According to Henry's law, as water becomes warmer, oxygen becomes less soluble in it. This leads to daily anoxic cycles on small geographic scales and seasonal cycles of anoxia on larger scales. Therefore, bodies of water are more exposed to anoxic conditions during the hottest times of the day and during summer months.
The geothermal gradient is measured with the respect to the changes in the temperature of the plates at the various depths. And away from the plate tectonic boundaries it goes on increasing and is expressed the 30 degrees per celsius and the earth internal heat comes to form the planets heat and planetary acceleration.
