A revised sea level history for the northern Strait of Georgia, British Columbia, Canada

Fedje, Daryl W.; McLaren, Duncan; James, Thomas S.; Mackie, Quentin; Smith, Nicole; Southon, John; Mackie, Alexander P.

doi:10.1016/j.quascirev.2018.05.018

Cited by 37 publications

(44 citation statements)

References 38 publications

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“…inference of declining salinity, as chrysophytes in general are abundant only in freshwaters (Cumming et al 1993). Isolation of the Lake Stowell basin is consistent in terms of timing with other diatom studies around Vancouver Island, which describe rapid declines in marine or polyhalobian taxa associated with RSL withdrawal at~14.0 ka (Hutchinson et al 2004, James et al 2009, Roe et al 2013, Fedje et al 2018).…”

Section: Sea-level History and Isolation Of Lake Stowellsupporting

confidence: 81%

“…, Fedje et al. ), which had previously been absent from the record. Formation of the newly isolated, freshwater basin was therefore coincident with warming toward the end of the Bølling/Ållerød Interstadial (Kuehn et al.…”

Section: Discussionmentioning

confidence: 92%

“…, Fedje et al. , Guiry and Guiry ). These taxa disappeared abruptly by 14.0 ka, indicating that the basin became isolated as RSL fell below +70 m (James et al.…”

Section: Discussionmentioning

confidence: 97%

“…, Fedje et al. ). The precise timing of these events at a local scale can be inferred from sediment records by identifying marine‐to‐freshwater transitions in diatom assemblages.…”

Section: Discussionmentioning

confidence: 99%

“…, Fedje et al. ), as these aquatic bio‐indicators have a broad range of salinity preferences among individual taxa (van Dam et al. , Fedje et al.…”

Section: Introductionmentioning

confidence: 99%

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Diatom responses to long‐term climate and sea‐level rise at a low‐elevation lake in coastal British Columbia, Canada

Neil

Lacourse

2019

Ecosphere

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Diatom assemblages from Lake Stowell, a low‐elevation lake in coastal British Columbia, were used to assess limnological responses associated with changes in relative sea level (RSL) and climate over the past 14,500 yr. Marine diatom taxa dominated the early record and disappeared abruptly by 14,000 cal yr BP in response to glacio‐isostatic uplift and an ensuing decrease in RSL. A brackish‐freshwater phase from 14,200 to 13,400 cal yr BP was marked by increases in several diatom taxa with tolerance for low‐to‐moderate salinity, after which assemblages became strictly freshwater. Biostratigraphic changes in both diatom and chironomid assemblages from Lake Stowell occurred more or less simultaneously throughout the record in response to long‐term changes in climate forcings, such as temperature. Increases in cold‐adapted diatom (Staurosirella pinnata, Staurosira construens, Staurosirella dubia) and chironomid (Sergentia) taxa between 12,900 and 11,700 cal yr BP coincided with Younger Dryas cooling, suggesting a direct link with summer temperature. Shifts in aquatic biota also reflected indirect mechanisms through which climate affected the Lake Stowell ecosystem, for example, by altering thermal stratification, disturbance regimes, and nutrient concentrations. For instance, high summer insolation and warm summer temperatures from 11,700 to 8500 cal yr BP were associated with greater abundances of Stephanodiscus hantzschii and especially Aulacoseira subarctica. A concurrent opening of the forest canopy triggered by warming would have exposed the lake to strong winds and enhanced mixing, favoring these more heavily silicified taxa as an indirect consequence of climatic changes. Diatom assemblages appear to have been impacted by the deposition of Mount Mazama tephra at 7600 cal yr BP; a notable increase in Aulacoseira tenella suggests a response to increased silica availability in association with tephra deposition.

