In the calcitic skeletons of marine organisms, the Ca atom is often replaced by other cations such as magnesium, cadmium, barium, strontium, iron, cobalt, zinc or nickel. In many cases, this substitution of elements is directly dependent on the element concentration of the surrounding seawater in which the organisms lived. In other cases, element incorporation is controlled by the organism itself - independent of the chemical signature of the surrounding water masses. The isotopic composition of certain elements in the shells of marine organisms is also directly dependent on the seawater isotope ratio and thus, allows the reconstruction of water masses.

An important prerequisite for the reconstruction of past oceans using chemical elements in biogenic carbonate or their isotopes is the knowledge of the processes according to which the different elements/isotopes are incorporated. While the stable carbon and oxygen isotopes in particular have been available for paleoceanographic reconstructions for decades, it is only in recent years that the great potential of trace elements in foraminiferal calcite for the reconstruction of the marine environment has become known. 


Paleo-ocean temperatures

Variations in the heat flux between the near-surface ocean and the atmosphere play an important role in global climate change. The variability of temperatures in the different layers of the ocean, hence, is of fundamental importance for water density, water mass stratification and thermohaline circulation. The reconstruction of the thermal structure of past oceans is thus a central concern of paleoceanography. 

Mg/Ca-paleothermometry is a widely used paleoceanographic tool, which in combined analysis with stable oxygen isotopes on the same biogenic calcite allows important conclusions about changes in the hydrography.

Mg/Ca-paleothermometry


Paleo-Salinities

The combined measurement of stable oxygen isotopes and Mg/Ca ratios in the calcite of foraminifera allows to extract the oxygen isotope signal of past water masses, which is directly related to salinity. This semi-quantitative approach allows a reliable estimation of the variability of salinity for different depth ranges of the ocean.

A new approach to reonstruct ocean salinity involves the analysis of Na/Ca ratios in planktonic foraminifers. For this purpose proxy, calibration studies are performed.

Na/Ca as salinity proxy

By means of Ba/Ca ratios in planktonic foraminifers, the precipitation conditions in the hinterland can be reconstructed, especially near the estuaries of river systems.

High-resolution reconstructions of the circulation in the eastern equatorial Atlantic

LOOP
2 million years of Indian Monsoon History



further: 2. Paleo-watermass mixing and circulation