- Email: [email protected]
Relationship between the chemical index of weathering (CIW) of dune sand from the Hunshandake Sandy Land and climate conditions
Abstracts / Quaternary International 279-280 (2012) 233–345
Mongolia, China, this paper aims to provide an primary interpretation for the past environmental change. The position of the plant root tube fossil samples is on one dune slope, about 3 m higher above the interdune depression. Most of samples are slightly white or fawn-colored, standing or leaning into sand layer, and the root shapes of some fossil samples keep integrity and clear horizontal texture. The cross sections of fossils are almost ringlike in texture. The mean values of inside diameter and outside diameter from 10 samples are 8.1 mm and 15.5 mm, respectively, and the mean thickness of the tube walls is about 3.6 mm. The average TIC (total inorganic carbonate content) from 5 samples is 28.0 %, varying between 18.5-23.5 %, which is notably higher than that of surface sands (1.28 %) from dune crest. The data of morphologic features, deposition information and TIC show that the fossils were mainly quartz mineral cemented by dissolved salts after the plant dead and then embeded in situ. The horizontal texture of the fossils might results from lake-level fluctuations. These indicate that the vegetations in situ must have flourished during some period of the past time and a lake environment must have existed. Although there is no chronological data, these in-situ plant root tube fossils imply strongly a wetter period in the south region of the Badain Jaran Desert during the past, and then a dry stage of climate followed, which was indicated by aeolian process of shift dunes building. COMPARISON OF MANGROVE AND SALT MARSH FORAMINIFERA AS SEA-LEVEL INDICATORS Simin Liu. University of Pennsylvania, United States E-mail address: [email protected]
Fossil foraminifera preserved in salt marsh sediments are used to reconstruct former Holocene sea-level from modern foraminiferal assemblages that are vertically zoned in response to the frequency and duration of tidal inundation. The use of foraminiferal-based transfer functions has improved the precision of many salt marsh-based sea-level reconstructions to better than< 0.10 m. Such reconstructions of Holocene sea-level have provided a fundamental basis for comparison with historical and present-day changes. In contrast, there are few studies using mangrove foraminifera to reconstruct former sea-level despite the importance of tropical localities for inferring the eustatic sea level component. We describe the foraminiferal distributions from both salt marsh and mangrove environments along the Atlantic coast of Florida. Florida is located in the southeastern United States, which has an ideal geographic location representing a transition between temperate and subtropical zones. Salt marshes are dominant in the northern Florida, while mangroves dominate the southern part. We collected surface sediment samples for foraminiferal analysis from two salt marshes in St. Marys River, northeastern Florida, and the mangrove area in Hobe Sound, southeastern Florida. We compared the foraminiferal distribution with a host of environmental variables (elevation, salinity, pH, organic content, grain size and vegetation cover and species diversity). We subsequently developed quantitative reconstruction techniques to apply to fossil foraminiferal assemblages preserved in salt marsh and mangrove sediments. This study clarifies the differences and similarity of mangrove and salt marsh foraminifera as sea-level indicators, and tests the robustness of these two proxies. Also, the study compares the differences of preservation conditions of these two environments, which is very important for reconstruction of relative sea-level changes. MID-HOLOCENE SEVERE DROUGHT EVENTS DEGRADATION REAPPEAR IN SEMI-ARID CHINA
AND
ECOLOGICAL
Hongyan Liu. Peking University, China E-mail address: [email protected]
Semi-arid ecosystems are vulnerable to climate extremes, which will in turn contribute to regional and even global climate change through changing surface albedo and long-distance dust transportation. We found, caused by climate warming, lakes are evaporated towards desiccation in the semi-arid region in China. Paleaoecological studies in Anguli Nuur Lake in this region show three drought events as indicated by shifting from freshwater to salty water, occurred from 7.5 to 6.4 ka BP. By examining climate proxies, we also found that climate in this region has an evident
285
shift from East Asian summer monsoon-dominance to winter monsoondominance, at about 5.2 ka BP. Expansion of steppe vegetation not following this shifting exactly. Although the effect of summer monsoon has been increasing since w3.0 ka BP, the recent summer monsoon decline resemled those drought events occurred from 7.5 to 6.4 ka BP. Drought event in the mid-Holocene was explained by over-evaporation with temperature rising but no significant increase in precipitation. These events led to lake desiccation, as a result, the replacement of forests by steppes, at time-scale of decade and century. We thus predict that the reported ecological degradation will remain under the future climate warming in this region. RELATIONSHIP BETWEEN THE CHEMICAL INDEX OF WEATHERING (CIW) OF DUNE SAND FROM THE HUNSHANDAKE SANDY LAND AND CLIMATE CONDITIONS Ziting Liu. Institute of Geology and Geophysics, Chinese Acade, China E-mail address: [email protected]
