26 research outputs found
Relict Late Wisconsinan Dune Fields of the Northern Great Plains, Canada
Late Wisconsinan dune activity is investigated within the present-day boreal forest and parkland regions of the northern Great Plains, Canada, to extend the understanding of the spatial and temporal eolian record. Optical ages from stabilized sand dunes document the timing of past activity. Eolian activity ranges from about 16 ka in west-central Alberta to 9 ka in northwestern Saskatchewan. Between about 16 and 13 ka, dune activity in central Alberta occurred in an ice-proximal tundra setting along the margins of the Laurentide and Cordilleran ice sheets. Predominant dune-forming winds were from the west and northwest. Dune activity continued in this area between about 13 and 11 ka within parkland and grassland settings as the Laurentide Ice Sheet retreated to the northeast. Winds continued to blow from the west and northwest, and the climate was likely influenced by an increasingly dominant Pacific air mass. Also beginning at about 13 ka, dune-forming winds along the margins of the retreating Laurentide Ice Sheet were influenced by anticyclonic winds from the southeast that were maintained until about 9 ka. As the Laurentide Ice Sheet retreated, these southeasterly anticyclonic winds were successively replaced by winds from the northwest associated with the Pacific air mass. Dune activity across the region terminated in a time-transgressive manner from the southwest, at about 11 ka, to the northeast, at about 9 ka, with the establishment of boreal forest vegetation and reduced wind strength.Les auteurs Ă©tudient lâactivitĂ© dunaire au Wisconsinien tardif dans la forĂȘt borĂ©ale et la prairie-parc actuelles des Grandes Plaines septentrionales du Canada, afin dâapprofondir les connaissances sur lâĂ©volution spatiotemporelle de lâactivitĂ© Ă©olienne. Les Ăąges optiques mesurĂ©s sur des dunes de sable stabilisĂ©es permettent de reconstituer la chronologie de lâactivitĂ© passĂ©e. Les Ăąges de lâactivitĂ© Ă©olienne sâĂ©chelonnent entre 16 ka dans le centre-ouest de lâAlberta et 9 ka dans le nord-ouest de la Saskatchewan. Entre 16 et 13 ka, lâactivitĂ© dunaire dans le centre de lâAlberta a eu lieu dans un environnement de toundra juxtaglaciaire le long des marges des inlandsis laurentidien et cordillĂ©rien. Les vents efficaces prĂ©dominants soufflaient de lâouest et du nord-ouest. LâactivitĂ© dunaire sâest poursuivie dans cette rĂ©gion entre 13 et 11 ka dans des environnements de prairie-parc et de prairie herbageuse, avec le recul de lâInlandsis laurentidien vers le nord-est. Les vents ont continuĂ© de souffler de lâouest et du nord-ouest, et le climat a probablement Ă©tĂ© influencĂ© par une masse dâair du Pacifique de plus en plus dominante. Ăgalement au dĂ©but de 13 ka, les vents efficaces le long des marges de lâInlandsis laurentidien en recul ont Ă©tĂ© influencĂ©es par des vents anticycloniques du sud-ouest, qui ont durĂ© jusquâĂ 9 ka. Avec le retrait de lâInlandsis laurentidien, ces vents ont Ă©tĂ© successivement remplacĂ©s par des vents du nord-ouest associĂ©s Ă la masse dâair du Pacifique. LâactivitĂ© dunaire dans la rĂ©gion sâest terminĂ©e de façon diachrone Ă partir du sud-ouest, vers 11 ka, jusquâau nord-est, vers 9 ka, par lâĂ©tablissement dâune vĂ©gĂ©tation forestiĂšre borĂ©ale et la diminution de la force des vents
Potential Aboriginal-Occupation-Induced Dune Activity, Elbow Sand Hills, Northern Great Plains, Canada
Geomorphological and archeological evidence indicates potential linkages between Plains aboriginal occupation and dune activity in the Elbow Sand Hills of southern Saskatchewan, Canada. Vegetation encroachment has rapidly outpaced migration of an active dune complex over the last 65 years. Optical ages of stabilized dune remnants indicate that dune activity predates Euro-Canadian settlement (ca. AD 1900). Early Euro-Canadian explorers observed local occupation and exploitation of the sand hills by aboriginal groups for herding and impounding bison. Mapping of archeological sites in relation to physiography reveals that sand dunes, in close proximity to permanent water resources, were preferred areas of occupation. Collectively, these results support the hypothesis that aboriginal occupation disturbance may have perpetuated dune activity in the Elbow Sand Hills until the late 19th century, and that Euro-Canadian settlement and land use emphasizing conservation may have encouraged recent stabilization. We propose that similar aboriginal occupation disturbances may have been responsible for perpetuating dune activity in other dune fields in the Great Plains. To this end, climatic variability should not be considered exclusive of other drivers of dune activity in semivegetated inland dune fields of the Great Plains
Scale-dependent perspectives on the geomorphology and evolution of beachdune systems
Despite widespread recognition that landforms are complex Earth systems with process-response linkages that span temporal scales from seconds to millennia and spatial scales from sand grains to landscapes, research that integrates knowledge across these scales is fairly uncommon. As a result, understanding of geomorphic systems is often scale-constrained due to a host of methodological, logistical, and theoretical factors that limit the scope of how Earth scientists study landforms and broader landscapes.
