What is a thermocline? --> What is a thermocline? A thermocline is the transition layer between warmer mixed water at the ocean's surface and cooler deep water below. The red line in this illustration shows a typical seawater temperature profile. In the thermocline, temperature decreases rapidly from the mixed upper layer of the ocean (called the epipelagic zone) to much colder deep water in the thermocline (mesopelagic zone). Below 3,300 feet to a depth of about 13,100 feet , water temperature remains constant. At depths below 13,100 feet, the temperature ranges from near freezing to just above the freezing point of water as depth increases. Bodies of water are made up of layers, determined by temperature. The top surface layer is called the epipelagic zone, and is sometimes referred to as the "ocean skin" or "sunlight zone." This layer interacts with the wind and waves, which mixes the water and distributes the warmth. At the base of this layer is the thermocline. A thermocline is the transition layer between the warmer mixed water at the surface and the cooler deep water below. It is relatively easy to tell when you have reached the thermocline in a body of water because there is a sudden change in temperature. In the thermocline, the temperature decreases rapidly from the mixed layer temperature to the much colder deep water temperature. In the ocean, the depth and strength of the thermocline vary from season to season and year to year. It is semi-permanent in the tropics, variable in temperate regions (often deepest during the summer), and shallow to nonexistent in the polar regions, where the water column is cold from the surface to the bottom. Thermoclines also play a role in meteorological forecasting. For example, hurricane forecasters must consider not just the temperature of the ocean's skin (the sea surface temperature), but also the depth of warm water above the thermocline. Water vapor evaporated from the ocean is a hurricane's primary fuel. The depth

Abstract Part of the heat transported poleward from the Tropics by the ocean is stored near the energetic western boundary currents. These storage reservoirs provide a source of interannual to decadal climate fluctuations through their impact on the ocean–atmosphere heat fluxes. Changes in ocean heat storage result from the difference between surface fluxes and the convergence of oceanic heat transport. To estimate the heat budget for 26°–40°N, 140°E–180°, sea surface temperature and subsurface temperatures are assimilated into a one-dimensional model of the upper ocean that is forced by heat fluxes from the NCEP–NCAR reanalysis. Heat transport convergences are inferred as the residual of the heat budget for the period 1970–2000 using the “unknown control” from a Kalman filter/smoother technique. The estimates of heat transport convergence compare qualitatively with direct estimates from a three-dimensional model that uses geostrophic currents from the TOPEX/Poseidon radar altimeter for 1993–99; this peri...

Abstract The impact of changes in shortwave radiation penetration depth on the global ocean circulation and heat transport is studied using the GFDL Modular Ocean Model (MOM4) with two independent parameterizations that use ocean color to estimate the penetration depth of shortwave radiation. Ten to eighteen percent increases in the depth of 1% downwelling surface irradiance levels results in an increase in mixed layer depths of 3–20 m in the subtropical and tropical regions with no change at higher latitudes. While 1D models have predicted that sea surface temperatures at the equator would decrease with deeper penetration of solar irradiance, this study shows a warming, resulting in a 10% decrease in the required restoring heat flux needed to maintain climatological sea surface temperatures in the eastern equatorial Atlantic and Pacific Oceans. The decrease in the restoring heat flux is attributed to a slowdown in heat transport (5%) from the Tropics and an increase in the temperature of submixed layer waters being transported into the equatorial regions. Calculations were made using a simple relationship between mixed layer depth and meridional mass transport. When compared with model diagnostics, these calculations suggest that the slowdown in heat transport is primarily due to off-equatorial increases in mixed layer depths. At higher latitudes (5°–40°), higher restoring heat fluxes are needed to maintain sea surface temperatures because of deeper mixed layers and an incre

A comprehensive understanding of the upper-ocean response to typhoons is critical for improving typhoon intensity prediction. Although background mesoscale environments modulate the upper ocean, how submesoscale dynamics specifically drive the three-dimensional reshaping of the post-typhoon wake remains unclear. Our study employs a one-way nested model configuration (9 km parent grid and 3 km child grid) to examine the multiscale oceanic response to Typhoon Noru (2022) within the frontogenetic Vietnam Offshore Current region of the South China Sea. Mixed-layer heat budget analysis revealed that wind-driven vertical mixing primarily governed the forced-stage cooling magnitude, regardless of model resolution. However, the thermal evolution within the post-typhoon cold wake exhibited a pronounced contrast between the two resolutions. Spatial scale decomposition confirmed that the enhanced fine-scale thermal variability was primarily driven by submesoscale flows advecting background temperature gradients. Furthermore, the high-resolution simulation successfully resolved coherent ageostrophic secondary circulations along these submesoscale fronts. These localized overturning motions produced a persistent positive vertical buoyancy flux that slumped horizontal density fronts, thereby driving rapid restratification. These fine-scale vertical exchanges effectively transported warm surface water downward, governing the thermal restructuring within the post-typhoon cold wake. The findi

Mineral dust aerosol can be transported over the nearby oceans and influence the energy balance at the sea surface. The role of dust-induced sea surface temperature (SST) responses in simulations of the climatic effect of dust is examined by using a general circulation model with online simulation of mineral dust and a coupled mixed-layer ocean model. Both the longwave and shortwave radiative effects of mineral dust aerosol are considered in climate simulations. The SST responses are found to be very influential on simulated dust-induced climate change, especially when climate simulations consider the two-way dust-climate coupling to account for the feedbacks. With prescribed SSTs and dust concentrations, we obtain an increase of 0.02 K in the global and annual mean surface air temperature (SAT) in response to dust radiative effects. In contrast, when SSTs are allowed to respond to radiative forcing of dust in the presence of the dust cycle-climate interactions, we obtain a global and annual mean cooling of 0.09 K in SAT by dust. The extra cooling simulated with the SST responses can be attributed to the following two factors: (1) The negative net (shortwave plus longwave) radiative forcing of dust at the surface reduces SST, which decreases latent heat fluxes and upward transport of water vapor, resulting in less warming in the atmosphere; (2) The positive feedback between SST responses and dust cycle. The dust-induced reductions in SST lead to reductions in precipitation (o