Unlike ice cores, which provide direct climate information, sediment cores provide indirect information. An example of this indirect evidence is the method for determining temperature. When sediment cores are analyzed researchers painstakingly sort out plankton shells which twist in different directions depending on the temperature of the water they grew in. By counting the number of shells that twist each way the temperature of the surface water at the time that they grew can be determined. Understanding the behavior of these plankton in the modern world is necessary to produce a historical record of temperature for the ocean.
Sediments also accumulate very slowly relative to snow on an ice sheet.
This results in much longer records from sediment cores, but a much reduced ability to resolve short term changes. While periods of hundreds to thousands of years might be resolved in a sediment core, annual and even seasonal resolutions are possible with ice cores. On the other hand, sediment cores can provide records which are as long as several million years compared with the several hundred thousand years of ice cores. Here the ice moves almost vertically down to the bottom and the annual layers get progressively thinner and thinner as they get deeper. This is the optimal place for drilling.