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

Sub-bottom profiling was conducted at eight sub-basins within the lower French River area, Ontario, to investigate deposits preserved within the ancient North Bay outlet. Ten cores were collected that targeted the four depositional acoustic facies identified in the sub-bottom profiling records. The rhythmically laminated/bedded glaciolacustrine deposits of facies I are interpreted to have aggraded within glacial Lake Algonquin and its associated recessional lakes that persisted between 13,000 and 11,300 cal BP (~11,100 and 9,900 BP). The majority of the facies II, III and IV lacustrine deposits accumulated between about 9,500 cal BP (~8,500 BP) and the mid-Holocene, based on radiocarbon-dated organic materials. These deposits represent sedimentation within a ‘large’ lake during the late portion of the Mattawa-Stanley phase, and the Nipissing transgression, Nipissing Great Lakes and post-Nipissing recession phases of lake levels. Two sets of organic-rich sand beds are preserved within facies II deposits and reveal that the large lake lacustrine depositional environment was interrupted during the late Mattawa-Stanley phase between 9,500–9,300 and 9,000–8,400 cal BP (~8,500–8,300 and ~8,000–7,600 BP), when the water surface of Lake Hough fell below the outlet threshold and the lake basin became hydrologically closed. Pre-9,500 cal BP (~8,500 BP), the early and middle portions of the Mattawa-Stanley phase were dominated by erosion, as reflected by an unconformity at the base of facies II that occurs widely in the sub-basins and the general lack of preserved deposits for these intervals in the cores. This erosion is attributed to wave action and fluvial scouring within the outlet mouth during the early and mid-Stanley-Hough low stages and relates specifically to the period when the flowing portion of the North Bay outlet was situated over the lower French River area. This study reveals that the majority of the post-glacial deposits accumulated after the outlet threshold had shifted permanently eastwards and the lower French River area was inundated under the multiple phases of the large lake occupying the Nipissing Lowlands and Georgian-Huron basins, extending well into the mid-Holocene. The occurrence of deposits marking two closed-basin intervals during the late Stanley-Hough stage are well preserved locally within the lacustrine depositional sequence, but identifying earlier closed-basin intervals from the French River stratigraphy is hindered by the lack of preserved pre-9,500 cal BP (~8,500 BP) post-glacial deposits.     

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

Multiple proxies record aridity in the northern Great Lakes basin ~8,800–8,000 cal (8,000–7,200) BP when water levels fell below outlets in the Michigan, Huron and Georgian Bay basins. Pollen-climate transfer function calculations on radiocarbon-dated pollen profiles from small lakes from Minnesota to eastern Ontario show that a drier climate was sufficient to lower the Great Lakes, in particular Georgian Bay, to closed basins. The best modern climate analog for the early Holocene late Lake Hough stage in the Georgian Bay basin is Black Bass Lake near Brainerd MN. Modern annual precipitation at Brainerd is ~35% lower than at Huntsville ON, in the Georgian Bay catchment; warmer summers and colder, less snowy winters make Brainerd drier than the Georgian Bay snow belt. These values parallel transfer function reconstructions for the early Holocene from pollen records at five small lakes in the Georgian Bay drainage basin. Higher evaporation and evapotranspiration due to greater seasonality during the early Holocene produced a deficit in effective moisture in Georgian Bay that is recorded by the jack/red pine pollen zone that spanned ~8,800–8,200 cal (8,000–7,500) BP. This deficit drove late Lake Hough ~5 m below Lake Stanley in the Huron basin, following diversion of Laurentide Ice sheet meltwater from the Great Lakes basin. The level of Georgian Bay largely depends not on fluvial input from its own drainage basin, but rather from Lake Superior, where the early Holocene moisture deficit was greater. Reconstruction of paleoclimates in Minnesota, northwestern Ontario and Wisconsin produced a closed lake in the Superior basin, which removed the main water input to Georgian Bay. Once the inflow through the St. Marys River was reduced and inflow from other tributary streams was adjusted for isostatic and climatic differences, input was <5% of modern values. Consequent high evaporation rates produced a significant fall in lake level in the Georgian Bay basin and a negative water budget. This reduction in basin supply, together with the high conductivity of stagnant water in late Lake Hough inferred from microfossils in lowstand sediments, peaked at the end of the jack/red pine zone, ~8,300–8,200 (7,450 ± 90) BP. These major hydrologic changes resulting from climate change in the recent geologic past draw attention to possible declines of the Great Lakes under future climates.     

