Lucky 13 Gets Us 250,000 Years of Sediment
We have been steaming and searching for locations on the seafloor where the sediments are accumulating undisturbed. We tried without luck to take cores at several promising locations, however the cores came up less than perfect. It turns out that much of the undersea portion of the Line Islands has ocean currents that remove and erode sediment. This erosion shows up in the sediment cores as sandy layers where the very small grains of sediment have been swept away. So, we kept up our vigil in the main lab area, closely monitoring the seafloor for small pockets of sediment that looked promising. Some pockets are only a few tenths of a mile across while others are a mile or two. Many that look beautiful from a distance turn out to be ugly on closer inspection.
On our 13th core attempt of the cruise, we got lucky. The corer came back full of the beautiful, white mud. The 20-foot core contains over 250,000 years of sediment and spans the last three glacial cycles in earth’s history. During each of these cycles the earth cooled and large ice sheets expanded over North America and elsewhere. In our core, these cycles are indicated by color changes from greenish brown to white and back.
After lucky 13, we began to hone our strategy and are finding more locations with good sediments. We now have lucky 15, 17, and many more; we now have over 30 cores and counting. Not all of them are perfect, but we are getting better at finding good sediments and faster at coring them.