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Lateglacial Climate Change and Chronology at Lurga, Western Ireland - Derived from Multiproxy and Microtephra Analysis

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Lateglacial Climate Change and Chronology at Lurga, Western Ireland - Derived from Multiproxy and Microtephra Analysis Lateglacial climate change and chronology at Lurga, western Ireland - derived from multiproxy and microtephra analysis - Master thesis M.C.H. Duijkers, 2009 Studentnr: 0314056 Supervised by Drs N. van Asch, Dr. W.Z. Hoek Department of Physical Geography Faculty of Geosciences Utrecht University Contents Pagea Figures 3 1. Introduction 5 2. Lateglacial Climate 7 2.1 Ice cores 7 2.2 Marine cores 11 2.3 The Lateglacial in northwest-Europe 14 2.4 The Lateglacial in Ireland 23 3. Study Area 31 4. Methods 33 4.1 Climate reconstruction 33 4.1.1 Lithostratigraphy 33 4.1.2 Loss on ignition 33 4.1.3 Isotope analysis 35 4.2 Chronological Framework 40 4.2.1 Tephra 40 5. Results 47 5.1 Climate reconstruction 47 5.1.1 Lithostratigraphy 47 5.1.2 Loss on ignition 50 5.1.3 Isotope analysis 52 5.2 Chronological Framework 56 5.2.1 Tephra 56 6. Discussion 58 6.1 Organic matter content 58 6.2 Isotope analysis 59 6.3 Tephra 55 6.4 Climate reconstruction 66 7. Conclusions 69 Acknowledgements 70 References 71 2 Figures Fig. 1: δ18O curve for the Lateglacial derived from the NGRIP ice core 5 Fig. 2: The last 150.000 years in the Quaternary period. The Lateglacial forms the transition from the Late 7 Weichselian to the Holocene. Fig. 3: Map of Greenland showing sites where ice cores were retrieved. 8 Fig. 4: δ18O curve for the Lateglacial derived from the NGRIP ice core). GICC05 chronology events are 9 indicated. Fig.5: Location of marine cores MD95-2006 and NA 87-22 11 Fig. 6: Correlation of grain parameters and planktonic foraminifera from marine core at Barra Fan to NGRIP 12 ice core oxygen isotope record. Fig. 7: Sea surface temperature and salinity estimates for core NA 87-22 off Ireland. Results are compared to 13 NGRIP δ18O record. Fig. 8: Nomenclature differences for the Lateglacial period on the British Isles and in Continental North-west 14 Europe. Fig. 9: Temperature curves for different regions in northwest Europe. The curves for Britain and the 16 Netherlands are based on fossil coleopteran records. The curves for Ireland and northwest Germany are based on palaeobotanical data. Fig. 10: Chironomid-inferred mean July air temperature record for Whitrig Bog, southeast Scotland compared 18 to NGRIP ice core oxygen isotope record. Fig 11: Chironomid-inferred mean July air temperature record for Hawes Water, northwest England (A) 19 compared to oxygen isotope record from the same core (B) and NGRIP oxygen isotope record (C). Fig. 12: Vegetation development for different regions in northwest Europe during the Lateglacial. 21 Fig. 13: Development of geomorphology and soils during the Lateglacial in northwest Europe. 22 Fig. 14: Glaciation limits during recent glaciations in Britain. Sites referred to in the text are indicated in the 24 figure. Fig. 15: LOI and Oxygen isotope record for Red Bog compared to the oxygen isotope record from NGRIP ice 25 core. Fig. 16: Oxygen isotope record for Lough Gur compared to the oxygen isotope record from NGRIP ice core. 26 Fig.17: Percentage pollen curves for Betula and Juniperus, and δ18O, erosion, and July temperature values 27 compared to NGRIP oxygen isotope record. 18 Fig. 18: Lithology (A), weight percent total calcite (B), weight percent total organic matter (C), δ Ocalcite values 28 vs. age in cal yr BP with significant climate events labeled in brackets and a 50-year moving average in grey 18 inllustrating first order trends, and the NGRIP δ Oice record for comparison. Fig. 19. Map or Ireland with the study site indicated (A), topographical map of study site Lurga (B) and a 31 detailed map of study site Lurga (C) Fig. 20: Bo-plot of SiO2 and K2O concentrations in tephras derived from the main European ash provinces 41 Fig. 21: Basaltic tephra shards of the Vedde ash from Loch Ashik, Scotland, exhibiting examples of chemical 42 alternations: (A) the formation of a leached Si gel layer, (B) pitting erosion through cation removal, (C) preferential leakage of particular phases of the glass and recrystalisation of leached products onto the glass surface. Fig. 22: Sample loss due to NaOH preparation on 20 paired samples of glass extracted from a bulk sample of 43 the Baia Averno tephra. Fig. 23: δ18O curve for the Lateglacial derived from the NGRIP ice core with expected microtephra layers in 46 Ireland Fig. 24: Coring transect Lurga, western Ireland. 