Southern Ocean radiocarbon

Figure 9 Measurements of " C/C ratio in a benthic coral from 1.8 km depth in the northern Atlantic reveal that the base has an apparent age 650 radiocarbon years younger than the top. Yet °Th ages on the base and crest are nearly identical (1.54XlO" yr calendar years). Adkins et al. (1998) (reproduced by permission of Jess Adkins) attribute this difference to an abrupt invasion of low " C and high cadmium content Southern Ocean water.

Figure 5 Abundance of radiocarbon age of black carbon in slowly accumulating ( 2.5 cm kyr ) deep-sea sediments from the Southern Ocean (54 °S 176° 40 W) (a) a plot of the ratio of black carbon to total organic carbon (BC/OC) with sediment depth and (b) A C (per mil) and C age (kyr BP) of BC (solid symbols) and non-BC sedimentary OC (open symbols) as a function of depth (after Masiello and Druffel, 1998).

Wang X.-C. and Druffel E. R. M. (2001) Radiocarbon and stable carbon isotope compositions of organic compound classes in sediments from the NE Pacific and Southern Oceans. Mar. Chem. 73, 65-81. 

Goldstein S. J., Lea D. W., Chakraborty S., Kashgarian M., and Murrell M. T. (2001) Uranium-series and radiocarbon geochronology of deep-sea corals implications for Southern Ocean ventilation rates and the oceanic carbon cycle. Earth Planet. Sci. Lett. 193, 167-182. 

Figure 4 Average vertical profiles for the major ocean basins. Except for the Southern Ocean the dotted line is for the Southern Hemisphere and the solid line for the Northern Hemisphere. The Pacific and Southern Ocean profiles were compiled from WOCE data the Atlantic profiles from TTO and SAVE data and the Indian Ocean profiles from GEOSECS data. In approximately the upper 1000 m = 1000 dB) of each profile, the natural A C is contaminated with bomb-produced radiocarbon.

One of the first applications of ocean radiocarbon data was as a constraint on the vertical diffusivity, upwelling, and oxygen consumption rates in the deep waters below the main thermocline. As illustrated in Figure 2, the oxygen and radiocarbon concentrations in the North Pacific show a minimum at mid-depth and then increase toward the ocean seabed. This reflects particle remineralization in the water column and the inflow and gradual upwelling of more recently ventilated bottom waters from the Southern Ocean. Mathematically, the vertical profiles for radiocarbon, oxygen (O2), and a conservative tracer salinity (5) can be posed as steady-state, 1-D balances ... 

BerKMAN P. a. and Forman S. L. (1996) Pre-bomb radiocarbon and the reservoir correction for calcareous marine species in the Southern Ocean. Geophys. Res. Lett. 23, 363 366. 

When calibrating a radiocarbon date, it is first important to determine the reservoir from which the sample draws its carbon (Northern Hemisphere Atmosphere, Southern Hemisphere atmosphere, ocean, etc.). For the oceans, it is also necessary to know how different the local ocean radiocarbon levels are from the ocean average. A useful reference for this is the Marine Reservoir Database (http //calib.qub.ac.uk/marine/), which provides a compilation of preindustrial values. It should be noted, however, that changes in ocean circulation over time make these values inherently uncertain this is especially true when considering pre-Holocene dates. 

The radiocarbon age of surface sediments averages around 2400 yr in the basins of southern California and around 2900 yr in the Atlantic Ocean (Emery and Bray, 1962 Berger et al, 1966 Benoit et al, 1979). Obviously, the measured age of organic matter in the surface sediment of the California basins is not unique to this environment, nor does it reflect a lack of... 

The ratio is fairly uniform within each atmospheric hemisphere. There is a small-amplitude annual oscillation of the order of 0.4 % in the preindustrial era (Kromer et al. 2001) with Imiger-term fluctuations due both to changing production rates and changes in the carbon cycle itself (particularly ocean circulation and ventilation). The Southern Hemisphere is typically depleted in radiocarbon compared to the Northern Hemisphere by about 0.5 %. 

This model estimate is supported by a comparison of radiocarbon monoxide ( CO) in low-latitude clean Southern Hemispheric air with that over the northern Indian Ocean, as measured from samples taken from the RW Brown. The clean air samples south of the ITCZ contained on average 55 parts per billion by volume (ppbv) of CO and 6.2 molecules of CO/cm whereas north of the ITCZ, this was 155 ppbv and 9.7 molecules/cm [26]. The CO difference between these air masses must be of biogenic origin, i.e., mainly biomass burning, because fossil fuels are radiocarbon-depleted. Previous analysis has shown that biomass burning adds 0.038 molecules of " CO/cm per ppbv of CO [26]. If we assume further that... 

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