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Mineral magnetic record of Late Quaternary Caspian Sea sediments
502
Abstracts / Quaternary International 279-280 (2012) 462–565
MINERAL MAGNETIC RECORD OF LATE QUATERNARY CASPIAN SEA SEDIMENTS Alina Tudryn. IDES UMR CNRS/UPSud 8148, France E-mail address: [email protected]
We present results on the mineral magnetic study from a w10 m long sediment core SR-9418 GS20, from Central Basin of the Caspian sea (4132'53''N; 5106'04''E; water depth of 479m) and from previously studied core SR-9402 GS05 from South Basin of the Caspian sea (38 45'39''N; 5132'16''E; water depth of 519m) (Chalié et al. 1997; Jelinowska et al., 1998; Jelinowska et al., 1999). Both Kullenberg cores present Late Pleistocene and Early-Mid Holocene sediments. They were collected during a cruise, which took place in 1994 as a part of the multidisciplinary study of the palaeolimnology of the Caspian Sea, conducted by a RussianFrench team (EU Contract 15-CT96-0112). Lower, Late Pleistocene part of both cores, consists on detrital rich and carbonate poor material, marked by a regular alternation (few mm) of black and grey layers, which rapidly disappear under oxidising conditions. The terrigenous components dominate here and show a constant input to the Caspian basin. The uppermost Early-Mid Holocene sediments are characterised by presence of carbonaceous mud. Greigite (Fe3S4), which is an early diagenetic mineral related to anaerobie, sulphate-reducing and fresh-water or brackish conditions, dominates the magnetic fraction in Late Pleistocene sediments. It is frequent in black laminae and rarer in grey laminae, where some magnetite of detrital origin was identified too. The results suggest that laminae are related to the differences in the content of greigite and its labile precursors in black and grey sediment, rather than to detrital origin. Such a syn-sedimentary formation of greigite indicates that the Late Pleistocene Caspian Sea was brackish or fresh water, poorly ventilated basin. The Holocene sediments are characterised by low contents of magnetic minerals, which are identified as detrital magnetite. This suggests a better ventilation of the basin and is probably related to the lower water level than in the Late Pleistocene. ENVIRONMENTAL CHANGES FOR LAST 18 KYRS RECORDED IN SEDIMENTS OF THE BLACK SEA Alina Tudryn. IDES UMR CNRS/UPSud 8148, France E-mail address: [email protected]
Environmental changes during the last 18 kyrs were studied on sediment cores from 55 to 2100 m depth in the western part of the Black Sea. This work has been done within two programmes: BlaSON and ASSEMBLAGE (EVK3-CT-2002-00090). The time frame of the record was based on radiocarbon chronology (AMS dating) although the correction of 14C data was difficult. The ages obtained from organic matter and fossil shells varied significantly at the same level. Partly it is due to changes in hydrological system of the Black sea which can vary from oxygenated freshwater to strongly stratified salty water. Final chronology, confirmed by a good correlation with other records was obtained by an analysis of Ca/ Mg carbonates content. It is shown that the organic matter in studied cores is predominantly of algal origin and that from Last Glacial Maximum to w7.5kyrs BP, the basin was a fresh water body with some variation of salinity, probably related to the water level variation. Smectite and illite dominate the clay mineral fraction in sediments showing possible variation of the detrital input into the basin. Previously the illite was attributed to the sources in Europe, while the smectite to Anatolia. This interpretation is however not necessary true as source rocks providing smectite may also be found in the East-European Platform. Magnetic mineral analysis shows the detrital magnetite in small quantities in the lower part of the sequence from the LGM to w13 kyrs B.P. confirming the good mixing and oxygenation of the basin for this period. In the upper part dominate iron sulphides indicating early diagenesis in anoxic conditions. Combined analysis of the magnetic properties and organic matter shows a pattern of salinity and oxygenation variation. VEGETATION SUCCESSION, PEAT AND CARBON ACCUMULATION IN A PRIMARY PALUDIFICATION GRADIENT: TESTING THE PERFORMANCE OF HOLOCENE PEAT MODEL Eeva-Stiina Tuittila. University of Helsinki, Finland E-mail address: eevastiina.tuittila@helsinki.fi
