DOI: 10.24378/exe.31123567
title: Late glacial and Holocene marine geology, palaeoceanography and palaeoecology of the Northern Isles of Scotland: supplement to the PhD thesis by Jane L Earland

description: This data is the supplement for the PhD Thesis "Late glacial and Holocene marine geology, palaeoceanography and palaeoecology of the Northern Isles of Scotland". Jane L Earland. The thesis is available in ORE at https://hdl.handle.net/10779/exe.31096174Datasets contain foraminiferal assemblage counts, foraminiferal isotope data, grain size, total organic carbon, and age models.<b>Abstract:</b>Marine palaeoenvironmental data are essential for understanding how the oceans respond to climate and environmental changes. These data can be used to guide climate models and characterise the environment in which human populations develop. During the Holocene, much of the northwestern North Sea has experienced low sediment accumulation rates, inhibiting the investigation regional palaeoenvironmental change using traditional marine sediment proxies. However, on the DY150 research cruise (2022), marine sediment cores were recovered from depositional basins around Shetland and Orkney, UK. Using palaeoenvironmental datasets generated from these cores (foraminiferal assemblages, stable isotopes, sediment physical properties, ITRAX XRF, grain size, and total organic carbon) this thesis aims to increase our understanding of the Late glacial and Holocene marine geology, palaeoceanography and palaeoecology of the northwestern North Sea.<br>Chapters 2 and 4 investigate the sedimentary expression of the Storegga tsunami event (ca. 8,150 cal a BP), and the implications for the semi-coeval 8.2 ka cooling event. Within the Holocene mud sequences collected in the Fetlar and St Magnus basins (Shetland), coarse-grained lenses are dated to the timing of the Storegga tsunami event. These lenses show sedimentological characteristics typical of deposits created by tsunami backwash-generated debris flows. No evidence of shallow water foraminiferal species is found in the deposits, likely due to high early Holocene sedimentation rates, or the lack of gradient between species found in shallow coastal waters and at the core site. Cool water species (which are indicative of glacial age sediments) are not abundant in foraminiferal assemblages within these lenses, suggesting that reworked material originates from Holocene sediments. Despite the lack of cool water species, radiocarbon dating of carbonate material within the deposits suggests reworking of older (&gt; 8.7 k cal a BP) material. Therefore, marine sediment records in the Storegga tsunami affected region likely do not provide a reliable palaeoceanographic record of the 8.2 ka cooling event.<br>Chapter 3 examines the Late glacial and Holocene palaeoceanographic record of a sediment core from the Fetlar Basin, Shetland. At the base of this record, foraminiferal assemblages and sedimentology are indicative of a cold climate, aligning with the Younger Dryas. A transition to warmer Holocene conditions occurs at 11.5 k cal a BP. During the mid-Holocene, isotope and assemblage data suggest a freshening of the water column, aligning with increased contributions of Modified North Atlantic Water, interpreted to result from an eastward expansion of the subpolar gyre (SPG). Conversely, from 4.2 ka to the present, data suggest a westward contraction of the SPG. This record highlights the connection of the North Sea to the wider North Atlantic throughout the Holocene, which has consequence for future paleoenvironmental reconstructions in the region.<br>Chapter 5 consists of a marine palaeoenvironmental reconstruction from a core spanning the Late glacial and Holocene in Scapa Flow, Orkney. This record aims to provide the paleoenvironmental backdrop for the pre- and presently-human occupied landscape. Data from the base of this record suggest a cool environment, coincident with terrestrial records of the Younger Dryas. During the early Holocene, the site developed into a shallow restricted basin with a stratified water column and high levels of organic matter. From 8.1 to 5.1 k cal a BP, Scapa flow transitioned from a stratified-frontal region to a well-mixed system, largely influenced by sea-level rise. From 5.1 k cal a BP to the top of the record, Scapa Flow is suggested to be a fully mixed, well oxygenated setting with active bottom water currents. The marine transition at 5.1 k cal BP occurs during the Neolithic period, but existing archaeological evidence does not suggest a synchronous shift in diet. From 5.2 k cal a BP sand content increases, however it is challenging to determine if this is a result of changing tidal dynamics or is related to Neolithic land disturbance. No evidence of nutrient enrichment related to increased population size or run-off was detected. The proxies used in this study indicate that changes in physical oceanographic processes have played a more dominant role in governing the productivity and ecosystem of Scapa Flow than human activity.