No description available.

No / his paper addresses the possible connections between the onset of human expansion in Europe following the Last Glacial Maximum, and the timing of abrupt climate warming at the onset of the Lateglacial (Bölling/Allerød) Interstadial. There are opposing views as to whether or not human populations and activities were directly forced by climate change, based on different comparisons between archaeological and environmental data. We review the geochronological assumptions and approaches on which data comparisons have been attempted in the past, and argue that the uncertainties presently associated with age models based on calibrated radiocarbon dates preclude robust testing of the competing models, particularly when comparing the data to non-radiocarbon-based timescales such as the Greenland ice core records. The paper concludes with some suggestions as to the steps that will be necessary if more robust tests of the models are to be developed in the future.

Lake sediments contain the remains of midge communities that may be used as biological proxies for inferring past environmental changes. Freshwater midges, including Chironomidae and Chaoboridae, from two alpine tarns (Pyramid Lake and Bullwinkle Lake) in the Cassiar Mountains of northern British Columbia were used to estimate Holocene palaeotemperature changes, and more specifically, to test for the presence of the Milankovitch thermal maximum, an early Holocene warm interval coinciding with peak Holocene summer solar insolation. Mean July air temperatures were reconstructed using midge-inference models developed via weighted averaging-partial least squares (WA-PLS) regression. Cold-tolerant midge taxa dominate the stratigraphies from both Pyramid and Bullwinkle Lakes; however, warm-adapted species are more common in Bullwinkle Lake. Early Holocene warming is apparent at both lakes, however it is unclear whether this is indicative of the Milankovitch thermal maximum. A decrease in temperature occurs from 8,700-7,900 cal. yr BP at Pyramid Lake, around the same time that the 8,200 cal. yr BP cooling event occurred in the northern hemisphere. During the middle Holocene, records from Pyramid Lake indicate an overall decrease in temperature, with a short period of warmer temperatures that peak at 5,100 cal. yr BP. Temperatures fluctuate little during this time at Bullwinkle Lake. A short warming phase is apparent at both lakes during the late Holocene. July temperatures are highest at 2,000 cal. yr BP (10.5°C) in Pyramid Lake and at 1,200 cal. yr BP (13°C) in Bullwinkle Lake. Thereafter, temperatures return to what they were before the warming occurred, and at Bullwinkle Lake, vary little throughout the remainder of the Holocene.

Lake sediments contain the remains of midge communities that may be used as biological proxies for inferring past environmental changes. Freshwater midges, including Chironomidae and Chaoboridae, from two alpine tarns (Pyramid Lake and Bullwinkle Lake) in the Cassiar Mountains of northern British Columbia were used to estimate Holocene palaeotemperature changes, and more specifically, to test for the presence of the Milankovitch thermal maximum, an early Holocene warm interval coinciding with peak Holocene summer solar insolation. Mean July air temperatures were reconstructed using midge-inference models developed via weighted averaging-partial least squares (WA-PLS) regression. Cold-tolerant midge taxa dominate the stratigraphies from both Pyramid and Bullwinkle Lakes; however, warm-adapted species are more common in Bullwinkle Lake. Early Holocene warming is apparent at both lakes, however it is unclear whether this is indicative of the Milankovitch thermal maximum. A decrease in temperature occurs from 8,700-7,900 cal. yr BP at Pyramid Lake, around the same time that the 8,200 cal. yr BP cooling event occurred in the northern hemisphere. During the middle Holocene, records from Pyramid Lake indicate an overall decrease in temperature, with a short period of warmer temperatures that peak at 5,100 cal. yr BP. Temperatures fluctuate little during this time at Bullwinkle Lake. A short warming phase is apparent at both lakes during the late Holocene. July temperatures are highest at 2,000 cal. yr BP (10.5°C) in Pyramid Lake and at 1,200 cal. yr BP (13°C) in Bullwinkle Lake. Thereafter, temperatures return to what they were before the warming occurred, and at Bullwinkle Lake, vary little throughout the remainder of the Holocene.

