Decompression:

This is my second mission in Aquarius. The first was in June of 1999, and now we're on this one in November of 2000. Since in my first mission I somehow found the time to write extensive mission journal entries and this is the first entry of this mission, I'll have to conclude that this has been the more intense mission.

We began with a suite of tools to fire at our research objective, hoping to throw enough techniques at the wall that something would stick. What we experienced was a series of excellent data collections, interspersed with frustrating instrument failures. We'd all like everything to work all the time. Unsurprisingly, it sometimes doesn't work that way.

From other mission logs, you can probably get a better impression of the flow of events than from mine - by this point it's all a bit of blur. Instruments needing repair, working again, failing, then working again. A final humiliating note: I'm typing this on a computer that has no A, Q, or Z keys (cut and paste is a wonderful, if tedious, thing).

For my part, it has been, once again, an extraordinary chance to work flat out at trying to understand something about how the ocean's life works, doing it from a place that is unique in the world. Living in this habitat is amazing. Inch thick steel doors, six people in a tube for ten days, wet suits always damp from the previous dive. And complementing that, the reef; getting up in the morning and looking out the window to check the "weather" (how clear today's water is); coming to know some of the reef citizens as friends.

Habitat friends

There's Bob the barracuda who hovers faithfully around the habitat, and the enormous jewfish that spends most of the time under the habitat, but of late has decided that he needs to hover in the middle of the "gazebo" (a small bubble dome just outside the habitat). There's the damselfish who comes close to a coronary incident through pure indignation every time we put an instrument into his little algal garden. One day in the midst of the trip, a greenish cowfish with a forlorn expression decided that we were friends, and insisted on snuggling up to my chest. He couldn't be dissuaded, and I was eventually forced to actually pick him up and pass him on to Moose, my dive partner, so that I could get some work done.

In one wonderful interlude, a large turtle (probably a loggerhead), swam right up to me out of the blue murk. It bounced a few times off the support lines to an anemometry mast we'd mounted in the sand, but eventually slid past, and headed straight for my chest, seemingly as oblivious to my presence as it had been to the support lines. I got to see the barnacles on its old back, and stroke the slippery layer of dust and algae on its back as it passed.

Research

And then, of course, there's the research. We do not travel lightly. On this trip we've brought back nearly all the tools we deployed on the last mission, plus an array of new toys. Our goal is to understand the details of how water flowing around corals affects their nutrition. To examine that question on the size scale at which we work, we've devised or purchased a diverse set of equipment.

Several of the techniques are expanded versions of things we first tried last year. There are the hot-bead anemometers, which we built based on designs from other laboratories. This year we're fielding two strings of three anemometers, rather than the single string of three we deployed last year. Besides the failure of a couple of probes, they performed well. Each day this year we deployed twice as many plaster coral models to look at their dissolution rates (which is a direct indicator of how coral shape affects nutrient transfer), adding a comparison of smooth and naturally rough surfaces. Through the last-minute assistance of a friend of Moose at Stanford, we were able to field twice as many brass models to compare effects of shape and surface texture on exchange rates (that experiment uses heat transfer as a direct analog to nutrient transfer around corals).

There are also some new tools. We've got a handheld acoustic doppler flow meter, commercially produced, that performed intermittently - its data recorder failed on three days. We've attempted sub-millimeter-scale oxygen concentration profiles around live coral heads to assess the effect of flow on the rate of oxygen transfer away from coral surfaces using a commercially designed oxygen probe system. We near-instantly broke one of our three oxygen probes, watched another have complete signal failure over a few hours, and realized that the electronic components of the system were "forgetting" their calibration constants. But (we think) we finally managed to get data from it using in-situ calibration techniques (a bottle of baker's yeast out on the reef - don't ask, you don't want to know). Finally, we used a submersible spectrophotometer (the commercially produced diving-PAM) to measure photosynthetic performance of coral zooxanthellae within and between corals in differing flow settings. Unlike all the other commercial equipment, the PAM seemed to perform well, without perplexing glitches.

Writing those prior two paragraphs now, at the end of the mission, helps clarify for me why it seemed like a rather hurried experience.

Decompression

We're now in decompression - the last phase before we emerge. Since we've spent the last nine days or so essentially on a very long dive to 45 feet or deeper, we need to take some hours in coming back to surface pressure so that the nitrogen dissolved in our tissues has the chance to gently come out of solution and be expired, rather than popping up as bubbles in our bodies. To be specific, we'll take about sixteen hours to go from the 45 foot depth back to the 0 foot depth.

We started with a massive cleanup - trying to get as much equipment packed and out of the habitat as possible. In the midst of that frenzy, we got a brief visit from Dr. Ott, the physician attending this mission, to make sure we were in good shape for decompression ("deco" as we now refer to it). Doug Kesling came in to serve as our "oxygen tender" - both to oversee our short period on pure oxygen and to help with the process of bringing the habitat pressure slowly up to surface level.

At 16:00 on Tuesday we locked in: the outermost inch-thick steel door was shut, and we sealed ourselves into the habitat for the deco ride. For the next sixteen hours we could not exit the habitat, nor could anyone visit us. Pressure in the habitat was set exactly to the 45 foot level, and we began three twenty minute periods on pure oxygen. A period on oxygen speeds the process of nitrogen removal. But that doesn't mean it's much fun. During the 60 minutes of oxygen (three twenty minute periods on oxygen plus two ten minute air breaks) we're constrained to lie nearly motionless, breathing through the BIBS ("built in breathing system") masks. The trick with these masks is that they cannot be strapped on (since they have to fall off in case of a seizure from oxygen toxicity), and have both an input hose for the oxygen and an output hose to take away our exhalation (to avoid adding oxygen to the cabin air). They're uncomfortable enough for most people, but for people with beards (like me), holding them on tightly enough for the full time is not so much fun.

The oxygen period over, we're now free to move about the cabin (until the captain turns off the seatbelt sign?). Of course, what do we do? Watch DVD movies on the computer. Normally, a computer screen would be a bit limiting, but in the habitat there isn't much space for us to spread out much, anyway.

As the night wore on, and the habitat pressure inched up to surface level, we've been fading out to sleep for a bit.

Tomorrow morning we'll be up and about, packing and cleaning the last of the research and personal bits out of the habitat, then doing a quick "dive" to exit the habitat. Since the inside pressure will be equivalent to surface pressure by then, we'll all seal into the entry lock of the habitat, and bring the pressure in there down to the 45 foot level in just a few minutes. This will then allow us to open the door to the wet porch again, where we'll be bundled out of the habitat, up to the surface, and back to the sun again.

But for now, it's time to curl up and catch a few hours sleep. But first, I'll get a last chance to gaze out the bunkroom window, inside the aquarium as a display for the fishes' amusement.