@ 02:27 GMT

Position: 36° 21.144 N x 56° 08.208 W

Speed: 9.2 kts

Course: 104° True

Guest blog written by Steve Ricci

Stories about pirates, treasure, ocean storms and ships cast adrift often reference the Gulf Stream and the Sargasso Sea. But what and where are these really? 

The Sargasso Sea covers much of the North Atlantic Ocean while the Gulf Stream runs along the east coast of the United States and then across the Atlantic toward Ireland. Among its descriptors:

The Gulf Stream is a “river in the ocean” transporting vast quantities of heated water from the Caribbean Sea to northwest Europe. It is a ribbon of deep blue water cutting across the north Atlantic and is a source of stormy weather churning up local seas and intensifying larger weather systems. For sea captains from olden times to now, it is a strong current that can help your eastward passage and will seriously slow your westward return if you don’t avoid it.

The Sargasso Sea is bounded by the Gulf Stream and other ocean currents that together encircle one million square miles of the North Atlantic. This ring of currents, known as the North Atlantic Gyre, isolates the Sargasso Sea from other waters and causes it to slowly rotate in a clockwise direction. The Sargasso is also an area of predominantly light winds and there are many tales and legends of distressed boats drifting in this big circle until eternity. Figure 1 depicts the Sargasso Sea, the N.A. Gyre and the currents that make it up. The Gulf Stream in the east and north and the westward flowing North Equatorial current to the south are big factor.

It takes a crew a day or two to get their sea legs – both from the motion of the waves and to the rhythm of life at sea in a small space with new people. This leg of the Sail For Epilepsy voyage started from Ft. Lauderdale and immediately needed to consider the impacts that the Gulf Stream would have on their first few days at sea. One immediate consideration was when to enter the Gulf Stream. Prior to departure there were winds blowing from north to south in a direction opposing the Gulf Stream current. This opposition of wind and current makes for treacherous conditions, so we waited for the wind to turn and blow from south to north.

We’ll first track the Gulf Stream in the waters off Miami and Ft Lauderdale in southern Florida. Here it is fed by currents emerging from the Gulf of Mexico (the Caribbean) and the Antilles Current wending through the deep waters off the Bahama Islands. The stream is near full flow; fifty miles wide, 350 feet deep and moving at 3-4 knots.   

The Stream’s position at these latitudes is given on local weather programs (as well as NOAA charts) which locate the west wall, or the edge of the stream closest to the mainland, generally 7-11 miles off the coast but can occasionally be much closer. The 3-4 knots at which the current is flowing to the north is substantial. Even mild winds blowing across but especially against that flow can amplify sea states dramatically. At fifty miles wide, boaters wanting to cross need to decide where they will enter and where they plan to exit.

Phil notes: I have crossed the stream a half dozen times. All were uneventful, but in each case, there had been a sense of apprehension until the crossing was complete. The boats and crew were all well prepared against classic contingencies such as lightning, high winds, steerage failure, etc. Prior to the Sail For Epilepsy departure the crew rehearsed procedures in case of equipment failure in the Gulf Stream. Fortunately, the crossing was uneventful, although current of the Stream did give us a good push north.

The Stream continues north along the coast for 700 miles as far as Cape Hatteras. It is now 60 miles wide and is transporting about 500 times as much water as the Amazon River does (The Amazon accounts for one sixth of all the freshwater flow globally). Here this river in the sea bends away from the continental shelf toward the northeast and as it progresses eastward the main body begins to meander with its shape changing over cycles of days to weeks. We’ll come back to this. 

The blue ribbon and its hitchhiker drifters

The stream is a deep, deep blue to contrast to the blue green or sometimes brownish green slope waters to the north and the seaweed littered surface of the Sargasso Sea to the south and east. The reason for the color is the stream is carrying no nutrients. It never reaches deep enough to mix with the rich deposits lying on the ocean floor and remains pristine until other mixing occurs. While it carries no nutrients, it is not sterile. It is home to a variety of transients with otherwise very limited mobility. Having left their tropical homes these hitchhikers ride the current to their temperate destinations. 

Plankton is the base of the oceanic food chain and it consists of two major components: 

Phytoplankton are microscopic plants drifting in the upper 300 ft of water where sufficient light reaches them. These tiny plants are efficient converters of light into food and account for 40% of all food produced by photosynthetic plants worldwide (Think of tomatoes growing in your garden). 