The Late Rhaetian (Late Triassic) extinction event is characterised by shelled species showing a reduction in size, and thickness, which together with changed mineralogy is thought to be as a result of increased atmospheric pCO2 levels. Similar morphological changes have been demonstrated for extant species exposed experimentally to high CO2 leading to the hypothesis that Late Triassic extinctions were linked with global ocean acidification and increased oceanic palaeotemperatures. Consequently, the aim of this present work was to test this ocean acidification hypothesis by investigating morphological changes in selected shelled fossil species across this extinction event, and attempt to correlate them with changes in environmental temperature and pCO2. The abundance, size, shell thickness and mineralogy was determined for three common species, the bivalves Liostrea hisingeri and Plagiostoma gigantea and the ostracod Ogmoconchella aspinata collected from Triassic and Jurassic rocks from two locations in southwest England. Palaeotemperature was reconstructed from examination of these fossils and from the literature and atmospheric pCO2 estimated from published accounts. The shell size of bivalves increased during periods of high pCO2 and high palaeotemperature at both locations. Ostracod carapace sizes increased at St Audrie’s Bay but decreased at Lyme Regis during periods of high pCO2, while ostracod carapace size decreased during periods of high palaeotemperature at St Audrie’s Bay. However, ostracod shell thickness increased and decreased as pCO2 increased but shows no relationship with palaeotemperature at either location. Laboratory experiments on the effect of elevated pCO2 and elevated temperature on three modern species of ostracod was carried out. Modern species Leptocythere sp. and L. castanea subjected to either elevated pCO2 or elevated temperature showed increased dissolution, however size and thickness did not significantly change. In the same experimental conditions L. lacertosa showed increased dissolution however size continued to increase, while thickness was maintained. Comparison of fossil bivalve and ostracod data to modern high pCO2 and high temperature experiments illustrates some correlations to the modern experiments results indicating high pCO2 and high palaeotemperature conditions could have been occurring during the Triassic-Jurassic boundary interval. From the evidence presented, combined with an appropriate trigger (CAMP volcanism), it can be concluded that both ocean acidification and palaeotemperature were contributing to the species adaptations identified across the Triassic-Jurassic boundary interval.

Lake sediments contain the remains of midge communities that may be used as biological proxies for inferring past environmental changes. Freshwater midges, including Chironomidae and Chaoboridae, from two alpine tarns (Pyramid Lake and Bullwinkle Lake) in the Cassiar Mountains of northern British Columbia were used to estimate Holocene palaeotemperature changes, and more specifically, to test for the presence of the Milankovitch thermal maximum, an early Holocene warm interval coinciding with peak Holocene summer solar insolation. Mean July air temperatures were reconstructed using midge-inference models developed via weighted averaging-partial least squares (WA-PLS) regression. Cold-tolerant midge taxa dominate the stratigraphies from both Pyramid and Bullwinkle Lakes; however, warm-adapted species are more common in Bullwinkle Lake. Early Holocene warming is apparent at both lakes, however it is unclear whether this is indicative of the Milankovitch thermal maximum. A decrease in temperature occurs from 8,700-7,900 cal. yr BP at Pyramid Lake, around the same time that the 8,200 cal. yr BP cooling event occurred in the northern hemisphere. During the middle Holocene, records from Pyramid Lake indicate an overall decrease in temperature, with a short period of warmer temperatures that peak at 5,100 cal. yr BP. Temperatures fluctuate little during this time at Bullwinkle Lake. A short warming phase is apparent at both lakes during the late Holocene. July temperatures are highest at 2,000 cal. yr BP (10.5°C) in Pyramid Lake and at 1,200 cal. yr BP (13°C) in Bullwinkle Lake. Thereafter, temperatures return to what they were before the warming occurred, and at Bullwinkle Lake, vary little throughout the remainder of the Holocene. / Irving K. Barber School of Arts and Sciences (Okanagan) / Earth and Environmental Sciences, Department of (Okanagan) / Graduate

