Dave Grant: Horse Latitudes, February 22, 2012



NOAA Teacher at Sea

Dave Grant
Aboard NOAA Ship Ronald H. Brown
February 15 – March 5, 2012

Mission: Western Boundary Time Series
Geographical Area: Sub-Tropical Atlantic, off the Coast of the Bahamas
Date: February 22, 2012

Weather Data from the Bridge

Position:26.30 N – 75.42 W
Windspeed: 0
Wind Direction: Calm
Air Temperature: 29 C
Water Temperature: 24 C
Atm Pressure: 1025
Water Depth: 4,410 meters
Cloud Cover: 0
Cloud Type: Slight haze

Science/Technology Log:

We are becalmed and even the veteran sailors onboard are remarking on how flat the sea has become. At about 30 degrees North and South Latitude, moist, low pressure air that was heated and lifted from the surface at the Equator has cooled and is now plunging back down to Earth, forming a line of light winds in a band across the sea. This dry, high pressure air becomes the Trade winds as it is drawn back towards the Equator along the sea surface in what is called a Hadley Cell (After its discoverer). We seem to be on the edge of this meteorological milepost, which was more than a nuisance in the days of sail. If stranded in its pattern too long, food and especially drinking water became an issue, and the first to suffer would be animals being transported from the Old World to the New. Legend has it that subsequent voyagers would come across their carcasses…hence the name Horse Latitudes.

While observing ships returning to port near his home, sixteen year-old future rock star Jim Morrison (The DOORS)  composed what is perhaps his most eerie ballot - Horse Latitudes.

“When the still sea conspires an armor
And her sullen and aborted
Currents breed tiny monsters
True sailing is dead
Awkward instant
And the first animal is jettisoned
Legs furiously pumping”

However, the stable ship makes deck work easier and I am catching up on samples under the microscope, including some of my own tiny “monsters” that the currents have bred.

It is the astonishing variety of life that makes the sea such a fascinating
hunting ground. Get a tow-net, dredge and simple microscope,
and a new world is yours – a world of endless surprises.”

(Sir Alister Hardy)

The chief survey technician set me up  with his  flow-through seawater system and I can leave a net under it to continuously gather plankton. I have noticed some patterns already.
One: Phytoplankton is scarce compared to temperate waters off of New Jersey, and this helps account for the clarity and
brilliant blue color of the water. The absence of large rivers here adding nutrients to the system, and little coastal
upwelling,  means that there is little to fertilize plantlife.
Two: More accumulates in the nets at night, confirming that Zooplankton rises to the surface at in the dark. This diurnal
pattern of the plankton community has been well documented ever since biologists and fishermen went to sea.
Three: Also, there is much more plankton at the surface than in deeper water. This is no surprise since sunlight is the
key ingredient at the surface of this ocean ecosystem.
Four: Creatures from offshore tend to have a more feathery look about them than inshore species. This added surface
area may use the turbulence to help support them near the surface  and increase their buoyancy.

It is said:  “Turn off the sun, and the oceans will starve to death in a week.”  It is assumed that among other stresses on the Biosphere that accompany disastrous impacts of large asteroids, dust and ash from these rare collisions block out enough sunlight to stifle photosynthesis, causing Phytoplankton (The “Pasture of the Sea”) to waste away, and setting the stage for the collapse of the Food Chain and mass extinction events. Fortunately we have plenty of brilliant sunshine here and no celestial catastrophes on the horizon.

Some of the most interesting Zooplankton are the Pteropods, the Sea Butterflies.

   
Empty shell and live pteropod specimen
(Images on the Ron Brown by Dave Grant)

The renowned oceanographer Alister Hardy used them as indicators of different water masses flowing around the British Isles; and New England’s great oceanographer, Alfred Redfield correlated their drifting with the anti-clockwise circulation of water in the Gulf of Maine. Although most are small and less than an inch long, they feed on a variety of creatures and in turn become food for many others. In surface waters they gather phytoplankton, some utilizing cilia and mucus to sweep food to the mouth; but in deeper waters, others are carnivorous.

