Paleoclimatology is the study of past climates through the use of climate proxies, geologic or biologic records that preserve evidence of temperature or precipitation prior to those periods recorded by humans. Stalagmites, mineral deposits formed from dripwater on the floor of caves, are useful as paleoclimate proxies for two reasons. First, they can be precisely dated to ~500,000 years ago, and second, carbon and oxygen isotopes in stalagmites track a variety of climate signals. Oxygen values change due to where the precipitation comes from, how much it rains, air temperature, and the distance the atmospheric moisture traveled, while carbon reflects moisture and plant activity above the cave system.
This project involves a stalagmite reconstruction of climate change from Cape Range, Western Australia over portions of the past 500,000 years. A prominent source of uncertainty in Australian paleoclimate is the influence of the Northern Hemisphere (NH), particularly heating of the Asian landmass, on Australian monsoon rainfall. Stalagmites from China have shown that the Eastern Asian Summer Monsoon (EASM) reflects NH insolation, the amount of solar radiation that reaches earth’s surface, which allows for heating of landmasses. However, the role of NH insolation on Australian paleoclimate has remained poorly constrained because Australia has few high-resolution continental records spanning hundreds of thousands of years.
Cape Range is well-situated for recording changes in Australian hydroclimate. This region marks the boundary between monsoon rainfall coming from the tropics and middle-latitude rainfall from the south. We find similarities between monsoon trends recorded by stalagmites from China and stable isotopic trends in stalagmites from Cape Range. Both oxygen and carbon isotopes in Cape Range stalagmites suggest that elevated rainfall occurred during times with a stronger EASM. These times of stronger EASM are marked with more positive oxygen values and more negative carbon values. The dates of these observed peaks are roughly 470,000; 270,000; 100,000; and 10,000 years ago. There are still unanswered questions as to why we see these peaks.
James Garrett, ’17