Lake Algonquin Research Articles

Onshore–offshore correlation of central Lake Erie glacial deposits

Dive observations, echogram transects, core sampling, and a seismic profile revealed that the lake bed of north-central Lake Erie is an extensive terrace cut by storm waves and currents. The terrace is an erosional unconformity on which Late Wisconsinan (Port Bruce and Mackinaw) glacial units crop out. Beds of massive diamictons, and glaciolacustrine sediments containing parallel reflections, crop out alternately from west to east, resulting from an oscillatory ice retreat. These beds correlate with the Port Stanley Drift (Port Bruce phase) and Wentworth Drift (Mackinaw phase) exposed in nearby shore bluffs and onshore moraines. The Port Bruce glacier and earlier readvances formed ice tongues and ice shelves in the central basin. Diamicton layers, some with debris flows, constitute the Port Stanley Till (offshore units M and O). A glaciolacustrine unit N was deposited during Port Bruce glacier recessions. Glaciolacustrine unit P lies between Port Bruce unit O and the Mackinaw Wentworth Till, unit Q. A subsequent glaciolacustrine unit R overlaps unit Q. The onshore Galt and Moffat moraines, composed of Wentworth Till, correlate with ridges of the Norfolk moraine unit Q which extend across Lake Erie between the base of Long Point, Ontario, and Erie, Pennsylvania. The onshore Paris moraine appears to have been eroded on the wave-cut terrace and is evident offshore only near the south shore of Lake Erie. Laminated unit S, younger than unit R, occurs in the western part of central Erie basin, and correlates with overflow of Lake Algonquin from the Huron basin.

A ∼14 000-year record of environmental change from Lake Simcoe, Canada

While the evolution of the Laurentian Great Lakes has been researched intensively, fewer studies have focused on reconstructing the history of Lake Simcoe, the fourth largest lake wholly within southern Ontario. This study uses proxy data, including ostracod valves, contained in lake sediments to reconstruct a ∼14 000-year history of paleoenvironmental change in the Lake Simcoe basin. First, oxygen-isotope compositions of ostracod valves (δ18Ovalve) are used to estimate the oxygen-isotope composition of ancient lake water, δ18Olake water. In Lake Simcoe, δ18Olake water is insensitive to changes in lake level but sensitive to shifts in temperature, capturing periods such as the early Holocene warming. This δ18Olake water record demonstrates that the delivery of meltwater from Lake Algonquin to Lake Simcoe began to slow at ∼12 050 cal yr BP, supporting previous research based on geophysical data. It also suggests that an isolated pulse of 16O-rich water from Early Lake Mattawa may have occurred from ∼10 699 to 10 591 cal yr BP. Next, stable carbon-isotope compositions of ostracod valves (δ13Cvalve) are used to estimate the stable carbon-isotope composition of dissolved inorganic carbon (δ13CDIC) in Lake Simcoe. These data, combined with ostracod assemblages, grain size, magnetic susceptibility (MS) and sediment mineralogy, support our interpretation of temperature-sensitive variation in δ18Olake water and provide further insights into in-lake conditions. A pronounced increase in accumulation rate, and subtler increases in grain size and detrital carbonate contents, between ∼8300 and ∼8000 cal yr BP may reflect the abrupt transition from cold and dry to wet and warm conditions resulting from the collapse of the Laurentide Ice Sheet (LIS) at ∼8200 cal yr BP. In summary, this study refines our understanding of the evolution of Lake Simcoe and provides a holistic picture of environmental change over the last ∼14 000 years.

Holocene, silty-sand loess downwind of dunes in Northern Michigan, USA

ABSTRACT In Michigan’s Upper Peninsula, sand dunes are widespread on the sandy floor of former Glacial Lake Algonquin, and many of the nearby uplands also have thin mantles of loess. Previous work concluded that these dunes formed during the early Holocene, long after the lake had drained. Where these dunes have migrated against bedrock uplands, many have accreted into larger dune complexes. South and east of these complexes, uplands are mantled with well-sorted sediment, comparatively rich in finer sands and much like the thin, locally sourced loess deposits in Wisconsin and Michigan. Near the dunes, this loess is typically 50–75 cm thick, and rich in very fine sands; presumably much of this sand was deposited as short-range “blow-over” while the dunes were forming. The loess thins to ≈45 cm and becomes siltier on sites farther downwind, to the southeast. Because the dune complexes contain almost no silt, the silt in the loess was likely generated by deflation of saltating sands on the lake plain, transported in suspension, and deposited generally uniformly across the forested uplands, as indicated by spatial trends in silt contents. Periodic Holocene drought may have thinned the forest and helped to intermittently facilitate this type of eolian activity.