This paper reviews recent advances in understanding of the geomorphology of beach-dune systems derived from over a decade of collaborative research from Prince Edward Island (PEI), Canada. A comprehensive summary of key findings is provided from short-term experiments embedded within a decade-long monitoring program and a multi-decadal reconstruction of coastal landscape change. Specific attention is paid to the challenges of scale integration and the contextual limitations research at specific spatial and/or temporal scales imposes.
A conceptual framework is presented that integrates across key scales of investigation in geomorphology and is grounded in classic ideas in Earth surface sciences on the effectiveness of formative events at different scales. The paper uses this framework to organize the review of this body of research in a 'scale aware' way and, thereby, identifies many new advances in knowledge on the form and function of subaerial beach-dune systems.
Finally, the paper offers a synopsis of how greater understanding of the complexities at different scales can be used to inform the development of predictive models, especially those at a temporal scale of decades to centuries, which are most relevant to coastal management issues. Models at this (landform) scale require an understanding of controls that exist at both âlandscapeâ and âplotâ scales. Landscape scale controls such as sea level change, regional climate, and the underlying geologic framework essentially provide bounding conditions for independent variables such as winds, waves, water levels, and littoral sediment supply. Similarly, an holistic understanding of the range of processes, feedbacks, and linkages at the finer plot scale is required to inform and verify the assumptions that underly the physical modelling of beach-dune interaction at the landform scale
Holocene Eolian Activity in South-central Saskatchewan and the Southern Canadian Prairies
The chronology and stratigraphy of eolian deposits at two sites in south-central Saskatchewan were studied in order to extend the spatial and temporal record of dune activity on the Canadian prairies. Optical ages document the timing of valley-infilling by sand dunes in the QuâAppelle River area, and of cliff-top eolian deposition along the South Saskatchewan River. These ages, along with published radiocarbon and optical ages, are used to develop a chronology of eolian activity for south-central Saskatchewan. Optical ages of eolian sands ranging from 5.7 to 0.14 ka (before AD 2000), with intervening paleosols, indicate alternating periods of eolian activity and dune stability during the late Holocene, supported by published radiocarbon ages. Other published radiocarbon ages ranging from 11.3 to 8.4 cal ka BP indicate early Holocene eolian activity. Mid-Holocene ages are predominantly absent from the chronology and this is interpreted as being due to extensive eolian reworking during at least the latter part of the mid-Holocene. The chronology in south-central Saskatchewan is similar to other parts of the southern Canadian prairies. It is likely that preserved mid-Holocene eolian deposits occur within depositional basins in the southern Canadian prairies, and at sites near the southern boreal forest boundary with the prairie ecozone.La chronologie et la stratigraphie des dĂ©pĂŽts Ă©oliens ont Ă©tĂ© Ă©tudiĂ©es dans deux sites situĂ©s au centre-sud de la Saskatchewan afin de reconstituer lâhistoire spatiale et temporelle de lâactivitĂ© dunaire. Les Ăąges optiques fournissent des renseignements sur la chronologie du comblement de la vallĂ©e de la riviĂšre QuâAppelle par des dunes de sable et de la mise en place de dĂ©pĂŽts Ă©oliens au sommet des falaises le long de la riviĂšre Saskatchewan du Sud. CombinĂ©s aux dates optiques et au radiocarbone dĂ©jĂ publiĂ©es, ces Ăąges ont servi Ă Ă©tablir une chronologie de lâactivitĂ© Ă©olienne dans le centre-sud de la Saskatchewan. Les Ăąges optiques des sables Ă©oliens, situĂ©s entre 5,7 et 0,14 ka (avant 2000), ainsi que les palĂ©osols intercalĂ©s, montrent quâil y a eu alternance entre pĂ©riodes dâactivitĂ© Ă©olienne et pĂ©riodes de stabilitĂ© dunaire Ă lâHolocĂšne supĂ©rieur, alternance confirmĂ©e par les dates au radiocarbone dĂ©jĂ publiĂ©es. Dâautres dates au radiocarbone Ă©chelonnĂ©es entre 11,3 Ă 8,4 cal ka BP montrent quâil y a aussi eu