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Section: Sea-level History and Isolation Of Lake Stowellsupporting

confidence: 81%

Section: Discussionmentioning

confidence: 92%

“…, Fedje et al. , Guiry and Guiry ). These taxa disappeared abruptly by 14.0 ka, indicating that the basin became isolated as RSL fell below +70 m (James et al.…”

Section: Discussionmentioning

confidence: 97%

“…, Fedje et al. ). The precise timing of these events at a local scale can be inferred from sediment records by identifying marine‐to‐freshwater transitions in diatom assemblages.…”

Section: Discussionmentioning

confidence: 99%

“…, Fedje et al. ), as these aquatic bio‐indicators have a broad range of salinity preferences among individual taxa (van Dam et al. , Fedje et al.…”

Section: Introductionmentioning

confidence: 99%

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Diatom responses to long‐term climate and sea‐level rise at a low‐elevation lake in coastal British Columbia, Canada

Neil

Lacourse

2019

Ecosphere

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Local adaptation in island populations of Plectritis congesta that differ in historic exposure to ungulate browsers

Skaien

Arcese

2020

Ecology

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Spatial variation in the occurrence of browsing ungulates can drive local adaptation in plant traits but also lead to trade‐offs among traits potentially enhancing competitive ability versus resistance or tolerance to browsing. Plectritis congesta populations co‐occurring on islands with and without ungulates offer striking examples of population‐level variation in traits, such as plant height and fruit morphology, which may also affect fitness. We monitored split‐plot common gardens exposed to and protected from browsing ungulates for 5 yr to test for local adaptation (local vs. foreign comparison) in P. congesta by comparing the survival and fecundity of 4,392 sown fruits from six island populations where ungulates were present (“historically exposed”) and six where they were absent (“historically naïve”). Our results indicate that local adaptation to browsing in P. congesta favored rosette formation, delayed flowering, reduced height, and the production of wingless fruits, all of which appeared to enhance survival, fecundity, and population growth in plants from populations historically exposed to ungulate browsers, as compared to plants from historically naïve populations. In contrast, plants from historically naïve populations displayed higher relative fitness in the absence of ungulates, increased in height, flowered earlier, and produced fewer but larger, winged fruits, often in large terminal inflorescences. Our results support the hypothesis that variation in the occurrence of ungulate browsers has led to (1) spatial heterogeneity in natural selection and rapid adaptation in P. congesta populations on islands, and (2) context‐dependent trade‐offs in the fitness value of traits linked to the resistance or tolerance of browsing versus success in competition for light, pollinators, or other resources. Because patterns of selection in plant communities will vary with the introduction or extirpation of top predators or browsers, we suggest historical context, local adaptation, and the capacity for rapid adaptation should be a focal concern of those aiming to maximize or predict population persistence under environmental change in conservation plans.

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Experimental Re-creation of the Depositional Context in Which Late Pleistocene Tracks Were Found on the Pacific Coast of Canada

McLaren

Mackie

Fedje

2021

Reading Prehistoric Human Tracks

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To better understand the depositional context of Late Pleistocene human tracks found at archaeology site EjTa-4 on Calvert Island, on the Pacific Coast of Canada, we present here the results of an experiment designed to recreate the conditions by which these tracks were formed, preserved and then revealed through excavation. Based on radiocarbon ages on small twigs and the analysis of sediments and microfossils, the interpretation of the site formation processes relate that the tracks were impressed into a clayey soil substrate just above the high tide line between 13,317 and 12,633 calBP. The features were subsequently encapsulated by black sand, which washed over the tracks from the nearby intertidal zone during a storm event. To test this interpretation, we enlisted the aid of high school student volunteers to recreate the conditions by which the tracks were formed. A clayey substrate was prepared in a laboratory setting at the University of Victoria and a few plant macrofossils were placed on top it. This was followed by having the students create tracks in the clay, which were then covered with a layer of sand. Upon excavation of these experimental tracks, we found that they had a very similar character to those found in the field, including the pressing of macrofossils into the clay by the weight of the track maker. These results support the interpretation and chronological assessment of the depositional events that occurred during late Pleistocene times at archaeology site EjTa-4.

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A revised sea level history for the northern Strait of Georgia, British Columbia, Canada

Cited by 37 publications

References 38 publications

Diatom responses to long‐term climate and sea‐level rise at a low‐elevation lake in coastal British Columbia, Canada

Diatom responses to long‐term climate and sea‐level rise at a low‐elevation lake in coastal British Columbia, Canada

Local adaptation in island populations of Plectritis congesta that differ in historic exposure to ungulate browsers

Experimental Re-creation of the Depositional Context in Which Late Pleistocene Tracks Were Found on the Pacific Coast of Canada

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