Scientists Report Surprising New Results from Caribbean Sea Expedition
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Crater fragments found more than 1,000 kilometers away from the impact site, unexpected ancient volcanoes, evidence of long-ago global warming, and clues to recent climate change are just a few of the surprising results of a recent National Science Foundation (NSF) Ocean Drilling Program (ODP) research expedition.
Departing from Miami a few days before Christmas, the research vessel JOIDES Resolution set out for the Caribbean Sea on a two-month expedition to gather new evidence of one of the greatest catastrophes in Earth's history: the meteorite impact that caused the extinction of the dinosaurs and other life forms 65 million years ago. Recent studies show that the meteorite impact occurred on the north end of the Yucatan Peninsula in Mexico, creating the 180-kilometer-wide Chicxulub crater, which is now buried under younger sedimentary rocks.
Says Robert Corell, NSF assistant director for geosciences, "The global effects of this impact were so severe that it closed one chapter in Earth history, and opened another. The Caribbean Sea ODP research expedition has led to new information about millions of years of our planet's past."
By drilling deep into the ocean floor in the Caribbean Sea, scientists on this expedition extracted valuable materials blasted out of the Chicxulub crater at the time of the great impact. These samples were recovered in three drill cores, one from a kilometer-deep drill hole north of Colombia, and two from half-kilometer-deep drill holes near Jamaica. The lowermost parts of the drill-core samples recovered in the Caribbean consist mainly of altered glass spheres, or tektites. These were formed when the explosive collision of the meteorite with Earth generated very high temperatures that melted the crustal rocks in the Yucatan Peninsula. The tektites were deposited up to 1,000 kilometers from the crater, a result of the impact.
Central American Volcanism Totally unexpected on this expedition was the discovery that volcanic eruptions in Central America have repeatedly spread volcanic ash over the Caribbean in the past. Evidence from new drill cores extracted from the ocean floor shows that thousands of volcanic ash layers occur in Caribbean sediments, with some individual layers up to 14 inches thick.
These ash layers indicate that Central American volcanic activity was particularly severe during two periods in the geologic record, about 34 and 19 million years ago. The sources of these volcanic ash layers lie over 1,000 kilometers to the west, in the ancient volcanoes of Guatemala, El Salvador, Nicaragua, and Honduras, from which the Mayans quarried volcanic rocks to build the great pyramid at Coban. The majority of these volcanic eruptions were larger than any recent-history volcanic event.
Ancient Global Warming, An Analogy to Today? Scientists have been probing the Earth's geologic record for past events that might help us understand the effects of rapid climate changes. During the last few years, geologists have found evidence, in sediment cored from the deep ocean basins, for dramatic global warming about 55 million years ago. This warming was coincident with massive extinction of microscopic organisms living on the sea floor, the most devastating event to strike these microorganisms in the past 100 million years.
During the expedition, striking records of the dramatic warming episode were brought up from the Caribbean's depths at two sites, one Just north of Colombia and the other south of Haiti. The finely layered sediments show, for the first time, direct evidence of oxygen-poor oceans. Sediments which are deposited under well-oxygenated conditions are continuously stirred up by worms and other deep-dwelling organisms. However, few organisms can live in stagnant conditions. At the two Caribbean sites, the sediments indicate that deep-dwelling organisms either temporarily inhabited other areas, or in many cases became extinct.
Clues to Recent Climate Change Bridging the gap between ancient and modern climate is a quarter-million-year record of tropical climate change preserved in Cariaco Basin on the northern margin of Venezuela. Cariaco Basin is the largest open-ocean example existing today of anoxic, or totally oxygen-free, conditions. Here, the stagnant waters and rapid accumulation of sediments result in a record of past climate and oceanic conditions of unparalleled resolution.
Scientists expect the Cariaco Basin sediments recovered to produce an important record of how tropical climate has varied on time scales of tens to thousands of years over the recent geologic past. This will allow for the first time a direct comparison of tropical and polar climate change over the past 250,000 years. The Cariaco Basin will also be studied as an analog for how anoxic conditions in more ancient oceans may have contributed to the formation of petroleum source rocks.
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