Thermohaline circulation

Thermohaline Circulation 2

Thermohaline Circulation (THC) is a part of the large-scale ocean circulation that is driven by global density gradients created by surface heat and freshwater fluxes. The term "thermohaline" combines "thermo-", referring to temperature, and "-haline", referring to salt content, factors which together determine the density of sea water. The Thermohaline Circulation plays an important role in supplying heat to the polar regions, thereby influencing the climate of the planet.

Overview

The Thermohaline Circulation is a global system of surface and deep-water currents that stretches across all ocean basins. It includes both the surface ocean currents driven by the wind and the deep ocean currents driven by density differences. The process involves warm, salty water cooling and sinking in the North Atlantic, flowing southward at depth, and then being upwelled in other parts of the ocean, or returning to the surface through mixing and wind-driven upwelling.

Mechanism

The driving force behind the Thermohaline Circulation is the density difference of sea water, which is affected by temperature (thermal effect) and salinity (haline effect). Cold, salty water is denser than warm, fresh water. In areas like the North Atlantic, the cooling of sea water and formation of sea ice remove freshwater from the ocean, leaving behind saltier, denser water. This dense water sinks to the bottom of the ocean and pushes the deep sea water ahead, creating a global current.

Components

The Thermohaline Circulation consists of two main components: the deep-water formation areas, primarily in the North Atlantic (the North Atlantic Deep Water (NADW)) and around Antarctica (the Antarctic Bottom Water (ABW)), and the upwelling zones, which are more diffusely distributed across the globe. The circulation moves water between these areas, transporting heat and nutrients around the world.

Impact on Climate

The Thermohaline Circulation has a significant impact on the world's climate. It is responsible for transporting heat from the equator towards the poles, influencing regional climates. For example, Western Europe benefits from the North Atlantic Drift, a part of the THC, which brings warmer waters and milder winters. Any significant changes in the THC could have profound effects on global climate patterns, potentially leading to cooler temperatures in Europe and shifts in rainfall patterns across the tropics and subtropics.

Threats and Changes

The Thermohaline Circulation is sensitive to changes in temperature and salinity. Global warming, by increasing surface temperatures and altering patterns of precipitation and evaporation, could freshen the surface waters in the North Atlantic, reducing their density and inhibiting the sinking that drives the THC. This could lead to a slowdown or even a shutdown of the THC, with significant climate impacts.

Research and Monitoring

Scientists use a variety of methods to study and monitor the Thermohaline Circulation, including satellite observations, oceanographic floats, and deep-sea probes. Understanding the current state and potential changes in the THC is crucial for predicting future climate scenarios.