activitĂ© Ă©olienne Ă lâHolocĂšne infĂ©rieur. Il nây a pour ainsi dire pas de dates de lâHolocĂšne moyen dans la chronologie, probablement en raison dâimportants remaniements Ă©oliens survenus, tout au moins, Ă la fin de la pĂ©riode. La chronologie du centre-sud de la Saskatchewan est semblable Ă celle dâautres rĂ©gions du sud des Prairies. Il est probable que des dĂ©pĂŽts Ă©oliens de lâHolocĂšne moyen aient Ă©tĂ© prĂ©servĂ©s dans les zones dâaccumulation du sud des Prairies et dans les rĂ©gions situĂ©es Ă lâinterface de la forĂȘt borĂ©ale et des Prairies.La cronologĂa y la estratigrafĂa de los depĂłsitos eĂłlicos provenientes de dos sitios del centro-sur de Saskatchewan fueron estudiadas a fin de determinar la variaciĂłn espacio-temporal de la actividad de las dunas en las praderas canadienses. La dataciĂłn Ăłptica puso en evidencia las variaciones temporales de invasiĂłn del valle por parte arenas de las dunas del QuâAppelle River y por depĂłsitos eĂłlicos en la cima del acantilado a lo largo del Saskatchewan River en la zona sur. Estos datos unidos a la dataciĂłn con radiocarbono y edades Ăłpticas publicadas anteriormente fueron utilizadas para establecer la cronologĂa de la actividad eĂłlica de la zona centro-sur de Saskatchewan. La edad Ăłptica de dunas de origen eĂłlico situada dentro del rango de 5700 a 1400 años anteriores al presente asĂ como los paleosuelos intercalados, indica periodos donde se alternan la actividad eĂłlica y la estabilidad de las dunas que se sitĂșan en el Holoceno tardĂo, y que coinciden con la dataciĂłn de radiocarbono publicada con anterioridad. Otras datos de radiocarbono situados entre los 11 300 y 8400 anteriores al presente indican una actividad eĂłlica durante el Holoceno temprano. La dataciĂłn correspondiente a edades situadas en el Holoceno medio se encuentran ausentes en la cronologĂa, probablemente como una consecuencia de un trabajo eĂłlico extensivo ocurrido a finales de dicho periodo. La cronologĂa de la regiĂłn centro-sur de Saskatchewan es similar a la de otras partes de las praderas australes canadienses. Es probable que algunos depĂłsitos datando del Holoceno medio existan en los sedimentos de la cuenca al sur de las praderas y en la interfase entre los bosques boreales australes y las praderas
Optical Dating of Modern and Late Holocene Dune Sands in the Brandon Sand Hills, Southwestern Manitoba
For any suite of optical dating samples two issues that must be considered are: do zero-age samples yield an optical age of zero, and are the optical ages consistent with independent stratigraphic and chronologic information? A test of the zero-age of dune sands was performed by dating samples from the crest, lee slope and stoss slope of an active dune in southwestern Manitoba. Three surface samples showed that, using 1.4 eV (infrared) excitation of K-feldspars, the equivalent dose, and hence âageâ, depended on whether the bleach used for the thermal transfer correction was infrared/red or sunlight, leading to an age uncertainty of about ±40 years. Optical ages for samples 50 cm below these, and calculated relative to them, were 8 ± 8, 1 ± 7, and 38 ± 7 years, independent of the bleach used. These ages are consistent with expectations for the crest, lee slope and stoss slope, respectively. Optical ages of late Holocene dune sand units at the Brookdale Road section, southwestern Manitoba, were consistent with radiocarbon ages from organic matter within intervening buried soils. The suite of optical and radiocarbon ages from the Brandon Sand Hills provides a record of dune activity and stability for the region, and tentatively identifies periods of eolian activity at about 2 ka, 3.1 to 4.0 ka, and prior to 5.2 ka.En datation optique, on doit tenir compte de deux aspects : les Ă©chantillons dâĂąge zĂ©ro livrent-ils bien un Ăąge optique de zĂ©ro ? Les Ăąges optiques correspondent-ils aux autres donnĂ©es dâordres stratigraphique et chronologique ? Un test a Ă©tĂ© rĂ©alisĂ© sur des Ă©chantillons dâĂąge zĂ©ro provenant dâune dune de sable active. Les rĂ©sultats obtenus sur trois Ă©chantillons de surface ont dĂ©montrĂ© quâen soumettant des feldspaths potassiques Ă un rayonnement infrarouge de 1,4 eV, la dose Ă©quivalente nĂ©cessaire, et par consĂ©quent lâĂąge, dĂ©pendait du type de transfert de correction thermique, radiation infrarouge/rouge ou solaire, ce qui entraĂźnait