Saturday, September 18, 2010

Capricious Seas and Symphonies

Station 8

42° 24.257’ N, 59° 17.522’ W

13:35 EST

Winds: 6.5 knots

Last night we were rolling and pitching, but yesterday morning was sublime. We hoisted the CTD back on deck at approximately 4 am and the seas began to rest. The ship was holding station and engines were quiet. In the blackness of night over the blackness of the sea, it was hard to tell if we were floating on water or floating in space. I was certain, however, that the sunrise would be a peaceful reward to a long night’s work.

And then it happened. Not suddenly, but subtly. Iridescent cirrus clouds began to shine. They failed to light the night, but rather snaked across like pale Northern Lights. We stood on the aft deck and watched in silence as the show evolved. To paraphrase my friend, Drew, it was a symphony. Strings and woodwinds brushed a heavenly canvas in smooth violet strokes. Occasionally, one instrument would outshine the others then fade into the palette. Slowly, almost imperceptibly, the kindle began to blaze. We moved to the bow and enjoyed the music that started our day.

But the seas keep us guessing. Our ship’s dynamic positioning (DP) system keeps us on station, while our Planet’s systems keeps flowing by. The Atmosphere can change on a much shorter time scale than our present occupation of Station 8. Which leads us to wonder, what movement will the symphony play next?

Thursday, September 16, 2010

Conductivity, Pressure, and Depth

Station 6

42° 53.684’ N, 59° 48.143’ W

21:23 EST

Winds: 21 knots

The CTD is back on Atlantis. What is it, anyway? While the letters “CTD” are shorthand for Conductivity, Temperature, Depth, “the CTD” commonly refers to a collection of instruments and water bottles (Niskin bottles) bundled onto a steel frame (see photo: WHOI's Joe Murray collects water from the CTD for Radium analyses, 14 Sep 2010). Collectively, this is the primary tool that I use to collect water samples anywhere between the surface and the bottom of the sea. I’m often asked if I dive to collect my samples. While I would love to experience the deep sea untethered, the CTD is a much easier way to grab a few liters of water. Here’s one reason why. Liquid water is a very dense fluid (1 gram per milliliter). Think of a gallon of milk. That’s about 8 pounds. Now think of a stack of 10,000 milk jugs resting one on top of the other on top of your head. That’s about how much pressure we would feel at the depths we are sampling. I would rather use the CTD.

Basically, we lower the CTD over the side of the ship while monitoring the instruments on a computer. This gives us a continuous readout of the water temperature, pressure, salinity (conductivity), oxygen concentrations, etc… throughout the water column beneath us. Among other things, this information reveals where life is most abundant, where particles are raining down, and where the water comes from. After the CTD reaches its maximum depth, we hoist it back to the surface, stopping frequently to fill our Niskin bottles with water samples. We can do all of this from the comforts of our ship.

Recovering the CTD takes a good team and clear communication. It is heavy. And it happens to swing from a crane above the perpetually wet deck of a rolling ship. So you gear up with steel-toe boots, a life vest, and a hard hat. You look over the rail at the wire that disappears beneath the waves. The winch operator keeps winding it in. Faintly, it comes into view—a pale blue leviathan rising from the deep. It breaches the surface with a roar and sprays foam through the waves. Our job at that moment is to grab the swinging mass with 20-foot long hooks, safely assist it over the rail and onto the deck, and then bolt it down for safety.

All of this takes time, of course. Our first CTD cast at Station-6 lasted 5 hours from deployment to recovery. It will be weeks before we can begin analyzing these water samples back at WHOI. It will be months before we will see results. In the meantime, we have 4 more CTD casts and 1 sediment core to complete before moving to deeper waters…

Wednesday, September 15, 2010

Light winds

Station 6, 20:10 EST

42° 53.684’ N, 59° 48.143’ W

Winds: 33 knots

The CTD on is on its way back to the surface. Two hours ago it was only 10 meters above the seafloor, 2984 meters down into the cold, calm darkness, gently hanging from a 1/4 inch cable. The journey started 3 hours ago when the seas were calm and the winds were light. But three hours can change everything. The winds have picked up to 33 knots, white caps cover the sea like stars cover the night, and Atlantis is starting to roll. And as I type, the sky opened up. It is pouring. But it could be worse... Time to suit up and get this thing back on deck.

Sunday, September 12, 2010

Safety First

42°14.385’N, 64°59.658’ W

We arrived at our test station tonight. This is where we work out the kinks in our procedures and equipment before continuing on. We have also sampled some sediment cores. It’s kind of like removing a straw full of milkshake from a cup, except that we dropped the straw 1 kilometer down to the bottom of the ocean, the Atlantic ocean is the cup, and the milkshake is marine sediment. Generally, the older sediment is at the bottom of the straw and the most recently deposited sediment is at the top. Therefore, these cores allow us to read a record of Earth’s history when we analyze their chemical composition from top to bottom. This is just one facet of our work on understanding the carbon cycle.

How do we know what to do each day? It’s planned well in advance, but the plan is constantly revised. For example, we ran into some choppy seas overnight that slowed our progress to this station. We also had some troubleshooting that took longer than expected, so one of our tests will be delayed. You get the idea. That’s why each day starts with an email telling us what to expect. Here is what I read this morning:

Plan of the Day - September 11, 2010

Hi All,

Here's the schedule for today's activities.

10:30 Fire and safety drill - rear of Main Lab.

13:00 Science party meeting - Library

~18:30 Arrive @ test station (1000 m water depth).

Tentative order of activities:

1. In situ pump test cast

2. Multicorer test.

3. Hybrid CTD rosette/pump test cast”

The first event today was a safety drill. We learned about the various alarms, where to muster if there is a problem, and how to get into a “gumby suit” (see photo) among other things. It’s all part of getting our sea legs. But tomorrow we steam to our first official station. Ready or not, the science begins!