Paleo Slide Set: The Ice Ages
Photo of Helenina anderseni

Sediment cores from the ocean floor contain types of information that scientists use 
to better understand the fluctuations of global climate. Perhaps the most important 
information is that gleaned from the microscopic shells of organisms such as this, 
called Foraminifera (forams for short). Forams provide two main types of information. 
First of all, different species of forams prefer different ocean temperature and nutrient 
conditions. Scientists can therefore learn much about the climatic conditions of a core site 
in the past by looking at which species once inhabited the area. Secondly, the shells of 
forams effectively lock in the oxygen and carbon isotopic composition of the waters in which 
they formed. Because past periods of glaciation changed the relative quantities of heavy oxygen 
(18O) and light oxygen (16O), scientists can use the isotopic composition of foram shells 
as a proxy signal for past changes in global ice volume. Other chemical measures are available 
as well by studying the composition of the shells. Data from ocean cores about past glaciation 
matches Milankovitch's theory remarkably well.

Photo Credits:
D. B. Scott
Centre for Marine Geology, Dalhousie University, Halifax, Nova Scotia, Canada