Thermohaline circulation

Summary

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 adjective thermohaline derives from thermo- referring to temperature and -haline referring to salt content, factors which together determine the density of sea water. Wind-driven surface currents (such as the Gulf Stream) travel polewards from the equatorial Atlantic Ocean, cooling en route, and eventually sinking at high latitudes (forming North Atlantic Deep Water). This dense water then flows into the ocean basins. While the bulk of it upwells in the Southern Ocean, the oldest waters (with a transit time of about 1000 years) upwell in the North Pacific. Extensive mixing therefore takes place between the ocean basins, reducing differences between them and making the Earth's oceans a global system. The water in these circuits transport both energy (in the form of heat) and mass (dissol

Official source

https://en.wikipedia.org/wiki/Thermohaline_circulation

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Thermohaline Flow in Seawater Intrusion in Shallow Coastal Aquifers

David Andrew Barry, Chenming Zhang

Temperature and salinity, with largely different diffusivities, make a perfect couple that drives thermohaline flow (double diffusive convection where heat and salt are the two main concerned properties) in porous media wherever their gradients co-exist. Studies of double diffusion convection have revealed various flow regimes generated by instable and even stable vertical stratification of heat and salt including diffusive, finger, and mixed flow regimes. In the context of seawater intrusion in shallow coastal aquifers, however, temperature and salinity gradients present more likely horizontal than vertical. Moreover, while salinity gradient is apparently seaward, the direction of temperature gradient may vary over the seasons. In such cases, understanding on how thermohaline flow exhibit and influence the overall state of seawater intrusion in near-shore aquifers remains largely deficient. In this study, we examine the occurrence and characteristics of thermohaline flow in seawater intrusion in coastal aquifers under various scenarios of salinity and temperature distribution by laboratory experiments and numerical simulation. Its effects on solute transport and saltwater circulation are also investigated.

2018

Effects of temperature on tidally influenced coastal unconfined aquifers

David Andrew Barry, Li Pu, Chenming Zhang

Aquifer-ocean temperature contrasts are common worldwide. Their effects on flow and salinity distributions in unconfined coastal aquifers are, however, poorly understood. Based on laboratory experiments and numerical simulations, we examined the responses of flow processes in tidally influenced aquifers to aquifer-ocean temperature differences. The extent of seawater intrusion and seawater circulation were found to vary with the aquifer-ocean temperature contrast. Compared with the isothermal case, an increase of up to 40% of the tide-induced seawater circulation rate in the intertidal zone was observed when seawater is warmer than groundwater. In contrast, saltwater circulation in the lower saltwater wedge declines notably no matter whether the seawater is warmer or colder than groundwater. As the seawater temperature rises, the contribution of tide-induced circulation to the overall increase of submarine groundwater discharge becomes more important compared with that of density-driven seawater circulation. Both the upper saline plume and the freshwater discharge zone expand significantly with warmer seawater whereas the lower saltwater wedge contracts.

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Stream Water Temperature Modeling For An Alpine Catchment

Vasco Andrea Neuhaus

Stream water temperature is an important key factor for water quality of rivers. Different approaches for stream temperature modeling have been developed over the past few decades and can basically be grouped into heat balance and stochastic models. Energy balance based stream temperature modeling depends on several types of heat fluxes and numerous approaches yet have tried to simplify this approach while scoping with accurate results. On the other hand strong correlation between air and stream water temperature has been reported since focus was put on stream temperature research. Therefore simple and reliable modeling approaches have been developed and verified for lowland streams. The objective of this work is to make use of an already developed spatially explicit hydrological response model in order to accurately simulate stream temperature for an alpine catchment based on estimated heat fluxes and thus further be able to providing information about water temperature at the sub-catchment scale. On the other hand the versatility of the existing stochastic modeling approaches is assessed with respect to the alpine area. The results reveal that (1) snow melt influences the energy balance approach significantly and thus makes parsimonious but accurate stream temperature modeling difficult and (2) regression approaches developed for lowland river systems are applicable to small alpine catchments.

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