North-central Baffin Island Research Articles

Moss kill dates and modeled summer temperature track episodic snowline lowering and ice cap expansion in Arctic Canada through the Common Era

Abstract. Most extant ice caps mantling low-relief Arctic Canada landscapes remained cold based throughout the late Holocene, preserving in situ bryophytes killed as ice expanded across vegetated landscapes. After reaching peak late Holocene dimensions ∼1900 CE, ice caps receded as Arctic summers warmed, exposing entombed vegetation. The calibrated radiocarbon ages of entombed moss collected near ice cap margins (kill dates) define when ice advanced across the site, killing the moss, and remained over the site until the year of their collection. In an earlier study, we reported 94 last millennium radiocarbon dates on in situ dead moss collected at ice cap margins across Baffin Island, Arctic Canada. Tight clustering of those ages indicated an abrupt onset of the Little Ice Age at ∼1240 CE and further expansion at ∼1480 CE coincident with episodes of major explosive volcanism. Here we test the confidence in kill dates as reliable predictors of expanding ice caps by resampling two previously densely sampled ice complexes ∼15 years later after ∼250 m of ice recession. The probability density functions (PDFs) of the more recent series of ages match PDFs of the earlier series but with a larger fraction of early Common Era ages. Post 2005 CE ice recession has exposed relict ice caps that grew during earlier Common Era advances and were preserved beneath later ice cap growth. We compare the 106 kill dates from the two ice complexes with 80 kill dates from 62 other ice caps within 250 km of the two densely sampled ice complexes. The PDFs of kill dates from the 62 other ice caps cluster in the same time windows as those from the two ice complexes alone, with the PDF of all 186 kill dates documenting episodes of widespread ice expansion restricted almost exclusively to 250–450 CE, 850–1000 CE, and a dense early Little Ice Age cluster with peaks at ∼1240 and ∼1480 CE. Ice continued to expand after 1480 CE, reaching maximum dimensions at ∼1880 CE that are still visible as zones of sparse vegetation cover in remotely sensed imagery. Intervals of widespread ice cap expansion coincide with persistent decreases in mean summer surface air temperature for the region in a Community Earth System Model (CESM) fully coupled Common Era simulation, suggesting the primary forcings of the observed snowline lowering were both modest declines in summer insolation and cooling resulting from explosive volcanism, most likely intensified by positive feedbacks from increased snow cover and sea ice and reduced northward heat transport by the oceans. The clusters of ice cap expansion defined by moss kill dates are mirrored in an annually resolved Common Era record of ice cap dimensions in Iceland, suggesting this is a circum-North-Atlantic–Arctic climate signal for the Common Era. During the coldest century of the Common Era, 1780–1880 CE, ice caps mantled >11 000 km2 of north-central Baffin Island, whereas <100 km2 is glaciated at present. The peak Little Ice Age state approached conditions expected during the inception phase of an ice age and was only reversed after 1880 CE by anthropogenic alterations of the planetary energy balance.

The variability of Baffin Bay seafloor sediment mineralogy: the identification of discrete glacial sediment sources and application to Late Quaternary downcore analysis

Quantitative X-ray diffraction (qXRD) mineralogy of bedrock, ice-rafted, and fluvial clasts, 239 seafloor samples (<2 mm), and samples from two long piston cores were used to (i) define regional patterns and sources within Baffin Bay, (ii) evaluate two areas from west Greenland and east Baffin Island in more detail, and (iii) apply these findings to the interpretation of downcore variations in sediment sources. A sediment-unmixing program is used to define surface regional mineral assemblages and to examine changes in sediment sources in cores HU2013029-77PC (southern Baffin Island slope) and HU2008029-8PC (Davis Strait) during Marine Isotope Stages 1 through 3. Distinct regional patterns are observed in the association between the mineralogy of surface sediments and carbonate and basalt bedrock outcrops. Detailed analysis of seafloor samples from the west Greenland troughs and Baffin Island fjords show regional differences in mineralogy, with sediments derived from the Foxe Fold Belt (north-central Baffin Island) being mineralogically distinct from sediments to the north and south. Grain-size spectra from the west Greenland troughs suggested an association between grain-size spectra and mineral assemblages. Sediment unmixing of qXRD data from the two piston cores shows discrete intervals where one or more mineral sources were dominant. However, chronological control is such that it is unclear whether the various ice streams draining into Baffin Bay behaved synchronously.

