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Miles D Lamare - One of the best experts on this subject based on the ideXlab platform.
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origin and transport of larvae of the sea urchin evechinus chloroticus echinodermata echinoidea in a new zealand Fiord
Marine Ecology Progress Series, 1998Co-Authors: Miles D LamareAbstract:Larval transport was investigated in a New Zealand Fiord by examining the reproductive cycles and larval distributions of the sea urchin Evechinus chloroticus Valenciennes, and the hydrography in Doubtful Sound over 2 sampling periods (SP). These were from 27 September 1993 to 24 March 1994 (SP1993/94) and 27 October 1994 to 11 May 1995 (SP1994/95). Reproductive cycles of E. chloroticus were monitored at 2-weekly or monthly intervals in 3 populations in the Fiord, while the transport and development of larvae were examined by plankton sampling every 2 wk at 4 permanent stations inside the Fiord, and 1 permanent station outside. To determine water exchange in Doubtful Sound, an S4 current meter was deployed at the entrance of the Fiord at 15 m depth. The Fiord has an estuarine circulation pattern with a thin low salinity surface layer flowing seaward, below which is a compensatory landward flow of seawater. A major, synchronous spawning of E. chloroticus was observed during SP1993/94 which produced a widespread, single cohort of larvae throughout the Fiord. In SP1994/95. spawning was fractional and asynchronous and resulted in 2 cohorts of larvae during the summer. Larval densities were an order of magnitude higher during SP1993/94 (2743.0 larvae tow-') than in SP1994/95 (155.3 larvae tow-'). E. chloroticus larval distribution patterns indicate that there was a high level of larval retention within the Fiord, consistent with the estuarine circulation pattern. During SP1993/94. average larval densit.ies 4 wk after spawning ranged from 65.3 to 461.0 larvae tow-' within the Fiord. compared to an average of 2.0 larvae tow-' at the outer site. Similarly, during SP1994/95 larval densities were consistently higher within Doubtful Sound than at the outer site. Larvae completed development within 4 to 6 wk in Doubtful Sound. These results suggest that recruitment of E chloroticus In Doubtful Sound is by larvae that have originated, been retained and completed development within the flord Reduced larval exchange provides a mechanism for observed genetic differentiation of this populatlon. K E Y WORDS: Echinoid . Sea urchin . Larval transport . Closed populatlon . Recruitment . Estuarine circulation . Fiord . Larval biology . Evechinus cl~loroticus
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mass spawning by the sea urchin evechinus chloroticus echinodermata echinoidea in a new zealand Fiord
Marine Biology, 1998Co-Authors: Miles D Lamare, B G StewartAbstract:A mass synchronous spawning of the sea urchin Evechinus chloroticus (Valenciennes) was observed in situ in Doubtful Sound, a large New Zealand Fiord. Spawning occurred between 17:30 hrs and 18:30 hrs on 27 January 1994 and coincided with a full moon, spring tides and a period of decreasing sea temperatures. During spawning, the sea urchins formed a dense spawning aggregation of both sexes, with >90% of the urchins observed spawning at the time. Spawned gametes clouded the water column, and some were eaten by small labrid fish species. The spawning, which may have been as widespread as 40 km, marked a 42 to 50% decrease in gonad indices and resulted in a widespread, dense cohort of E. chloroticus larvae within the Fiord.
B G Stewart - One of the best experts on this subject based on the ideXlab platform.
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Fiord populations of astrobrachion constrictum ophiuroidea asteroschematidae show little genetic differentiation for mitochondrial dna
New Zealand Journal of Zoology, 2015Co-Authors: D J Steel, B G Stewart, Steven A Trewick, Graham P WallisAbstract:The Fiords of southwestern New Zealand may promote the existence of genetically divergent populations as a result of geological and ecological isolation. The ophiuroid Astrobrachion constrictum lives on black coral in these Fiords, and is thought to have a relatively short pelagic larval duration that may limit dispersal among populations. Samples of A. constrictum were collected from seven sites (four Fiords) in Fiordland. Analysis of the mitochondrial COI gene using single-stranded conformational polymorphism revealed eight haplotypes, representatives of which were sequenced. These included nine variable sites, none of which were phylogenetically informative. G-test and AMOVA revealed little structuring of samples within or among Fiords, but there was evidence for reduced gene flow among the most geographically separated Fiords. We conclude that Fiords do not house relict populations from earlier glaciations, and that little differential sorting of haplotypes has occurred in the last 10,000 years.