une marge dâerreur possible de ±40 ans. Les Ăąges optiques des Ă©chantillons situĂ©s Ă 50 cm sous ces derniers, calculĂ©s en fonction de ceux-ci, Ă©taient de 8 ± 8, 1 ± 7, et 38 ± 7 ans, peu importe le type de remise Ă zĂ©ro. Ces Ăąges correspondent aux valeurs attendues dans tous les cas. Les Ăąges optiques de sables dunaires de lâHolocĂšne supĂ©rieur obtenus Ă la coupe de Brookdale Road correspondaient aux Ăąges au radiocarbone de la matiĂšre organique dans les sols enfouis. La sĂ©rie des Ăąges optiques et au radiocarbone obtenus dans les Brandon Sand Hills rĂ©vĂšle lâexistence de pĂ©riodes dâactivitĂ© et de stabilitĂ© des dunes dans la rĂ©gion et indique lâexistence probable de pĂ©riodes dâactivitĂ© Ă©olienne vers 2 ka, de 3,1 Ă 4,0 ka et avant 5,2 ka BP.A fin de establecer la edad Ăłptica de una muestra dos aspectos necesitan ser considerados: primero saber si muestras estimadas a una edad cero llevan a obtener una edad Ăłptica cero y segundo si la edad Ăłptica coincide con la informaciĂłn obtenida a partir de datos estratigrĂĄficos y cronolĂłgicos independientes. Durante el presente estudio una prueba de edad-cero de las dunas de arena fue realizada a partir de muestras provenientes de la cima, y de las laderas a sotavento y a barlovento de una duna activa situada al sudoeste de Manitoba. Tres muestras superficiales mostraron que usando un rango de excitaciĂłn infrarrojo de 1,4 eV sobre feldespato potĂĄsico, la dosis equivalente y por lo tanto la âedadâ depende de si el excitante empleado para obtener la correcciĂłn de transferencia tĂ©rmica se sitĂșa en la regiĂłn del rojo/infrarrojo o de la luz solar y proporciona un margen de error de ±40 años. La edad Ăłptica de muestras de 50 cm situadas por debajo se estimaron respecto a las anteriores. Los resultados obtenidos las sitĂșan entre 8 ± 8, 1 ± 7, y 38 ± 7 años, independientemente del excitante empleado. Estas edades concuerdan con lo que se esperaba para la cima y las laderas a sotavento y a barlovento, respectivamente. La edad Ăłptica correspondiente a dunas de arena datando del Holoceno superior en la secciĂłn de Brookdale Road al sudoeste de Manitoba coincidiĂł con la edad estimada con carbono radioactivo obtenida a partir de la materia orgĂĄnica en diversos suelos sepultados. Los datos correspondientes a la edad Ăłptica y la estimada con radiocarbono en la zona de Brandon Sand Hills proporcionan un registro de la actividad de las dunas e igualmente de la estabilidad de la regiĂłn. Podemos ademĂĄs suponer que identifican periodos de actividad eĂłlica que los sitĂșan entre 2000, 3100 a 4000 y 5200 años anteriores al presente, respectivamente
Rapid carbon accumulation following managed realignment on the Bay of Fundy
<div><p>Salt marshes are highly effective carbon (C) sinks and have higher rates of soil C burial (per square meter) than terrestrial ecosystems. Marsh reclamation and anthropogenic impacts, however, have resulted in extensive losses of salt marshes. Restoration of marshes drained and âreclaimedâ for agriculture (referred to in Canada as dykelands) and degraded marshes can generate C credits, but only if C burial is reliably quantified. To date, studies reporting on C burial rates have been limited primarily to restored marshes which are more than 10 years old. Here we report on a study which assessed C burial six years after the return of tidal flooding to a section of dykeland in Aulac, New Brunswick on Canadaâs Bay of Fundy. The C burial rate in the restored marsh averaged 1 329 g C m<sup>-2</sup> yr<sup>-1</sup>, more than five times the rate reported for a nearby mature marsh. Carbon density in the recovering marsh was relatively consistent with depth and although salt marsh cordgrass (<i>Spartina alterniflora</i>) became established in 2012, the bulk of the C in the new marsh deposit is assumed to be allochthonous. Financial constraints are a barrier to marsh restoration projects and C markets could provide a considerable source of funding for restoration work in the future. For marsh restoration projects to be recognized in C crediting systems, however, it must also be demonstrated that the allochthonous C would not otherwise have been sequestered; the potential for this is discussed.</p></div
Areal C storage vs. core length in a recovering salt marsh.
<p>Areal C storage vs. core length in a recovering salt marsh.</p