Another of the interesting capabilities available to us from Aquarius is the ability to re-fill our scuba tanks while we're out diving on the reef. The reef "fill station," or gazebo, is a large inverted bell filled with air and anchored to the bottom with enough room for two divers to stand up half way out of the water while filling. It only takes ten minutes or so to refill our tanks (the tanks stay on our backs) and then we’re back on our way. Today we worked at a site called the ‘Pinnacle,’ which is about a 10 to 15 minute swim from Aquarius so it really saves a lot of time to be able to re-fill the tanks right on site. That way, we get back to work rather than returning to the Habitat each time we need to fill our tanks.

Diving at the Pinnacle is interesting because the topography is significantly steeper than it is on the slope in front of the Habitat. Now that we’ve been here for a week and seen cold water bores on most days, it has become relatively possible to predict when the next one will arrive. In general, the forcing mechanism that creates the internal bores is tied to the semi-diurnal internal tide. This has the same period (approximately 12 hours) as the surface tide although it is not necessarily in phase with the surface tide. The main point is that having seen an internal bore or a packet of bores one day, a reasonable guess for when the next set might arrive is 12 hours later, and this is exactly what happened this morning just after 9:00 when we were at our 32 m site: a wave of cool water came sloshing up the reef. Later in the day we also managed to catch a similar event at about 8:30 this evening on our late dive. Diving late gives the added opportunity to dive at night, and in many ways the reef seems most alive at night. This is when most of the suspension feeding corals extend their polyps to feed on zooplankton. It is also a great time to see other reef creatures that you don’t really see much during the day; especially the basket stars suspension-feeding from the tops of soft corals, and lobsters out on the prowl looking for prey.