Using in situ cosmogenic 10Be, 14C, and 26Al to decipher the history of polythermal ice sheets on Baffin Island, Arctic Canada

Constraining the timing of past ice-sheet change is important for assessing the cryospheric expression of climate change and improving our understanding of ice sheet dynamics. Geochronology used to construct past ice-sheet reconstructions, however, can be ineffective in polar environments where ice sheets were polythermal and left varying imprints on landscapes. Cosmogenic-nuclide exposure dating, for example, is especially hampered by the lack of ice-sheet erosion and resultant cosmogenic nuclide inheritance. Here, we apply in situ cosmogenic 10Be, 14C and 26Al methods to decipher various elements of the Laurentide Ice Sheet history of north-central Baffin Island. A clearly defined erosion boundary across the landscape reveals the transition in basal ice-sheet conditions as ice flow became channelized into northern Baffin Island fiords. 10Be and 26Al concentrations indicate that the boundary represents a juxtaposition of sliding, erosive ice and cold-bedded ice that preserved ancient bedrock that has not been significantly impacted by the ice sheet in perhaps one to two million years. We combine 10Be measurements from ice-sculpted bedrock with measurements of in situ14C, which has no inheritance due to its quick decay during ice-sheet cover, to determine the local timing of deglaciation. The average 10Be and in situ14C ages for upland deglaciation in north-central Baffin Island are 7.7 ± 0.9 and 8.4 ± 1.4 ka, respectively. Finally, in situ14C measurements from surfaces being uncovered by present-day retreat of small ice caps mantling uplands within the study area have concentrations too low to be compatible with continuous post-glacial exposure. These samples require shielding by ice for a significant portion of the Holocene, and more burial than during the Little Ice Age alone. Simple exposure-burial modeling suggests that 2400–2900 yr of total ice cover during Neoglaciation is required to explain measured in situ14C inventories. Combined, multiple cosmogenic nuclides with varying half-lives can be used to decipher many aspects of the history in landscapes occupied by polythermal ice sheets.

Glacial erosion and sediment dispersion from detrital cosmogenic nuclide analyses of till

Field evidence based on sedimentology, geomorphology, and sediment provenance, supported by thermo-mechanical ice sheet model simulations, are used to classify the thermal regime of paleo-ice cover in northern central Baffin and evaluate the spatial and temporal variability of those conditions. A new means to identify paleo-glacier polythermal conditions from the measurement of terrestrial in situ cosmogenic nuclides (TCN) in till was developed to test the assertion that glacial erosion and till production are partially controlled by the thermal regime at the base of a glacier. Concentrations of cosmogenic 10Be and 26Al in 19 till samples from north central Baffin Island reflect the spatial pattern of areas classified as warm-based or cold-based (end member) systems. An ice sheet simulation of bed conditions produces the same pattern. The 26Al/ 10Be ratio is also used to confirm the long cold-based ice burial histories of surfaces that have not been significantly eroded. The data suggest that till and regolith near the current terminus of the Oliver Glacier preserve a record of >3 Ma of continuous glacial cover. In three localities resembling intermediate cases (i.e., where field observations yield conflicting interpretations of basal thermal regime), the TCN concentrations and 26Al/ 10Be reveal that the surface experienced a combination of cold-based ice burial and glacial erosion. When coupled with a high-resolution ice sheet model, the 10Be concentrations in till provide a more robust means of establishing the temporal and spatial variability in glacial erosion, and can be an important new tool for mineral exploration in glaciated terrain.

Geology, geochronology, and geochemistry of Archean rocks in the Eqe Bay area, north-central Baffin Island, Canada: constraints on the depositional and tectonic history of the Mary River Group of northeastern Rae Province

