Somerset Island Research Articles

Sedimentary biomarkers and bone specimens reveal a history of prehistoric occupation on Somerset Island (Arctic Canada).

Archaeological studies of pre-historic Arctic cultures are often limited to artefacts and architecture; such records may be incomplete and often do not provide a continuous record of past occupation. Here, we used lake sediment archives to supplement archaeological evidence to explore the history of Thule and Dorset populations on Somerset Island, Nunavut (Canada). We examined biomarkers in dated sediment cores from two ponds adjacent to abandoned Thule settlements (PaJs-3 and PaJs-13) and compared these to sediment cores from two ponds without past human occupation. Coprostanol and epicoprostanol, δ15N measurements, sedimentary chlorophyll a and the ratio of diatom valves to chrysophyte cysts were elevated in the dated sediment profiles at both sites during Thule and Dorset occupations. Periods of pronounced human impact during the Thule occupation of the site were corroborated by 14C-dated caribou bones found at both sites that identified intense caribou hunting between ca 1185 and 1510 CE. Notably, these sediment core data show evidence of the Dorset occupation from ca 200 to 500 CE at sites where archaeological evidence was heretofore lacking. We highlight the utility of lake sediments in assisting archaeological studies to better establish the timings, peak occupations and even lifestyle practices of the Dorset and Thule Arctic peoples.

Eastern High Arctic–Baffin Bay beluga whale (Delphinapterus leucas) estuary abundance and use from space

IntroductionThe Eastern High Arctic–Baffin Bay (EHA-BB) beluga whale (Delphinapterus leucas) population spends summer in estuaries around Somerset Island, Nunavut, Canada. A single abundance estimate from 1996 suggests an abundance >21,000 beluga whales; however, more information on abundance and distribution is needed to ensure effective management of this population, especially in estuaries where previous surveys provided minimal coverage. To assess the feasibility of using Very High Resolution (VHR) satellite imagery to obtain estuary abundance estimates for this beluga population, we evaluated a citizen science crowd counting initiative that was designed to monitor remote beluga whale populations and their estuary use.MethodsIn July and August 2020 the WorldView 2 and 3, and GeoEye 1 satellites were tasked to collect VHR imagery (30–41 cm) of estuaries previously known to be used by Eastern High Arctic–Baffin Bay beluga whales. The objectives were to obtain an estuary abundance estimate for this population from satellite imagery, and to evaluate the effectiveness of having imagery annotated using a crowd-source platform. Almost 3,800 km2of ocean imagery was analyzed using Maxar’s Geospatial Human Imagery Verification Effort (GeoHIVE) Crowdsourcing platform. Expert readers then manually compared counts to those performed by crowd-counters to determine variance in observer counts.Results and DiscussionThe estuary abundance estimate from 11 core estuaries was 12,128 (CV 36.76%, 95% confidence interval 6,036–24,368) beluga whales. This represents an estuary abundance estimate only, as the greater Peel Sound and Prince Regent Inlet areas were not photographed. The estuaries with the largest abundance of beluga whales were Creswell Bay, Maxwell Bay, and Prince Whales Island, with over 2,000 crowd-counted whales in each estuary. Although VHR imagery has potential to assist with surveying and monitoring marine mammals, for larger estuaries it was not always possible to photograph the entire area in a single day, and cloud cover was an issue for sections of most images. This work will assist with planning large-scale aerial surveys for monitoring beluga whale populations, identifying high-use areas and important beluga habitat, and highlights the utility of using VHR imagery to enhance our understanding of estuary abundance and distribution of Arctic whales.