A Multi-Proxy Reconstruction of Environmental Change in the Vicinity of the North Bay Outlet of Pro-Glacial Lake Algonquin

We present a multi-proxy study of environmental conditions during and after the recessional phases of pro-glacial Lake Algonquin in the vicinity of the North Bay outlet, Great Lakes Basin. Data presented comes from a new sedimentary profile obtained from the Balsam Creek kettle lake c. 34 km north-east of the city of North Bay. This site lies close to the north-east margin of the maximum extent of the post-Algonquin lake sequence, which drained through the Ottawa-Mattawa valley system. Our data are presented against a Bayesian age-depth model, supporting and extending regional understanding of vegetation succession in this part of north-east Ontario. The core profile provides a minimum age for the formation of the glacial outwash delta in which the kettle is set, as well as tentative timing for the Payette (post-Algonquin) lake phase. We highlight two discrete intervals during the Early Holocene, with modelled mean ages of: 8475–8040 cal. BP (332–316 cm) and 7645 cal. BP (286 cm), when climatic aridity affected the growth of vegetation within the kettle vicinity. Association with volcanic activity is posited. Cryptotephra dating to 7660–7430 cal. BP (mean age: 7580 cal. BP) is chronologically and geochemically assigned to the Mazama climactic eruption, while an earlier ash accumulation 8710–7865 cal. BP is tentatively sourced to an unknown eruption also in the Cascades region of Oregon. Outside of these periods, the Balsam Creek sequence shows considerable habitat stability and a character akin to that seen at more southerly latitudes. On this evidence we propose that access to reliable resources within kettle features could have aided the initial colonisation of northern Ontario’s environmentally dynamic early post-glacial landscape.

Evolution and diversity of two cisco forms in an outlet of glacial Lake Algonquin.

The diversity of Laurentian Great Lakes ciscoes (Coregonus artedi, sensu lato) arose via repeated local adaptive divergence including deepwater ciscoes that are now extirpated or threatened. The nigripinnis form, or Blackfin Cisco, is extirpated from the Great Lakes and remains only in Lake Nipigon. Putative nigripinnis populations were recently discovered in sympatry with artedi in a historical drainage system of glacial Lake Algonquin, the precursor of lakes Michigan and Huron. Given the apparent convergence on Great Lakes form, we labeled this form blackfin. Here, we test the hypothesis that nigripinnis may have colonized this area from the Great Lakes as a distinct lineage. It would then represent a relict occurrence of the historical diversity of Great Lakes ciscoes. Alternatively, blackfin could have evolved in situ in several lakes. We captured more than 600 individuals in the benthic or pelagic habitat in 14 lakes in or near Algonquin Provincial Park (Ontario, Canada). Fish were compared based on habitat, morphology, and genetic variation at 6,676 SNPs. Contrary to our expectations, both cisco and blackfin belonged to an Atlantic lineage that colonized the area from the east, not from the Great Lakes. Sympatric cisco and blackfin were closely related while fish from different lakes were genetically differentiated, strongly suggesting the repeated in situ origin of each form. Across lakes, there was a continuum of ecological, morphological, and genetic differentiation that could be associated with alternative resources and lake characteristics. This study uncovers a new component of cisco diversity in inland lakes of Canada that evolved independently from ciscoes of the Laurentian Great lakes. The diversity of cisco revealed in this study and across their Canadian range presents a challenge for designating conservation units at the intraspecific level within the framework of the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).