Results of stratigraphic, U–Pb geochronological, and geochemical study are reported for rocks in a 2800 km2 area along the southeastern margin of the Archean Rae Province on north-central Baffin Island. Archean rocks include a gneiss complex, two greenstone belts of the Mary River Group, and various younger plutonic rocks. The 3000–2800 Ma gneiss complex contains intrusions of orthogneiss, dated at 2780–2770 Ma. Intermediate-felsic volcanism in overlying greenstone belts occurred at 2740–2725 Ma and was accompanied and outlasted by calc-alkaline plutonism (2730–2715 Ma). Peraluminous plutonism at ca. 2700 Ma, possibly associated with low- to medium-pressure metamorphism, represents the culmination of the Archean tectonic cycle. Dating of metamorphic zircon and titanite in Archean gneissic rocks indicates that overprinting, high-grade metamorphism in the northwest part of the area (footwall of the Isortoq fault zone) is Paleoproterozoic (ca. 1820 Ma). A weaker, somewhat older thermal disturbance (ca. 1850–1840 Ma with large errors) is recorded in the hanging wall of this zone. Additional tectonothermal events at ca. 1500–1400 Ma and ca. 700 Ma may, respectively, correlate with Mesoproterozoic faulting and emplacement of the Franklin dyke swarm. Unlike their age-correlative counterparts in the Mary River area and on the mainland to the southwest, the greenstone belts at Eqe Bay lack abundant orthoquartzite and komatiitic volcanic rocks: calc-alkaline volcanic rocks predominate, suggesting a fundamentally different tectonic environment. Striking similarities, both in lithology and age, to greenstone belts of the Minto block of the Superior Province raises the question of Rae–Superior correlation.

Distinguishing between Archean and Paleoproterozoic tectonism, and evolution of the Isortoq fault zone, Eqe Bay area, north-central Baffin Island, Canada

Structural, metamorphic, and U–Pb geochronological data bear on the distinction between Archean and Paleoproterozoic tectonism along the southeastern margin of the Rae Province on Baffin Island. Archean rocks include ca. 3.0–2.8 Ga gneiss, two greenstone belts of the Mary River Group, and various younger granitoid intrusions. In the greenstone belts, intermediate–felsic volcanism (2.74–2.725 Ga) was accompanied and outlasted by calc-alkaline plutonism (2.73–2.715 Ga). Deformation, low- to medium-pressure metamorphism, and peraluminous plutonism followed at ca. 2.7 Ga. Archean rocks and the locally overlying Piling Group (ca. 2.2–1.9 Ga) were deformed and metamorphosed together during development of the Paleoproterozoic Foxe fold belt. Tectonism is linked to the Isortoq fault zone, a major southeast-dipping structure marking an abrupt northwestward transition to granulite facies. Within a 5-km-wide zone, tight folds of the Archean Mary River Group give way down-section to moderately southeast-dipping, highly transposed, high-grade gneissic rocks. Several northeast- and north-striking ductile–brittle faults, some recording normal-sinistral oblique displacement, truncate early gneissosity and folds. This progression, along with U–Pb metamorphic ages, suggests early northwest-directed thrusting, starting at ca. 1.85 Ga, with peak metamorphism in the footwall at ca. 1.83–1.82 Ga. Later extensional displacement caused juxtaposition of lower grade on higher grade rocks. Archean ages of metamorphism (and deformation) are well preserved only in the hanging wall and the youngest metamorphic ages are restricted to the footwall. The data indicate that mountain building involved thrust-related thickening followed by gravitational collapse, a sequence characteristic of Phanerozoic orogens.

Paleoecology and age of the Flitaway and Isortoq interglacial deposits, north-central Baffin Island, Northwest Territories, Canada

Peats and woody-detrital deposits at two localities close to the Barnes Ice Cap at approximately 70°N contain insect faunas and mosses that indicate that these sites were situated close to tree line during the period of deposition. Modern tree line occurs some 1325 km (820 mi) to the south and southwest of these sites. Attempts to provide numeric ages based on the U-series of woody fragments were not successful. Although it has been assumed in the past that these peats were laid down during the last interglaciation, the inferred paleoclimatic conditions based on the insect faunas and plant remains suggest a substantially older (possible late Tertiary to mid Quaternary) age. The Flitaway and Isortoq sites probably had an annual average temperature at the time of deposition which was between −8 and −9 °C, i.e., about 4 – 5 °C warmer than today. Such information is important to calibrate and check global climatic models that predict substantial high-latitude greenhouse-gas warming.

Little Ice Age Snow-Cover Extent and Paleoglaciation Thresholds: North-Central Baffin Island, N.W.T., Canada

On air photographs, light-colored areas representing reduced lichen cover indicate the maximum extent of permanent snow cover in the recent past. Lichen-free areas were mapped on 1:50,000, 1:250,000, and 1:1,000,000 map sheets of north-central Baffin Island using air photographs and LANDSAT-1 satellite imagery. Present ice and lakes cover 37% of the study area (97,000 km2). During the Little Ice Age (350 to 100 yr BP), ice and lakes covered about 50% of the study area-an increase of 35%. The amount of lichen-free area is greatest in the elevational range of 450 to 600 m a.s.l. A limited amount of lichenometrical measurements indicate that the lichen-free areas probably represent a period of more extensive

