Oxygen-isotope Variations in Post-glacial Lake Ontario

• Published in: Quaternary Science Reviews
• Main Authors: Hladyniuk, Ryan, Longstaffe, Fred J
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: Scholarship@Western 2016
• Subjects: Lake Ontario; oxygen isotopes; glacial meltwater; Laurentide Ice Sheet; late Quaternary climate change; Earth Sciences; Glacial Lake; North Bay; Ice Sheet
• Online Access: https://ir.lib.uwo.ca/earthpub/4; https://doi.org/10.1016/j.quascirev.2016.01.002; https://ir.lib.uwo.ca/context/earthpub/article/1004/viewcontent/Hladyniuk___Longstaffe__2016___Quaternary_Science_Reviews.pdf

The role of glacial meltwater input to the Atlantic Ocean in triggering the Younger Dryas (YD) cooling event has been the subject of controversy in recent literature. Lake Ontario is ideally situated to test for possible meltwater passage from upstream glacial lakes and the Laurentide Ice Sheet (LIS) to the Atlantic Ocean via the lower Great Lakes. Here, we use the oxygen-isotope compositions of ostracode valves and clam shells from three Lake Ontario sediment cores to identify glacial meltwater contributions to ancient Lake Ontario since the retreat of the LIS (~16,500 cal [13,300 14C] BP). Differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime. The average lakewater δ18O of –17.5 ‰ (determined from ostracode compositions) indicates a significant contribution from glacial meltwater. Upon LIS retreat from the St. Lawrence lowlands, ancient Lake Ontario (glacial Lake Iroquois) lakewater δ18O increased to –12 ‰ largely because of the loss of low-18O glacial meltwater input. A subsequent decrease in lakewater δ18O (from –12 to –14 ‰), accompanied by a median sediment grain size increase to 9 μm, indicates that ancient Lake Ontario received a final pulse of meltwater (~13,000-12,500 cal [11,100-10,500 14C] BP) before the onset of hydrologic closure. This meltwater pulse, which is also recorded in a previously reported brief freshening of the neighbouring Champlain Valley (Cronin et al., 2012), may have contributed to a weakening of thermohaline circulation in the Atlantic Ocean. After 12,900 cal [11,020 14C] BP, the meltwater presence in the Lake Ontario basin continued to inhibit entry of Champlain seawater into early Lake Ontario. Opening of the North Bay outlet diverted upper Great Lakes water from the lower Great Lakes causing a period (12,300-8,300 cal [10,400-7,500 14C] BP) of hydrologic closure in Lake Ontario (Anderson and Lewis, 2012). This change is demarcated by a shift to higher δ18Olakewater (~ –7 ‰), driven in part by strong evaporative conditions ...