This research will provide past climate reconstructions of the Northwest Pacific region from Mount Logan cores to be used by the International Panel on Climate Change (IPCC) summary reports and by the Past Global Changes (PAGES) of IGBP the International Geosphere-Biosphere Programme (IGBP). Project scientists will complete analyses of stable isotopes, major ions, pollen, accumulation rates and dust concentrations in order to establish a paleoenvironmental reconstruction from the ice cores.

For more information:
David Fisher

Mount Logan Ice Cores Reveal Abrupt Shifts in Water Cycle of The North Pacific over the last 2000 Years

Three ice cores obtained from Mt Logan in southern Yukon and a lake core Jelly Bean Lake near Whitehorse have revealed that the water cycle of the North Pacific undergoes abrupt changes in stable isotopes . The oxygen 18 isotopic (del-18O) record in this region reflects the source of the moisture rather than the site's temperature. The Aleutian low pressure system dominates the weather of the North West Pacific and much of the climate of western North America, (Figure 1).

Figure 1. Mount Logan ice core site and the dominant Aleutian Low Pressure System. larger image [JPEG, 60.5 kb, 538 X 411, notice]

Under modern conditions the region receives water from a range of latitudes from the tropics to the North Pacific and the source Sea Surface Temperatures (SST) range from +30 to +10 °C , (Figure 2) . At various periods in the past the Aleutian Low has been weaker resulting in the sites in southern Yukon receiving much less water from the distant tropics. During such periods the del-18O records reflect source water SSTs that are much lower , (+15 to +10 °C). The derived variable called the deuterium excess , d , corroborates these shifts at the same times as the del-18O does.

Figure 2. The sea surface temperatures of potential source water for the Logan sites. Under modern conditions water sources have a range of SST from +30 to +10 C, but during earlier time periods, like the 'little Ice Age', the sources were limited to the higher latitudes where SSTs are about +15 to +10 °C. This effects the del-18O observed in the ice core and lake records of southern Yukon. larger image [JPEG, 20.8 kb, 348 X 284, notice]

The last 2000 years of del-18O and d for the 5400 m asl ice core (Fisher et al., 2005) and the 800 m asl Lake core (Anderson et al., 2005) are shown in Figure 3. Unlike most del-18O records from Greenland and the eastern High Arctic , which reflect the site temperatures, this region's source water history is revealed by its stable isotopes. During the \'Little Ice Age\' from about 1600 to 1840 AD the southern Yukon received its water more from the high latitudes of the North Pacific. The Aleutian Low pressure centre was probably weaker and not in its modern position during this period. High level (5400 m asl) sites received less accumulation during this period (Moore et al., 2003) but intermediate sites (3000 m asl) received more accumulation (Kaplan et al., in preparation).

The shift from the \'Little Ice Age\' moisture regime that ended in the middle 1800s to the modern was very abrupt at the high and the low elevation sites, appearing to take a few years at most, (Figure3) . Another shift occurred about 800 AD .

Figure 3. The last 2000 years of oxygen isotope and deuterium excess records from the 5400 m asl Mt Logan (blue) and 800 m asl Jelly Bean Lake site (red) in the Southern Yukon. They both show that during the 'Little Ice Age' (1600 to 1840 AD), the del-18O values are larger and d are smaller , both signatures of much colder source water originating from the North Pacific . At such times the Aleutian Low must have been weaker and removed from its present position . larger image [JPEG, 64.8 kb, 479 X 590, notice]

The last 50 years of del-18O record seems to follow the Pacific Decadal Oscillation (PDO) , whose changes have been connected to changes in the vigor of tropical ENSO (El Nino Southern Oscillation) . The changes in recent times in the Mt Logan record are small by comparison to those that occurred in 1840 and 800 AD. Since the modern PDO era changes have had a profound effect on the climate of western North America one can but wonder at the change that would occur if an 1840 AD sized change occurred again with its apparent suddenness.

Figure 4 shows the three drilling parties that obtained ice cores from/or near Mt Logan at 5400 , 4200 and 3000 m asl.

Figure 4. The international group drilled three ice cores on/or near Mt Logan in 2001 and 2002. The Canadians lead the consortium and obtained the core from 5400 m asl and their colleagues from Japan (National Institute of Polar Research, Tokyo) and the United States (Universities of New Hampshire and Maine) obtained the cores from King Col 4200 m asl and Eclipse Dome at 3000 m asl. This sort of cooperation at the scientific, logistics and budgetary level was essential to the success of the project. The Jellybean Lake record was obtained independently by the University of Massachusetts. larger image [JPEG, 32.7 kb, 426 X 343, notice]

The Plateau of Mt Logan is a beautiful but harsh and dangerous place to work. Figure 5 shows it at its best on those very rare days when there is little wind or cloud.

Figure 5. The Prospector Russell Peak Col of Mount Logan where the GSC team obtained the Ice Cores in 2001 and 2002. This 5400 m asl site is often beautiful but always potentially dangerous and the scientific teams that carried out the field work had to overcome many trials. Over the years of the field work the GSC team rescued several climbers caught out in the often ferocious weather of Canada's highest peak. larger image [JPEG, 20.4 kb, 572 X 363, notice]

The Logan Team

GSC: David Fisher, Chris Zdanowicz, Mike Demuth, Jocelyne Bourgeois, Fritz Koerner, James Zheng, John Sekerka, Murty Parnanadi

University of New Hampshire: Cameron Wake, Kaplan Yalcin

University of Maine: Karl Kreutz, Erich Osterberg, Paul Mayewski

University of Washington: Eric Steig, Summer Ruper

University of Massachusetts, Amherst: Leslie Anderson

University of Copenhagen: Dorthe Dahl-Jensen

National Institute of Polar Research, Tokyo: Kumiko Goto-Azuma

References:

Anderson L, Abbott M B , Finney B P and S J Burns. In press (2005). Regional atmospheric circulation change in the North Pacific during the Holocene inferred from Lascustrine carbonate oxygen isotopes, Yukon Territory, Canada. Quat. Res.

Moore G W K, Holdsworth G and K Alverson. 2003. The impact that elevation has on the ENSO signal in precipitation records from the Gulf of Alaska Region. Climate Change, 59, 101-121.