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 it’s the wind that is the primary factor in station holding dynamics,” says Captain Chris Curl. “But for the last few stations we’ve 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 ship’s 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.”

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