Figure 1. Will Sager examining a sample in the core lab of the JOIDES Resolution. Sections of the core are laid out, in order of depth, on the bench.

Figure 2. A cross-section through a core showing fossil plant stem and roots from ancient sediments on Allison Guyot. The dark parts are the plant remains and the lighter gray are ancient sediments. The plant roots indicate a marshy environment. The dark coloration of the sediments also comes partly from bits of volcanic rock, indicating some of the ancient volcano beneath the carbonate platform was exposed. Together, these clues tell us that the environment was at the seashore of an ancient volcanic island, perhaps like Bora Bora is today.

Figure 3. Cores from Cretaceous carbonate rocks (approximately 98 million years old) from the Allison Guyot in the underwater Mid-Pacific Mountains. The whitish color is typical of carbonates and the brown stain comes from millions of years of exposure to seawater. These rocks are composed of many fragments of shells and corals. Sometimes the drill bit makes a nice cylindrical core and sometimes you just get little fragments. That’s why core liners aren’t always full. A label identifies the location and depth of the core.

The neat thing about sampling beneath the ocean floor is that we can use the cores [Fig. 2] like a time machine. In many places sediments have piled up for millions upon millions of years, trapping particles and chemical elements that tell about the past [Fig. 3]. In some ways, being a marine geologist is like being a dectective who is sent to a crime scene with no survivors— you have to use all the clues you can gather to figure out what happened and ‘who’ was involved. Most of these “crime scenes” consist of tiny particles of minerals, such as silicates and dead micro-organisms; often mostly plankton, diatoms and cocolithophores [Fig. 4]. This material accumulates year after year and is compressed over time, water is squeezed out and eventually the loose sediment turns into rock. Geological oceanographers examine very thin slices of core [Fig 5]. From analyzing the minerals, their physical form [Fig. 6] and micro-fossils [Fig. 7], they can infer the temperature of the ocean and its characteristics compared to the current oceans. You can’t do this as easily on land because there erosion is common, but in the oceans, the nearly constant rain of sediments to the ocean floor builds up a much more continuous record of the past.

Figure 4. Cocolithophores are tiny single-celled organisms that make a home from calcareous (i.e., calcium carbonate) disks or plates. This is a single cocolithophore, shown at 9800 x magnification. When the organism dies, the little plates, known as microfossils because they are so small, fall to the bottom of the sea, where they become part of the sediment. Photo credit: Dr. Stefan Gartner

Working with the ocean drilling program is very exciting, although it means being at sea for about two months at a time, working 12 or more hours a day, seven days a week. The most exciting thing is that I can really concentrate on doing science, and it is also great to be able to discuss what I find with the other scientists on board. Because many countries are involved it is also a great opportunity to meet scientists from all over the world. In 1998, which is the Year of the Ocean, I will make plans to drill in an area that I am studying. The area is an oceanic plateau, which is a large undersea mountain range [Fig. 8]. The one I am studying contains a huge volcano about the size of Arkansas that may have been an island during the Jurassic when dinosaurs were still wandering Earth. We don’t see volcanoes like that today, and it implies that Earth operated somewhat differently then—and like a good detective, I want to know how and why. Acknowledgments:
Video material is taken from ‘A Planet In Motion’ produced by The Ocean Drilling Program.

Figure 5. Fossil gastropod (a snail) shell in ancient lagoon sediments from the Allison Guyot carbonate rocks. Luckily, the fossil just happened to be in the middle of the core so we have a sample of the whole fossil. This animal is Cretaceous in age and is indicative of a shallow water environment.

Figure 6. Micro-stalagmite from the limestone rocks of the Allison Guyot. Stalagmites like this are formed in limestone caves and from this we know that at one time, this area was above water.

Figure 7. A photo of a currently existing foraminifer called “Globigerina”. The shell of this organism is also made of calcium carbonate. The magnification here is only 90x, so this foram is much larger than the cocolithophores; they look like tiny sand grains. Foram shells (called “tests”) can be so abundant that they make up most of the sediment in places. Paleontologists can tell the age of sediments containing foram shells by identifying the species. Photo credit: Dr. Stefan Gartner

Figure 8. Color contour map of the southern part of Shatsky Rise. This mountain, which we call “TAMU Massif,” is a huge volcano about 2 miles high and with about the same area as Arkansas. My colleagues and I have studied this and similar volcanoes because they appear to have formed very rapidly, and so they may have had widespread environmental effects during the Cretaceous. What is more, it appears that there were a number of similar volcanoes during the Cretaceous, but not during the Cenozoic Period, the last 65 million years.

Figure 9. Basalt rocks from a dredge of Shatsky Rise taken on the R/V Thompson during our 1994 survey. A good example of basaltic rock (an ancient lava flow).