Thermohaline circulation is a large-scale movement of ocean water shaped by differences in density. This lesson introduces the role of temperature and salinity, explains how surface processes connect to deep currents, and traces key developments in the scientific understanding of the circulation.
The word thermohaline combines thermo, referring to temperature, and haline, referring to salt content. Together, temperature and salinity influence the density of seawater, which is a key factor in the large-scale circulation of the oceans.
All flashcards
North Atlantic Deep Water (NADW)
Deep water formed when cold, salty North Atlantic surface water becomes dense enough to sink.
Antarctic Bottom Water (AABW)
Very dense water formed near Antarctica as surface cooling and brine rejection increase seawater density.
Upwelling
The return movement of older deep water toward the ocean’s upper layers.
Diapycnal mixing
Mixing across surfaces of constant density, which can be caused by tidal currents.
RAPID programme
A measurement programme estimating overturning circulation strength at 26.5°N in the North Atlantic.
Quiz questions
Why can surface water in the North Atlantic become dense enough to sink and contribute to NADW?Answer: Cooling and evaporation increase its density by lowering temperature and raising salinity.
How does brine rejection help form Antarctic Bottom Water?Answer: Salt excluded from forming sea ice increases the salinity and density of nearby seawater.
Why can North Atlantic Deep Water not flow directly into the Pacific through the Bering Strait?Answer: The strait is narrow and shallow, preventing passage of this deep flow.
What does the RAPID programme estimate at 26.5°N in the North Atlantic?Answer: Overturning circulation strength using current, cable, temperature, and salinity measurements.
How should projections of a possible major circulation change be interpreted?Answer: A slowdown is not a complete collapse, and the timing and impacts remain uncertain.