This thesis focuses on reconstructing past temperatures using Scots pine (Pinus sylvestris L.) tree-ring chronologies developed from Scotland. The research aims to fill a spatial and temporal gap in understanding northwest European climate dynamics, thus providing the context for assessing future climate changes in this region. Development of both a spatially complete reconstruction from an extensive network of 44 'living' Scottish tree-ring chronologies for the last few centuries, but also a near-millennium length chronology from central Scotland using mainly lake-derived 'subfossil' wood material was undertaken. Before reconstruction development, a combination of treegrowth modelling and disturbance removal methodologies was utilised in order to understand the drivers of pine growth in the Scottish Highlands, and to assess and remove anthropogenic disturbance and other non-climatic influences on growth. The advantages and limitations of utilising the relatively new 'Blue Intensity' (BI) parameter was also explored and assessed, particularly in relation to its possible utilization as a more affordable surrogate for maximum latewood density in the development of temperature reconstructions and for crossdating validation of undated samples. Although BI showed much promise for dendroclimatology, elimination of low frequency biases resulting from sample discolouration still requires further attention. Chronologies from the Cairngorms in central Scotland were identified as most suitable for reconstruction development, while reconstructions based on chronologies from other areas in the west were found to be weaker due to a range of factors including disturbance. In order to maximise reconstruction strength, BI and ring width (RW) data were combined to produce composite high-frequency BI / low-frequency RW chronologies. Although it was possible to develop an ~800 year reconstruction of temperature from central Scotland, there is substantial potential to further extend this reconstruction back in time.

Water filters and sediment trap samples were collected weekly from late May to early September 2009 from four lakes of the Lofoten archipelago, northwestern Norway, and were used to explore the applicability of the alkenone unsaturation index (UK37) for temperature reconstruction in limnic systems in the area. For the first time, we observed the occurrence of long-chain alkenones (LCAs) within the water columns of lakes in this region. Water filters from two of the four studied lakes contained measurable concentrations of alkenones that were restricted to spring turnover and disappeared with the onset of summer stratification. These results indicate that alkenones in the lake sediment of these lakes reflect biological production and temperature during lake mixing, taking place in late spring to early summer. Measurements from sediment trap material collected over the sampling season combined with water temperature measurements from automated data loggers provide an in situ calibration of the alkenone paleothermometer (Temperature = 33.0 x UK37 + 22.8; N=10; R2=0.95). Notably, this calibration reveals a UK37 sensitivity to temperature (i.e., the slope of the relationship) that is very similar to previous calibrations reported from both marine and lacustrine environments. LCAs can therefore serve as the first quantitative proxy for reconstructing past temperature variability from the Lofoten Islands. Based on this temperature calibration, a high-resolution temperature record was reconstructed over the past millennium, which shows unprecedented lake surface temperature warming during the past decades.

Fossil midge remains from a sediment core from Lake Stowell, Saltspring Island (48°46’54”N, 123°26’38”W) were used to produce quantitative estimates of mean July air temperature over the last 14,000 years. Chironomid and Chaoborus remains were identified, and multiple models of past temperatures based on transfer functions of northern North American calibration datasets were evaluated. The selected model was used to create the first quantitative paleotemperature estimates for the Gulf Islands region. Inferred paleotemperatures at Lake Stowell varied between 12.1 °C and 18.6 °C over the last 14,000 calendar years. Several major climate phases were identified based on changes in paleotemperature. The base of the record is characterised by a cool lateglacial interval with a minimum inferred July temperature of 12.1 °C. Inferred temperatures generally increased by ~4 °C between ~14,200 and 10,300 cal yr BP but this warming was interrupted by cooling, coincident with the Younger Dryas Chronozone, when inferred temperatures drop ~2 °C from the temperatures immediately preceding this interval. A warm early Holocene extends from ~10,300 to 8100 cal yr BP with temperatures regularly exceeding 16 °C. Following the early Holocene, inferred temperatures decreased to approximately 14.9 °C in the mid-Holocene. After a brief warm peak in the late Holocene, inferred temperatures cooled towards the present. Inferred changes in paleotemperature from Lake Stowell are consistent with other paleoenvironmental studies conducted in southern British Columbia and throughout much of the Northern Hemisphere. Temperature changes at Lake Stowell are muted in comparison to continental sites, which may be due to the influence of marine conditions. This research provides context for other studies in the region, and contributes to our understanding of environmental change since the last glacial maximum. / Graduate / 2017-08-17 / 0426 / 0793 / 0353 / jillian.lemmen@gmail.com