I am informed by our English colleagues that on Europe’s fishing grounds, they are sometimes fed upon by herring, cod and haddock; which is bad news for British fishermen, whose catch rapidly decays and is not marketable. Such fish are referred to as “black gut” or “stinkers.”

How concentrated are pteropods? Whales and seabirds that we hope to encounter later in the cruise are sustained by them, and in the warmer waters of the Atlantic, at relatively shallow depths and on the tops of submerged peaks at around 2,000 meters, R.S. Wimpenny reports considerable deposits of “pteropod ooze” from their descending shells, covering an estimated 1,500,000 square kilometers of the bottom of the Atlantic (An area the size of the Gulf of Mexico.). Like the Foraminifera, in deeper waters the aragonite in their shells (a more soluble form of calcium carbonate) dissolves, and other sediments like silicates from diatoms accumulate instead. Check out any oceanography text and you are likely to find a picture of this biogenic pteropod mud, as well as other types of deposits.

At least 90% of the animals in the ocean are meroplankton – spending time in this itinerant stage before becoming adults. This phase may vary from a few days to over a year, depending on the creature. (European eels larva are the long distance champions; for over a year, drifting from below us in their Sargasso Sea breeding grounds, all the way to rivers in Britain and France.)

Drifting larvae are cheap insurance for a species, filling the surrounding habitat with individuals of your own kind, settling in new areas and expanding ranges, and particularly, not lingering around their birthplace and competing with the parent stock. However, most individuals simply end up as food for other creatures that are higher on the food chain.

Not surprising, there are copepods, the “cattle of the sea” grazing on smaller organisms.

  
(Images on the Ron Brown by Dave Grant)

Calanus finmarchicus is sometimes called the most abundant animal in the world and is found throughout the oceans, sustaining many types of marinelife; even right whales and basking sharks off the coast of New England.

Other sea soup and children of the sea that author David Bulloch likes to call them, drift by me and swim circuits trapped by surface tension in the water drop under the microscope.

  
Radiolaria are single cell Protozoa that not only ensnare food with mucous, but harbor mutualistic algae
among their spines. (100 x’s)


More live pelagic snails. (Pteropod means winged foot.)

  
An empty shell with  copepod sheltered inside. Other skeletons filled with Paramecia, and a mixed sample of shells
and dust particles.  (Images on the Ron Brown by Dave Grant)

Now that is calm, everyone seems to have their sea legs and are comfortable talking about their bouts of mal de mer.
Here is the worst story about sea sickness I have come across:

 From Dave Grant’s collection of sea stories:
The world’s worst tale of seasickness.
As told by Ulysses S. Grant in his Memoirs

One amusing circumstance occurred while we were lying at anchor in Panama Bay. In the regiment there was a Lieutenant Slaughter who was very liable to seasickness. It almost made him sick to see the wave of a table-cloth when the servants were spreading it. Soon after his graduation [from West Point] Slaughter was ordered to California and took passage by a sailing vessel going around Cape Horn. The vessel was seven months making the voyage, and Slaughter was sick every moment of the time, never more so than while lying at anchor after reaching his place of destination. On landing in California he found orders that had come by way of the Isthmus [Panama], notifying him of a mistake in his assignment; he should have been ordered to the northern lakes. He started back by the Isthmus route and was sick all the way. But when he arrived back East he was again ordered to California, this time definitely, and at this date was making his third trip. He was sick as ever, and had been so for more than a month while lying at anchor in the bay. I remember him well, seated with his elbows on the table in front of him, his chin between his hands, and looking the picture of despair. At last he broke out, “I wish I had taken my father’s advice; he wanted me to go into the navy; if I had done so, I should not have had to go to sea so much.”

Poor Slaughter! It was his last sea voyage. He was killed by Indians in Oregon.

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