and deep boundary currents, although the proportions are known only vaguely as yet. See Nowlin, Jr. (1986).

Antarctic Circumpolar Water (AACW)

A type of water in the seas surrounding Antarctica with temperatures ranging from 0 to 0.8$^\circ$ C, salinities from 34.6 to 34.7 ppt, and a depth range from a few hundred meters to about 1000-2000 m [3000 m (Tchernia)] It is formed from a mixture of overlying North Atlantic Deep Water (NADW) and underlying (at 1000-2000 m) Antarctic Bottom Water (AABW). It has a temperature maximum around 500-600 m and a salinity maximum between 700-1300 m. This was originally called Warm Deep Water (WDW) by Deacon, but renamed AACW by Sverdrup. See Tomczak and Godfrey (1994), pp. 83, 287 and Tchernia (1980).

Antarctic Circumpolar Wave

Interannual variations in the atmospheric pressure at sea level, wind stress, sea surface temperature and sea-ice extent that propagate eastwards around the Southern Ocean. These anomalies propagate with the circumpolar flow with a period of 4-5 years and taking 8-10 years to circle the pole. See White and Peterson (1996).

[http://acw.ucsd.edu/]

Antarctic Convergence

See Polar Front.

Antarctic Divergence

In physical oceanography, a region of rapid transition located in the Antarctic Zone of Southern Ocean between the Continental Water Boundary to the south and the Polar Front to the north. It can be distinguished hydrographically by a salinity maximum below about 150 m caused by the upwelling of water of high salinity, i.e. North Atlantic Deep Water. Above this the maximum is blurred by high precipitation and the melting of ice. Its position corresponds reasonably well to the demarcation between the east and west wind drifts which, in the light of Ekman dynamics, at least partially explains its divergent nature. See Tomczak and Godfrey (1994), pp. 76-79.

Antarctic Front

In meterology, a front which develops and persists around the Antarctic continent at about 60-65$^\circ$ S, and divides Antarctic Air from the maritime Polar Air to the north.

Antarctic Intermediate Water (AAIW)

In physical oceanography, a type of water mass in the Southern Ocean thought to originate mainly through convective overturning of surface waters during winter west of South America, after which it is injected into the subtropical gyre and fills the southern subtropics and tropics from the east.

In the Atlantic, the densest SAMW found in the Subantarctic Zone between the Subantarctic Front and the Subtropical Front is thought to be the primary precursor to AAIW, although some postulate substantial input across the Subantarctic Front. The AAIW in the South Atlantic originates from a surface region of the circumpolar layer, especially in the northern Drake Passage and the Falkland Current loop. AAIW from the Indian Ocean is added to the Atlantic AAIW via Agulhas Current leakage. The AAIW is recognized by a subsurface oxygen maximum and a salinity minimum north of about 50$^\circ$S, although the oxygen maximum becomes weak north of 15$^\circ$S. The oxygen maximum is found at a slightly lower density than the salinity minimum.

The salinity minimum is found at about 300 m near the Subantarctic Front at around 45$^\circ$S, descends northward to 900 m at 30$^\circ$S near the subtropical gyre center, and rises again to 700 m at the equator. The AAIW spreads to the North Atlantic, identified by a salinity minimum near the equator at a $\sigma_\theta$ value of about 27.3. This minimum has been found to 24$^\circ$N, although traces of AAIW can be followed as far north as 60$^\circ$N. AAIW is characterized by a temperature near 2.2$^\circ$ C and a salinity around 33.8 near its formation region, but erodes by the time it reaches the Subtropical Front to values closer to 3$^\circ$ C and 34.3. See Piola and Georgi (1981), Whitworth and Jr. (1987), Tsuchiya (1989), Tomczak and Godfrey (1994), Boebel et al. (1997) and Schmid et al. (2000).

Antarctic Polar Front

See Polar Front.

Antarctic Polar Frontal Zone (APFZ)

A concept originated in the 1960s following a detailed study of the Polar Front. This was later transformed into the concept of the Polar Frontal Zone. See Gordon (1971), Gordon (1977), and Belkin and Gordon (1996).

Antarctic Surface Water (AASW)

In physical oceanography, a water mass in the Antarctic Zone of the Southern Ocean AASW is found in the upper 200 m south of the Polar Front (PF) and is cold, fresh, and high in oxygen and nutrients relative to the subantarctic surface waters, although it is high in nutrients compared to underyling waters. The most easily distinguishable characteristics of AASW in summer sections is a intense temperature minimum at about 200 m that marks the base of the winter mixed layer. The water around this minimum is also commonly known as Winter Water, and ranges from 50 m deep in the Weddell Gyre to nearly 1000 m just north of the PF. It is characterized by very low temperatures ranging down to the freezing point of -1.9$^\circ$ C and low salinities as the result of ice melting in the summer in the upper 100-250 m of the water column. See Tomczak and Godfrey (1994) and Whitworth and Jr. (1987).

Antarctic Zone

A name given to the region in the Southern Ocean between the Polar Front to the north and the Southern ACC Front to the south. The AZ is one of four distinct surface water mass regimes in the Southern Ocean, the others being the Continental Zone (CZ) to the south and the Polar Frontal Zone (PFZ) and Subantarctic Zone (SAZ) to the north. See Orsi et al. (1995).

ANTARES

A research program whose overall objective is to describe and model the biogeochemical processes controlling the dynamics of nutrients (C, N, S, P) and silica in the Southern Ocean. More detailed objectives include investigating the seasonal ice zone, deploying arrays of sediment traps, and studying benthic processes.

The first program cruise, ANTARES I, took place from March 29 to May 18, 1993 on board the R. V. Marion Dufresne. Stops were made at the Kerguelan and Crozet Islands on a ship track that traversed an area between 40$^\circ$ and 60$^\circ$ S and 50$^\circ$ and 75$^\circ$ E in the Southern Ocean. Hydrographic and nutrient data were acquired with rosette hydrocasts and CTD and oxygen profiles were obtained with a Neil Brown Mark III B probe. Various core samples were also taken at a total of 20 stations where 142 hydrological and coring sampling operations were performed. See Gaillard (1997).

anticyclone

An atmospheric pressure distribution in which there is a high central pressure relative to the surroundings. This term was selected to imply the possession of characteristics opposite to those found in a cyclone or depression. As such, the circulation about the center of an anticyclone is clockwise (counter-clockwise) in the northern (southern) hemisphere, and the weather is generally quiet and settled.

anticyclonic

The direction of rotation around a center of high pressure. This is clockwise in the northern hemisphere and counter-clockwise in the southern.

Antilles Current

More later.

antitriptic wind

A type of wind that occurs when the pressure gradient is balanced by the force of friction. These are the atmospheric analogs of Poisseuille flow. See Dutton (1986).

ANZFLUX

Acronym for the Antarctic Zone Flux experiment, the objective of which was to measure the magnitude of heat flux through the air-sea-ice interface and to describe the mechanisms that drive and control the fluxes of heat, salt and momentum. It took place aboard the RV Nathaniel B. Palmer in the Eastern Weddell Sea from June 27 to August 24, 1994. See the ANZFLUX Web site.