The chemical index of weathering (CIW), controlled by environmental conditions, is proposed as a sensitive proxy to indicate the degree of chemical weathering of sediment. However, the relationship between CIW and climate is still not clear, although it is a key to make an accurate interpretation while using CIW to reconstruct palaeoclimate. The Hunshandake Sandy Land, located in northeastern China, spans a distance of ca. 350 km in east-west direction, with a clear climate gradient. The mean annual precipitation (MAP) decreases from 400 mm in the southeast to 150 mm in the northwest, and the mean annual temperature is around 2 degree C, with cold winters. We measured the major elements of dune sand samples collected from fixed, semi-fixed and drifting dunes in the Hunshandake Sandy Land by X-ray fluorescence analysis, and examined the relationship between the CIW values and regional MAP. Our results show that the CIW values of samples generally decrease from the east to the west, in accordance with the variation trend of regional MAP. But the trend becomes blurred in the western portion where it colder and drier. In general, there is a clear correlation between CIW and vegetation coverage on a small scale, with the CIW values obviously higher in the samples from fixed and semi-fixed dunes where dense vegetation occurs, than those in drifting dunes without meaningful vegetation coverage. It implies that in addition to regional MAP, local biological factors like vegetation are crucial to CIW also. GEOMORPHIC SIGNATURE PALAEO-ICE STREAMS
OF
THREE
CONTRASTING
ANTARCTIC
Stephen Livingstone. University of Durham, United Kingdom E-mail address: [email protected]
The ability to capture the complex spatial and temporal variability exhibited by ice streams in Antarctica and Greenland at short (decadal) time-scales, remains one of the key challenges in numerical modelling and underlies current uncertainties with predicting future contributions of ice sheets to sea-level rise. This has made ice streams a major focus for current glaciological research, particularly with regard to the processes occurring at the ice-bed interface. Such studies unfortunately, only provide a ‘snap-shot’ of the life-cycle of an ice stream, limited to the last few decades, and so there is a need for complementary investigations of former zones of fast flow in palaeo-ice sheets. The ability to observe directly the former beds of palaeo-ice streams has allowed important spatial and temporal information to be obtained on the processes that occurred at the ice-bed interface and on ice dynamics associated with the evolution of palaeo-ice streams. We present new glacial geomorphological evidence from three Antarctic palaeo-ice streams (Marguerite Bay, Belgica Trough & Joides Basin) that underwent contrasting styles and rates of retreat following the LGM, ranging from rapid, through episodic to slow. The landform assemblage of these palaeo-ice stream systems have been derived from the mapping of glacial landforms from high-resolution multibeam swath-bathymetry data and input into a GIS database. The result is detailed high resolution maps of the basal character of each palaeo-ice stream. Analysis of the spatial distribution and geomorphic relationships between landforms
Mongolia, China, this paper aims to provide an primary interpretation for the past environmental change. The position of the plant root tube fossil samples is on one dune slope, about 3 m higher above the interdune depression. Most of samples are slightly white or fawn-colored, standing or leaning into sand layer, and the root shapes of some fossil samples keep integrity and clear horizontal texture. The cross sections of fossils are almost ringlike in texture. The mean values of inside diameter and outside diameter from 10 samples are 8.1 mm and 15.5 mm, respectively, and the mean thickness of the tube walls is about 3.6 mm. The average TIC (total inorganic carbonate content) from 5 samples is 28.0 %, varying between 18.5-23.5 %, which is notably higher than that of surface sands (1.28 %) from dune crest. The data of morphologic features, deposition information and TIC show that the fossils were mainly quartz mineral cemented by dissolved salts after the plant dead and then embeded in situ. The horizontal texture of the fossils might results from lake-level fluctuations. These indicate that the vegetations in situ must have flourished during some period of the past time and a lake environment must have existed. Although there is no chronological data, these in-situ plant root tube fossils imply strongly a wetter period in the south region of the Badain Jaran Desert during the past, and then a dry stage of climate followed, which was indicated by aeolian process of shift dunes building. COMPARISON OF MANGROVE AND SALT MARSH FORAMINIFERA AS SEA-LEVEL INDICATORS Simin Liu. University of Pennsylvania, United States E-mail address: [email protected]
Fossil foraminifera preserved in salt marsh sediments are used to reconstruct former Holocene sea-level from modern foraminiferal assemblages that are vertically zoned in response to the frequency and duration of tidal inundation. The use of foraminiferal-based transfer functions has improved the precision of many salt marsh-based sea-level reconstructions to better than< 0.10 m. Such reconstructions of Holocene sea-level have provided a fundamental basis for comparison with historical and present-day changes. In contrast, there are few studies using mangrove foraminifera to reconstruct former sea-level despite the importance of tropical localities for inferring the eustatic sea level component. We describe the foraminiferal distributions from both salt marsh and mangrove environments along the Atlantic coast of Florida. Florida is located in the southeastern United States, which has an ideal geographic location representing a transition between temperate and subtropical zones. Salt marshes are dominant in the northern Florida, while mangroves dominate the southern part. We collected surface sediment