Marine sediments climate

The geochemistry of marine sediments is a major source of information about the past environment. Of the many measurements that provide such information, those of the U-series nuclides are unusual in that they inform us about the rate and timescales of processes. Oceanic processes such as sedimentation, productivity, and circulation, typically occur on timescales too short to be assessed using parent-daughter isotope systems such as Rb-Sr or Sm-Nd. So the only radioactive clocks that we can turn to are those provided by cosmogenic nuclides (principally or the U-series nuclides. This makes the U-series nuclides powerful allies in the quest to understand the past ocean-climate system and has led to their widespread application over the last decade. 

Ice cores have been drilled at several places in the Antarctic, including the research outposts at Vostok and Byrd Station. What they tell us is largely consistent with the climate records obtained from the Greenland ice sheets on the other side of the world, as well as with those from marine sediment cores. One can double-check these ice-core records because the ratio of H to deuterium in the water molecules of the ice also acts as an atmospheric thermometer (Fig. 156). 

Much of what is currently known about the Earth s climate comes from the application of stable isotopes collected from ocean drill cores in marine sediments (e.g., Zachos et al. 2001). These isotopic data sets provide detailed records of how the Earth s oceans have responded to changing climate and are extremely valuable in assessing global climate histories down to millennial scales. Similar detailed isotopic records for terrestrial systems are, however, uncommon and frequently continuous terrestrial climate records that span millions to tens of millions of years are not preserved in the terrestrial geologic record. With the advent of paleoaltimetry studies targeted directly at the coupled isotopic effects of changes in climate... 

Mahowald, N., et al. (1999). Dust sources and deposition during the last glacial maximum and current climate A comparison of model results with paleodata from ice cores and marine sediments. 

Mahowald N., Kohfeld K., Hannson M., BaUcanski Y., Harrison S. P., Prentice I. C., Schulz M., and Rodhe H. (1999) Dust sources during the last glacial maximum and current climate a comparison of model results with paleodata from ice cores and marine sediments. J. Geophys. Res. 104, 15895-15916. 

The ratio of oxygen isotope 18 to oxygen isotope 16 is often used to measure past climate because it is directly related to atmospheric temperature. Oxygen isotopes are used as a proxy for temperature in studies of marine sediments, ice cores, faunal remains, and other materials. The abundance of the two isotopes depends on temperature-related fractionation processes such as evaporation, condensation, and transpiration. 

Environmental variables such as temperature, salinity or nutrients cannot be directly measured for the past, but are determined via proxy data (see Fischer Wefer 1999). The minute tests of planktic foraminifera represent one of our best archives of these proxies. Their excellent preservation, global occurrence and high abundance in carbonate rich marine sediments above the lyso-cline are prime reasons for their extensive use in palaeoceanographic and palaeoclimatic studies. Analyses of elemental and isotopic compositions in addition to species abundances (see Fischer Wefer 1999 for review) have proven to be valuable proxies to understand past climate. 

Madsen, O. S. (1976). Wave climate of the continental margin Elements of its mathematical description. In Marine Sediment Transport and Environmental Management (D. J. Stanley and D. J. P. Swift, eds.), pp. 65-87. Wiley, New York. 

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