Advances in scanner technology have made it possible to obtain high resolution (6000 dpi) images of tree samples. Due to the images’ increased capability of resolving anatomical wood structures, the new technology could be of benefit to dendroclimatology.  This study attempts to expand on Rydval et al.’s (2017) previous 800 years reconstruction of Scottish summer temperatures by assessing whether a higher image resolution of samples has the ability to improve the accuracy of the region’s temperature reconstruction. Two independent blue intensity (BI) chronologies, based on differing image resolutions (6000 dpi and 2400 dpi) of Scots pine samples, were developed and subjected to standard detrending procedures. Raw data from Rydval et al.’s (2017) prior study was used to develop the chronology which was based on the 2400 dpi images. On the other hand, newly acquired data was utilized for the other chronology. In order to resolve the primary question that this paper explores, the characteristics and strength of the two BI chronologies’ climatic signals were compared. In addition, the newly acquired data was used to develop a 318 years reconstruction of mean July/August temperatures for Scotland.  Calibrations against meteorological data indicated that the improved image resolution did not generate a positive effect on the chronology’s ability to retain a reliable climatic signal. The study’s findings were thus inconclusive in showing that a higher image resolution of Scots pine samples improves the accuracy of temperature reconstructions for Scotland. Future studies are encouraged to investigate the applicability of dendroclimatic computer softwares (i.e. CooRecorder) with regard to a high image resolution.  From a broader perspective, this study contributes to setting climate change in a more accurate long term spatiotemporal context. This is crucial in predicting future climate variability, as well as understanding the role and extent of anthropogenic forcing. / Framsteg inom skannerteknik har gjort det möjligt att få bilder av trädprover med hög upplösning (6000 dpi). På grund av bildernas ökade förmåga att lösa anatomiska träd strukturer kan den nya tekniken vara till nytta för dendroklimatologi.  Denna studie strävar mot att utveckla Rydval et al.s (2017) tidigare 800 års rekonstruktion av skotska sommartemperaturer genom att bedöma om en högre bildupplösning av prover har förmågan att förbättra noggrannheten för regionens temperaturrekonstruktion. Två oberoende blåintensitet (BI) -kronologier, baserade på olika bildupplösningar (6000 dpi och 2400 dpi) av skotska träprover, framtogs och utsattes för standardförfaranden. Rådata från Rydval et al.s (2017) tidigare studie användes för att utveckla kronologin som baserades på 2400 dpi-bilderna. Å andra sidan användes nyförvärvade data för den andra kronologin. För att besvara den primära frågan som denna studie undersöker jämfördes egenskaperna och styrkan hos de två BI-kronologins klimat signaler. Dessutom används de nyförvärvade uppgifterna för att utveckla en 318 års rekonstruktion av genomsnittliga juli/augusti temperaturer för Skottland.  Kalibreringar mot meteorologiska data indikerade att den förbättrade bildupplösningen inte genererade en positiv effekt på kronologins förmåga att behålla en pålitlig klimat signal. Studiens resultat var således otvetydiga när de visade att en högre bildupplösning av skotsk tallprover förbättrar noggrannheten i temperatur rekonstruktioner för Skottland. Framtida studier uppmuntras att undersöka användbarheten av dendroklimatiska datorprogram (dvs CooRecorder) med avseende på en ultrahög bildupplösning.  Ur ett bredare perspektiv bidrar denna studie till att placera klimatförändringarna i ett mer exakt långsiktigt rumsligt tidsmässigt sammanhang. Detta är avgörande för att förutsäga framtida klimatvariationer samt förstå rollen och omfattningen av antropogen tvingande.