Polar desert environments are limiting in plant available nutrients, mainly nitrogen (N) and phosphorus (P) that severely limit plant growth and establishment. Cryogenic activity regularly patterns the ground into a patchwork of frost boils – sorted circles that are associated with an increase in moisture, fertility and plant cover. Within some frost boils, the accumulation of ice-rich soil at the permafrost table can cause an upward flow of soil organic carbon (SOC) enriched permafrost material into the active layer. These diapiric intrusions are predicted to fuel microbial activity and enrich the horizon in N and P; however, the enrichment of the diapir horizon and accessibility by plants has yet to be studied. The aim of this research was to characterize the N distribution within diapir horizons located in frost boils and the effect of these intrusions on vascular plant N uptake in a polar desert ecosystem of the Canadian High Arctic. Natural abundance and enriched isotope 15N techniques were used to trace the flow of N through the soil-plant system. Surface and diapir horizons contained the highest total C and total N content within frost boils. Natural abundance δ15N analysis indicated that uptake by Salix arctica plants located on frost boils in the absence of a diapir horizon were sourcing N from the surface. However, when diapir nutrients became available, S. arctica plants began sourcing N from the diapir horizon and underlying low SOC sources in the soil, while reducing uptake from the surface. The altered foraging strategy of S. arctica in response to diapir horizon formation was further indicated by significant uptake of atom%15N nutrients that were injected directly into diapir horizons. These findings suggest diapir horizons are enriched in N and accessible by plants roots as an important nutrient source that is instrumental in their survival within frost boils of a polar desert ecosystem in the high arctic.

Sclerochronology affirms the well-established fact that banded growth increments in marine molluscs accurately record oscillations in climate and environment for the past millennia or more. This study considers how such records can enhance understanding of environmental shifts across the 18th to 20th centuries. Specifically, it investigates whether sclerochronological data are fundamentally associated with stable carbon and oxygen isotope values and if the climate phenomenon of the Little Ice Age impacts the marine radiocarbon reservoir effect. Furthermore, this study compares the North Sea and the Irish Sea to discover whether observed environmental changes are equivocal or not. Three shells of Arctica islandica were retrieved from the Dutch natural history museum "Naturalis" in Leiden, the Netherlands, to construct a chronology dating back to the 18th century from growth increments. Collection dates for the three shells vary between 1882 and 1954 in the North Sea and the Irish Sea. Shells were prepared, photographed and milled for calcium carbonate material. Digital images allowed counting of increments while the milled material was measured for stable carbon and oxygen isotopes and was radiocarbon dated. The ontogenetic bias was removed from sclerochronological data using MATLAB software to produce a purely environmental growth signal. The results agreed with the proposed hypothesis that there is a link between growth increments and the stable isotope data. However, further analysis is required to validate the presence of the Little Ice Age in the radiocarbon reservoir effect. These results indicate that the stable carbon and oxygen isotopes and growth increments are a good indicator of favourable growth conditions for Arctica islandica. Therefore, this study highlights that Arctica islandica is a suitable proxy for the North Sea and Irish Sea palaeoenvironment reconstructions. On this basis, future climate research can accurately depend on sclerochronological data to aid in understanding the patterns of anthropogenic climate change.

No / The potential of Mg in Arctica islandica as a climate proxy is explored through analysis of live-collected shells from Irvine Bay, NW Scotland. Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) analysis of the right hand valve from two specimens indicates that seasonal Mg/Ca variations do not correlate with seawater temperature. The highest Mg/Ca typically occurs at the annual growth checks in ~ November¿February. Mg/Ca variations between growth checks are significant in one specimen but usually not significant in the other. Mg/Ca measurements taken laterally across the band (i.e. perpendicular to direction of the growth) to determine heterogeneity of the aragonite deposited at the same time indicates that Mg/Ca concentration decreases with increasing distance from the periostracum in both shells. X-ray Absorption Near Edge Spectroscopy (XANES) indicates that Mg is not substituted into aragonite but is hosted by a disordered phase e.g. organic components or nanoparticles of an inorganic phase. Shell Mg/Ca variations may reflect changes in the concentration or composition of the disorded phase, as well as changes in the composition of the extrapallial fluid used for calcification. Such changes could reflect the relative transportation rates of Mg and Ca to the calcification site.

