We propose to investigate the causes and effects of changes in the circulation and carbon fluxes of these nutrient-rich polar ocean regions over glacial/interglacial cycles and during warmer intervals of the Cenozoic such as the Pliocene warm interval, the most recent geological analog of the predicted anthropogenic climate. In particular, we seek to understand the role of the polar oceans in past atmospheric carbon dioxide changes, a question of central importance to predicting the future of carbon dioxide and climate in the context of human perturbation. The climate sensitivies of polar ocean circulation and biological productivity are also critical in their own right, as the polar ocean regions affect global heat transport, albedo, continental ice dynamics, and marine biological resources. Our goal is to characterize the climate thresholds and feedbacks that might emerge in a warmer world. One aspect of this work will deal with the central importance of the vertical stability in the polar oceans as a driver of atmospheric carbon dioxide changes over the course of the Neogene via changes in the efficiency of the so-called 'biological pump'. We will measure downcore records of (1) sediment elemental composition as measured by non-destructive scanning XRF (including important und with previous instruments undectectable elements like Ba and Al), (2) bulk sediment nitrogen isotopes and diatom and foraminifera bound nitrogen isotopes, (3) redox-sensitive trace metals (U, Mo) and (4) a set of biomarkers such as Uk37, Tex86 and pigments on new sediment cores from the subarctic North Pacific and the polar and subpolar Southern Ocean.