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Exactly what caused the upwelling is not clear, but many scientists believe the world was already undergoing a natural warming cycle, possibly due to a slight periodic change in earth's orbit. This suddenly ended the last Ice Age, in turn changing ocean currents and wind patterns. The hypothesis favored by paper's authors is that sudden disintegration of northern ice sheets during this initial warming slowed or halted deep Atlantic Ocean circulation. This in turn warmed the Antarctic, causing massive retreats of sea ice and allowing deep Antarctic waters to surface. Thus, it is possible that the signal detected in the Pacific ultimately originated on the other side of the world.


"Once the CO2 started rising, it probably helped the warming process along—but exactly how much, we can't say," said Robert Anderson, a Lamont-Doherty expert in ocean circulation who was not involved in the study. "And there is still huge uncertainty as to how the oceans will respond to current warming." Anderson says the study should be a wake-up call to the scientific community to expand studies of the oceans' relationship to climate change.