Proposed observations and sampling of the Tonga Trench A. Aristides Yayanos Scripps Institution of Oceanography University of California San Diego La Jolla, CA 92093-0202 Scientists from Scripps Institution of Oceanography have studied the Tonga Trench for nearly 50 years. Most of those studies, however, are on the geology and geophysics of the region. The work that will be done on the R/V Melville beginning in late December of this year is on the biology of the Tonga Trench. We will collect a variety of samples from depths of 2000 meters down to the maximum depth of approximately 10,800 meters. The types of samples we will collect include: sediments, water, rocks, and animals such as deep-sea fish and invertebrates. The samples will be collected with rock dredges, towed nets, traps, coring devices, and Niskin bottles. The samples will be used principally as sources of inocula for culture media to grow deep sea microorganisms and for the determination of the diversity of trench microbial inhabitants. The inoculated culture media are incubated at low temperatures and high pressures. Based on experience with microorganisms from other trenches, microorganisms from the deepest parts of the Tonga Trench will not grow at atmospheric pressure. We have three main interests in the inhabitants of the Tonga Trench, as follows. First, the Tonga Trench is the coldest known habitat having a depth of 10,800 meters. Judging from determinations made in the 1950s, we expect that the temperature in the Tonga Trench at its greatest depths will be close to 2°C. This contrasts to the temperature in the Mariana Trench of approximately 2.5°C at a comparable depth. The surprising aspect of small temperature differences in the deep sea is that they have a profound influence on the physiology of the inhabitants. We will be able to quantify these differences through physiological studies of Tonga Trench microorganisms. These studies may help us to form an estimate of the upper pressure limit to life processes and to understand how changes in Earth's climate might ultimately affect deep-sea life. A second interest in the inhabitants of the Tonga Trench is that we know very little about them. For example, our previous work in the Peru-Chile Trench, the Philippine Trench, the Palau Trench, and the Mariana Trench shows that Amphipods (crustacea) are the dominant mobile scavengers. It will be great interest to see if these animals are also present in the Tonga Trench and whether they are related to those inhabiting other trenches. The only previous studies of life in Tonga Trench date back to the Danish Galathea Expedition that ended in 1952. The third overall goal of our studies is to determine the distribution of thermophilic microorganisms in the ocean. Studies in distant parts of the world have shown that thermophilic microorganisms disburse widely and are found in cold water. They do not grow in these cold environments but will grow when incubated at high temperatures. The Tonga Trench is one of the most seismically active trenches in the world. As such, it is conceivable that thermophilic organisms inhabiting deep parts of the seafloor are constantly released into the cold overlying ocean. It is also conceivable that thermophilic microorganisms are found in the deep waters of the Tonga Trench because of its close proximity to submarine hydrothermal activity in the Lau Basin. We propose to collect samples from the Lau Basin at the end of our cruise track in order to compare thermophilic microorganisms isolated from the Lau Basin with those isolated from the deep parts of the Tonga Trench. The above 3 points summarize our primary studies. In the course of these studies, we will conduct bathymetric surveys and document, as time allows, visual observations of birds and mammals. The proposed work in the Tonga Trench is funded by the National Science Foundation. The overall goals of work are entirely scientific. There is absolutely no commercial purpose. The following Table lists some of the possible locations of sampling stations. Points along transect........Latitude........Longitude ..............................Deg S Min S Deg W Min W Northern most start point......15..........0.......173.........30 Trench axis....................17.........30.......172.........30 Capricorn Seamount.............18.........40.......172.........50 Trench axis....................18.........45.......172.........45 Trench axis....................20.........15.......173.........15 Trench axis....................23..........0.......174.........40 Trench axis....................24..........0.......175.........25 Trench axis....................26.........30.......175.........15 Trench axis....................29.........15.......176.........15 Southern limit.................31.........45.......178..........5 Lau Basin Stations.............23.........15.......177..........0 A close approximation to the cruise track we propose to follow is shown in the attached Figure. Although most of our work will be done along the axis of the Tonga Trench, we will also conduct a few transects, as time allows, perpendicular to the trench axis.