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.
The primary goal of the CARIACO Ocean Times Series program is to examine changes in the oceanography and ecology of the waters along the northern coast of Venezuela over both short (monthly) and longer (annual to decadal) time periods and to determine whether these changes seem to be related to larger scale changes in the ocean and climate. The study site, the Cariaco Basin, is a deep depression on the continental margin of Venezuela which lies below an area of high productivity strongly affected by seasonal upwelling. Because of the geometry of the Basin, waters below about 250 meters are completely depleted of oxygen. The Stony Brook University component of this interdisciplinary and international program has focused on variations in the microbial communities in the water column, including the presence and activity of specific groups, and the manner in which they interact with the chemistry of the water. We are particularly interested in the role of microbes in this system’s cycling of carbon, examining the fate of carbon fixed by phytoplankton as a portion of it sinks to the seafloor. We have also focused on microorganisms involved in the sulfur and nitrogen cycles in particular, because cycling of these important elements is dramatically altered in deoxygenated waters compared to oxygenated waters. While most of the world’s ocean is oxygenated, the geographic extent and intensity of oxygen depletion have increased over the last few decades. The Cariaco water column has sharp gradients in several chemical forms of sulfur and nitrogen which are influenced by transport of oxygen and organic matter from the shallow shelves to the South and from the Caribbean to the North. Thus changes in regional circulation or in the intensity of upwelling likely influence the chemistry and microbiology of the basin’s interior to a significant extent. In our studies, we have observed large variations on a decadal scale in the extent to which water from the Caribbean mixes into the basin and upwelling of deeper nutrient rich-water to the surface. Observed declines in upwelling appear to be a response to weakening Trade Winds in the region through time which are likely driven by global climatic change. Associated with these changes, we have observed dramatic changes in the depth of oxygen penetration in this restricted system (Fig. 1). We have also reported ecological shifts both in surface waters and deeper in the water column. In surface waters over the course of our project, average temperature has risen more than 1°C, nutrient availability has declined (Fig. 2), and has led to dwindling phytoplankton production (Fig. 3), altered plankton community structure and collapse of the local sardine fishery. In the deeper waters, the microbial community has primarily responded to changes in the depth distribution of important chemicals caused by changes in oxygen supply. In short, our study has documented the imprint of global climate change on the southern Caribbean Sea. Our work has provided opportunities to collaborate extensively with scientists from other institutions in the US (University of South Carolina, University of South Florida) as well as with scientists from Venezuela (Fundacion La Salle, Universidad de Simon Bolivar, IVIC). We have assisted the Venezuelans in improving their oceanographic capabilities and have taken a number of US and International (Vietnamese, Chinese, Chilean, Spanish) students and scientists to Venezuela, enhancing international cooperation.