AODW

Abbreviation for Arctic Ocean Deep Water.

AOGCM

Abbreviation for atmosphere/ocean general circulation model, a numerical model that has fully dynamical atmosphere and ocean components that are somehow coupled.

AOIPS

Abbreviation for Atmospheric and Oceanographic Information Processing System. See Hasler and desJardins (1987).

AOMIP

Acronym for Arctic Ocean Model Intercomparison Project, an effort designed to identify systematic errors in Arctic Ocean models under realistic forcing. The main goals of the proposed research are to examine the ability of Arctic Ocean models to simulate variability on seasonal to interannual scales, and to qualitatively and quantatively understand the behaviour of different Arctic Ocean models. AOMIP's major objective is to use a suite of sophisticated models to simulate the Arctic Ocean circulation for the periods 1946-1998 and 1899-1998. Forcing will use the observed climatology and the daily atmospheric pressure and air temperature fields. Model results will be contrasted and compared to understand model strengths and weaknesses.

[http://fish.cims.nyu.edu/project_aomip/overview.html]

AOML

Abbreviation for Atlantic Oceanographic and Meteorological Laboratory.

AOS

Acronym for Arctic Ocean Section.

AOSB

Abbreviation for Arctic Ocean Sciences Board, a non-governmental body including members and participants from research and governmental institutions from several nations. The long-term mission of the AOSB is to facilitate Arctic Ocean research by the support of multinational and multidisciplinary natural science and engineering programs. It was established in May 1984.

[http://www.aosb.org/]

AOSN

Abbreviation for Autonomous Ocean Sampling Network, a project whose long-term goals are to create and demonstrate a reactive survey system capable of long-term unattended deployments in harsh environments. The scientific objectives include:

• to create small, high performance mobile platforms capable of deployments lasting for several months, with both propellor-driven, fast survey vehicles and buoyancy-driven glider vehicles being developed;
• to create an infrastructure that supports controlling, recovering data from, and managing the energy of remote deployed mobile platforms, with structure elements including moorings, docking stations, acoustic communications, two-way satellite communcations, and the Internet;
• to demonstrate these capabilities in science-driven field experiments; and
• to develop adaptive sampling strategies to most efficiently meet deployment objectives.

See Curtin et al. (1993).

[http://auvlab.mit.edu/MURI/index.html]

AOU

Abbreviation for Apparent Oxygen Utilization, defined as the difference between the observed oxygen content and the saturation oxygen content of a sample of sea water. This is a method of estimating the amount of dissolved oxygen utilized by organisms via respiration, although it is called "apparent" for a reason. Surface waters may more than likely carry more than the saturation amount of oxygen due to the nonlinearity in the solubility of oxygen with temperature. The effects of this nonlinearity are small, though, and the AOU is usually quite close to TOU, the True Oxygen Utilization. See Broecker and Peng (1982).

APARE

Acronym for East Asian/North Pacific Regional Experiment, an IGAC activity. The scientific goals of APARE are to quantify the oxidising efficiency, and atmospheric acidification by studying the emission, transport, chemical transformation, and deposition of primary and secondary chemical species over the East Asian Continental Rim Region and northwestern Pacific Ocean. The objectives are:

• to assess transport and chemical transformations of air pollutants over the East-Asian continent and the northwestern Pacific Ocean, with particular emphasis on distribution and photochemistry of reactive species to understand oxidizing efficiency and the 03 budget in the region; and
• to determine the deposition of primary and secondary pollutants in the East Asian region, with major emphasis on understanding the present status and future prospects of acidification of the atmosphere and deposition of acidic species in the region.

[http://web.mit.edu/afs/athena.mit.edu/org/i/igac/www/sub_pages/apare.html]

APE

Abbreviation for available potential energy.

APEX

Acronym for Arctic Polynya Experiment. See Pease et al. (1985).

APFZ

Abbrevation for Antarctic Polar Frontal Zone.

aphotic zone

The region below the euphotic zone where no light is available for photosynthesis.

APO

Abbreviation for Association of Physical Oceanography, the name of what is now known as the IAPSO from 1929 to 1948.

APROPOS

Acronym for Advances and Primary Research Opportunities in Physical Oceanography Studies, a workshop for physical oceanographers held at Monterey, California from December 15-17, 1997. The goal was to evaluate the current status of research in physical oceanography and to identify future opportunities and infrastructure needs. Similar workshops were held at the time for biological oceanography (sf OEUVRE), ocean chemistry (FOCUS) and marine geology and geophysics (FUMAGES).

Future directions and problems mentioned in the final report included:

• the difficulties inherent in global climate prediction wherein the decadal timescale only allows scientists to observe a few realizations in their lifetimes, and the need to circumvent this by expanding the current database and framing hypotheses about past climate change and ocean circulation using paleoceanographic studies;
• better understanding the ocean's role in the hydrologic cycle;
• advancements on fundamental issues such as the causes of the temperature-salinity relationship, thermocline maintenance, and interhemispheric water mass exchanges;
• the increasing use of observational tools such as satellites and tomography to obtain large-scale, detailed and long-term measurements of the oceans;
• emerging issues concerning connections between large- and small-scale motions, e.g. between small-scale turbulent mixing and large-scale meridional overturning circulation;
• better understanding of the processes involved in cross-shelf transports;
• increased understanding of inland waters such as estuaries, wetlands, tide flats and lakes will probably lead to progress on the general circulation problem;
• unraveling the connections between the spatial and temporal distribution of turbulent mixing, the large-scale meridional overturning circulation, and climate variability;
• radical advances in knowledge of the structure of the ocean on scales between the mesoscale (50 km) and the microscale (less than 10 m) via the use of towed and autonomous vehicles; and
• general circulation model components greatly in need of improvement include deep convection, boundary currents and benthic boundary layers, the representation of the dynamics and thermohaline variability of the upper mixed layer, fluxes across the air-sea interface, diapycnal mixing and topographic effects.

[http://www.joss.ucar.edu/joss_psg/project/oce_workshop/apropos/]

ARABESQUE

A U.K.-led, international program of upper-ocean biogeochemistry investigations in the Arabian Sea region. It was conducted during two contrasting seasons, i.e. the waning of the southwest monsoon in August/September, and the intermonsoon-northeast monsoon transition in November/December 1994. Biogeochemical studies were carried out along three transects in the Gulf of Oman and the Arabian Sea, with the main transcect, 1590 km in length, orthogonal to the southern Oman coast. See Burkill (1999).

Arabian Gulf

See Persian Gulf.

Arabian Sea

A regional sea, centered at approximately 65$^\circ$ E and 15$^\circ$ N, that is bounded by Pakistan and Iran to the north, Oman, Yemen and the Somali Republic to the west, India to the east, and the greater Indian Ocean to the south. The southern boundary, from an oceanographic point of view, runs from Goa on the Indian coast along the west side of the Laccadive Islands to the equator, and thence slightly to the south to near Mombasa on the Kenyan coast. It covers an area of about 7,456,000 km$^2$.