A new water-level history for Lake Ontario basin: evidence for a climate-driven early Holocene lowstand

Piston cores from deep-water bottom deposits in Lake Ontario contain shallow-water sediments such as, shell-rich sand and silt, marl, gyttja, and formerly exposed shore deposits including woody detritus, peat, sand and gravel, that are indicative of past periods of significantly lower water levels. These and other water-level indicators such as changes in rates of sedimentation, mollusc shells, pollen, and plant macrofossils were integrated to derive a new water-level history for Lake Ontario basin using an empirical model of isostatic adjustment for the Great Lakes basin to restore dated remnants of former lake levels to their original elevations. The earliest dated low-level feature is the Grimsby-Oakville bar which was constructed in the western end of the lake during a near stillstand at 11–10.4 (12.9–12.3 cal) ka BP when Early Lake Ontario was confluent with the Champlain Sea. Rising Lake Ontario basin outlet sills, a consequence of differential isostatic rebound, severed the connection with Champlain Sea and, in combination with the switch of inflowing Lake Algonquin drainage northward to Ottawa River valley via outlets near North Bay and an early Holocene dry climate with enhanced evaporation, forced Lake Ontario into a basin-wide lowstand between 10.4 and 7.5 (12.3 and 8.3 cal) ka BP. During this time, Lake Ontario operated as a closed basin with no outlets, and sites such as Hamilton Harbour, Bay of Quinte, Henderson Harbor, and a site near Amherst Island existed as small isolated basins above the main lake characterized by shallow-water, lagoonal or marsh deposits and fossils indicative of littoral habitats and newly exposed mudflats. Rising lake levels resulting from increased atmospheric water supply brought Lake Ontario above the outlet sills into an open, overflowing state ending the closed phase of the lake by ~7.5 (8.3 cal) ka BP. Lake levels continued to rise steadily above the Thousand Islands sill through mid-to-late Holocene time culminating at the level of modern Lake Ontario. The early and middle Holocene lake-level changes are supported by temperature and precipitation trends derived from pollen-climate transfer functions applied to Roblin Lake on the north side of Lake Ontario.     

The sedimentation history of Lake Huron and Georgian Bay: results from analysis of seismic reflection profiles

An extensive seismic reflection profile survey conducted concurrently with a sediment coring program in northern Lake Huron, Georgian Bay, and the North Channel revealed a detailed Holocene lake level history. Seven acoustic sequences were identified in the seismic stratigraphy, and these sequences show great variation in both the character and the spatial distribution of sediment deposition through time. The depths to the acoustically-defined sequence boundaries were digitized from the analog seismic records and merged with Loran-C navigation records from the cruise, yielding a three-dimensional record of the location of each sequence boundary. Thicknesses of the sequences were calculated from these depths, and a minimum-curvature spline surface was fit to the thickness data. These surfaces were used to construct isopach maps which show the trends in thickness of sediment accumulation throughout the lake basins for each of the sequences. ¹⁴C-AMS dates of materials from the cores fixed the dates of the sediment sequence boundaries, allowing sediment accumulation rates to be calculated. The distribution of sedimentation in the basins as shown on the isopach maps allowed assessment of sediment transport and water flow through the basins over time, which when combined with the work of Lewis & Anderson (1989), provides a detailed record of the transport and drainage of water through these basins as the Wisconsinan ice sheet retreated and isostatic rebound opened and closed outlets. Reversals of flow direction through the Straits of Mackinac and through the channels connecting Lake Huron and Georgian Bay and the North Channel are indicated by changes in sediment thickness distributions.     

Constraining Holocene lake levels and coastal dune activity in the Lake Michigan basin

Sediment cores collected from embayed lakes along the east-central coast of Lake Michigan are used to construct aeolian sand records of past coastal dune mobility, and to constrain former lake levels in the Lake Michigan basin. Time series analysis of sand cycles based on the weight-percent aeolian sand within lacustrine sediment, reveals statistically significant spectral peaks that coincide with established lake level cycles in Lake Michigan and the Gleissberg sunspot cycle of minima. Longer cycles of ~ 800 and ~ 2200 years were also identified that correspond to solar cycles. Shorter cycles between 80 and 220 years suggest a link between coastal dune mobility, climate, and lake levels in the Lake Michigan basin. Radiocarbon-dated sedimentary contacts of lacustrine sediment overlying wetland sediment record the Nipissing transgression in the Lake Michigan basin. Lake level rise closely mimics the predicted uplift of the North Bay outlet, with lake level rise slowing when outflow was transferred to the Port Huron/Sarnia outlet. The Nipissing highstand was reached after 5000 cal (4.4 ka) BP.     