Little Ice Age Snow-Cover Extent and Paleoglaciation Thresholds: North-Central Baffin Island, N.W.T., Canada

Little Ice Age Snow-Cover Extent and Paleoglaciation Thresholds: North-Central Baffin Island, N.W.T., Canada

An Early Tertiary Outcrop in North-Central Baffin Island, Northwest Territories, Canada: Environment and Significance

A thin, impure limestone was found in situ on Precambrian bedrock at latitude 70°36.6′ N and longitude 75°20′ W some 26 km northwest of the Barnes Ice Cap. The unit consists of undulating laminations composed of alternating fine- and coarse-grained sediment, which are interpreted as a series of algal mats or algal-laminated sediments. An analysis of enclosed palynomorphs indicates the presence of Ulmus, Taxodiutm, Liriodendron, Carpinus, and Engelhardtia plus other genera. On the basis of the microflora a Paleogene age is assigned to the unit. The climate at that time was warm-temperate and the environment suggested is a freshwater marsh or swamp. The outcrop is restricted to a single hill summit and its location suggests considerable Neogene geomorphological activity, primarily river-cutting associated with vertical movements along the western margin of the Davis Strait/Baffin Bay Tift.

Dental Anomalies in Caribou, Rangifer tarandus

The dentitions of 43 of 1226 caribou (Rangifer tarandus) skulls examined had anomalies. Of the 43, 13 had supernumerary teeth, 25 had missing teeth, and five had extreme variations in root development and abnormal dentary patterns. These anomalies appear to be genetically produced and further study from the standpoint of evolutionary origin might be fruitful. sented. The 1176 caribou were taken from the Kaminuriak population, which calves and summers in the District of Keewatin, Northwest Territories, and winters for the most part in northwestern Manitoba and northeastern Saskatchewan. The 50 caribou were from a herd that is resident in north-central Baffin Island. Anomalies in the dentitions of Cervidae are generally uncommon. They are regularly reported in Odocoileus, a genus in which maxillary canines, in particular, appear with some frequency. Canines in the maxillae are normal in the genus Rangifer, the accepted dental formula for which is 0/3, 1/1, 3/3, 3/3 = 34 (Banfield, 1961:26). The associated maxillae, mandibles, and anomalous teeth were examined for evidence of the possible origin of anomalies from trauma. The incisiform teeth were extracted. The absence of normal sockets or the presence of extra sockets was determined, as was the possible migration of incisiform teeth due to the absence of one or more teeth from the incisiform row. The classification of the present or absent tooth was based on the form, size, and position of existing teeth.

Lichenometry to Evaluate Changes in Glacial Mass Budgets: As Illustrated from North-Central Baffin Island, N.W.T.

Lichenometry to Evaluate Changes in Glacial Mass Budgets: As Illustrated from North-Central Baffin Island, N.W.T.

Lichenometry to Evaluate Changes in Glacial Mass Budgets: As Illustrated from North-Central Baffin Island, N.W.T.

Lichenometry to Evaluate Changes in Glacial Mass Budgets: As Illustrated from North-Central Baffin Island, N.W.T.

OBSERVATIONS OF TURBULENT DIFFUSIONIN A NATURAL CHANNEL

Fluid flow is a diffusion process. For homogeneous turbulence, dispersion occurs normally about the center of the process, the rate of growth depending on the diffusion coefficients Ki.Measurements of Ki for longitudinal and lateral diffusion are presented for the Lewis River, a proglacial stream in north-central Baffin Island. In the river, flows up to 250 m3/s, fully turbulent, are characterized by 'roller eddies'. Observations were made by electro-chemical recording of longitudinal dispersion of salt solutions and by photography of lateral dispersal of dye plumes. It is shown that the K-values depend on the scale of flow, while the overall pattern of diffusion depends on the flow and channel geometry of the stream.The geomorphological consequences of diffusion include the phenomenon of momentum transfer in the channel and resultant shear stresses brought to bear on the walls, and the pattern of sediment transport.

