Rivers in the Ocean - Currents
01 deg 28'S
Longitude: 90 deg 45W
Wind Direction: SSE
Wind Speed: 10 Knots
Sea State 3
Swell(s) Height: 2-3 Foot
Sea Temperature: 68°F (20°C)
Barometric Pressure: 1014.8 MB
Visibility: 12 Nautical Miles
Eggs and potatoes
Bacon, ham and sausage
(Dried cereal is always available in the pantry)
OJ in a bucket
Chicken kum po
September 18, 2001
by Christina Reed
The water around the Galápagos Islands moves like the flow
of a multi-level interstate highway. Although the currents
at the surface of the ocean may follow the direction of the
wind, not far below, they often flow in different directions.
Current flow patterns result from a variety of influences: the rotation
of the Earth, the density of water at different depths, and
the movement of different water masses in the ocean. Like a
spiraling wind-chime, each layer of water influences the other,
but the weight and the friction of the water at depth may slow
the movement down. As the Earth spins, it makes these slower
currents move in a different direction from the current at
the surface. Lowering equipment, like a dredge, attached to
3,000 meters of steel wire is challenging. The wire has a tendency
to arc out in the direction of the currents, rather than go
straight to the seafloor. If currents are pushing against the
stern of the ship, the cable could potentially be dragged underneath,
near the propellers, so we always dredge with the wire trailing
directly behind or at an angle to the stern.
If the currents are strong enough, they can
make staying on an exact position for dredging difficult. Often its the wind that is the primary factor
in station holding dynamics, says Captain Chris Curl. But for the
last few stations weve done, the ocean current has been the dominant factor.
A 1-knot current can push the ship more than a 15- to 20-knot wind. Near
Floreana Island, we've been measuring surface currents that range from 1- to
1.5-knots and generally are flowing to the west-northwest.
To stay on station, the Captain and the mates
program the ships computer
with our desired latitude and longitude. We have three propellers: a bow and
two stern thrusters, which can turn 360 degrees. These help us drive against
the wind and currents.
For the past few weeks, as we have worked west
of Fernandina and Isabela, the Captain and the Mates generally
pointed Revelle into the direction of the wind: south-southeast
and dredged to the east up the slopes of the volcanoes. For those
stations, the ship moved sideways like a crab as the trawl wire
attached to the dredge trailed behind.
Now that we are south of Floreana the ship
is maintaining its position during dredging by pointing East
and we are dredging up the terraced slopes to the north-northeast. Jump
to the left and step to the right, Chris says. As ship handlers we
like to minimize the amount the thrusters have to work, and use the wind and
currents to our best advantage.
Dive and Discover
Sea Quiz #2
What is often found on the outside of submarine basalts, and how does it form?
What phylum do holothurians belong to?
What four types of instruments have we deployed to retrieve samples
of rocks and sediment from the ocean floor?
What is Phelliactis robusta?
What is the green-yellow crystal that we found in some of the basalts?
Which volcano has partially collapsed into the ocean?
Which type of bird that we commonly see has a red throat pouch (gular
sac) on the male?
Which two types of data does the MR1 sidescan-sonar collect?
How many boxes of cereal have we eaten while onboard the Revelle?
[Back to top]