- Email: [email protected]
A drought history of south-eastern Australia: evidence from documentary, early instrumental and palaeoclimate records
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Abstracts / Quaternary International 279-280 (2012) 121–232
CLIMATE EVOLUTION AND SOIL EROSION DURING THE LAST 2000 YEARS RECONSTRUCTED FROM ICELANDIC LAKE SYSTEMS
ADVANCES IN RECONSTRUCTING CLIMATE VARIABILITY OVER THE LAST 2000 YEARS: RECENT PROGRESS FROM AUSTRALASIA
Áslaug Geirsdóttir. University of Iceland, Iceland
Joelle Gergis. University of Melbourne, Australia
E-mail address: [email protected]
E-mail address: [email protected]
Rapid sedimentation (w4.5 m ka 1) in two Icelandic lakes with very different catchment characteristics (a glacier-dominated and a non-glacier lake), provides a high-resolution archive of climate and environmental change over the past 2 ka. Over this interval biogenic silica (BSi) reflects April-May temperatures, whereas total organic carbon (TOC) is dominated by the flux of carbon from eolian-derived soil carbon following dry, windy winters and cold summers. Multiproxy-based temperature reconstructions show a distinct perturbation beginning about 550 AD lasting until 650 AD, followed by a short period of relative summer warmth. A second shift towards colder periods occurred between 780 and 820 AD. These brief perturbations were followed by generally warm summers from 950 to 1250 AD in both lake systems, but this warmth was punctuated by multi-decadal cold intervals, the most apparent around 1150 AD. The transition into the Little Ice Age is recorded by initial summer cooling 1250-1300 AD, more severe drops in summer temperatures 1450 to 1550 AD, followed by cold spikes in the early 1600s, mid 1700s and mid 1800s AD, when peak summer cold was achieved. Both lake systems record LIA cold perturbations that coincide with periods of known, severe explosive volcanism. Both lakes indicate that the Little Ice Age was by far the coldest interval since the Holocene Thermal Maximum, The glacier-dominated lake shows that LIA glaciers were most extensive since deglaciation with their maximum positions attained between 1600 AD and mid 19th century. Although severe soil erosion in Iceland is frequently equated with settlement, our reconstructions indicate that soil erosion began several centuries before settlement, whereas for several centuries after settlement, when summer temperatures were relatively high, there was little or no soil erosion. Only during the transition into and during the Little Ice Age did soil erosion become a major feature of the record.
Reconstructions of past climate variability from Australasia are globally significant as they encompass several major atmospheric and oceanic boundaries that may be highly sensitive under future climate change scenarios. Global circulation features in the region include the El Niño– Southern Oscillation (ENSO), Inter-decadal Pacific Oscillation (IPO), Indian Ocean Dipole (IOD), the Southern Annular Mode (SAM) and the Australasian Monsoon. While the suite of global, hemispheric and continentwide reconstructions that have emerged during the last decade now form an important basis for the Intergovernmental Panel on Climate Change's (IPCC's) estimates of climate variations over the last millennium, they still suffer from inadequate estimates of the range of Southern Hemisphere variability. Results produced by the South American 2K working group (LOTRED-SA) suggest that the temperature history of the ‘water hemisphere’ may vary considerably from Northern Hemisphere. Given the implications on global circulation, there is a now an urgent need to understand how climate has fluctuated in the Australasian region, and how it compares with variations recorded in the Northern Hemisphere over the past 2,000 years. A review of progress from the Aus2K working group will be presented. Recent developments include: Development of new ensemble approach to climate reconstruction calibration/verification; Results of a multi-proxy precipitation reconstruction from Australia; Reassessment of all annually-resolved Southern Hemisphere proxy records for multi-variate climate sensitivity; Progress toward a spatial field temperature reconstruction for Australasia spanning the past millennium.
APPLICATION OF RADIONUCLIDE 137CS AS A TRACER TO ESTIMATE SOIL EROSION IN THE QILIAN SHAN, N.W. CHINA
A DROUGHT HISTORY OF SOUTH-EASTERN AUSTRALIA: EVIDENCE FROM DOCUMENTARY, EARLY INSTRUMENTAL AND PALAEOCLIMATE RECORDS Joelle Gergis. University of Melbourne, Australia E-mail address: [email protected]
Hao-peng Geng. Lanzhou University, China E-mail address: [email protected]
Fallout 137Cs has been used as a tracer to study the present-day erosion and sediment delivery processes in the past decades, but few studies have been conducted to explore the feasibility of this method in high mountainous basins. Here, a study was set to apply it in Xiying Basin in the eastern Qilian Shan, on the northeast margin of the Tibetan Plateau. One reference point and two sampling points characterized by distinct rainfalls (i.e., 367 mm/ a in BSG and 182 mm/a in JTL) were studied; and in each sampling point, two transects of different slope (i.e., 14 for BSG-A, 27 for BSG-B, 12 for JTL-A, 26 for JTL-B) were selected. Then, sectioned samples were collected with an interval of 2 cm to the depth of 40 cm from the reference point, while bulk samples were collected to the depth of 40 cm from the four transects. In the reference point, 137Cs distributes in the upper 14 cm of the soil profile with total inventory of 15.9 kBq/m2, and its activity shows a quasi exponential decline trend with peak values in the subsurface 2-4 cm, which shows the possibility of using fallout 137Cs to estimate erosion rates in the study basin. By comparing the 137Cs inventories redistributed along those transects with that of the reference point, a simplified 137Cs transport model is employed to estimate erosion rates of 0.10 mm/a for BSG-A, 0.15 mm/a for BSG-B, 0.07 mm/a for JTL-A and 0.08 mm/a for JTL-B, all assuming a mean rock density of 2650 kg/m3. These 137Cs derived erosion rates are consistent with the average value of w0.09 mm/a (Pan et al., 2010) derived from total sediment yield in the study basin. Furthermore, the estimated erosion rate from the steep transect, as expected, is generally greater than that from the gentle one in respective sampling points. Therefore, this study indicates that radionuclide 137Cs as a tracer to estimate soil erosion in high mountainous basins is applicable.
