Updated 09/15/98
MCR Calibration
To calibrate the paleotemperature reconstructions for Beringia, we performed a test using modern data. Sites were selected for the test of observed versus predicted modern TMAX and TMIN based on several factors. First, we selected sites for which there is at least 30 years of meteorological data. Second, we selected sites represented by at least four species from our list of beetles (i.e., species for which we have developed climate envelopes). Third, we tried to find a combination of sites from northern and southern coastal and interior regions of both Alaska and the Yukon Territory. We found 21 localities that met our criteria; the number of beetle species used in the MCR predictions of modern TMAX and TMIN ranged from four at Denali Park, Alaska and Shingle Point, Yukon Territory, to 21 at Kodiak, Alaska. In all cases the overlap of the climate envelopes yielded reasonably well-constrained MCR temperature estimates to compare with the modern observed temperatures. Linear regressions of predicted on observed values for TMAX and TMIN yielded the following equations:
TMAX (calibrated) = [(median value) X 0.52] +6.13
TMIN (calibrated) = [(median value) X 0.72] - 6.4
It became readily apparent during this initial test that while both coastal and interior site MCR predictions fit the observed TMAX values reasonably well, the TMIN predictions for coastal sites fall consistently below the observed TMIN values. In other words, the beetle faunas living in coastal sites in Alaska are indicative of colder winter temperatures than are indicated by the observed mean January or February (coldest month) temperatures. This appears to be caused by the frequent incursion of very cold arctic air masses into coastal regions of Alaska. While these cold temperature events are not sufficiently frequent to substantially lower mean monthly winter temperatures in these regions, they have occurred several times during each decade of this century. The intense cold may last for days or weeks. We believe that episodes of extremely cold temperatures at coastal sites are sufficiently severe to kill the more maritime-adapted beetle species that could otherwise live there. Hence the beetle faunas of coastal Alaskan regions include many species adapted to the more continental climates of the interior. This domination by more cold-adapted species skews our estimate of coastal winter temperatures. However, it is important to keep in mind that during glacial intervals, the southern and western coasts of Alaska were displaced as much as 1000 km seaward, as the continental shelves were exposed when sea level was lowered.
