References of "Bertrand, Sébastien"
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See detailUsing the N/C ratio to correct bulk radiocarbon ages from lake sediments: Insights from Chilean Patagonia
Bertrand, Sébastien; Arraneda, A.; Vargas, P. et al

in Quaternary Geochronology (2012), 12

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See detailBulk organic geochemistry of sediments from Puyehue Lake and its watershed (Chile, 40°S): Implications for paleoenvironmental reconstructions
Bertrand, Sébastien; Sterken, Mieke; Vargas-Ramirez, Lourdes et al

in Palaeogeography, Palaeoclimatology, Palaeoecology (2010), 294

Since the last deglaciation, the mid-latitudes of the southern Hemisphere have undergone considerable environmental changes. In order to better understand the response of continental ecosystems to ... [more ▼]

Since the last deglaciation, the mid-latitudes of the southern Hemisphere have undergone considerable environmental changes. In order to better understand the response of continental ecosystems to paleoclimate changes in southern South America, we investigated the sedimentary record of Puyehue Lake, located in the western piedmont of the Andes in South-Central Chile (40°S). We analyzed the elemental (C, N) and stable isotopic ([delta]13C, [delta]15N) composition of the sedimentary organic matter preserved in the lake and its watershed to estimate the relative changes in the sources of sedimentary organic carbon through space and time. The geochemical signature of the aquatic and terrestrial end-members was determined on samples of lake particulate organic matter (N/C: 0.130) and Holocene paleosols (N/C: 0.069), respectively. A simple mixing equation based on the N/C ratio of these end-members was then used to estimate the fraction of terrestrial carbon ([latin small letter f with hook]T) preserved in the lake sediments. Our approach was validated using surface sediment samples, which show a strong relation between [latin small letter f with hook]T and distance to the main rivers and to the shore. We further applied this equation to an 11.22 m long sediment core to reconstruct paleoenvironmental changes in Puyehue Lake and its watershed during the last 17.9 kyr. Our data provide evidence for a first warming pulse at 17.3 cal kyr BP, which triggered a rapid increase in lake diatom productivity, lagging the start of a similar increase in sea surface temperature (SST) off Chile by 1500 years. This delay is best explained by the presence of a large glacier in the lake watershed, which delayed the response time of the terrestrial proxies and limited the concomitant expansion of the vegetation in the lake watershed (low [latin small letter f with hook]T). A second warming pulse at 12.8 cal kyr BP is inferred from an increase in lake productivity and a major expansion of the vegetation in the lake watershed, demonstrating that the Puyehue glacier had considerably retreated from the watershed. This second warming pulse is synchronous with a 2 °C increase in SST off the coast of Chile, and its timing corresponds to the beginning of the Younger Dryas Chronozone. These results contribute to the mounting evidence that the climate in the mid-latitudes of the southern Hemisphere was warming during the Younger Dryas Chronozone, in agreement with the bipolar see-saw hypothesis. [less ▲]

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See detailGeochemical evidence (C, N and Pb isotopes) of recent anthropogenic impact in south-central Chile from two environmentally distinct lake sediment records
Fagel, Nathalie ULg; Bertrand, Sebastien; Mattielli, Nadine et al

in Journal of Quaternary Science (2010), 25(7), 1100-1112

In this paper, we compare the elemental and isotopic (C, N, Pb) geochemistry of lake sediments from two contrasted environments in south-central Chile. The first lake, Laguna Chica de San Pedro (LCSP), is ... [more ▼]

