Palaeogeography, Palaeoclimatoh~gy, Palaeoecology Elsevier Publishing Company, Amsterdam Printed in The Netherlands

CHRONOLOGY OF PEAT GROWTH IN CANADA

HARVEY NICHOLS l

Meteorology Department, U, iversity of Wisconsi,, Madison, ~Tsc. (U.S.A.)

(Received August 13. 1968)

SUMMARY

Published and unpublished radiocarbon dates from immediately above the unconformable mineral bases of ombrogenous peat bogs are compared with the climatic history of Canada during the last 4,000 years. Most of the determinations group around a few periods of established climatic deterioration (such as 3,500 and 2,400 B.P.) which suggests that large tracts of Canadian peat originated almost simultaneously under the stimulus of climatic change.

RADIOCARBON DATES AND CLIMATIC HISTORY

Fragmentary information exists in the literature concerning the age of fossil organic accumulations in Canada in the form of scattered 14C dates (mostly in Radiocarbon) of material from the base of peat bogs. Further samples have recently been recovered by the author and Dr. R. A. Bryson and have been dated by Dr. M. M. Bender; they form a substantial fraction of the few existing radio- carbon assays of such material from Canada, and they are interesting for their similarity to existing dates for comparable material. The published and unpublished determinations for the last four millennia are here collected and compared with the imperfectly known climatic history of Canada.

As far as can be judged from the published descriptions of the sites the data which are reviewed here do not relate to organic accumulations which formed immediately after deglaciation (e.g., as pro-Glacial lake sediments) but to deposits which seem to be unconformable with their minerogenic bases and which appear to represent mere fractions of local post-Glacial time. Their origin apparently reflected some change in environmental conditions, probably climatic. The peat which is discussed here is ombrogenous, i.e., its genesis and continued growth depend on a balance of precipitation over evaporation; it does not primarily owe its origin to very favourable and localized topographic situations (e.g., basins). During periods of very rapid growth under wet conditions such peat receives

Present address: Biology Department and Institute of Arctic and Alpine Research, Univcl~ity of Colorado, Boulder, Colo., (U.S.A.).

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62 H. NICHOLS

almost all its small supply of minerals from precipitation and is very acid, being composed primarily of species of Sphagnum (bog moss). In Canada, this type of widespread shallow ombrogenous peat is called muskeg, and it resembles the blanket peat of northern Europe (TANSLEV, 1939). In Europe the growth of this type of peat was stimulated by climatic deteriorations (marked by increased ef- fective precipitation) such as that which marked the beginning of the Sub-Atlantic Period ca 2,800-2,400 years ago.

Given the occurrence of a climatic change sufficient to promote peat growth on mineral soil there may of course be considerable local variation in the timing of paludification related to local site factors (soil type, drainage, topography). However, there exist in Canada very large territories where changes in relief, soils, and climate are small, such as the old bed of Glacial Lake Agassiz and the recently- emerged coastal lowlands of Hudson Bay. On such approximately homogeneous mineral bases it might a priori be expected that peat accumulation due to climatic change might be more nearly synchronous than the recurrence of growth in an already established bog. Radiocarbon-dated recurrence surfaces are rare in Canada, and they have been omitted from this account. The recognition and sampling of basal peat overlying mineral matter is less open to error than the identification and correct sampling of recurrence surfaces in bogs.

The unpublished basal peat dates (from material collected in August 1967) are: 4,350___70 B.P. (before present, i.e., before 1950 A.D.) (WIS-280), Mann Lake, Alberta, 54°10'N, 111°28'W; 3,450+90 B.P. (WIS-283), Keg River, Alberta, 57°46'N, 117°37'W; 3,410___55 B.P. (WIS-281), Mackenzie Highway, Alberta, 59°12'N, 117°30'W; 2,410+60 B.P. (WIS-269), Waskesiu, Saskatchewan, 53°55'N, 106°0YW; 1,870___60 B.P. (WIS-282), North Star, Alberta, 56°42'N, 117°38'W; these will appear in current volumes of Radiocarbon (BENDER et al., 1968, 1969). It has seemed logical to include two dates from Alaska on the list of determinations in Table I.

Table I shows that 6 of the 23 dates group around 2,400 B.P. (average 2,360), and another 6 average 3,480 B.P.; 4 fall into the range 700-300 B.P., and the rest are ca. 4,200, 1,900, 1,600 and 1,000 B.P. It has previously been shown by radiocarbon-dated palynological and stratigraphic studies that ca. 3,500 B.P. and 2,400 B.P. were times of climatic deterioration in Canada, as was the period from ca. 700 B.P. (NICHOLS, 1967a,b,c). These periods saw the southward retreat of the Boreal forest limit (BRYSON et al., 1965; NICHOLS, 1967c), the expansion of tundra towards the south, and the cessation of peat growth in the Arctic due to drier colder climatic conditions. Thus the majority of the basal peat dates coincide with established periods of climatic deterioration to colder conditions.