U-Pb detrital zircon geochronological constraints on Siderian and Orosirian rocks of Boothia Peninsula and Somerset Island (Nunavut, Canada)

Boothia Peninsula–Somerset Island is an under-explored frontier region of Arctic Canada, long considered part of the Rae craton, that exposes widespread semipelitic rocks with minor quartzite, marble, and calc-silicate, and late Neoarchean-Paleoproterozoic plutonic rocks. Detrital zircon U-Pb SHRIMP analyses constrain the timing of deposition and provenance of three sequences. An older clastic succession (sequence 1), deposited after ca. 2500 Ma, is characterized by major modes at 2560–2510 Ma, consistent with unroofing of Boothia basement rocks and local derivation of detrital grains. Minimal detritus representative of Rae craton (i.e., 2970 Ma, 2790–2600 Ma) suggests the basin formed either at a thin margin of the western Rae craton or as part of a distinct terrane (Boothia-Somerset) separate from the western Rae craton at ca. 2500 Ma. An extensional setting during deposition of sequence 1 may relate to slab retreat. Texturally and chemically mature quartzite (sequence 2) was deposited between 2280 and 2020 Ma in a shallow or beach-like environment indicative of a passive-margin setting. Younger clastic rocks (sequence 3) associated with, and thought to overlie, carbonate strata are characterized by a significant population of 2020–1970 Ma detrital grains, consistent with exhumation of the Thelon magmatic arc and deposition of its detritus between 1960 and 1940 Ma. Overall, this detrital dataset highlights a polycyclic ca. 600 million year evolutionary history on, or outboard of, a thinned Rae cratonic margin. These results strengthen the possible linkages to the central and northern Canadian Shield and open up the potential for a distinct ribbon terrane, which may have connections to the China and Yangtze cratons.

Oxidation state and metasomatism of the lithospheric mantle beneath the Rae Craton, Canada: strong gradients reflect craton formation and evolution

We present the first oxidation state measurements for the subcontinental lithospheric mantle (SCLM) beneath the Rae craton, northern Canada, one of the largest components of the Canadian shield. In combination with major and trace element compositions for garnet and clinopyroxene, we assess the relationship between oxidation state and metasomatic overprinting. The sample suite comprises peridotite xenoliths from the central part (Pelly Bay) and the craton margin (Somerset Island) providing insights into lateral and vertical variations in lithospheric character. Our suite contains spinel, garnet-spinel and garnet peridotites, with most samples originating from 100 to 140 km depth. Within this narrow depth range we observe strong chemical gradients, including variations in oxygen fugacity (ƒO2) of over 4 log units. Both Pelly Bay and Somerset Island peridotites reveal a change in metasomatic type with depth. Observed geochemical systematics and textural evidence support the notion that Rae SCLM developed through amalgamation of different local domains, establishing chemical gradients from the start. These gradients were subsequently modified by migrating melts that drove further development of different types of metasomatic overprinting and variable oxidation at a range of length scales. This oxidation already apparent at ~ 100 km depth could have locally destabilised any pre-existing diamond or graphite.

Narwhal Abundance in the Eastern Canadian High Arctic in 2013

In summer, narwhals (Monodon monoceros) migrate from Baffin Bay to northeastern Canada and northwest Greenland, where they are hunted by Inuit for subsistence. To prevent localized depletion, management of narwhals is based on summer stocks. The High Arctic Cetacean Survey (HACS), conducted in August 2013, was the first survey to estimate abundance of all 4 Canadian Baffin Bay narwhal summer stocks, as well as putative stocks in Jones Sound and Smith Sound, in the same summer. Narwhal abundance was estimated using a double-platform aerial survey. Distance sampling methods were used to estimate detection probability away from the track line. Mark-recapture methods were used to correct for the proportion of narwhals missed by visual observers on the track line (i.e., perception bias). We used a data-driven approach to identify single and duplicate sightings, using 4 covariates to compare differences in sightings made by front and rear observers based on: time of sighting, declination angle, group size, and species identity. Abundance in fjords was estimated using density surface modelling to account for their complex shape and uneven coverage. Estimates were corrected for availability bias (narwhals that are not available for detection because they are submerged when the aircraft passes overhead) using a new analysis of August dive behaviour data from narwhals equipped with satellite-linked time depth recorders. Corrected abundance estimates were 12,694 (95% CI: 6,324–25,481) for the Jones Sound stock; 16,360 (95% CI: 3,833–69,836) for the Smith Sound stock; 49,768 (95% CI: 32,945–75,182) for the Somerset Island stock; 35,043 (95% CI: 14,188–86,553) for the Admiralty Inlet stock; 10,489 (95% CI: 6,342–17,347) for the Eclipse Sound stock; and 17,555 (95% CI: 8,473–36,373) for the East Baffin Island stock. Total abundance for these 6 stocks was estimated at 141,908 (95% CI: 102,464–196,536). Sources of uncertainty arise from the high level of clustering observed, in particular in Admiralty Inlet, Eclipse Sound, and East Baffin Island, as well as the difficulty in identifying duplicate sightings between observers when large aggregations were encountered.