The flow pattern in the Arabian Sea is seasonal, changing with the monsoon winds. In the northeast monsoon season (from November until March) the winds are light and the surface circulation is dominated by a weak westward, counter-monsoon flow (as an extension of the North Equatorial Current) with velocities usually under 0.2 m/s. This pattern starts in November with water supplied by the East Indian Winter Jet flowing around the southern tip of Indian and heading northwestward along the western Indian shelf.

Westward flow dominates in the southern parts until late April with the north gradually shifting into a weak anticyclonic pattern. With the advent of the southwest monsoon in April, the Somali Current and its northward extension, the East Arabian Current, both develop into strong, northeastward flowing currents by mid-May. The anticyclonic pattern in the eastern Arabian Sea is simultaneously being gradually replaced by a moderate eastward flow composed of extensions of the Somali Current and the Southwest Monsoon Current. This pattern lasts for 4-5 months, peaking in June and July at about 0.3 m/s and weakening rapidly in October as the eastward flow around southern India once again pushes northwestward.

From May to September there is strong upwelling in the East Arabian Current along Oman, accompanied by a 5$^\circ$ C or more lowering of coastal temperatures due to the cold upwelling water. This upwelling isn't as conducive to primary production as elsewhere due to the rapidly moving current removing much of the upwelled additional biomass before it can be utilized. See Qasim (1982) and Schott and Fischer (2000). See the Arabian Sea Study Web site.

Arabian Sea High Salinity Water (ASHSW)

See Kumar and Prasad (1999)

Arabian Sea Process Study (ASPS)

A 1995 JGOFS program. See Shi et al. (1999).

Arafura Sea

Part of the southeastern Australasian Mediterranean Sea centered at about 10$^\circ$ S and 137$^\circ$ E. It is bounded by Irian Jaya and Papua/New Guinea to the north and northeast, the Timor Sea to the west, and Australia and the Gulf of Carpenteria to the south and the southeast. It is mostly a large shelf (covering about 650,000 km$^2$) ranging from 50 to 80 m deep, although it can get as deep as 3650 m to the northwest in the Aru Basin.

There is a steady westward flow along the southern side of the Sunda Islands that is part of the larger pattern of throughflow through the Australasian Mediterranean from the Pacific to the Indian Ocean. South of this the circulation varies with the monsoon and trade winds that drive it. The deep water is renewed from the northwest via the Timor Trough.

Sea surface temperatures range from a maximum of 28.4$^\circ$ in Dec.-Feb. to a minimum of 26.1$^\circ$ in Jun.-Aug., while salinities annually range from 34.2-34.8 in the deeper parts to the north to 34.2 to 35.0 on the Arafura Shelf. See Fairbridge (1966) and Tomczak and Godfrey (1994).

Aral Sea

See Zenkevich (1957) and Zenkevitch (1963).

ARCANE

A French research program to observe and model the movement of the Mediterranean Water (MW) in the eastern North Atlantic Ocean in the interior and along the eastern boundary. It is a joint civilian and military exercise taking place between 40 and 50$^\circ$ N with most of the work to be done east of 14$^\circ$ E up to the 200 meter isobath, although some float work will take place out to 25$^\circ$ W to link with the proposed U.S. RAFOS deployments in this region. The plans call for the release of 60 RAFOS and 40 MARVOR floats. Also deployed will be 7 acoustic sources for tomographic work, 40 drifting buoys drogued at 150 meters mostly on the continental slopes of the Iberian Peninsula, 6 current meter moorings (with a total of 27 current meters) on and near the continental slopes of the Iberian Peninsula for 3 years, and a bottom mounted ADCP to be moored for several 3 month periods. This program is scheduled to last until 1999 and is a companion program to EUROFLOAT.

[http://www.ifremer.fr/lpo/arcane/]

ARCSS

Abbreviation for ARCtic System Science, an NSF global change program. The goals of ARCS are to understand the chemical, physical, biological and social processes of the arctic system that interacts with the total earth system and thus contributes to or is influenced by global change in order to advance the scientific basis for predicting environmental change on a decade to centuries time scale. See the ARCSS Web site.

ARCTEMIZ

See Richez (1998).

Arctic Atmosphere Program (AAP)

A component of ACSYS whose goal is to better understand the Arctic atmosphere that provides the dynamic and thermodynamic forcing of the Arctic Ocean circulation and sea ice. The objectives of AAP include:

• to encourage intercomparisons of reanalysis efforts and the assembly of long-term datasets from these intercomparisons;
• to identify shortcomings and implement improvoed parameterizations in the atmospheric modeling systems used for future reanalysis efforts and in climate models;
• to promote intercomparisons of the high latitude performance of climate models;
• to promote the quality control, archiving, updating, publication on CD-ROM, and migration to relevant data centers of key atmospheric datasets;
• to promote strategies for rescue of at-risk atmospheric datasets; and
• provide a polar clouds and radiation program through the GEWEX Clouds and Radiation Panel and other programs.

[http://acsys.npolar.no/impplan/atmosphere.htm]

Arctic Bottom Water

In physical oceanography, a water mass type which fills the deep basins in the Arctic Sea at depths less than 3000 m. Its formation process involves the interplay of two sources, GSDW and water from the Arctic shelf regions. The salinities of ABW are generally close to 34.95 but highest in the Canada Basin. The potential temperature in most basins is between -0.8$^\circ$ C and -0.9$^\circ$ C, although the Lomonossov Ridge prevents ABW colder than -0.4$^\circ$ C from entering the Canada Basin. Its main impact in the overall ocean circulation is its contribution to the formation of NADW in the depth range between 1000 m and 4000 m. See Tomczak and Godfrey (1994), pp. 99, 282.

Arctic Circumpolar Boundary Current (ACBC)

The main water transformations in the Arctic Mediterranean take place in a boundary current of Atlantic Water, which enters the Arctic across the Greenland-Scotland Ridge. After entering, it flows around the Arctic Ocean before exiting as the East Greenland Current, primarily via the Denmark Strait. On route, it experiences many branchings and mergings. The details of its journey around the Arctic are summarized by Rudels et al. (1999):

The circulation is dominated by the movement of warm Atlantic Water entering across the eastern part of the Greenland-Scotland Ridge into the Norwegian Sea. It flows along the Norwegian coast as the Norwegian Atlantic Current. When it reaches the latitude of the Bear Island Channel, its first major bifurcation occurs. A substantial fraction flows eastward and enters the Barents Sea, while the main part continues northward as the West Spitsbergen Current. Several branches are deflected westward from the current: north of the Greenland Sea basin, north of the Boreas basin and in Fram Strait. Only a smaller part of the West Spitsbergen Current eventually enters the Arctic Ocean and flows eastward along the Eurasian continental slope. North of the Kara Sea the boundary current meets the branch that turned east and entered the Barents Sea north of Norway. This branch reaches the Arctic Ocean by crossing the Barents Sea and the northern part of the Kara Sea. The combined boundary current continues eastward a short distance before it again splits. Branches leave the continental slope along bathymetric features, particularly along the Nansen-Gakkel Ridge, the Lomonosov Ridge and the Mendeleyev Ridge. However, a part of the boundary current follows the continental slope around the entire Arctic Ocean. As this part recrosses the Lomonosov Ridge into the Eurasian Basin it meets and mixes with the other branches as they converge east of the Morris Jesup Plateau. The waters exit the Arctic Ocean through Fram Strait, where they combine with the recirculating waters of the West Spitsbergen Current to continue southward along the Greenland continental slope as the East Greenland Current. The boundary current again diverges at bathymetric features, in this case the Greenland Fracture Zone and the Jan Mayen Fracture Zone, and branches from the boundary current enter the interior of the Boreas Basin and the Greenland Sea Basin. Exchanges in both directions occur, and the East Greenland Current is resupplied with water masses formed in the subpolar seas. The main part of the boundary current exits the Arctic Mediterranean through the 600 m deep Denmark Strait, but its denser fractions are deflected eastward along the Jan Mayen Fracture Zone and along the Iceland shelf slope and eventually enter the Norwegian Sea. The upper part of these waters then returns to the North Atlantic through the 850 m deep Faeroe-Shetland Channel.

