- Email: [email protected]
Hillslope and Drainage Basin Evolution in an Ice-Cored Landscape, Peel Plateau, Northwest Territories, Canada
Abstracts / Quaternary International 279-280 (2012) 462–565
503
mouth of the valley is the sink for most of the sediment eroded from the watershed. It began to form during deglaciation at the end of the Pleistocene and contains almost all of the postglacial coarse-textured and much of the finer material eroded from the watershed. Radiocarbon dating of fan sediments allowed us to calculate rates of Holocene aggradation. The sediment budget takes into account the relative quantities of coarsetextured material (gravel), sand, and fines (clay and silt). Approximately 2.8 km3 of material was eroded from Chilliwack Valley during the Holocene; this amount includes estimated losses of fine material transported beyond the fan a shallow lake in nearby Sumas Valley and to the Fraser River. The budget shows significantly higher rates of sediment yield immediately after deglaciation, decreasing throughout the Holocene to the rates presently observed.
Recent studies of South America Monsoon Season use new climate indexes based on daily precipitations - grouped in pentads- to better define SAMS timing, regional dynamics and variability. We apply this approach to PMIP model simulations at 6k aiming reconciliation between data and models in this region. The calculated monsoon index indicates a Mid-Holocene longer dry season (from 0 to 60 days depending on the model). This is mainly due to an earlier ending of the SAMS.
HILLSLOPE AND DRAINAGE BASIN EVOLUTION IN AN ICE-CORED LANDSCAPE, PEEL PLATEAU, NORTHWEST TERRITORIES, CANADA
The climate of Northeast Brazil is strongly related to ITCZ position upon Tropical Atlantic ocean during South Hemisphere summer and autumn. This position is related to SST gradients and Northeast Brazil is thus a key region for past ITCZ reconstructions. It is generally considered, in paleoclimate studies, that during phases of ITCZ southern shift, the climate in northern South America is drier while it is wetter in Amazonia and Northeast Brazil. Two cores have been collected and studied in the frame of ANR project ESCARSEL in lake Boqueirão (5 25’S, 35 55’W). The proxies of lake level variations at this site are sand content, bulk sedimentary organic matter characteristics (TOC, C/N, Hydrogen Index, Oxygen Index, d13C, d15N) and organic markers as PTMES and des-A-triterpens. The lake level, which was very variable until 200 BC, presented low levels at 350, 800 and 1300 AD. The lowest level of the last 2000 years has occurred between 1450 and 1960 AD when the lake completely dried. Comparison with other South America data does not show a good agreement between observations and ITCZ shift hypothesis, particularly during the LIA which is cold in the Northern Hemisphere and dry in both northern and southern tropical Atlantic. During the medieval period, analysis of a Coupled Global Circulation Model (MILL5 simulation from CERFACS) at 1250 AD suggests an influence of volcanic eruptions on the dry phase observed in Northeast Brazil region at that time.