Constrained age of Glacial Lake Narragansett and the deglacial chronology of the Laurentide Ice Sheet in southeastern New England

The lack of radiocarbon ages and correlated varve sequences in southeastern New England has left the deglacial chronology of the region poorly constrained. A 265-year varve series from Glacial Lake Narragansett was constructed from eight continuous sediment cores collected from the Providence River, Narragansett Bay, Rhode Island. This varve series could not be correlated with either the North American Varve Chronology or other varve sequences from southern New England or southeastern New York. The uncorrelated varve sequences presented here represent the minimum time of deposition within the northern segment of Glacial Lake Narragansett. These sequences, used in conjunction with the calibrated North American Varve Chronology and cosmogenic exposure ages from recessional end moraines, provide minimum (>19,400 cal BP) and maximum (<20,500 cal BP) ages for Glacial Lake Narragansett. Correlations with the updated Greenland (NGRIP and GRIP) ice core records suggest that cold periods associated with moraine formation are 200–250 years older than the cosmogenic exposure ages. Whereas many studies refer to the last glacial maximum occurring from 20,000 to 18,000 cal BP, the constrained age of Glacial Lake Narragansett suggests that at least for the southeastern portion of the Laurentide Ice Sheet, deglaciation was well underway by this time.     

An 8,900-year-old forest drowned by Lake Superior: hydrological and paleoecological implications

Exposures along the lower Kaministiquia River (near Thunder Bay, Ontario, Canada) provide insight into early Holocene lake level fluctuations and paleoenvironmental conditions in the northwestern Lake Superior basin. These exposures show at least two large paleochannels which were downcut into offshore sediments, and were later filled with >2 m of sand, ~3 m of rhythmically laminated silt and clay, and ~6 m of interbedded silt and sand. Buried by the rhythmically laminated silty clay unit is a well-preserved organic deposit with abundant plant macrofossils from terrestrial and emergent taxa, including several upright tree trunks. Three AMS radiocarbon ages were obtained on wood and conifer cones from this deposit: 8,135 ± 25 (9,130–9,010 cal), 8,010 ± 25 (9,010–8,780 cal), and 7,990 ± 20 (8,990–8,770 cal) BP. This sequence records an early postglacial high-water phase, followed by the Houghton lowstand, and reflooding of the lower Kaministiquia River Valley. The drop in lake level associated with the Houghton phase forced the ancestral Kaministiquia River to downcut. By ~9,100 cal (~8,100) BP, older channels eroded into subaqueous underflow fan deposits in the Thunder Bay area near Fort William Historical Park (FWHP) were abandoned and colonized by a Picea-Abies-Larix forest. Based on stratigraphic data corrected for differential isostatic rebound, the lake was below the Sault Ste. Marie bedrock sill between at least 9,100 cal (8,100) and 8,900 cal (8,000) BP. Shortly after 8,900 cal BP, the lake quickly rose and buried in situ lowland vegetation at FWHP with varved sediments. We argue that this transgression was due to overflow from glacial Lakes Agassiz or Ojibway associated with the retreat of the Laurentide Ice Sheet from the Nakina moraine and/or the Cochrane surge margins in the Hudson Bay Lowlands. A continued rise in lake level after 6,420 ± 20 (7,400 cal) BP at FWHP may record uplift of the North Bay outlet above the Sault Ste. Marie bedrock sill and the onset of the Nipissing transgression in the Lake Superior basin.     

Sediment geochemistry of Lake Daihai,north-central China: implications for catchment weathering and climate change during the Holocene

A 12.87-m-long sediment core was retrieved from closed-basin Lake Daihai in the monsoon–arid transition zone of north-central China. Oxides of major elements and their ratios normalized to Al in the AMS-¹⁴C-dated core were employed to evaluate chemical weathering intensity (CWI) in the lake drainage basin, which reflects hydrothermal conditions in the study area. Lower CWI periods occurred prior to 14.5 ka BP, and during the intervals ca. 11.7–10.3, 3.5–3.2, 2.6–1.7 ka BP, and 1.2–0 ka BP, indicating relatively low temperatures and moisture availability. Greater CWI during the intervening periods ca. 14.5–11.7, 10.3–9.0, 3.2–2.6, and 1.7–1.2 ka BP, with the maximum CWI at ca. 6.7–3.5 ka BP, imply ameliorated hydrothermal conditions in the lake basin, i.e. higher temperatures and precipitation. Exceptionally low CWI, associated with high CaO/MgO ratio during ca. 9.0–6.7 ka BP, suggests higher evaporation rates in the area under warmer temperature. Overall, CWI displays in-phase variations with changes in organic matter (TOC, TN), carbonate (CaCO₃) and pollen assemblages, all of which are related to variations in monsoon effective precipitation. High CWI indicates strong monsoon-induced precipitation, whereas low CWI reflects a weak precipitation regime. The optimum hydrothermal status, recorded by the strongest CWI and maximum monsoon effective precipitation during ca. 6.7–3.5 ka BP defines the Holocene climate optimum (HCO) in the Lake Daihai region. These results indicate that the HCO prevails after the early Holocene in the monsoon–arid transition zone of north-central China. Temperature and precipitation variations during most of the Holocene, inferred from the lake sediments, are due largely to insolation forcing. Dry but warm conditions ca. 9.0–6.7 ka BP, however, probably reflect the complex interactions between insolation and geography (e.g. altitude and local topography).     