See Rudels et al. (1999).

arctic domain

A hydrographic division sometimes used in the North Atlantic Ocean to distinguish it from the polar domain to the north and the Atlantic domain to the south. In this region upper layer waters are relatively cold (0 to 4$^\circ$ C) and saline (34.6 to 34.9). The most significant indication that this domain is not just a smooth transition zone between the polar and Atlantic domains is that the waters are markedly denser than either of the surface source water masses (i.e. $\sigma_t$ ranges from 27.5 to greater than 28). See Swift (1986).

Arctic Frontal Zone (AFZ)

A frontal zone that runs meridionally between about 5 and 8$^\circ$ E in the Greenland Sea. It separates warm, salty, northward-flowing Norwegian Atlantic Water (NwAtW) in the Norwegian Atlantic Current and the West Spitsbergen Current to the east from the cooler and fresher Arctic Surface Water (ASW) in the Greenland Sea gyre to the west.

The AFZ consists of two semipermanent frontal interfaces with warm, saline Norwegian Atlantic Water to the east and Arctic Water from the Greenland Sea gyre to the west. These two interfaces bound a band of shallow cyclonic cold eddies and anticyclonic warm eddies with horizontal scales on the order of 40-50 km, consistent with the local Rossby radius. Drifter trajectories show a mean surface velocity across the AFZ to the north, and the mean northward geostrophic transport (relative to 1000 dbar) connected with the zonal density gradient in the AFZ is about 3.8 Sv. The accompanying transports of heat and fresh water across the AFZ are thought to be of great importance for the control of deep convection processes in the Greenland Sea gyre. See van Aken (1995).

Arctic Intermediate Water (AIW)

A water mass found at intermediate depths in the arctic domain in the North Atlantic Ocean. It is identified by a temperature minimum at a depth of about 75 to 150 m as well as temperature and salinity maximums at depths ranging from about 250 to 400 m, with the extremes being the product of winter cooling and sinking in the arctic domain. It is useful to separate this water mass into lower and upper AIW.

The lower AIW contains the temperature and salinity maximums but generally not the temperature minimum, with temperatures ranging from 0 to 3$^\circ$ C and salinities greater than 34.9, with the maximums clear signs that this water mass is produced by the cooling and sinking of Atlantic Water (AW). The upper AIW is defined as including the denser portion of the water associated with the temperature minimum, including much of the water column from the minimum up to the temperature maximum. It is characterized by temperatures less than 2$^\circ$ C in the salinity range 34.7 to 34.9 (with a lower limit of 34.6 suggested by some).

The definitions for upper and lower AIW deliberately overlap in density, with upper AIW in the Iceland Sea having a temperature of 0$^\circ$ C, S = 34.88 and $\sigma_t$ = 28.03 as opposed to a portion of the lower AIW in the northern Greenland Sea having T = 3$^\circ$ C, S = 35.05, and $\sigma_t$ = 27.95. This is only true of the northeastern Greenland Sea, however. Elsewhere, upper AIW always overlies lower AIW. See Swift (1986).

Arctic Mediterranean Sea

The area comprising the Greenland Sea, the Iceland Sea, the Norwegian Sea and the Arctic Ocean. The first three are sometimes referred to as the Nordic Seas.

The area has restricted communication with the rest of the world ocean, with the passages being:

• to the Pacific via the Bering Strait;
• to the North Atlantic via the Greenland-Scotland Ridge; and
• through the Canadian Arctic Archipelago and the Davis Strait west of Greenland.

Arctic Ocean

The smallest and most poorly studied of the oceans on earth. It covers an area of 14 million square km that is divided by three submarine ridges, i.e. the Alpha Ridge, the Lomonosov Ridge, and an extension of the mid-Atlantic ridge. It is also nearly landlocked, covered year-round by pack ice, and one-third of its area is continental shelf containing marginal seas. The marginal seas of the Arctic are the Beaufort Sea, the Chukchi Sea, the East Siberian Sea, the Laptev Sea, the Kara Sea and the Barents Sea. An important climatic function of the Arctic and its adjacent seas is the production of the dense water than drives the global transports of heat and fresh water between the high latitude North Atlantic and the Pacific.

The physical processes that combine to produce the circulation in the Arctic and its marginal seas include:

• salt rejection from sea-ice growth forming dense water that continues surface buoyancy forcing after the freezing point is reached, preferentially where offshore winds maintain open waters for prolonged periods;
• advection of ice produced in marginal seas that exports fresh water from the basin, compensating for the freshening effect of precipitation and run-off from Arctic rivers; and
• drainage of dense shelf water from the Arctic shelves into the deep Eurasian basin, a process that affects the deep water properties in the convective gyres via exchanges through the Fram Strait.

See Coachman and Aagaard (1974).

Arctic Ocean Circulation Program (AOCP)

A component of ACSYS designed to investigate the feedback between changes in the upper Arctic Ocean and its ice cover and changes in the global heat balance. The AOCP consists of four components:

• Arctic Ocean Hydrographic Survey - A program to collect a high quality hydrographic database representative of the Arctic Ocean with the goal of determining the general circulation and its transit times, and the rate of transformation of the different water masses.
• Arctic Ocean Shelf Studies - A program aimed at understanding how the shelf processes partition salt and fresh water components, how the resulting buoyancy fluxes are coupled to the ocean interior, at defining the dynamics and thermodynamics of the shelf waters sufficiently to permit realistic modeling, and at determining the variability on the shelves and how that affects the interior ocean.
• Arctic Ocean Variability Project - A program designed to assess the variability of the circulation and density structure of the Arctic Ocean including exchanges with the surrounding seas, to find the rates and variability of the processes important in maintaining present ocean conditions, and to provide a basis for further monitoring of climate change in the Arctic.
• Arctic Ocean Climate Database Project - A project to establish a universally available digital hydrographic database for the Arctic Ocean for analysis of climate-related processes and variability, and to provide a dataset suitable for the initialization and verification of Arctic climate and circulation models.

[http://acsys.npolar.no/impplan/ocean.htm]

Arctic Ocean Deep Water (AODW)

See Swift (1986).

