The Pleistocene Champlain Sea

The weight of a glacier depresses the earth’s crust, a geological process known as crustal downwarping.  The Laurentide Ice Sheet covered most of eastern Canada during the Last Glacial Maximum, but a sudden warm phase of climate led to the rapid recession of its southern lobe.  About 13,000 years ago ocean water flooded into this glacial depression located in the present day region of eastern Quebec and Vermont, creating the Champlain Sea. The transgression of ocean water into land recently depressed by a glacier is termed eustatic sea level rise.  The Champlain Sea was bordered on its northern edge by melting ice cliffs formed by the retreating glacier, while a marshy tundra existed on its south side.  Over time this tundra was colonized by spruce trees.  This boreal forest was in turn replaced by a landscape of mixed conifers and northern hardwoods.  Meltwater and falling chunks of ice from the glacial cliffs reduced the salinity of the Champlain Sea, making it a brackish estuary teaming with a rich diversity of marine life.

Map of the pre-historic Champlain Sea.  It was created by crustal downwarping and fed by melting glaciers.  Ocean water flooded into this basin via the St. Lawrence River.  Isostatic rebound terminated the existence of this sea.

Lévis is located in Southern Quebec

Location of Levis, Quebec.  An excellent fossil site is found in the St. Nicholas borough of this city, containing many species that lived in the defunct Champlain Sea.

The fossil record suggests the white whale ( Delphinapterus leucas ) was the most common large mammal living in the Champlain Sea.  The white whale feeds upon fish, cephalopods, and shellfish.  The presence of a large population of white whales indicates an abundance of fish, and this is corroborated by the remains of both fresh and saltwater species found in deposits dating to this age here, including cod, tomcod, eelpout, capelin, smelt, spoonhead sculpin, lake cisco, lake char, wrymouth, long-nosed sucker, lumpfish, 3-spine stickleback, sturgeon, and salmon or trout.  Humpback, finback, and bowhead whales, and harbor porpoises also frequented the Champlain Sea.  Harp and bearded seals bred on pack ice, ringed seals bred on the shore, and harbor seals swam in the open water.  Herds of walruses rested on the ice edge.  Scientists have even excavated the remains of birds here–long-tailed ducks, thick billed murres, common eiders, and arctic terns.  The foot bone of an old arthritic grizzly bear was found at St. Nicholas, the best fossil site in the region where the remains of many species were buried under tidal current sands.  Polar bears probably roamed along the shores, but fossil evidence of their presence here has yet to be discovered.Image result for beluga whale

Fossil evidence suggests white whales were the most common whale species in the Champlain Sea.

In 1849 geologists were surprised to find whale bones and the remains of marine invertebrates such as clams, scallops, mussels, barnacles, and sea urchin in landlocked Vermont, and it took them a while to determine a vast inland sea resulting from retreating glaciers was the explanation for the presence of these fossils.  The sea existed from about 13,000 BP to ~10,000 BP.  Saline levels often fluctuated, depending upon the varying quantities of meltwater, and the sea gradually became more shallow as the earth’s crust rebounded.  The rise of the earth’s crust following the retreat of a glacier is known as isostatic rebound–the opposite of crustal downwarping.  The sea also became warmer over time.  Arctic saxicoue was an early dominant clam, but eastern soft-shelled clams, a warmer water species, replaced them.

Eventually, isostatic rebound split the Champlain Sea into 2 freshwater lakes and blocked their outlets to the St. Lawrence River and Atlantic Ocean.  Lake Lampsilis, named after a common species of freshwater mussel ( Lampsilis radiati ), lasted until ~8,000 years BP, when isostatic rebound completely eliminated the basin that held the lake.  Today, Lake Champlain is a freshwater relic of what was formerly an enormous brackish sea.

Image result for champlain lake

Champlain Lake is a tiny remnant of the once vast Champlain Sea.

Reference:

Harrington, C. Richard; Marc Coornoup, Michael Chastia, Tara Fulton, and Beth Shapiro

“Brown Bear (Ursus arctos) (9880 BP) from Late Glacial Champlain Sea Deposts at St. Nicholas, Quebec, Canada, and the Dispersal History of Brown Bears”

NRC Press 2014

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One Response to “The Pleistocene Champlain Sea”

  1. ina puustinen-westerholm Says:

    As usual..another richly rewarding ‘flyover..in time’ for the area covered. Thank you.

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