A robust peat growth model is a crucial tool for successfully predicting and managing the fate of the large carbon pool and methane emissions in the northern peatlands under changing climate conditions. Further, building such a model tests our current understanding of the past peat accumulation and interplay among peat characteristics, hydrology and plant community succession. It is considered that in time sedge dominated fens that are groundwater fed and minerogenic systems develop towards only rainwater fed bogs as the peat height increases. Bogs in turn represent a final stage of peatland succession. Key questions are 1) why changes in hydrology and vegetation occur and 2) to what extend these changes are controlled by climate forcing and by internal processes? Here we present past plant community and peat accumulation data in peat cores collected from the land uplift coast of the Baltic Sea. Additionally, we present modern vegetation survey data from the same study site covering a transect of wetlands from Phragmites stands of sea shore to recently exposed land and finally to a ca. 3000 years old bog. We will test the applicability of the recently-developed simulation model of long-term peat accumulation, Holocene Peat Model (HPM) for these young peatlands. The HPM includes feedback mechanisms between changes in hydrology, plant communities and peat properties. It introduces plant functional types (PFT) as a simplification of vegetation, reflecting current water table and peat depths and consequent fertility status. HPM has been developed largely based on the knowledge from a single site, Mer Bleue bog, in Ontario, Canada, but it is essential to test the model performance in different geographical and climatic settings. We will compare simulated and observed plant community, peat and carbon accumulation data, productivity and water table depth in different mire succession stages. ACTIVE SUBGLACIAL LAKES AND THEIR INFLUENCE ON ICE STREAM DYNAMICS Slawek Tulaczyk. University of California, United States E-mail address: [email protected]
Antarctic active subglacial lakes have been first reported in 2005 (Gray et al., 2005) and within several years the number of documented active increased to over 120 (Smith et al., 2009). It appears that a significant fraction of all the subglacial water generated beneath the Antarctic ice sheet is routed through active subglacial lakes. Given the well-established general dependence of ice flow rates on subglacial water dynamics, it is important to investigate if the time-variable water flow through active subglacial lakes results in ice velocity fluctuations. Here, we will report the results of a GPS and passive seismic study focused on the response of Whillans Ice Stream, West Antarctica, to variability in active subglacial lakes. During the three years covered by this work one medium-sized active subglacial lake experienced a full cycle of filling and drainage while another one continued to fill. GPS data document that presence and activity of subglacial lakes do influence spatial and temporal patterns of ice flow, although the magnitude of ice flow sensitivity to subglacial water distribution and dynamics appears to be modest in the study region. We use our field observations to discuss the rates at which the strength of icebed coupling varies through spatially and temporally. Studies of modern subglacial conditions serves to inform numerical ice sheet models that can be used to predict future sea level changes and to reproduce past ice sheet behavior. RECONSTRUCTING THE POST-GLACIAL SEDIMENT BUDGET OF A MOUNTAIN VALLEY-FILL SYSTEM, CHILLIWACK VALLEY, BRITISH COLUMBIA, CANADA Jon Tunnicliffe. Carleton University, Canada E-mail address: [email protected]
Chilliwack Valley is a large (1230 km2), mountainous watershed in the North Cascades, southwestern British Columbia. We developed a postglacial sediment budget for the watershed using dating and stratigraphic evidence from the eroded valley fill and a fan at the valley mouth. A Lidar survey of relict terrace surfaces provides the detail required for reconstructing paleosurfaces in the valley and for analysing the total volume of sediment removed from the main valley and its tributaries. Optically stimulated luminescence (OSL) ages on river terraces provide constraints on the pace of downcutting by mainstem Chilliwack River. The fan at the
