A review of the ice-core literature and data (e.g. Koerner and Fisher 1981; Bradley 1990; Koerner 1992) presenting the history of the climate in the Canadian Arctic in the Holocene period and particularly in last two to three millennia shows that in this part of the world the MWP is rarely distinguished. Generally most researchers indicate a steady decrease in temperature from 2000-3000 BP until the LIA period. Similar results have also been obtained based on glacial geology records (Blake 1981, 1989) as well as on peat, driftwood, whalebone, and mollusc studies (Blake 1975, Dyke and Morris 1990; Dyke et al. 1996, 1997). Recently, however, Koerner (1999) has suggested that the MWP could have occurred from A.D. 1200 to A.D. 1400. This statement is only partly documented by the 5lflO record (see Figure 10.11), which shows that this was really only the case during the periods A.D. 12001250 and A.D. 1350-1400.
■■U i li IN 1
L 1 L J_ _J--1 1__ J---L_
\h n if b 111 i > ■ i ii
Figure 10.11. Five-year averages of oxygen isotope (5) for the last 800 years from Devon Island ice cap (Alt 1985) (after Alt ct al. 1992, modified).
On the other hand, the LIA period is distinctly visible in the light of the available proxy data. For example, both ice-core records (Figures. 10.11 and 10.12), from the high Canadian Arctic (Devon Island and Ellesnierc Island) reveal the existence of an LIA ranging from A.D. 1400-1550 to 1900. However, given the results of Bradley's review (Bradley 1990), most researchers assume that start of the LIA probably occurred in the mid-16,h century. The LIA is particularly clcarly distinguished in the records showing the core area affected by melting (Figure 10.12). Only melting on the Devon Island Ice Cap had above normal values in the mid-16(h century and in the short period centred around 1780 A.D. On the other hand, the isotope record shows the existence of fluctuations in climate around the long-term mean. However, the dominance of cold spells is unquestionable (Figure 10.11). The warmest periods during the LI A occurred in the mid-15'h century (also seen in Agassiz Ice Cap, Figure 10.12(2)).
1400 1450 1500 1550 1600 1650 1700 1750 1600 1B50 1900 1950 2000
Figure 10.12. Reconstructed summer temperature anomaly for Svalbard (I). Agassiz ice cap (2) and Devon Island ice cap (3) (referenced to the mean of each series from 1860-1959). The Svalbard record is of summer melt from the Lomonosov ice cap in Svalbard (Spitsbergen Tnrussov 1992). The series from the Agassiz (Northern F.llesmere Island) and Devon Island ice caps (Canada) are based on ice core studies (Koerner 1977a, Koemer and Fisher 1990). All records show the core area affected by melting, expressed as percentage departures from the mean (after Bradley and Jones 1993),
The slight maximum of temperature around A.D. 1600 was significantly lower and interrupted by short cold spells, and probably therefore it is not registered in summer melting records. Other proxy data (lake sediment and tree-ring records) collected for the last four centuries (see Figure 2 in Overpeck et al. 1997) clearly indicate the presence of the LIA prior to A.D. 1850-1900. The existing documentary records from the Canadian Arctic used mainly the Hudson Buy Company Archives from remote trading posts from the 18"' and 19th centuries (e.g. Moodie and Catchpole 1975; Wilson 1988, 1992; Ball 1983, 1992; Catchpole 1985, 1992a, b). All these investigations clearly confirm the exceptionally cold conditions of the early 19lh century. Bradley (1990), summarising proxy data from the Queen Elizabeth Islands, has identified the LIA period from 400 to 100 years BP as particularly severe. Moreover, he writes
Figure 10.12. Reconstructed summer temperature anomaly for Svalbard (I). Agassiz ice cap (2) and Devon Island ice cap (3) (referenced to the mean of each series from 1860-1959). The Svalbard record is of summer melt from the Lomonosov ice cap in Svalbard (Spitsbergen Tnrussov 1992). The series from the Agassiz (Northern F.llesmere Island) and Devon Island ice caps (Canada) are based on ice core studies (Koerner 1977a, Koemer and Fisher 1990). All records show the core area affected by melting, expressed as percentage departures from the mean (after Bradley and Jones 1993), that this period "may have been the coldest period in the entire Holocene". On the other hand, Evans and England (1992) did not find any well-recorded geomorphological evidence on northern Ellesmere Island confirming the existence of the LIA. Nevertheless, they noted further that undated dual advances by some glaciers might reflect mid-Holocene and the LIA accumulations. They add also that the formation and destruction of ice wedge polygons in sandar indicate respective reduction and increase in meltwater discharge associated with the LIA and then recent warming.
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