Cisco diversity in a historical drainage of glacial Lake Algonquin

Cisco (Coregonus artedi (sensu lato) Lesueur, 1818) forms matching in appearance to Blackfin Cisco from the Laurentian Great Lakes occur in four lakes in Algonquin Park, Ontario, Canada, a historical drainage of glacial Lake Algonquin (precursor of lakes Michigan and Huron). Their occurrence may represent colonization from glacial Lake Algonquin drainage patterns 13 000 calibrated years BP or independent evolution within each lake. Gill-raker numbers, temperature at capture depth during lake stratification, and hurdle models of habitat distribution are summarized. Blackfin (nigripinnis-like) in the four lakes had higher gill-raker numbers than artedi-like cisco captured in nearby lakes or within the same lake. Two lakes have a bimodal gill-raker distribution that indicate co-occurrence of two forms. Blackfin occupied the hypolimnion with a peak depth distribution at 20–25 m. Maximum depth for blackfin was 35–40 m. The presence of the opossum shrimp (Mysis diluviana Audzijonyte and Väinölä, 2005) appears necessary for the occurrence of cisco diversity in lakes but not sufficient in all cases. The presence of two forms of cisco in at least two lakes points to the possibility of the colonization hypothesis or the ecological speciation hypothesis as accounting for this phenomenon. Genetic analysis is needed to determine which of these hypotheses best accounts for the occurrence of blackfin in Algonquin Park.

Artificial Sweeteners Reveal Septic System Effluent in Rural Groundwater.

It has been widely documented that municipal wastewater treatment plant effluents are a major source of artificial sweeteners to surface waters. However, in rural areas, the extent to which septic systems contribute these same compounds to groundwater aquifers is largely unknown. We examined the occurrence of four commonly used artificial sweeteners in an unconfined sand aquifer that serves as a water supply for rural residents, as a receptor of domestic wastewater from septic systems, and as a source of baseflow to the Nottawasaga River, ON, Canada. Groundwater from the Lake Algonquin Sand Aquifer in the southern Nottawasaga River Watershed was collected from private domestic wells and as groundwater seeps discharging along the banks of the Nottawasaga River. Approximately 30% of samples had detectable levels of one or more artificial sweeteners, indicating the presence of water derived from septic system effluent. Using acesulfame concentrations to estimate the fraction of septic effluent in groundwater samples, ∼3.4 to 13.6% of the domestic wells had 1% or more of their well water being derived from septic system effluent. Similarly, 2.0 to 4.7% of the groundwater seeps had a septic effluent contribution of 1% or more. No relationship was found between the concentration of acesulfame and the concentration of nitrate, ammonium, or soluble reactive phosphorus in the groundwater, indicating that septic effluent is not the dominant source of nutrients in the aquifer. It is expected that the occurrence of artificial sweeteners in shallow groundwater is widespread throughout rural areas in Canada.

Sediment sequences and palynology of outer South Bay, Manitoulin Island, Ontario: Connections to Lake Huron paleohydrologic phases and upstream Lake Agassiz events

South Bay on the southern coast of Manitoulin Island is a fjord-like embayment connected to Lake Huron by a natural narrow gap in the bay's outer sill 6.5–14 m above the lake. A seismic profile, pollen, plant macrofossil, grain size analyses, and other sediment properties of two piston cores from a shallow outer basin of the bay document a 9 m-thick sediment section comprising rhythmically laminated clay under silty clay containing zones with small molluscan shells and marsh detritus. A sandy pebbly layer under soft silty clay mud overlies these sediments. This stratigraphy represents inundation by deep glacial Lake Algonquin followed by the shallowing Post Algonquin series of lakes, and exposure in the early Holocene by 5 Lake Stanley lowstands in the Lake Huron basin separated by 4 Lake Mattawa highstands. Overflow from South Bay in the first lowstand is thought to have eroded the outer sill gap. Marsh environments are inferred to have formed in the bay during subsequent lowstands. The Lake Mattawa highstands are attributed to outburst floods mainly from glacial Lake Agassiz. Palynological evidence of increased spruce occurrence, an apparent regional climate reversal, during the dry pine period is attributed to cold northwest winds from the Lake Superior basin and a lake effect from the Mattawa highstands in the Lake Huron basin. Lake waters transgressed South Bay following the pine period to form the Nipissing shore on Manitoulin Island. Transfer of Lake Huron basin drainage to southern outlets and continued glacioisostatic uplift of the region led to the present configuration of South Bay and Lake Huron.

