Shatsky Rise is an oceanic plateau that is located in the Northwest Pacific Ocean off of the coast of Japan. The main goals and objectives of Ocean Drilling Program (ODP) Leg 198 at the Shatsky Rise was to gain a better understanding of abrupt climatic event transitions, “greenhouse” climactic events, and climactic events in general. Shatsky Rise is an excellent location to study such events because it contains sediments of Cretaceous (145.5–65.5 million years ago) and Paleogene (66–23.03 million years ago) ages at relatively shallow burial depths on three distinct highs. Understanding past climatic events such as warming or cooling can play a key role in understanding and predicting similar climatic events in the future.
ODP Leg 198 took place from August 27th, 2001 to October 23rd, 2001. The expedition began at a port located in Yokohama, Japan and ended at a port in Honolulu, Hawaii. The large quantity of sediment cores that were collected on this expedition were helpful in meeting the goals of Leg 198, partially due to the fact that many of the cores contained a clear record of nanno- and microfossils, which are tiny microscopic fossils such as diatoms and foraminifera, that can be an incredibly useful tools to better understand geologic climatic events. Foraminifera, for example, create their shells from ions in the surrounding seawater in which they live, and as such the chemistry of their shells largely reflects the chemistry of the ocean at the time they built their shells. From these fossils and their chemistry, scientists and researchers are able to measure and reconstruct past ocean conditions such as temperature, salinity, and water productivity.
There were three main findings that researchers discovered on Leg 198 that were related to paleomagnetism, climatic transitions, and a cooling event. Paleomagnetism, which is a branch of geophysics, is a field of study that uses rocks or sediment to study the direction and intensity of Earth’s magnetic field at the time of sediment or rock formation. At Site 1208, Leg 198 recovered many mixed siliceous-calcareous Neogene aged (23.03–2.58 million years ago) sediments that were identified to have strong paleomagnetic cycles making them useful for paleoceanographic and paleomagnetic records in the Pacific Ocean during the Neogene (~23-2.58 million yeasr ago). Leg 198 also found climactic transitions related to dysoxic (low-oxygen) or anoxic (no oxygen) environments at the bottom of the seafloor, clear records of nannofossil and planktonic foraminiferal assemblage transformations at the time of major environmental upheavals and transitions, and transitions from paleodepths at the shallower sites that were less sensitive to chemical changes in the deep ocean to those that were at depth ranges highly sensitive to changes. They also found an important deep water cooling event that is related to glaciation in the Antarctic during the Eocene–Oligocene transition (33.9 million years ago), which is important for better understanding the deepening of the calcite compensation depth (CCD), which is the point at which calcium carbonate (CaCO3) is not preserved due to the bottom ocean waters being too acidic. Below the CCD organisms that secrete shells, such as corals, foraminifera, and nannoplankton are not preserved in the sediment.
References
Bains, S., Corfield, R.M., and Norris, R.D., 1999. Mechanisms of climate warming at the end of the Paleocene. Science, 285:724-727.
Bralower, T.J., Premoli Silva, I., Malone, M.J., et al., 2002 Proceedings of the Ocean Drilling Program, Initial Reports Volume 198
————, 1995. Carbon-isotope stratigraphy and paleoceanographic significance of the Lower Cretaceous shallow-water carbonates of Resolution Guyot, Mid-Pacific Mountains. In Winterer, E.L., Sager, W.W., Firth, J.V., and Sinton, J.M. (Eds.), Proc. ODP, Sci. Results, 143: College Station, TX (Ocean Drilling Program), 99-104.
