# General Introduction

U.S. GLOBEC's interest in the biological and chemical environments of regions with strong physical forcing leads us to propose investigation of zooplankton and fish stock processes in the monsoon regime of the Arabian Sea. Strong, steady winds during the southwest (May-August) monsoon generate coastal and oceanic upwelling zones of great extent and upward transport. The biological response is dramatic, featuring intense phytoplankton blooms. The northeast monsoon (December-February) produces strong surface convection in the north and, again, blooms. There are regular lull periods between the monsoons in which the Arabian Sea transforms to a tropical-subtropical oligotrophic condition. The monsoonal oscillation makes the Arabian Sea a unique study case for mixed-layer development, adjustment of the interior density and current fields to onset of forcing, and (most important to U.S. GLOBEC) response of the pelagic ecosystem to changes in the physical environment. The massive downward flux of organic matter generated by the monsoonal blooms, coupled with the advection at depth, creates a suboxic mesopelagic zone between 180 and 1500 m, modifying the interaction between surface and mesopelagic communities, thus providing an opportunity for examining the role of mesopelagic processes in oceanic ecology generally.

The large vertical turn-over of dissolved carbon associated with monsoonal blooms makes the northwestern Indian Ocean a key site in the carbon budget of the global ocean. Thus, the region is important to global climate control and worthy of a prolonged research effort by the international oceanographic community. This should include a U.S. GLOBEC effort on zooplankton and fish stocks, parallel to the U.S. JGOFS and ONR efforts already planned for the middle 1990's. A workshop was held in June 1992 to explore the scientific issues and formulate a research plan for a U.S. GLOBEC effort in the Arabian Sea. Three working groups addressed questions associated with zooplankton, fish, and technology. Reports of the working groups and a workshop summary are included in this document as Appendices A-D. The U.S. GLOBEC Arabian Sea implementation plan described here developed from discussions initiated at that workshop.

In this document we review the physical setting of the Arabian Sea, detail the status of knowledge of mesozooplankton and fish stocks in the region, and lay out general implementation plans for two levels of U.S. GLOBEC effort in the Arabian Sea. The first level is to take advantage of and to supplement U.S. JGOFS and ONR efforts already planned for the middle 1990's. It focuses on processes affecting mesozooplankton stocks along the U.S. JGOFS transect from Oman out into the central and southern Arabian Sea. The scale of this first-level plan has been set by the amount of support considered likely for a U.S. GLOBEC Arabian Sea program at the time of writing (late 1992). It fits the model for U.S. GLOBEC studies in that (1) target species are designated, (2) population processes of those species are the principal foci of the program, and (3) the studies will be designed to enable prediction of the impacts of global change on those key species.

The second-level plan is for a study adequate to examine the dynamics of the interaction between mesozooplankton stocks and the abundant mesopelagic fish, primarily migratory myctophids, which feed upon them in the Arabian Sea. The scale of this second-level plan has been kept within reasonable limits for a project funded primarily by the U.S., but it requires a dedicated ship, some specialized and expensive technology, and substantial numbers of personnel working in the Arabian Sea for a period of several years. Again, population processes of the target species are the focus, and the studies are designed to enable the prediction of the impacts of global change on those animal stocks. Because the target species can be designated with much more confidence in the case of the second-level plan, this study can be designed more explicitly and promises greater returns than the first-level plan.