LATE QUATERNARY INTERGLACIAL STAGES WARMER THAN PRESENT

Literature on warm interglacials from both deep sea and continental records is reviewed. Although there is no unanimity, most deep sea data covering the late Quaternary (in this case, 500 ka to present) indicate that Oxygen Isotope Stage 11 (423-362 ka) was warmer than succeeding interglacials. Similarly, continental data imply warm intervals covering those interglacials between Stages 11 to 15 but with Stage 11 as the warmest. There are no direct data, however, to suggest that either the West Antarctic or Greenland Ice Sheets collapsed during warm interglacials. Indeed, recent work suggests that there may be a problem with assuming that collapse occurred as a result of, and during, a warmer than present interglacial; data from ice cores recovered on the Greenland Ice Sheet indicate that over the past 250 ka, excluding the last 8 ka, climate was unstable with rapid mode switches occurring during both glacials and interglacials and with modes lasting from 70 years to 5 ka. If warming is invoked as the underlying cause of collapse then warm intervals may not have been long enough to cause substantial melting. This suggests that, along with warmer than present interglacials, alternate mechanisms invoking forcing internal to the ice sheet and its substrate be seriously considered. Future studies should focus on these alternate mechanisms as well as on the interval equivalent to Oxygen Isotope Stage 11.