The ocean and Earth sciences are on the threshold of a dual revolution involving new questions and novel technologies. Since Darwin's voyage on the Beagle, we have largely studied the ocean basins with ships that were used in an expeditionary mode designed to discover what is out there. The emphasis has been on understanding different regions of the oceans in the three dimensions of space. This approach has provided society with a broad understanding of the fundamental principles that regulate physical, chemical, biological, and geological processes in the ocean. However, timely advances in our knowledge of the oceans are now limited by the lack of sustained observations over extended periods and large areas.

The study of change extends across many disciplines of science including the dynamics of the lithosphere and mantle, climate, biogeochemical cycles in the upper ocean, and the interrelationships between fluids and life in the crust. A successful observatory network must be, therefore, multidisciplinary in nature, providing physical, meteorological, chemical, biological, and geophysical time-series observations and enabling new understanding for all of these users. Many processes are characterized by very low signal-to-noise ratios (e.g., seismology or acoustic thermometry), and only long-term observations can be used to enhance these signal vis-à-vis noise processes. An observatory network requires the establishment of a permanent presence in the oceans; Leg 203 is a critical step in this direction.

Dynamics of Earth and Ocean Systems (DEOS) is a network of observatories focused on the ocean and the Earth beneath it. Whereas observatories have been commonly used on land for centuries for many purposes, long-term observations of natural phenomena in the oceans are rare. However, such time-series measurements are the only means for observing transients or changes. A component of DEOS seeks to establish a global network of ocean observatories through the use of moorings (Fig. F1) for power supply and high bandwidth telemetry. The drilling at the equatorial Pacific International Ocean Network (ION) multidisciplinary observatory provides an ideal location for the initial installation of one of these moorings in the 2003-2004 time frame.