A Study of Late-Quaternary Plant-Bearing Beds in North-Central Baffin Island, Canada

Plant-bearing beds, exposed by downcutting of the Isortoq River at the northern end of the Barnes Icecap, have been folded, apparently by east-west moving overriding ice, truncated and overlain by horizontal alluvial sediments. Radiocarbon dates for plant material from the Isortoq River (folded unit), Flitaway Lake, and Lewis Glacier localities are >30,000 to >40,000 yr BP, from the horizontal beds, 14,000 ± 400 yr BP. The vegetation was probably similar to that of southern Baffin Island today; the Isortoq beds are assigned to the Sangamon interglacial. Pollen diagrams and description of the present vegetation and climate are included.

Till Fabrics of the Cross-Valley Moraines of North-Central Baffin Island, Northwest Territories, Canada1

Analyses of 103 till fabrics taken from proximal and distal slopes of distinctive cross-valley moraines in the Isortoq Valley of north-central Baffin Island show variations in fabric pattern with respect to slope and location within the valley. Changes in dip patterns and fabric strengths are also associated with variations in moraine morphology. Four distinct morphological moraine types are delimited and are called simple-linear, s-shaped, hooked, and asymmetric. There is no gradation in type along a single moraine. Orientation and dip strength are found to vary with moraine type as well as between distal and proximal slopes. Dip patterns of elongate pebbles from proximal and distal sites are also shown to vary with slope, location within the valley and moraine type. These results indicate that the hooked, asymmetric, and simple-linear moraines are formed by either dissimilar processes or changes in intensity of the same process. S-shaped moraines differ morphologically from simple-linear but have the same fabric characteristics. The possibility of annual deposition is examined and concluded to be possible though in no sense proven. The cross-valley moraines are thought to form at the base of an ice cliff grounded in a glacial lake. The influx of summer meltwater provides a possible trigger mechanism and explains the association between the moraines and water-deposited kame features. The asymmetric moraines were deposited by overriding and pushing. Moraines at right angles to the ice cliff were formed by the squeezing of till into basal crevasses or melt-water tunnels.

Surface boulder orientation studies around the northwestern margin of the Barnes ice cap, Baffin Island, Canada

ABSTRACT The paper examines the orientation of 37 surface boulder fabrics taken from three depositional environments around the Barnes Ice Cap, north-central Baffin Island. These were the surface of ground moraine, including both till plains and boulder fields, in front of end, or lateral, moraines and on outwash plains. The results are tested by vector analysis. They show that the orientation of surface boulders in the first two environments correspond very closely with the known ice movement. This method is both more accurate and faster than ground moraine till fabric techniques.

Indications of Recent Extensive Glacierization in North–Central Baffin Island, N.W.T.

AbstractStudies of the geomorphology and rock lichen development north of the Barnes Ice Cap prompt the conclusion that 70 per cent of this extensive, interior region was covered by permanent ice some 300 to 400 yr. ago. Contemporaneously the northern Barnes Ice Cap was significantly larger than today; it dammed up a lake in the upper Isortoq valley, over 80 km. long and up to 300 m. deep. Excluding the ice cap less than 2 per cent of the area is glacierized today; this represents a dramatic reduction in surface area of the former ice cover. Similarly, significant recession of the ice cap implies that glaciers of the “Baffin type” are in a less healthy budgetary state than hitherto has been assumed.Proof of former extensive ice cover rests largely upon restricted rock lichen development. When sufficient time has elapsed for complete colonization, few indications of the former existence of an ice cover will remain. This type of glacierization may have affected large areas in the high Arctic. Absence of evidence ofglaciation, therefore, cannot be relied upon to delimit nunatak areas (plant refugia) during the last glaciation.

Indications of Recent Extensive Glacierization in North–Central Baffin Island, N.W.T.

AbstractStudies of the geomorphology and rock lichen development north of the Barnes Ice Cap prompt the conclusion that 70 per cent of this extensive, interior region was covered by permanent ice some 300 to 400 yr. ago. Contemporaneously the northern Barnes Ice Cap was significantly larger than today; it dammed up a lake in the upper Isortoq valley, over 80 km. long and up to 300 m. deep. Excluding the ice cap less than 2 per cent of the area is glacierized today; this represents a dramatic reduction in surface area of the former ice cover. Similarly, significant recession of the ice cap implies that glaciers of the “Baffin type” are in a less healthy budgetary state than hitherto has been assumed.Proof of former extensive ice cover rests largely upon restricted rock lichen development. When sufficient time has elapsed for complete colonization, few indications of the former existence of an ice cover will remain. This type of glacierization may have affected large areas in the high Arctic. Absence of evidence ofglaciation, therefore, cannot be relied upon to delimit nunatak areas (plant refugia) during the last glaciation.