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Glacial and Deglacial Trends in the Atlantic Sector of Antarctica during the last 25 ka
Quaternary International 279-280 (2012) 462–565
Contents lists available at SciVerse ScienceDirect
Quaternary International journal homepage: www.elsevier.com/locate/quaint
INQUA 2011 Abstracts: 2001–2467
GLACIAL AND DEGLACIAL TRENDS IN THE ATLANTIC SECTOR OF ANTARCTICA DURING THE LAST 25 KA Daniela Sprenk. University of Cologne/Institute of Geology and Min, Germany E-mail address: [email protected]
Ice-sheets are very sensible to climatic, especially temperature changes. Therefore, research on Quaternary ice-sheet fluctuations can provide important information on past climate evolution. In particular, the transition from the Last Glacial to the recent Interglacial is of main interest for scientists to predict future climate changes. The timing of the final East Antarctic ice-sheet retreat at the end of the Last Glacial is still only partially understood. We use deep-sea sediments from the Antarctic continental margin, southeastern Weddell Sea, to reconstruct glacial ice-sheet dynamics. The cores originate from sediment ridges located on a terrace of the continental slope in 2500–3000 m water depth. They mainly consist of late glacial detrital varves, presumably formed by a seasonally variable thermohaline current. New tools allow for automated varve counting in order to gain better constraints on the chronology. In addition to that spectral analysis on the thickness variability of the varves through time shall reveal whether or not sunspot cycles, as a means of solar forcing, are present in the time series. To obtain more detailed information about the glacial dynamics and the deglacial trends of the sediment components such as total organic carbon, total inorganic carbon, and biogenic silica we apply the newly developed Fourier Transform Infrared Spectroscopy method. Furthermore, physical dating evidence (e. g., AMS14C, ash layers) allows for a better understanding of the glacial ice-sheet dynamics during Marine Isotopic Stage 3. Also, the stratigraphic evidence from the sediment ridges is used to evaluate the timing of the final ice-sheet retreat and potential asynchronies between the East Antarctic and West Antarctic Ice Sheets. The results of the above mentioned methods hopefully lead to the identification of chronostratigraphic marker horizons, which can help to correlate the sediment cores among each other and possibly to the EDML ice core. FLUVIAL RESPONSE TO MAJOR HOLOCENE CLIMATE EVENTS: A COMPARISION FROM RIVER BASINS OF GUJARAT, WESTERN INDIA Alpa Sridhar. The M.S.University of Baroda, India E-mail address: [email protected]
The study is based on the premise that south west monsoon has varied during the Holocene and fluvial systems respond to the short and long term climatic and hydrologic fluctuations. The response of the Mahi and Narmada Rivers in western India to the major climatic perturbations is spectacular and globally recorded Holocene Climatic Optimum, the Medieval Warm Period and the Little Ice Age are well manifest. These inferences are based on the sedimentology and chronostratigraphy of sediments, flood deposits and palaeochannel dimensions. Results indicate that these rivers experienced dry climate with low discharge and precipitation till upto 9.2 ka when gravels were deposited as alluvial fans in the Narmada and braid bars in the Mahi basin by streams with low competence and stream power.
