ABSTRACT The late early to middle Miocene period (18–12.7 Ma) was marked by profound environmental change, as Earth entered into the warmest climate phase of the Neogene (Miocene climate optimum) and then transitioned to a much colder mode with development of permanent ice sheets on Antarctica. Integration of high-resolution benthic foraminiferal isotope records in well-preserved sedimentary successions from the Pacific, Southern, and Indian Oceans provides a long-term perspective with which to assess relationships among climate change, ocean circulation, and carbon cycle dynamics during these successive climate reversals. Fundamentally different modes of ocean circulation and carbon cycling prevailed on an almost ice-free Earth during the Miocene climate optimum (ca. 16.9–14.7 Ma). Comparison of δ 13 C profiles revealed a marked decrease in ocean stratification and in the strength of the meridional overturning circulation during the Miocene climate optimum. We speculate that labile polar ice sheets, weaker Southern Hemisphere westerlies, higher sea level, and more acidic, oxygen-depleted oceans promoted shelf-basin partitioning of carbonate deposition and a weaker meridional overturning circulation, reducing the sequestration efficiency of the biological pump. X-ray fluorescence scanning data additionally revealed that 100 k.y. eccentricity-paced transient hyperthermal events coincided with intense episodes of deep-water acidification and deoxygenation. The in-phase coherence of δ 18 O and δ 13 C at the eccentricity band further suggests that orbitally paced processes such as remineralization of organic carbon from the deep-ocean dissolved organic carbon pool and/or weathering-induced carbon and nutrient fluxes from tropical monsoonal regions to the ocean contributed to the high amplitude variability of the marine carbon cycle. Stepwise global cooling and ice-sheet expansion during the middle Miocene climate transition (ca. 14.7–13.8 Ma) were associated with dampening of astronomically driven climate cycles and progressive steepening of the δ 13 C gradient between intermediate and deep waters, indicating intensification and vertical expansion of ocean meridional overturning circulation following the end of the Miocene climate optimum. Together, these results underline the crucial role of the marine carbon cycle and low-latitude processes in driving climate dynamics on an almost ice-free Earth.

ABSTRACT Climate during the Last Glacial Maximum (LGM) varied substantially across North America, strongly influencing changes in plant and animal distributions and causing variations in the timing and relative magnitude of ice expansion and recession. The Olympic Peninsula is a mountainous maritime terrain in northwestern Washington, where the climate today is most strongly influenced by Pacific weather systems. However, what about during the LGM, when ice sheets covered most of northern North America? Fossil beetle assemblages of LGM age contain species that currently inhabit riparian and lacustrine habitats in the boreal zone of Canada and Alaska, and in higher elevations in the Cascades and Rocky Mountains. They include three Olophrum species that today are unknown from the Olympic Peninsula. Olophrum consimile is especially well represented, and its occurrence today above 1000 m elevation in the Cascades of northern Washington State indicates summers during the LGM would have been at least 4 °C cooler than today. The absence of wood-boring beetles, in contrast to assemblages from deposits correlating with marine isotope stage (MIS) 3, supports an open rather than a forested landscape. The insect fossils also include an undescribed species of a blind trechine ground beetle, likely endemic to the Pacific Northwest with biogeographic affinities to Asia. Pollen and plant macrofossil evidence for a Sitka spruce and mountain hemlock parkland with similarities to the vegetation of modern southeast Alaska also supports an interpretation of a climate with summer temperatures ~4 °C cooler than today. Both the vegetation and the insects provide evidence that the climate was wet with persistent snow cover and not as dry as has been reported from the Puget Lowland to the east. Glacial geology provides evidence that during the colder climate of the LGM, mountain glaciers advanced down the western valleys of the Olympic Peninsula to the lowlands but not as far as they had extended during MIS 3. The amount of climatic cooling on the Olympic Peninsula during the LGM was less than at similar latitudes in midcontinental or eastern North America, indicating a strong modulation of climate by the Pacific Ocean.

Abstract The submerged sill in the Strait of Messina, which is located today at a minimum depth of 81 m below sea level (bsl), represents the only land connection between Sicily and mainland Italy (and thus Europe) during the last lowstand when the sea level locally stood at about 126 m bsl. Today, the sea crossing to Sicily, although it is less than 4 km at the narrowest point, faces hazardous sea conditions, made famous by the myth of Scylla and Charybdis. Through a multidisciplinary research project, we document the timing and mode of emergence of this land connection during the last 40 kyr. The integrated analysis takes into consideration morphobathymetric and lithological data, and relative sea-level change (both isostatic and tectonic), resulting in the hypothesis that a continental land bridge lasted for at least 500 years between 21.5 and 20 cal ka BP. The emergence may have occurred over an even longer time span if one allows for seafloor erosion by marine currents that have lowered the seabed since the Last Glacial Maximum (LGM). Modelling of palaeotidal velocities shows that sea crossings when sea level was lower than present would have faced even stronger and more hazardous sea currents than today, supporting the hypothesis that earliest human entry into Sicily most probably took place on foot during the period when the sill emerged as dry land. This hypothesis is compared with an analysis of Pleistocene vertebrate faunas in Sicily and mainland Italy, including a new radiocarbon date on bone collagen of an Equus hydruntinus specimen from Grotta di San Teodoro (23–21 cal ka BP), the dispersal abilities of the various animal species involved, particularly their swimming abilities, and the Palaeolithic archaeological record, all of which support the hypothesis of a relatively late land-based colonization of Sicily by Homo sapiens .