Explain the fact that the presence of a large body of water nearby, such as a sea or ocean, tends to moderate the temperature extremes of the climate on adjacent land.

Convection is the mode of transmission of heat, through fluids, in which the particles of fluids acquire heat from one region and deliver the same to the other regions by leaving their mean positions and moving from one point to the other.
Large body of water such as sea or ocean will act as a sink like in a Carnot engine. Since the thermal capacity of water is high, so the large body of water will store heat in summer time and release this heat in winter time to adjacent land by the process of heat convection. Thus in summer time the climate of adjacent land will cool whereas in winter time it will warm. That is why the presence of a large body of water nearby, such as a sea or ocean, tends to moderate the temperature extremes of the climate on adjacent land.