Paleoflooding: Difference between revisions

The Champlain Sea was located to the north of present-day [[New York]] and [[Vermont]], on the southern fringes of [[Quebec]] and was open to the Northern [[Atlantic Ocean]] on its northeast arm. During the last deglaciation as the [[Laurentide Ice Sheet]] retreated, two major glacial lakes formed to the west of the Champlain Sea - [[Lake Agassiz]] and [[Lake Algonquin]] (Fig. 1). As these lakes continued to expand, freshwater flooded eastward toward and into the Champlain Sea. However, uncertainty still exists regarding the location of the drainage and its exact effects on ocean salinity. Because of the Champlain Sea’s openness to the Atlantic Ocean, changes in the salinity of the Champlain Sea could have translated into the Northern Atlantic, thus possibly causing changes in ocean circulation and climate.<ref name="Cronin08" /> In fact, the melting of the Laurentide Ice Sheet was so extensive that its melt water entered the [[Gulf of Mexico]], [[Arctic Ocean]], and [[Hudson Bay]] (Fig. 2) in addition to the Champlain Sea and the Atlantic Ocean.<ref name="Teller02" />

 

 

Terrestrial plant material, seeds, and marine shells from Champlain Sea core samples have been used as proxies for [[paleosalinity]]. By studying [[δ13C|δ¹³C]] (change in carbon-13) of marine mollusks, it can be inferred that when they existed in the Champlain Sea, conditions were [[brackish]] (mixture of fresh and salt water) about 10.8 ka BP. The δ¹³C value of a core sample Melo-1 (see Fig. 3 for location) indicates the amount of light carbon that is present. Biota preferentially intake light carbon, so the more that is present in a sample, the more biota that was present at that time. Additionally, core samples from the Champlain Sea indicate a change in assemblages from those that inhabit marine environments to those that live in much less saline conditions at about 11.4 to 11.2 ka BP (Fig. 4). In the specific core sample (core Melo-5, location noted in Fig. 3) analysis shown in Fig. 4, there is a change in assemblages from almost 100% ''E. clavata'' (which inhabits marine environments) to >50% ''E. albiumbilicatum'' (which prefers less saline conditions)—both species of ''[[Elphidium]]''. This transition seems to be probable, as it has been corroborated by multiple studies. The overall decrease in salinity has been estimated to be from 25 psu to less than 15 psu ([[practical salinity unit]]s).<ref name="Cronin08" /> The decrease in salinity starting at Melo-1 and moving to Melo-5 indicates a downstream translation of freshening.