- Email: [email protected]
Holocene micro-charcoal record from lake Ifrah (Middle Atlas – Morocco): climatic implications
Abstracts / Quaternary International 279-280 (2012) 346–461
To understand climate system dynamics, it is essential to have a closer look at global climate change signals and their terrestrial documents. Here we focus on the timing of the advance and retreat of glaciers in the past. During the Last Glacial Maximum (LGM), huge piedmont lobes covered large areas of the northern Alpine foreland. This is evidenced by the distribution of erratic boulders at different terminal positions of the paleoglaciers. A timing of the maximum extent and the retreating phases of the LGM can be established by exposure dating of these erratic boulders with cosmogenic nuclides. For this purpose three boulders in the lower Reuss Valley were sampled for surface exposure dating with cosmogenic 10Be. Two boulders are located on moraines of the LGM maximum extent. The third boulder is located between two retreating stadial positions. Radiocarbon ages from a site located only several kilometers eastward of our study area yield a time span between the maximum extent and the recession of two retreating stadials between approximately 32 kcal. BP and 23 kcal. BP. Our surface exposure ages for the maximal extent and the retreating phases are younger. The oldest age is around 22 ka, and the boulder representing the local deglaciation is around 18 ka old. The exposure ages fit well with the global LGM around 21 ka. Former studies suggest a two-cycle model for the maximal extension of the last glaciation in the Swiss northern Alpine foreland. Consequently, further boulders have to be dated to verify this argument founded on field observations. It is important to ensure that the detected time shift is not only caused by different dating methods. DIATOM DIVERSITY VS. SILICA DISSOLUTION DURING THE LAST GLACIAL-INTERGLACIAL CYCLE IN LAGUNA POTROK AIKE (PATAGONIA) Cristina Recasens. University of Geneva, Switzerland E-mail address: [email protected]
Laguna Potrok Aike is a maar lake located in southernmost Patagonia and, as one of the few permanent lakes in the area, provides an exceptional continuous sedimentary record. Diatom assemblages were analyzed at high resolution on the composite core 5022-2CP, obtained within the framework of the ICDP-sponsored project PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Program). More than 216 species, varieties and forms have been identified so far, including endemic species and some new to science. The quantitative analysis reveals diatom abundances ranging from nearly none to 460 million valves per gram of dry sediment, with substantial fluctuations along the record. During Glacial times, floristic assemblages are relatively stable with plankton being dominated by Discostella stelligera. Remarkable diatom concentration peaks at different depths in the core most probably reflect variations in the nutrient availability in the system. The causes for these changes in nutrients supply will be inferred from the analyses of other proxies and a more detailed age model. The Late Glacial to Holocene transition is defined by a diversification of the plankton, with the occurrence of Cyclostephanos patagonicus at approximately 15’550 cal yrs BP and its decline and stepwise replacement by indicators of more brackish conditions, Thalassiosira patagonica and Cyclotella agassizensis, from approximately 11’500 cal yrs BP to present day. Additionally, a high degree of valve dissolution can be noticed in the top 10 m of the record, corresponding to very low values of diatom concentration in the sediment. Likewise, samples at the sediment-water interface, present equally dissolved specimens of Cyclotella agassizensis. The mechanisms behind this dissolution, together with variations in the diatom abundance and species distribution will shed some new light on the behavior of this lake, its internal chemistry and nutrient supply as well as lake level variations and periods of ice-cover. HOLOCENE MICRO-CHARCOAL RECORD FROM LAKE IFRAH (MIDDLE ATLAS – MOROCCO): CLIMATIC IMPLICATIONS Hanane Redda. UAE. Faculty of Sciences and Techniques-Tangier, Morocco E-mail address: [email protected]
Paleo-fire activity in North Africa and its connections with past climatic changes still remains poorly documented. A high resolution multiproxy
395
analysis (using organic and inorganic matter, major and trace elements, magnetic susceptibility, charcoal and pollen data) from Lake Ifrah (Middle Atlas – Morocco) provides new insights for better understanding paleo-fire occurrence during the Late-Pleistocene and Holocene periods. The comparison between size-classes micro-charcoal distribution and lacustrine reconstructed environmental variables further highlights the variability of paleo-fire activity that is interpreted in term of climate-driven changes. Increases in micro-charcoal abundance associated to changes in arboreal pollen composition likely testify regional emissions from forest fires and atmospheric transport. Such biomass burning events were associated to prolonged periods of drought, as inferred by synchronous abrupt decrease in major and trace elements contents (e.g., titanium which is a proxy of surface runoff input) and increase in carbonate concentration. In fact, the reconstructed fire activity not only follows the climatic variability that occurred during the Late-Pleistocene and Holocene (known by millennial phases of pronounced aridity), but also strikingly synchronizes with the major phases of aridity previously highlighted by Damnati (2009), Chaddadi et al. (1998), Benkaddour et al. (2005), and Rhoujjati et al. (2010). CHIRONOMID-INFERRED PLEISTOCENE AND HOLOCENE TEMPERATURE RECORDS FROM TASMANIA, AUSTRALIA Andrew B.H. Rees. University of New Brunswick, Canada E-mail address: [email protected]