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mass spawning by the sea urchin evechinus chloroticus echinodermata echinoidea in a new zealand Fiord
Marine Biology, 1998Co-Authors: Miles D Lamare, B G StewartAbstract:A mass synchronous spawning of the sea urchin Evechinus chloroticus (Valenciennes) was observed in situ in Doubtful Sound, a large New Zealand Fiord. Spawning occurred between 17:30 hrs and 18:30 hrs on 27 January 1994 and coincided with a full moon, spring tides and a period of decreasing sea temperatures. During spawning, the sea urchins formed a dense spawning aggregation of both sexes, with >90% of the urchins observed spawning at the time. Spawned gametes clouded the water column, and some were eaten by small labrid fish species. The spawning, which may have been as widespread as 40 km, marked a 42 to 50% decrease in gonad indices and resulted in a widespread, dense cohort of E. chloroticus larvae within the Fiord.
Robert Gilbert - One of the best experts on this subject based on the ideXlab platform.
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Holocene glacimarine sedimentary environments in Fiords of Disko Bugt, West Greenland
Quaternary Science Reviews, 2002Co-Authors: Joseph R. Desloges, Robert Gilbert, Niels Nielsen, Morten Rasch, Christian Christiansen, Rikke ØhlenschlägerAbstract:Abstract Acoustic and sedimentary properties of three Fiord systems were examined in the region of Disko Bugt, West Greenland to understand variability in the processes, rates and sources of sediment delivery during the late glacial and Holocene. Kangerluk and Kangersooq of western Disko are dominated by meltwater inputs of sediment from local ice fields of the island interior. Modern sediments are delivered primarily via overflow currents (rainout), occasional bottom currents and small amounts of iceberg rafting where exposure to Baffin Bay allows penetration of the West Greenland Current. 14 C and acoustic-derived accumulation rates for the last 1–2 ka vary from about 1 mm a −1 in distal Fiord settings to more than 5 mm a −1 in proximal sites adjacent to actively building deltas. These rates are generally larger than has been observed in other Greenland and Baffin Bay Fiords. The tidewater terminus of Inland Ice at Ikerasak is also meltwater dominated but produces lower than expected sediment accumulation due to low gradients of the outlet ice and resistant substrates. These high latitude West Greenland Fiords are subarctic in character and contrast significantly with colder polar-type Fiords at similar latitudes in East Greenland. Sediment deposition which was focused in the outer Disko Fiords during the late-glacial and early Holocene, is due to one of two possible mechanisms: standstill of local ice or enhanced rafting of sediment from Disko Bugt icebergs. This study contributes to the debate on the extent of glaciation and Holocene spatial variability in Fiord processes of West Greenland.
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Environmental assessment from the sedimentary record of high-latitude Fiords
Geomorphology, 2000Co-Authors: Robert GilbertAbstract:The sedimentary record of Fiords at high latitude where global change may be occurring earliest and will be greatest has the potential for assessment of environmental change at both low resolution (the scale of millennia) and high resolution (decadal to less than daily). Unlike the lacustrine record which has been used very successfully in these studies, the sedimentary processes and thus the sedimentary deposits of Fiords differ (1) in the role of salt water in inhibiting mixing and promoting flocculation, and through the role of sea-ice, (2) in the exchange of mass and energy with the much larger ocean beyond, and (3) in the role of benthic biota in the sedimentary environment. The work reviewed in this paper shows that Fiord sediments are being used to assess sedimentary and oceanic processes, as well as glacial, periglacial and geomorphic history, and that they are important proxies for long-term climate and hydrology. Recommendations for advancing this work include long-term monitoring of conditions in Fiords and their drainage basins so that the transfer relations can be more solidly constructed from the proxy of Fiord sediment. Integration of results from Fiords in opposite polar latitudes, and among proxies especially from lacustrine and ice-core records will produce valuable insights. Assessment of the range of conditions in Fiords from the most polar to temperate regions is important to building models of their processes and understanding of the paleoenvironmental signals that can be interpreted from each type.
