Day 4 (But being written on Day 5.) Phew. Yes, we're starting to get tired. So my recollections of yesterday (Day 4) are already a bit hazy. We've been rolling along very well with data collection. By Day 4 we'd achieved a good routine of running observations. We start with a tour of our three plaster-dissolution sites (two divers - Matt and I). We retrieve the models from the previous day, shuttle them back to the habitat, and install the new ones. We had a bit of a hitch since we didn't realize just how long it takes to prep up a set of new models, so there was a bit of "hurry up and wait" on the wet porch. But they're all out. Flow recordings at each site, and then we're back.

The next round was chilled brass trials - another great series of sets. Remarkably, these techniques seem to work (at least the data look plausible - we'll have to wait until after the mission for a detailed analysis).

A highlight for today was a "flyby" by a big manta ray. It's wings were about 7 ft. across. We were staring around anyway, since we could hear the props of some unauthorized boats (and we vaguely feared fishhooks...). Then out of the haze came flapping this huge black and white manta, about 10 feet above the bottom. Flying to within a few feet of me, it seemed unconcerned about us, just taking care of its own business. Beautiful. Then back to work...

The other thrill was a power failure. Nifty. We were thrashing around getting some divers out of the water, and noticed that the lights on the wet porch got awfully dim. Um, dark, in fact. Bop back into the main compartment - yes, we have no power, but no one seems awfully concerned. The assumption is that the generator in the buoy above has quit. By coincidence, the support boat was already on its way out for other reasons. When they arrived a few minutes later, a bit of radio discussion ascertained that the generator had, indeed, quit thanks to low oil. Then the backup failed to run properly. Much joking about "this is it - we're doomed", and we're also watching the carbon dioxide meter trudge steadily upwards. Hmmm... Eventually, after a couple of false starts - we're rolling again. And the meter steadily dips down. Much better. And we're back at work. We were never really in trouble as Aquarius has backup battery power for about five days, sufficient to run DC carbon dioxide scrubbers, lights, and VHF radios. There's also enough compressed air storage to last for three days, including a full decompression.

In the evening there was a fantastic display of small crustaceans at the main porthole. Thousands of tiny animals clustering towards the light. They were so thick on the window that the falling ones piled up a half inch deep on the rim at the window's base. We played "identify that invertebrate" for half an hour. Chaetognaths, shrimp, cumaceans, copepods, and lots of "ULBs" (unidentifiable little bugs). Fish moved in for dinner. Shining a flashlight out the window, we could see bigger fish hovering in the distance.

Then off to bed - no trouble falling asleep when you're this tired.