- Email: [email protected]
Achieving consistent species identifications of fossil pollen - case study Picea
388
Abstracts / Quaternary International 279-280 (2012) 346–461
MANGROVE DYNAMICS AND HOLOCENE SEA LEVEL CHANGE: RECORDS FROM THE TANZANIAN COAST Paramita Punwong. York Institute of Tropical Ecosystem Dynamics, Env, United Kingdom
pre-Quaternary studies. At the time of abstract submission, we are testing the ability of our algorithms to correctly classify North American Quaternary pollen samples. GROUNDWATER DATING AND PAST CLIMATE RECONSTRUCTION
E-mail address: [email protected]
Roland Purtschert. University of Bern, Switzerland Holocene mangrove vegetation dynamics have been studied from the Rufiji Delta, and the western coast of Zanzibar, Tanzania. Pollen and stratigraphical analyses, set within a radiocarbon dated chronological framework, are used to reconstruct past changes in ecosystem composition. A vegetation survey of mangrove zonations along the elevation gradients has been used to establish the environmental (sea level) extent of the different major vegetation associations using a differential GPS in order to characterize low, middle and high tide vegetation associations. From the northern Rufiji Delta, sediment cores were collected from three locations across a 10 km salinity gradient and the basal dates were 394 14 C yr BP, 4931 14C yr BP and 1292 14C yr BP from the seaward, central and landward cores, respectively. Pollen analysis from these three cores shows that mangroves existed in the Rufiji Delta from circa 4900 14C yr BP. After 4751 14C yr BP, and prior to 4167 14C yr BP, a lower sea level may have occurred as indicated by an increase in terrestrial grasses and reduced mangrove. Mangroves expanded circa 1200 14C yr BP. Relatively minor fluctuations between mangrove, back-mangrove and terrestrial grass occurred probably suggesting unstable sea level until circa 900 14C yr BP. Subsequently, fringing mangroves gradually changed to the upper intertidal mangroves, to inland vegetation, and paddy field has completely replaced mangrove communities at the present day suggesting less inundation by sea water and/or increased human impact. Future work will develop the application of the modern link between mangrove zonations and elevations to infer sea level changes through the development of a sea level transfer function. We are also concentrating on palaeoecological indicators to trace past human activity to understand how the human interaction with the mangrove ecosystem has changed; vital to inform present day management strategies of community mangrove use. ACHIEVING CONSISTENT SPECIES IDENTIFICATIONS OF FOSSIL POLLEN CASE STUDY PICEA Surangi Punyasena. Department of Plant Biology, University of Illinoi, United States E-mail address: [email protected]
Pollen is among the most ubiquitous of terrestrial fossils and often preserves an extended, continuous record of vegetation change. However, this temporal continuity has often come with a taxonomic trade-off. Most pollen grains are often only identified to genus, with some morphologically homogenous clades only identified to family. Species identifications are often only possible in low-diversity samples, where the pool of potential species is already known. Improving the taxonomic precision of pollen identifications would expand the research questions that could be addressed by the palynological record. Ecological hypotheses on species assembly and changing community structure could be tested for the first time. Our proposed solution to the taxonomic limitations of palynology is the development of machine learning algorithms sensitive to the subtle variations in pollen morphology. Our test case is the classic Quaternary example of black and white spruce. White spruce (Picea glauca) signifies drier climates while black spruce (Picea mariana) is associated with wetter periods. Given this paleoclimatic importance, there is an extensive literature on Picea morphology, but despite three decades of analysis, inconsistency in identification remains a persistent problem. However, our results using supervised instancebased learning (n-nearest neighbor) algorithms demonstrate that consistent discrimination of black and white spruce is possible, with >90% accuracy in the identification of modern spruce specimens, and w100% accuracy in the discrimination of spruce from other saccate genera (Pinus, Abies). The algorithms used are robust to some folding, tearing, and compression of the grains, suggesting that these methods would be applicable to the identification of palynomorphs in both Quaternary and
E-mail address: [email protected]
In the past decade aquifers have increasingly become palaeoclimatic archives in their own right alongside ice cores, sediments and other proxy records. The main tool for this task has been the noble gas palaeo-thermometer in combination with quantitative groundwater dating using radionuclides. Noblegas radionuclides play a unique role as tracers in environmental studies due to their chemical inertness and low concentration making them ideal tracers. The same properties on the other hand make them difficult to measure on natural concentration levels. Therefore for decades low level counting (LLC) was the only method for detecting radioisotopes of argon and krypton at an atmospheric level. In recent times and with the increase of interest and potential applications the analytical efforts with novel detection methods have been intensified. In the talk noble gas groundwater dating techniques over times scales from decades to millions of years are discussed in relation to noble gas palaeo records at different locations in Europe and elsewhere. TIMING OF THE LAST MOUNTAIN-GLACIER MAXIMUM AT MIDDLE LATITUDES NORTH AND SOUTH Aaron Putnam. University of Maine, United States E-mail address: [email protected]