Formation and early history of Lakes Pepin and St. Croix of the upper Mississippi River

Study of Lake Pepin and Lake St. Croix began more than a century ago, but new information has permitted a closer look at the geologic history of these two riverine lakes located on the upper Mississippi River system. Drainages from large proglacial lakes Agassiz and Duluth at the end of the last glaciation helped shape the current valleys. As high-discharge outlet waters receded, tributary streams deposited fans of sediment in the incised river valleys. These tributary fans dammed the main river, forming riverine lakes. Lake Pepin was previously thought to be a single long continuous lake, extending for 80 km from its dam at the Chippewa River fan all the way up to St. Paul, with an arm extending up the St. Croix valley. Recent borings taken at bridge and dam locations show more than a single section of lake sediments, indicating a more complex history. The Minnesota and Mississippi Rivers did not always follow their current paths. Valleys cut into bedrock but now buried by glacial sediment indicate former river courses, with the most recent of these from the last interglacial period marked at the surface by chains of lakes. The morphology of the Mississippi valley bottom, and thus the morphology of Lake Pepin as it filled the valley, is reflect in part by the existence of these old valleys but also by the presence of glacial outwash terraces and the alluvial fans of tributary streams. A sediment core taken in Lake Pepin near Lake City had a piece of wood in gravels just below lake sediments that dated to 10.3 ka cal. BP, indicating that the lake formed as the Chippewa River fan grew shortly after the floodwaters of Lakes Agassiz and Duluth receded. Data from new borings indicate small lakes were dammed behind several tributary fans in the Mississippi River valley between the modern Lake Pepin and St. Paul. One tributary lake, here called Early Lake Vermillion, may have hydraulically dammed the St. Croix River, creating an incipient Lake St. Croix. The tributary fans from the Vermillion River, the Cannon River, and the Chippewa River all served to segment the main river valley into a series of riverine lakes. Later the growth of the Chippewa fan surpassed that of the Vermillion and Cannon fans to create a single large lake, here called late Lake Pepin, which extended upstream to St. Paul. Sediment cores taken from Lake Pepin did not have significant organic matter to develop a chronology from radiocarbon dating. Rather, magnetic features were matched with those from a Lake St. Croix core, which did have a known radiocarbon chronology. The Pepin delta migration rate was then estimated by projecting the elevations of the top of the buried lake sediments to the dated Lake Pepin core, using an estimated slope of 10 cm/km, the current slope of Lake Pepin sediment surface. By these approximations, the Lake Pepin delta prograded past Hastings 6.0 ka cal BP and Red Wing 1.4 ka cal BP. This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue.     

A sedimentary and geochemical record of water-level changes from Rantin Lake, Yukon, Canada

A multi-proxy analysis of two sediment cores from Rantin Lake are used to reconstruct past lake-level changes and to make inferences about millennial-scale variations in precipitation/evaporation (P/E) balance in the southern Yukon, Canada between 10,900 and 3,100?cal?yr BP. Analyses of calcium carbonate and organic matter concentration, magnetic susceptibility, titanium content, dry bulk density, and macrofossils are used to reconstruct water-level changes. The development of sand layers and deformed sediments at the deep-water core site (i.e. Core A-06) prior to ~10,900?cal?yr BP suggest that lake level was lower at this time. Fine-grained organic sediment deposited from 10,600 to 9,500?cal?yr BP indicates a rise in lake level. The formation of an unconformity at the shallow cores site (Core C-06) and the deposition of shallow-water calcium carbonate-rich facies at the Core A-06 site between ~9,500 and ~8,500?cal?yr BP suggest lower lake levels at this time. Shallow-water facies gradually transition into a sand layer that likely represents shoreline reworking during an extreme lowstand that occurred at ~8,400?cal?yr BP. Following this low water level, fine-grained organic-rich sediment formed by ~8,200?cal?yr BP, suggesting deeper water conditions at core site A-06. Calcium carbonate concentrations are relatively low in sediment deposited from ~6,300 to 3,100?cal?yr BP in Core A-06, indicating that lake level was comparatively higher during the middle and late Holocene. In general, results from this study suggest that the early Holocene was characterized by high P/E from ~10,500 to 9,500?cal?yr BP, low P/E from ~9,500 to 8,400?cal?yr BP, and return to higher P/E from ~8,200 to 3,100?cal?yr BP.     

