Climatic influences on streamflow and sediment flux into Lake C2, northern Ellesmere Island, Canada

Streamflow, suspended sediment transport and meteorological variables at two elevations were measured through the 1990–1992 field seasons at Lake C2, Northern Ellesmere Island, as part of the Taconite Inlet Lakes Project. The objectives were to determine the extent to which suspended sediment flux responded to climatic variability, and to ascertain which meteorological variable was most strongly associated with daily discharge and sediment load. This study provided a partial test of our hypothesis that the annually-laminated sediments of Lake C2 contain a paleoclimate signal. Streamflow to the lake was almost exclusively the result of snowmelt, in response to inputs of atmospheric energy as measured by air temperature at the median watershed elevation (520 m). Sea-level air temperature, global solar and net all-wave irradiance were less clearly associated with discharge. Fluctuations of discharge and suspended sediment concentration were nearly synchronous, and non-linearly related. Daily sediment discharge was therefore linked by streamflow, with a time lag, to the energy available for snowmelt. Mean daily air temperature and cumulative degree-days above 0 °C, at 520 m elevation, were successfully used to predict the daily and seasonal discharge of runoff and sediment to the lake.This is the third in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.     

Five thousand years of sediment transfer in a high arctic watershed recorded in annually laminated sediments from Lower Murray Lake,Ellesmere Island,Nunavut, Canada

Sediments in Lower Murray Lake, northern Ellesmere Island, Nunavut Canada (81°21′ N, 69°32′ W) contain annual laminations (varves) that provide a record of sediment accumulation through the past 5000+ years. Annual mass accumulation was estimated based on measurements of varve thickness and sediment bulk density. Comparison of Lower Murray Lake mass accumulation with instrumental climate data, long-term records of climatic forcing mechanisms and other regional paleoclimate records suggests that lake sedimentation is positively correlated with regional melt season temperatures driven by radiative forcing. The temperature reconstruction suggests that recent temperatures are ~2.6°C higher than minimum temperatures observed during the Little Ice Age, maximum temperatures during the past 5200 years exceeded modern values by ~0.6°C, and that minimum temperatures observed approximately 2900 varve years BC were ~3.5°C colder than recent conditions. Recent temperatures were the warmest since the fourteenth century, but similar conditions existed intermittently during the period spanning ~4000–1000 varve years ago. A highly stable pattern of sedimentation throughout the period of record supports the use of annual mass accumulation in Lower Murray Lake as a reliable proxy indicator of local climatic conditions in the past.

A late Holocene varved sediment record of environmental change from northern Ellesmere Island, Canada

A composite record of varve sedimentation is presented from high arctic meromictic Lake C2. The combination of a short runoff and sediment transport season with the strong density stratification of the lake lead to the formation of annual sediment couplets. This conclusion was confirmed by ²¹⁰Pb determinations. High intra-lake correlation of the varves allowed the construction of a composite record of varve sedimentation from overlapping segments of multiple sediment cores. Cross-dating between core segments isolated counting errors in individual cores, that could be attributed to minor sediment disturbances and vague structures. Resolving counting errors by cross-dating reduced the chronological error of the composite series to an estimated ±57 years.The Lake C2 series is the first non-ice cap, high resolution late-Holocene environmental record from the Canadian high arctic. The composite varve series compares favorably with other high resolution proxies from the arctic, in particular with the ice core records from Devon Island and Camp Century, Greenland. A general correspondence between the varve record and other North American proxies for the little Ice Age period (1400–1900 AD) suggests that the Lake C2 record is sensitive to large-scale synoptic changes.This is the tenth in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.     

Recent sedimentation in a high arctic lake, northern Ellesmere Island, Canada

A multiple core study was conducted on laminated minerogenic sediments from Lake C2, Northern Ellesmere Island, Canadian High Arctic. Lateral persistence, distal thinning, variation in grain size of these laminations as well as present-day processes of highly seasonal sediment transfer into the lake basin suggest that clastic varves have been formed. Sedimentation rates based on ²¹⁰Pb dating agree well with sedimentation rates based on lamination counts giving further evidence that laminations are annual. Errors in varve counting were reduced from 12% to < 2% using the multi-core approach of cross-correlating all records. Varved sediments are occasionally interrupted by thick coarse-grained layers, which are interpreted as deposits of turbidity currents and may be related to extremely high discharge events and slope failures of the delta front. Micro-laminated sediments spanning the last two centuries were studied in detail. Suspension settling is the dominant process of deposition depending upon stream discharge which is controlled by nival melt and summer temperatures. Application of varve chronology thus allows to use lamination thickness measurements as source of high resolution proxy data for palaeoclimatic reconstruction.This is the fifth in a series of papers published in this issue on the Taconite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.     

