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Environment and extinction in the late Cenozoic of the North Atlantic area - insights from sclerochronologySclerochronology is the sister-field of dendrochronology, the study of tree rings. It involves analysis of the size and composition of increments within mineralised skeletons formed by accretion, such as those of bivalve molluscs, corals and coralline algae. Detailed information can be obtained on the age, growth-rate and environment of the organism concerned. In this talk I will show how sclerochronology is providing insights into Plio-Pleistocene changes in marine productivity and temperature in the North Atlantic region: their nature, cause and possible links to bivalve mass extinction during this interval (45% and 65% loss of species in the eastern and western Atlantic, respectively). This information may inform prediction of future extinction associated with global warming.
Seasonally resolved isotopic temperature data as a tool for identifying the cause of marine climate change in the PlioceneAlteration in the pattern and vigour of ocean currents has often been invoked as the principal driver of changes in regional climate, including cases in the recent past (Pliocene, Pleistocene and Holocene) and instances predicted in the near future. The theory behind such interpretations is, however, suspect (e.g. Crowley, 1996; Seager et al., 2002), and it may be that other regional or global drivers are more important. The present cool temperate marine climate on the US eastern seaboard north of Cape Hatteras (northernmost North Carolina and Virginia) reflects the influence of cool southward-flowing currents, and a similar influence can be inferred in the Early Pliocene (Johnson et al., 2017). Change to a warm temperate (or marginally subtropical) marine climate in the Late Pliocene has been ascribed to the impingement on the area of warm, northward-flowing currents, assisted by the absence of a barrier equivalent to Cape Hatteras (e.g. Williams et al., 2009). Seasonally resolved oxygen isotope (δ18O) data from bivalve shells reveals, however, that seasonal temperature range was often in excess of that characteristic of the area south of Cape Hatteras (influenced by warm currents), and indicates the continuing influence of cold currents from the north (Johnson et al., 2017). Some isotopic evidence of seasonal temperature range from bivalves is consistent with warm-current influence (Winkelstern et al., 2013), but otherwise the evidence points to a different control (probably global climatic change) on the Late Pliocene warming of marine climate on the US eastern seaboard that is shown by isotopic data for annual average temperature. References: Crowley, T.J. (1996) Pliocene climates: The nature of the problem. Marine Micropaleontology, 27, 3-12. Johnson, A.L.A., Valentine, A., Leng, M.J., Sloane, H.J., Schöne, B.R., Balson, P.S. (2017) Isotopic temperatures from the Early and Mid-Pliocene of the US Middle Atlantic Coastal Plain, and their implications for the cause of regional marine climate change. PALAIOS, 32, 250-269. Seager, R., Battisti, D.S., Yin, J., Gordon, N., Naik, N.H., Clement, A.C., Cane, M.A. (2002) Is the Gulf Stream responsible for Europe's mild winters? Quarterly Journal of the Royal Meteorological Society, 128, 2563-2586. Williams, M., Haywood, A.M., Harper, E.M., Johnson, A.L.A., Knowles, T., Leng, M.J., Lunt, D.J., Okamura, B., Taylor, P.D., Zalaziewicz, J. (2009) Pliocene climate and seasonality in North Atlantic shelf seas. Philosophical Transactions of the Royal Society of London, Series A, 367, 85–108. Winkelstern, I., Surge, D., Hudley, J.W. (2013) Multiproxy sclerochronological evidence for Plio-Pleistocene regional warmth: United States Mid-Atlantic Coastal Plain. PALAIOS, 28, 649-660.