Spatially discontinuous modern sedimentation in Georgian Bay, Huron Basin, Great Lakes

High-resolution seismic reflection profile data show that the modern sediment cover (over the last 150 years) in Georgian Bay is thin and spatially discontinuous. Sediments rich in ragweed pollen, largely derived from siltation linked to land clearing and European settlement, form a thin, discontinuous veneer on the lakebed. Much of the lakebed consists of exposed sediments deposited during the late glacial or early postglacial. Accumulation rates of modern sediments range from < 0 mm/year (net erosion) to ∼3.2 mm/year, often within a few hundred metres spatially. These rates are much lower than those reported for the main basin of Lake Huron and the other Great Lakes, and are attributed to the low sediment supply. Only a few small rivers flow into Georgian Bay, and most of the basin is surrounded by bedrock of Precambrian gneiss and granite to the east, and Silurian dolostone, limestone and shale to the west. Thick deposits of Pleistocene drift, found on the Georgian Bay shoreline only between Meaford and Port Severn, are the main sediment source for the entire basin at present. Holocene to modern sediments are even absent from some deep basins of Georgian Bay. These findings have implications for the ultimate fate of anthropogenic contaminants in Georgian Bay. While microfossil assemblages in the ragweed-rich sediments record increased eutrophication over the last 150 years, most pollutants generated in the Georgian Bay catchment are not accumulating on the lakebed and are probably exported from the Bay.     

Early Holocene brackish closed basin conditions in Georgian Bay, Ontario, Canada: microfossil (thecamoebian and pollen) evidence

Microfossils have been critical in unravelling the complex postglacial history of Georgian Bay. Thecamoebians (testate amoebae/rhizopods) record paleolimnological conditions, and pollen stratigraphy allows correlation across the basin, where sedimentation has been spatially and temporally discontinuous. Because parts of Georgian Bay have been non-depositional or erosional since the end of the Nipissing transgression (~5,000 (5,800 cal) BP), early Holocene features are exposed on the lakebed. Among these are shoreline features, such as submerged beaches and relict channels, associated with low-level Lake Hough that was driven far below the level of basin overflow. Cores taken throughout Georgian Bay record the existence of closed basin conditions that persisted several centuries around 7,500 (8,300 cal) BP, corresponding to the late Lake Hough lowstand. Evidence for hydrologic closure includes a low-diversity centropyxid-dominated thecamoebian fauna around the boundary between pollen subzones 2a and 2b in the Flowerpot Beach core, Flowerpot and Killarney basins, and in Severn Sound. This low-diversity centropyxid-dominated fauna is interpreted as recording the development of slightly brackish conditions as a result of a hydrologic deficit associated with relatively arid conditions in the Great Lakes basin during the early Holocene pine zone (~8,800–7,200 (9,900–8,050 cal) BP). The rest of the Holocene record in Georgian Bay (where it is preserved) is more diverse and dominated by difflugiid thecamoebians: predominantly Difflugia oblonga prior to human settlement, and Cucurbitella tricuspis since high-density human occupation and agriculture (and resulting eutrophication) began with the Wendat First Nations people around Severn Sound about 750 years ago. The implication that water budget fluctuations leading to discernible variations in lake level and water chemistry occurred in the relatively recent geologic past is significant to studies of global climate change and resource management in the Great Lakes, one of the world’s largest freshwater resources.     

