Glacial/interglacial variations in atmospheric carbon dioxide

Twenty years ago, measurements on ice cores showed that the concentration o f carbon dioxide in the atmosphere was lower during ice ages than it is tod ay. As yet, there is no broadly accepted explanation for this difference. C urrent investigations focus on the ocean's 'biological pump', the sequestra tion of carbon in the ocean interior by the rain of organic carbon out of t he surface ocean, and its effect on the burial of calcium carbonate in mari ne sediments. Some researchers surmise that the whole-ocean reservoir of al gal nutrients was larger during glacial times, strengthening the biological pump at low latitudes, where these nutrients are currently limiting. Other s propose that the biological pump was more efficient during glacial times because of more complete utilization of nutrients at high latitudes, where much of the nutrient supply currently goes unused. We present a version of the latter hypothesis that focuses on the open ocean surrounding Antarctica , involving both the biology and physics of that region.