Trace element and stable isotope analysis elucidate stock structure in a narwhal (Monodon monoceros) population with no genetic substructure

Chemical composition of tissues can act as a biological tag to discriminate among groups of animals that inhabit different areas. In Canada, subsistence hunting of the Baffin Bay narwhal (Monodon monoceros Linnaeus, 1758) population is managed as stocks represented by summer aggregations. However, narwhals are highly mobile and are hunted during the migration while stocks mix. Thus, information that can help managers decipher the stock origin of hunted individuals to prevent overexploitation of animals adapted to particular summering grounds is needed. Stable isotope and trace element analyses were conducted on narwhal skin tissues from five stocks in the eastern Canadian Arctic from 1990 to 2015. Discriminant analysis showed a significant difference between Admiralty Inlet and Eclipse Sound stocks in the summer residency period and both differed from Jones Sound and Somerset Island. During the migration season, there was more overlap and less distinction among stocks, but 75% of animals were classified correctly to their defined stocks in both periods. Together stable isotope and trace element analyses are useful for delineating stocks and could be used to complement other stock discrimination approaches.

Assessing the Contributions of Atmospheric/Meteoric Water and Sea Ice Meltwater and Their Influences on Geochemical Properties in Estuaries of the Canadian Arctic Archipelago

Salinity and stable oxygen isotope (δ18O) data collected from eight estuaries distributed throughout the Canadian Arctic Archipelago were used to apportion contributions from local meteoric water (MW) and sea ice meltwater (SIM) sources during July and August of 2015 and 2016. The size of the rivers flowing into the estuaries varied by an order of magnitude (in terms of mean annual discharge); however, the inventories of MW were always greater or equal to SIM inventories, indicating that MW was the dominant freshwater source. Residence times of MW generally ranged between 1 and 8 days, with longer times (> 20 days) computed for estuaries in the Somerset Island and Baffin Island regions. Shorter residence times indicate, but do not confirm, that river waters move through the estuaries and proceed offshore relatively quickly. Despite this swift transport, nonconservative behaviors were observed for barium and dissolved organic carbon (DOC). These behaviors were identified via examination of total alkalinity, barium, and DOC concentrations that remained after accounting for contributions from MW and seawater . Remaining concentrations/anomalies that deviated significantly from a linear correlation with SIM were attributed to nonconservative behaviors (e.g., desorption of barium from river-borne particles, remineralization of DOC) or inaccurate assignments of endmember values in the water type analyses. Thus, these anomalies offer a means to better inform water type analyses in the correct assignment of endmember properties that best represent the environment studied.