The sedimentary and palynological records of Serpent River Bog,and revised early Holocene lake-level changes in the Lake Huron and Georgian Bay region

Serpent River Bog lies north of North Channel, 10 m above Lake Huron and 15 m below the Nipissing Great Lake level. A 2.3 m Holocene sequence contains distinct alternating beds of inorganic clastic clay and organic peat that are interpreted as evidence of successive inundation and isolation by highstands and lowstands of the large Huron-Basin lake. Lowstand phases are confirmed by the presence of shallow-water pollen and plant macrofossil remains in peat units. Twelve ¹⁴C dates on peat, wood and plant macrofossils combined with previously published ¹⁴C ages of lake-level indicators confirm much of the known early Holocene lake-level history with one notable exception. A new Late Mattawa highstand (8,390 [9,400 cal]–8,220 [9,200 cal] BP) evidenced by a sticky blue-grey clay bed is tied to outburst floods of glacial Lake Minong during erosion of the Nadoway drift barrier in the eastern Lake Superior basin. A subsequent Late Mattawa highstand (8,110 [9,040 cal]–8,060 [8,970 cal] BP) is attributed to enhanced meltwater inflows that first had deposited thick varves throughout Superior Basin. Inundation by the Nadoway floods and possibly the last Mattawa flood were likely responsible for termination of the Olson Forest (southern Lake Michigan). A pollen diagram supports the recognized progression of Holocene vegetation, and defines a subzone implying a very dry, cool climate about 7.8–7.5 (8.6–8.3 cal) ka BP based on the Alnus crispa profile during the Late Stanley lowstand. A new date of 9,470 ± 25 (10,680–10,750 cal) BP on basal peat over lacustrine clay at Espanola West Bog supports the previous interpretation of the Early Mattawa highstand at ca. 9,500 (10,740 cal) BP. The organic and clastic sediment units at these two bogs are correlated with other records showing coherent evidence of Holocene repeated inundation and isolation around northern Lake Huron. Taken together the previous and new lake-level data suggest that the Huron and Georgian basin lakes were mainly closed lowstands throughout early Holocene time except for short-lived highstands. Three of the lowstands were exceptionally low, and likely caused three episodes of offshore sediment erosion which had been previously identified as seismo-stratigraphic sequence boundaries.     

Lake levels in the Erie Basin of the Laurentian Great Lakes

Water levels in the Lake Erie basin are inferred from glacial lake times to present. An era of early to middle Holocene lowstands is defined below outlets by a submerged paleo-beach, and truncated reflectors in glaciolacustrine sediment beneath a mud-covered wave-cut terrace. Also, the glacial clay surface above the paleo-shore level has elevated shear strength because of porewater drainage during subaerial exposure. Below the paleo-shore where exposure did not occur, clay strength remained normal. Sedimentation rates were reduced during the lowstands. The distortion of once-level shore zone indicators by differential glacial rebound was removed by computing original elevations of the indicators using an empirical model of rebound based on observations of upwarped former lake shorelines. Erie water-level history was inferred from a plot of the original elevations of lake-level constraints and outlets versus age. The lake history was validated by reference to ~83 water-level indicators, not used as constraints. During the deglaciation, lake-crossing moraines were likely eroded by fluvial drainage into low-level Lake Ypsilanti and a subsequent unnamed low lake to produce the Lorain Valley and Pennsylvania Channel. Once inflow from the upper Great Lakes basins was directed to Ottawa Valley about 10,400 (12,270 cal BP), Erie water levels descended in a dry, evaporative climate to a closed lowstand during which ostracode δ¹⁸O increased ~2‰ above present values. Lake level began to rise 6,000 to 7,000 (6,830 to 7,860 cal) BP in response to increased atmospheric moisture and later, to northern inflow as the Nipissing Transgression returned upper Great Lakes drainage to Lake Erie by about 5,200 (6,000 cal) BP. At that time, the lake overflowed the uplifted Lyell–Johnson Sill north (downstream) of the present Niagara Falls at higher-than-present levels. After recession of the Falls breached this sill about ~3,500 (~3,770 cal) BP, Lake Erie fell 3–4 m to its present Fort Erie–Buffalo Sill. The extended low-water phase with its isolated sub-basins could have restricted migration of aquatic fauna. The early to middle Holocene closed-basin response highlights the sensitivity of Lake Erie to climatic reductions in its water budget.     

Late-Glacial and Holocene Record of Lake Levels of Mathews Pond and Whitehead Lake,Northern Maine,USA

Paleohydrology studies at Mathews Pond and Whitehead Lake in northern Maine revealed synchronous changes in lake levels from about 12,000 ¹⁴C yrs BP to the present. We analyzed gross sediment structure, organic and carbonate content, mineral grain size, and macrofossils of six cores from each of the two lakes, and obtained 72 radiocarbon dates. Interpretation of this paleo-environmental data suggests that the late-glacial and Younger Dryas climate was dry, and lake levels were low. Early Holocene lake levels were considerably higher but declined for an interval from about 8000 to 7200 ¹⁴C yrs BP. Sediment of both lakes contains evidence of a dry period at ∼7400 ¹⁴C yrs BP (8200 cal yr). Lake levels of both sites declined abruptly about 4800 ¹⁴C yrs BP and remained low until 3000 ¹⁴C yrs BP. Modern lake levels were achieved only within the past 600 years. The west-to-east, time-transgressive nature of lake-level changes from several sites across northeastern North America suggests periodic changes in atmospheric circulation patterns as a driving force behind observed moisture balance changes. Electronic supplementary material to this article is available at and accessible for authorized users.     

