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Full article available in PDF version.

Full article available in PDF version.

Abstract In the present contribution, we address the relationship between climate and atmospheric carbon-dioxide (CO 2 ) concentration on different timescales, from long-term trends through the Cenozoic to short-term variations in the recent past. The inverse relationship between stomatal frequency of angiosperm leaves and the CO 2 concentration of the ambient air is used as a robust method for quantifying paleoatmospheric CO 2 levels. Short-term, century-scaled CO 2 fluctuations are reflected in the stomatal frequency pattern of early Holocene birch leaves. Changes in paleoatmospheric CO 2 correlate with major environmental and climatic changes, indicated in the terrestrial palynological record and by δ 18 O fluctuations in polar ice. Further evidence for significant perturbations in the global carbon cycle during the early Holocene is revealed by concomitant changes in atmospheric radiocarbon ( 14 C) content. Warm climatic phases during the Cenozoic represent a particularly challenging test of our understanding of stomatal frequency response to past CO 2 concentrations. The principal question is whether an enhanced greenhouse effect was responsible for these periods of increased global temperature. The data available so far indicate that during the late Neogene, when the temperature was significantly increased for the last time in the geological history, the paleoatmospheric CO 2 concentration was close to the present level of about 360 parts per million volume (ppmv). During the peak warmth of the early middle Eocene, however, paleoatmospheric CO 2 concentration was significantly elevated, to about 500 ppmv.

Abstract The IUGS Commission on Stratigraphy recently acccepted and ratified a proposal to establish an Eocene/Oligocene (E/O) boundary stratotype section and point (GSSP) in the pelagic Massignano section (central Italy), characterized by the last occurrence of the Hantkeninidae (planktonic foraminifera). However, detailed dinoflagellate cyst zonation of the E/O transition interval in the Mediterranean area indicates that this newly selected ’golden spike’ horizon correlates to the middle part of the classic (marginal marine) Priabonian type section in northeast Italy. The coeval level occurs well below two earlier proposed E/O boundary stratotypes at Priabona. In this paper, it is outlined that selection of either one of the proposed boundary-stratotypes at Priabona is more suitable than a hantkeninid-based E/O boundary. These boundary levels can be traced in different lithofacies by recognition of either the TA4.3/4.4 sequence boundary, or the last occurrence of the dinoflagellate cyst Areosphaeridium diktyoplokus. Particularly, a sequence stratigraphic concept of the E/O boundary enables a reasonable correlation of the upper boundary of the Priabonian with the base of the Rupelian (i.e., base Oligocene) as recognized in its type-area in Belgium. The acceptance of the position of the ’golden spike’ at Massignano as the top of the Priabonian Stage thus creates a new Priabonian/Rupelian boundary problem at the very time old uncertainties and controversies on the mutual delimitation of these stages are becoming resolved. Since only stage boundaries should serve to define chronostratigraphic units of higher rank, it is concluded that the IUGS Commission on Stratigraphy should re-evaluate the status of the Massignano section as the E/O boundary GSSP.