Mantle composition, age and geotherm beneath the Darby kimberlite field, west central Rae Craton

The Rae Craton, northern Canada, contains several diamondiferous kimberlite fields that have been a focus of episodic diamond exploration. Relatively little is known about the deep mantle lithosphere underpinning the architecturally complex crust. We present bulk and mineral element and isotopic compositional data for peridotite and pyroxenite/eclogite xenoliths from the Darby kimberlites representing fragments of the west central Rae lithosphere, as well as the first kimberlite eruption age of 542.2±2.6 Ma (2 σ; phlogopite Rb-Sr isochron). Darby peridotites have low bulk Al2O3 contents with highly-depleted olivine (median Mg# = 92.5) characteristic of cratonic lithosphere globally, but more depleted than peridotites from other Rae Craton localities. One peridotite xenolith contains a harzburgitic G10D garnet. Re-Os TRD model ages appear to be the oldest measured to date from peridotites of the Rae lithosphere, having a mode in the early Neoarchean and ranging to the Paleoproterozoic (~2.3 Ga). Concentrate clinopyroxene defines a well constrained mantle geotherm indicating the existence of a ~200 km thick lithosphere at the time of kimberlite eruption, greater than the lithospheric thickness beneath Somerset Island and in good agreement with modern seismic constraints. Nickel-in-garnet thermometry in grains that record temperatures below the mantle adiabat, indicates mantle sampling dominantly in the graphite stability field whereas Al-in-olivine thermometry shows a distinct mantle sampling mode in the diamond stability field. Abundant pyroxenite and eclogite xenoliths are recovered across the Darby property and low-Cr garnet (Cr2O3 < 1 wt%) is the most abundant garnet type recovered in kimberlite concentrate. Based on thermometry, these rocks range in likely depths of equilibration, from the lower crust into the shallow lithospheric mantle. They give variable Os model ages, with the oldest ages in the Mesoarchean. The abundance of this mafic material reflects derivation from a large mafic body possibly evident in the layered structure of the Rae Craton mantle root defined by new seismic studies.

The North America mid‐Cretaceous kimberlite corridor: Wet, edge‐driven decompression melting of an OIB‐type deep mantle source

AbstractThirty new high‐precision U‐Pb perovskite and zircon ages from kimberlites in central North America delineate a corridor of mid‐Cretaceous (115–92 Ma) magmatism that extends ∼4000 km from Somerset Island in Arctic Canada through central Saskatchewan to Kansas, USA. The least contaminated whole rock Sr, Nd, and Hf isotopic data, coupled with Sr isotopic data from groundmass perovskite indicates an exceptionally limited range in Sr‐Nd‐Hf isotopic compositions, clustering at the low ɛNd end of the OIB array. These isotopic compositions are distinct from other studied North American kimberlites and point to a sublithospheric source region. This mid‐Cretaceous kimberlite magmatism cannot be related to mantle plumes associated with the African or Pacific large low‐shear wave velocity province (LLSVP). All three kimberlite fields are adjacent to strongly attenuated lithosphere at the edge of the North American craton. This facilitated edge‐driven convection, a top‐down driven processes that caused decompression melting of the transition zone or overlying asthenosphere. The inversion of ringwoodite and/or wadsleyite and release of H2O, with subsequent metasomatism and synchronous wet partial melting generates a hot CO2 and H2O‐rich protokimberlite melt. Emplacement in the crust is controlled by local lithospheric factors; all three kimberlite fields have mid‐Cretaceous age, reactivated major deep‐seated structures that facilitated kimberlite melt transit through the lithosphere.

The geological record of base metal sulfides in the cratonic mantle: A microscale 187Os/188Os study of peridotite xenoliths from Somerset Island, Rae Craton (Canada)

