LOW-LATITUDE ICE CORE EVIDENCE FOR ASYNCHRONOUS GLACIATION

As continental ice sheets form only in higher latitudes, those regions provide most of the evidence for the pulsing of Quaternary glaciations. In low latitudes, glaciers are restricted to high mountain peaks in the Andes, the Himalayas and a few isolated spots such as East Africa, New Guinea and Hawaii. Eight long tropical ice core histories are now available to explore the synchroneity of the last glaciation between the low latitudes and polar regions.

Ice cores from Sajama and Huascarán extend back ~25 kyr and ~19 kyr, respectively into the Late Glacial Stage (LGS) and both glaciers survived the early Holocene warm period (9 to 6 kyr B.P.). Interestingly, neither extends through the entire LGS into the previous interglacial suggesting these areas were ice free at a time considered to have been much colder than the Holocene. Similarly, the ice fields atop Kilimanjaro began to grow approximately 11.7 kyr B.P. at the onset of the Holocene and the African Humid Period. The Dasuopu and Puruogangri records suggest that the ice existing today in the southern and central Tibetan Plateau formed in the early to mid-Holocene warm period. Glaciers on the northern edge of the Tibetan Plateau such as the Guliya Ice Cap have records that rival the polar ice cores in length. If true, these observations suggest that a globally synchronous pattern of glaciation for the Earth must be reconsidered. Evidence from these ice cores suggests a northward migration of the ´age of glacier formation´ through the low and mid-latitudes in response to the northward migration of the Intertropical Convergence Zone. This precessional migration provides a powerful working hypothesis for investigating records to be recovered from future sites and the concept of asynchronous glaciations may emerge as an accepted paradigm. Fortunately, this paradigm can be tested with newly recovered and well-dated cores from Bona-Churchill, Alaska and Coropuna, Peru. Likewise, newly proposed ice cores from the Tibetan Plateau, along with well-dated moraine deposits will provide key information for improving our understanding of the timing of glaciation. The nature of this relationship has implications for understanding the processes that control global climate, and for accurate interpretation of the current rapid and often accelerating retreat of glaciers worldwide.