Tasmania is ideally situated to study past climate because it is positioned between two important controls of synoptic-scale climate: Antarctica to the south and the Western Pacific Warm Pool to the north. Consequently, Tasmania has the potential to respond in concert with hemispheric climate change. However, few well-dated, quantitative, paleoclimate records exist for the region so that important questions regarding the timing and magnitude of climate events, such as the Antarctic Cold Reversal (ACR) and Holocene Thermal Maximum (HTM), remain unanswered. We present a consensus reconstruction for Mt. Field National Park, south-central Tasmania, based on three chironomid-inferred temperature (TWARM) records spanning the lateglacial and Holocene periods. Preliminary results from Lake Selina, a site in western Tasmania that dates back to the previous interglacial, are also presented. Based on the consensus reconstruction, TWARM reached modern values by approximately 13 200 cal a BP and remained high until 12 500 cal a BP. After this early warm period, temperatures began to steadily cool, reaching a minimum around 8500 cal a BP. Subsequently, temperatures increase to culminate in a HTM around 4500 cal a BP. There is no evidence for any major temperature reversal during deglaciation based on chironomid temperature inferences. OZ-INTIMATE: TOWARD A CLIMATE EVENT STRATIGRAPHY FOR THE AUSTRALIAN REGION, 0-35 KA Jessica Reeves. RMIT University, Australia E-mail address: [email protected]
INTIMATE (INTegration of Ice-core, MArine and TEerrestrial records) is a core programme of the INQUA (International Union for Quaternary Research) Palaeoclimate Commission (PALCOMM). The purpose of INTIMATE is to gain a better understanding of 'geologically recent' climate changes, particularly during the Last Ice Age (Glaciation) and the worldwide transition from ice age climates to the present 'interglacial' climate. In 2003, an Australasian project (AUS-INTIMATE) commenced, with formal recognition from INQUA (Project Number 0806), and comprising two centres of activity, one in Australia (OZ-INTIMATE) and one in New Zealand (NZ-INTIMATE). After an initial successful workshop in 2004, the Australian chapter became somewhat dormant, and was reinvigorated in 2009, with a commitment made to the development of an Australian Climate Event Stratigraphy (CES) covering the last thirty thousand years. To approach the >60 degrees latitude, the Australia region was initially divided into four broad climatic zones: tropical, temperate, arid interior, Southern Ocean. From this, a minimum dataset to describe the major climatic events across the continent has been determined. A key time
To understand climate system dynamics, it is essential to have a closer look at global climate change signals and their terrestrial documents. Here we focus on the timing of the advance and retreat of glaciers in the past. During the Last Glacial Maximum (LGM), huge piedmont lobes covered large areas of the northern Alpine foreland. This is evidenced by the distribution of erratic boulders at different terminal positions of the paleoglaciers. A timing of the maximum extent and the retreating phases of the LGM can be established by exposure dating of these erratic boulders with cosmogenic nuclides. For this purpose three boulders in the lower Reuss Valley were sampled for surface exposure dating with cosmogenic 10Be. Two boulders are located on moraines of the LGM maximum extent. The third boulder is located between two retreating stadial positions. Radiocarbon ages from a site located only several kilometers eastward of our study area yield a time span between the maximum extent and the recession of two retreating stadials between approximately 32 kcal. BP and 23 kcal. BP. Our surface exposure ages for the maximal extent and the retreating phases are younger. The oldest age is around 22 ka, and the boulder representing the local deglaciation is around 18 ka old. The exposure ages fit well with the global LGM around 21 ka. Former studies suggest a two-cycle model for the maximal extension of the last glaciation in the Swiss northern Alpine foreland. Consequently, further boulders have to be dated to verify this argument founded on field observations. It is important to ensure that the detected time shift is not only caused by different dating methods. DIATOM DIVERSITY VS. SILICA DISSOLUTION DURING THE LAST GLACIAL-INTERGLACIAL CYCLE IN LAGUNA POTROK AIKE (PATAGONIA) Cristina Recasens. University of Geneva, Switzerland E-mail address: [email protected]
Laguna Potrok Aike is a maar lake located in southernmost Patagonia and, as one of the few permanent lakes in the area, provides an exceptional continuous sedimentary record. Diatom assemblages were analyzed at high resolution on the composite core 5022-2CP, obtained within the framework of the ICDP-sponsored project PASADO (Potrok Aike Maar Lake Sediment Archive Drilling Program). More than 216 species, varieties and forms have been identified so far, including endemic species and some new to science. The quantitative analysis reveals diatom abundances ranging from nearly none to 460 million valves per gram of dry sediment, with substantial fluctuations along the record. During Glacial times, floristic assemblages are relatively stable with plankton being dominated by Discostella stelligera. Remarkable diatom concentration peaks at different depths in