Arctic Ocean Section (AOS)

A 1994 expedition in which two icebreakers - the USCGC Polar Sea and the CCGS Louis S. St. Laurent - sailed from Nome, Alaska to the North Pole across the entire Arctic basin, covering over 2000 nautical miles. The purpose of AOS was the increase understanding about the role of the Arctic in climate change and gather baseline data on contaminants in the region. See Tucker and Cate (1996) and Wheeler et al. (1996).

The significant science findings of the expedition were:

• the Atlantic layer of the Arctic Ocean was found to be 0.5-1.0$^\circ$C warmer than prior to 1993;
• a large eddy of cold fresh water was found centered at 1000 m on the periphery of the Makarov Basin;
• biological productivity was estimated to be ten times greater than previous estimates;
• an active microbial community was found; and
• mesozooplankton biomass was found to increase with latitude.

[http://www.crrel.usace.army.mil/news/news-archives/arctic-crossing/monthly.htm]
[http://www.crrel.usace.army.mil/library/pub97fyo.htm]

Arctic Sea Ice Program (ASIP)

A component of ACSYS whose objectives are:

• to assemble a climatological archive which documents the state of pack ice in both the Arctic and Antarctic seas; and
• to study the interaction of polar pack ice with other elements of the global climate system.

The elements of the implementation strategy include:

• assembling a climatology of Arctic and Antarctic sea ice based on available historical observations and new observing initiations within ACSYS;
• determining the southward flux of pack ice;
• studying the processes by which pack ice, the ocean and the atmosphere interact; and
• studying sea ice mechanics at spatial scales ($>$ 1 km) relevant to its behavior in a geophysical context.

[http://acsys.npolar.no/impplan/seaice.htm]

Arctic Surface Water (ASW)

A water mass found in the arctic domain in the North Atlantic Ocean. The ASW is the summer surface water mass above the seasonal thermocline and has temperatures greater than 0$^\circ$ C for the salinity range 34.4 to 34.7 and greater than 2$^\circ$ C for the range 34.7 to 34.9. See Swift (1986).

Argentine Basin

An ocean basin located in the western South Atlantic Ocean off the coast of Argentina. It is separated from the Brazil Basin to the north by the Rio Grande Rise and includes the Argentine Abyssal Plain. See Fairbridge (1966).

Argo

A global array of 3,000 free-drifting profiling floats that will measure the temperature and salinity of the upper 2000 m of the ocean. This will allow the continuous monitoring of the climate state of the ocean. Once the full network is in place in 2002 or thereabouts, Argo will provide 100,000 T/S profiles and reference velocity measurements per year from floats distributed over the oceans at about a 3 degree spacing. The floats will cycle to 2000 m depth every 10 days, with a planned 4-5 year lifetime for individual instruments. All data will be made publicly available in near real-time via the GTS, and in scientifically quality-controlled form within a few months.

[http://www-argo.ucsd.edu/]

Argon-39

An isotope of argon that is useful as a tracer in ocean studies. It is a radioactive inert gas with a half life of 269 years and is produced in the atmosphere by cosmic ray interactino with Argon-40. It is well-mixed through the troposphere and its variation in concentration over the last 1000 years has been estimated to be no more than about 7%. This means that its distribution in the atmosphere and ocean is in steady state.

It enters the ocean by gas exchange with the equilibrium time between the surface mixed layer and the atmosphere being about a month. The equilibrium concentration in surface water is calculated from the solubility of argon, a well known function of temperature and salinity, and the also well known concetration of Ar-39 in the atmosphere. The surface concentration in regions of deep water formation, where the surface water may not equilibrate with the atmosphere due to rapid convection processes, can be determined from measurements. Measurement is at present an onerous process requiring 1500 liters of water, and the concentration measured is reported in % modern, i.e. the Ar-39:Ar:40 ratio of the sample divided by the Ar-39:Ar:40 ratio of the troposphere. The minimum detectable limit is about 5% modern (with an error of 3-5% modern) which corresponds to an age of 1100 years with a resolution of about 50 years.

Argon-39 is an ideal tracer for investigating mixing and circulation in the deep ocean and in the mid to lower thermocline. Its distribution is in steady state and the boundary conditions are well known, i.e. there is no flux across the ocean bottom and the surface water concentration is known everywhere. Its distribution in the ocean interior is affected only by circulation, mixing and radioactive decay process, and since the decay rate is know it serves as a clock for circulation and mixing processes. See Loosli (1983), Sarmiento (1988) and Broecker and Peng (1982).

ARIES

Acronym for Autosampling and Recording Insrumental Environmental Sampler, a multi-function sampling device providing high resolution concurrent sampling of physical, chemical and biological parameters throughout the water column from a moving ship. ARIES is modular, being composed of a water sampling unit, a plankton sampling unit and an oceanographic sensor unit. See Dunn et al. (1993).

Arlindo Project

A joint oceanographic research endeavor of Indonesia and the United States whose primary goal is to study the circulation and water mass stratification within the Indonesian Seas, especially to determine sources, pathways, and mixing histories of the throughflow water masses for the monsoon extremes. ``Arlindo'' is an acronym for Arus Lintas Indonesia, meaning ``throughflow'' in the Bahasa Indonesian language.

The first stage of the project, Arlindo Mixing, consisted of a suite of CTD measurements extending to the seafloor or 3000 dbar, tracer chemistry, and biological productivity stations obtained from the Indonesian research vessel Baruna Jaya I during the southeast monsoon of 1993 (Aug. 6 to Sept. 12) and northwest monsoon of 1994 (Jan. 25 to Mar. 3). The results have been summarized as:

The primary interocean throughflow path in the upper thermocline is that of North Pacific thermocline water flowing through the Makassar Strait into the Flores and southern Banda Seas before curling southward into the Timor Sea and Indian Ocean. This path tracks the mostxi persistent course of water masses core layer indicators along a potential throughflow pathway. Even in the southern Banda Sea the North Pacific core layer indicators are evident, albeit very attenuated; they are not observed in the northern Banda Sea, which attests to the Makassar/Flores origin. The sill at the southern end of Makassar Strait is about 550 m deep. No signs of deep water upwelling lifting over the sill is evident. An attenuated, fragmented thermocline salinity and CFC maximum layer in Makassar Strait during the NWM relative to the SEM, suggests that the throughflow slackens in that season, allowing accumulative effects of local mixing.

East of Sulawesi there is little evidence of North Pacific water mass throughflow into the Banda Sea. The North Pacific thermocline water entering the northwest corner of the Maluku Sea, exits back to the north in the northeast corner of the Maluku Sea. The presence of relatively salty water of South Pacific origin is observed in the 10°-14°C interval in the Seram Sea. This water enters the Seram Sea directly from the South Pacific via the New Guinea Coastal Current and Halmahera Sea (sill depth near 500 m). Below the thermocline the main source of the throughflow is South Pacific water masses, though they are derived from a more indirect route, via the North Pacific's Mindanao Current, entering the Indonesian Seas at the Maluku Sea. It is this water that spills over the 1940 m deep Lifamatola Sill into the depths of the Banda Sea.

The second stage was called Arlindo Circulation, whose goal was to resolve the throughflow transport and velocity field across the central passages of the Indonesian Seas. It took place from Nov. 20-Dec. 15, 1996 and Feb. 17-Mar. 7, 1988. The third stage is called Arlindo Monitoring and is intended to provide a long term data set of the throughflow to enable study at timescales of ENSO events. It is scheduled from 1998 to 2007. See Ilahude and Gordon (1996).