Australia is one of the countries hit hardest by the adverse impacts of El Niño–Southern Oscillation (ENSO) events. El Niño years are commonly associated with major drought conditions, while La Niña conditions typically deliver bring above average rains. There are now concerns that the historical relationship between Australian rainfall and ENSO may be shifting. For example, despite three recent La Niña episodes (1998, 1999–2000, 2007–2009), all failed to relieve the 14-year ‘Big Dry’ affecting south-eastern Australia – where around 60% of Australia's population lives. The recent 14-year drought in south eastern Australia has had devastating impacts on the agricultural sector and water availability, promoting major research efforts to determine if the recent drought is within the range of natural climate variability, or a manifestation of the projected drying of the mid-latitudes with anthropogenic climate change. Our current knowledge of Australian drought is largely confined to the 20th century, the period when an extensive network of meteorological observations exists. Colonial archive reports, personal diaries and newspaper accounts have provided an opportunity to reconstruct droughts experienced in the SEA region since the time of first European settlement in 1788. Significantly, documentary records provide first-hand accounts of the societal impacts of past droughts in an area of Australia where meteorological and annually-resolved palaeoclimate records are limited. Here we present recent advances in the development of a documentary drought chronology from south eastern Australia. We compare the new drought chronology with pre20th century instrumental data and a recently developed multi-proxy rainfall reconstruction for the region. Finally we assess the stability of regional Australian rainfall teleconnection pattern associated with largescale ENSO fluctuations.
Abstracts / Quaternary International 279-280 (2012) 121–232
CLIMATE EVOLUTION AND SOIL EROSION DURING THE LAST 2000 YEARS RECONSTRUCTED FROM ICELANDIC LAKE SYSTEMS
ADVANCES IN RECONSTRUCTING CLIMATE VARIABILITY OVER THE LAST 2000 YEARS: RECENT PROGRESS FROM AUSTRALASIA
Áslaug Geirsdóttir. University of Iceland, Iceland
Joelle Gergis. University of Melbourne, Australia
E-mail address: [email protected]
E-mail address: [email protected]
Rapid sedimentation (w4.5 m ka 1) in two Icelandic lakes with very different catchment characteristics (a glacier-dominated and a non-glacier lake), provides a high-resolution archive of climate and environmental change over the past 2 ka. Over this interval biogenic silica (BSi) reflects April-May temperatures, whereas total organic carbon (TOC) is dominated by the flux of carbon from eolian-derived soil carbon following dry, windy winters and cold summers. Multiproxy-based temperature reconstructions show a distinct perturbation beginning about 550 AD lasting until 650 AD, followed by a short period of relative summer warmth. A second shift towards colder periods occurred between 780 and 820 AD. These brief perturbations were followed by generally warm summers from 950 to 1250 AD in both lake systems, but this warmth was punctuated by multi-decadal cold intervals, the most apparent around 1150 AD. The transition into the Little Ice Age is recorded by initial summer cooling 1250-1300 AD, more severe drops in summer temperatures 1450 to 1550 AD, followed by cold spikes in the early 1600s, mid 1700s and mid 1800s AD, when peak summer cold was achieved. Both lake systems record LIA cold perturbations that coincide with periods of known, severe explosive volcanism. Both lakes indicate that the Little Ice Age was by far the coldest interval since the Holocene Thermal Maximum, The glacier-dominated lake shows that LIA glaciers were most extensive since deglaciation with their maximum positions attained between 1600 AD and mid 19th century. Although severe soil erosion in Iceland is frequently equated with settlement, our reconstructions indicate that soil erosion began several centuries before settlement, whereas for several centuries after settlement, when summer temperatures were relatively high, there was little or no soil erosion. Only during the transition into and during the Little Ice Age did soil erosion become a major feature of the record.
