It takes more energy to heat and cool large bodies of water than air or land, so these bodies tend to stay in a more narrow range of temperatures. This ability to store heat and release it slowly is called thermal mass. Stone and earth also have this capacity. These bodies tend to move heat more slowly, collecting heat during the day, releasing at night, collecting cool air at night and releasing it in the daylight, so they don’t get as cold, or as hot, as surrounding land. Thus large bodies of water regulate temperature, preventing extremes.
In Florida, the south side of large lakes like Apopka can support mangos, while the north side supports trees that need more chill hours like plums. The cold northern air hits the land on the upper part of the lake, but the lake is able to warm it up before it reaches the mangos. There can be other factors, but water mass tends to moderate temperatures to some degree for nearby areas.
Oceans regulate temperatures substantially. In Central and North Florida, the shores are up to one zone warmer than inland settlements. The warmth of the Gulf and Atlantic contribute to our subtropical climate.
The Jet Stream, a major wind pattern in the US, brings cold air in the winter and can override the moderating influence of the Gulf to some degree. Thus, we do get freezes on our farm during those events, even though we are only six miles from the Gulf. But just directly west of us right on the water, it doesn’t get as cold as it does on our farm even when directly hit with the Jet Stream.
In the Pacific, currents from the north keep much of the west coast from San Francisco and on up cool for most of the year. But the Alaska coast is warmer than inland Alaska because the Pacific modulates the temperature.
The cold Pacific currents ensure that coastal areas of Southern california stay balmy year around, and there are no hot extremes or freezing temperatures. This allows some parts of the region near the ocean to be able to grow bananas and coffee commercially. This effect continues inland for miles in the valley, but land that is cut off from the ocean influence by hills can experience extreme heat and much colder winters.
We lived in the foothills of Los Angeles, and at several hundred feet higher than the valley, we had snow a couple of years (that didn't’ stick), and 110F days in summer. In Santa Monica, temperatures stay in the 70’s or low 80’s during the summer, and 50’s when other parts of LA approach freezing.
Temperatures influenced by ocean thermal mass and altitude. For instance, Big Bear is in the mountains, surrounded by lower altitude drylands and desert temperatures. Note the island temperature (Avalon).
There is a microclimate on the ocean side of many mountain ranges when they are close to the ocean or a large water body that is sometimes a ½ to full USDA Zone warmer than the same altitude on the opposite side of the mountains. This is mainly caused by wind patterns and thermal mass from water. In general, climates influenced by oceans are cooler in summer and warmer in winter than inland areas.
The UK is snow free in many areas and can grow USDA Zone 7 or even Zone 8 plants, even though it is at the same latitude as Maine or Canada (mostly Zone 4).
The thermal mass from oceans contributes to weather, like hurricanes. The warmer the ocean, the stronger hurricanes can become.
Thermal mass can also be created by rock, or by buildings and concrete. Temperature in cities can vary by 10F or more depending on whether the thermal mass of sidewalks or buildings are shaded or exposed to sunlight.