Diatom-based Holocene paleoenvironmental records from continental sites on northeastern Ellesmere Island, high Arctic, Canada

Stratigraphic changes in diatom assemblages from four small lakes on northeastern Ellesmere Island, high Arctic, Canada, provide a proxy lake-ice cover and paleoenvironmental record. Low absolute diatom abundances and a benthic Fragilaria (sensu lata) dominated assemblage during the postglacial (< 7.6 ka B.P.) to mid-Holocene record the moderating effects of locally retreating glaciers. Around 5.5 ka B.P. diatom concentrations begin to rise, reaching their highest levels (10⁹ valves per g dry sediment) between 4.2 and 3 ka B.P., interpreted to be the warmest period in this region. Topoclimatic differences between lakes on Hazen Plateau and those lower in Lake Hazen Basin account for the initial decline in diatom abundances in the upper lakes after 3 ka B.P. This change is thought to reflect a lowering of the regional snowline, accordant with widely recognized Neoglacial advances on Ellesmere Island and Greenland. Lakes in lower Lake Hazen Basin maintained extensive summer ice free conditions until ~ 1.9 ka B.P., after which diatom abundances declined, suggesting prolonged summer lake-ice cover through the remainder of the recovered Holocene record. Differences between the records presented here and those from coastal areas of the Canadian high Arctic highlight the unique topoclimatic characteristics and continentality of the Lake Hazen region, and possible effects that local marine environments may have had on coastal records. Such differences serve to demonstrate the inherent geographic variability of paleoenvironmental records from the high Arctic.     

Inferences concerning climatic change from a deeply frozen lake on Rundfjeld,Ellesmere Island,Arctic Canada

A small lake on top of Rundfjeld, central Ellesmere Island, at an elevation of approximately 830 m, is frozen to the bottom, and the thickness of lake ice present is at least 5.45 m. Under present climatic conditions the lake does not thaw to the bottom, even during the warmest summers; i.e., 3 to 4 m of ice still floored the deepest part of the lake in mid-August 1987. A radiocarbon age determination via accelerator mass spectrometry (AMS) on a sample of the filamentous green alga Mougeotia sp., recovered from the lake ice at a depth below 4 m, gave 5730±70 BP (TO-530). The date indicates that the lake was probably completely open for an unspecified period of time during the warmest part of the Hypsithermal Interval. This situation is in agreement with data derived from a variety of other sources in Ellesmere Island and adjacent Greenland.     

Stratification patterns in Taconite Inlet, Ellesmere Island, N.W.T.

The middle arm of Taconite Inlet shows many features in common with high-Arctic fjords and coastal meromictic lakes. The surface mixed layer is fresh, and a relatively constant 5.5 m deep, indicating a layer of ice of approximately the same thickness blocks communication with the Arctic Ocean. Below the primary halocline to a depth of 85 m, at least partial communication with the Arctic Ocean exists as indicated by the oxygen, salinity and thermal structures. A sill is probably found between 40 and 85 m depth, reducing circulation below it and contributing to the oxycline. For a long but undetermined period prior to the separation of lakes C1, and C2 from the middle arm of Taconite Inlet, the surface water of the inlet was probably strongly brackish to marine suggesting that the entrance to Taconite Inlet was not blocked by an ice shelf at the time of separation. The deep water of these future lakes probably became isolated from the general estuarine circulation and began to develop some of their present limnological features prior to actual separation of the surface waters of the lakes from the inlet.This is the seventh in a series papers published in this issue on the Tactonite Inlet Lakes Project. These papers were collected by Dr R. S. Bradley.     

A high resolution proxy-climate record from an arctic lake with annually-laminated sediments on Devon Island, Nunavut, Canada

Sediments from a 3 ha lake (75 °34.34N, 89 °18.55W) from the coastal region of northern Devon Island, Nunavut, Canada, contain discrete laminations in the deepest part of the basin. The laminations are varves as indicated by the correspondence between counts and thickness measurements of the couplets and ²¹⁰Pb dating. A 14 cm core representing 150 years of sedimentation contained laminated couplets consisting of a lighter inorganic layer with a higher percentage of calcium and magnesium, alternating with fine darker bands, typically more cohesive, and comprising higher proportions of silica and carbon. A reddish oxidation zone with higher iron and aluminum frequently separates the laminations. The dark layer represents a biogenic component deposited in summer and is made cohesive by bacterial filaments among the other particles. The light inorganic layer represents clastic deposition from allochthonous sources. Deposition rates were relatively consistent through the core with an increase in varve thickness in the 1950s. Diatom concentrations in the sediments increased by two orders of magnitude in this century, with major increases in the 1920s and 1950s. The increase in varve thickness and diatom abundance coincides with an increase in summer melt percentage in an ice core from the Devon Island Ice Cap (Koerner, 1977). The relatively high sedimentation rate (0.15 cm yr^-1) coupled with the consistency of deposition makes this lake a significant indicator for recent climate changes of the Canadian Arctic Archipelago.     