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Contrasting glacimarine sedimentary environments of two arctic Fiords on Disko, West Greenland
Marine Geology, 1998Co-Authors: Robert Gilbert, Niels Nielsen, Joseph R. Desloges, Morten RaschAbstract:Abstract Two Fiords, Kangerluk and Akulliit, on the island of Disko, central West Greenland have very different sedimentary regimes caused by differences in the characteristics of their drainage basins and in the exposure of their waters to the open sea of Baffin Bay. Their insular location also results in much lower input of water and sediment than in nearby Fiords on the mainland of Greenland that are affected by glaciers from the Greenland Ice Cap. Akulliit has a small drainage basin and low input of water and sediment; it is directly exposed to the higher energy wave environment of Baffin Bay. As a consequence, the mean thickness of Holocene glacimarine sediment assessed in acoustic records is less than 6 m in the inner and middle reaches of the Fiord (mean Holocene accumulation, 0.4 mm/a) and about 11 m (1 mm/a) near the mouth. Dated core sediment indicates that rates are less than 0.5 mm/a in the outer Fiord in the last 2 ka. The larger, more glacier-covered drainage basin of Kangerluk contributes much larger loads of sediment to a Fiord environment protected from the open sea. As a result, Holocene glacimarine sediment is more than 80 m thick in the inner Fiord (mean Holocene accumulation up to 5 mm/a), decreasing to 10–40 m (about 1 mm/a) in the middle reaches. Accumulation rates in Kangerluk are within the range of arctic Fiords, including those of Baffin Island, but those in Akulliit are near the lower limit. The decrease in thickness distally in Kangerluk is typical of arctic Fiords, but the opposite trend in Akulliit is probably due to erosion and re-distribution of sediment in the higher energy environment there.
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marine mollusca from expedition Fiord western axel heiberg island northwest territories canada
Arctic, 1996Co-Authors: Alec E Aitken, Robert GilbertAbstract:Marine molluscs, including bivalves, gastropods and scaphopods, were recovered by dredging at depths of 3-82 m in Expedition Fiord, Axel Heiberg Island, Canada. Cluster analysis, based on presence/absence data at 27 stations, defined two mollusc associations within the Fiord. A Portlandia-Thyasira association, characterized by the abundance of Portlandia arctica and Thyasira gouldi , inhabits silty clay substrates at depths of 32-82 m throughout the Fiord. An Astarte association, characterized by the abundance of Astarte borealis and Astarte warhami , inhabits sandy mud substrates at depths of 3-32 m in the middle and outer Fiord. The absence of this mollusc association at the Fiord head suggests that the suspension-feeding molluscs that constitute this association, such as Astarte , Hiatella , Mya and Trichotropis , are intolerant of the lowered salinities and high suspended-sediment concentrations created by the discharge of Expedition River into the Fiord-head environment. The Expedition Fiord molluscan fauna is compared to the molluscan fauna recorded in Jorgen Bronlund Fjord, Greenland. In the latter Fiord, shallow-water (5-19 m) molluscan faunas are characterized by the abundance of Portlandia arctica and Hiatella arctica , while deep-water (22-48 m) faunas are characterized by the abundance of Thyasira dunbari . Molluscs recovered live in both of these Fiords are distributed widely in high-latitude Fiord and continental shelf environments. Key words: mollusca, Fiords, Canadian Arctic, Axel Heiberg Island, Greenland, ecology, zoogeography
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Early Holocene deglaciation of Expedition and Strand Fiords, Canadian High Arctic
Canadian Journal of Earth Sciences, 1994Co-Authors: Donald S Lemmen, Alec E Aitken, Robert GilbertAbstract:Terrestrial and marine records provide the first reconstruction of past glacial events on west-central Axel Heiberg Island. Lateral moraines along Expedition Fiord define an early Holocene ice margin when a trunk glacier occupied the inner half of the Fiord. Limited sediment accumulation in the outer Fiord ( 8.4 ka BP, principally by calving of an unstable ice front to a position well upvalley of the present ice limit. Rapid deglaciation is evidenced by (i) an absence of ice marginal landforms and related marine biofacies; (ii) a scarcity of raised marine sediments; and (iii) exceptionally thin sediments (
Colin K Bloom - One of the best experts on this subject based on the ideXlab platform.
