简单的答案是,冰冷的海水的密度比温暖的海水,这水池和填空深海海洋。水满了深海海洋来自极地。这是一个1990年代的温度在大西洋,检索从[WOCE大西洋Atlas] [1]: [![在这里输入图像描述][2]][2]你可以看到最冷的水是来自南极地区(深蓝色东西情节的左边)和传播。如果你看看1990年代盐度相反(策划)你可以看到水从北极不是那么冷,但很咸(黄色部分的情节从上方的右手边,坐在水北来自南极洲)。[![在这里输入图像描述][3]][3]考虑海洋的密度时,重要的是要记住,海洋不是注满水,它充满了_seawater_。海水包含每公斤(约35克盐的海水][4]。因此,海水的密度取决于(温度和盐度)[5]。你可以写成$ $ \ρ= T + \ \αβS $ $这对我们需要足够正确。 (Small aside, the density also depends on pressure and the coefficients $\alpha$ and $\beta$ depend on pressure, salinity, and temperature - you can see this in the curvature of the lines of constant density in [this figure][5]. Truly understanding the density of seawater is a massive undertaking.) The salt makes two other very important things happen: 1. as seawater gets colder, it keeps getting denser (but $\alpha$ gets pretty small at low temperatures, so salinity really dominates the density) 2. seawater freezes at ~-2°C This is why we see water at -0.4°C spreading away from Antarctica in the bottom left corner of that figure. It was colder when it was near the surface, but as it sank it entrained ambient fluid, and warmed up. This explains how we get cold water down into the abyss, but why doesn't the geothermal heat flux simply warm it up? The reason that the geothermal heat flux doesn't heat up the abyssal ocean is that it is too small. The [geothermal heat flux][6] is up to ~0.5 W/m$^{2}$. By comparison, [heat fluxes at the surface of the ocean][7] range from -200 W/m$^{2}$ to 200 W/m$^{2}$ (where positive means into the ocean in both cases). The surface heat fluxes and ocean dynamics simply overwhelm the much much smaller geothermal heat flux. Lots of models include a heat flux through the ocean floor, but because it is so small the abyssal ocean remains cold. Here's an [example of the heat budget][8] from an ocean model that includes a flux of heat through the seafloor. So, not much hard maths in there, but I'm not sure we need it. [1]: http://sam.ucsd.edu/whp_atlas/atlantic_index.html [2]: https://i.stack.imgur.com/EicYM.jpg [3]: https://i.stack.imgur.com/RsY0S.jpg [4]: https://en.wikipedia.org/wiki/Salinity#Seawater [5]: https://en.wikipedia.org/wiki/Seawater#/media/File:WaterDensitySalinity.png [6]: https://en.wikipedia.org/wiki/Earth%27s_internal_heat_budget#/media/File:Earth_heat_flow.jpg [7]: https://www.pmel.noaa.gov/ocs/air-sea-fluxes [8]: https://ecco-v4-python-tutorial.readthedocs.io/ECCO_v4_Heat_budget_closure.html#Geothermal-flux