Résumés
Abstract
Post-glacial pollen spectra over a wide area of southeastern Canada have been interpreted as showing that the general warmth-adapted trend of regional vegetation change was interrupted between 10 000 and 8000 14C yr BP, reverting to conditions associated with a markedly cooler climate. This biotic reversal has been attributed to a climatic cooling caused by discharge of frigid water from glacial Lake Agassiz, through the Great Lakes to the Goldthwait Sea in the Gulf of St. Lawrence basin. Here, we assemble geological evidence from widely scattered localities in and around the Gulf of St. Lawrence, all previously reported, a majority unexplained, and ascribe it collectively to the same climatic cooling. We interpret the marine diamicts and other faunal reversals as the products of cooling, which intensified sea-ice conditions during the interval 10 000-8000 14C yr BP, specifically at 9300 14C yr (9170 yr, reservoir corrected), conditions resulting from that meltwater influx. This age was several centuries too young to be correlated with the Preboreal Oscillation, but several easterly overflows of Lake Agassiz occurred before and after this date, and may have increased sea-ice in the Goldthwait Sea, singly or by hysteresis. Other truly glacial features in southeastern Canada, such as moraine systems and diamictons, are also referred to this cooling.
Résumé
Les spectres polliniques post-glaciaires d’une vaste région du sud-est du Canada montrent que la tendance générale au réchauffement qu’impliquent les changements de végétation régionaux a été interrompue entre 10 000 et 8000 ans 14C BP, revenant à des conditions typiques d’un climat plus froid. Cette inversion biotique a été attribuée à un refroidissement climatique causé par la décharge des eaux froides du lac glaciaire Agassiz, via les Grands Lacs jusqu’à la mer de Goldthwait en passant dans le Golfe du Saint-Laurent. Nous examinons ici plusieurs indices géologiques aux alentours du Golfe du Saint-Laurent, tous déjà publiés, la plupart inexpliqués, et les attribuons collectivement au même refroidissement. Nous interprétons les diamictons marins et les inversions biotiques comme étant le produit d’un refroidissement qui a intensifié les conditions de glace de mers entre 10 000 et 8000 ans BP, plus particulièrement il y a 9300 ans BP (9170 ans, avec correction du réservoir marin), ces conditions résultant des apports d’eau de fonte. Cet âge est trop jeune de plusieurs siècles pour être corrélé à l’oscillation du Préboréal, mais plusieurs épisodes de décharge du lac Agassiz se sont produites avant et après cette date, et peuvent avoir favorisé un plus grand couvert de glace dans la mer de Goldthwait, chacun ou par hystérésis. D’autres traits typiquement glaciaires, tels les systèmes morainiques, sont également associés à ce refroidissement dans le sud-est du Canada.
Parties annexes
References
- Andersen, C., Koc, N. and Morris, M., 2004. A highly unstable Holocene climate in the sub-polar North Atlantic : evidence from diatoms. Quaternary Science Reviews, 23 : 2155-2166.
- Anderson, T.W. and Lewis, C.F.M., 1992. Climatic influences of deglacial drainage in southern Canada at 10 to 8 ka suggested by pollen evidence. Géographie physique et Quaternaire, 46 : 255-272.
- Anderson, T.W., Levac, E. and Lewis, C.F.M., 2007. Cooling in the Gulf of St. Lawrence and estuary region at 9.7 to 7.2 14C ka (11.2-8.0 cal ka) : Palynological response to the PBO and 8.2 cal ka cold events, Laurentide Ice Sheet air mass circulation and enhanced freshwater runoff. Palaeogeography, Palaeoclimatology, Paleoecology, 246 : 75-100.
- Andrews, J.T. and Ives, J.D., 1972. Late and postglacial events (<10,000 BP) in the eastern Canadian Arctic with particular reference to the Cockburn Moraines and the break-up of the Laurentide Ice Sheet, p. 149-174. In Y. Vasari, H. Hyvarinen and S. Hicks, eds., Climatic Changes in Arctic Areas During the Last 10,000 Years. Universitet Ouluensis Acta, Series A, Scientiae Naturae, no. 3, Geologia, no. 1, 511 p.
- Blake, W. Jr., 1986. Geological Survey of Canada Radiocarbon Dates-XXV. Geological Survey of Canada, Ottawa, Paper 85-7.
- Blake, W. Jr., 1988. Geological Survey of Canada Radiocarbon Dates-XXVII. Geological Survey of Canada, Ottawa, Paper 97-7.