Next are zooplankton, tiny non-photosynthetic animals that feed on the phytoplankton. For both the animals and plants minimizing the amount of energy expended in not sinking is crucial. When viewed under a microscope the extraordinary variety of shapes is striking. The shapes are designed to retard sinking. In some case the animals have developed or acquired tiny oil bubbles to aid their buoyancy.

Larger than plankton, a famous passenger is the eel. These eels born in the Sargasso Sea[MOU1] are transparent and so called “glass eels”, drifting over a year to the rivers of North America or two years to the rivers of Europe. After roughly twenty years all return to a still unknown location in the Sargasso to mate and begin the cycle of life again.

Lastly jellyfish and the Portugese Man of War also ride the big blue ribbon north and east. The Sail for Epilepsy crew have reported numerous sightings of these jellyfish!

The Weathermaker

Temperature readings of 80+ degrees F are a reliable indicator that one is in the stream. This high temperature contrasts with much cooler adjacent waters to the north and still is well above water temps to the south. The current drags air near the surface along with it: a potent brew with potential weather consequences. Warm air can carry more water vapor than cooler air. The surface air is saturated (i.e. holds all the moisture it can at that temperature) but as the sun induces evaporation and former surface air climbs to great heights where it is much colder the air is wrung out like a sponge. Heavy downpours and strong downdrafts are common with squalls of 50 plus knots. (insert picture from Ingwe if we get a good one of a squall). These are localized weather cells but the Gulf Stream also injects energy into high and low pressure weather systems, influencing (usually intensifying) weather over large areas removed from the stream’s actual location. Mariners are constantly monitoring the local as well as the wide area forecasts to get the full picture of what weather will impact them immediately, as well as a few days in the future. 

Rings and Cores (warm or cold)

As the stream continues eastward it begins to meander. A bend in the main direction evolves over days or weeks. You may ask why is there a bend? Imagine you are pushing a piece of rope over a table. The rope will not stay straight but will bend or meander. Occasionally the bend becomes so sharp that the stream closes back on itself as seen in figure 2. In the cases of “pinched off” flow, a ring is created and shed either to the north or the south. These rings at 150 – 300 km in diameter and continue to rotate with speeds near their edges of 2+ kts. 

What is fascinating is that a ring ejected toward the south has a core of cold water that it captures from the north of the stream sea, with all its nutrients and marine life. While a ring ejected to the north encloses a core of warm Sargasso Sea water. Warm core rings rotate counterclockwise and cold cores clockwise. The cold rings are a significant source of nutrient rich water into the Sargasso Sea and the warm water cores persist for many months carrying prized warm water fish species to the northern latitudes. (These warm water fish stay in the slowly decaying ring and are a target of sword fishermen as far as 1000 miles east of Nova Scotia.)

Eventually the Stream loses its force having given up much of its energy primarily to the winds which now carry much of the original warmth to NW Europe. The south flowing currents of the Gyre now take over and eventually the flow turns back west with the North Equatorial current.

One might assume that as a warm water ocean the Sargasso would be rich in marine life – plant and animal; but that is not the case. The Sea, like the stream, is very nutrient poor. The cold deep waters above the rich ocean floor are dense and provide for little or no vertical mixing to the upper layers. The sea plants that float on the Sargasso’s surface have evolved over millennia to cope with the sparse nutrients. Cold water rings shed by the Gulf stream provide some nutrient injection. Another significant source that occurs in the south is from the dust and sands blown off the African continent. Composed of iron and other minerals, these enrich the water for the plankton that develops later.

The Sail For Epilepsy voyage from Fort Lauderdale had one major consideration to take into account about how long to stay with the push of the Gulf Stream current. The crew knew that they would have to head northeast to get favorable winds to head east to the Azores. One option was to ride the current to Cape Hatteras before turning east, or to head northeast once we had passed the Bahamas. The major determinant was the three-day wind strength and direction forecast. As they left Fort Lauderdale, they saw no concern of a wind coming from the north, so in principle they could ride the favorable current of the Stream further north. BUT, the wind forecast showed little to no wind over the Stream over several days on the way to Cape Hatteras, whereas northeast of the Bahamas there was going to be favorable wind though little current. Hence they decided to ride the stream to the northern edge of the Bahamas, then turn NNE towards Bermuda and use favorable winds to their advantage.

While the ride to the Bahamas was on the slow side, Ingwe has been dancing along at a nice clip for the past 24-36 hours, with speeds over ground exceeding 10kts at times. It is definitely “one hand for you, one hand for the ship” conditions, but Ingwe and her crew are loving the progress and after sailing 193 nautical miles in the past 24 hours, have our sights set on a 200nm day soon!