Cariaco Trench

De Baar, H.J.W., German, C.R., Elderfield, H. and Van Gaans, P. (1988) Rare earth element distributions in anoxic waters of the Cariaco Trench. Geochim. Cosmochim. Acta, 52, 1203-1219. 

Figure 1. Vertical concentration profiles for DMS, chlorophyll a and DMSP in the western basin of the Cariaco Trench off Venezuela (10° 39 N, 65°30 W). DMS was determined by sparging and gas chromatography with a flame photometric detector. Particulate DMSP was determined bv base treatment of material collected on 0.22 pm filters and analysis of the DMS released free DMSP was determined as DMS released upon base treatment of sparged water samples obtained after initial DMS analysis. Chlorophyll a data from W. Cooper and R. Zika (personal communication).

We thank W. Cooper and R. Zika for chlorophyll a data from the Cariaco Trench, and M. Hardisky for biomass data from Great Marsh, Lewes, DE. E. Canuel and L. Hare provided laboratory assistance. This research was... 

The suboxic zone is defined as the region between where oxygen decreases to near zero (O2 < 10 xM) and where sulfide first appears (H2S > 1 iM) [16, 17]. Many important redox reactions involving Fe, Mn, N, and other intermediate redox elements occur in the suboxic zone. Similar redox reactions take place in sediments throughout the world s oceans, but they are easier to study in the Black Sea because they are spread out over a depth scale of tens of meters (rather than centimeter or millimeter scales as in sediments). The Black Sea suboxic layer hydrophysical structure is very stable compared with other ocean redox regions such as Cariaco Trench, which is influenced by mesoscale eddies, or the Baltic Sea that is influenced by inflows of the North Sea saline oxygenated waters in cold winters. 

Ward, B. B., and Kilpatrick, K. A. (1991). Nitrogen transformations in the oxic layer of permanent anoxic basins The Black Sea and the Cariaco Trench. In Black Sea oceanography (Izdar and Murray, eds.). Kluwer, Dordrecht, The Netherlands, p. 111-124. 

There is also water column denitrification in Black Sea, Cariaco Trench and smaller anoxic basins and fjords, as well as within the more transient hypoxic zones over the continental shelves. The recent work by Kuypers et al. (2005) indicated that the denitrification rate off south west Africa is about 1.5 Tg a . Codispoti et al., 2002 have estimated the total denitrification in these smaller/more transient sites to be 10 Tg a. Finally, denitrification has been reported to take place in microenvironments within the oxygenated water column such as organic aggregates Aldredge and Cohen, 1987 Wolgast et al, 1998). However no quantitative estimates of the global importance of microsite denitrification are available. 

Kilpatrick (1991) and oxygen deficient zones of the Cariaco Trench... 

Richards, F. A., and Benson, B. B. (1960). Nitrogen/argon and nitrogen isotope ratios in two anaerobic environments, the Cariaco Trench in the Caribbean Sea and Dramsfjord, Norway. Deep-Sea Res. 7, 254-264. 

Reeburgh W. S. (1976) Methane consumption in Cariaco Trench waters and sediments. Earth Planet. Sci. Lett. 28, 337-344. 

Fry B., Jannasch H. W., Molyneaux S. J., Wirsen C. O., Muramoto J. A., and King S. (1991) Stable isotope studies of the carbon, nitrogen and sulfur cycles in the Black Sea and the Cariaco Trench. Deep-Sea Res. 38, S1003-S1019. 

Jacobs L., Emerson S., and Huested S. S. (1987) Trace metal geochemistry in the Cariaco Trench. Deep-Sea Res. 34, 965-981. 

Tuttle J. H. and Jannasch H. W. (1979) Microbial dark assimilation of CO2 in the Cariaco Trench. Limnol. Oceanogr. 24, 747-753. 

As seen in Table 14.4.2, pyrolysis of some kerogens generates mainly hydrocarbons. However, the pyrolysate of some other kerogens have a much more complex composition than the Wild Harbor shale sample from Table 14.4.1 and 14.4.2. As an example, a sample from Cariaco Trench (dark olive calcareous clay 1.3 10 years old) [41] generates by pyrolysis at 610° C a variety of compounds that are listed in Table 14.4.3. 

Foraminifera from the sediments of the Cariaco Trench (Fig. 7.6) (Hughen et al, 2004). Since the sediments of this anoxic basin are varved, the age filter applied to most sediment cores by bioturbation is not an issue. Calendar ages of the varves in the sediments of this basin were determined by matching the percent reflectance (a measure of the color of the sediments) with 5 0 variations in the ice of a Greenland ice core (described later in Fig. 7.19). Since the latter record is precisely dated back to 40 000 years by actual counting of annual ice layers, and the two records are undeniably correlated, it was possible to determine an accurate calendar age for the Cariaco Trench sediment core by using variations in the percent reflectance record. The results in Fig. 7.6 indicate offsets of up to 5 ky between C age and calendar age at about 30 ky BP and an abrupt shift at 40 calendar kiloyears (cal. ky) BP in which 7000 C years elapsed in only 2000 y. The results have been explained as variations in the source function and the ventilation of the deep sea and are now used to correct C dates back to more than 40 cal. ky BP. 

A C activity versus calendar age of sediments from the Cariaco Trench. The carbon-14 dates illustrated by the dots were determined on the shells of planktonic Foraminifera preserved in the sediments. Calendar ages were determined by correlating sediment reflectance measurements from the cores with 5 0 changes in the GISP2 ice core from Greenland (see Fig. 7.19). 

Sediments in this category are not very extensive in today s ocean. The largest anoxic basins are the Black Sea in Eurasia and the Cariaco Trench on the continental shelf of Venezuela. Bottom waters reach nearly complete oxygen depletion in the oxygen minima off of the western continental margin off North and South America and Southern Africa. The global area of these sediments has been estimated to be only 0.3% of the total sea floor. 

The aliphatic hydrocarbon distribution (Figure 6) of a sediment from the Cariaco Trench (DSDP 15-147C-3-3) off Venezuela contains two structural families of diagnostic compounds in addition to the steroids and triterpenoids in the polycyclic region. 

Figure 8. Reconstituted ion chromatogram (RIC) from gc-ms analysis of the sterols (as TMS ethers) of a Quaternary sediment from the Cariaco Trench (DSDP 15-147B-4-2). Peak assignments are given i Table I. Solid, stippled and hatched peaks are 2i Stenols, 5o<(H)-stanols and 4o<-methylstanols, respectively.

Cariaco Trench Obtained from J. Farrington (WHOI). This was the top 10 cm of an anaerobic organic-rich ooze from the Cariaco Trench at 10°42.5 N 65°10.5 W. This was a core sample. 

Campbell Nodules Field 402 Cape Basin 37/118,120,227 Cape Lookout Bight 283 Cariaco Trench 126, 283, 359 Caribbian Sea 20,23,243 Carolina Rise 284 Cascadian margin 486,497/... 

Simoneit, 1977b). A higher value, 1.51, is given by Dastillung and Corbet (1978) for the reducing sediments from the Cariaco Trench. 

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