In this paper, we compare the elemental and isotopic (C, N, Pb) geochemistry of lake sediments from two contrasted environments in south-central Chile. The first lake, Laguna Chica de San Pedro (LCSP), is situated in the urbanised area of the Biobio Region (36°S). The second lake, Lago Puyehue (40° S), is located 400 km to the southeast of LCSP and within an Andean national park. Our aim is to identify environmental impacts associated with increasing industrial activities and land degradation during the last 150 a. In LCSP, shifts in C/N atomic ratios, 13C and 15N from 1915-1937 to the late 1980s are attributed to successive land degradation episodes in the lake watershed. Based on a Pb isotopic mixing model, we estimate that up to 20% of lead in LCSP sediments is supplied from urban atmospheric pollution. By contrast, human impact in the watershed of Lago Puyehue is very limited. We observe no change in organic geochemistry during the last 150 a and lead contamination remains lower than 5%, even during the last decades. Although contamination levels are much higher in LCSP than in Lago Puyehue, a peak in anthropogenic Pb is recorded during the same period (1974-1976) at both sites. This maximum contamination level is consistent with increased industrial activity in the vicinity of Concepción. [less ▲]

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See detailNature, origin, transport and deposition of andosol parent material in south-central Chile (36-42 degrees S)
Bertrand, Sebastien; Fagel, Nathalie ULg

in Catena (2008), 73(1), 10-22

The andosols of south-central Chile (36-42 degrees S) are developed on yellow-brown loams that cover the region with a thickness of several meters. In the literature, several hypotheses concerning the ... [more ▼]

The andosols of south-central Chile (36-42 degrees S) are developed on yellow-brown loams that cover the region with a thickness of several meters. In the literature, several hypotheses concerning the nature, origin, mode of transport and deposition of the andosol parent material have been advanced but no general agreement has been found. In this paper, we test these hypotheses by analyzing new representative outcrops located around Icalma (38 degrees 50'S) and Puyehue (40 degrees 40'S) lakes by a pluri-methodological approach. Our data demonstrate that the andosol parent material has the typical mineralogical and geochemical signature of the regional volcanism and that these deposits are post-glacial in age. The grain size of the deposits and the morphology of the coarse grains evidence that most of these particles haven't been re-transported by wind but are direct volcanic ash falls deposited throughout the Late Glacial and Holocene. Because of the prevailing westerly winds, most of these volcanic ashes have been transported to the East. Following the deposition of the volcanic particles, weathering and pedogenetic processes have transformed part of the volcanic glasses and plagioclases into allophane and have wiped out the original layering. This work demonstrates that most of the andosols that occur in the Andes and in the eastern part of the Intermediate Depression of south-central Chile are developed on volcanic ashes directly deposited by successive volcanic eruptions throughout the Late Glacial and Holocene. (C) 2007 Elsevier B.V. All rights reserved. [less ▲]

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See detailLate Quaternary climatic changes in southern Chile, as recorded in a diatom sequence of Lago Puyehue (40 degrees 40 ' S)
Sterken, Mieke; Verleyen, Elie; Sabbe, Koen et al

in Journal of Paleolimnology (2008), 39(2), 219-235

A late Quaternary diatom stratigraphy of Lago Puyehue (40 degrees 40'S, 72 degrees 28'W) was examined in order to infer past limnological and climatic changes in the South-Chilean Lake District. The ... [more ▼]

A late Quaternary diatom stratigraphy of Lago Puyehue (40 degrees 40'S, 72 degrees 28'W) was examined in order to infer past limnological and climatic changes in the South-Chilean Lake District. The diatom assemblages were well preserved in a 1,122 cm long, C-14-dated sediment core spanning the last 17,900 years, and were in support of an early deglaciation of Lago Puyehue. The presence of a short cold spell in South Chile, equivalent to the Younger Dryas event in the Northern Hemisphere, the Antarctic Cold Reversal in Antarctica, or the Huelmo-Mascardi event in southern South America, was not clearly evidenced in the diatom data, although some climate instability may have occurred between 13,400 and 11,700 cal. yr. BP, and a relatively long period (between 16,850 and 12,810 cal. yr. BP) with low absolute abundances and biovolumes could be tentatively interpreted as a period of low rainfall and/or temperatures. An increase in the moisture supply to the lake was tentatively inferred at 12,810 cal. yr. BP. After 9,550 cal. yr. BP, inferred stronger and longer persisting summer stratification, may have been the result of the higher temperatures associated with an early-Holocene thermal optimum. The mid-Holocene appeared to be characterized by a decrease in precipitation, culminating around 5,000 cal. yr. BP, and rising again after 3,000 cal. yr. BP, likely associated with a previously documented lowered frequency and amplitude of El Nino events. An increase in precipitation during the late Holocene (3,000 cal. yr. BP-present) might have marked subsequent increased frequency of El Nino occurrences, leading to drier summers and slightly moister winters in the area. [less ▲]