- Brookes, I.A., 1974. Late Wisconsin glaciation of southwestern Newfoundland (with special reference to the Stephenville map area). Geological Survey of Canada, Ottawa, Paper 73-40.
- Brookes, I.A. and Stevens, R.K., 1985. Radiocarbon age of rock-boring Hiatella arctica (Linne) and post-glacial sea-level change at Cow Head, Newfoundland. Canadian Journal of Earth Sciences, 22 : 136-140.
- Came, R.E., Oppo, D.W. and McManus, J.F., 2007. Amplitude and timing of temperature and salinity variability in the sub-polar North Atlantic over the past 10 ky. Geology, 35 : 315-318.
- Connolly, J.R., Needham, H.D. and Heezen, B.C., 1967. Late Pleistocene and Holocene sedimentation in the Laurentian channel. Journal of Geology, 75 : 131-147.
- Dansgaard, W., Johnsen, S.J., Clausen, H.B. and Langway, C.C., 1971. Climatic record revealed by the Camp Century ice core, p. 37-56. In K.K. Turekian, ed., The Late Cenozoic Glacial Ages. Yale University Press, New Haven, 606 p.
- Dionne, J.-C., 1977. La Mer de Goldthwait au Québec. Géographie physique et Quaternaire, 31 : 61-80.
- Dionne, J.-C., 1993. Sediment load of shore ice and ice rafting potential, upper St. Lawrence estuary, Quebec. Canadian Journal of Coastal Research, 9 : 628-646.
- Dubois, J.-M. and Dionne, J.-C., 1985. The Quebec North Shore Moraine System : a major feature of late Wisconsin deglaciation, p. 125-133. In H.W. Borns, Jr., P. LaSalle and W.B. Thompson, eds., Late Pleistocene History of Northeastern New England and Adjacent Quebec. Geological Society of America, Special Paper 197.
- Dyke, A.S., 2004. An outline of North American deglaciation with emphasis on central and northern Canada, p. 373-424. In J. Ehlers and P.L. Gibbard, eds., Quaternary Glaciations-Extent and Chronology, Vol. II, North America. Developments in Quaternary Science, Elsevier, Amsterdam, 450 p.
- Dyke, A.S. and Prest, V.K., 1987. Palaeogeography of northern North America, 18 000-5 000 years ago. Geological Survey of Canada, Ottawa, Map 1703A, 1 :12 500 000.
- Dyke, A.S., McNeely, R., Southon, J., Andrews, J.T., Peltier, W.R., Clague, J.J., England, J.H., Gagnon, J.-M. and Baldinger, A., 2003. Preliminary assessment of Canadian marine reservoir ages. Canadian Quaternary Association, 11th Biennial Meeting, Dalhousie University, Halifax, Nova Scotia, June 2003, Program and Abstracts : A23-A24.
- Fairbanks, R.G., Mortlock, R.A., Chiu, T.-C., Cao, L., Kaplan, A., Guilderson, T.P., Fairbanks, T.W. and Bloom, A. L., 2005. Quaternary Science Reviews, 24 : 1781-1796.
- Fisher, T.G., Smith, D.G. and Andrews, J.T., 2002. Pre-Boreal Oscillation caused by a Glacial Lake Agassiz flood. Quaternary Science Reviews, 21 : 873-878.
- Grant, D.R., 1988. Surficial geology, Sandy Lake-Bay of Islands, Newfoundland. Geological Survey of Canada, Ottawa, Map 1664A, 1 :250 000.
- Grant, D.R., 1989. Quaternary geology of the Atlantic Appalachian region of Canada, p. 391-440. In R.J. Fulton, ed., Quaternary Geology of Canada and Greenland. Geological Survey of Canada, Ottawa, Geology of Canada No. 1.
- Grant, D.R., 1992. Quaternary geology of St. Anthony-Blanc Sablon area, Newfoundland and Quebec. Geological Survey of Canada, Ottawa, Memoir 427.
- Grant, D.R., 1994a. Quaternary geology, Port Saunders map area, Newfoundland. Geological Survey of Canada, Ottawa, Paper 91-20.
- Grant, D.R., 1994b. Quaternary Geology, Cape Breton Island, Nova Scotia. Geological Survey of Canada, Ottawa, Bulletin 482.
- Guilbault, J.-P., 1984. Late glacial foraminiferal localities in raised marine sediments in western Newfoundland. Geological Survey of Canada, Ottawa, Open File Report 1003.
- Hillaire-Marcel, C. and Occhietti, S., 1977. Fréquence des datations au 14C de faunes marines postglaciaires de l’est du Canada et variations paléoclimatiques. Palaeogeography, Palaeoclimatology, Palaeoecology, 21 : 17-54.