Spits formed in Glacial Lake Algonquin indicate strong easterly winds over the Laurentian Great Lakes during late Pleistocene

We report on a unique, new dataset: 49 spits that formed in the various phases of Glacial Lake Algonquin in the northern Great Lakes region, between approximately 13,200 and 11,500 years BP. The spits, which are now subaerially exposed well above the level of the current Great Lakes, trail off from former Lake Algonquin islands and headlands. Several exceed 10 km in length. Steep, eroded headlands coupled with their coarse-textured sediments, suggest that spit development was driven by large waves and strong longshore currents. The lake’s islands and exposed headlands are usually strongly eroded on their eastern margins. Additionally, spits within ≈150–200 km of the former ice margin, and especially the very large spits in northern Michigan, trail to the west, particularly the WNW and SW. Some small spits that lie farther south trail to the east, and others, within confined bays, better reflect the localized littoral circulation systems. Together, these features provide on-the-ground evidence for persistent, easterly, summertime winds in the late Pleistocene in the northern Great Lakes region, supporting paleoclimate models that show southeasterly to easterly air flows, originating from a glacial anticyclone above the Laurentide Ice Sheet. Our research suggests that strong, anticyclonically driven, easterly winds were a key part of the regional circulation within ≈150–200 km of the southern ice margin, while acknowledging that winds may have been more dominantly westerly at locations farther south. The latter conclusion reconciles with the record of loess transport and dune formation on westerly winds during this (and earlier) time periods in the south-central Great Lakes region and the Great Plains of North America.

Delineation of Paleowind Direction from Dunes in Simcoe County, Ontario

Dune fields that developed along paleolake shorelines in Ontario are a product of paleoenvironmental conditions, which developed as a result of glacially influenced geological processes. In Simcoe County, Ontario, many dune fields were created between 3 and 12 ka, when this area was covered by a series of lakes, bordered by thick sandy beaches. Coastal sediments of the glacial Lake Algonquin and the Nipissing phase of the upper Great Lakes were reworked primarily by paleowind activity and intense periodic storms once lake levels had decreased. This formed dunes, which are now common along the south-eastern coast of Georgian Bay in Simcoe County. Dunes that developed earlier (8–10 ka) have a different average orientation than dunes that developed later (3–5 ka). Various geomorphometric techniques are tested to construct a replicable methodology for determining paleowind direction. Through identification of parabolic dunes, azimuth angles were determined and used to infer the dominant paleowind directions. Dunes on the paleolake Algonquin plain commonly have a north-east to south-west orientation, whereas dunes associated with Nipissing phase shorelines formed via north-westerly winds. These data may suggest changing prevailing winds in the Great Lakes region during deglaciation.

Glaciolacustrine history of the Huron-Erie lowland in the southeastern Great Lakes region (USA) revisited

Abstract The glaciolacustrine history of the Huron-Erie lowland is reinterpreted using a closed basin model (CBM), based on ground surveys, LiDAR imagery, and digital elevation mapping (DEM). According to the CBM, paleolakes Utica, St. Clair, and Rouge were formed about 13,813 cal yr BP in closed depressions as the level of glacial Lake Elkton dropped below that of bounding morainal swells. The CBM explains why no physical connections could be established previously between paleolakes Algonquin and St. Clair, or between paleolakes St. Clair and Rouge. The CBM obviates the need for a spillway at Port Huron during the time of early Lake Algonquin. The Port Huron spillway is reinterpreted as having first formed about 5,728 cal yr BP simply as a consequence of early Holocene glacial rebound, southward tilting of the Lake Huron basin, and rising water level during the Nipissing transgression. LiDAR and DEM maps suggest that spillway development in the Port Huron moraine caused catastrophic flooding during initial formation of the St. Clair River channel. Channeled scablands-like topography in the form of braided scour channels, streamlined erosional residuals, and boulder lag deposits downriver from Detroit suggest that the Detroit River may have formed by outburst flooding as the Detroit moraine was breached by the rising water level of paleolake St. Clair.