samples for foraminiferal analysis from two salt marshes in St. Marys River, northeastern Florida, and the mangrove area in Hobe Sound, southeastern Florida. We compared the foraminiferal distribution with a host of environmental variables (elevation, salinity, pH, organic content, grain size and vegetation cover and species diversity). We subsequently developed quantitative reconstruction techniques to apply to fossil foraminiferal assemblages preserved in salt marsh and mangrove sediments. This study clarifies the differences and similarity of mangrove and salt marsh foraminifera as sea-level indicators, and tests the robustness of these two proxies. Also, the study compares the differences of preservation conditions of these two environments, which is very important for reconstruction of relative sea-level changes. MID-HOLOCENE SEVERE DROUGHT EVENTS DEGRADATION REAPPEAR IN SEMI-ARID CHINA
AND
ECOLOGICAL
Hongyan Liu. Peking University, China E-mail address: [email protected]
Semi-arid ecosystems are vulnerable to climate extremes, which will in turn contribute to regional and even global climate change through changing surface albedo and long-distance dust transportation. We found, caused by climate warming, lakes are evaporated towards desiccation in the semi-arid region in China. Paleaoecological studies in Anguli Nuur Lake in this region show three drought events as indicated by shifting from freshwater to salty water, occurred from 7.5 to 6.4 ka BP. By examining climate proxies, we also found that climate in this region has an evident
285
shift from East Asian summer monsoon-dominance to winter monsoondominance, at about 5.2 ka BP. Expansion of steppe vegetation not following this shifting exactly. Although the effect of summer monsoon has been increasing since w3.0 ka BP, the recent summer monsoon decline resemled those drought events occurred from 7.5 to 6.4 ka BP. Drought event in the mid-Holocene was explained by over-evaporation with temperature rising but no significant increase in precipitation. These events led to lake desiccation, as a result, the replacement of forests by steppes, at time-scale of decade and century. We thus predict that the reported ecological degradation will remain under the future climate warming in this region. RELATIONSHIP BETWEEN THE CHEMICAL INDEX OF WEATHERING (CIW) OF DUNE SAND FROM THE HUNSHANDAKE SANDY LAND AND CLIMATE CONDITIONS Ziting Liu. Institute of Geology and Geophysics, Chinese Acade, China E-mail address: [email protected]
The chemical index of weathering (CIW), controlled by environmental conditions, is proposed as a sensitive proxy to indicate the degree of chemical weathering of sediment. However, the relationship between CIW and climate is still not clear, although it is a key to make an accurate interpretation while using CIW to reconstruct palaeoclimate. The Hunshandake Sandy Land, located in northeastern China, spans a distance of ca. 350 km in east-west direction, with a clear climate gradient. The mean annual precipitation (MAP) decreases from 400 mm in the southeast to 150 mm in the northwest, and the mean annual temperature is around 2 degree C, with cold winters. We measured the major elements of dune sand samples collected from fixed, semi-fixed and drifting dunes in the Hunshandake Sandy Land by X-ray fluorescence analysis, and examined the relationship between the CIW values and regional MAP. Our results show that the CIW values of samples generally decrease from the east to the west, in accordance with the variation trend of regional MAP. But the trend becomes blurred in the western portion where it colder and drier. In general, there is a clear correlation between CIW and vegetation coverage on a small scale, with the CIW values obviously higher in the samples from fixed and semi-fixed dunes where dense vegetation occurs, than those in drifting dunes without meaningful vegetation coverage. It implies that in addition to regional MAP, local biological factors like vegetation are crucial to CIW also. GEOMORPHIC SIGNATURE PALAEO-ICE STREAMS
OF
THREE
CONTRASTING
ANTARCTIC
Stephen Livingstone. University of Durham, United Kingdom E-mail address: [email protected]
The ability to capture the complex spatial and temporal variability exhibited by ice streams in Antarctica and Greenland at short (decadal) time-scales, remains one of the key challenges in numerical modelling and underlies current uncertainties with predicting future contributions of ice sheets to sea-level rise. This has made ice streams a major focus for current glaciological research, particularly with regard to the processes occurring at the ice-bed interface. Such studies unfortunately, only provide a ‘snap-shot’ of the life-cycle of an ice stream, limited to the last few decades, and so there is a need for complementary investigations of former zones of fast flow in palaeo-ice sheets. The ability to observe directly the former beds of palaeo-ice streams has allowed important spatial and temporal information to be obtained on the processes that occurred at the ice-bed interface and on ice dynamics associated with the evolution of palaeo-ice streams. We present new glacial geomorphological evidence from three Antarctic palaeo-ice streams (Marguerite Bay, Belgica Trough & Joides Basin) that underwent contrasting styles and rates of retreat following the LGM, ranging from rapid, through episodic to slow. The landform assemblage of these palaeo-ice stream systems have been derived from the mapping of glacial landforms from high-resolution multibeam swath-bathymetry data and input into a GIS database. The result is detailed high resolution maps of the basal character of each palaeo-ice stream. Analysis of the spatial distribution and geomorphic relationships between landforms