Abstract High-latitude polar regions of the Earth have experienced cold, cool, and temperature paleoclimates in the course of their geologic history, but they have probably always been colder than low-latitude continents and oceans. Extreme climates leading to development of extensive frozen and ice-covered regions at high latitudes can, however, only be documented for a few, relatively short intervals of the Earth’s history, separated by long time spans with little or no ice (Frakes, 1979). The Cenozoic evolution of glacial-type climates during the past 30 to 40 m.y. is the most recent period of extreme climate, and differs from the preceding ones. During the Cenozoic, plate-tectonic processes generated climatically isolated land areas and ocean basins in both the Southern and Northern Hemispheres, which were repeatedly affected by glaciations. For glacial-type paleoclimates older than the Cenozoic, we have only been able to document unipolar glaciation because the opposite high-latitude area was situated in wide and deep ocean basins and was probably relatively ice free due to advection of warmer surface water from lower latitudes. Despite the apparent similarity of Quaternary high-latitude paleoclimates, the development of glacial-type paleoceanographies of the northern and southern polar oceans have revealed important differences, and they are not easily compared with each other. Our understanding of Cenozoic Southern Hemisphere paleoclimates is much more advanced than it is for the Northern Hemisphere. It is particularly intriguing that the available data appear to indicate that the Southern Hemisphere may have become cold more than 20 m.y. earlier than its northern counterpart.

Floral, faunal, and stable isotope evidence in a continuous sequence of latest Cretaceous and earliest Tertiary shallow-water marine carbonates in the Mangyshlak Peninsula, northeast of the Caspian Sea, USSR, suggest severe environmental changes at the Cretaceous/Tertiary (K/T) boundary. Time frame is provided by nanno-, micro-, and macrofossils as well as by magnetic stratigraphy and an iridium spike. Oxygen-isotopic analyses of the bulk sediments, composed of nanno- and micro-plankton skeletal remains, show a sharp positive spike from −4.2 ‰ to −1.2 ‰ at the K/T boundary. Since the sediments have undergone diagenesis, a process that results in depletion of oxygen 18, the positive spike at the boundary was attenuated by diagenesis and represents a minimum value. This shift is primarily attributed to abrupt and severe cooling, possibly accompanied by increased salinities of the surface mixed layer. A reversal in the δ 18 O signal from −1.2‰ to −4.6 ‰ at 1 mm above the boundary is interpreted to be indicative of marked warming and decreased salinities. The echinoids and benthonic foraminifera exhibit a modest shift in δ 18 O, suggesting much less pronounced temperature and salinity changes of the bottom water. Independent geological evidence indicates that the terminal Cretaceous temperature decline was coeval with widespread and intense volcanism, which peaked at the close of the Mesozoic Era. It is proposed that volatile emissions from massive volcanic eruptions led to acid rain, which depressed the surface-water pH, temporarily prohibiting calcite nucleation of the surface-dwelling warm-water plankton. Superimposed upon severe and rapid climatic changes, decreased alkalinity caused the extinction of calcareous phyto- and zooplankton. The extinction appears to have extended over several hundred thousand years.