OCEAN CURRENTS AND WEATHER

OCEAN CURRENTS AND WEATHER

OCEAN CURRENTS AND WEATHER (MOVEMENT OF AIR CURRENTS) ARE CONNECTED.

WIND INFLUENCES OCEAN CURRENTS.

OCEAN CURRENTS INFLUENCE WEATHER.

BOTH ARE DRIVEN BY THE UNEVEN HEATING OF THE EARTH’S SURFACE BY THE SUN.

THERE ARE TWO KINDS OF OCEAN CURRENTS:

1. SURFACE CURRENTS - USUALLY LIMITED TO THE TOP 400 METERS OF THE OCEAN - MAKE UP ABOUT 10% OF THE WATER IN THE OCEAN

2. DEEP CURRENTS - MAKE UP 90% OF THE WATER IN THE OCEANS - DRIVEN BY DENSITY DIFFERENCES AND GRAVITY

WHAT DRIVES SURFACE CURRENTS?

1. SOLAR HEATING - THE SUN HEATS THE WATER ALONG THE EQUATOR. THIS CAUSES THE WATER TO EXPAND. THE WATER ALONG THE EQUATOR IS ABOUT 8 CM HIGHER THAN IN THE MIDDLE LATITUDES. THIS CAUSES A SLIGHT RISE, AND WATER WANTS TO FLOW DOWN THAT RISE.

2. WIND - THE FRICTION OF THE WIND BLOWING ON THE WATER WILL TEND TO PUSH THE WATER IN THE DIRECTION THE WIND IS BLOWING. WIND BLOWING ON THE SURFACE OF THE OCEAN FOR 10 HOURS WILL MOVE THE WATER AT 2% OF THE WIND SPEED.

WATER PILES UP IN THE DIRECTION THE WIND IS BLOWING.

3. GRAVITY - WATER WANTS TO FLOW DOWN HILL AGAINST THE PRESSURE GRADIENT.

4. CORIOLIS FORCE - THE CORIOLIS FORCE TURNS THE CURRENTS TO THE RIGHT IN THE NORTHERN HEMISPHERE AND TO THE LEFT IN THE SOUTHERN HEMISPHERE.

ALL OF THESE FORCES COMBINE TO FORM CIRCULAR CURRENTS CALLED GYRES.

THE NORTH ATLANTIC GYRE IS DIVIDED INTO 4 CONNECTED CURRENTS - THE NORTH EQUATORIAL CURRENT, THE GULF STREAM, THE NORTH ATLANTIC CURRENT, AND THE CANARY CURRENT.

THIS SHOWS THE COMPLEXITY OF THE EARTH’S MAJOR OCEAN CURRENTS. THE PICTURE ALSO SHOWS THAT ALTHOUGH THE OCEANS HAVE DIFFERENT NAMES, THEY ARE ALL CONNECTED.

THE GULF STREAM ACTUALLY BEGINS OFF THE COAST OF AFRICA AS THE NORTH EQUATORIAL CURRENT.

PART OF THIS CURRENT FLOWS INTO THE CARIBBEAN, THROUGH THE YUCATAN CHANNEL, INTO THE GULF OF MEXICO, AND THEN THROUGH THE STRAITS OF FLORIDA.

THE WATER IS RESTRICTED AS IT FLOWS THROUGH THE STRAITS OF FLORIDA AND BUILDS UP QUITE A BIT OF FORCE (LIKE PUTTING YOUR THUMB OVER THE END OF A HOSE).

ITS VELOCITY REACHES AROUND 6 KNOTS AT THIS POINT.

THE GULF STREAM WAS DISCOVERED BY JUAN PONCE DE LEON IN 1513 AND WAS USED BY THE SPANISH IN SAILING BACK TO EUROPE.

LATER, IN 1768, BENJAMIN FRANKLIN (THEN POSTMASTER GENERAL) TRIED TO CONSTRUCT A MAP OF THE GULF STREAM SO THAT COLONIAL SHIPS COULD USE IT TO THEIR ADVANTAGE IN SAILING THE ATLANTIC.

THE GULF STREAM PARALLELS THE COAST OF THE U.S. UNTIL IT GETS TO CAPE HATTERAS.

