Dry Climate Disconnected the Laurentian Great Lakes

Abstract

Recent studies have produced a new understanding of the hydrological history of North America's Great Lakes, showing that water levels fell several meters below lake basin outlets during an early postglacial dry climate in the Holocene (younger than 10,000 radiocarbon years, or about 11,500 calibrated or calendar years before present (B.P.)). Water levels in the Huron basin, for example, fell more than 20 meters below the basin overflow outlet between about 7900 and 7500 radiocarbon (about 8770–8290 calibrated) years B.P. Outlet rivers, including the Niagara River, presently falling 99 meters from Lake Erie to Lake Ontario (and hence Niagara Falls), ran dry. This newly recognized phase of low lake levels in a dry climate provides a case study for evaluating the sensitivity of the Great Lakes to current and future climate change.

Sub-bottom profiling and coring of sub-basins along the lower French River, Ontario: insights into depositional environments within the North Bay outlet

“…Part of the explanation for this undoubtedly relates to the complexity of the bedrock-dominated landscape that controlled the outlet course between North Bay-Trout Lake-Talon Lake-Mattawa Valley as well as the lack of readily accessible alluvial deposits from which an outlet history could be interpreted. Understanding the outlet is further complicated by the recent recognition of major water level fluctuations, and consequently outflow depths, that occurred during the MattawaStanley phase of lake levels (between 11,300 and 8,400 cal BP (*9,900 to 7,600 BP)) arising from the intermittent large-scale influx of meltwater from glacial Lake Agassiz and/or the Laurentide Ice Sheet driving the high 'Mattawa' stages and a cooler-drier climate (than present) during the 'Stanley-Hough' low stages (see Lewis and Anderson 1989;Lewis et al 1994Lewis et al , 2005Lewis et al , 2007Lewis et al , 2008. The net effect of these fluctuations, in combination with gradual differential tilting of the outlet course, caused the control of lake level to shift between topographic features along the modern French River course [e.g., sills at the Dalles and Chaudière rapids ( Fig.…”

Early Holocene drought in the Laurentian Great Lakes basin caused hydrologic closure of Georgian Bay

“…5, 6; Table 1). Isostatic rebound of the North Bay outlet contributed to rising lake levels, ultimately producing the Nipissing Great Lakes in the Huron-Michigan basin (Lewis et al 2008a). Peak aridity shifted west of the Great Lakes basin after *8,000 cal (*7,200) BP, and a modern climate was established at Hayes Lake northwest of Lake Superior by 7,800 cal (7,000) BP (Fig.…”

“…The lakes owe their origin to the multiple Quaternary glaciations that scoured their basins from pre-glacial river Fig. 1 Early Holocene lake level in the Georgian Bay and main Lake Huron basins (modified from Lewis et al 2008a). Except for short Mattawa highstands, lake level fell to or below the North Bay outlet (NB) following retreat of Laurentide ice, which produced closed lakes in the basins of the Laurentian Great Lakes.…”

“…Lake level fell *30 m below the sills in the North Bay outlet, approximately 5 m below the level of late Lake Stanley in the main basin of Lake Huron valleys. These currently interconnected lakes drain into the Atlantic Ocean via the St. Lawrence River, but the modern drainage pattern only developed during the mid-Holocene, when postglacial isostatic rebound transferred drainage from the upper Great Lakes to the lower Great Lakes during the Nipissing Great Lakes phase (Lewis et al 2008a). Variations in the ice front and in the elevation of the land early in postglacial time produced the complex hydrology of the early Great Lakes, with its remarkable lake level fluctuations (Rea et al 1994;Lewis et al 2008a).…”

Evidence of early Holocene closed-basin conditions in the Huron-Georgian basins from within the North Bay outlet of the upper Great Lakes

“…Previous research has attributed these fluctuations to glacial Lake Agassiz overflow, Laurentide Ice Sheet runoff, and non-glacial runoff and evaporation that reflect contemporary climatic conditions, all superimposed upon gradual differential tilting of the basins (see Lewis and Anderson 1989;Lewis et al 1994Lewis et al , 2005Lewis et al , 2007Rea et al 1994b). The closed-basin interval occurring between 9.0 and 8.4 ka cal BP is thought to be the product of a climate that was colder-drier and possibly windier than present (Lewis et al 2005(Lewis et al , 2007(Lewis et al , 2008, and it developed after overflow from glacial Lake Agassiz and Laurentide Ice Sheet meltwater became diverted into glacial Lake Ojibway and thus bypassed the upper Great Lake basins.…”