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See detailClimate variability of southern Chile since the Last Glacial Maximum: a continuous sedimentological record from Lago Puyehue (40 degrees S)
Bertrand, Sebastien; Charlet, Francois; Charlier, Bernard ULg et al

in Journal of Paleolimnology (2008), 39(2), 179-195

This paper presents a multi-proxy climate record of an 11 m long core collected in Lago Puyehue (southern Chile, 40 degrees S) and extending back to 18,000 cal yr BP. The multi-proxy analyses include ... [more ▼]

This paper presents a multi-proxy climate record of an 11 m long core collected in Lago Puyehue (southern Chile, 40 degrees S) and extending back to 18,000 cal yr BP. The multi-proxy analyses include sedimentology, mineralogy, grain size, geochemistry, loss-on-ignition, magnetic susceptibility and radiocarbon dating. Results demonstrate that sediment grain size is positively correlated with the biogenic sediment content and can be used as a proxy for lake paleoproductivity. On the other hand, the magnetic susceptibility signal is correlated with the aluminium and titanium concentrations and can be used as a proxy for the terrigenous supply. Temporal variations of sediment composition evidence that, since the Last Glacial Maximum, the Chilean Lake District was characterized by three abrupt climate changes superimposed on a long-term climate evolution. These rapid climate changes are: (1) an abrupt warming at the end of the Last Glacial Maximum at 17,300 cal yr BP; (2) a 13,100-12,300 cal yr BP cold event, ending rapidly and interpreted as the local counterpart of the Younger Dryas cold period, and (3) a 3,400-2,900 cal yr BP climatic instability synchronous with a period of low solar activity. The timing of the 13,100-12,300 cold event is compared with similar records in both hemispheres and demonstrates that this southern hemisphere climate change precedes the northern hemisphere Younger Dryas cold period by 500 to 1,000 years. [less ▲]

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See detailChanges in diatom, pollen, and chironomid assemblages in response to a recent volcanic event in Lake Galletue (Chilean Andes)
Urrutia, Roberto; Araneda, Alberto; Cruces, Fabiola et al

in Limnologica (2007), 37(1), 49-62

Several lakes in Chile are near important volcanic areas where eruption impacts can limit the quality of lacustrine sediments for reconstructing past environmental changes. In this study, we report ... [more ▼]

Several lakes in Chile are near important volcanic areas where eruption impacts can limit the quality of lacustrine sediments for reconstructing past environmental changes. In this study, we report changes in diatoms, pollen, and chironomids assemblages after a tephra deposition in Lake Galletue (Chilean Andes). A sediment core obtained from Lake Galletue (40 m water depth) was sliced in I cm intervals and subsamples were taken to analyze each proxy. Pb-210 and 137 Cs activities were measured to obtain the geochronology and mineralogical analyses were performed to determine the mineral composition of the tephra. Diatom species composition and productivity were modified when the lake received the tephra; Aulacoseira granulata decreased and was later replaced by Cyclotella af. glomerata. After the tephra input, Aulacoseira granulata abundance increased to pre-disturbance levels and Cyclotella af. glomerata decreased. These changes seem to suggest a momentary increase in lake nutrient levels after the tephra deposition. Chironomid assemblages also decreased in head capsules just after the tephra deposition, but the most important change was the replacement of Ablabesmyia by Parakiefferiella, probably due to the sedimentological changes produced by the input of coarse tephra grains. Furthermore, unlike other studies, chironomid assemblages in Lake Galletue did not show a decrease drastically in diversity within the tephra layer. The pollen analysis indicated that, prior to the volcanic event, the vegetal community was dominated by Nothofagus sp., Araucaria araucana, and Blechnum sp.-type. After the tephra deposition, the same taxa are dominant, indicating that the volcanic event seems not produce changes in the vegetation. Nevertheless, within the tephra layer it is possible to see an increase in Poaceae, which represent - due to the percolation process - the effect of eruption on the vegetation. According to our results, diatoms were the most sensitive proxy for describing the changes produced by tephra deposition into the aquatic ecosystem and, despite the noticeable changes in its sedimentological properties; the lake seems to have a high resilience capacity, allowing it to return to pre-tephra input conditions. (c) 2006 Elsevier GmbH. All rights reserved. [less ▲]