[http://www.ldeo.columbia.edu/physocean/Arlindo/]

Arons, Arnold (1916-2001)

Co-creator of the Stommel-Arons theory of deep circulation.

[http://world.conk.com/world/phaskell/aa.html]

arrested salt wedge estuary

One of four principal types of estuaries as distinguished by prevailing flow conditions. This is a type in which there is a relatively stationary interface between an underlying stable salt wedge of sea water and an overlying strong flow of fresh river water.

ASCAP

Acronym for the Air-Sea interaction, Cloud And Precipitation experiment over the Baltic Sea, a component of BALTEX. ASCAP is a comprehensive campaign for an air-sea interaction field campaign in the Baltic Sea, with the central aim being to improve model parameterization schemes via a better understanding of the physical mechanisms and validation of remote sensing algorithms. The objectives are:

• measurements of parameters determining air-sea interaction processes, the sea state, and wave spectra;
• in-situ measurements and observations of clouds, water vapor and precipitation;
• parameterization of air-sea interaction processs in region models;
• validation of algorithms to estimate cloud parameters, water vapor and precipitation from radar and satellite data; and
• validation of numerical models against long-term measurements.

The measurement phase took place from 1995 until 1997.

[http://w3.gkss.de/english/Baltex/campaign2.html]

ASEAMS

Acronym for Association of Southeast Asian Marine Scientists.

aseismic ridge

An undersea ridge that is not seismically or volcanically active. Examples of aseismic ridges are the Walvis Ridge, the Rio Grande Plateau, the Kerguelen Plateau, the Seychelles Ridge and the Lomonosov Ridge. See Fairbridge (1966).

ASGAMAGE

An acronym that is the contraction of ASGAS-EX (for Air Sea Gas Exchange project) and MAGE. The ASGAMAGE project started on March 1, 1996 and lasted until March 1, 1999. The scientific objectives were:

• to find relationships between the transport coefficients for the gas fluxes and any relevant geophysical parameters;
• to test new methods and new equipment for the measurement of air-sea fluxes of CO$_2$, DMS and other gases;
• to intercompare different methods and systems to measure the transfer velocity of trace gases over the sea; and
• to find out whether and, if at all, under what conditions there can be a significant vertical gradient in the CO$_2$ concentration in the upper meters of the water column.

ASGAMAGE consisted of two experimental periods, with the first taking place from May 6 to June 7, 1996. It involved taking measurements at and around the Meetpost Noordwijk (MPN), a research platform 9 km off the Dutch coast. The second period, taking place from Oct. 7 to Nov. 8, 1996, involved more measurements at MPN and a cruise of the RRS Challenger. The measurement activities were primarily aimed at a determination of air-sea gas transfer coefficients with the differential tracer method being made simultaneously with micrometeorological experiments.

[http://www.knmi.nl/onderzk/oceano/special/asgamage/]

ASHES

Acronym for Axial Seamount Hydrothermal Emissions Study.

ASHSW

Abbreviation for Arabian Sea High Salinity Water.

ASIAEx

Acronym for Asian Sea International Acoustics Experiment, a scientific collaboration between the U.S., China, Korea, Japan, Taiwan, Russia and Singapore. The ASIAEx major field experiments began in 2000, one focusing on acoustic bottom reverberation and the other on acoustic cross-shelf progagation.

[http://www.arl.nus.edu.sg/asiaex/]

Asia Minor Current (AMC)

A meandering current flowing westward and then northward along the Turkish coast and the southeastern coast of Rhodes. It borders the northwest part of the Rhodes gyre, and originates as part of the mid-Mediterranean jet branching to the north. There is a major branch in the AMC in the region of the Rhodes and Karpathos Straits. Both branches intrude into the south Aegean Sea and meander in the northeastern Cretan Sea as a continuation of the AMC. The branches carry warm and saline Levantine waters within the upper 300-400 dbar layer. See Theocharis et al. (1999).

ASLO

Acronym for the American Society of Limnology and Oceanography, the purposes of which are to promote the interests of limnology, oceanography and related sciences, to foster the exchange of information across the range of aquatic science, and to further investigations dealing with these subjects. ASLO originated with the Limnological Society of America (LSA), which was established in 1936 to furhter interest and research in limnological science. In 1948 LSA merged with the Oceanographic Society of the Pacific to become ASLO, and currently has over 3800 memebers from 50 countries. See the ASLO Web site.

ASREX

Acronym for Acoustic Surface Reverberation Experiment.

[http://uop.whoi.edu/data/uopdata.html]

ASW

See Arctic Surface Water.

ATEX

Acronym for Atlantic Trade Winds Experiment, an experiment designed to study the development of the boundary layer in the trade winds near the ITCZ. It was conducted in 1969 and based on a triangle of ships drifting with the NE trades. Spatial structures of the boundary layer were gathered. Air-sea fluxes were measured by the profile method and the eddy correlation technique was used on two separate buoys, i.e. a stable, wave-following buoy for profiles and a servo-stabilized buoy for eddy fluxes. Sea Dunckel et al. (1974) and Geernaert (1990).

Atlantic domain

One of three regions into which the North Atlantic Ocean is sometimes divided for the purposes of describing water mass formation processes in the region, with the other two being the (northward lying) arctic domain and the polar domain. Surface source water masses from the Atlantic domain (called Atlantic Water (AW), are carried into the arctic domain by the Norwegian Atlantic Current and, to a much smaller extent, by the North Icelandic Irminger Current. See Swift (1986).

Atlantic Multidecadal Oscillation (AMO)

A 65-80 year cycle with a 0.4$^\circ$C range observed in North Atlantic sea surface temperature for 1856-1999. AMO warm phases occurred during 1860-1880 and 1940-1960, with cool phases during 190-1925 and 1970-1990. The signal is global in scope, with a positively correlated co-oscillation in parts of the North Pacific, although it is most intense in the North Atlantic and covers the entire basin.

During AMO warmings most of the U.S. experiences less than normal rainfall, including Midwest droughts in the 1930s and 1950s. Mississippi River outflow varies by 10% between warm and cool phases. The geographical pattern of variability is influenced mainly by changes in summer rain. Winter patterns of interannual rainfall variability associated with ENSO are significantly changed between AMO phases.

Atlantic Ocean

Much more later. See Peterson and Stramma (1991) and Stramma and England (1999).

Atlantic-Indian Basin

One of three major basins in the Southern Ocean. It extends from its western border with the Pacific-Antarctic Basin at the Scotia Ridge and Drake Passage (at about 70$^\circ$ W) to its eastern border with the Australian-Atlantic Basin at the Kerguelan Plateau (about 75$^\circ$ E). It consists of the Enderby and Weddell Abyssal Plains and is bounded to the north below 4000 m by the Mid-Atlantic and South-West Indian Ridges except for deeper connections into the Argentine Basin in the western Atlantic and into the deep basins of the western Indian Ocean.