We report detailed petrographic investigations along with 187Os/188Os data in Base Metal Sulfide (BMS) on four cratonic mantle xenoliths from Somerset Island (Rae Craton, Canada). The results shed light on the processes affecting the Re-Os systematics and provide time constraints on the formation and evolution of the cratonic lithospheric mantle beneath the Rae craton.When devoid of alteration, BMS grains mainly consist of pentlandite+pyrrhotite±chalcopyrite. The relatively high BMS modal abundance of the four investigated xenoliths cannot be reconciled with the residual nature of these peridotites, but requires addition of metasomatic BMS. This is especially evident in the two peridotites with the highest bulk Pd/Ir and Pd/Pt. Metasomatic BMS likely formed during melt/fluid percolation in the Sub Continental Lithospheric Mantle (SCLM) as well as during infiltration of the host kimberlite magma, when djerfisherite crystallized around older Fe-Ni-sulfides. On the whole-rock scale, kimberlite metasomatism is visible in a subset of bulk xenoliths, which defines a Re-Os errorchron that dates the host magma emplacement.The 187Os/188Os measured in the twenty analysed BMS grains vary from 0.1084 to >0.17 and it shows no systematic variation depending on the sulfide mineralogical assemblage. The largest range in 187Os/188Os is observed in BMS grains from the two xenoliths with the highest Pd/Ir, Pd/Pt, and sulfide modal abundance. The whole-rock TRD ages of these two samples underestimate the melting age obtained from BMS, demonstrating that bulk Re-Os model ages from peridotites with clear evidence of metasomatism should be treated with caution.The TRD ages determined in BMS grains are clustered around 2.8–2.7, ∼2.2 and ∼1.9Ga. The 2.8–2.7Ga TRD ages document the main SCLM building event in the Rae craton, which is likely related to the formation of the local greenstone belts in a continental rift setting. The Paleoproterozoic TRD ages can be explained by addition of metasomatic BMS during (i) major lithospheric rifting at ∼2.2Ga and (ii) the Taltson-Thelon orogeny at ∼1.9Ga. The data suggest that even metasomatic BMS can inherit 187Os/188Os from their original mantle source. The lack of isotopic equilibration, even at the micro-scale, allowed the preservation of different populations of BMS grains with distinct 187Os/188Os, providing age information on multiple magmatic events that affected the SCLM.

Interactions between climate and landscape drive Holocene ecological change in a High Arctic lake on Somerset Island, Nunavut, Canada

This study presents a diatom-based analysis of the post-glacial Holocene environmental history at Lake RS29 on Somerset Island in the Canadian High Arctic. Earliest post-glacial diatom assemblages (10 200–10 000 cal yr BP) consisted mainly of small, benthic fragilarioid taxa. Poor diatom preservation in the early Holocene (~10 000–6200 cal yr BP) is associated with warm conditions, as determined by pollen data from the same core and other paleoclimate estimates from the region. Analysis of this and other sites from across the Canadian Arctic suggest that zones of poor diatom preservation or diatom absence in lake sediment records may be associated with warm conditions. After 6200 cal yr BP, acidophilic assemblages consisting of Aulacoseira spp. and a suite of periphytic taxa indicate acidification since the mid-Holocene. During this time period, cooling causing changes in lake ice phenology was likely a major driver of the reconstructed mid-Holocene pH decline. Watershed processes, including reduced fluxes of base cations as the rate of sediment accumulation slowed, may also be contributors to long-term shifts in lake water pH and associated changes in diatom assemblages. The uppermost sediments in the Lake RS29 record were characterized by abrupt declines in Aulacoseira alpigena and increases in benthic diatom taxa Cyclotella sensu lato, suggesting an increase in lake water pH and longer ice-free seasons.

Maximum pile-up heights for grounded ice rubble

Large grounded ice features can be found in all regions of the world where there is moving ice. This paper compiles over 230 reported ice pile-ups from several international locations including the Baltic Sea, Gulf of Bothnia, Caspian Sea, Lake Simcoe, Stonehaven Harbour (New Brunswick), west Newfoundland, Alaskan and Canadian Beaufort Sea, Norton Sound, Bering Sea, Somerset Island and offshore Sakhalin. The NRC Particle-in-Cell numerical model is used to augment the data. A plot of the rubble sail height as a function of the ice block thickness shows considerable scatter but a general increase in sail height with increasing ice thickness. The scatter in the data is real and is attributed to the fact that the conditions for producing the maximum sail height are not met in most situations. An upper bound of the data can be represented by Hs,max=19 hB0.33 where Hs,max is the maximum pile-up height (in m), and hB is the block ice thickness (in m). This equation covers the data range up to 2m in ice thickness. The data also clearly show that high pile-ups (on the order of 10 to 12m high) can be generated from thin ice less than 0.5m thick. Further, sail heights up to 30m are possible for thicker sea ice.