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See detailChanges of sub-fossil chironomid assemblages associated with volcanic sediment deposition in an Andean lake (38 degrees S), Chile
Araneda, Alberto; Cruces, Fabiola; Torres, Laura et al

in Revista Chilena de Historia Natural (2007), 80(2), 141-156

Chironomid assemblages and sedimentological parameters (grain size, organic content, mineralogy) of a short sediment core from Lake Galletue (38 degrees 41' S, 71 degrees 17' W) were analysed. The ... [more ▼]

Chironomid assemblages and sedimentological parameters (grain size, organic content, mineralogy) of a short sediment core from Lake Galletue (38 degrees 41' S, 71 degrees 17' W) were analysed. The sedimentary record includes one volcanic ash (tephra) layer, which has a completely different composition than the host sediment in terms of organic content, grain size, and mineralogy. According to the geochronology (Pb-210 and Cs-137), this ash layer corresponds to the eruption of Llaima Volcano in 1956-1957. The tephra deposition had an impact on chironomid assemblages producing, among other changes, an increase in Parakiefferiella and a decrease in Ablabesmyia, although no noticeable change was detected in the diversity index. When compared with other studies, our results also show an impact in terms of the presence of chironomid head capsules within the tephra. The presence of these head capsules could result from the effects of percolation, since the coarse grain size of the tephra particles provides large interstitial spaces. The recovery in the abundances of some taxa after the tephra input, suggests the lake is probably restoring the conditions prevailing before the tephra fall. [less ▲]

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See detailChanges in diatom assemblages in an Andean lake in response to a recent volcanic event
Cruces, Fabiola; Urrutia, Roberto; Parra, Oscar et al

in Archiv für Hydrobiologie (2006), 165(1), 23-35

Galletue Lake (38 degrees 41'S; 71 degrees 17'W, IX Region-Chile) is located in an area that is highly influenced by eruptive activity of the Lonquimay and Llaima volcanoes. As a consequence, during the ... [more ▼]

Galletue Lake (38 degrees 41'S; 71 degrees 17'W, IX Region-Chile) is located in an area that is highly influenced by eruptive activity of the Lonquimay and Llaima volcanoes. As a consequence, during the last century tephra was deposited into the lake. Sedimentary diatom assemblages were reconstructed in order to establish the tephra effect on their composition and productivity. This was done by taking a sediment core from Galletue Lake at 40 m depth and sectioning it in 1 cm intervals. The core age was obtained with Pb-210 and Cs-137 activities and the mineral composition of the tephra was determined with mineralogical analyses. Furthermore, sedimentological analyses were performed and total organic matter was determined in the profile. The diatom assemblages were analysed using light and electronic microscopy. The results showed that the diatom stratigraphy can be separated in three zones recognizing the periods before and after tephra input. Aulacoseira granulata decreased during the tephra influx and was replaced by Cyclotella aff. glomerata. When the tephra disappeared from the sedimentary record, A. granulata returned to pre-volcanic event levels. At the same time, Cyclotella aff. glomerata decreased within the assemblages. Asterionella formosa and Urosolenia eriensis increased after the tephra input, with values surpassing earlier ones. These results indicate that, after the tephra input, the lake recovered its previous nutrient levels, which agrees with the organic matter content in the sedimentary matrix. Finally, the results reveal that the volcanic disturbance changed the structure and productivity of diatom assemblages in Galletue Lake. [less ▲]

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