Geological and geophysical evidence for pre-Nipissing (>5,000 years BP) transgression infilled valleys in the Lake Huron basin,Ontario

Lake Algonquin, the largest glacial lake of the Great Lakes area, ended prior to 10,000 years BP by drainage to the Ottawa Valley as the North Bay outlet was deglaciated. At that time, the outlet area was isostatically downwarped more than 100 m; resulting low water, river-linked lakes Chippewa, Stanley, and Hough, lowstands in the basins of lakes Michigan, Huron, and Georgian Bay respectively, were much below present lake level. While water levels were low, about half of the present lake area was dry land. The land above the lowstands was dissected by streams and became forested. Uplift of the North Bay outlet between 10,000 and 5,000 years BP raised lake level to above the present (the Nipissing transgression), submerging the forest and valley system. Submerged stumps from those forests have often been encountered on the present lake floor; some stumps have been dated. Four sites in Ontario (Parkhill, Owen Sound, St. Joseph Island, Meaford) provide on-land evidence of pre-Nipissing drainage and valley formation. Radiocarbon ages of valley fill organic materials range from 7,310 to 5,410 years BP. At three sites, present drainage is known to be displaced from the pre-Nipissing drainage. Geophysical methods (EM, GPR, resistivity) have been used to refine valley location and morphology at Parkhill and Meaford. There is the potential of tracing the valleys down slope to the low-water shorelines with shipboard geophysics, with implications for archaeology, hydrology and hydrogeology, paleogeography, and Great Lakes history. This is the eighth in a series of ten papers published in this special issue of Journal of Paleolimnology. These papers were presented at the 47th Annual Meeting of the International Association for Great Lakes Research (2004), held at the University of Waterloo, Waterloo, Ontario, Canada. P.F. Karrow and C.F.M. Lewis were guest editors of this special issue.     

Variations in the oxygen-isotope composition of ancient Lake Superior between 10,600 and 8,800 cal BP

Variations in the oxygen-isotope composition of paleo-water bodies in the Lake Superior Basin provide information about the timing and pathways of glacial meltwater inflow into and within the Lake Superior Basin. Here, the oxygen-isotope compositions of Lake Superior have been determined using ostracodes from four sediment cores from across the Basin (Duluth, Caribou and Ile Parisienne sub-basins, Thunder Bay trough). The δ¹⁸O values indicate that lake water (Lake Minong) at ~10,600–10,400 cal [~9,400–9,250] BP was dominated by glacial meltwater derived from Lake Agassiz and the Laurentide Ice Sheet (LIS). From that time to ~9,000 cal [~8,100] BP, a period associated with formation of thick varves across the Lake Superior Basin, the δ¹⁸O values of Lake Minong decreased even further (−24 to −28‰), symptomatic of an increasing influx of glacial meltwater. Its supply was reduced between ~9,000 and ~8,900 cal [~8,100–8,000] BP, and lake water δ¹⁸O values grew higher by several per mil during this period. Between ~8,900 and ~8,800 cal [~8,000–7,950] BP, there was a return to δ¹⁸O values as low as −29‰ in some parts of the Lake Superior Basin, indicating a renewed influx of glacial meltwater before its final termination at ~8,800–8,700 cal [~7,950–7,900] BP. The sub-basins in the Lake Superior Basin generally displayed very similar patterns of lake water δ¹⁸O values, typical of a well-mixed system. The final stage of glacial meltwater input, however, was largely expressed near its input (Thunder Bay trough) and recognizable in dampened form mainly in the Duluth sub-basin to the west. Water in the easternmost Ile Parisienne sub-basin was enriched in ¹⁸O relative to the rest of the lake, particularly after ~10,000 cal [~8,900] BP, probably because of a strong influence of local precipitation/runoff, and perhaps also enhanced evaporation. By ~9,200 cal [~8,250] BP, lake water δ¹⁸O values in the Ile Parisienne sub-basin were similar to the adjacent Lake Huron Basin, suggesting a strong hydraulic connection between the two water bodies, and common responses to southern Ontario’s shift to warmer and dry climatic conditions after ~9,000 cal [~8,100] BP.     

