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Marine sediments are significant long-term stores of carbon. Carbon burial within sediments has provided a climate regulation service over geological timescales. Despite marine sediments holding vast quantities of carbon, the spatial distribution of this carbon store is not well constrained. This information is critical to assessing and monitoring the seabed and in identifying carbon hotspots that may be vulnerable to disturbance and loss. This study focuses on marine sediments within Scotland's seas. Scotland has a marine area six times its land area making it an exemplar nation to investigate novel methods to improve the spatial understanding of significant sedimentary carbon stores. Here, a novel methodology has been developed that uses multibeam acoustic backscatter data to map surficial sedimentary organic carbon and quantify surface stocks within a model fjordic system. In the proof-of-concept study, a strong correlation between sediment type, backscatter intensity, and organic carbon was found. The heterogeneous nature of the seabed within fjords was highlighted with implications for carbon storage, supporting the need for a greater spatial understanding of marine sediments in carbon accounting. A further study tested the opportunities and limitations of the wider application of backscatter to map sedimentary organic carbon in different coastal settings, potentially providing a cost-effective mapping tool. Results from this project also highlighted the role of estuaries on the east coast of Scotland in delivering significant amounts of terrestrial carbon to inshore sediments. Quality assessments of this organic carbon within shelf sediments indicated that remineralisation losses due to disturbance may be minimal, however anthropogenic pressures on the seabed can affect the burial potential of sediments, thereby limiting the ability of the seabed to provide climate benefits. The findings from this research can be used to provide tools to decision-makers to identify vulnerable carbon stores on the seabed, address evidence gaps relating to the transfer of carbon between ecosystems and implement targeted spatial interventions for their protection.

The global ocean has experienced an alteration of its seawater chemistry due to the continuing uptake of anthropogenic carbon dioxide (CO₂) from the atmosphere. This ongoing process called Ocean acidification (OA) has reduced seawater pH levels, carbonate ion concentrations (CO₃⁻℗ø) and carbonate saturation state (Î♭) with implications for the diversity and functioning of marine life, particularly for marine calcifiers such as foraminifera. The vulnerability of this ubiquitous calcifying group to future high ̧˜łCO₂ /low pH scenarios has been assessed naturally and experimentally in the last decades. However, little is known about how benthic foraminifera from coastal environments such as intertidal environments will respond to the effects of OA projected by the end of the century. This research aimed to quantify the effects of OA on a series of biological parameters measured on the benthic foraminifera ̧˜Œ̧˜Ư̧˜ł̧˜♭̧˜®̧˜Æ̧˜®̧˜œ̧˜ʼ ̧˜ı̧˜®̧˜Ư̧˜Ư̧˜®̧˜Ø̧˜ʼ̧˜þ̧˜ʻ̧˜¯̧˜® and ̧˜̧˜Ø̧˜ð̧˜¯̧˜Œ̧˜þ̧˜®̧˜¯̧˜Ø ̧˜·̧˜Œ̧˜đ̧˜ʼ̧˜Ø̧˜¯̧˜®̧˜Þ̧˜Ø through a laboratory-based experimental approach where future scenarios of a high CO₂ atmosphere and low seawater pH were explored. Experimental evidence revealed that survival rates, test weight and size-normalized weight (SNW) of ̧˜Œ. ̧˜ı̧˜®̧˜Ư̧˜Ư̧˜®̧˜Ø̧˜ʼ̧˜þ̧˜ʻ̧˜¯̧˜® were negatively affected by OA. Whereas ̧˜. ̧˜·̧˜Œ̧˜đ̧˜ʼ̧˜Ø̧˜¯̧˜®̧˜Þ̧˜Ø was positively affected (i.e. enhanced growth rates) showing a species-specific response to OA at 13℗ʻC. However, the combined effect of OA and temperature (15℗ʻC) reduced survival and growth rates for ̧˜Œ̧˜Ư̧˜ł̧˜♭̧˜®̧˜Æ̧˜®̧˜œ̧˜ʼ ̧˜ı̧˜®̧˜Ư̧˜Ư̧˜®̧˜Ø̧˜ʼ̧˜þ̧˜ʻ̧˜¯̧˜® and ̧˜̧˜Ø̧˜ð̧˜¯̧˜Œ̧˜þ̧˜®̧˜¯̧˜Ø ̧˜·̧˜Œ̧˜đ̧˜ʼ̧˜Ø̧˜¯̧˜®̧˜Þ̧˜Ø. Test morphology (i.e. test surface and feeding ornamentation) of live ̧˜Œ. ̧˜ı̧˜®̧˜Ư̧˜Ư̧˜®̧˜Ø̧˜ʼ̧˜þ̧˜ʻ̧˜¯̧˜® and ̧˜. ̧˜·̧˜Œ̧˜đ̧˜ʼ̧˜Ø̧˜¯̧˜®̧˜Þ̧˜Ø were severely affected after 6 weeks by OA, negatively influencing the uptake of 13C-labelled diatoms of ̧˜•̧˜Ø̧˜ʺ̧˜®̧˜Þ̧˜œ̧˜Ư̧˜Ø ̧˜þ̧˜ł., notably for ̧˜Œ. ̧˜ı̧˜®̧˜Ư̧˜Ư̧˜®̧˜Ø̧˜ʼ̧˜þ̧˜ʻ̧˜¯̧˜®. Test dissolution rates were enhanced by OA and negatively affected foraminiferal morphology of recently dead assemblages with implications for net accumulation and preservation. These results imply that the long-term storage of inorganic carbon and cycling of carbon in coastal benthic ecosystems will be considerably altered by future OA.