- Josenhans, H. and Lehman, S., 1999. Quaternary stratigraphy and glacial history of the Gulf of St. Lawrence, Canada. Canadian Journal of Earth Sciences, 36, 1327-1345.
- Koutitonsky, V.G. and Bugden, G.L., 1991. The physical oceanography of the Gulf of St. Lawrence : a review with emphasis on the variability of the motion, p. 57-90. In J.-C. Theriault, ed., The Gulf of St. Lawrence : Small Ocean or Big Estuary ? Canadian Journal of Fisheries and Aquatic Sciences, 113.
- Levac, E., 2003. Detecting Holocene meltwater transit through the St. Lawrence River-Evidence from marine palynological records. Canadian Quaternary Association, 11th Biennial Meeting, Dalhousie University, Halifax, Nova Scotia, June 2003, Program and Abstracts : A61.
- Loring, D.H., 1975. Surficial geology of the Gulf of St. Lawrence, p. 11-34. In W.J.M. van den Linden and J.A. Wade, eds., Offshore Geology of Eastern Canada. Geological Survey Canada, Ottawa, Paper 74-30, vol. 2.
- Loring, D.H. and Nota, D.J.G., 1973. Morphology and sediments of the Gulf of St. Lawrence. Fisheries Research Board of Canada Bulletin, 182, 147 p.
- Lowdon, J.A. and Blake, W. Jr., 1973. Geological Survey of Canada Radiocarbon Dates-XIII. Geological Survey of Canada, Ottawa, Paper 73-7.
- McNeely, R. and Jorgensen, P.K., 1992. Geological Survey of Canada Radiocarbon Dates-XXX. Geological Survey of Canada, Ottawa, Paper 90-7.
- Rodrigues, C.G., Ceman, J.A. and Vilks, G., 1993. Late Quaternary palaeoceanography of deep and intermediate water masses off Gaspé Peninsula, Gulf of St. Lawrence : foraminiferal evidence. Canadian Journal of Earth Sciences, 30 : 1390-1403.
- Shaw, J., Gareau, P. and Courtney, R.C., 2002. Palaeogeography of Atlantic Canada 13-0 kyr. Quaternary Science Reviews, 21 : 1861-1878.
- Stea, R.R., Piper, D.J.W., Fader, G.B.J. and Boyd, R., 1998. Wisconsin glacial and sea-level history of Maritime Canada and the adjacent continental shelf : a correlation of land and sea events. Geological Society of America Bulletin, 110 : 821-845.
- Stea, R.R., Mott, R.J., Godfrey-Smith, D.I. and Fastook, J.L., 2003. Younger Dryas glacierization in the Gulf of St. Lawrence. Canadian Quaternary Association, 11th Biennial Meeting, Dalhousie University, Halifax, Nova Scotia, June 2003, Program and Abstracts : A114.
- Teller, J.T., 1985. Glacial Lake Agassiz and its influence on the Great Lakes, p. 1-16. In P.F. Karrow and P.E. Calkin, eds., Quaternary Evolution of the Great Lakes. Geological Association of Canada, Special Paper 30.
- Teller, J.T., 1987. Proglacial lakes and the southern margin of the Laurentide Ice Sheet, p. 39-69. In W.F. Ruddiman, H.E. Wright, Jr., eds., North America and Adjacent Oceans during the Last Deglaciation : Decade of North American Geology, vol. K-3. Geological Society of America, Boulder, 501 p.
- Teller, J.T., 1990. Volume and routing of late-glacial runoff from the southern Laurentide Ice Sheet. Quaternary Research, 34 : 12-23.
- Teller, J.T. and Thorleifson, L.H., 1983. The Lake Agassiz—Lake Superior connection, p. 261-290. In J.T. Teller, L.W. Clayton, eds., Glacial Lake Agassiz. Geological Association of Canada, Special Paper 26.
- Teller, J.T., Leverington, D.W. and Mann, J.D., 2002. Freshwater outbursts to the oceans from glacial Lake Agassiz and their role in climate change during the last deglaciation. Quaternary Science Reviews, 21 : 879-887.
- Ten Brink, N.W. and Weidick, A., 1974. Greenland ice sheet history since the last glaciation. Quaternary Research, 4 : 429-440.
- Waitt, R.B., 1981. Radial outflow and unsteady retreat of Late Wisconsin to early Holocene icecap in the northern Long Range upland, Newfoundland. Geological Society America Bulletin, 92 : 834-838.