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Our project focuses on obtaining long biomarker records from young (1.5-10 Ma) hemipelagic sediments exposed on land in central and southern Italy, and comparing results of specific biomarker analyses to those obtained from unaltered sediments of the same age recovered by ocean drilling in the Eastern Mediterranean. In the past year, we made significant progress in piecing together the climatic history of the region from ~1.4 Myr to 14 Myr, or from the early Pleistocene to the mid-Miocene periods. The initial results show very large amounts of temperature change over time, with superimposed shorter-term (20,000-40,000 year) cycles superimposed on the trends.

We completed data analysis on three overlapping outcrops sequences that together span the time range 1.4-3.6 Myr. This is a critical period in earth history: it is the time during which permanent ice sheets appeared in the Northern hemisphere and began cyclic ice age sequences. 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 composite paleotemperature sequence, based on the alkenone unsaturation index determined on outcrop samples collected at an interval corresponding to 3,000 year apart, shows conditions 5-6 oC warmer in the mid-Pliocene, the time just before northern hemisphere glaciation. We also see cycles of 20,000 years duration in reconstructed sea surface temperature, but with an amplitude on the order of only 1 oC. Beginning at about 2.4 Myr, cold episodes corresponding to the high latitude glaciations, become evident in our temperature time series. These intensify to amplitudes of 6-8 oC beginning at ~1.9 Myr. Not coincidentally, this timing corresponds to the classical boundary between the Pliocene and the Pleistocene, although such a temperature change has not been documented before. We attribute the intensified coolings to expansion of the northern hemisphere ice sheets into Europe at this time.

We have extended this time series to a long outcrop along the Adriatic coast that exposes a continuous sequence of sediments that range from 6 Myr to 18 Myr. Our first collection aimed to define trends from 6 Myr to 14 Myr by sampling at ~100,000 year intervals, and then supplementing that coarse resolution sampling by picking intervals of 200,000 year duration at equal spacings over the 8 Myr span, in order to investigate the variance of temperatures at the orbital time scale. We have now analyzed over 300 samples from the Monte Dei Corvi outcrop for the alkenone UkÕ37 proxy. We find some major trends in temperature, some of which correlate to known climatic events, and some of which hint at processes that have not been detected by other studies. Our major finding is that conditions prior to ~9 Myr were extremely warm on average- at 27-28 oC, or equal to the Òwarm poolÓ regions of the ocean today, and 9oC 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 UkÕ37 estimates, and confirm the extremely warm SST conditions we inferred for the mid-Miocene of the Mediterranean region.

We also have detected a notable cooling that began at ~8.8 Myr ago and yielded a step-change into the late Miocene. This cooling between 8.8 and 6.5 Myr corresponds to known climate change on land (Asian, Africa), but has not been documented from marine sections before. The cooling trend also apparently initiated higher amplitude temperature changes at the orbital scale as well, in a small-scale preview of the much more dramatic change we see at the Plio-Pleistocene boundary.

This work is being carried out jointly at Brown by P.I. Herbert and second year graduate student Alexandrina Tzanova. Funding provided by the A.C.S. will allow Tzanova to complete a MasterÕs thesis on the implications of the Miocene temperature changes. The P.I. finds his research horizons extended now to recognize the major steps in climate evolution that seem implied by our new Miocene data. 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.