scholarly journals Geological evidence of a palynologically defined cooling in southeastern Canada at 10 000-8000 14C yr BP

2010 ◽  
Vol 61 (2-3) ◽  
pp. 217-224
Author(s):  
Ian A. Brookes ◽  
Douglas R. Grant
Keyword(s):  
Sea Ice ◽  
Great Lakes ◽  
Vegetation Change ◽  
Glacial Lake ◽  
Lake Agassiz ◽  
Geological Evidence ◽  
Glacial Lake Agassiz ◽  
Before And After ◽  
Ice Conditions ◽  
Climatic Cooling

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.

Changes in the Bathymetry and Volume of Glacial Lake Agassiz Between 11,000 and 9300 14C yr B.P.

2000 ◽  
Vol 54 (2) ◽  
pp. 174-181 ◽  
Author(s):  
David W. Leverington ◽  
Jason D. Mann ◽  
James T. Teller
Keyword(s):  
Atlantic Ocean ◽  
Great Lakes ◽  
Ocean Circulation ◽  
North Atlantic ◽  
North Atlantic Ocean ◽  
Glacial Lake ◽  
Lake Agassiz ◽  
The North ◽  
Glacial Lake Agassiz ◽  
The North Atlantic

The volume and surface area of glacial Lake Agassiz varied considerably during its 4000-year history. Computer models for seven stages of Lake Agassiz were used to quantify these variations over the lake's early history, between about 11,000 and 9300 14C yr B.P. (ca. 13,000 to 10,300 cal yr B.P.). Just after formation of the Herman strandlines (ca. 11,000 14C yr B.P.), the volume of Lake Agassiz appears to have decreased by >85% as a consequence of the abrupt rerouting of overflow to its eastern outlet from its southward routing into the Mississippi River basin. This drainage released about 9500 km3 of water into the North Atlantic Ocean via the Great Lakes and Gulf of St. Lawrence. Following closure of this eastern routing of overflow, the lake reached its maximum size at about 9400 14C yr B.P. with an area of >260,000 km2 and a volume of >22,700 km3. A second major reduction in volume occurred shortly after that, when its volume decreased >10% following the opening of the Kaiashk outlet to the east into the Great Lakes, and 2500–7000 km3 of water was released into the North Atlantic Ocean. These discharges may have affected ocean circulation and North Atlantic Deep Water production.

Paleotopographic reconstructions of the eastern outlets of glacial Lake Agassiz

2003 ◽  
Vol 40 (9) ◽  
pp. 1259-1278 ◽  
Author(s):  
David W Leverington ◽  
James T Teller
Keyword(s):  
Great Lakes ◽  
Lake Level ◽  
Ice Sheet ◽  
Laurentide Ice Sheet ◽  
Glacial Lake ◽  
Lake Agassiz ◽  
Flow Paths ◽  
Southern Margin ◽  
Glacial Lake Agassiz ◽  
Complex Manner

Paleotopographic reconstructions of the eastern outlets of glacial Lake Agassiz provide a foundation for understanding the complex manner in which terrain morphology controlled the routing of overflow through the eastern outlets during the lake's Nipigon Phase (ca. 9400–8000 14C years BP) and for understanding the causes of outlet-driven declines in lake level during that period. Although flow paths across the divide between the Agassiz and Nipigon basins were numerous, eastward releases from Lake Agassiz to glacial Lake Kelvin (modern Lake Nipigon) were channeled downslope into a relatively small number of major channels that included the valleys of modern Kopka River, Ottertooth Creek, Vale Creek, Whitesand River, Pikitigushi River, and Little Jackfish River. From Lake Kelvin, these waters overflowed into the Superior basin. The numerous lowerings in lake level between stages of the Nipigon Phase, controlled by topography and the position of the retreating southern margin of the Laurentide Ice Sheet, had magnitudes of between 8 and 58 m, although some of these drawdowns may have occurred as multiple individual events that could have been as small as several metres. The total volumes of water released in association with these drops were as great as 8100 km3, and for all Nipigon stages were probably between about 140 and 250 km3 per metre of lowering. The topographic reconstructions demonstrate that Lake Agassiz occupied the area of glacial Lake Nakina (located northeast of modern Lake Nipigon) by the The Pas stage (ca. 8000 14C years BP) and that Lake Agassiz drainage through the Nipigon basin to the Great Lakes ended before the succeeding Gimli stage.

Postglacial Diatom Stratigraphy in Relation to the Recession of Glacial Lake Agassiz

1975 ◽  
Vol 5 (4) ◽  
pp. 529-540 ◽  
Author(s):  
J.C. Ritchie ◽  
L.K. Koivo
Keyword(s):  
Sandy Beach ◽  
Sedimentary Environment ◽  
Glacial Lake ◽  
Lake Agassiz ◽  
Organic Detritus ◽  
Sedimentary Environments ◽  
Grand Rapids ◽  
Glacial Lake Agassiz ◽  
Diatom Stratigraphy ◽  
Beach Sands

The sediment and diatom stratigraphy of a small pond on The Pas moraine, near Grand Rapids, Manitoba, reveals a change in sedimentary environment related directly to the last stages of Glacial Lake Agassiz. Beach sands were replaced by clay 7300 14C y. a., then by organic silt and, at 4000 14C y. a. by coarse organic detritus; the corresponding diatom assemblages were (I) a predominantly planktonic spectrum in beach sands, (II) a rich assemblage of nonplanktonic forms, and (III) a distinctly nonplanktonic acidophilous spectrum. These results confirm Elson's (1967) reconstruction of the extent and chronology of the final (Pipun) stage of Glacial Lake Agassiz. The sedimentary environments change from a sandy beach of a large lake at 7300 BP to a small, shallow eutrophic pond with clay and silt deposition from 7000 to 4000 BP. From 4000 BP to the present, organic detritus was deposited in a shallow pond that tended toward dystrophy.

Micromorphology of iceberg scour in clays: Glacial Lake Agassiz, Manitoba, Canada

2012 ◽  
Vol 55 ◽  
pp. 125-144 ◽  
Author(s):  
Lorna D. Linch ◽  
Jaap J.M. van der Meer ◽  
John Menzies
Keyword(s):  
Glacial Lake ◽  
Lake Agassiz ◽  
Glacial Lake Agassiz ◽  
Iceberg Scour
Sign in / Sign up

Export Citation Format

Share Document