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2009 Daily Log

08/10/09 – Gulf Stream

“There is a river in the ocean. In the severest droughts it never fails and in the mightiest floods it never overflows; its banks and bottom are of cold water, while its current is of warm, the Gulf of Mexico is its fountain, and its mouth is the Arctic Sea.” —Matthew Fontaine Maury, from “The Physical Geography of the Sea and Its Meteorology” 1855

blue gulf stream waterThe water out here is blue — a mesmerizing, deep, delicious blue that makes many of us envy the sub crew member who gets to jump overboard with the line for retrieving the submersible. The blue is an indicator of clean water, with little sediment or microscopic plant and animal life suspended within it. It is like the color of glacial water, trapped above a frozen river of ice. But with each swell, the water rises and falls, almost like some ancient enormous beast breathing. When we look over the side, the sunlight penetrates deeply, creating shafts of light that dance like starbursts when the ship moves forward. In 1855, Matthew Fontaine Maury described the color of the Gulf Stream, “Its waters, as far from the Gulf as the Carolina coasts, are of an indigo blue. They are so distinctly marked that their line of junction with the common sea-water may be traced by the eye.”

We are off Cape Canaveral in the Florida Current, which is sometimes called the beginning of the Gulf Stream. Carrying warmth from near the equator towards the Arctic, the Gulf Stream's warm water (usually above 80° F) is as noticeable as its color. In the 15th century, John Cabot noticed that beer stored in the hold of wooden sailing ships got warm and went bad in the Gulf Stream. Ben Franklin became interested in locating the Gulf Stream as a way of improving the mail service to Europe. He started using thermometers to measure the water temperature and recorded the information over several voyages. His nephew, Jonathan Williams inherited this interest and went on to publish “Thermometrical Navigation” in 1799 which identified the Gulf Stream for mariners.

To this day, we use temperature to help map the flow of this constantly shifting stream of water; but now, instead of lowering a bucket over the side and inserting a thermometer, we use satellites with infrared sensors to produce images of the ocean. This mapping is important because the stream moves constantly, with eddies of water spiraling off. At Cape Hatteras, the Gulf Stream has a speed of 4 knots down to about 1,000 feet. This current transports more than 2 billion cubic feet of water every second — more than 500 times the capacity of the Amazon.

In the submersible, however, we descend greater than 1,000 feet. At these depths we know the water will be cold — quite cold, but we can’t always predict the current. The Microlander launched and recovered by Murray Roberts collected some of the only continuous data we have about the current in the deepwater coral habitats. When we know more about the current at the bottom, we will begin to understand the dispersal and feeding strategies of deepwater organisms such as Lophelia coral. Dr. Cheryl Morrison has been collecting data on the genetics of the deepwater corals. The distribution of different populations can suggest the direction of the current. After every sub dive she takes small samples of the coral tissue to analyze back at her lab. An understanding of the larval biology and timing of spawning along with genetic data will help make a more accurate prediction of the current flow. Understanding the current also allows us to develop a model of how food (energy) moves through the system. The corals are fixed to the bottom, and are dependent upon the current to bring their food past their polyps.

While the incredible blue of these warm waters has been known for centuries, it is only recently that we have begun to understand the cold environment of these deep water habitats below the Gulf Stream.

Background information for today's log entry was found in “The Gulf Stream: Tiny Plankton, Giant Bluefin, and the Amazing Story of the Powerful River in the Atlantic” by Stan Ulanski published by the University of North Carolina Press, Chapel Hill, 2008.

08/10/09 - Q & A
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