OCEAN SECTIONS
Collecting oceanographic data is an expensive and often dangerous pursuit. Early scientists relied on occasional observations made by sea-going commercial vessels to collect data on ocean properties such as temperature, salinity and ocean life. Only late in the 19th century were vessels designed specifically for ocean exploration and expeditions sent out with equipment on board specifically designed to collect oceanographic data.
Although the number of oceanographic expeditions grew throughout the 20th century, it was not until after World War II that the systematic study of the entire world's oceans began. These expeditions were driven largely by the research goals of particular institutions and scientists and it was not until the 1970's that coordinated efforts were undertaken to systematically study large areas of the world's ocean in a relatively continuous and intensive fashion. These efforts led to an explosive growth in oceanographic data collection.
Because of the spotty, limited nature of data collected up until the latter part of the 20th century, oceanographers relied on graphical presentations of the results of data collection exercises at specific locations - usually presented as plots of some parameter against depth (profiles). The most commonly collected data were temperature and salinity, along, of course, with marine organisms. The collection of this data allowed oceanographers to define both surface and deep ocean currents and water masses. Rarely, but with increasing frequency throughout the late 20th century, oceanographers also collected other data - dissolved oxygen, nutrients, radioactive tracers like 14C and tritium (3H), productivity, and other parameters. Such data is today being collected not only from ships, but also from satellites in space, submarines, automatic buoys, and other platforms.
So much data has been and is being collected that oceanographers are now able to look at many variables besides just temperature and salinity over vast areas of the planet's oceans in two, three and even four (time) dimensions.
Presented below are a few figures generated from a software system created and distributed on a CDROM by the Physical Oceanographic Distributed Active Archive Center (PO.DAAC) division of JPL (Jet Propulsion Laboratory). I used a data exploration application titled Ocean Data View (J. Swift, P. Rhines, and R. Schlitzer) to generate these figures, and I've made a few brief comments on my interpretation of what these figures illustrate about deep ocean currents.
Undoubtedly, this type of presentation of data will become the standard way in which oceanographers of the future will look at and study deep ocean water properties.
GEOSECS - 1978
One of the earliest cooperative ventures among several oceanographic institutions was GEOSECS. The small globe below shows the track of a section of the Atlantic Ocean from the North Atlantic near Iceland and Greenland to the South Atlantic near Antarctica. Each 2D plot of a parameter against depth is color coded and the latitude given along the horizontal axis.
Temperature
You can clearly see the two pools of warm surface water in the north and South Atlantic and the isolated pool of very cold water in the Arctic Basin. It is also fairly clear that deep water is originating at about 60o N & S with the coldest, deepest water in the South Atlantic basin.
Salinity
Salinity data provides a clearer picture of the two water masses originating in the Antarctic as well as the massive North Atlantic Deep Water (NADW) mass moving down and south from about 60oN. Note also that salinity is highest towards the center of the North and South Atlantic gyres, not at the equator.
Oxygen
Oxygen data is related to three major factors - mixing with the atmosphere, temperature (oxygen is most soluble in cold water) and productivity/respiration. Thus, not surprisingly, the Arctic and Antarctic waters have the highest levels of dissolved oxygen. NADW is also obviously carrying a good supply of oxygen into the deep Atlantic. But what is happening near the equator at intermediate depths and in the Antarctic at nearly all depths?
Phosphate
Phosphate is an essential nutrient for organisms and in short supply in the oceans. Phosphate data reflect both primary productivity (lowering phosphate concentrations) and respiration (elevating phosphate concentrations). Note the clear source of phosphate in Antarctic waters and its clear transport north in AAIW and AABW. Note also how the north and south Atlantic gyres are almost devoid of this nutrient.
Silica
Silica is required for the growth of several important marine organisms - both plant and animals. Diatoms are plants that make up an important component of planktonic ecosystems and construct their shells (tests) from dissolved silica. Radiolarians are planktonic animals that similarly makes their shells from dissolved silica. Silica can and certainly is provided by freshwater input from continental weathering and erosion. But this figure also suggests that something else is going on within the ocean basins themselves with respect to silica.