Physical oceanography

The study of physical properties and processes in the oceans, including fluid flow, waves and transport of heat.

The Labrador Sea is a North Atlantic basin between Greenland and northeastern North America, studied as a site of deep ocean convection. Winter surface heat loss can increase near-surface water density until mixing reaches much deeper layers, forming Labrador Sea Water.

Repeated temperature and salinity profiles distinguish deepening convection from ordinary seasonal surface changes. The resulting water spreads into the wider circulation and helps ventilate the ocean interior. The depth of mixing varies between years; a single winter or one observing station cannot characterize the entire overturning circulation.^[ref]

Labrador Sea Water is a water mass formed by deep winter mixing in the Labrador Sea, identifiable by its temperature, salinity, density and ventilation history. Surface heat loss increases density and can deepen convection, producing a relatively uniform water column that subsequently spreads into the surrounding North Atlantic.^[ref]

A motivating measurement combines shipboard profiles of temperature, salinity and dissolved oxygen with repeated profiling-float observations. A deep layer with weak vertical property gradients indicates mixing; oxygen and other tracers help reveal recent contact with the atmosphere. Comparing successive winters distinguishes renewed formation from the later movement of an older water mass. Surface freshening can preserve stable stratification even during substantial cooling, so heat loss alone does not determine the depth reached by convection.^[ref]

The observational lesson is that a water mass is identified through a combination of properties and history. A cold reading at one depth is insufficient to establish its origin or to measure the whole ocean overturning circulation.

An ocean current is organized water motion that transports mass, heat, salt and other properties through the ocean. Surface winds, pressure gradients, buoyancy changes, Earth's rotation and friction all contribute, with their relative importance depending on scale and depth.

A steady large-scale interior flow can approximately balance a horizontal pressure gradient against the Coriolis force, while boundary currents require additional dynamics. Henry Stommel showed that the latitude dependence of rotation, combined with friction in a wind-driven basin, can concentrate the return flow on the western side. The circulation is therefore not simply water moving in the direction of the local wind.^[ref]

An oceanographer studies ocean systems through observations and models. Physical questions concern currents, waves and heat transport; chemical and biological questions connect seawater composition and living systems with those motions.

A physical oceanographer might combine temperature and salinity profiles with velocity measurements to infer water-mass formation and transport. Sampling location and time matter because a single profile is a local observation in a changing three-dimensional ocean.

Melvin E. Stern was a physical oceanographer who developed a mathematical account of the instability now called salt fingering. His 1960 paper The Salt-Fountain and Thermohaline Convection by Melvin E. Stern explained how warm, saline water above cooler, fresher water can become unstable even when the combined density stratification is gravitationally stable.^[ref]

The decisive ingredient is that heat spreads by heat conduction much faster than salt spreads by diffusion. A displaced parcel can lose its temperature anomaly while retaining its salinity anomaly, changing the restoring or overturning density difference. Stern's paper made this into a stability problem and asked whether the resulting motions could matter for vertical ocean mixing. This connected small-scale molecular transport with a possible large-scale oceanographic consequence, while leaving its environmental importance as an observational question. He taught at Florida State University from 1987 to 2006.^[ref]

Portrait: Melvin Stern in the Florida State Times remembrance, page 11.

Adrian Jenkins studies interactions between the ocean and ice shelves. With Lars H. Smedsrud, he developed a model of frazil formation in buoyant ice-shelf-water plumes. As a plume rises into lower pressure, its freezing temperature changes, allowing supercooling and growth of suspended ice crystals.

Their model couples plume flow, heat, salt and crystal populations, linking microscopic freezing with marine-ice accumulation beneath an ice shelf.^[ref]

Lars H. Smedsrud coauthored a model of frazil ice in ice-shelf-water plumes with Adrian Jenkins. It follows buoyant water along an ice-shelf base and includes the growth of crystals of different sizes after the plume becomes supercooled.

Suspended ice affects buoyancy, heat and salt balances, while deposition can build marine ice. The model therefore connects an evolving crystal population with large-scale ocean-ice exchange rather than treating freezing as one prescribed boundary flux.^[ref]

Henry Stommel explained a mechanism for the western intensification of wind-driven ocean currents. His 1948 basin model combined wind stress, a latitude-dependent Coriolis parameter and linear bottom friction; the resulting circulation concentrated streamlines on the western side.

The result connects a global transport balance with a narrow boundary current. Friction is essential to closing the circulation even when it is weak in much of the interior, illustrating why a small local effect can control the structure of an entire flow.^[ref]

Igor Yashayaev authored a report on oceanographic conditions in the Labrador Sea. Such observations connect temperature and salinity profiles with deep-water formation and ocean ventilation; comparing years requires consistent sampling and measurement interpretation.^[ref]

A physical oceanographer whose work includes tropical Pacific observations and El Niño–Southern Oscillation dynamics. Author of El Niño and La Niña: Causes and Global Consequences by Michael J. McPhaden.

Coupled variability of the tropical Pacific ocean and terrestrial atmosphere, including the warm El Niño phase, the cold La Niña phase, and associated changes in surface pressure, trade winds and the thermocline.

The cold phase of El Niño–Southern Oscillation, with central and eastern equatorial Pacific surface cooling.

The warm phase of the coupled tropical Pacific El Niño–Southern Oscillation, with central and eastern equatorial Pacific surface warming and a weakened Walker circulation. Changes of trade winds, thermocline depth, and equatorial Kelvin waves and equatorial Rossby waves participate in its evolution.

A water layer across which temperature changes rapidly with depth. In a reduced gravity description of the upper ocean, its displacement is represented by the interface between warm surface water and colder deep water. Deepening the eastern tropical Pacific thermocline makes upwelling less effective at cooling the surface during El Niño.

A physical oceanographer studies the ocean's motion and physical state, including ocean currents, waves, temperature, salinity and mixing. Observations and mathematical models connect local measurements with transport over much larger distances.

For example, temperature and salinity influence mass density, which affects stratification and buoyancy-driven motion. Interpreting a current therefore requires both fluid dynamics and the physical properties of seawater.

James F. Price is a physical oceanographer whose research addresses upper-ocean response to wind and heating, internal waves, and the interaction between hurricanes and the ocean. His institutional curriculum vitae lists studies of storm wakes, diurnal heating and cooling, and wind-driven currents.^[ref]

In Draining a Tank by James F. Price, experiments connect Torricelli's law to measured drainage through openings and outlet pipes. He compares observed flow with successive models incorporating surface tension and viscous drag, using dimensional analysis to organize the measurements. The study shows how apparently simple outflow can depart from an ideal-fluid law as the head decreases or the outlet geometry changes.^[ref]