Tides

The tides are caused mainly by the gravitational pull of the Moon on the waters of the Ocean.  The attraction of the Moon is strongest on the side of the Earth which is facing it.  Here the above-average pull causes the waters to bulge out towards the Moon in a high tide.  At the same time, on the far side of the Earth, the Moon’s attraction is at its weakest and the waters on that side bulge away from the Moon in an equal and opposite high tide.

In the course of just over 24 hours, the rotating Earth passes through both of these liquid bulges, producing two high tides, with two low tides in between them.

The Sun, too, has a gravitational effect on the Earth.  The effect of the Sun’s gravity on the tides, is approximately half that of the Moon because it is much farther away, although its mass is far greater than the Moon’s,  When, every other week, the Sun and the Moon are both in line with the Earth, at New and Full Moon, the two gravitational forces are added together. Exceptionally high tides called Spring tides are produced.  In the intervening weeks, when the Sun and the Moon are at 90º to each other, at the first and third quarters of the Moon, the pull of the Sun cancels out half of the Moon’s gravitational effect and weak tides called Neap tides occur.

This theoretical pattern does not operate in every part of the world’s seas.  The shape of the continents prevents water from flowing uninterrupted across the surface of the planet.  This has complex effects on the regularity and number of tides for instance, Southampton Water UK has four high tides in 24 hours and SW Australia only has one high and one low tide a day.  At a few places on the Ocean’s surface all the tidal forces cancel each other out and the tides are consequently very small.

In restricted seas like the Mediterranean the tides are almost imperceptible. In other areas such as the long and narrow Bay of Fundy Canada  the range between high and low tide may be up to 15 m at Spring tide.

The most spectacular tidal effect often occurs at the Spring and Autumn Equinoxes when the combined gravitational effect of the Sun and Moon is at its strongest.  At these times, the sudden rush of water into an estuary creates a visible wave front called a bore.  The bore at the mouth of the Amazon is more than 1 km wide and 5m high sweeping inland at 21kmh.

The Mizen Peninsula has two high tides and two low tides in 24 hours.  The tide goes out for 6 hours (low tide); it waits for 20 minutes then comes in for 6 hours (high tide) then waits 20 mins before going out again.  In 24 hours 1 hour is added to the time so it means that every day the high tide is one hour later.   The range (distance between high and low tide) is up to 4.5m.

CURRENTS

The currents in the world’s oceans are the veins and arteries of a living Earth.  As part of our planet’s system of heat exchange, they bring vast amounts of warmth from the tropics into the colder latitudes that would be uninhabitable without them.  Along with the winds, by which they are driven, the currents maintain the steady balanced temperatures that are on Earth.   Without them the Tropics would grow steadily hotter and the higher latitudes more and more frozen.

The scale on which the currents work is enormous.  The Gulf Steam alone carries 50-70 times as much water as all the world’s rivers alone. These currents are so effective at smoothing out the differences in the temperatures of the oceans that 90% of all sea water varies by no more than 18º.

The global pattern is one of extraordinary symmetry.  In each hemisphere of the world’s three great oceans- the Pacific, the Atlantic and the Indian - there are rotating whorls of surface currents called gyres.  In each of these giant whirlpools, thousands of miles across, warm water moves up the western side of the ocean, cools the higher latitudes and is then brought back in a wide stream down the eastern side of the Ocean towards the Equator.  Strong westward-flowing Equatorial currents complete the cycle.

The Mizen Peninsula benefits from temperate seas warmed by the Gulf Stream coming from the west across the Atlantic Ocean all year round.  There is rarely frost or snow