Dn-Dz

DOC

Abbreviation for dissolved organic carbon, which consists of three pools:

• a refractory pool not readily usable by biological organisms with a turnover time on the order of ocean mixing cycles,
• a usable labile pool with turnover time from hours to a day, and;
• a semi-labile pool with a turnover time of months to season.

Analyses of the composition of DOC indicate bulk C:N ratios ranging from 16 to 38, and that 22-33% of the total DOC is $>$ 1000 molecular weight and composed largely of carbohydrate material, with C:N ratios from 15-22. See Ducklow (1995).

Dole effect

Defined as the difference between the ${\delta^{18}}O$ of atmospheric $O_2$ in air and the ${\delta^{18}}O$ of contemporaneous seawater. This effect mainly reflects the isotopic composition of $O_2$ produced by marine and terrestrial photosynthesis, as well as the extent to which the heavy isotope is discriminated against during respiration. Secondary factors include changes in terrestrial and marine fertility, varying isotope fractionation associated with the hydrologic cycle, and changes in respiratory isotope effects on either a species or community level. See Bender et al. (1994).

DOM

Abbreviation for Dissolved Organic Matter. This includes colloidal as well as purely dissolved material and is operationally defined as all organic matter that will pass through a filter with a fine mesh size, typically between about 0.1 and 1 $\mu$m. See Najjar (1991).

DON

Abbreviation for dissolved organic nitrogen.

Donde Va?

An oceanographic experiment which took place in the Alboran Sea (in the western Mediterranean) during June-October 1982. It was conducted to study the large anticyclonic gyre formed by the inflowing jet of low salinity Atlantic Water. The objective was to better understand the kinematics and dynamics of the gyre using numerical modeling, remote sensing, and field measurements. See Va (1984).

Doodson filter

A Doodson X0 filter is a simple filter designed to damp out the main tidal frequencies. It takes 19 values on either side of a central value and calculates a weighted average. If the initial values are at a higher frequency than hourly, then they are first averaged to give hourly values.

[http://www.pol.ac.uk/psmslh/gloup/doodson_X0.html]

DORIS

Acronym for the Doppler orbitography and radiopositioning integrated by satellite instrument flown on the TOPEX/POSEIDON mission. This instrument provides, in addition to the LRA instrument, satellite tracking data, although DORIS uses microwave Doppler rather than laser techniques. The basic operational principle is based on the accurate measurement of the Doppler shift of radio frequency signals emitted by ground beacons and received by the satellite. It is composed of an on-board receiver and a network of ground transmitting stations, the latter of which are equipped with meteorological sensors the measure temperature, humidity, and atmospheric pressure for correcting for atmospheric effects on the transmitted signals. The DORIS signals are transmitted at two frequencies (401.25 and 2036.25 MHz), one for Doppler measurement and another to allow the removal of the effects of ionospheric free electrons on the tracking data. The DORIS system is also being installed in the SPOT mission series as well as on ENVISAT. See the DORIS Web site.

DOTREX

Acronym for Deep Ocean Tracer Experiment.

double diffusion

In physical oceanography, this refers to the difference in the molecular diffusion rates of heat and salt in sea water, the molecular diffusion rate of heat being about 100 times that of salt. If two water masses with the same density but different combinations of temperature and salinity are in contact, the double (or differential) diffusion can give rise to density changes that render the layers unstable. Two phenomena that are possible consequences of this are double diffusive instability and layering. This is also known as salt fingering. See Schmitt (1994).

double diffusive convection

See double diffusive instability.

double diffusive instability

In physical oceanography, this is a consequence of the double diffusion phenomena. If a layer of warmer, saltier water overlies a layer of cooler, fresher water such that the density of the upper layer is equal to or less than the density of the lower layer, the saltier water at the interface will lose heat to the cooler water below faster than it will lose salt because of the differences in molecular diffusivities. This may cause the water immediately above/below the interface to become denser/lighter which will cause it to sink/rise to the lower/upper layer. These fallings and risings occur in thin columns and the process is referred to as salt fingering, and the process of the water actually moving as double diffusive convection (also thermohaline or thermosolutal convection).

double high water

See double tide.

double Kelvin wave

To be completed.

double tide

Either a high water consisting of two maximums of about the same height separated by a relatively small depression or a low water consisting of two minimums separated by a relatively small elevation. This has also been called a double high water, an agger, and a gulder.