Atlantic Meridional Transect

An ongoing research program that exploits the twice-annual passage of the RRS James Clark Ross between the U.K. and the Falkland Islands - before and after its use in the Antarctic research program in the Austral Summer - to obtain spatially-intensive time and space series data over the 13,500 km transect. The transect starts at the U.K. and heads southwest to the first waypoint at a JGOFS time-series station at 47$^\circ$N, 20$^\circ$W. From there it follows the 20$^\circ$W meridian to 13$^\circ$N, after which it heads south and west to Montevideo (Uruguay) and Stanley (Falkland Islands).

The objectives of the AMT program include:

• gauging the effects of anthropogenically induced environmental change on the physical and biological systems along the transcent;
• improving knowledge of marine biogeochemical processes, ecosystem dynamics, food webs and fisheries, as well as characterize physical and biogeochemical provinces;
• developing a research strategy to integrate shipboard measurements with remote sensing, modeling, etc. to maximally exploit the time and space series obtained on the transect;
• providing calibration and validation of satellite sensors of ocean color, sea surface temperature, and solar radiation;
• quantifying ecosystem responses to changes in the abundance of radiatively and chemically active trace gases; and
• developing coupled physical-biological models of production and ecosystem dynamics.

The progress and limitations of AMT as of 2000 has been synthesized by Aiken et al. (2000) as:

AMT cruises 1 to 7 (1995-1998) have seen the completion of phase 1 of the AMT programme, wherein many of the new, autonomous technologies and operational approaches have been pioneered and proven. There are obvious limitations in the programme, particularly one which has objectives related to issues of climate change. Notably, the physical oceanography is superficial, CTD casts have been limited to 200 m in most cases with no geostrophic reference and the spatial resolution of circa 400 km from typically 1 cast per day is too coarse. As a basin scale programme the AMT samples the temperate N. Atlantic poorly; there is no sampling north of 50$^\circ$N. As a programme focused on climate change, a time series based on samples only twice a year has severe limitations, with no adequate resolution of the seasonal cycle in any province. Nevertheless, the fledgling four-year time series can already provide measurements of inter-annual variability, which is an essential pre-requisite for any study of decadal trends. With another 10 cruises planned over five years (1999-2003) during phase 2, the basis of a study of climate change will be well established. During this period there must be a focus on those measurements that are sensitive to climate forcing or are known indices of anthropogenic influences on climate. Collaboration with other European national research activities is planned to improve the coverage of the seasonal cycle in the north Atlantic and create a European Atlantic Time and Space Series (EATSS) project. Core to this are the twice yearly transects of the other Antarctic research vessels, the Polarstern (Germany), the Hesperides (Spain) and the Pelagia (Netherlands) with opportunistic research cruises in the area 20-63$^\circ$N, 20$^\circ$W, by UK, German, French, Dutch, Belgian and Spanish vessels. If this develops, it will be true to say, that the AMT programme has laid down the foundation for a study of decadal trends in the marine ecosystems of the Atlantic Ocean with which to understand and model their responses to climate change.

See Aiken and Bale (2000) and the other papers in a special AMT results issue.

Atlantic period

A post-LGM European climate regime. This refers to the period from about 6000-3000 BC that spans most of the warmest postglacial times. It is also known as the Postglacial Climatic Optimum. It was preceded by the Boreal period and followed by the Sub-Boreal period. See Lamb (1985), p. 372.

Atlantic Water (AW)

A water mass traditionally defined as any water with salinity greater than 35.0 entering the arctic domain from the Atlantic domain. AW first entering the Iceland and Norwegian Seas typically has temperatures of 6-8$^\circ$ C and a salinity range of about 35.1-35.3, although the property ranges of other waters obviously connected with AW have prompted some to expand the definition to include all waters warmer than 3$^\circ$ C and more saline than 34.9. Estimates of the total influx of AW range as high as 9 Sv. See Swift (1986).

ATLAS

Acronym for Autonomous Temperature Line Acquisition System, a taut-line mooring with sensors measuring surface winds, air temperature, relative humidity, sea surface temperature, and ten subsurface temperatures to a depth of 500 m. Daily mean data are telemetered to shore in near real-time via NOAA's polar orbiting satellites and Service Argos. The standard ATLAS mooring has a design lifetime of one year, with over 500 having been deployed sine 1984.

[http://www.pmel.noaa.gov/toga-tao/atlas.html]

atmospheric tide

Those oscillations in any atmospheric field whose periods are integral fractions of either a lunar or a solar day. These differ from ocean tides in several ways, one of which is that atmospheric tides are excited not only by the tidal gravitational potential of the sun and moon but also (and to the larger extent) by daily variations in solar heating. Another difference is that the atmosphere is a spherical shell and thus there are no coastal boundaries to worry about. Finally, the response of the atmosphere to tidal forcing is by means of internal gravity waves rather than the barotropic surface waves of the sea. See Lindzen (1971).

atmospheric turbulence

See Wyngaard (1992).

ATOC

Abbreviation for Acoustic Thermometry of Ocean Climate, a program composed of two complementary enviromental initiatives: (1) to gather information about temperatures in the ocean using acoustic tomography to verify the predictions of existing climate models; and (2) to assess the potential effects of low frequency sound transmissions on marine mammals and sea turtles through its MMRP component. See the ATOC Web site.

atoll

One of three geomorphologically distinct types of coral reefs, the other two being fringing reefs and barrier reefs. An atoll is an annular reef formed around a subsiding volcanic island. See Barnes and Hughes (1988).

ATSR

Abbreviation for Along-Track Scanning Radiometer microwave sounder, a satellite-borne instrument designed to measure land and ocean surface temperatures. The ATSR is a passive two-channel radiometer that scans the near-infrared and middle-infrared bands with a spatial resolution of 1 km x 1 km and a swath width of 500 km. It views the Earth from an orbit of about 800 km and can measure ocean temperature to within 0.3$^\circ$ C. The ATSR can be used to detect exceptional local incidents, large scale changes, and general trends in the Earth's climate. See the ATSR Web site.

ATTOM

Acronym for Acoustic Travel Time Ocean Current Monitor.

austausch coefficient

A German term for a quantity equivalent to the eddy viscosity coefficient.

Australasian Subantarctic Front

See Subantarctic Front.

Australian-Antarctic Basin

One of three major basins in the Southern Ocean. It extends from its eastern boundary with the Pacific-Antarctic Basin at the longitude of Tasmania (at about 145$^\circ$ E) to the Kerguelan Plateau (at about 75$^\circ$ E). The South-East Indian Ridge separates it from the Indian Ocean at depths greater than 4000 m except for a gap in the Ridge at 117$^\circ$ E.

Australasian Mediterranean Sea

The region on either side of the equator between the islands of the Indonesian archipelago. This has the most complicated topography of any of the regional seas of the world, consisting of a series of deep basins with limited interconnections, each characterized by its own type of bottom water of great age. The basins comprising this include the Banda, Sulawesi (formerly Celebes), Molucca, Halmahera, Serman, Sulu, Flores, Java and Sawu Seas, with the Banda being the largest and deepest.