Jon Tunnicliffe. Carleton University, Canada E-mail address: [email protected]
The Peel Plateau is a unique periglacial landscape, tundra terrain developed on gently undulating moraine sediments and underlain by more than 40 m of massive, segregated Holocene ice and relict Laurentide ice that has been in place at least since the waning phase of the last glaciation, roughly 13 ka B.P. The plateau region (24 000 km2) extends from the Richardson Mountains to the Peel River in the Yukon and Northwest Territories, Canada. Approximately 20% of the plateau surface has been incised by a network of gullies that show local relief of up to 150 m. The incised hillslope morphology shows evidence of large-scale thaw processes shaping segments of the gully boundaries over the course of the Holocene, including broad scarp basins, detrital fans and blankets, and lake-filled depressions. Remote sensing and field studies were carried out at Stony Creek, a 1025 km2 catchment that drains into the Peel River. Fieldwork focused on two major (41 and 45 ha) thaw slumps driven by melt in the ice-rich terrain. The slumps have headwalls up to 500 m in width and 30 m in height. Once the failed sediment has been mobilized it can move downslope as slug flow; in one case, the sediment mass blocked the fluvial system in the master channel, impounding a large lake (3.8 ha). Mobility of the slump material and stream suspended sediment flux is correlated with solar inputs and, most importantly, with major precipitation events. Observations taken in 2010 show that sediment yield from the catchment is strongly dominated by contributions from these thaw slumps, which occupy a relatively small proportion of the basin area. Thaw slumps are an important mode of drainage basin development in the Holocene, and their relative prominence and rates of failure are likely governed by changes in climate. Progress toward understanding the mode of initiation and propagation of these thaw features will be of great importance for managing impacts on infrastructure, water quality and habitat in the North. DATA-MODEL COMPARISON FOR DURING THE MID-HOLOCENE
SOUTH
AMERICAN
MONSOON
Bruno Turcq. IRD LOCEAN, France E-mail address: [email protected]
Existing data for the Holocene period reveals marked changes in South American Monsoon. Lacustrine level studies show a lower precipitation/ evaporation budget than present in the beginning of the period, with the lowest lake levels between 8500 and 6800 cal BP. Although the dominant Holocene vegetation has always been the rainforest in central Amazonia, pollen and soil d13C indicates a forest expansion over savannas areas in Northern and Southeast Brazil during the mid-Holocene. This period (8000-4000 cal BP) is also characterized by repeated occurrences of forest fires, marked by the presence of charcoals in soils and lacustrine sediments. Moreover, pioneer elements of the rainforest developed during the mid-Holocene and the best example is those of Cecropia, between 9000 and 5000 cal BP. Palynologists interpreted these data as the result of a longer dry season. PMIP GCM simulations for Mid-Holocene indicate a decrease in the Monsoon due to lower summer insolation but this decrease has a small effect on annual precipitation since it is counterbalanced by a September to November rainfall increase that also tend to reduce the dry season length.
PALEOCLIMATE OF THE LAST TWO MILLENIA IN NORTHEAST BRASIL REVEALED BY LAKE BOQUEIRÃO SEDIMENTATION Bruno Turcq. IRD LOCEAN, France E-mail address: [email protected]
RECONSTRUCTION OF PAST CLIMATIC EVENTS USING PRINCIPAL COMPONENT ANALYSIS OF THE TRACE ELEMENT PROFILES IN A SEDIMENT CORE (JOIDES BASIN, ANTARCTICA) Clara Turetta. C.N.R. - IDPA, Italy E-mail address: [email protected]
Principal Component Analysis has been used to characterize the climatic events in a sediment core on the basis of chemical analysis. We have analysed 78 samples from a 473 cm marine sediment core collected from the Joides Basin, Ross Sea- Antarctica. These were collected during an oceanographic sampling survey in 2002-2003 within the frame of the XVIII Italian expedition to Antarctica. Several trace elements were determined (Ag, Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Ga, Li, Mn, Mo, Ni, Pb, Sb, Se, Th, Tl, U, V, Y, Zn and REE). One of the extracted components highlights a succession of peaks, which correspond to climatic events clearly recognized elsewhere. This trend is in agreement with TOC and Biogenic silica core profiles. Core chronology has been established on the basis of correlations with dated samples in the same area. The sediments taken, span from the last glacial maximum to present. During the transition from the LGM to the Holocene a climatic event that can be attributed to the Antarctic Cold Reversal (ACR) has been observed. GREEN ALGAE OF GENUS PEDIASTRUM AS BIOINDICATORS IN LAKE SEDIMENTS: A NOVEL APPROACH BASED ON SIZE-MEASUREMENTS Falko Turner. Leibniz Universität Hannover / Institut für Geobot, Germany E-mail address: [email protected]
Although subfossil remains of Pediastrum-species (green algae, Fam. Hydrodictyaceae) are frequently found in limnic sediments, very few studies deal with their use as palaeoclimatic and palaeolimnologic indicators. In our investigations on Late Glacial sediments from shallow lakes in two regions in Northern and Central Germany, analyses of Pediastrumalgae provide valuable information on limnological and climatic parameters. Determination to subspecies level and comparison with sediment
503
mouth of the valley is the sink for most of the sediment eroded from the watershed. It began to form during deglaciation at the end of the Pleistocene and contains almost all of the postglacial coarse-textured and much of the finer material eroded from the watershed. Radiocarbon dating of fan sediments allowed us to calculate rates of Holocene aggradation. The sediment budget takes into account the relative quantities of coarsetextured material (gravel), sand, and fines (clay and silt). Approximately 2.8 km3 of material was eroded from Chilliwack Valley during the Holocene; this amount includes estimated losses of fine material transported beyond the fan a shallow lake in nearby Sumas Valley and to the Fraser River. The budget shows significantly higher rates of sediment yield immediately after deglaciation, decreasing throughout the Holocene to the rates presently observed.