In his version of the orbital theory of ice ages, Milutin Milankovitch suggested that summer insolation intensity at 65 N drove Northern Hemisphere ice sheets, and that anti-phased local insolation variations governed mountain glacier behavior at latitudes south of the equator. Here we present an interhemispheric chronological test of Milankovitch's hypothesis. We combine detailed glacial geomorphic mapping and >480 precise 10Be surface-exposure ages of moraine ridges to reconstruct mountain glacier behavior during and since the last ice age in the Wind River Range and Sierra Nevada of the western United States, and the New Zealand Southern Alps. Data show that (1) glaciers achieved maximum positions coevally in both hemispheres and (2) the onset of the last glacial termination, defined here as a major increase in glacier retreat rate, occurred first in the Southern Hemisphere. The onset of deglaciation of northern mountain glaciers was delayed until 2,000 years later. Once underway, recession was rapid in both the Southern Alps and western United States; mountain glaciers were reduced by more than 50% of their last glacial maximum extents within the first 1,000 years of the onset of glacier retreat. These results present two problems for the Milankovitch version of the orbital theory of ice ages. First, mountain glaciers persisted at their maximum configurations in middle latitudes of both polar hemispheres despite opposite local insolation-intensity signatures. Second, rapid Southern Hemisphere deglaciation occurred despite declining southern insolation intensity, whereas glacier recession in the Northern Hemisphere was delayed despite rising northern insolation intensity. We discuss alternative hypotheses and consider the roles of orbital variability, ocean-atmosphere dynamics, and greenhouse gases in producing the observed pattern of mountain glaciation in both polar hemispheres. PROGRESSIVE GLACIER RETREAT SINCE THE EARLY HOLOCENE IN THE SOUTHERN ALPS, NEW ZEALAND Aaron Putnam. University of Maine, United States E-mail address: [email protected]
Most Northern Hemisphere glaciers achieved their maximum Holocene extents during the late Holocene, culminating with the ‘classic' Little Ice Age advances in the mid-to-late AD1800s. Whether Southern Hemisphere glaciers also registered progressive cooling over the Holocene is key for discerning potential climate drivers over the present interglaciation. Here,
Abstracts / Quaternary International 279-280 (2012) 346–461
MANGROVE DYNAMICS AND HOLOCENE SEA LEVEL CHANGE: RECORDS FROM THE TANZANIAN COAST Paramita Punwong. York Institute of Tropical Ecosystem Dynamics, Env, United Kingdom
pre-Quaternary studies. At the time of abstract submission, we are testing the ability of our algorithms to correctly classify North American Quaternary pollen samples. GROUNDWATER DATING AND PAST CLIMATE RECONSTRUCTION
E-mail address: [email protected]
Roland Purtschert. University of Bern, Switzerland Holocene mangrove vegetation dynamics have been studied from the Rufiji Delta, and the western coast of Zanzibar, Tanzania. Pollen and stratigraphical analyses, set within a radiocarbon dated chronological framework, are used to reconstruct past changes in ecosystem composition. A vegetation survey of mangrove zonations along the elevation gradients has been used to establish the environmental (sea level) extent of the different major vegetation associations using a differential GPS in order to characterize low, middle and high tide vegetation associations. From the northern Rufiji Delta, sediment cores were collected from three locations across a 10 km salinity gradient and the basal dates were 394 14 C yr BP, 4931 14C yr BP and 1292 14C yr BP from the seaward, central and landward cores, respectively. Pollen analysis from these three cores shows that mangroves existed in the Rufiji Delta from circa 4900 14C yr BP. After 4751 14C yr BP, and prior to 4167 14C yr BP, a lower sea level may have occurred as indicated by an increase in terrestrial grasses and reduced mangrove. Mangroves expanded circa 1200 14C yr BP. Relatively minor fluctuations between mangrove, back-mangrove and terrestrial grass occurred probably suggesting unstable sea level until circa 900 14C yr BP. Subsequently, fringing mangroves gradually changed to the upper intertidal mangroves, to inland vegetation, and paddy field has completely replaced mangrove communities at the present day suggesting less inundation by sea water and/or increased human impact. Future work will develop the application of the modern link between mangrove zonations and elevations to infer sea level changes through the development of a sea level transfer function. We are also concentrating on palaeoecological indicators to trace past human activity to understand how the human interaction with the mangrove ecosystem has changed; vital to inform present day management strategies of community mangrove use. ACHIEVING CONSISTENT SPECIES IDENTIFICATIONS OF FOSSIL POLLEN CASE STUDY PICEA Surangi Punyasena. Department of Plant Biology, University of Illinoi, United States E-mail address: [email protected]