The net transport is believed to be westward at all times, from the Pacific to the Indian Ocean, with a maximum in August (estimated at 12-20 Sv) and a minimum in February (estimated at 2-5 Sv). It takes the form of a western boundary current that is strongest along Mindanao and and Kalimantan. The transport also occurs mainly in the upper layers with little transport below 500 m and about 75% above 150 m. Most of the high salinity input occurs across the sill between the Pacific and the Sulawesi Sea, while most of the low salinity output is through various narrow passages between the south Indonesian islands, with both input and output occurring over the entire water depth over the sills.

The freshening of the throughput occurs due to both high freshwater input from seasonal precipitation and to strong turbulent mixing that effects water mass conversion in the upper 1000 m of the water column, with the turbulence probably due to locally strong tidal currents. This mixing process imparts a unique character to the Australasian Mediterranean in that the salinity field in the upper 1000 m is nearly homogeneous while the temperature field is still stratified. This occurs because even though both temperature and salinity are strongly mixed the intense solar heating in the region serves to maintain the temperature stratification. See Tomczak and Godfrey (1994).

authigenic

One of three major components of deep sea sediments, the other two being detrital and biogenic. Authigenic minerals are those formed by spontaneous crystallization within the sediment or water column, and make up only a small fraction of the total sediment volume. The most important of this type of sediment is the iron-manganese oxide material formed by reduction of these metals deep in the sediment column. The resultant material migrates upwards and is deposited in the oxygenated upper layers of sediment. It can also be produced as a by-product of hydrothermal activity near ridge crests. See Broecker and Peng (1982).

Autonomous Ocean Sampling Network (AOSN)

A network which uses man small, low-cost AUVs operating from a network of moorings to gather data in oceanographic field programs. A pilot system is currently under development led by the MIT Sea Grant program. See the AOSN Web site.

Autosub

An autonomous underwater vehicle (AUV), i.e. a robotic vehicle designed to carry a varying scientific payload which is changed to suit each mission. See Collar and McPhail (1995).

[http://www.soc.soton.ac.uk/PR/Autosub.html]

autotrophic

Self-nourishing organisms with the ability to synthesize organic molecules from CO$_2$ using either photosynthesis or chemosynthesis.

AUV

Abbreviation for autonomomous underwater vehicle, a vehicle that can roam the ocean and collect data on its own. They can wait for episodic, short-lived events and change course immediately to concentrate on the most interesting areas during an experiment. The MIT/WHOI program built the first prototype AUV, called the Sea Squirt, in 1988 which was used to take various measurements in rivers, harbors, lakes and ponds. The second prototype, called the Odyssey I, was first launched from an oceanographic research vessel in early 1993 in the Antarctic. It was capable of operating at depths of 6000 m. The third prototype, the Odyssey II, was designed to operate at full ocean depths. It was designed to be mass produced and to be configurable in a number of ways depending on mission requirements. An on-board computer executes navigation and control programs, and an acoustic modem is used for two-way digital communication. The first full-scale test of the Odyssey II took place in February 1998 in midwinter in the Labrador Sea. The plan of the experiment was to have the AUVs gather data about bottom water formation for three months, recharging and dumping data at an underwater docking station at regular intervals. A mechanical problem limited the experiment to two weeks, although much useful data was gained for the improvement of future experiments.

[http://auvlab.mit.edu/]

available potential energy (APE)

A quantity first derived in Lorenz (1955) in an investigation to discover what portion of total potential energy could be transformed into kinetic energy under the constraint of quasi-hydrostatic and adiabatic processes. Available potential energy (APE) was defined as the difference between a system's mass integrated total potential energy and the total potential energy of a hydrostatic reference state, i.e. the difference in potential energy between the actual physical state and the reference state, where the latter is defined as the state of minimum potential energy that can be reached through reversible adiabatic processes. In the reference state, all density surfaces are level. This was extended in Van Mieghem (1956) to deal with non-hydrostatic states. See Reid et al. (1981), Oort et al. (1989), Kucharski (1997) and Huang (1998).

AVHRR

Abbreviation for Advanced Very High Resolution Radiometer, a five channel scanning radiometer with channels in the visible, visible near infrared, and infrared water vapor window. These were selected for production of quantitative sea surface temperature products and visible and IR imagery depicting clouds and thermal features, e.g. the Gulf Stream. The AVHRR produces 1 km resolution data.

AVP

Abbreviation for Absolute Velocity Profiler, an instrument developed at the APL to measure velocity profiles in the ocean. This dropsonde references an electromagnetically inferred velocity profile to one measured near the sea floor. See Sanford et al. (1985).

AW

Abbreviation for Atlantic Water.

AXBT

Abbreviation for airborne expendable bathythermograph, an air-deployed, expendable, ocean temperature profiling probe. The AXBT consists of a temperature probe, 300-1000 meters of cable, a VHF transmitter and antenna, and a salt water activated battery. When the AXBT hits the ocean surface and stabilizes, the transmitter is activated and the temperature probe released. The surface transmitter telemeters the temperatures measured by the falling probe to a data gathering system on the aircraft that released it.

[http://aol11.wff.nasa.gov/axbt/]

AXCP

Abbreviation for airborne expendable current profiler.

AXCTD

Abbreviation for airborne expendable conductivity, temperature and depth profiler.

azoic zone

Term used to describe the part of the deep sea thought lifeless in the mid-19th century. It was thought that the abyss was filled with a thick layer of 4$^\circ$ C (since sea water was thought to be densest at that temperature), motionless water which, combined with the tremendous pressures and absence of sunlight, virtually guaranteed an absence of life. The term was coined by the naturalist Edward Forbes in the 1840s who, after dredging for life forms in various regions, postulated eight bands or depth zones, each characterized by a particular assemblage of animals. These zones extended to a lower limit he set at about 300 fathoms below which the existence of life was highly unlikely. His results (and therefore perceptions) on this issue were skewed by an 1841 cruise in the eastern Mediterranean where he dredged for life forms at depths up to 230 fathoms in what is now known to be a relatively barren area. The contrast of this with the rich hauls he made in shallower waters around England led to his thinking the abyss devoid of life. See Schlee (1973).

Azores Current

The northern branch of the subtropical gyre in the North Atlantic Ocean. This carries around 15 Sv of water along 35-40$^\circ$ N to the western part of the gyre, i.e. the Canary Current. See Sy (1988) and New et al. (2001).

Azores Countercurrent (AzCC)

A band of westward transport all across the North Atlantic at about the latitude of the Azores. The driving mechanism is an anomaly in the meridional change of the wind stress curl in the eastern North Atlantic. See Onken (1993).

Azores Front

See Rudnick and Luyten (1996).

Azores High

A center of action centered near the Azores Islands (near 35$^\circ$ N and 25$^\circ$ W). It extends from near the western end of the Mediterranean Sea westward almost to Florida in the summer months, with the western section in summer sometimes referred to as the Bermuda High. See Angell and Korshover (1974).

Azov, Sea of

A large gulf or lagoon, centered at about 46$^\circ$ N and 37$^\circ$ E, connected to the Black Sea by the narrow and shallow (around 5 m sill depth) Kerch Strait. The Sea of Azov covers around 38,000 sq. km which comprises 9% of the area of the Black Sea system but only 0.5% of the volume. See Zenkevitch (1963).