Paleoproductivity and organic matter sources in Late Quaternary Lake Ontario

Abstract We have examined δ 13 C of ostracode valves and clam shells, carbon and nitrogen mass accumulation rates (C- and N-MAR), atomic C/N and δ 13 C OM from Lake Ontario since ~ 16,000 cal BP to evaluate the impacts of the Laurentide Ice Sheet (LIS) and regional paleohydrology on primary lacustrine productivity and sources of OM. Samples were obtained from piston cores from each of the Niagara, Mississauga and Rochester basins, which geographically span Lake Ontario from west to east. During the glacial period, variations in inputs directly from the LIS versus up-stream glacial Lake Algonquin and (or) ancient Lake Erie controlled the DIC pool in ancestral Lake Ontario. Cold and dry conditions limited primary productivity in the Ontario basin (low C/N ~ 7.5). Increased contributions of glacial meltwater from glacial Lake Algonquin during the latter stages of deglaciation provided a uniform supply of DIC to ancestral Lake Ontario and other lakes then occupying the Huron and Erie basins, stabilizing the δ 13 C DIC pool at ~− 4‰ (VPDB). Upon hydrologic closure of early Lake Ontario at the onset of post-glacial conditions (12,300 cal BP), a growing divergence between the δ 13 C of ostracode valves (decreases to − 6‰) and clam shells (increases to + 1‰) indicates differences in summer versus spring DIC pools. The end of glacial meltwater input to early Lake Ontario also made it possible to detect changes in primary lacustrine productivity using the isotopic and C/N proxies. Increasing δ 13 C OM (from ~− 29 to − 27.5‰) and low C/N (

High-resolution seismic sub-bottom reflection record of low hypsithermal lake levels in Ontario lakes

Recently published work in mid-continent North America based on coring of Lake Huron sediments and paleo-environmental analysis of their included pollen and microorganisms has revealed low water levels during the warmth of the mid-Holocene hypsithermal, suggesting the Great Lakes were largely disconnected from each other sometime shortly before 8000years ago. We have supported this hypothesis by interpreting a large database of high-resolution seismic reflection track lines (~2000km) from sixteen lakes in Ontario found principally on the Canadian Shield and within the limits of former glacial Lake Algonquin. Geophysical data show a common seismo-stratigraphy of late and postglacial sediment sequences bounded by distinct erosion surfaces that are regionally correlative. These can be correlated with published data on cored and dated seismic sequence boundaries from the French River area of Georgian Bay in northeastern Lake Huron together with other subsurface data from the central basin of Lake Huron. A consistent regional paleo-environmental picture emerges of lowered water levels when glacial Lake Algonquin drained approximately 11,000 ybp, fluctuating lake levels thereafter (the Mattawa–Stanley phase) accompanied by the cutting of a distinct erosion surface subaerially or in shallow water across older lacustrine sediments between approximately 9,000 and 8,000 ybp that identifies a regional lacustrine response to a much dryer mid-continent hypsithermal climate. Younger postglacial sediments deposited as lake levels recovered during more humid Neoglacial climates are spatially discontinuous across lake floors occurring as mounds and sheets similar to marine contourite deposits (“drifts”) reflecting modern sediment-starved conditions and strong wind-driven bottom currents.

Late-Pleistocene paleowinds and aeolian sand mobilization in north-central Lower Michigan

Abstract Simulation of late glacial atmospheric conditions with atmospheric general circulation models suggest a strong anticyclone over the Laurentide Ice Sheet and associated easterly winds along the glacial margin. In the upper Midwest of North America, evidence supporting this modeled air flow exists in the orientation of paleospits in northeastern Lower Michigan that formed ∼13 ka in association with glacial Lake Algonquin. Conversely, parabolic dunes that developed between 15 and 10 ka in central Wisconsin, northwestern Indiana, and northwestern Ohio resulted from westerly winds, suggesting that the wind gradient was indeed tight. Study results refine our understanding of late-Pleistocene wind conditions even closer to the ice margin in the upper Midwest by focusing on the timing of aeolian sand mobilization in north-central Lower Michigan at the Rosco dune field. The area was deglaciated ∼16 ka, and parabolic dunes have westerly orientations, indicating that they resulted from westerly winds. Optical ages suggest that mobilization last occurred between about 13 ka and 10 ka. The close proximity (∼150 km) of this dune field to more northerly paleolacustrine landforms resulting from easterly winds suggests that anticyclonic circulation indeed extended only a very short distance south of the ice sheet, which is consistent with modeled airflow and the orientation of dunes in central Canada. This study also presents evidence suggesting that, in addition to prevailing winds, dunes likely formed because the sparsely-vegetated local outwash plain was deflated.