Late Quaternary deposits have been investigated from three main study areas from 'western Britain in an attempt to define lithological and biostratigraphic changes. Detailed analyses of included benthonic foraminiferal assemblages are presented and a systematic section included which describes and illustrates over 200 distinct forms. Chronostratigraphic control is provided by radiocarbon dates, amino acid analysis and tephrachronology. The three study areas yield distinctive records of the depositional environments characterizing the climatic events of the Late Quaternary. From the Hebridean Shelf, B.G.S. vibrocores have been analysed within the context of a previously established seismostratigraphic sequence. Foraminiferal faunas allow the reconstruction of a regional climatostratigraphic sequence for the Lateglacial period (c. 14,000 to 10,000 BP) and this sequence is correlated, through 9 radiocarbon (AMS) dates, to the established climatostratigraphy of the Lateglacial period from N.W. Europe. Reconstructions of notional water depths during this period allow glacio-isostatic components from the shelf to be estimated and these confirm a generally accepted pattern of changing relative sea-level, from initial regression following deglaciation and subsequent transgression as the eustatic component over-takes the isostatic component. Rising sea-levels are most notable after about 10,000 BP. A cliff section at Aberdaron on the western Lleyn Peninsula provides an insight into the controversy surrounding the question of depositional origin of the "Irish Sea Drift" sequences bordering the Irish Sea. Diamicts and sorted layers from the section contain mixed boreo-arctic, temperate and pre-Quaternary species, and allochthonous/autochthonous elements are identified. While lithological changes within the section are marked, the foraminiferal assemblages maintain relatively constant faunal ratios. None of the foraminifera are considered to be in situ, but instead entrained by the Irish Sea glacier during its passage along the Basin and deposited at the site by basal melt-out processes. The third study area, the southwestern Celtic Sea, records geomorphological evidence of previously extensive glaciation in the region. Microfaunas, both foraminifera and Ostracoda, are analysed and record a transition from grounded ice lodgement facies to quiet, glacial marine facies at about 49°30 N. Amino acid analysis confirms the geomorphological evidence for glacial marine accumulation during the Late Devensian.

