Earth’s climate system has changed dramatically in the past. Figure 1 shows a reconstruction from the Last Glacial Maximum (20,000 years ago) illustrating the large ice sheets (more than 3 km thick) that covered North America and Northern Europe at that time and the corresponding temperatures changes. Reconstructions of past changes in climate and biogeochemical cycles are important to understand how the climate system works and how its components (atmosphere, ocean, cryosphere and biosphere) interact with each other. They also may hold the key to better predict future climate. Since measurements with reliable instruments are available only for the last 150 years, indirect methods are used to infer prior variations. Temperatures of the ocean surface, for example, are reconstructed using fossils of marine microorganisms found in sea floor sediments (Figure 2 & Figure 3). Concentrations of greenhouse gases such as carbon dioxide and methane are measured in bubbles of air trapped in ancient ice (Figure 4 & Figure 5). Isotopic measurements of cave deposits reveal changes in precipitation (Figure 6). Combining these observations with model simulations (Figure 7) allows testing hypotheses about forcing mechanisms of and interactions within the climate system.
An project illustrating OEB research into the paleoclimate is "Reconstructing Glacial Nitrogen and Carbon Cycling using Isotopes" led by Andreas Schmittner and Alan Mix. Building on earlier efforts, this work will use a modeling approach to reconstruct iron, nitrogen and carbon cycling in the ocean during the Last Glacial Maximum. Model results will be compared to measurements of d15N, d13C and D14C from ocean sediments.
Figure 1 Climate reconstruction of the Last Glacial Maximum (LGM). Colors show the surface temperature difference LGM minus today. (Back to top of page)
Figure 2 Multi corer used to collect sediments from the sea floor. (Back to top of page)
Figure 3: Ocean sediment core reveals layers of paleooceanographic changes. (Back to top of page)
Figure 4: Ice core. (Back to top of page)
Figure 5 Bubbles in ice from a polar ice core. (Back to top of page)
Figure 6 Alan Mix taking dripwater samples in a cave. (Back to top of page)
Figure 7. Climate model simulation of the LGM. Colors show surface air temperature changes comparable to Figure 1. (Back to top of page)