Oxygen-isotope variations in post-glacial Lake Ontario

QUATERNARY SCIENCE REVIEWS

卷:134

Article

Hladyniuk, Ryan¹  Longstaffe, Fred J.¹ 

[1] Univ Western Ontario, Dept Earth Sci, London, ON N6A 5B7, Canada

关键词: Lake Ontario;    Oxygen isotopes;    Glacial meltwater;    Laurentide ice sheet;    Late-Quaternary climate change;   

DOI  :  10.1016/j.quascirev.2016.01.002

来源: Elsevier

【 摘 要 】

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 (similar to 16,500 cal [13,300 C-14] BP). Differences in mineralogy and sediment grain size are also used to identify changes in the hydrologic regime. The average lakewater 5180 of -17.5%o (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 delta O-18 increased to -12%o largely because of the loss of low-O-18 glacial meltwater input. A subsequent decrease in lakewater delta O-18 (from 12 to -14 parts per thousand), accompanied by a median sediment grain size increase to 9 mu,m, indicates that post-glacial Lake Ontario received a final pulse of meltwater (similar to 13,000-12,500 cal [11,100-10,500 C-14] 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 C-14] BP, the meltwater presence in the 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 (12,300-8300 cal [10,400 7500 14C] BP) of hydrologic closure in Lake Ontario (Anderson and Lewis, 2012). This change is demarcated by a shift to higher delta O-18(lakewater) (similar to-7 parts per thousand), driven in part by strong evaporative conditions in the Ontario basin and in part by increasing delta O-18(precipitation) at this time. The delta O-18(iakewater) then fluctuated only slightly upon the eventual return of the upper Great Lakes water during the Nipissing phase at 5800 cal [5090 14(C)] cal BP (Anderson and Lewis, 2012), after which shelly fauna are no longer preserved in the sediment record. (C) 2016 Elsevier Ltd. All rights reserved.

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