Changes in diatom assemblages in Lake C2 (Ellesmere Island, Arctic Canada): response to basin isolation from the sea and to other environmental changes

Diatoms preserved in the sediments of Lake C2 (82°50 N, 76°00 W), a high arctic meromictic lake, track changes in the lake's salinity which have occurred as the basin was isolated from the sea. An assemblage dominated by marine taxa, such as Chaetoceros species, Nitzschia cylindrus and Diploneis spp., was replaced by a Cyclotella kuetzingiana var. planetophora dominated freshwater flora. A brief brackish period separates the two assemblages. Relatively little floristic change occurred within either the marine or freshwater periods, indicating rather stable environmental conditions, except that rheophilous diatoms fluctuated in relative abundance during the lacustrine phase, perhaps tracking past changes in discharge from inflowing streams. These may reflect periods of warmer, wetter environmental conditions.This is the eighth in a series of papers published in this issue on the Taconite Lakes Project. These papers were collected by Dr R. S. Bradley.     

Climate of the past millennium inferred from varved proglacial lake sediments on northeast Baffin Island,Arctic Canada

This study uses ^239+240Pu-dated varved sediments from Big Round Lake, a proglacial lake on northeast Baffin Island, Arctic Canada to generate a 1000-year-long, annual-resolution record of past climate. Varve thickness is positively correlated with July–August–September temperature measured at Clyde River, 70 km to the north of the lake (r = 0.46, p < 0.001). We therefore interpret the variability and trends in varve thickness to partially represent summer temperature. The coolest Little Ice Age temperatures occurred in this record from 1575 to 1760 AD and were approximately 1.5°C cooler than today (average from 1995 to 2005 AD) and 0.2°C cooler than the last millennium (average from 1000 to 2000 AD). Pre-twentieth-century warmth occurred during two intervals, 970–1150 AD and 1375–1575 AD; temperatures were approximately 1.2°C cooler than today, but 0.1°C warmer than the last millennium. The Big Round Lake varve-thickness record contains features similar to that reconstructed elsewhere in the eastern Canadian Arctic. This high-resolution quantitative record expands our understanding of arctic climate during the past millennium.

Little Ice Age recorded in summer temperature reconstruction from vared sediments of Donard Lake, Baffin Island, Canada

Clastic varved sediments from Donard Lake, in the Cape Dyer region of Baffin Island, provide a 1250 yr record of decadal-to-centennial scale climate variability. Donard Lake experiences strong seasonal fluctuations in runoff and sediment fluxes due to the summer melting of the Caribou Glacier, which presently dominates its catchment. The seasonal variation in sediment supply results in the annual deposition of laminae couplets. A radiocarbon date measured on moss fragments, with a calibrated age of 860 ± 80 yrs before present (BP), is in close agreement with the age based on paired-layer counts. Together with the fabric of the laminae determined from microscope analysis, the age agreement demonstrates that the laminae couplets are annually deposited varves. Comparisons of varve thickness and average summer temperature from nearby Cape Dyer show a significant positive correlation (r= 0.57 for annual records, r = 0.82 for 3-yr averages), indicating that varve thickness reflects changes in average summer temperature. Varve thickness was used to reconstruct average summer temperatures for the past 1250 yrs, and shows abrupt shifts and large amplitude decadal-to-centennial scale variability throughout the record. The most prominent feature of the record is a period of elevated summer temperatures from 1200-1375 AD, followed by cooler conditions from 1375-1820 AD, coincident with the Little Ice Age.     