49 Fig. 25: a) lithology of the studied sediment core. b) the organic matter content in percentages derived from 51 the loi-method. The red lines define the different sample series which were placed in the oven for combustion. c) the organic matter content corrected for carbonates partially burned in the oven dependent on their position. After correction many values were below zero, as this is not possible these were set to zero percent. Fig. 26: Percentage of calcite burned after combustion at 550 ºC for four hours. The top of the figure is the 51 back of the furnace and the bottom part of the figure corresponds with the front of the furnace. Fig. 27: Measured calciumcarbonate percentages (LU-A) 52 Fig. 28: Oxygen isotope result for the study site Lurga 53 Fig. 29: Wigglematched δ18O curve of the study site (from a depth of 770 cm) to the NGRIP δ18O curve 54 Fig. 30: Estimated accumulation rate at the study site compared to the δ18O curve of the study site 54 Fig. 31: LU-A δ13C results compared to LU-A δ18O results 55 Fig. 32: Graph with potential tephra shards found in core LU-A 56 Fig. 33: Shard population found at the study site in core LU-A at a depth of 750 cm 57 Fig. 34: Glass shard found during optical identification of tephra shards, thought to originate from (with glass 57 shards) contaminated cover glass. Fig. 35: Organic matter content from the study site (LU-A) compared to LOI results from a previous research 59 at Lurga Fig. 36: Carbonate percentages (of this study) compared to the NGRIP δ18O and to a carbonate curve from a 60 study at Tory Hill Fig. 37: Oxygen isotope result compared to the NGRIP δ18O curve 61 Fig. 38: Oxygen isotope results for a) Red Bog b) Lough Gur (Ahlberg et al., 1996) c) Lurga (this study) and d) 62 the NGRIP ice core Fig. 39: Sea surface and salinity estimates for core NA 87-22 off the west-coast of Ireland. Results are 62 3 compared to the δ18O result of this study. Fig. 40: Composite pollen curves from a previous research at the study site Lurga 64 Fig. 41: δ13C values of the study site compared to a δ13C record from a previous study at Tory Hill 65 Fig. 42: Multiproxy analysis on sediment core LU-A at the study site Lurga. Results include lithology, 67 carbonates, oxygen and carbon isotope ratios Fig. 43: LU-A δ18O results compared to results for a chronomid detrended correspondence analysis (DCA in 68 standard deviation units) on the LU-A sediment core 4 1. Introduction The Quaternary is a geological period which is characterized by the alternation of glacial and interglacial periods. The transition from the last glacial to the present interglacial (the Lateglacial) was a period of relative rapid climate fluctuations. The most important drivers of the Lateglacial climate are variations in the size of ice sheets, seasonal insolation, and greenhouse gas concentrations (Ruddiman, 2001). The Lateglacial climate fluctuations are recorded in ice cores from the Greenland Ice Sheet (figure 1). ka b. 2000 AD 11.0 12.0 13.0 14.0 15.0 -44-42-40-38-36-34 NGRIP delta18O (per mille) Fig. 1: δ18O curve for the Lateglacial derived from the NGRIP ice core (based on data from NGRIP members, 2004, Rasmussen et al., 2005, Rasmussen et al., 2006b). Changes in climate do not always occur simultaneously, ice core records are used to compare timing in marine and terrestrial records with. In terrestrial records, climate changes are recorded by changes in physical and chemical properties of the sediment. Lake sediments are useful for climate reconstruction because they provide a continuous record of changes in ecosystems, lake sediment processes and climate. The environmental change recorded in Ireland’s lake sediments is highly similar to a maritime environment as the climate in Ireland is for a large part affected by the Atlantic Ocean. To explore the correlation between marine, ice core and terrestrial records near western Ireland, this study examines the Lateglacial climate change and chronology in western Ireland 5 and compares the results with marine and ice core records in its vicinity. Several climate proxies were examined to present a reliable estimate of Lateglacial climate at the study site. The climate proxies investigated are organic matter content and isotope ratios (δ18O and δ13C); previous research, ice core and marine records are used for correlation. In addition to this, microtephra analysis was performed to construct a chronological framework. The following research questions were formulated: 1. How did climate change during the Lateglacial at the study site? 2. Is tephra deposited at the study site and if so, can shards be appointed to a known tephra? 3. How do the results of the multiproxy analysis correlate to previous research in the region? 4. How do the results from this study correlate to results from marine and ice cores? The thesis is structured as follows. First, Lateglacial climate in northwest Europe and Ireland is presented as known from literature (chapter 2). Next, the study area is described (chapter 3).
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