The Petrockstowe and Bovey basins are two similar pull apart (strike slip) basins located on the Sticklepath – Lustleigh Fault Zone (SLFZ) in Devon, SW England. The SLFZ is one of the several faults on the Cornubian Peninsula and may be linked to Variscan structures rejuvenated in Palaeogene times. The bulk of the basins’ fill consists of clays, silts, lignites and sands of Palaeogene age, comparable to the Lough Neagh Basin (Northern Ireland), which is also thought to be part of the SLFZ. In this study a multiproxy approach involving sedimentary facies analysis, palynological analysis, stable carbon isotope (δ13C) analysis and organic carbon palaeothermometer analyses were applied in an attempt to understand the depositional environment in both basins. A negative carbon isotope excursion (CIE) with a magnitude of 2‰ was recorded at ~ 580 m in the siltstone, silty clay to clay lithofacies in the lower part of Petrockstowe Basin, with minimum δ13CTOC values of -28.6‰. The CIE spans a depth of 7 m. Palynological characteristics of this excursion are correlated with the Cogham Lignite in the southern UK, which is the only established PETM section in the UK, and other continental sections to test whether the palynology associated with this CIE can be used to date it. The age model proposed herein correlates the CIE to the Eocene Thermal Maximum -2 (ETM2; ~ 52.5Ma) event. Key pollen and spore assemblages found in the lower Petrockstowe Basin are Monocolpopollenites, Inaperturopollenites, Laevigatisporites, Bisaccate conifer pollen and Tricolporopollenites, which suggest an Eocene age, while those occurring in the upper part of the Petrockstowe and Bovey basins are Arecipites, Inaperturopollenites, Monocolpopollenites, Tricolporopollenites, Sequoiapollenites, and Pompeckjodaepollenites, which have suggested botanical affinities to modern tropical to sub-tropical genera signifying a climate that was frost-free at the time of sediment deposition. This assemblage further suggests that these sediments are Oligocene to middle Oligocene in age. In the upper part of the Petrockstowe Basin, reconstructed mean annual air temperatures (MAT) demonstrate a clear departure from the mean temperature of 24.5oC at 10 m to 19.5oC towards the top of the core, indicating a steady continuous decline similar to the temperature departures seen in the Solent Group in the Hampshire Basin, Isle of Wight, UK which has an established Eocene – Oligocene succession.

The potential of Arctica islandica, a long lived marine bivalve with a lifespan of over 300 years, to reconstruct a high resolution (sub-annual) climate record is explored in this thesis. Fluctuations in trace element and isotopic data from live-collected specimens from Irvine Bay, NW Scotland are compared to instrumental (particularly temperature) data. X-ray absorption spectroscopy data demonstrate the coordination state of Sr and Mg within the shell. These are consistent with models in which Sr substitutes ideally for Ca in aragonite, and Mg is bound predominantly to organic molecules. Sr/Ca incorporation may be influenced by changes in the crystal nucleation, propagation and growth rate as well as vital effects. However any effect of seawater temperature on Sr/Ca incorporation was obscured by these other factors. Mg concentration is not a linear function of a single environmental variable or organic content within the shell, indicating that Mg uptake is biologically mediated. Ba variation shows sporadic increases (of >500% above baseline) in both shells, the timing of which is similar between the prismatic layer and umbo region. The maxima are, however, not synchronous between the two shells analysed. The controls on Ba uptake require further research, but low Ba/Ca may reflect Ba/Ca concentrations within the seawater. Aliquots taken from cod otoliths show that micromilling has negligible effect on δ¹⁸O. The range of reconstructed temperature from δ¹⁸O profiles Arctica islandica shows good agreement with the sea surface temperature data from the nearby Millport marine station to within 2.1 °C. However, both the interannual and intra-annual variation appears to be sensitive to changes in temporal resolution resulting from changes in growth rates. Modelling of δ¹⁸O highlights dependence on changes in temporal resolution of the sampling, in addition to temperature and salinity. Results from the radiocarbon pilot study show that Arctica islandica is a suitable archive for changes in radiocarbon associated with anthropogenic ¹⁴C fluxes.