At Pelly Lake, northern Keewatin, the growth of peat at 1,060+55 B.P. was related to a climatic amelioration which is thought to have brought increased warmth and moisture to this cold Arctic desert (H. Nichols, in preparation). The growth of peat at two sites in Arctic Quebec at 1,600_+ 140 (GSC-537) and

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CHRONOLOGY OF PEAT GROWTH IN CANADA 63

T A B L E I

RADIOCARBON DETERMINATIONS OF TIlE AGE OF BASAL PEAT SAMPLES

GIVEN IN YEARS B,P. (BEFORE PRESENT, I.E. BEFORE 1 9 5 0 A.D.)

FROM CANADA AND ALASKA,

31C assay Lab. m~. Location Reference

I. 270 ! 130 (GSC-305) 49 ' 13'N 80°38 , W Ontar io Radiocarbon 1966, 8: 106. 2. 390 ! 90 (GX-438) 4 7 ' 1 0 ' N 125 45 'W Vancouver Is. Racfiocarbon 1966, 8 :147 3. 525 L 100 (NPL-59) 61 ' 46 ' N 74 05 'W Quebec Radiocarbon 1965, 7 :160 4. 6 8 0 ± 1 8 0 (GSC-591) 62 ' 51 ' N 6 9 ' 5 0 ' W Baffin Is. Radiocarbon 1967, 9 :181 5. 1,060 ~ 55 (WIS-263) 6 6 0 8 ' N 101 0 4 ' W Keewatin Radiocarbon 1968 10:476 6. 1,600[ 140 (GSC-537) 62 ~ 10'N 75~48'W Quebec Radiocarbon 1967, 9 :179 7. 1,625 ~ 175 (1-727) 61~31'N 7 4 ' 0 5 ' W Quebec Arctic 1966, 19:114 8. 1,870 ~: 60 (WIS-282) 56 ' 42 ' N 117 38 'W Alberta Radiocarbon 1969, in press 9. 2,050:t 130 (GSC-281) 46"45 'N 6 0 ' 5 1 ' W Nova Scotia Radiocarbon 1966, 8 :100

10. 2 ,330±150 (GSC-300) 66 ' 32 ' N 103-15 'W Mackenzie Radiocarbon 1966, 8 :118 11. 2,350~t200 ( L a m o n t 2 1 9 ) 51~28'N 78~45 ' W Quebec Science 1954, 119:908 12. 2,380J~ 90 (WIS-I) 54 07'N 101 '17 'W Mani toba Radiocarbon 1965, 7 :405 13. 2,410 ]- 60 (WIS-269) 53 :55 'N 106 0 3 ' W Saskatchewan Radiocarbon 1968, 10:477 14. 2 ,640~130 (GSC-497) 46 08'N 7 0 17'W Quebec Radiocarbon 1967, 9 :158 15. 3 ,360" 70 (WIS-216) 66"05'N 101 04 'W Keewatin Racfiocarbon 1968, 10:168 16. 3,410 I 55 (WIS-281) 59 ° 12'N 117 30 'W Alberta Radiocarbon 1969, in press 17. 3 ,450+ 90 (W1S-283) 57'~46'N 117 37 'W Alberta Radiocarbon 1969, in press 18. 3,450~ 200 0-506) 58' 44'N 157°02'W Alaska Radiocarbon 1966, 8 :163 19. 3,470~ 180 (!-1) 57' 34'N 154 ~ 28 'W Alaska Radiocarbon 1959, 1 :30 20. 3 ,750--150 (GSC-499) 54 ': 19'N 116 35 'W Alberta Radiocarbon 1967, 9 : 1 7 0 21. 4,060-5:130 (GSC-374) 81' 24'N 76 ~ 10'W Ellesmere Is. Radiocarbon 1967, 9 : 1 9 4 22. 4,2001 130 (GSC-494) 54 33'N 105"32'W Saskatchewan Ratfiocarbon 1967, 9 :167 23. 4,350 ! 70 (W1S-280) 54 ~ 10'N 111 28 'W Alberta Radiocarbon 1969, in press

1,625+ 175 (1-727) was reported to have occurred immediately after a climatic amelioration (MAYCOCK and MATTHEWS, 1966). This was deduced from the per- centages of Pinus and Picea pollen in the peat, which were higher than expected from the present location of the site 300 miles north of the forest limit, and it was considered that the tree line must have been farther north than at present. At Ennadai Lake, southern Keewatin, changes in Sphagnum growth and sporogenesis due to environmental (probably climatic) change occurred at 1,510+80 B.P. (NICHOLS, 1967a). Another date from Quebec (525+ 100 B.P., NPL-59) was also reported to be associated with a climatic amelioration. There is no a priori reason to think that Arctic Quebec should have experienced climatic changes in phase with those of central Canada; perhaps, from its position relative to the standing (Rossby) waves in the upper Westerlies, the reverse might be expected.

