The CARIACO Ocean Time-Series: two decades of biogeochemistry and ecological research to understand ocean and climate variability

The CARIACO Ocean Time-Series project, located in the Cariaco Basin off the coast of Venezuela, seeks to understand the relationships between hydrography, primary production, community composition, microbial activity, particle fluxes, and element cycling in the water column, and how variations in these processes are preserved in sediments accumulating in this anoxic basin. CARIACO uses autonomous and shipboard measurements to understand ecological and biogeochemical changes in the tropical continental margin of Northern South America and how these relate to regional and global climatic and ocean variability. This Time-Series program is a model for national ocean observing programs in Central/South America, and has been developed as a community facility platform with open access to all data generated during the project (http://imars.marine.usf.edu/cariaco). CARIACO is also part of ANTARES (www.antares.ws), a biogeochemical ship-based time-series network throughout the Americas. The automated sediment trap measurements have effectively captured episodic and short-lived events (e.g., earthquakes, floods, etc.), which are missed by shipboard measurements, while also enabling long term trends in particle flux to be observed. During the 20 years of research that this time-series has conducted, a decline in POC flux has been measured throughout the water column using sediment traps, likely in response to declining Chl-a concentrations and smaller phytoplankton which have replaced the larger taxa over the past decade. This biological community shift, from large to smaller taxa, appears to be caused by regional changes in the physical regime. “Excess” sinking particulate fluxes have been measured at depth, and it is hypothesized that biologically mediated coagulation of suspended particles within the redoxcline contributes to this enhanced flux at and below the oxic/anoxic interface. The observations of CARIACO are critical for better understanding the biological pump on upwelling-dominated continental margins, and to predict potential impacts of climate change on its carbon sequestration efficiency.