THEN, IT MOVES OUT TO SEA, CONTINUES TO MOVE IN A NORTHERLY DIRECTION.

IT SPLITS INTO SEVERAL CURRENTS, THE LARGEST OF WHICH IS THE NORTH ATLANTIC CURRENT. THIS FEEDS ALONG THE WESTERN COAST OF EUROPE.

WHAT DOES THE GULF STREAM DO?

1. IT MOVES WARM WATER ALONG THE WEST COAST OF EUROPE. THE WINDS BLOWING OFF THIS WARM WATER MAKE EUROPE MUCH WARMER THAN IT WOULD BE. FOR EXAMPLE, THE AVERAGE LOW IN LONDON IN DECEMBER IS 42o F, WHILE THE AVERAGE LOW IN ST. JOHN’S NEWFOUNDLAND IS 27o F.

2. IT STRENGTHENS HURRICANES AND CHANGES WEATHER.

3. IT ADDS TO THE DIVERSITY OF OCEAN LIFE. FOR EXAMPLE, THE WATERS OFF MASSACHUETS ARE MUCH MORE DIVERSE BECAUSE OF THE WARM CURRENTS.

WHAT WOULD HAPPEN IF THE GULF STREAM SHUT DOWN?

WHAT WOULD HAPPEN IF THE GULF STREAM SHUT DOWN?

EUROPE WOULD GET COLDER.

SCIENTIST THINK THIS IS WHAT HAPPENED ABOUT 12,000 YEARS AGO.

AT THE END OF THE LAST ICE AGE, TEMPERATURES WERE WARMING, AND ICE WAS MELTING. THEN, THERE WAS A “LITTLE ICE AGE.” EUROPE GOT MUCH COLDER FOR SEVERAL HUNDRED YEARS.

SO MUCH FRESH WATER WAS RELEASED INTO THE NORTH ATLANTIC THAT THE GULF STREAM STOPPED.

OCEAN CURRENTS ARE DRIVEN IN PART BY WIND AND IN PART BY DIFFERENCES IN DENSITY.

COLDER WATER IS DENSER THAT WARM WATER.

WATER WITH A HIGHER SALINE CONTENT (MORE SALT) IS DENSER.

AS THE WARM GULF STREAM MOVES NORTH, EVAPORATION IS OCCURING, SO THE WATER BECOMES SALTIER. THE WATER IS ALSO COOLING.

IT EVENTUALLY REACHES A POINT WHERE IT IS ACTUALLY DENSER THAN THE SURROUNDING WATER, AND IT SINKS AND BECOMES A DEEP WATER CURRENT.

AS THE GULF STREAM MOVES NORTH, IF IT WERE DILUTED WITH FRESH WATER, IT WOULD NOT BE DENSE ENOUGH TO SINK, AND CIRCULATION WOULD STOP.

THIS IS WHAT SCIENTISTS THINK HAPPENED APPROXIMATELY 12,000 YEARS AGO.

COULD THIS HAPPEN AGAIN?

OCEAN GYRES ARE NOTORIOUS COLLECTION SPOTS FOR TRASH WASHED INTO THE OCEAN.

MUCH OF THIS IS PLASTIC DEBRIES OF VARIOUS TYPES.

AS PLASTIC WEATHERS, IT CAN BREAK INTO VERY SMALL FRAGMENTS WHICH RESEMBLE PLANKTON AND CAN BE INGESTED BY SMALLER MARINE CREATURES.

THE NORTH PACIFIC GYRE HAS GOTTEN THE MOST ATTENTION, AS IT PROBABLY CONTAINS THE MOST TRASH.

http://mindfully.org/Plastic/Ocean/Moore-Trashed-PacificNov03.htm

THIS IS AN ARTICLE BY CHARLES MOORE WHO WAS ONE OF THE FIRST PEOPLE TO CALL ATTENTION TO THE NORTH PACIFIC GYRE.

PLASTIKI, A 60 FT. SAILING CATAMARAN WAS BUILT TO CALL ATTENTION TO THE PROBLEMS OF PLASTIC WASTE IN THE OCEANS.

THE HULL IS MADE OUT OF 13,000 PRESSURIZED 2 L PLASTIC BOTTLES.