Peat growth ca. 4,200 B.P. in Alberta coincides with the end of a dry grass- land episode in a pollen diagram from Porcupine Mountain, southern Manitoba, 4,180_+ 75 (W1S-286), and the start of wet conditions at Colville Lake, Mackenzie Territory, 4,130_+55 (WIS-294) (H. Nichols, in preparation). Several of the

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64 H. NICHOLS

Fig.1. Location of radiocarbon dated basal peat samples in Canada and Alaska (see Table I).

periods of peat accumulation mentioned above coincide with glacial advances

in North America (H. Nichols, in preparation) and climatic changes in Alaska

(HEUSSER, 1967; PORTER and DENTON, 1967) and Greenland (FREDSKILD, 1967).

A number of these climatic events have previously been compared with the North

European chronology of climatic change (NICHOLS, 1967b,c). GRANLUND (1932)

estimated the age of the most prominent recurrence surfaces in Swedish peat

bogs at 4,200, 3,200, 2,500, 1,600 and 700 B.P., on the basis of varve chronology,

palynology and archaeology. More recent work based on radiocarbon dates has

suggested that the problem is more complex than originally appeared, but it is

interesting to note the similarity in the dates for basal peat growth in Canada and

the early estimates for recurrence of peat growth in Sweden.

CONCLUSIONS

This small group of dates for basal peat growth shows a striking similarity

to the timing of climatic changes already established for Canada, and it seems

reasonable to suppose that shifts of climate to cooler and/or wetter conditions

caused such accumulations. It is likely that further radiocarbon assays of the age

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CHRONOLOGY OF PEAT GROWTH IN CANADA 65

of basal peat in Canada will prove to be similar to the chronology of climatic

events already established there. When more basal peat dates become available it may be possible to draw

a map of peat isochrones for Canada, which would delineate the areas of simul- taneous peat growth. Modern peat accumulation in Canada occurs mainly within the Boreal forest and is controlled by factors (presumably primarily climatic) which have not yet been fully investigated. If certain types of contemporary peat growth prove to be related to a particular regional climate the geographical distribution of fossil peat may prove to be an approximate guide to the former location of such climatic regimes, it is interesting that recent regional divisions of peat bogs in Finland have been based on differences in peatland vegetation

controlled by climate (RuuttlJ~,RVl, 1960).

ACKNOWLEI)GEMENTS

I thank Dr. M. M. Bender for the radiocarbon determinations, and Dr. R. A. Bryson for assistance during fieldwork. Research supported by Atmospheric Sciences Divisions, NSF, (GP-5572X).

REFERENCES

BENDER, M. M., BRYSON, R. A. and BAERREIS, D. A., 1968. University of Wisconsin radiocarbon dates, 5. Radiocarbon, 10(2): 473~-78.

BENDER, M. M., BRYSON, R. A. and BAERREIS, D. A., 1969. University of Wisconsin radiocarbon dates, 6. Radiocarbon, 11, in press.

BRYSDN, R. A., IRVING, W. N. and LARSEN, J. A., 1965. Radiocarbon and soil evidence of former forest in the southern Canadian tundra. Science, 147: 46M8.

EREDSKILD, B., 1967. Palaeobotanical investigations at Sermermiut, Jakobshavn, West Green- land. Medd. Gronland, 178(4):1 54.

GOLDTHWA|T, R. P., 1967. Evidence from Alaskan glaciers of major climatic changes. In: Worhl Climate from 8000 to 0 B.C., Roy. Meteorol. Soc., London, pp.40 53.

GRANLUND, E., 1932. De svenska hOgmossernas geologi. Sveriges Geol. Umlers6kn., ,4rsbok, Ser. C, Avhandl. Uppsal., 373(26): 1 193.

HEUSSER, C. J., 1967. Polar hemispheric correlation: palynological evidence from Chile and the Pacific northwest of America. In: Worhl Climate 8000 to 0 B.C., Roy. Meteorol. Soc., London, pp.124-141.

MAYCOCK, P. F. and MATTHEWS, B., 1966. An Arctic forest in the tundra of Northern Ungava, Quebec. Arctic, 19: 114-144.

NICHOLS, H., 1967a. Pollen diagrams from sub-arctic central Canada. Science, 155:1665 1668. NICHOLS, H., 1967b. Central Canadian palynology and its relevance to northwestern Europe

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Soc. " Vanamo", 31(1 ): 1-360. TANSLE¥, A. G.. 1939. The British lslamls and Their Vegetation. Cambridge Univ. Press, London,

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