Reconstructions of past climate variability from Australasia are globally significant as they encompass several major atmospheric and oceanic boundaries that may be highly sensitive under future climate change scenarios. Global circulation features in the region include the El Niño– Southern Oscillation (ENSO), Inter-decadal Pacific Oscillation (IPO), Indian Ocean Dipole (IOD), the Southern Annular Mode (SAM) and the Australasian Monsoon. While the suite of global, hemispheric and continentwide reconstructions that have emerged during the last decade now form an important basis for the Intergovernmental Panel on Climate Change's (IPCC's) estimates of climate variations over the last millennium, they still suffer from inadequate estimates of the range of Southern Hemisphere variability. Results produced by the South American 2K working group (LOTRED-SA) suggest that the temperature history of the ‘water hemisphere’ may vary considerably from Northern Hemisphere. Given the implications on global circulation, there is a now an urgent need to understand how climate has fluctuated in the Australasian region, and how it compares with variations recorded in the Northern Hemisphere over the past 2,000 years. A review of progress from the Aus2K working group will be presented. Recent developments include: Development of new ensemble approach to climate reconstruction calibration/verification; Results of a multi-proxy precipitation reconstruction from Australia; Reassessment of all annually-resolved Southern Hemisphere proxy records for multi-variate climate sensitivity; Progress toward a spatial field temperature reconstruction for Australasia spanning the past millennium.
APPLICATION OF RADIONUCLIDE 137CS AS A TRACER TO ESTIMATE SOIL EROSION IN THE QILIAN SHAN, N.W. CHINA
A DROUGHT HISTORY OF SOUTH-EASTERN AUSTRALIA: EVIDENCE FROM DOCUMENTARY, EARLY INSTRUMENTAL AND PALAEOCLIMATE RECORDS Joelle Gergis. University of Melbourne, Australia E-mail address: [email protected]
Hao-peng Geng. Lanzhou University, China E-mail address: [email protected]
Fallout 137Cs has been used as a tracer to study the present-day erosion and sediment delivery processes in the past decades, but few studies have been conducted to explore the feasibility of this method in high mountainous basins. Here, a study was set to apply it in Xiying Basin in the eastern Qilian Shan, on the northeast margin of the Tibetan Plateau. One reference point and two sampling points characterized by distinct rainfalls (i.e., 367 mm/ a in BSG and 182 mm/a in JTL) were studied; and in each sampling point, two transects of different slope (i.e., 14 for BSG-A, 27 for BSG-B, 12 for JTL-A, 26 for JTL-B) were selected. Then, sectioned samples were collected with an interval of 2 cm to the depth of 40 cm from the reference point, while bulk samples were collected to the depth of 40 cm from the four transects. In the reference point, 137Cs distributes in the upper 14 cm of the soil profile with total inventory of 15.9 kBq/m2, and its activity shows a quasi exponential decline trend with peak values in the subsurface 2-4 cm, which shows the possibility of using fallout 137Cs to estimate erosion rates in the study basin. By comparing the 137Cs inventories redistributed along those transects with that of the reference point, a simplified 137Cs transport model is employed to estimate erosion rates of 0.10 mm/a for BSG-A, 0.15 mm/a for BSG-B, 0.07 mm/a for JTL-A and 0.08 mm/a for JTL-B, all assuming a mean rock density of 2650 kg/m3. These 137Cs derived erosion rates are consistent with the average value of w0.09 mm/a (Pan et al., 2010) derived from total sediment yield in the study basin. Furthermore, the estimated erosion rate from the steep transect, as expected, is generally greater than that from the gentle one in respective sampling points. Therefore, this study indicates that radionuclide 137Cs as a tracer to estimate soil erosion in high mountainous basins is applicable.
Australia is one of the countries hit hardest by the adverse impacts of El Niño–Southern Oscillation (ENSO) events. El Niño years are commonly associated with major drought conditions, while La Niña conditions typically deliver bring above average rains. There are now concerns that the historical relationship between Australian rainfall and ENSO may be shifting. For example, despite three recent La Niña episodes (1998, 1999–2000, 2007–2009), all failed to relieve the 14-year ‘Big Dry’ affecting south-eastern Australia – where around 60% of Australia's population lives. The recent 14-year drought in south eastern Australia has had devastating impacts on the agricultural sector and water availability, promoting major research efforts to determine if the recent drought is within the range of natural climate variability, or a manifestation of the projected drying of the mid-latitudes with anthropogenic climate change. Our current knowledge of Australian drought is largely confined to the 20th century, the period when an extensive network of meteorological observations exists. Colonial archive reports, personal diaries and newspaper accounts have provided an opportunity to reconstruct droughts experienced in the SEA region since the time of first European settlement in 1788. Significantly, documentary records provide first-hand accounts of the societal impacts of past droughts in an area of Australia where meteorological and annually-resolved palaeoclimate records are limited. Here we present recent advances in the development of a documentary drought chronology from south eastern Australia. We compare the new drought chronology with pre20th century instrumental data and a recently developed multi-proxy rainfall reconstruction for the region. Finally we assess the stability of regional Australian rainfall teleconnection pattern associated with largescale ENSO fluctuations.