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Browsing by Author "Blasco, Steve"

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    11,000 yrs of environmental change in the Northwest Passage; a multiproxy core record from central Parry Channel, Canadian High Arctic
    (2013) Pieńkowski, Anna J.; England, John H.; Furze, Mark F.A.; Blasco, Steve; Mudie, Peta J.; MacLean, Brian
    a rare paleoenvironmental archive from the understudied west-central Canadian Arctic Archipelago. Lithological, biogeochemical, and microfossil (dinoflagellate cysts, non-pollen palynomorphs, benthic and planktonic foraminifera) characteristics, in combination with a chronostratigraphy based on seventeen radiocarbon dates, show seven prominent paleoenvironmental episodes since the end of the last regional glaciation. The basal diamict (Zone I) records decoupling of previously grounded glacial ice, followed by ice-proximal conditions (Zone IIa) commencing at ~ 10.8 cal ka BP (age-depth model extrapolation). After an interval of pervasive sea-ice (Zone IIb), ice-distal conditions are established (Zone IIc). Although sparse microfossils are present in glaciomarine sediments (Zone II), noticeable biological activity with heightened abundances and diversities across all groups begins in the postglacial Zone III (10.3–10.0 cal ka BP) when planktonic foraminifera (Neogloboquadrina pachyderma) appear. As planktonics are excluded from the study area today (due to shallow inter-channel sills), this likely signals the inflow of relatively warm and saline Atlantic-derived Arctic Intermediate Water below 250 m, presumably facilitated by glacio-isostatically enhanced deglacial water depths. The subsequent Zone IV (10.0–7.0 cal ka BP), characterized by heightened biological productivity in both plankton and benthos and reduced seasonal sea-ice cover, may correspond to a previously proposed Holocene Thermal Maximum. This apparent amelioration ends by the mid Holocene (Zone V; 7.0–5.7 cal ka BP) when Arctic Intermediate Water is excluded from the study area and water depths approach modern values. High-Arctic conditions with seasonal sea-ice cover, a circulation dominated by Arctic Ocean Surface Water, and microfossil assemblages similar to modern are found from ~ 5.7 cal ka BP onwards (Zones VI–VII). As only minor environmental fluctuations are apparent during the late Holocene, shorter-term climatic episodes (e.g. Little Ice Age) are not recognized in this record.
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    Atlantic water inflow in the early Holocene Northwest Passage marked by planktonic foraminifera (Neogloboquadrina pachyderma)
    (2015) Pieńkowski, Anna J.; Cage, Alix; Furze, Mark F.A.; Figueiredo Martins, Ana Sílvia de; England, John H.; McLean, Brian; Blasco, Steve
    Four marine piston cores from the central Canadian Arctic Archipelago (CAA), investigated for sedimentology, micropalaeontology, and biogeochemistry (52 AMS radiocarbon dates), uniformly show the prominent early Holocene (˜10 cal ka BP) appearance of planktonic foraminifera immediately following deglaciation.
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    The deglacial to postglacial marine environments of SE Barrow Strait, Canadian Arctic Archipelago
    (2012) Pieńkowski, Anna J.; England, John H.; Furze, Mark F.A.; Marret, Fabienne; Eynaud, Frederique; Vilks, Gustav; MacLean, Brian; Blasco, Steve; Scourse, James D.
    Core 86027-144 (74°15.56′N, 91°14.21′W) represents a rare, continuous record of Late Pleistocene to Holocene sediments from High Arctic Canada extending from the end of the Last Glaciation. Based on microfossils (dinocysts, non-pollen palynomorphs, benthic and planktonic foraminifera), foraminiferal δ18O and δ13C, and sedimentology, seven palaeoenvironmental zones were identified. Zone I (>10.8 cal. ka BP) records deglaciation, ice-sheet destabilization, float-off and subsequent break-up. Zone II (c. 10.8–10.4 cal. ka BP) shows ice-proximal to ice-distal glaciomarine conditions, interrupted by pervasive land-fast sea-ice marked by a hiatus in coarse sediment deposition. Significant biological activity starts in Zone III (10.4–9.9 cal. ka BP), where planktonic foraminifera (Neogloboquadrina pachyderma) suggest early oceanic throughflow. Surface waters flowed NW–SE; however, the deep-water origin remains unclear (potentially NW Arctic Ocean or Baffin Bay). Postglacial amelioration (open-water season greater than present) in Zone IV (9.9–7.8 cal. ka BP) perhaps corresponds to the regional ‘Holocene Thermal Maximum’ previously proposed. A transitional period (Zone V; 7.8–6.7 cal. ka BP) of rapid environmental change fluctuating on a scale not observed today is marked by increasing sea-ice and reduced oceanic influence. This probably signals the exclusion of deeper Atlantic water owing to the glacio-isostatic shallowing of inter-island sills, coupled with generally cooling climate. Conditions analogous to those at present, with increased sea-ice and modern microfossil assemblages, commence at c. 6.7 cal. ka BP (zones VI–VII). Although climate ultimately forces long-term environmental trends, core 86027-144 data imply that regional dynamics, especially changes in sea-level, exert a significant control on marine conditions throughout the Canadian Arctic Archipelago.
