Is MWP 1A Real and Could It have Originated in the Northern Hemisphere in Response to Bolling Warming

Sean D. Birkel

As of 2002, Degree of Master of Science (MS) Quaternary and Climate Studies published under the auspices of the Climate Change Institute.


Meltwater Pulse 1A (MWP 1A) is thought to have encompassed an abrupt rise in sea-level of 19 - 24 m ca. 14,000 calendar years B.P. The postulated rate of sea-level rise during the event was 24 - 50 mrnJyr. In contrast, the average rate of change during the overall glacial termination was 13 mrn/yr. Although MWP 1A is commonly accepted at face value, a compilation of all basic data points casts doubts on its validity. The Laurentide Ice Sheet (LIS) is commonly cited as the source of MWP 1A. Accelerated discharge of freshwater from the ice sheet could have weakened the formation of North Atlantic deep water. However, with the exception of sea-water freshening observed in cores from the Gulf of Mexico and Bermuda Rise, there is little geologic evidence to support a pulse from the LIS during the time of MWP 1A. An alternative suggestion is that MWP 1A originated in Antarctica. One possibility is that a meltwater pulse could have been derived by exploding ice shelves followed by accelerated seaward discharge from ice streams. However, Antarctica contributed at most 18 m, but probably less than 14 m to total LGM sea-level lowering. Furthermore, West Antarctica, which contained two-thirds of the excess Antarctic ice volume at the LGM, did not undergo substantial deglaciation until mid to late-Holocene time, well after MWP 1A. The University of Majne Ice Sheet Model (UMISM) was employed to explore the physical plausibility of MWP 1A coming from the LIS. A GISP2 record of temperature was used as input to drive mass-balance calculations. However, the extremely low temperatures in the climate signal prevented the model from generating a realistic ice sheet. Based on similarities to sea-level reconstructions, the EPICA Dome C ice core record was then used as an alternate proxy for climate. Results indicate that a 10.5 m meltwater pulse is possible in response to climatic warming at the beginning of the Bolling-Allerijd interstadial. However, in order to achieve this result, it was necessary to superimpose on the EPICA forcing a modem climate regime over the ice sheet for 300 model years. Thus both geological and glaciological results cast serious doubts on the existence of MWP 1A. Even if the constraining sea-level data are interpreted as permitting such a pulse, the glaciological model input must be stimulated by artificial warming superimposed on an Antarctic signal to produce both the correct termination and the postulated magnitude and timing of MWP 1A.