Multiple ecological and hydrological changes recorded in varved sediments from Sanagak Lake,Nunavut, Canada

A combination of biotic, sedimentary and biogeochemical proxies was used to investigate the timing and causes of post-18th century changes in the stratigraphic record of a large, deep lake on the Boothia Peninsula, Nunavut, Canada (70°15′ N, 94°30′ W). A varve chronology verified with radioisotopic dating (²¹⁰Pb and ¹³⁷Cs) revealed a complex pattern of environmental dynamics since c. AD 1830. An increase in the diatoms Asterionella formosa, Stephanodiscus minutulus and Cyclotella atomus and a decrease in Aulacoseira taxa in the uppermost centimetre of sediment suggested that environmental conditions have favoured the growth of smaller and/or lighter planktonic species since the 1980s. Longer term changes in some benthic species, the chrysophyte cysts to diatom valve ratio, %C, and C/N ratios suggest declined river inflow and a relative reduction in allochthonous inputs during the last century. Higher than average δ¹⁵N values in the late 19th to early 20th centuries coincide with changes in bulk carbon and nitrogen profiles, and below average values since approximately 1950 may be associated with increased atmospheric N loading or reduced productivity. Biogenic silica and organic carbon accumulation in the sediments suggest a possible decline in lake production during the 20th century that may be associated with changes in the river discharge regime. The short and long-term ecological and biogeochemical trends were also reflected in the sedimentary structure through declining varve thickness for the duration of the record and an abrupt change in sedimentology in the uppermost 1 cm, coinciding with deposition since ca. AD 1987. Together, these biological and physical changes suggest changes in hydroclimatic conditions in the 20th century, and an increase in planktonic diatom taxa since the 1980s that coincides with a distinct period of climate warming.     

A 300 year record of environmental change from Lake Tuborg, Ellesmere Island, Nunavut, Canada

Lamination thickness measurements in sediments from Lake Tuborg, northern Ellesmere Island, Canada document an increase in high-energy hydrologic discharge events from ∼1865 to 1962. The timing of these events corresponds with evidence for an increase in the amount of melt on the adjacent Agassiz Ice Cap, as recorded in ice cores. There appears to have been a non-linear change in depositional energy resulting from a dramatic increase in Agassiz meltwater discharge, particularly after ∼1908. A strong correlation between the Lake Tuborg varve thickness record, the amount of melting on the Agassiz Ice Cap and Eureka 900 mb air temperature records suggests that changes in the height of the freezing level in the atmosphere have affected the extent of summer melting on the Agassiz Ice Cap, leading to high volume discharge events and associated sediment flux to Lake Tuborg.     

Spatial uniformity of sediment accumulation in varved lake sediments in northern Sweden

As part of an investigation aimed at assessing the potential of northern Swedish varved lake sediments for fine-resolution reconstruction of past climatic conditions, the following questions were addressed; how representative is a single core, does the appearance of varves change as the sediment ages, and how can varve thickness and within-varve structures be digitized? Analyses of replicate cores from Kassjön, using sample sequences of seasonal, annual and centennial time resolution, show that spatial variability of sediment accumulation in the varved sediment is very low. Comparisons of intensity curves from image analysis of freeze cores of recent sediments from Lake Nylandssjön, sampled in 1980 and 1985, indicate that the varves acquire their appearance at the sediment-water interface during sedimentation and that the varve structures are preserved during diagenetic processes. Measurement of varve thicknesses with a tree-ring microscope and with image analysis gave similar results. However, with image analysis, within-varve structures such as colour variations and thicknesses of seasonal layers, can also be recorded, increasing the possibilities for palaeolimnological and palaeoclimatic inferences.     

Quantitative estimates of recent environmental changes in the Canadian High Arctic inferred from diatoms in lake and pond sediments

Diatoms were examined in three lacustrine sediment records from Alert, northern Ellesmere Island, and from Isachsen, Ellef Ringnes Island. Diatom assemblages changed markedly since the mid-19th century following relatively stable community composition that spanned centuries to millennia. Three different assemblages, primarily composed of Fragilaria pinnata, Diadesmis spp., or Pinnularia spp., dominated the pre-1850 period at the three sites, but were replaced with different, more diverse assemblages in recent sediments. These species shifts occurred in the mid- to late-19th century in the Isachsen sites, and in the mid- to late-20th century in our Alert site. This difference in timing appears to be a result of the different sensitivities of lakes and ponds to environmental change, rather than of site-specific chemical properties. Reconstructions of pH using diatom inference models indicated increases from 0.5 to 0.8 pH units at these sites over this period of assemblage change. The diatom-inferred pH record from Alert showed agreement with measured climate data from Alert over the last 30 years. These marked community changes suggest that these sensitive high arctic sites have recently crossed important ecological thresholds due to environmental change, most likely related to recent warming.     

Meteorological observations 2003 at the Sermilik Station,Ammassalik Island,Southeast Greenland

Geografisk Tidsskrift, Danish Journal of Geography 105(2):49–56, 2005

Meteorological stations have been in operation since 1993 at Sermilik (65°40'N, 38°10'W), located in southeast Greenland. This note presents meteorological observations for the year 2003, including ground temperature, orographic effect (liquid precipitation) and air temperature lapse rates between two meteorological stations, Station Nunatak (515 m a.s.l.) and Station Coast (25 m a.s.l.).     

