Foraminiferans planktonic

These shallow-water deposits were the sole source of biogenic carbonate until the evolution and proliferation of planktonic calcifiers, namely the coccolithophorids and the foraminiferans, around 250mybp. This enabled a shift in the site of sedimentary carbonate acciunulation from the shallow waters to the deep sea. At present, about half of the sedimentary carbonates are being buried on the shelves and the other half in the deep sea and slopes. 

Of particular concern are the impacts of seawater acidification on biocalcification and the burial rates of sedimentary carbon. Carbonate ion concentrations in the surface waters have already declined by 16%. Thus, it is not surprising that the abundance of tropical/subtropic planktonic foraminiferan species appears to have declined since the 1960s. This information was obtained by studying the rapidly accumulating sediments of the Santa Barbara Basins off the coast of California. 

Contemporaneous D/0 signals are shown in Fig. 7.22 for sediment cores from the Santa Barbara Basin (SBB), the Cariaco Basin (CB) in Venezuela, the Bermuda Rise (BR), and the GISP2 ice core. Planktonic foraminiferan 8 0 indicates surface water temperature change in SBB and BR the color reflectance change of the CB sediments is controlled by the oxidation state of the overl5dng waters. There are many locations where Y/D events have been well documented (Broecker, 2004) and many others with the full suite of D/0 events. 

Perhaps the best known of the mass extinctions is that associated with the demise of the dinosaurs at the Cretaceous—Tertiary boundary, which has been attributed to a meteorite impact (Alvarez et al. 1980 Kruge et al. 1994 Skelton et al. 2003), although natural climate change may also have been a factor. Planktonic organisms (particularly foraminiferans, calcareous phytoplankton and radiolarians) were also severely affected. On land, trees seem to have been devastated, with the recovery period marked by the proliferation of ferns. The pollen record is dominated by fern spores, and hence known as the fern spike, which is observed... 

Data from planktonic foraminiferans can provide information on sea-surface temperature (Epstein et al. 1953). This information can be more difficult to interpret because it is superimposed on the ice-volume effect and because sea-surface temperature patterns and the factors that affect them can be quite complex. A major factor is the balance between evaporation and precipitation, which affects salinity. All other conditions being constant, a fall of 1 °C results in an increase in 5180 of c.0.2%o. If independent estimation of surface-water temperature is possible (e.g. U ), 5180 values for planktonic foraminiferans can... 

This temperature calibration (Fig. 5.44) is derived from a range of culture experiments, sediment-trap data and sedimentary cores calibrated against 5180 values for planktonic species of the foraminiferan Globigerina (Prahl Wakeham 1987 Prahl et al. 1988). The U37 parameter can be measured to an accuracy of 0.02 units, potentially allowing temperature to be determined to within 0.5 °C. 

J0RGENSEN, B. B., Erez, J., Revsbech, N. P. Cohen, Y. 1985. Symbiotic photosynthesis in a planktonic foraminiferan, Globigerinoides sacculifer (Brady), studied with microelectrodes. Limnology Oceanography, 30, 1253-1267. 

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