A robust and consistent taxonomy underpins the use of fossil material in palaeoenvironmental research and long-term assessments of biodiversity. However, the successful identification of benthic foraminiferal species is often challenged by enigmatic morphological species boundaries, nomenclatural uncertainty and the recent advent of molecular techniques and the identification of cryptic species. This thesis sought to reconcile molecules and morphology in two scientifically important yet taxonomically challenging groups of benthic foraminifera, the genus Ammonia and the family Elphidiidae, in samples obtained widely across the NE Atlantic shelf seas. Through the production of detailed quantitative morphometric analysis of over 750 genetically sequenced specimens, coupled with assessments of their biogeographical distributions, this thesis provides the most comprehensive re-evaluation of these taxa conducted to date. The integration of these new lines of taxonomic evidence has refined interspecific boundaries, clarified key diagnostic morphological features and has unveiled the presence of a number of enigmatic species boundaries (particularly within the genus Ammonia). The results highlight that classical morphospecies concepts may not always accurately reflect the genetic diversity currently found within this region, which could have important repercussions for applied taxonomic investigations. The extensive sampling across the NE Atlantic has also enabled one of the first re-evaluations of intraspecific morphological variability, revealing that many specimens taken from distinct sampling localities can be morphologically delineated. In a first step to addressing temporal dynamics of previously unrecognised cryptic species, a time series study was conducted in the NW Scottish shelf seas, which unveiled subtle seasonal partitioning between two sympatric species of Ammonia. Finally, a new taxonomic framework was developed which bridges the current discontinuity between molecular and morphological lines of evidence. This new framework, applied to Elphidium williamsoni (Haynes, 1973), provides the first clear link between morphologically characterised type material and a unique genotype.

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.

It is now accepted that the last British-Irish Ice Sheet (BIIS) was highly dynamic and drained by numerous fast flowing ice streams. This dynamic nature combined with its maritime location made the BIIS sensitive to the rapid climate change that characterised the Last Glacial Interglacial Transition. Gaining an understanding of the behaviour of the BIIS at this time is important to explore the nature of forcing between ice sheets and climate. This thesis presents new chronological data relating to the deglaciation of the northwest sector of the BIIS (NW-BIIS) from onshore dating of moraines using cosmogenic exposure dating. This improved chronological framework is supported by offshore data in the form of a newly constructed Ice Rafted Detritus (IRD) record from the offshore sediment core MD95-2007. These data suggest that deglaciation commenced sometime after 18 ka and that the NW-BIIS was located close to the present day shoreline by 16 ka. Further provenance analysis of the IRD using U-Pb dating of detrital minerals demonstrates that during the Last Glacial-Interglacial Transition MD95-2007 was being supplied distal IRD from a source(s) to the west. The absence of diagnostic Scottish material suggests that after retreat to the coastline at 16 ka calving margins were not re-established during Greenland Interstadial 1. By combining these results with existing data relating to the deglaciation of the NW-BIIS it is possible to summarise the deglaciation history of the NW-BIIS from the continental shelf to mountainous source regions and compare this to numerical models of BIIS behaviour during this time. With a better understanding of the chronology of NW-BIIS retreat it is possible to relate the timing of initial deglaciation to possible forcing factors and gain a better understanding of the response of a marine based sector of an ice sheet to rapid climate change.

