Measurement of ocean motions and property distributions, and the exchange of momentum, heat, energy, and materials between the atmosphere and the ocean, are at the heart of physical oceanographic science. Our capacity to understand, model, and predict ocean conditions hinges directly on our ability to observe the ocean accurately and reliably across a broad spectrum of space and time scales, from millimeters to thousands of kilometers, and from seconds to decades and beyond. CEOAS researchers use a wide variety of instruments and technologies to measure and quantify physical oceanographic variability over this extensive range of spatial and temporal scales.
Examples of faculty research projects include:
Historically, the term hydrography has meant the scientific study of the physical conditions of systems of water. Within the field of physical oceanography, hydrography is the branch of our field which looks to understand the movements of the ocean through its measurable physical properties, including: temperature, salinity, and oxygen, and chemical constituents such as phosphates, silicates, CFC's, tritium and helium.
1751: Captain Henry Ellis reported to the Royal Society of London the earliest recorded measurements in the open ocean to significant depths:
"Upon the passage, I made several trials with the bucket sea-gage, in latitude 25'-13" north; longitude 25'-12" west. I charged it and let it down to different depths from 360 feet to 5346 feet; when I discovered, by a small thermometer of Fahrenheit's, made by Mr Bird, which went down in it, that cold increased regularly, in proportion to depths, till it descended to 3900 feet: from whence the mercury in the thermometer came up at 53 degrees; and tho' I afterwards sunk it to a depth of 5346 feet, that is a mile and 66 feet, it came up no lower. The warmth of the water upon the surface, and that of the air, was at the time by the thermometer 84 degrees. I doubt not but that the water was a degree or two colder, when it enter'd the bucket, at the greatest depth, but in coming up had acquired some warmth"
(From Deep Circulation of the World Ocean by B. Warren in Evolution of Physical Oceanography, MIT Press, Cambridge MA, 1981.)
Captain Ellis had found one example of a ubiquitous physical characteristic of the oceans - that is the decrease in temperature with increasing depth. Although he underestimated the crudeness of his results, he correctly surmised that his instrument was not capable of measuring the true temperature of the ocean.
Measuring the properties of the ocean continues to be a difficult task. The sheer size of the World Ocean which covers 71% earth's surface makes adequate coverage extremely difficult, especially since so many scales of motion and variability exist. Observation is further complicated by the great depth ( > 10 km in some of the deepest trenches) of the ocean, by the strength of the motions themselves, as well as the corrosive nature of the marine environment. Nevertheless, we persevere and today our ability to measure the physical properties of the ocean has been vastly improved through advances in technology.
A seven meter vertical temperature profile (a) near the coast of Oregon as measured by the loosely tethered profiler Chameleon. The expanded view of the turbulent patch at 100 m (b) indicates that temperature fluctuations on centimeter length scales are being resolved by the thermocouple sensor. (Nash, Caldwell, Zelman and Moum, 1999: A thermocouple probe for high speed measurements in the ocean, J. Atmos Ocean. Tech. 16, 1474-1482)
Modern hydrographic research encompasses all possible scales of motions and variability. Here at OSU, hydrography is being used to study the ocean's microstructure (centimeter to meter scales), meso-scale (patterns 100 to 300 km in size) (Coastal Oceanography) and the much larger basin and global-scale circulation patterns described under this theme page. The natural variability requires that vastly different techniques be used to observe the different scales of motion. The Seasoar instrument on Oceanus provides high-resolution upper-ocean measurements of temperature and salinity over large areas. The climatology described in the North Pacific Hydrobase Page is a collection of hydrographic measurements (temperature, salinity, oxygen and nutrients) going back to the beginning of the century which may provide useful insight into decadel and longer temporal variations of the Pacific circulation.
Research on Ocean Observations at CEOAS is funded by the National Aeronautics and Space Administration, the National Science Foundation, the National Oceanic and Atmospheric Administration, and the Office of Naval Research.