http://dx.doi.org/10.1016/j.quaint.2012.08.1544
The incision of gravels began post 9 ka with the improved monsoon and may have continued till 4 ka correlating with Holocene Climatic Optimum. Palaeodischarge estimations from the terrace sediments dated to 3.8 to 1.7 ka in the Mahi and 2 to 1.4 ka in Narmada basin suggest higher discharge and enhanced monsoon. The sediment facies and pattern of the terrace sediments in both the basins are the same but there is a time lag; the deposition in the Narmada basin appears to have commenced much later than the Mahi basin. The incision of these sediments initiated post 1.7 ka in the Mahi and w1.4 ka in the Narmada basin. The younger organic rich clay terraces are dated to 0.9 –1 ka in the Narmada basin. The incision of these sediments and the flood records in the upper reaches indicate an enhanced hydrological regime corresponding to the Medieval Warm Period. High magnitude flood events dated to 0.5 and 0.3 ka in the Mahi basin can be inferred as rare storm floods in an a low precipitation regime of the Little Ice Age. It is evident that multi proxy data for long term fluctuations may agree across climatic zones however, short term changes from different regions may not correlate. SENSITIVITY OF THE FOREST-GRASSLAND ECOTONE TO HISTORICAL RAINFALL VARIATION IN PRISTINE OPEN WOODLAND SAVANNA OF EQUATORIAL EAST AFRICA Immaculate Ssemmanda. Makerere University, Uganda E-mail address: [email protected]
Fossil pollen records provide key insight into the sensitivity of terrestrial ecosystems to climate change. However, tracing vegetation response to relatively modest historical climate fluctuation is often complicated by the overriding signature of anthropogenic disturbance on the landscape. As a result it is almost impossible to estimate the magnitude of climate change (e.g., moisture-balance variation) responsible for a specific change in pollen assemblage, and to translate pollen assemblage changes into reconstructions of past landscape-scale vegetation change. Here we use high-resolution pollen data from a w250-year lake-sediment record in western Uganda (equatorial East Africa) to assess the sensitivity of natural vegetation in the ecotone between grassland and open woodland savanna to historical trends in annual rainfall on the order of 10% lasting for several decades. Specifically we trace regional vegetation response to two episodes of increased rainfall w1865–1885 (modestly continuing until the 1920s) and 1962–1985. During these wetter episodes we find an immediate increase in pollen abundance from woodland shrubs Myrica, Rhus, Celtis, Macaranga and Alchornea, and herbs such as Asteraceae and Swertia usumbarensis-type. Conversely, herbs such as Commelina and Justicia expanded during the mid-20th century dry episode w1920–1962. Increases in Acalypha and Phoenix reclinata-type, two woodland taxa with strong influence on grass pollen percentage, are delayed on the order of 15 years, suggesting that this response represents a real but temporary expansion of woodland relative to grassland. Pollen from cultivated plants and exotic trees appears from the 1970s onwards, but the combined influence of this long-distance influx fails to mask regional vegetation response to natural rainfall variability.
Contents lists available at SciVerse ScienceDirect
Quaternary International journal homepage: www.elsevier.com/locate/quaint
INQUA 2011 Abstracts: 2001–2467
GLACIAL AND DEGLACIAL TRENDS IN THE ATLANTIC SECTOR OF ANTARCTICA DURING THE LAST 25 KA Daniela Sprenk. University of Cologne/Institute of Geology and Min, Germany E-mail address: [email protected]
Ice-sheets are very sensible to climatic, especially temperature changes. Therefore, research on Quaternary ice-sheet fluctuations can provide important information on past climate evolution. In particular, the transition from the Last Glacial to the recent Interglacial is of main interest for scientists to predict future climate changes. The timing of the final East Antarctic ice-sheet retreat at the end of the Last Glacial is still only partially understood. We use deep-sea sediments from the Antarctic continental margin, southeastern Weddell Sea, to reconstruct glacial ice-sheet dynamics. The cores originate from sediment ridges located on a terrace of the continental slope in 2500–3000 m water depth. They mainly consist of late glacial detrital varves, presumably formed by a seasonally variable thermohaline current. New tools allow for automated varve counting in order to gain better constraints on the chronology. In addition to that spectral analysis on the thickness variability of the varves through time shall reveal whether or not sunspot cycles, as a means of solar forcing, are present in the time series. To obtain more detailed information about the glacial dynamics and the deglacial trends of the sediment components such as total organic carbon, total inorganic carbon, and biogenic silica we apply the newly developed Fourier Transform Infrared Spectroscopy method. Furthermore, physical dating evidence (e. g., AMS14C, ash layers) allows for a better understanding of the glacial ice-sheet dynamics during Marine Isotopic Stage 3. Also, the stratigraphic evidence from the sediment ridges is used to evaluate the timing of the final ice-sheet retreat and potential asynchronies between the East Antarctic and West Antarctic Ice Sheets. The results of the above mentioned methods hopefully lead to the identification of chronostratigraphic marker horizons, which can help to correlate the sediment cores among each other and possibly to the EDML ice core. FLUVIAL RESPONSE TO MAJOR HOLOCENE CLIMATE EVENTS: A COMPARISION FROM RIVER BASINS OF GUJARAT, WESTERN INDIA Alpa Sridhar. The M.S.University of Baroda, India E-mail address: [email protected]
The study is based on the premise that south west monsoon has varied during the Holocene and fluvial systems respond to the short and long term climatic and hydrologic fluctuations. The response of the Mahi and Narmada Rivers in western India to the major climatic perturbations is spectacular and globally recorded Holocene Climatic Optimum, the Medieval Warm Period and the Little Ice Age are well manifest. These inferences are based on the sedimentology and chronostratigraphy of sediments, flood deposits and palaeochannel dimensions. Results indicate that these rivers experienced dry climate with low discharge and precipitation till upto 9.2 ka when gravels were deposited as alluvial fans in the Narmada and braid bars in the Mahi basin by streams with low competence and stream power.
