Cretaceous Climate Change, What Can it Teach Us?

Wyoming is an excellent place to learn about how ancient ecology compares to modern times. Because of the frequency and quality of fossil-bearing outcrops, prehistoric life and conditions can be interpreted with accuracy, painting a detailed picture of how the landscape has changed over time. One of our first lessons exploring deep-time was an analysis of four different rock sites from three formations, namely, the Mowry, Frontier, and Niobrara. Grain size, rock color, and fossil presence are some of the main methods used to tease apart the environmental conditions during deposition in the Cretaceous seaway that once covered Wyoming. In doing so, we were able to identify changes in Carbon content, sea level, and productivity over time. What we found was a positive correlation between sea level and Carbon content, with changes often stemming from volcanic activity. The amount of Carbon Dioxide dissolved in the oceans dictates changes in pH and therefore ability of organisms to utilize Calcium Carbonate in shell building. High amounts of dissolved Carbon Dioxide lowers pH, dissolving Calcium Carbonate. During periods of high volcanism, Carbon Dioxide levels were high, and biodiversity of the seas were low; most of the fossil finds were small fish. As levels dropped over time during sequestration, there was a steady rise in Calcium Carbonate shelled organisms such as bivalves, clams, and ammonites, with a culmination at the Niobrara formation. The outcrop is formed almost entirely from chalk, a result of calcite deposition after the death of microorganisms. Carbonate deposits like these and other limestones now work to form a buffering system that has largely protected the ocean from the effects of Carbon Dioxide.

Interpreting the qualities of ancient seas is important in its own right, but it also allow us to understand how modern ecology can be expected to change as Carbon Dioxide levels grow and warm the planet. At the moment, the oceans have been buffered against acidity and temperature changes, but eventually the carbonate buffer will be overwhelmed, and temperature and pH will rise and fall respectively. What we can expect then, based off data from the past, is greater difficulty in Calcium Carbonate shell forming and a population decrease in shelled species and corals. Many shelled organisms are vital to their ecosystems and losing them would have devastating upstream consequences on fish and marine mammal populations as well. A change in shellfish population is just one of the many consequences of climate change, though, and water expansion/ice melt threatens to flood much of the coast, just as a sea intruded through central North America millions of years ago. By understanding these events of the past, we can better prepare ourselves for the future and hopefully develop an understanding of Carbon systems that aids in mitigating or potentially reversing the increasing effects of climate change.

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