Recent studies of South America Monsoon Season use new climate indexes based on daily precipitations - grouped in pentads- to better define SAMS timing, regional dynamics and variability. We apply this approach to PMIP model simulations at 6k aiming reconciliation between data and models in this region. The calculated monsoon index indicates a Mid-Holocene longer dry season (from 0 to 60 days depending on the model). This is mainly due to an earlier ending of the SAMS.
HILLSLOPE AND DRAINAGE BASIN EVOLUTION IN AN ICE-CORED LANDSCAPE, PEEL PLATEAU, NORTHWEST TERRITORIES, CANADA
The climate of Northeast Brazil is strongly related to ITCZ position upon Tropical Atlantic ocean during South Hemisphere summer and autumn. This position is related to SST gradients and Northeast Brazil is thus a key region for past ITCZ reconstructions. It is generally considered, in paleoclimate studies, that during phases of ITCZ southern shift, the climate in northern South America is drier while it is wetter in Amazonia and Northeast Brazil. Two cores have been collected and studied in the frame of ANR project ESCARSEL in lake Boqueirão (5 25’S, 35 55’W). The proxies of lake level variations at this site are sand content, bulk sedimentary organic matter characteristics (TOC, C/N, Hydrogen Index, Oxygen Index, d13C, d15N) and organic markers as PTMES and des-A-triterpens. The lake level, which was very variable until 200 BC, presented low levels at 350, 800 and 1300 AD. The lowest level of the last 2000 years has occurred between 1450 and 1960 AD when the lake completely dried. Comparison with other South America data does not show a good agreement between observations and ITCZ shift hypothesis, particularly during the LIA which is cold in the Northern Hemisphere and dry in both northern and southern tropical Atlantic. During the medieval period, analysis of a Coupled Global Circulation Model (MILL5 simulation from CERFACS) at 1250 AD suggests an influence of volcanic eruptions on the dry phase observed in Northeast Brazil region at that time.
Jon Tunnicliffe. Carleton University, Canada E-mail address: [email protected]
The Peel Plateau is a unique periglacial landscape, tundra terrain developed on gently undulating moraine sediments and underlain by more than 40 m of massive, segregated Holocene ice and relict Laurentide ice that has been in place at least since the waning phase of the last glaciation, roughly 13 ka B.P. The plateau region (24 000 km2) extends from the Richardson Mountains to the Peel River in the Yukon and Northwest Territories, Canada. Approximately 20% of the plateau surface has been incised by a network of gullies that show local relief of up to 150 m. The incised hillslope morphology shows evidence of large-scale thaw processes shaping segments of the gully boundaries over the course of the Holocene, including broad scarp basins, detrital fans and blankets, and lake-filled depressions. Remote sensing and field studies were carried out at Stony Creek, a 1025 km2 catchment that drains into the Peel River. Fieldwork focused on two major (41 and 45 ha) thaw slumps driven by melt in the ice-rich terrain. The slumps have headwalls up to 500 m in width and 30 m in height. Once the failed sediment has been mobilized it can move downslope as slug flow; in one case, the sediment mass blocked the fluvial system in the master channel, impounding a large lake (3.8 ha). Mobility of the slump material and stream suspended sediment flux is correlated with solar inputs and, most importantly, with major precipitation events. Observations taken in 2010 show that sediment yield from the catchment is strongly dominated by contributions from these thaw slumps, which occupy a relatively small proportion of the basin area. Thaw slumps are an important mode of drainage basin development in the Holocene, and their relative prominence and rates of failure are likely governed by changes in climate. Progress toward understanding the mode of initiation and propagation of these thaw features will be of great importance for managing impacts on infrastructure, water quality and habitat in the North. DATA-MODEL COMPARISON FOR DURING THE MID-HOLOCENE