http://dx.doi.org/10.1016/j.quaint.2012.08.1544
The incision of gravels began post 9 ka with the improved monsoon and may have continued till 4 ka correlating with Holocene Climatic Optimum. Palaeodischarge estimations from the terrace sediments dated to 3.8 to 1.7 ka in the Mahi and 2 to 1.4 ka in Narmada basin suggest higher discharge and enhanced monsoon. The sediment facies and pattern of the terrace sediments in both the basins are the same but there is a time lag; the deposition in the Narmada basin appears to have commenced much later than the Mahi basin. The incision of these sediments initiated post 1.7 ka in the Mahi and w1.4 ka in the Narmada basin. The younger organic rich clay terraces are dated to 0.9 –1 ka in the Narmada basin. The incision of these sediments and the flood records in the upper reaches indicate an enhanced hydrological regime corresponding to the Medieval Warm Period. High magnitude flood events dated to 0.5 and 0.3 ka in the Mahi basin can be inferred as rare storm floods in an a low precipitation regime of the Little Ice Age. It is evident that multi proxy data for long term fluctuations may agree across climatic zones however, short term changes from different regions may not correlate. SENSITIVITY OF THE FOREST-GRASSLAND ECOTONE TO HISTORICAL RAINFALL VARIATION IN PRISTINE OPEN WOODLAND SAVANNA OF EQUATORIAL EAST AFRICA Immaculate Ssemmanda. Makerere University, Uganda E-mail address: [email protected]
Fossil pollen records provide key insight into the sensitivity of terrestrial ecosystems to climate change. However, tracing vegetation response to relatively modest historical climate fluctuation is often complicated by the overriding signature of anthropogenic disturbance on the landscape. As a result it is almost impossible to estimate the magnitude of climate change (e.g., moisture-balance variation) responsible for a specific change in pollen assemblage, and to translate pollen assemblage changes into reconstructions of past landscape-scale vegetation change. Here we use high-resolution pollen data from a w250-year lake-sediment record in western Uganda (equatorial East Africa) to assess the sensitivity of natural vegetation in the ecotone between grassland and open woodland savanna to historical trends in annual rainfall on the order of 10% lasting for several decades. Specifically we trace regional vegetation response to two episodes of increased rainfall w1865–1885 (modestly continuing until the 1920s) and 1962–1985. During these wetter episodes we find an immediate increase in pollen abundance from woodland shrubs Myrica, Rhus, Celtis, Macaranga and Alchornea, and herbs such as Asteraceae and Swertia usumbarensis-type. Conversely, herbs such as Commelina and Justicia expanded during the mid-20th century dry episode w1920–1962. Increases in Acalypha and Phoenix reclinata-type, two woodland taxa with strong influence on grass pollen percentage, are delayed on the order of 15 years, suggesting that this response represents a real but temporary expansion of woodland relative to grassland. Pollen from cultivated plants and exotic trees appears from the 1970s onwards, but the combined influence of this long-distance influx fails to mask regional vegetation response to natural rainfall variability.