Diving for Underwater Offerings - NYTimes.com We did not leave for the field until 9:30 a.m. Because our exploration diver Chip Petersen is using trimix (oxygen, nitrogen and helium) gases, double-checking the gas tanks before and after the hour-plus trip to Pool 1 is critical. Using this gas mix will allow him to safely and effectively explore depths beyond traditional scuba diving, and that is where we expect to find Maya offerings. At Pool 1, as the divers began getting their gear in order, Ernesto, Cleofo, Juan Antonio and Stanley constructed a ladder that the divers need to enter the pool, since the surface is eight feet below ground level. Our videographer, Marty O'Farrell, noticed last season that the bottom of the pool is roughly half the size of its surface, because of the slope beginning on the south side going down toward the cave opening. Andrew explored the shelf approximately 15 feet below the surface beneath Structure 1, the ceremonial building (likely a water shrine) on the southwest edge of the pool. Why is this significant? Because this underwater topography (bathymetry) determines where divers search for offerings. If the Maya made offerings from this building, they probably would have either landed on the shelf 15 feet below or rolled all the way down, 150 to 200-plus feet. The depth is the first challenge. The second challenge is negotiating the numerous trees that have collapsed into the cenote over who knows how many centuries. Naturally, the highest density of trees is found immediately under Structure 1. The third challenge has to do with visibility, as the following film clip of Andrew emerging from hydrogen sulfide clouds shows. These clouds are in the upper regions of the pool; below, it is crystal clear. Even worse is the fine silt that has settled throughout the pool - any slight movement results in thick clouds through which no technology can penetrate. But it was a productive day. Below the possible water shrine, about 15 feet under water, Chip, who was exploring the side wall by fanning the silt, found a jar neck sherd that dates to around A.D. 800-900. This is an exciting find because all test excavations on surface buildings at Pool 1 and other pools yield predominantly wide-mouth jars - that is, water jars. And they all date to this same time period, which as I mentioned in an earlier post is a period with several multiyear droughts. Such jars were used in major water and rain ceremonies (think of all the famous Maya caves with similar jars) at the pool. After all, it was not just a pool to the ancient Maya, but a portal into the underworld (Xibalba), as well as a place where Chaak, the Maya rain god, resided. Before leaving, the divers discuss the next day's plans, which will consist of taking a five-gallon plastic bucket and shovel 200 feet down to the bottom of the slope to excavate. What will they find?