This study presents a stratigraphic investigation of the marine sediment core MD04-2822 from the Rockall Trough (56° 50.54' N, 11° 22.96' W; 2344 m water depth). This core is currently the only available high resolution record for the calibration of Late Quaternary sedimentary sequences of the British (Hebridean) margin. It therefore offers an unprecedented archive of changing sedimentological and climatological conditions for the last 175,000 years. The high resolution, multi-proxy records have enabled surface and deep water conditions within the Rockall Trough to be reconstructed. In addition, the fluctuating nature of ice-rafted debris (IRD) inputs to the MD04-2822 site allows a first order attempt of BIS dynamics for the entirety of the last glacial period (i.e. from the demise of the last interglacial to the decay of the Devensian/Weichselian ice sheet) as well as the majority of the penultimate (Saalian/MIS 6) glaciation. Sediment core MD04-2822 is ideally located to capture the dynamics of the British Ice Sheet (BIS) via a continuous record of IRD and fine-grained terrigenous inputs. Fundamental to this is the construction of a robust chronology. This was achieved via: the correlation of the benthic δ¹⁸O record to a global δ¹⁸O stack (SPECMAP); the correlation of the surface proxies (% N. pachyderma (sinistral) and XRF Ca) to the Greenland δ¹⁸O and Antarctic methane ice core records; and radiocarbon dating. This chronology was validated using both radiocarbon dating and tephra horizons. An evaluation of the event stratigraphy approach used in the construction of the MD04-2822 chronology is presented. The marine record provides a valuable archive of past ice sheet dynamics as much terrestrial evidence is removed or obscured by subsequent ice sheet oscillations MD04-2822 provides the first evidence for the expansion of the BIS onto the Hebridean Margin during MIS6 (thereby confirming previous long-range seismic correlations). The continuous sedimentation at MD04-2822 enabled the first insights into the early dynamics of the last BIS. Increases in IRD and fine grained terrigenous material delivered to the MD04-2822 at ca. 72 kyr represent the first significant delivery of material from the BIS across the continental shelf to the core site. The BIS would therefore have attained a marine calving margin by this time. A multi-proxy investigation of provenance was undertaken, however unequivocal provenance determinations remain problematic. The location of the core suggest the proximal BIS as the most likely source of terrigenous inputs. The expanded nature of the MD04-2822 sediments during the penultimate deglacial (Termination II) provides the first details of BIS dynamics for this period: the interplay of large inputs of freshwater from the decay of the Saalian (MIS 6) ice sheets (including the BIS) upon the surface and deep water circulation of the North Atlantic is investigated. In addition, sub-orbital climatic variability is documented at this location throughout the last interglacial (MIS 5e) and appears to be an intrinsic feature of both the N.E. Atlantic surface and deep water circulation of the last 175 kyr.

The first study to exploit the sedimentary archives of Loch Sunart, a relatively well-flushed fjord on the NW coast of Scotland, for palaeoenvironmental reconstruction is presented. In order to understand environmental influences on past environments, the modern physical, chemical and biological conditions of the loch and surrounding catchment were studied. Both observational and computer modelled annual inner basin salinity show a clear response to climatic forcing, modulated by NAO behaviour. Main basin salinity appears to remain very stable and a well-defined salinity: δ18O relationship suggests excellent potential for palaeotemperature reconstructions based on foraminiferal δ18O . Multi-variate statistical analyses identified 4 benthic foraminiferal assemblage groups in the surface sediments of the loch: A) restricted basin (E. scaber); B) very high current activity (C. lobatulus-A. mammilla -A. beccarii); C) calm environment undera stratified water column (B. marginata-N. turgida-S. fusiformis) and D) coastal water influence and mild/episodic current activity (A. beccarii-C. lobatulus-S. wrightii-E. excavatum). Using assemblage data, an existing benthic foraminiferal transfer function was modified in order to reconstruct Loch Sunart bottom water temperature (BWS); these reconstructions agree well with Scottish coastal temperature series (Millport). C. lobatulus appears to calcify close to theoretical equilibrium δ18O calcite (Δδ18O = -0.11 ± 0.17 %), probably during the warm bottom water temperatures (BWT) of late autumn, and predominantly reflects changes in BWT rather than BWS in the main basin of Loch Sunart. The first late Holocene high resolution palaeoenvironmental reconstruction from the deep (121 m) main basin of Loch Sunart is presented; gravity core (GC023) is 3 m long and spans the last 2,000 years. Despite difficulties with geochronology, palaeoenvironmental reconstructions from Loch Sunart suggest that these high resolution sedimentary archives have the potential to resolve inter-annual marine climate variability of the order of 1-2°C and capture an integrated record of changes in the catchment and marine environment.