Abstracts / Quaternary International 279-280 (2012) 462–565
MINERAL MAGNETIC RECORD OF LATE QUATERNARY CASPIAN SEA SEDIMENTS Alina Tudryn. IDES UMR CNRS/UPSud 8148, France E-mail address: [email protected]
We present results on the mineral magnetic study from a w10 m long sediment core SR-9418 GS20, from Central Basin of the Caspian sea (4132'53''N; 5106'04''E; water depth of 479m) and from previously studied core SR-9402 GS05 from South Basin of the Caspian sea (38 45'39''N; 5132'16''E; water depth of 519m) (Chalié et al. 1997; Jelinowska et al., 1998; Jelinowska et al., 1999). Both Kullenberg cores present Late Pleistocene and Early-Mid Holocene sediments. They were collected during a cruise, which took place in 1994 as a part of the multidisciplinary study of the palaeolimnology of the Caspian Sea, conducted by a RussianFrench team (EU Contract 15-CT96-0112). Lower, Late Pleistocene part of both cores, consists on detrital rich and carbonate poor material, marked by a regular alternation (few mm) of black and grey layers, which rapidly disappear under oxidising conditions. The terrigenous components dominate here and show a constant input to the Caspian basin. The uppermost Early-Mid Holocene sediments are characterised by presence of carbonaceous mud. Greigite (Fe3S4), which is an early diagenetic mineral related to anaerobie, sulphate-reducing and fresh-water or brackish conditions, dominates the magnetic fraction in Late Pleistocene sediments. It is frequent in black laminae and rarer in grey laminae, where some magnetite of detrital origin was identified too. The results suggest that laminae are related to the differences in the content of greigite and its labile precursors in black and grey sediment, rather than to detrital origin. Such a syn-sedimentary formation of greigite indicates that the Late Pleistocene Caspian Sea was brackish or fresh water, poorly ventilated basin. The Holocene sediments are characterised by low contents of magnetic minerals, which are identified as detrital magnetite. This suggests a better ventilation of the basin and is probably related to the lower water level than in the Late Pleistocene. ENVIRONMENTAL CHANGES FOR LAST 18 KYRS RECORDED IN SEDIMENTS OF THE BLACK SEA Alina Tudryn. IDES UMR CNRS/UPSud 8148, France E-mail address: [email protected]
Environmental changes during the last 18 kyrs were studied on sediment cores from 55 to 2100 m depth in the western part of the Black Sea. This work has been done within two programmes: BlaSON and ASSEMBLAGE (EVK3-CT-2002-00090). The time frame of the record was based on radiocarbon chronology (AMS dating) although the correction of 14C data was difficult. The ages obtained from organic matter and fossil shells varied significantly at the same level. Partly it is due to changes in hydrological system of the Black sea which can vary from oxygenated freshwater to strongly stratified salty water. Final chronology, confirmed by a good correlation with other records was obtained by an analysis of Ca/ Mg carbonates content. It is shown that the organic matter in studied cores is predominantly of algal origin and that from Last Glacial Maximum to w7.5kyrs BP, the basin was a fresh water body with some variation of salinity, probably related to the water level variation. Smectite and illite dominate the clay mineral fraction in sediments showing possible variation of the detrital input into the basin. Previously the illite was attributed to the sources in Europe, while the smectite to Anatolia. This interpretation is however not necessary true as source rocks providing smectite may also be found in the East-European Platform. Magnetic mineral analysis shows the detrital magnetite in small quantities in the lower part of the sequence from the LGM to w13 kyrs B.P. confirming the good mixing and oxygenation of the basin for this period. In the upper part dominate iron sulphides indicating early diagenesis in anoxic conditions. Combined analysis of the magnetic properties and organic matter shows a pattern of salinity and oxygenation variation. VEGETATION SUCCESSION, PEAT AND CARBON ACCUMULATION IN A PRIMARY PALUDIFICATION GRADIENT: TESTING THE PERFORMANCE OF HOLOCENE PEAT MODEL Eeva-Stiina Tuittila. University of Helsinki, Finland E-mail address: eevastiina.tuittila@helsinki.fi