Geomorphic relations among glacial Lake Algonquin and the Munising and Grand Marais moraines in eastern Upper Michigan, USA

Data obtained from ground-penetrating radar (GPR), optically stimulated luminescence (OSL) dating, and geostatistical reconstructions of Lake Algonquin water planes indicate that high-standing outwash aprons flanking the Munising moraine's southern margin in eastern Upper Michigan terminate as large, coalescing Gilbert-type ice-contact deltas graded to the Main level of Lake Algonquin. Nearly 30km of GPR imagery provides clear evidence of topset and foreset beds diagnostic of deltaic deposition. Landform assemblages suggest that the deltas likely evolved from subaqueous grounding line fans formed along a retreating ice margin characterized by widespread stagnation. In time, these deltas aggraded to the Main Lake Algonquin level as the ice margin stabilized. An OSL date of 12.5±1.1ka on a nearby beach ridge associated with the Main Algonquin shoreline is consistent with this interpretation. These new data, coupled with the presence of nested fans at the downstream end of meltwater channels incised into the delta, indicate that Lake Algonquin was falling as delta deposition waned, eventually reaching a level concordant with the Lower Orillia level before final abandonment. Large, regionally extensive heads of outwash marking the crest of the Munising moraine are graded to the upper margins of these deltas and, by inference, must also correlate with Main Lake Algonquin and the associated Two Rivers deglaciation ca. 13–12.5ka. The deltas, in turn, are conspicuously crosscut by outwash aprons that are graded to levels much lower than any recognized upper group Lake Algonquin shoreline. Because these aforementioned heads of outwash, part of Drexler and others' Grand Marais moraine, correlate with the Marquette moraine farther west, they likely date to the Marquette advance ca. 11.5ka. Thus, landforms related to Two Rivers and to Marquette glaciations appear to comingle across the study area. In the absence of extensive exposures and datable materials, our work highlights the fact that crosscutting relationships and distinct differences in base level can provide an important first step for untangling the complicated landform relationships in this part of Michigan.

Postglacial lake shoreline surveys and lacustrine paleobiotic records in northern Bruce and Grey counties, Ontario, Canada

Northern Grey and Bruce counties are situated centrally in the Lake Huron basin of the Great Lakes area of North America and are similarly central to the area of glacial Lake Algonquin, the largest glacial lake of the Great Lakes area. Ten survey traverses at sites in northern Grey and Bruce counties have documented the continuation of Lake Algonquin and Nipissing phase shorelines onto the Bruce Peninsula from previous work to the east. The Algonquin shoreline near 240m ASL (above sea level) rises northward above land high enough to record it near Lion's Head. The Nipissing shoreline at 191m ASL defines a shallow strait across the Bruce Peninsula near Ferndale, which was flooded temporarily at the maximum of the Nipissing transgression, separating northern Bruce Peninsula from the mainland. Uplift and Port Huron outlet downcutting later rejoined the island to the mainland as it is today. Raised beaches define Algonquin and Nipissing regressions by uplift using the Port Huron outlet. Paleobiotic records in a sand dune at Oliphant (molluscs), a Nipissing shorebluff along Sucker Creek (molluscs) and several sites in the former Nipissing shallow water strait near Ferndale (molluscs, ostracodes, plant macrofossils), provide paleoenvironmental data and supplement prior pollen studies at Lake Charles, Slough of Despond, and Hope Bay. Lake Algonquin deep water rhythmite clays are barren of fossils, whereas Nipissing shallow water silts are fossiliferous.