The flora of Cunningham Inlet, Somerset Island, Nunavut: history, analysis, and new collections of vascular plants, mosses, lichens, and algae

New collections of vascular plants, bryophytes, lichen, and algae are reported for Cunningham Inlet on the north coast of Somerset Island, Nunavut. This list of 48 species of vascular plants, 13 bryophytes, 10 lichens, and five algae includes 136 specimens collected in 2013 and 39 previously unreported specimens from the National Herbarium of Canada at the Canadian Museum of Nature (CAN), Agriculture and Agri-Food Canada’s Vascular Plant Herbarium (DAO), and University of Alberta (ALTA). Ten vascular plants from previous collecting in 1958 are re-reported here to give a comprehensive account of the vascular plant flora of the region. Two vascular plants are recorded for the first time for Somerset Island: Smooth Draba (Draba glabella Pursh) and Edlund’s Fescue (Festuca edlundiae S. G. Aiken, Consaul &amp; Lefkovitch).

‘The last duty of an officer’: Lieutenant de vaisseau Joseph-René Bellot, 1826–1853, in the Franklin Search

ABSTRACTLieutenant de vaisseau Joseph René Bellot, (1826–1853) participated, as second-in command, in Lady Franklin's private expedition in search of her missing husband on boardPrince Albert, under the command of Captain William Kennedy in 1851–1852. Having wintered at Batty Bay on the east coast of Somerset Island, Kennedy and Bellot sledged south in the spring of 1852, to Bellot Strait, which they discovered. Having passed through the strait, they crossed Peel Sound, and continued west across Prince of Wales Island to Ommanney Bay, then back across Prince of Wales Island, north to Cape Walker, and back to Batty Bay via the north coast of Somerset Island and Prince Leopold Harbour. They discovered no trace of the missing Franklin expedition. In 1853 Bellot again volunteered to go to the Arctic, this time as supernumerary on board the supply shipPhoenix, Captain Edward Inglefield. From Beechey Island, Bellot volunteered to carry dispatches north up Wellington Channel to Captain Sir Edward Belcher who was in that vicinity. Having been driven out of sea on an ice-floe, Bellot disappeared during a gale, and it is assumed that he was blown off the ice into the water and was drowned. Memorials to Bellot may be found on Beechey Island, at Greenwich, England and at Rochefort, France, but probably the most enduring memorial to him is the name ‘Bellot Strait’, applied by Kennedy to the narrow strait between Somerset Island and Boothia Peninsula which represents an integral component of one variant of the northwest passage.