A robust peat growth model is a crucial tool for successfully predicting and managing the fate of the large carbon pool and methane emissions in the northern peatlands under changing climate conditions. Further, building such a model tests our current understanding of the past peat accumulation and interplay among peat characteristics, hydrology and plant community succession. It is considered that in time sedge dominated fens that are groundwater fed and minerogenic systems develop towards only rainwater fed bogs as the peat height increases. Bogs in turn represent a final stage of peatland succession. Key questions are 1) why changes in hydrology and vegetation occur and 2) to what extend these changes are controlled by climate forcing and by internal processes? Here we present past plant community and peat accumulation data in peat cores collected from the land uplift coast of the Baltic Sea. Additionally, we present modern vegetation survey data from the same study site covering a transect of wetlands from Phragmites stands of sea shore to recently exposed land and finally to a ca. 3000 years old bog. We will test the applicability of the recently-developed simulation model of long-term peat accumulation, Holocene Peat Model (HPM) for these young peatlands. The HPM includes feedback mechanisms between changes in hydrology, plant communities and peat properties. It introduces plant functional types (PFT) as a simplification of vegetation, reflecting current water table and peat depths and consequent fertility status. HPM has been developed largely based on the knowledge from a single site, Mer Bleue bog, in Ontario, Canada, but it is essential to test the model performance in different geographical and climatic settings. We will compare simulated and observed plant community, peat and carbon accumulation data, productivity and water table depth in different mire succession stages. ACTIVE SUBGLACIAL LAKES AND THEIR INFLUENCE ON ICE STREAM DYNAMICS Slawek Tulaczyk. University of California, United States E-mail address: [email protected]
Antarctic active subglacial lakes have been first reported in 2005 (Gray et al., 2005) and within several years the number of documented active increased to over 120 (Smith et al., 2009). It appears that a significant fraction of all the subglacial water generated beneath the Antarctic ice sheet is routed through active subglacial lakes. Given the well-established general dependence of ice flow rates on subglacial water dynamics, it is important to investigate if the time-variable water flow through active subglacial lakes results in ice velocity fluctuations. Here, we will report the results of a GPS and passive seismic study focused on the response of Whillans Ice Stream, West Antarctica, to variability in active subglacial lakes. During the three years covered by this work one medium-sized active subglacial lake experienced a full cycle of filling and drainage while another one continued to fill. GPS data document that presence and activity of subglacial lakes do influence spatial and temporal patterns of ice flow, although the magnitude of ice flow sensitivity to subglacial water distribution and dynamics appears to be modest in the study region. We use our field observations to discuss the rates at which the strength of icebed coupling varies through spatially and temporally. Studies of modern subglacial conditions serves to inform numerical ice sheet models that can be used to predict future sea level changes and to reproduce past ice sheet behavior. RECONSTRUCTING THE POST-GLACIAL SEDIMENT BUDGET OF A MOUNTAIN VALLEY-FILL SYSTEM, CHILLIWACK VALLEY, BRITISH COLUMBIA, CANADA Jon Tunnicliffe. Carleton University, Canada E-mail address: [email protected]
Chilliwack Valley is a large (1230 km2), mountainous watershed in the North Cascades, southwestern British Columbia. We developed a postglacial sediment budget for the watershed using dating and stratigraphic evidence from the eroded valley fill and a fan at the valley mouth. A Lidar survey of relict terrace surfaces provides the detail required for reconstructing paleosurfaces in the valley and for analysing the total volume of sediment removed from the main valley and its tributaries. Optically stimulated luminescence (OSL) ages on river terraces provide constraints on the pace of downcutting by mainstem Chilliwack River. The fan at the