Exercises in oceanography.

• Cast

  same as station.

• Convection

  movement in a fluid (such as the ocean, the atmosphere and the earth's interior) with significant vertical movement. While in the ocean and atmosphere most movement is predominantly horizontal, convection is characterised by the fact that the horizontal and vertical components of the motion are of comparable strength.

• Convergence

  a location in a fluid (such as the ocean, the atmosphere and the earth's interior) where the movement results in an accumulation of fluid at the surface, forcing fluid down towards deeper layers. This downward movement is called downwelling.
  The situation where the movement results in a fluid deficit at the surface, forcing fluid up from deeper layers, is called divergence, and the associated upward movement is called upwelling.

• Degree

  in geodesy a unit of distance. One degree is divided into 60 minutes, one minute into 60 seconds. The distance 2 degrees 45 minutes 12 seconds is written as 2° 45' 12''.
  One minute of latitude is defined as one nautical mile (1 naut. mile or 1 nm, equivalent to 1.582 km), so one degree (1°) of latitude corresponds to 60 nautical miles or approximately 111 km.
  The length of one degree (1°) of longitude varies because the meridians converge towards the poles. At the equator one degree of longitude is nearly the same as one degree of latitude (60 nm). (It would be exactly the same if the earth were a perfect sphere.) This reduces to zero at the poles.

• Detritus

  dead organic matter from the euphotic zone which sinks to the ocean floor, being remineralised on its way.

• Divergence

  see Convergence.

• Diurnal

  of one day's duration.

• Euphotic zone

  the depth range in the ocean which can be reached by sunlight. Plants extract energy from light through photosynthesis. The euphotic zone is therefore the depth range where marine plants can grow. In extremely clear water the euphotic zone can be up to 200 m deep. In most situations it is much shallower, because the presence of marine plants such as algae reduces the clarity of the water.

• Great Circle

  a circle on the earth's surface which has its centre in the centre of the earth. All meridians are great circles by definition. Of all circles that can be drawn on the earth's surface, great circles have the smallest curvature and therefore come closest to straight lines.
  Because circles in space are uniquely defined by two points and their centre, it is always possible to find one and only one great circle through two points on the earth's surface. This great circle then gives the shortest distance between the two points. Ships and aircraft follow great circles as much as possible, unless other circumstances (such as land masses, bad weather, volcanic eruptions etc.) force them to choose a different route.

• Kelvin (K)

  the temperature scale used in physics and chemistry. It is equivalent to the Celsius scale but has a different zero point: 0 K = -273.2°C. This corresponds to "absolute zero", the lowest temperature that any matter can achieve. The Kelvin scale is therefore also called the absolute temperature scale. Note that it is not expressed in degrees as the Celsius scale: 20°C = 293.2 K.

• Latitude

  the position of a point on the surface of the earth relative to the equator. Points at identical latitudes are connected by circles running parallel to the equator; these circles are therefore also known as "parallels". The equator is the 0° (zero degree) line of constant latitude or 0° parallel, from where latitudes increase to +90° or 90°N at the North Pole and -90° or 90°S at the South Pole.

• Longitude

  the position of a point on the surface of the earth relative to a reference meridian. Different reference meridians have been used during different periods in history. Today, the meridian through Greenwich near London, England, is used as the 0° (zero degree) longitude. The 180° longitude is a meridian in the Pacific Ocean east of New Zealand known as the dateline. East of Greenwich longitude is counted as "degrees east", west of Greenwich it is counted as "degrees east". Thus New York is at 74°W and Moscow at 37° 42'E.

• Lunar

  related to the moon.

• Meridian

  a line connecting both poles and therefore running in north-south direction. The 0° (zero degree) meridian goes through Greenwich near London, England, the 180° meridian through the dateline in the Pacific Ocean east of New Zealand. The term "meridional" denotes a line or movement along a meridian, ie in north-south direction. All meridians are great circles. See also longitude.

• Nautical mile

  a unit of distance. 1 nautical mile (1 naut m or 1 nm) equals 1.852 km. It is defined as one minute of latitude. See also degree.

• Profile

  the change of an ocean property (such as temperature) with depth. See also station.

• Section

  an arrangements of oceanographic observations which gives a two-dimensional picture of various ocean properties along a ship's track. It is usually obtained by stopping the vessel at regular intervals along its track and lowering an instrument to measure the properties of interest (such as temperature, salinity,oxygen and others) as functions of depth. The information from several such stations is combined into a display of the various properties against distance along the track and depth. The term section is now also used if the data are derived from a numerical model.

• Semidiurnal

  of half a day's duration.

• Solar

  related to the sun.

• Station

  a set of observations obtained by a ship at sea by lowering instrumentation from the surface to depth while the ship is stopped; also called a cast. The observed change of a property (such as temperature etc) with depth is known as a profile.

• Sverdrup (Sv)

  a unit of volume transport. 1 Sverdrup (Sv) = 10⁶ m³ s^-1.

• Zonal

  running in east-west direction, ie in the direction of constant latitude.