Case Study: How Widespread was the Warming at the Paleocene-Eocene Thermal Maximum (PETM)?
Global Warming and Paleoclimate
As humankind continues to add CO2 and other greenhouse gases to the atmosphere, we are contributing to the possibility of tipping the climate to one that is dramatically different from anything our species has ever experienced. Many ask: What changes will this new climate state trigger, and how will the Earth systems respond?
According to the records in the ocean sediment cores, our best example of a relatively abrupt increase in global CO2 concentrations (and subsequent temperature increase) occurred 56 millions years ago, during the Paleocene-Eocene Thermal Maximum (PETM). The relatively rapid10,000 yearincrease in Earth's temperature significantly altered life on Earth, and in the ocean. The new climate state lasted roughly 150,000 years. This time period, known as the Eocene Optimum, lasted from 52 million years ago to 50 million years ago.
Abrupt Changes for Life on Earth
The impacts of the PETM were not limited to changes in Earth's atmosphere and surface temperature. Because Earth's systems are coupled, the ocean acts as a buffer to the atmosphere, absorbing CO2 that is released from natural and anthropogenic (man-made) sources. CO2 increases in the atmosphere cause acidification, or a decrease in the pH, of the ocean. During the PETM the ocean "soured." As this acidification occurred, ocean animals with calcified shells were generally unable to adapt to the rapid change. As a result, 30-50% of the benthic foraminifera became extinct. Not only did living animals disappear in the acidic ocean, calcareous microfossils were also dissolved. Previously hard, carbonate-rich sediments were transformed into clay ooze.
Some Species Flourish in the New Climate
However "optimum" the Early Eocene was for life in general, it was beyond the ideal thermal range for humankind. If we compare the PETM to the projected warming for 2100 of 5 to 6 degrees Celsius, we see changes that are comparable to the dramatic temperature change that ended the last Ice Age. Given our current climate conditions, as well as the human population density and distribution, a change of this magnitude would be catastrophic to the human species and would, once again, rearrange the landscape and living species on Earth.
This chapter focuses on the Paleocene-Eocene Thermal Maximum (PETM), which occurred approximately 56 million years ago (MA). In this chapter, you will be examining ocean core records for changes in planktonic foraminifera. These planktonic species continuously fall to the ocean floor, and are preserved as fossils in the accumulating sediment. Naturally, the more fossils preserved in the record, the better the resolution of data. Higher resolution data makes it easier to identify rapid species changes associated with changing ocean temperature.
The Integrated Ocean Drilling Project (IODP) has thousands of marine sediment core data, which can be accessed using Virtual Ocean. Users of this chapter will use graphing tools within Virtual Ocean to create an age-depth plot (ADP). They then will create species diversity curves to search for abrupt changes associated with Paleocene-Eocene Thermal Maximum (PETM).