www.acsprf.org

Our project focuses on the extending the use of organic biomarkers to measure past environmental change in “deep time”. Specifically, we are investigating the use of algal (“U^k’₃₇) and crenarcheotal (“TEX₈₆”) biomarkers in marine sediments to illuminate the Miocene and Pliocene climate changes that led to the great ice ages of the past few Myr.  It is also a time of drying in northern Africa and critical steps in the evolution of the hominid lineage, presumably related to climatic change in the region. 

Our primary focus has been to create a continuous record of ocean temperature changes in the Mediterranean region for the past 14 Myr, using marine sediments that now outcrop on land because of tectonic movements. Our major finding is that conditions prior to ~9 Myr were extremely warm on average- at 27-28 ^oC, or equal to the “warm pool” regions of the ocean today, and 9^oC warmer than modern eastern Mediterrranean sea surface temperatures.  Because these temperatures are so warm, we called on an independent proxy to verify this rather startling finding.  We have now performed a number of TEX 86-based SST determinations on the same samples.  The TEX SST proxy comes from biomarker compounds unrelated to the alkenones we conventionally measure.  The TEX-based temperature estimates come, if anything, even warmer than the U^K’₃₇ estimates, and confirm the extremely warm SST conditions we inferred for the mid-Miocene of the Mediterranean region.    We were also able to confirm the very warm mid-Miocene temperatures using an Ocean Drilling Program site from the Western Mediterranean.

In the past year, we sought to broaden our research to determine whether the large changes we found in the Mediterranean region were typical of the Northern Hemisphere.  Our most detailed work comes from the North Atlantic and North Pacific, using cores available from the ODP.  Our initial results show substantial (6-8 ^oC) cooling in the late Miocene, more or less synchronously with the change in the Mediterranean. We also found a major change in biological productivity in the North Pacific at precisely the time interval where we first detected the major change in the Mediterranean. These changes almost certainly involve migration of high latitude wind and precipitation belts. Our results call for a revival of the idea of a significant drop in atmospheric CO₂ content in the late Miocene, as first championed by Ture Cerling and others, based on ecological changes on land.

This work is being carried out jointly at Brown by P.I. Herbert and third year graduate student Alexandrina Tzanova. Funding provided by the A.C.S. allowed Tzanova to complete a Master’s thesis on the implications of the Miocene temperature changes.  Tzanova and Herbert have presented results at national and international conferences this past year. The research also led to a current graduate seminar focused on the enigma of late Miocene climate change. We continue to collaborate with Dr. Laura Cleaveland, who finished her dissertation at Brown with funding from this A.C.S. grant, and with Dr. Sandro Montanari of the Osservatorio Geologico di Coldigioco.