Chapter 7 Biogeography of the Ordovician and Silurian Stromatoporoidea

Abstract Stromatoporoid sponges first appeared during the late Mid-Ordovician (mid–late Darriwilian) accompanying an important ‘Chazy’ reef-building episode. Representatives of the order Labechiida appeared first, initially splitting into two sister groups: those from North China (nine genera) and those from Laurentia (four genera). Two genera were common to the two regions, but others in North China and Siberia were endemic. This initial provincialism was not maintained into the Late Ordovician (Sandbian) as labechiids attained a wider dispersal, covering Laurentia with peripheral terranes in Northwest Scotland and Chukchi Peninsula, cratonic Siberia, the Urals (eastern margins of Baltica), and East Gondwanan blocks of Tarim North China, marginal Tasmania and the peri-Gondwanan New South Wales island-arc terrane. Only a few endemics remained present in the Sandbian – three in Laurentia, and one in Tarim. In the Katian, maximum diversification of labechiids occurred (19 genera, including a genus possibly transitional to first actinostromatids). Also four genera of the Clathrodictyida first appeared, and overall distribution continued to increase. The Hirnantian marked a dramatic decline in the global distribution (only Anticosti Island, Manitoba, Norway and Estonia) and marked diversity loss of labechiids. Altogether c. 70% of stromatoporoid species disappeared in response to end-Ordovician global cooling events. Llandovery stromatoporoids were widespread in Laurentia, Baltica and Siberia, with clathrodictyids as dominant and labechiids accessory (the latter group more common in Siberia and China). Gradual diversification and expansion of stromatoporoids followed in the late Llandovery, with appearances of the orders Actinostromatida and Stromatoporida. The stromatoporoids became most widespread and most diversified during the Wenlock, with clathrodictyids maintaining their leading position, and the appearances of the earliest Stromatoporellida and Syringostromatida. Rapid spread of new phylogenetic stocks indicates that widespread pandemism prevailed among Wenlock stromatoporoids. The Ludlow was characterized by final closure of the Iapetus Ocean, accompanying uplift of palaeocontinental regions, and declining prominence of stromatoporoid-bearing shallow carbonate shelves. However, clathrodictyids and actinostromatids remained dominant, whereas the incoming of Amphiporida in several regions (Somerset Island, Baltic area, West Ukraine, West and East Urals, Novaya Zemlya, Tien Shan, Japan and New South Wales) and restricted distribution of some other taxa suggest a certain provincialism developed. With regional regression and stratigraphic hiatuses, the stromatoporoids (mostly hangovers from the Ludlow) became less common in the Pridoli, and apparently even entirely absent from Gondwana and Siberia.

A new cyathaspid (Agnatha, Heterostraci) with an articulated oral cover from the Late Silurian of the Canadian Arctic

ABSTRACT A new genus and species of cyathaspid heterostracan, Capitaspis giblingi, gen. et sp. nov., is described from the Late Silurian (Pridolian) Upper Member of the Somerset Island Formation, Northwest Territories, Canada. The new species is most closely related to Pionaspis in the subfamily Cyathaspidinae, family Cyathaspididae, showing similarity in the presence of distinct central, anterior, and lateral epitega and in overall size and proportions, but differing in details of the ridge pattern. The unique specimen of the new taxon has an articulated oral cover that consists of a series of postoral and oral plates. Because the oral cover is almost unknown for cyathaspids, this specimen increases our knowledge of the range of oral structures in this family beyond the simple structures known for Poraspis and Anglaspis.

Hydrologic Thresholds of Ponds in a Polar Desert Wetland Environment, Somerset Island, Nunavut, Canada

Evaluation of the water storage in several ponds near Creswell Bay, Somerset Island, Canada, an area experiencing a polar desert climate (cool, moist), served to reveal factors that are important in the sustainability of these freshwater ecosystems within a larger wetland complex. Our study focused on the hydrology of 12 ponds of different sizes in various geomorphologic settings: moraine, bedrock, and coastal areas. A positive water balance plays an important role in the survival of the ponds experiencing variable climatic conditions and survival over the season depends largely on the local enrichment of water through various hydrologic linkages. Pond inputs and losses are governed by the pond catchment topography, substrate, hydrology, and seasonal climatic conditions. Low hydrologic energy and long hydroperiod (e.g., ponds in surface-flow dominated systems with multiple hydrologic linkages) are associated with a high degree of pond sustainability. Ponds with high hydrologic energy and short hydroperiods (e.g., ponds in precipitation and groundwater-dominated systems) show limited hydrologic sustainability. We suggest that these latter ponds in this polar desert environment will be the most vulnerable to future climate warming in the Canadian High Arctic.