Proxy Evidence for Easterly Winds in Glacial Lake Algonquin, from the Black River Delta in Northern Lower Michigan

We examined a large, Late Pleistocene delta in northern Lower Michigan, formed by the Black River in Glacial Lake Algonquin. Today, this sandy, arcuate, wave-influenced delta stands several meters above the lake floor. The Black River transported mainly well-sorted, medium, and fine sands to the delta—at remarkably rapid rates. Our subsurface data, taken at 153 sites across the delta, show subtle and consistent trends in sediment texture across the delta surface. Although found in low amounts, gravel and very coarse sands are concentrated near the shoreline, presumably eroded by waves from the till and bedrock that crop out there. Sediments of very fine sand size (and finer) exist in higher concentrations near the eastern shore, sourced from eroded tills and also carried there on longshore currents. A clear sediment plume of medium and finer sands also traverses the delta SE to NW, which we interpret as evidence of sand transport by longshore currents flowing east to west, driven by easterly winds. High, perched spits on the head of the delta also suggest westerly longshore drift. These paleoclimate proxy data support previous interpretations of strong easterly winds here during the Late Pleistocene, probably in association with a glacial anticyclone.

The Cabot Head Archipelago: evidence of glacial Lake Algonquin on the Northern Bruce Peninsula, Ontario

The occurrence of abandoned shoreline bedrock erosional features at the edge of the Niagara Escarpment at Cabot Head indicates the existence of a group of islands in glacial Lake Algonquin during early postglacial time, referred to herein as the Cabot Head Archipelago. The abandoned shoreline features are situated as much as 80 m above the level of contemporary Georgian Bay. The range of abandoned shoreline bedrock erosional features, including shoreline cliffs, adjacent wave-cut platforms, wave-cut notches, shore stacks, shore caves, and other features, are described. The occurrence of these features is thought to be the result of the interaction between wave action in glacial Lake Algonquin and two distinct lithological facies representing the Wiarton – Colpoy Bay and Lions Head members of the Amabel Formation. The exceptional development of the abandoned shoreline bedrock erosional features in massive reefal dolostone between elevations of ∼250 and 255 m above sea level (asl) is interpreted as representing the relatively long-lived and stable Main stage of glacial Lake Algonquin (∼11 000–10 200 years BP). Shoreline erosional forms at elevations between ∼240 and 250 m asl may be indicative of declining lake levels partially controlled by bedrock structural factors. The final abandonment of the glacial Lake Algonquin shoreline in this area occurred when the eastern outlets of the lake became ice-free and its level dropped rapidly some 10 200 years BP. The Cabot Head Archipelago and the associated suite of raised and abandoned shoreline bedrock erosional features represent a rare assemblage of landforms within the Great Lakes basin, and possibly within Canada.

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.

Mapping the phases of Glacial Lake Algonquin in the upper Great Lakes region, Canada and USA, using a geostatistical isostatic rebound model

This study reviews Glacial Lake Algonquin, examines the Main and two “Upper Group” phases in northern Michigan and nearby Ontario, reports their spatial extents, and reassesses the lake history in light of isostatic rebound. Our paper presents the most accurate and detailed maps of Glacial Lake Algonquin in this region that have yet been published. Fieldwork was conducted at 243 ancient shoreline sites, which yielded position data that support geostatistical models that represent differentially upwarped water planes. Model parameters that describe water plane tilt are reported for the Main, Ardtrea and Upper Orillia phases. Geostatistical water plane models were used to adjust a digital contemporary elevation model, thereby creating a digital proglacial elevation model for each phase. Maps of these phases and the data that support them suggest (1) proto-Cockburn Island, Ontario existed as an islet in the lake that was deglaciated before the outlet at North Bay, Ontario was opened, (2) the Main and Ardtrea phases of the lake extended into the northern Lake Michigan basin, and (3) the Main and Ardtrea water planes intersect at places near Little Traverse Bay (by Lake Michigan) and Thunder Bay (by Lake Huron). Mapped isobases generally conform to those published in other works and suggest the regional pattern of isostatic adjustment has not changed substantially during the last 13,000 years.