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    Iceshelf instability and the collapsing NW margin of the Laurentide Ice Sheet: core evidence from Viscount Melville Sound, Arctic Canada
    (2013) Furze, Mark F.A.; Pieńkowski, Anna J.; England, John H.; Esteves, Mariana da Silveira Ramos; Bennett, Robbie; Krywko, Jack; Glembiski, Danna; McLean, Brian; Blasco, Steve
    Recent work in the western Canadian Arctic Archipelago has seen a dramatic re-evaluation of the timing and extent of Late Wisconsinan glaciation by a primarily cold-based Laurentide Ice sheet. This has included the occupation by ice of formerly-considered ice free terrain and the extension of grounded ice from the main channels of the Northwest Passage, westwards onto the Beaufort Sea continental shelf. Nonetheless, while the pattern of ice extent and initial retreat is now well constrained, significant questions remain regarding the main phase of ice retreat southeastwards onto mainland Canada and the stability of the retreating margin in response to ameliorating climate and sea-level change.
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    The late Quaternary environmental evolution of marine Arctic Canada; Barrow Strait to Lancaster Sound
    (2014) Pieńkowski, Anna J.; England, John H.; Furze, Mark F.A.; MacLean, Brian; Blasco, Steve
    A marine sediment core from the east-central Canadian Arctic Archipelago (Core 86027-154; 74° 22.01′N 89° 51.26′W; 329 m water depth), studied by a multiproxy approach [lithostratigraphy, biogeochemistry, micropalaeontology (dinoflagellate cysts, other non-pollen palynomorphs, benthic and planktonic foraminifera, ostracods)], and encompassing 14 AMS 14C dates, provides valuable insights into regional deglacial to Holocene palaeoenvironments. Six palaeoenvironmental zones are recognized, based on prominent changes in the litho- and biostratigraphy. The waterlain diamicton of Zone I records immediate deglaciation, being derived from lift-off and calving of previously grounded glacial ice. Though deglacial timing is complicated by the sparsity of dating materials and the Portlandia Effect, age–depth model extrapolation places deglaciation at 11.54 cal ka BP. Zone II (11.5–11.0 cal ka BP) represents a distinct progression from initially ice-proximal to increasingly ice-distal conditions, interrupted by an interval of pervasive sea-ice (11.4–11.2 cal ka BP). Noteworthy biological activity commences in Zone III (11.0–9.7 cal ka BP) with a prominent signal of planktonic foraminifera (Neogloboquadrina pachyderma). This likely signifies penetration of deeper, Atlantic-derived water through the central Canadian Arctic Archipelago upon deglaciation, facilitated by the greater, glacioisostatically-induced water depths (+80 m), and implies separation of Laurentide and Innuitian ice sheets by ∼11.0 cal ka BP. Zone IV (9.7–7.2 cal ka BP) records ameliorated, biologically favourable conditions with reduced seasonal sea-ice accompanied by high microfossil species diversity and the presence of subpolar taxa. Zone V (7.2–6.5 cal ka BP) signals the exclusion of Atlantic-derived water, concomitant with increasing sea-ice, simultaneously representing the termination of the dynamic deglacial to early Holocene environments (zones I–IV). Conditions similar to modern typified by uniform sediment characteristics, present-day microfossil assemblage structures, and sparse benthic foraminifera were established by 5.6 cal ka BP (Zone VI).
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    The late Quaternary environmental evolution of the Northwest Passage: a marine perspective
    (2012) Pieńkowski, Anna J.; Furze, Mark F.A.; MacLean, Brian; Vilks, Gustav; Blasco, Steve
    Here we present direct marine data from three long (piston and trigger weight) sediment cores from the central Northwest Passage (Lancaster Sound/Barrow Strait: core 86027-154; southeastern Barrow Strait: 86027-144; western Barrow Strait: 9722-004), investigated in a multiproxy approach for sedimentological characteristics, microfossils (dinocysts, non-pollen palynomorphs, benthic and planktonic foraminifera, ostracods), and stable isotope ratios.
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    Late Quaternary marine records from High Arctic Canada: problems, solutions, and multiproxy perspectives
    (2013) Pieńkowski, Anna J.; Furze, Mark F.A.; England, John H.; MacLean, Brian; Von Prause, Markus; Blasco, Steve
    The Canadian Arctic Archipelago (= CAA) constitutes a significant geographic region within the Arctic Ocean Basin, influencing its oceanography, biology, ecology, and climate. Yet comparatively little is known about the long-term (post-Late Wisconsinan) environmental history of the marine channels of this region (the “Northwest Passage” = NWP). New marine data emerging from the central CAA extending back to regional deglaciation highlight the potential of multiproxy approaches in high-latitude settings.