Pollen is among the most ubiquitous of terrestrial fossils and often preserves an extended, continuous record of vegetation change. However, this temporal continuity has often come with a taxonomic trade-off. Most pollen grains are often only identified to genus, with some morphologically homogenous clades only identified to family. Species identifications are often only possible in low-diversity samples, where the pool of potential species is already known. Improving the taxonomic precision of pollen identifications would expand the research questions that could be addressed by the palynological record. Ecological hypotheses on species assembly and changing community structure could be tested for the first time. Our proposed solution to the taxonomic limitations of palynology is the development of machine learning algorithms sensitive to the subtle variations in pollen morphology. Our test case is the classic Quaternary example of black and white spruce. White spruce (Picea glauca) signifies drier climates while black spruce (Picea mariana) is associated with wetter periods. Given this paleoclimatic importance, there is an extensive literature on Picea morphology, but despite three decades of analysis, inconsistency in identification remains a persistent problem. However, our results using supervised instancebased learning (n-nearest neighbor) algorithms demonstrate that consistent discrimination of black and white spruce is possible, with >90% accuracy in the identification of modern spruce specimens, and w100% accuracy in the discrimination of spruce from other saccate genera (Pinus, Abies). The algorithms used are robust to some folding, tearing, and compression of the grains, suggesting that these methods would be applicable to the identification of palynomorphs in both Quaternary and
E-mail address: [email protected]
In the past decade aquifers have increasingly become palaeoclimatic archives in their own right alongside ice cores, sediments and other proxy records. The main tool for this task has been the noble gas palaeo-thermometer in combination with quantitative groundwater dating using radionuclides. Noblegas radionuclides play a unique role as tracers in environmental studies due to their chemical inertness and low concentration making them ideal tracers. The same properties on the other hand make them difficult to measure on natural concentration levels. Therefore for decades low level counting (LLC) was the only method for detecting radioisotopes of argon and krypton at an atmospheric level. In recent times and with the increase of interest and potential applications the analytical efforts with novel detection methods have been intensified. In the talk noble gas groundwater dating techniques over times scales from decades to millions of years are discussed in relation to noble gas palaeo records at different locations in Europe and elsewhere. TIMING OF THE LAST MOUNTAIN-GLACIER MAXIMUM AT MIDDLE LATITUDES NORTH AND SOUTH Aaron Putnam. University of Maine, United States E-mail address: [email protected]
In his version of the orbital theory of ice ages, Milutin Milankovitch suggested that summer insolation intensity at 65 N drove Northern Hemisphere ice sheets, and that anti-phased local insolation variations governed mountain glacier behavior at latitudes south of the equator. Here we present an interhemispheric chronological test of Milankovitch's hypothesis. We combine detailed glacial geomorphic mapping and >480 precise 10Be surface-exposure ages of moraine ridges to reconstruct mountain glacier behavior during and since the last ice age in the Wind River Range and Sierra Nevada of the western United States, and the New Zealand Southern Alps. Data show that (1) glaciers achieved maximum positions coevally in both hemispheres and (2) the onset of the last glacial termination, defined here as a major increase in glacier retreat rate, occurred first in the Southern Hemisphere. The onset of deglaciation of northern mountain glaciers was delayed until 2,000 years later. Once underway, recession was rapid in both the Southern Alps and western United States; mountain glaciers were reduced by more than 50% of their last glacial maximum extents within the first 1,000 years of the onset of glacier retreat. These results present two problems for the Milankovitch version of the orbital theory of ice ages. First, mountain glaciers persisted at their maximum configurations in middle latitudes of both polar hemispheres despite opposite local insolation-intensity signatures. Second, rapid Southern Hemisphere deglaciation occurred despite declining southern insolation intensity, whereas glacier recession in the Northern Hemisphere was delayed despite rising northern insolation intensity. We discuss alternative hypotheses and consider the roles of orbital variability, ocean-atmosphere dynamics, and greenhouse gases in producing the observed pattern of mountain glaciation in both polar hemispheres. PROGRESSIVE GLACIER RETREAT SINCE THE EARLY HOLOCENE IN THE SOUTHERN ALPS, NEW ZEALAND Aaron Putnam. University of Maine, United States E-mail address: [email protected]
Most Northern Hemisphere glaciers achieved their maximum Holocene extents during the late Holocene, culminating with the ‘classic' Little Ice Age advances in the mid-to-late AD1800s. Whether Southern Hemisphere glaciers also registered progressive cooling over the Holocene is key for discerning potential climate drivers over the present interglaciation. Here,