I learnt something damn cool in physics today!! It wasn't exactly part of the syllabus but more of background information needed for something else.
Water has an anomalous expansion, whereby its density is actually highest at 4 degrees Celsius. Practically everything expands when heated, so the hotter it gets, the lower its density. However, from 0 degrees to 4 degrees, as water is heated, it actually CONTRACTS instead, and density INCREASES. Before 0 degrees and after 4 degrees it follows the same pattern as any other stuff does.
Since convection currents are due to density (hot air/water rises because it has a lower density), convection currents (if it is still called that) brings the COLDER water (above 0 degrees below 4 degrees) up instead of the warmer water. This means that at the bottom of any pond, the water is ALWAYS at 4 degrees. Many people know that marine life is able to survive in cold winter as ponds freeze over because below the ice, the water is not frozen, well, this is the reason.
As the weather gets colder, the layer of ice at the top becomes thicker, but the bottom of the pond always remains at 4 degrees.
Of course this is but a very simplified explanation and there certainly are some abnormalities, but eh, its DAMN COOL RIGHT.
And oh dear, my GDC cannot update sigh. Jialat jialat jialat. How to do my IB exams liddat.