Understanding the Link between the Ocean Surface and the Sinking Flux of Particulate Carbon in the Cariaco Basin
Since November 1995, the CARIACO (CArbon Retention In A Colored Ocean) Ocean Time Series program has been studying the relationship between surface primary production (carbon fixation rates by photosynthesis of planktonic algae), regional hydrography, physical forcing variables (such as the wind), and the settling flux of particulate organic carbon in the Cariaco Basin. This tectonic depression, located on the continental shelf of Venezuela (Map), shows marked seasonal and interannual variation in hydrography and primary production induced in part by the regular migration of the Intertropical Convergence Zone (ITCZ).
The Cariaco Basin hydrography is affected by North-Atlantic gyre-scale processes, including dispersal of Subtropical Underwater and western boundary current variability, cross-equatorial flow of water masses (Wust, 1964; Muller-Karger et al., 1989), wind-driven upwelling compounded by geostrophic circulation (Richards, 1975; Muller-Karger and Aparicio-Castro, 1994i), ventilation forced by Caribbean Sea eddies (Astor et al., 2003), and river discharge (Yarincik et al., 2000; Lorenzoni, et al. 2009). Due to its restricted circulation and high primary production, the basin is anoxic below ~250 m (Muller-Karger et al., 2001; 2010). In the late 1990's and early 2000's, CARIACO observations measured annual primary production rates of more than 500 gC/m²y, of which over 15-20% was generated by events lasting one month or less. Since 2004 there has been a decrease in primary production rates (annual averages of less than 400 gC/m²y). Still, the annual primary production rates in the Cariaco Basin are comparable to rates estimated using time series observations for Monterey Bay (460 gC/m² y; Chavez, 1996), and higher than rates estimated for Georges Bank, the New York Shelf, and the Oregon Shelf (380, 300, and 190 gC/m² y, respectively; Walsh, 1988). Primary production and vertical particulate organic matter fluxes in the Cariaco Basin are higher than those observed at the oligotrophic BATS and HOT locations (Karl et al., 2001; Steinberg et al., 2001; Thunell et al., 2007). The Basin also experiences sedimentological events caused by earthquakes (Thunell et al., 1999; Lorenzoni et al., 2012) and coastal flooding (Percy et al., 2008; Lorenzoni et al., 2009). All of these phenomena can influence the sediments.
Due to its high rates of sedimentation (30 to >100 cm/ky; Peterson et al., 2000) and excellent sediment preservation, the varved sediments of the Cariaco Basin offer the unique opportunity to study high resolution paleoclimate and better understand the role of the tropics in global climate change ( Black et al., 1999; Peterson et al., 2000; Haug et al., 2001; Black et al., 2004; Hughen et al., 2004 ). An ocean time series in the Cariaco Basin is particularly important as it helps elucidate the connection between forcing mechanisms, processes in the water column and how they are translated into the sedimentary record (Montes et al., 2012). Sediment traps maintained by the CARIACO program show that over 5% of autochtonous material reaches 275 m depth, and that nearly 2% reaches 1,400 m. The significance of this flux is that it represents a sink for carbon and that it helps explain the record of ancient climate stored at the bottom of the Cariaco Basin (Thunell et al., 2000).
Acknowledgements: This ocean time series work was supported by the National Science Foundation (NSF), the National Aeronautics and Space Administration (NASA), and Venezuela's Fondo Nacional de Ciencia, Tecnología e Innovación (FONACIT). For more information please see this Acknowledgements link.