Reconstructing lake and drainage basin history using terrestrial sediment layers: analysis of cores from a post-glacial lake in New England, USA

Four sediment cores and twenty-five ¹⁴C ages from Ritterbush Pond in northern Vermont provide a detailed and continuous temporal record of Holocene lake and watershed dynamics. Using visual logs, carbon content, magnetic susceptibility, stable isotope signatures, and X-radiography, all measured at 1-cm scale, we identify and date discrete layers of terrestrially-derived sediment in the organic-rich, lacustrine gyttja. These inorganic layers range in thickness from <1 mm to >10 cm and range in grain size and sorting from homogeneous silt to graded sand. AMS radiocarbon ages both from macrofossils within the thickest layers, and gyttja bracketing these layers, provide the basis for correlation among the cores, the dating of 52 basin-wide sedimentation events, and the development of a detailed sedimentation chronology for the Holocene.Physical, chemical, and isotopic analyses suggest the inorganic layers are terrestrially derived and result from hydrologic events large enough to erode and transport sediment from the watershed into the pond. The temporal and spatial distribution of the inorganic layers suggests changing basin-wide sedimentation and thus erosion dynamics since deglaciation over 12,000 years ago. Specifically, for intervals lasting 400 to 1000 years, during the early (>8600 cal yBP), middle (6400 to 6800 cal yBP) and late Holocene (1800 to 2600 cal yBP), the Ritterbush Pond watershed eroded more rapidly than at other times and terrestrially derived material poured into the pond. Analysis of Ritterbush Pond sediments demonstrates the potential for North American lakes to preserve a record of drainage basin dynamics.     

Paleolimnology of three Jackman Sound Lakes,Southern Baffin Island,based on down-core diatom analyses

Three lakes, informally named Lakes Inqua, Instaar and Mercer, from the Jackman Sound area in Southern Baffin Island were cored. The elevation of the three lakes are 36 m above high tide (aht), 10 m aht and 1 m aht. The cores from Lakes Inqua and Mercer penetrated the marine/lacustrine boundary; the core from Lake Instaar is estimated to have come within ca. 5 cm of this boundary. In addition, grab samples and water samples were retrieved from the lakes. The cores have been ¹⁴C dated (AMS). Emergence of the three lake basins from the sea occurred approximately 8650 BP (Lake Inqua), 8630 BP (Lake Instaar) and 7900 BP (Lake Mercer, averaged date). This suggests a very rapid rate (>5 m/100 yrs) of glacio-isostatic rebound for this area. Down-core analyses of diatom assemblages indicate that the paleolimnology in the three lakes was similar. The diatom analyses suggest a change in climate between approximately 8000 and 6000 BP, which is also reflected in the marine record from the same area, and the onset of the neoglacial period around 4500 to 3800 BP. A decrease in diatom-inferred pH is evident in the lakes' development and can probably be related to the general change of the watershed vegetation with time.     

Holocene sedimentation in Lake Winnipeg, Manitoba, Canada: implications of compositional and textural variations

Two seismic facies were recognized in the sedimentary sequence overlying acoustic basement in Lake Winnipeg. The upper facies, which overlies a regional unconformity, is termed the Lake Winnipeg Sequence. Based on the seismostratigraphy, lithostratigraphy, and radiocarbon dates of approximately 4000 and 7000 yr BP from material collected directly over the unconformity in the southern and northern parts of the lake, respectively, this facies has been interpreted as representing Holocene sedimentation. Results of compositional and textural analyses of the Holocene sediment (Winnipeg sediment) from thirteen long (>2 m) cores indicate a transgressional sequence throughout the basin. In the South Basin, the generally fining upward sequence is characterized at the base by silt-sized detrital carbonate minerals, quartz and feldspar which decrease in concentration upward. In this basin, the high carbonate content and V/Al and Zn/Al ratios are indicative of a Paleozoic and Cretaceous provenance for sediment derived from glacial deposits through shoreline erosion and fluvial transport, via the Red River. Sedimentation in the central part of the lake and the North Basin is attributed to shoreline erosion of sand and gravel beaches. Consequently, the texture of these sediments is generally coarser than in the South Basin, and the composition primarily reflects a Paleozoic and Precambrian provenance. The basin-wide decrease in Ca, total carbonate minerals, dolomite and calcite concentrations upward in the cores is reflected by a decrease in the detrital carbonate component in all but the most northern cores. Other basin-wide trends show an upward increase in organic content in all cores. An increase in grain size near the top of most cores suggests a major, basin-wide change in sedimentation within the last, approximately 900 years in the South Basin.