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catastrophic landscape modification from a massive landslide tsunami in taan Fiord alaska
Geomorphology, 2020Co-Authors: Dan H Shugar, Bretwood Higman, Jeremy G Venditti, Colin K Bloom, Breanyn Macinnes, Bruce M Richmond, Eric L BilderbackAbstract:Abstract The October 17th, 2015 Taan Fiord landslide and tsunami generated a runup of 193 m, nearly an order of magnitude greater than most previously surveyed tsunamis. To date, most post-tsunami surveys are from earthquake-generated tsunamis and the geomorphic signatures of landslide tsunamis or their potential for preservation are largely uncharacterized. Additionally, clear modifications described during previous post-tsunami surveys are often ephemeral and unlikely to be preserved. Documented geomorphic modifications of several low gradient fan deltas within Taan Fiord make it an excellent laboratory for characterizing signatures of a landslide tsunami event. Geomorphic changes to fan deltas in Taan Fiord caused by the landslide-generated tsunami included complete vegetation loss over more than 0.6 km2 of fan surfaces, formation of steep fan front scarps up to 10 m high, extensive local alterations of fan topography, and formation of new tsunami return-flow channels. Two relatively stable fan deltas in Taan Fiord were heavily vegetated prior to the Taan event and may preserve features of tsunami modification for decades to centuries. If this is the case, fan deltas may be a previously unrecognized location for preservation of tsunami signatures in the recent past. Fans in poorly monitored regions, such as Greenland, could thus hold evidence of previously unidentified recent landslide tsunami events.
C F Larsen - One of the best experts on this subject based on the ideXlab platform.
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sedimentology and geomorphology of a large tsunamigenic landslide taan Fiord alaska
Sedimentary Geology, 2017Co-Authors: Anja Dufresne, Marten Geertsema, Dan H Shugar, Michele Koppes, Bretwood Higman, Peter J Haeussler, Colin P Stark, Jeremy G Venditti, Doug Bonno, C F LarsenAbstract:Abstract On 17 October 2015, a landslide of roughly 60 × 10 6 m 3 occurred at the terminus of Tyndall Glacier in Taan Fiord, southeastern Alaska. It caused a tsunami that inundated an area over 20 km 2 , whereas the landslide debris itself deposited within a much smaller area of approximately 2 km 2 . It is a unique event in that the landslide debris was deposited into three very different environments: on the glacier surface, on land, and in the marine waters of the fjord. Part of the debris traversed the width of the fjord and re-emerged onto land, depositing coherent hummocks with preserved source stratigraphy on an alluvial fan and adjacent moraines on the far side of the fjord. Imagery from before the landslide shows that the catastrophic slope failure was preceded by deformation and sliding for at least the two decades since the glacier retreated to its current terminus location, exposing steep and extensively faulted slopes. A small volume of the total slide mass remains within the source area and is topped by striated blocks (> 10 m across) and standing trees that were transported down the slope in intact positions during the landslide. Field work was carried out in the summer of 2016, and by the time this paper was written, almost all of the supraglacial debris was advected into the fjord and half the subaerial hummocks were buried by glacial advance; this rapid change illustrates how highly active sedimentary processes in high-altitude glacial settings can skew any landslide-frequency analyses, and emphasizes the need for timely field investigations of these natural hazards.