This thesis investigates the potential of the bivalve Arctica islandica (Linnaeus, 1767) from fjordic sites in NW Scotland for reconstructing past marine environmental /climatic variability. Using dendrochronological and sclerochronological techniques, six master chronologies were created which when compared show little common variability between the sites, indicating no common response to regional scale forcing. The chronologies were compared to local and regional scale SST and land based datasets, with no significant, time stable responses to climate found. It is clear the growth/climate response of A. islandica from these sites is complex, potentially due to the shallow nature of the sample sites, direct local drivers such as food availability and, potentially, anthropogenic activity in the region. Geochemical analyses of the shell material were undertaken to examine the timing and magnitude of the radiocarbon bomb-peak and the stable carbon isotope signature of the oceanic Suess Effect. The timing of the radiocarbon bomb-peak in Loch Etive does not appear to match previously published results from other marine locations and are a potentially serious challenge to the assumption that A. islandica GI are always annual features. Results comparing δ¹³C values and the age of the specimen when these values are incorporated into the shell material strongly indicate an ontogenetic control over δ¹³C, meaning the Suess Effect could not be effectively investigated. To take these ontogenetic influences into account it is suggested that any data from the juvenile period of shell life is not used. Analysis of shell biometrics and morphology indicate significant relationships between shell age and height and age and weight, however the errors for these are large (±78 years and ±80 years respectively). These results indicate that despite large errors shell height, as a predictor of age, has the potential to be used for in situ population studies.

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.

The sediment Core SWERUS-L2-2-PC1 (2PC) retrieved from the Chukchi Sea, Arctic Ocean sits in an oceanographically dynamic location at the Arctic-Pacific Ocean gateway. The 8.3 m-long core was retrieved in Herald Canyon at the marginal ice zone at 57 m depth. Core 2PC is well-positioned to record variability in inflow of Bering Sea Water (BSW) and Pacific Water (PW) in Herald Canyon. With the 2PC high sedimentation rate (200 cm/kyr), two independent age models (radiocarbon and palaeomagnetism) based on tephra age markers, and a richness in well-preserved siliceous sediment, validate 2PC as an outstanding sequence for applying diatom assemblage analysis as a proxy for ocean-climate change back to 4250 years BP, including the past few hundred years where global warming and sea ice decline is recorded by instrumental records. These characteristics make Core-2PC a useful record for investigating the role of PW on sea ice variability in the Chukchi Sea, both in the past and predicting the future. To investigate the impact of PW on ocean and sea ice conditions in the Chukchi Sea, diatom assemblage analysis was performed on 49 samples through the Late Holocene. The over-arching goal was to test the hypothesis, suggested by existing research on 2PC using benthic foraminifera Mg/Ca palaeothermometry, that the strength of PW inflow into the Chukchi Sea via Herald Canyon has varied on a time scales of ~500-1000 years in the past 4000 years. PW is slightly warmer than resident Arctic surface waters and is known to be an important control on Arctic sea-ice. The diatom assemblage approach assumes that there are recognizable differences between end-member diatom assemblages that are characteristic of PW versus Arctic Ocean type environments associated with extensive sea-ice conditions. The mapping of species in the Herald Canyon was used to test the idea of variability of sea-ice extent and the role of the Pacific Ocean forcings into the western Chukchi Sea. The results reveal diverse diatom assemblages throughout the past 4000 years in Herald Canyon, showing this core to be very useful for diatom palaeoclimate reconstructions. A total of 126 species with abundance >1% are recognized. Several generalist species typically dominate assemblages especially Chaetoceros, ice-algae, marine-neritic and near ice or cold-water planktic centric diatoms. Distinct changes in stratigraphy are illustrated by changes in identified diatom assemblage zones. The 2PC diatom assemblages were contrasted with records from Chukchi-, Laptev-, East Siberian- and Bering Sea and North Pacific Ocean. At 2PC, sympagic (sea-ice related), planktic and neritic species abundance varies on time scales of ~500-1000 years. Importantly, there is a clear similarity between the timing of diatom assemblage changes and the 2PC benthic foraminifera Mg/Ca bottom water temperature (BWT) reconstruction. In particular, abundance changes in the warm water species Thalassionema nitzschioides, Shionodiscus oestrupii and Thalassionema simonsenii, tychoplanktic Paralia sulcata, Ice algae- and sympagic assemblages and cold-water indicators correspond best to BWT fluctuations shown by the Mg/Ca reconstruction. These oscillations are suggestive of changes in warmer PW inflow. Other aspects of the diatom data appear to correlate with colder and warmer climate events and suggest that changes in PW inflow amplified the effects of these events in the Chukchi Sea region through the Late Holocene in the Northern Hemisphere. It can thus, be concluded that diatoms from 2PC, support the palaeoceanographic reconstruction suggested by the benthic foraminifera Mg/Ca palaeothermometry and that variations in PW inflow through Herald Canyon is an important driver of sea ice variability on thousand-year time scales.