Constraining the rate and magnitude of Last Interglacial (LIG) sea-level change in North West Europe using newly collected cores from the southern North Sea

The RISeR project seeks to reconstruct the rates, magnitude and spatial patterns of sea-level change during the Last Interglacial. As part of this we seek to develop new high-resolution reconstructions of Last Interglacial sea-level change for northwest Europe using previously unstudied offshore sedimentary archives from the southern North Sea. We also aim to provide the first chronological constraints on the timing, and therefore rates, of relative sea-level change in northwest Europe.

Reconstructing Past Sea Level

We will be using a multi-proxy approach to reconstruct past sea level, including:

Foraminiferal, diatom, and molluscan assemblages
Detailed sedimentological analysis such as ITRAX-XRF and particle size

When combined with our new model of Glacial Isostatic Adjustment for NW Europe (GIA; Pollard et al., 6th January, 1.20 pm), a new subsidence model (Cohen et al., in review), and our new age-depth models, the RSL inferred from the reconstructions should provide multiple Sea Level Index Points (SLIPs).

Our new SLIPs will add further constraints to ongoing reconstructions of the rate and magnitude of relative sea level change for NW Europe, adding to the WALIS (World Atlas of Last Interglacial Shorelines) Database.

A map of the southern North Sea showing the outline of an offshore windfarm positioned around 20 m North East of the Dutch coastline.

A map, in the shape of the windfarm outline shown in Fig 1, showing the depth of the seabed below lowest astronomical tides using shades from green to pink. Five stars on the map are labelled Sites 1, 7, 5, 4, 2, and 6, ordered from left to right, with the furthest left sites being furthest from the present day coastline, and, generally, the deepest seabed.

↑ Fig 1: Location of the study area in the southern North Sea showing the Hollandse Kust Zuid (HK) wind-farm, adapted from Cartelle et al., 2021.

← Fig 2: Location of the RISeR boreholes within the Hollandse Kust Zuid (HKZ) wind-farm, showing the depth of the sea bed below present day lowest astronomical tide (LAT).

A succession of 5 stratigraphic diagrams, plotted from left to right, showing the reduced depth of the peat layer. An annotation connects the sites using the top of this layer, which is labelled Eemian flooding surface.

Fig 3: Stratigraphic logs of the 5 RISeR sediment cores, plotted against depth. For the location of the cores see Fig 3.

A sequence of 11 1m sections of sediment core, showing multiple transitions between lithologies including peat, clays, and sands.

Fig 4: Images of the RISeR sediment core from Site 5 obtained using MSCL (a) and x-ray laminography (b) facilities at BOSCORF.

Dating Last Interglacial Sequences

As LIG sequences are beyond the upper age limit of radiocarbon dating approaches, we are applying a range of absolute and relative dating techniques across the 5 sites, including:

Biostratigraphy: pollen analysis (Eemian pollen zones of NW Europe) and molluscan faunal analysis.
Luminescence dating: sand-rich sediments will be dated using Optically Stimulated Luminescence (OSL)
Amino Acid Racemization (AAR): if suitable faunal remains are found, these will be submitted for AAR analysis.
Tephrochronology: the identification of volcanic ash layers.

The resulting ages, and their associated uncertainties, will be used to construct a chronology for each individual site using Bayesian age-depth modelling.

A schematic showing the RISeR sampling approach across the peat to clay transition, with pollen samples throughout the transition, OSL samples above the transition, opercula AAR samples within the peats, and foraminifera AAR samples within the clays. A tephra tie point is highlighted, which links the cores.