The glacilacustrine sedimentary environment of Bowser Lake in the northern Coast Mountains of British Columbia, Canada

Bowser Lake, a fiord lake in the northern Coast Mountains of British Columbia, contains a thick Holocene fill consisting mainly of silt and clay varves. These sediments were carried into the lake by proglacial Bowser River which drains a high-energy, heavily glacierized basin. Sedimentation in the lake is controlled by seasonal snow and ice melt, by autumn rainstorms, and by rare, but very large jökulhlaups from glacier-dammed lakes in the upper Bowser River basin which complicate environmental inferences from the sedimentary record. Sediment is dispersed through the deep western part of the lake by energetic turbidity currents. The turbidity currents apparently do not overtop a sill that separates the western basin from much shallower areas to the east. Large amounts of silt and clay are deposited from suspension in the eastern part of the lake, but sediment accumulation rates there are much lower than to the west. Several strong acoustic reflectors punctuate the varved fill in the western basin; these may be thick or relatively coarse beds deposited during jökulhlaups or exceptionally large storms. The contemporary sediment yield to Bowser Lake, estimated from sediments in the lake, is about 360 t km^-2a^-1. This is a relatively high value, but it is less than yields insome other, similar montane basins with extensive snow and ice cover.The most likely explanation for the difference is that large amounts of sediment have been, and continue to be, stored on the Bowser delta andin small proglacial lakes.     

Tracking recent recovery from eutrophication in a high arctic lake (Meretta Lake, Cornwallis Island, Nunavut, Canada) using fossil diatom assemblages

Meretta Lake (Resolute Bay, Cornwallis Island, Nunavut, Canada) is a high arctic lake that received raw sewage for almost 50 years from the Canadian Department of Transport Base. The lake was sampled from 1968–72 during the International Biological Programme, as part of the Char Lake Project. As the number of users at the Transport Base declined throughout the 1990s, so too did the lake's nutrient levels, and Meretta Lake is now classified as oligotrophic. A previous diatom-based paleolimnological study revealed marked species assemblage shifts coincident with sewage inputs beginning in the late 1940s; however, because the core was taken at a time when nutrient levels were still relatively high (i.e., 1993), the diatom record did not yet track any signs of recovery. In this present study, we examined fossil diatom assemblages from a sediment core taken in 2001. Our results indicate a shift to the pre-impact diatom assemblages in the most recent sediments, indicating that the paleolimnological record is tracking the decreased nutrient inputs to this high arctic lake, and confirms that no significant lags exist in these largely ice-covered lakes.     

Radiometric dating of lake sediments from Signy Island (maritime Antarctic): evidence of recent climatic change

Sediment cores from three lakes (Moss, Sombre and Heywood) in the maritime Antarctic (Signy Island, South Orkney Islands) have been successfully dated radiometrically by²¹⁰Pb and¹³⁷Cs. The core inventories of both fallout radionuclides are an order of magnitude higher than that which can be supported by the direct atmospheric flux at this latitude. The elevated values may be explained by fallout onto the catchment during the winter being delivered directly to the lakes during the annual thaw. Two of the lakes (Sombre and Heywood) show marked increases in sediment accumulation afterc. 1950. This appears to be associated with a documented rise in temperature in the South Orkney Islands, which has caused extensive deglaciation at Signy Island.This is the tenth of a series of papers to be published by this journal following the 20 ^th anniversary of the first application of²¹⁰Pb dating of lake sediments. Dr P.G. Appleby is guest editing this series.     

Spatial and interannual variations in sedimentation patterns recorded in nonglacial varved sediments from the Canadian High Arctic

Multiple cores taken throughout Nicolay Lake in the Canadian High Arctic contain laminated sediments that are interpreted as varved. Annual sediment accumulation during the last 197 years reveals three major patterns that have important implications for hydroclimatic reconstruction. Widespread sediment dispersal is evident during most years and contrasts with years when anomalous localized and bifurcating patterns of deposition occur. Localized deposition is limited to the centre of the lake and is attributed to turbidity currents that originate on the delta foreslope. In contrast, a bifurcating pattern is produced when the river supplying the delta switches from one to two delta distributaries, resulting in altered proximal accumulation. Principal component analysis reveals additional accumulation anomalies that are sedimentologically indistinct, but constitute important sources of localized variance. The recognition and removal of anomalous deposition patterns is critical for accurate reconstruction of sediment flux from the catchment, particularly in long records where geomorphic conditions may have changed. This study identifies potentially misleading depositional artifacts and a methodology to recognize similar depositional controls in other lakes.