DOVETAIL

Acronym for Deep Ocean VEntilation Through Antarctic Intermediate Layers, a research program whose main goal is to understand the physical processes in the Weddell-Scotia Confluence (WSC) region sufficiently to quantify the ventilation of the world ocean achieved by the Weddell Sea water masses. The program objectives are:

• to assess the quantity, physical and chemical characteristics of Weddell Sea source waters for the WSC;
• to describe the dominant physical processes associated with spreading and sinking of dense Antarctic waters within the WSC region;
• to estimate the ventilation rate of the world ocean from the Weddell Sea; and
• to estimate seasonal fluctuations in region ocean transport and hydrographic structure, and assess the likely influence of interannual variability on rates of ventilation by Weddell Sea waters.

[http://www.esr.org/dovetail/dovetail.html]
[http://www.awi-bremerhaven.de/Modelling/BRIOS/dovetail.html]

DRAKE

Acronym for Dynamic Response And Kinematics Experiment, an ISOS program consisting of a series of experiments to obtain measurements of various quantities in the Drake Passage. One took place in 1977 (DRAKE 77) and another in 1979 (DRAKE 79).

DRAKE 79 was a year long (1979-1980) measurement program spanning the entire Drake Passage. The current meter array consisted of two major parts. The main line (ML) array was designed to measure the total transport through the passage, and a cluster of moorings in the central passage was a mapping and statistics (MS) array for sampling the flow variability in the Polar Frontal Zone (PFZ). The current meters were positioned at nominal depths of 500 m and 2500 m on all moorings, and at 1400 m on the MS moorings. See Nowlin, Jr. (1986) and Klinck (1985).

Drake Passage

A narrow constriction between South America and Antarctica between 56 and 63$^\circ$ S through which the Antarctic Circumpolar Current (ACC) must accelerate and squeeze in its trip around the globe. It is about 780 km wide at a depth of 500 m. Direct current and bottom pressure measurements in the Passage have led to estimates of ACC flow of around 110-130 Sv through it.

DSL

Abbreviation for deep scattering layer.

DSRT

Abbreviation for Deep-Sea Reversing Thermometer.

DWBC

1. Abbreviation for Deep Western Boundary Current. 2. Abbreviation for Deep Water Brazil Current.

dynamic depth

See dynamic height.

dynamic distance

See dynamic height.

dynamic height

In oceanography, this refers to the pressure associated with a column of water. Horizontal variations of this (due to horizontal variations in temperature and salinity) are mapped to determine what is called the dynamic topography and its corresponding geostrophic flow field in the ocean. The dynamic height is measured in dynamic meters and is defined by

$$D({p_1},{p_2})\,=\,{\int_{p_1}^{p_2}}\,\delta(T,S,p)\,dp$$

where $p_1$ and $p_2$ are two reference pressure levels, $\delta$ the specific volume anomaly, $T$ the temperate, $S$ the salinity, and $p$ the pressure. This is analogous to a meteorologist's use of a pressure chart, with the direction of flow aligned with the contours and the intensity of flow inversely proportional to the contour spacing. Dynamic heights are preferred over geometric heights in oceanography and meteorology because energy is generally lost or gained when a parcel of fluid moves along a surface of equal geometric height but not when it moves along a surface of equal dynamic height. This quantity has also been called dynamic thickness, dynamic distance, geopotential height, geopotential thickness, and geopotential distance.

dynamic meter

In oceanography, a unit of gravity potential used to express the amount of work that is performed or gained in moving a unit mass from one level to another. A dynamic meter represents the work performed in lifting a unit mass nearly 1 m and is defined as 10$^5$ dyn-cm/gm or 10 J/kg. The depth in dynamic meters is related to the depth in geometric meters via $D\,=\,gh/10$, where $g$ is the gravitational acceleration and $h$ the geometric depth, i.e. 1 dynamic meter corresponds roughly to 1.02 geometric meters. This is used instead of the geometric meter since gravity is the most important of the acting forces and as such a coordinate system based on gravity is advantageous.

dynamic method

See geostrophic method.

dynamic thickness

See dynamic height.

dynamic topography

In oceanography, a field of horizontally varying dynamic heights in the ocean, analogous to, for example, a topography field on land. This is also called geopotential topography.

dynamic velocity

See friction velocity.

DYOME

Acronym for the Dynamique Oceanique a Moyenne Echelle, an experiment taking place in 1981-1982. See Astraldi et al. (1990).