ABSTRACT

This award will provide funds to continue operating the oceanographic time series started in November 1995, in the Cariaco Basin at 10º 30'N, 64º 40'W, for five years. CARIACO (CArbon Retention In A Colored Ocean) is one of three ocean biogeochemistry time series stations supported by the National Science Foundation (NSF). The time series addresses the scientific objective of understanding ocean processes that affect the flux of particles sinking to the bottom of the Cariaco Basin, by continuing collection of a carefully-selected set of biological, chemical, geological and physical measurements. A key objective of this effort is to serve the Ocean Carbon and Biogeochemistry (OCB) and the paleoclimate research communities by maintaining an observing facility in the Cariaco Basin. The facility permits studies of the temporal variability and trends that span seasonal, interannual and interdecadal time scales, provides a set of core observations and samples to share with the community, and facilitates access to this unique oceanographic setting. CARIACO is a joint research effort by scientists at three U.S. institutions supported by NSF (University of Massachusetts at Dartmouth, Stony Brook University, and the University of South Carolin at Columbia) in partnership with the Fundacion LaSalle de Sciencias Naturales and the Centro Internacional de Ecologia Tropical in Venezuela.

The Cariaco Basin is a 1,400-m deep depression located on the Venezuelan continental margin in the southeastern Caribbean Sea, openly connected to the surface tropical Atlantic Ocean above a shallow (~140 m) sill. Because of slow turnover, decomposition of sinking material leads to anoxia below about 250 m. These conditions preserve an excellent sediment record that is used by the international community to study Holocene and late Pleistocene changes in climate. Understanding processes that affect the sinking material is the key to understanding the "biological carbon pump" that transfers materials from the surface ocean to the bottom, and to understanding the ocean?s role in past, present, and future climate. In this regard, CARIACO aids in the interpretation of the climate history preserved in this sediment record. The CARIACO program also seeks to educate the public about this relationship.

Intellectual merit: The scientific program is guided by the following hypotheses: (1) The sinking flux of particulate matter contains a record of event- to interannual-scale changes in upper ocean conditions, including upwelling, ventilation, productivity, and terrigenous input events. (2) Changes in nutrient availability results in ecosystem shifts that are preserved in the chemistry and amount of sinking particles. (3) Temporal changes in the hydrography of the basin are directly related to regional wind variability, the passage of Caribbean Sea eddies near the sill, and circulation changes in the Atlantic Ocean. (4) Bacterial production and carbon decomposition near the oxic-anoxic transition zone are controlled by lateral transport of dissolved oxygen at mid-depth (ventilation events). (5) Chemoautotrophic bacteria near the oxic-anoxic transition zone alter the composition and amount of the vertical particulate flux and the dissolved organic matter concentration.

CARIACO generates observations used to assess variability in lateral transport and upwelling, forcing and variations in water column chemistry, phytoplankton, zooplankton and bacteria community composition, variations in primary productivity and bacterial production (chemoautotrophic and heterotrophic), and resulting changes in water column chemistry and the composition and quantity of particulate flux sinking to the bottom. This program uses intensive traditional oceanographic and meteorological techniques, as well as modern tools including satellite and molecular observations.

Broader impacts: CARIACO addresses some of the highest priorities identified in the U.S. government's Ocean Research Priorities Plan and Implementation Strategy and the Strategic Plan for the U.S. Climate Change Science Program. The uninterrupted, long-term tropical record is of value to investigations of the relationship between climate change and large-scale ocean biogeochemistry. Many scientists believe the tropics play a pivotal role in these basin-wide processes on a variety of time scales including those relevant to society. CARIACO measurements will also help understand processes that affect regional fisheries and catastrophic weather patterns. CARIACO has established a policy of open sharing of data, samples, and infrastructure, to facilitate the conduct of broader studies or of process studies in the Cariaco Basin by third parties. This project brings together an international workforce of physical, chemical, geological and biological oceanographers. It has technology transfer and human resource development impacts, providing an opportunity for scientists, technicians and students from Latin America to participate in logistics planning, fieldwork, data analysis, and joint publications that address issues of local and global relevance. These exchanges also have an important educational impact on U.S. students including minorities. The Venezuelan government considers CARIACO among their most important oceanographic research programs, and will continue significant funding to local participants.