Constraints on the depth and thermal history of cratonic lithosphere from peridotite xenoliths, xenocrysts and seismology

Despite the relatively long-standing availability of numerical approaches for estimating palaeogeotherms using peridotite xenolith Pressure–Temperature (P–T) data, the practise of fitting xenolith P–T arrays to simple models of lithospheric heat generation, in a non-quantitative manner, remains widespread. The lack of quantification in both the magnitude and uncertainty of heat flow and lithosphere thickness estimates leads to difficulty in evaluating proposed models for lithosphere evolution on a local and regional scale.Here, we explore the advantages of using a numerical approach to palaeogeotherm fitting, in terms of the ability to make objective comparisons of the effect that differing thermobarometer combinations and varying states of mineral and textural equilibrium have on the shape of the palaeogeotherm, and the resulting estimates of lithospheric thickness and heat flow. We also make quantitative comparisons between lithospheric mantle properties estimated using peridotite xenoliths versus single mineral xenocrysts. Using two reference peridotite xenolith databases from Bultfontein (S. Africa) and Somerset Island (Canada) we show that the same lithospheric mantle properties are predicted using harzburgite versus lherzolite thermobarometry methods. Filtering mineral data for the effects of inter-mineral disequilibrium does not produce significantly different palaeogeotherms but does increase the quality of fit of the palaeogeotherm to the P–T data, allowing more confidence to be placed in comparisons between locations. Palaeogeotherms calculated using xenocryst data, screened for peridotitic affinities, show misfits that are 2–3 times greater than those obtained using xenoliths. Lithospheric properties calculated from the Somerset Island xenocryst-based geotherm yield results that are within error of the xenolith estimate.A mutually consistent and quantitative palaeogeotherm fitting approach is used to evaluate existing hypotheses for the evolution of the southern African lithosphere. We find very similar estimates for the heat flow and thickness of the lithosphere between SW Namibia (off-craton) and Bultfontein (on-craton). This supports suggestions of a cratonic thermal regime and equivalent lithospheric thickness across that region of southern Africa at the time of kimberlite sampling, with concurrent local thermal disturbance evident in Namibia. Complimentary, novel, seismically-obtained geotherm estimates show that the lithosphere in Namibia is now significantly thinner than the estimate at 70Ma obtained from xenolith thermobarometry.

The Sunrise Mission

The first science flight of the balloon-borne Sunrise telescope took place in June 2009 from ESRANGE (near Kiruna/Sweden) to Somerset Island in northern Canada. We describe the scientific aims and mission concept of the project and give an overview and a description of the various hardware components: the 1-m main telescope with its postfocus science instruments (the UV filter imager SuFI and the imaging vector magnetograph IMaX) and support instruments (image stabilizing and light distribution system ISLiD and correlating wavefront sensor CWS), the optomechanical support structure and the instrument mounting concept, the gondola structure and the power, pointing, and telemetry systems, and the general electronics architecture. We also explain the optimization of the structural and thermal design of the complete payload. The preparations for the science flight are described, including AIV and ground calibration of the instruments. The course of events during the science flight is outlined, up to the recovery activities. Finally, the in-flight performance of the instrumentation is discussed.

The Bermuda Company, the Privy Council, and the Wreck of the San Antonio, 1621–23

In September 1621, Governor Nathaniel Butler of Bermuda was woken in the middle of the night to hear a report that one hundred Spaniards had landed on the west part of the islands. Bermuda had long been at risk of attack because of its close proximity to the homebound route of the Spanish treasure fleet, so Butler understandably went on the defensive. He ordered the manning of several forts and repaired to the landing area with twenty armed men, expecting to pick up additional strength along the way. Rather than find an invading enemy, Butler and his men found a group of Portuguese and Spanish men, women, and children, whose ship—the 300-tonne, Portuguese-owned San Antonio—had been separated from the treasure fleet by a bad storm and wrecked upon the rocks ten miles west of the islands. Saving what goods they could carry, most of the castaways made their way to Mangrove Bay at the north part of Somerset Island in a small cockboat.