Dave Grant: Sea State, Sick Bay and Longitude, February 26, 2012

February 15 - March 5, 2012

Mission: Western Boundary Time Series Geographical Area: Sub-Tropical Atlantic, off the Coast of the Bahamas Date: February 26, 2012 Weather Data from the Bridge Position: 26.30N Latitude – 71. 55W Longitude Windspeed: 15 knots Wind Direction: South (bearing 189 deg) Air Temperature: 23.2 C / 74 F Atm Pressure: 1013.9 mb Water Depth: 17433 feet Cloud Cover: 30% Cloud Type: Cumulus

Sea State, Sick Bay and Longitude

“Now would I give a thousand furlongs of sea for an acre of barren ground.” Shakespeare – The Tempest.

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There is considerable excitement on board since the winds have come up; adding to the work load of the deck crew and scientists struggling to snag the mooring buoy and haul in the miles of cable and sensors that are arrayed below. With swells arriving from two directions and wind chop on top of that, the ship’s motion is unpredictable. So there is no room for error above or below the waterline and the heaving of the ship and spray mean everyone must be alert and ready to respond instantly if anything swings loose. We are “line-sailing” on this cruise, steaming back-and-forth while maintaining a straight course on Latitude 26.30; deploying and servicing various sampling devices on the electronic “picket fence” dividing the Atlantic. Watching the deck crew cutting heavy wire and even heavier chain, banging on metal, wrestling with equipment and sweating under the sun all day as they back-track along the same line doing back-breaking work, I can almost hear them singing an old Mississippi Delta field holler - Line ‘em:

“All I hate 'bout linin' track These ol' bars 'bout to break my back Moses stood on the Red Sea shore Smotin' that water with a two-by-four If I could I surely would Stand on the rock where Moses stood”

Line-sailing is also an old technique used when mariners could only accurately determine their latitude North or South of the equator by means of the sun and stars. Simply stated, one would sail North or South to the known latitude of a destination, then sail East or West until it was found. The Polynesians perfected this - line-sailing the latitude of specific stars that they knew had islands beneath them. On clear nights we go out on the shadowy deck, so far away from the glare of lights on land, and marvel at the great spectacle of stars. The two brightest above us are Arcturus and Sirius – known to the Polynesians as Hōkūleʻa (Star of Joy) and Ka'ulua (Queen of Heaven). Navigators steered under Arcturus to reach Hawaii, and returned to Tahiti by sailing under Sirius. Tahiti lies under Sirius, and Hawaii under Arcturus, providing navigators with bright sign posts to guide them to those jewels in the vast Pacific. From the deck on the Ron Brown it looks like our zenith star could be Pollux, one of twins in Gemini. This seems appropriate “By Jiminy” for good luck, since early sailors swore an oath to those Twins - the protectors of ships. Still, Longitude remained a problem because its measure is the time East or West from a fixed point –Greenwich, England and the Prime Meridian. Until accurate ship’s chronometers were perfected, navigators had to rely on repeated estimates of their speed and direction – Dead Reckoning. Since early clocks relied on a pendulum and inferior materials, and the challenge of perfecting an accurate timepiece became apparent to me while weighing-in at Sick Bay. The roll of the ship has that up-down effect you feel in an elevator, and your weight on the scale fluctuates accordingly. (Mine swings between 165 and 225 pounds, depending on the size of the swells; so I’ll have to wait until we reach port for more accuracy.) Navigators had to wait until 1764 when watchmakers finally perfected sturdy, spring-powered and rust-resistant chronometers accurate enough to satisfy the British Admiralty to guide ships across the featureless ocean waters. Incidentally, William Harrison’s chronometer was hardly portable. It weighed 85 pounds (!). I am going to try two experiments later. One, fashion a simply pendulum and see how the ship's rocking affects it, and two, try some dead reckoning to determine current speed. (Interesting coincidences: My office at work is in the shadow of Sandy Hook Lighthouse, the entrance to NY Harbor. This important beacon is the oldest continuously lit lighthouse in America - and first lighted in 1764 (!). Also, with the perfection of wireless communication; in 1904, the US Navy established the first radio station to continuously broadcast the time for navigators to set their ship's chronometers - at Navesink, NJ, across Sandy Hook bay and within the sight of my office window.)

A Biologist's Bouillabaisse

With the help of Danny, one of the ship's engineers, I have struck gold sampling marinelife. He alerted me to the intake screen for sea water that he was removing to clear and I was able to sort through it. It is a bonanza, as you can see in the image.

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Although most of the material is Sargassum weed, and some bits of plastic, there is a great assortment of material here to keep me busy for the rest of the day. I will start from the bottom. Besides the sargassum, there is other plant material swept here from shallow water. Sea grasses from around the islands support turtles and a thriving subtidal community. One colleague in Puerto Rico thinks that these meadows are as productive as an ecosystem in the ocean. Not obvious is the Aufwuchs community covering the grass blades, but under the microscope, one piece is enough to keep a class busy for hours identifying the specimens in this "fouling community."

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Clik here to view. Bryozoa, worm tubes and coralline algae cover a slender blade of grass.