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.
CARIACO is a unique time-series of oceanographic observations that captures present ecological, biological, geological, and chemical change in the Cariaco Basin. This basin reflects changes occurring over spatial scales spanning the Atlantic Ocean and time scales spanning millennia. The Cariaco Basin provides a natural laboratory to study contemporary biogeochemical and ecological processes relevant to dynamic oxygen minimum zones (OMZ), the ecology of a dynamic wind-driven upwelling system, and the large carbon fluxes associated with a continental margin. The time-series also provides the basic information required to interpret the paleoclimate record stored in the varved sediments of the Cariaco Basin. These fine sediments contain a history of the climate and biogeochemistry of the tropical and subtropical Atlantic Ocean. Cariaco Basin sediment cores covering over 1 million years have been used as a fundamental chronology for other paleoclimate records. The primary objective of this time series is to understand linkages between oceanographic processes, including the ecology, the production, and remineralization and sinking flux of particulate matter in the Cariaco Basin, and to understand climatic changes and paleoclimate in the region, as well as in the Atlantic Ocean. We have collected a time series of core, high-quality oceanographic observations, and made these available to the science community quickly and openly. The time series operates as a community facility that promotes and facilitates research in the Cariaco Basin. It provides opportunities for education, outreach, and technical training. The CARIACO program seeks to improve linkages between the scientists in the US, Venezuela, and other countries. All data are easily available to the science community and to the public through various Internet portals, including: 1) BCO-DMO/WHOI (www.bco-dmo.org/project/2047) and 2) the CARIACO web site (http://imars.marine.usf.edu/cariaco). Since 1995, the CARIACO core observations show a long-term decrease in the intensity of the Trade Winds. The Trade Winds fell from an average of >6 m s-1 during the upwelling season to an average of <6 m s-1 in the early 2000’s. This led to weaker upwelling and a steady decrease in annual average phytoplankton concentration and primary productivity. An ecosystem-level shift occurred around 2004. While diatoms dominated the phytoplankton community all year-round between 1996 and 2004, after 2004 there was an abrupt shift to smaller phytoplankton. These long-term changes were associated with an increase in zooplankton biomass and variability in the vertical particulate organic carbon flux to the bottom of the basin. The changes were also associated with a collapse of the regional sardine fishery. Collectively, our results reveal an ecological state change in the southern Caribbean Sea. The weakening trade winds and dependent local variables are largely explained by trends in two climatic indices, namely the northward migration of the Azores High pressure center and the northeasterly progression of the ITCZ Atlantic centroid. CARIACO has also contributed to understanding climate-driven changes in the ocean’s CO2 system. It is one of the longest pCO2 records from tropical seas. CARIACO shows a steady increase in CO2 fugacity (fCO2) associated with the warming and decreasing NPP of these tropical waters. The pH of surface water in the Cariaco Basin is decreasing at an average 0.001 ± 0.0002 per year and has already shown a decrease of 0.02 pH units in the last 18 years. CARIACO helps understand natural acidification due to upwelling of CO2-rich waters and the role of anthropogenic CO2 in increasing acidification in such upwelling zones. In addition to these direct measurements, analyses of sediment trap and sediment core samples have documented the uptake of anthropogenic CO2 in the Caribbean during the last century (Suess Effect).
