Alexander R. Simms

Understanding past relative sea level (RSL) is important for constraining the timing and magnitude of changes in the cryosphere, providing critical benchmarks for models used to project future sea-level change, and supplying a datum for constraining past vertical motion. Past sea-level records from Antarctica can help determine the extent to which small or large changes in ice cover induce a response of the solid Earth in tectonically active settings. Here, we examine raised beaches located at Duthoit Point, Nelson Island, Antarctica. We combine geomorphic mapping and high-resolution topographic surveys to reconstruct RSL change and glacial fluctuations during the Holocene. Our study is the first record from Duthoit Point and identifies sea-level changes associated with up to four Holocene ice advances, likely occurring between ∼7000 and ∼4800 cal yr BP, at ∼2000 cal yr BP, at ∼500 cal yr BP, and during a more recent advance younger than ∼500 cal yr BP. Our findings support assertions that uplift rates are primarily driven by glacial isostatic adjustment and changes in ice extent modulate isostatic responses at centennial to millennial timescales. Improved constraints on Holocene uplift histories provide important benchmarks for evaluating isostatic adjustment models used to reconstruct past ice-sheet change and project future sea-level change.

Raised shorelines provide important constraints on past sea levels, glacial isostatic adjustment (GIA), and rates and directions of vertical crustal motion. Although most raised shorelines across NW Scotland relate to post‐Last Glacial Maximum (LGM) glacial‐isostatic rebound, many undated shorelines lie above the marine limit established from isolation basins. Here, we present new optically stimulated luminescence (OSL) ages for a raised marine terrace at an elevation of 28 m in Slaggan Bay of NW Scotland. Four OSL ages suggest the feature is pre‐LGM, likely Marine Isotope Stage (MIS) 3. Global mean sea levels (GMSL) during MIS 3 are thought to have been ~40–60 m below present across most of the globe. We use a pair of GIA models to determine what ice sheet and sea‐level scenarios might provide an explanation for these anomalously high sea levels during MIS 3. Our results suggest that in the absence of tectonic activity, such high MIS 3 shorelines across NW Scotland require a MIS 4 ice sheet in Scotland, with postglacial rebound of the crustal depression following its demise during MIS 3 responsible for the elevated shoreline features at that time.

During past Interglacial periods, global ocean volume increased as a result of the higher temperatures and the melting of ice sheets, consequently leading to a rise in global sea levels. However, on timescales ranging from years to a few decades, regional sea level variability deviates from the global pattern, due to a combination of vertical land movements (earth’s crust viscoelastic response to glacial and ice sheet melting, tectonics), thermohaline circulation, wind forcing and land water storage. Therefore, decoding the regional sea-level variability during Interglacial periods is crucial for advancing climate models’ precision, especially for vulnerable coastlines.Beach ridge plains are valuable fossil geological archives, offering significant potential for the analysis of sea-level fluctuations, climatic shifts and catastrophic events. The extraction of these information can be achieved through the measured elevation of the dune-beach contact and the beach berm, the analysis of the fossil beach ridge orientation, the geometry of the internal stratigraphy and by dating of the beach deposits using optically stimulated luminescence (OSL) signals from quartz.In this study, we present results from our fieldwork campaign in the northern Gulf of Mexico, where we utilized a GNSS RTK station to obtain centimeter-level precision in measuring the elevation of the beach ridge sets, originally detected through freely available LIDAR datasets. Concurrently, a Ground Penetrating Radar (GPR) was employed to determine the stratigraphy of the beach ridge plains. Both surveyed areas, Apalachicola and Pensacola, contain fossil beach ridge sets varying in elevation from +2.5m up to a maximum of +7.5-8m above mean sea level, detected in more inland locations. Recent studies suggest that during the Last Interglacial period sea level in the area reached up to ~5m. The exact timing of the formation of the more elevated inland beach ridges remains uncertain, as does the question of whether their present elevation is attributable to post-Last Interglacial vertical land movements. Through in-depth analysis of the data collected during the WARMCOASTS ERC project, we aim to unravel the formation processes of these beach ridges and trace their development and evolution over time.

Evidence for the Storegga tsunami, which was generated by one of the world’s largest submarine slides, is well documented in Scotland, but the southerly extent of tsunami inundation in the UK is far more uncertain. Here, we combine new sedimentological, geochemical, microfossil, and ground-penetrating radar datasets to investigate the origins of two sand beds at Budle Bay, Northumberland. The lower of these two sand deposits is a fine- to medium-grained sand that fines upwards, is dominated by fragmented marine diatom taxa, and is characterised by elevated calcium concentrations. Two radiocarbon dated samples provide minimum age constraints on the timing of the deposition of the lower sand at around 8120–8380 cal yr BP. It is tentatively interpreted as being deposited by the Storegga tsunami. The upper sand bed is generally finer grained than the lower sand, and the calcium concentrations are considerably lower. One hypothesis is that the upper sand was deposited by the 1953 CE storm surge, but additional chronological control is required to test this interpretation. Our findings highlight the challenges associated with differentiating between storm and tsunami deposits and confirm the localised nature of preservation of Storegga tsunami deposits.

Bayhead deltas form at the interface between fluvial and estuarine systems. As such, they are sensitive to processes operating in both the fluvial catchment and the marine realm, including past relative sea‐level changes. The Nakdong valley is a small and confined incised valley containing a bayhead delta that provides a record of fluvial sediment input and accommodation changes. Based on a facies analysis that included 833 sediment textures and 118 optically stimulated luminescence and radiocarbon ages within five cores up to 70 m long, this study reconstructed the development of a fully filled bayhead delta in response to relative sea‐level changes through the early to late Holocene. Sixteen facies are defined and grouped into eight facies associations: alluvial plain; fluvial channel and floodplain; oxidized fluvial channel; tidal flat; tidal bar; central basin and bayhead prodelta; bayhead delta front; and bayhead delta plain. The sequence stratigraphy of the Nakdong valley fill can be divided into three systems tracts: a lowstand systems tract, a transgressive systems tract and a highstand systems tract. Overall sedimentary analyses suggest six depositional stages corresponding to variations between sediment inputs and sea‐level rise of the developing bayhead delta in the Nakdong valley. The depositional model tracks relative sea‐level rise in the Nakdong valley after 12 ka during the early to late Holocene. These analyses on the Nakdong bayhead delta succession illustrate the balance between sediment inputs and periods of accelerating and decelerating relative sea‐level rise during the Holocene. The architecture of the valley fill also records two abrupt disequilibrium events from 9 to 8 ka and 5 to 3 ka, likely resulting from rapid sea‐level rise during the deglacial outburst flooding of the early Holocene and decreased sediment inputs during regional climatic changes associated with the middle Holocene, respectively.