the core most probably reflect variations in the nutrient availability in the system. The causes for these changes in nutrients supply will be inferred from the analyses of other proxies and a more detailed age model. The Late Glacial to Holocene transition is defined by a diversification of the plankton, with the occurrence of Cyclostephanos patagonicus at approximately 15’550 cal yrs BP and its decline and stepwise replacement by indicators of more brackish conditions, Thalassiosira patagonica and Cyclotella agassizensis, from approximately 11’500 cal yrs BP to present day. Additionally, a high degree of valve dissolution can be noticed in the top 10 m of the record, corresponding to very low values of diatom concentration in the sediment. Likewise, samples at the sediment-water interface, present equally dissolved specimens of Cyclotella agassizensis. The mechanisms behind this dissolution, together with variations in the diatom abundance and species distribution will shed some new light on the behavior of this lake, its internal chemistry and nutrient supply as well as lake level variations and periods of ice-cover. HOLOCENE MICRO-CHARCOAL RECORD FROM LAKE IFRAH (MIDDLE ATLAS – MOROCCO): CLIMATIC IMPLICATIONS Hanane Redda. UAE. Faculty of Sciences and Techniques-Tangier, Morocco E-mail address: [email protected]
Paleo-fire activity in North Africa and its connections with past climatic changes still remains poorly documented. A high resolution multiproxy
395
analysis (using organic and inorganic matter, major and trace elements, magnetic susceptibility, charcoal and pollen data) from Lake Ifrah (Middle Atlas – Morocco) provides new insights for better understanding paleo-fire occurrence during the Late-Pleistocene and Holocene periods. The comparison between size-classes micro-charcoal distribution and lacustrine reconstructed environmental variables further highlights the variability of paleo-fire activity that is interpreted in term of climate-driven changes. Increases in micro-charcoal abundance associated to changes in arboreal pollen composition likely testify regional emissions from forest fires and atmospheric transport. Such biomass burning events were associated to prolonged periods of drought, as inferred by synchronous abrupt decrease in major and trace elements contents (e.g., titanium which is a proxy of surface runoff input) and increase in carbonate concentration. In fact, the reconstructed fire activity not only follows the climatic variability that occurred during the Late-Pleistocene and Holocene (known by millennial phases of pronounced aridity), but also strikingly synchronizes with the major phases of aridity previously highlighted by Damnati (2009), Chaddadi et al. (1998), Benkaddour et al. (2005), and Rhoujjati et al. (2010). CHIRONOMID-INFERRED PLEISTOCENE AND HOLOCENE TEMPERATURE RECORDS FROM TASMANIA, AUSTRALIA Andrew B.H. Rees. University of New Brunswick, Canada E-mail address: [email protected]
Tasmania is ideally situated to study past climate because it is positioned between two important controls of synoptic-scale climate: Antarctica to the south and the Western Pacific Warm Pool to the north. Consequently, Tasmania has the potential to respond in concert with hemispheric climate change. However, few well-dated, quantitative, paleoclimate records exist for the region so that important questions regarding the timing and magnitude of climate events, such as the Antarctic Cold Reversal (ACR) and Holocene Thermal Maximum (HTM), remain unanswered. We present a consensus reconstruction for Mt. Field National Park, south-central Tasmania, based on three chironomid-inferred temperature (TWARM) records spanning the lateglacial and Holocene periods. Preliminary results from Lake Selina, a site in western Tasmania that dates back to the previous interglacial, are also presented. Based on the consensus reconstruction, TWARM reached modern values by approximately 13 200 cal a BP and remained high until 12 500 cal a BP. After this early warm period, temperatures began to steadily cool, reaching a minimum around 8500 cal a BP. Subsequently, temperatures increase to culminate in a HTM around 4500 cal a BP. There is no evidence for any major temperature reversal during deglaciation based on chironomid temperature inferences. OZ-INTIMATE: TOWARD A CLIMATE EVENT STRATIGRAPHY FOR THE AUSTRALIAN REGION, 0-35 KA Jessica Reeves. RMIT University, Australia E-mail address: [email protected]
INTIMATE (INTegration of Ice-core, MArine and TEerrestrial records) is a core programme of the INQUA (International Union for Quaternary Research) Palaeoclimate Commission (PALCOMM). The purpose of INTIMATE is to gain a better understanding of 'geologically recent' climate changes, particularly during the Last Ice Age (Glaciation) and the worldwide transition from ice age climates to the present 'interglacial' climate. In 2003, an Australasian project (AUS-INTIMATE) commenced, with formal recognition from INQUA (Project Number 0806), and comprising two centres of activity, one in Australia (OZ-INTIMATE) and one in New Zealand (NZ-INTIMATE). After an initial successful workshop in 2004, the Australian chapter became somewhat dormant, and was reinvigorated in 2009, with a commitment made to the development of an Australian Climate Event Stratigraphy (CES) covering the last thirty thousand years. To approach the >60 degrees latitude, the Australia region was initially divided into four broad climatic zones: tropical, temperate, arid interior, Southern Ocean. From this, a minimum dataset to describe the major climatic events across the continent has been determined. A key time