SOUTH
AMERICAN
MONSOON
Bruno Turcq. IRD LOCEAN, France E-mail address: [email protected]
Existing data for the Holocene period reveals marked changes in South American Monsoon. Lacustrine level studies show a lower precipitation/ evaporation budget than present in the beginning of the period, with the lowest lake levels between 8500 and 6800 cal BP. Although the dominant Holocene vegetation has always been the rainforest in central Amazonia, pollen and soil d13C indicates a forest expansion over savannas areas in Northern and Southeast Brazil during the mid-Holocene. This period (8000-4000 cal BP) is also characterized by repeated occurrences of forest fires, marked by the presence of charcoals in soils and lacustrine sediments. Moreover, pioneer elements of the rainforest developed during the mid-Holocene and the best example is those of Cecropia, between 9000 and 5000 cal BP. Palynologists interpreted these data as the result of a longer dry season. PMIP GCM simulations for Mid-Holocene indicate a decrease in the Monsoon due to lower summer insolation but this decrease has a small effect on annual precipitation since it is counterbalanced by a September to November rainfall increase that also tend to reduce the dry season length.
PALEOCLIMATE OF THE LAST TWO MILLENIA IN NORTHEAST BRASIL REVEALED BY LAKE BOQUEIRÃO SEDIMENTATION Bruno Turcq. IRD LOCEAN, France E-mail address: [email protected]
RECONSTRUCTION OF PAST CLIMATIC EVENTS USING PRINCIPAL COMPONENT ANALYSIS OF THE TRACE ELEMENT PROFILES IN A SEDIMENT CORE (JOIDES BASIN, ANTARCTICA) Clara Turetta. C.N.R. - IDPA, Italy E-mail address: [email protected]
Principal Component Analysis has been used to characterize the climatic events in a sediment core on the basis of chemical analysis. We have analysed 78 samples from a 473 cm marine sediment core collected from the Joides Basin, Ross Sea- Antarctica. These were collected during an oceanographic sampling survey in 2002-2003 within the frame of the XVIII Italian expedition to Antarctica. Several trace elements were determined (Ag, Al, As, Ba, Be, Cd, Co, Cr, Cu, Fe, Ga, Li, Mn, Mo, Ni, Pb, Sb, Se, Th, Tl, U, V, Y, Zn and REE). One of the extracted components highlights a succession of peaks, which correspond to climatic events clearly recognized elsewhere. This trend is in agreement with TOC and Biogenic silica core profiles. Core chronology has been established on the basis of correlations with dated samples in the same area. The sediments taken, span from the last glacial maximum to present. During the transition from the LGM to the Holocene a climatic event that can be attributed to the Antarctic Cold Reversal (ACR) has been observed. GREEN ALGAE OF GENUS PEDIASTRUM AS BIOINDICATORS IN LAKE SEDIMENTS: A NOVEL APPROACH BASED ON SIZE-MEASUREMENTS Falko Turner. Leibniz Universität Hannover / Institut für Geobot, Germany E-mail address: [email protected]
Although subfossil remains of Pediastrum-species (green algae, Fam. Hydrodictyaceae) are frequently found in limnic sediments, very few studies deal with their use as palaeoclimatic and palaeolimnologic indicators. In our investigations on Late Glacial sediments from shallow lakes in two regions in Northern and Central Germany, analyses of Pediastrumalgae provide valuable information on limnological and climatic parameters. Determination to subspecies level and comparison with sediment