The fossil bivalve Angulus benedeni benedeni: a potential seasonally resolved stable isotope-based climate archive to investigate Pliocene temperatures in the southern North Sea basin

Abstract

Abstract. Obtaining temperature data from the mid-Piacenzian warm period (ca. 3 Ma, Pliocene epoch) is a key factor in outlining the impact of projected anthropogenic climate change. The mid-Piacenzian warm period was a high-CO2 world with a paleogeography similar to modern times. The time interval has been used to validate and improve climate model retrodictions, which in turn enables assessing the predictive strength of these models. Validating climate models requires a large array of robust proxy data. Here, we increase the potential of this proxy database by showing that the extinct tellinid bivalve Angulus benedeni benedeni can be used for stable isotope-based temperature reconstructions. This species is found in the Pliocene sediments of the southern North Sea basin. Oxygen isotope and carbonate clumped isotope measurements on the shell of A. benedeni benedeni resulted in a mean annual temperature reconstruction of 13.5±3.8 °C. This is 2.5 °C warmer than today, 3.5 °C warmer than the pre-industrial North Sea, and in line with global Pliocene temperature estimates of +2–4 °C compared to the pre-industrial climate. Limited amounts of clumped isotope data hindered determining summer and winter temperatures, but the oxygen isotope record shows that the growth band spacing of A. benedeni benedeni allows for sampling at a resolution of 2–3 months. The species could live for up to a decade, and therefore has the potential to be used for multiannual seasonality reconstructions. The pristine nature of the aragonitic shell material was verified through electron backscatter diffraction analysis (EBSD), and backed by light microscopy, X-ray diffraction, and X-ray fluorescence. The various microstructures as obtained from the EBSD maps have been described, and they provide a template of pristine A. benedeni benedeni material to which potentially altered shells may be compared. The bivalve A. benedeni benedeni is suitable for high resolution isotope-based paleoclimatic reconstruction and it can be used to unravel the marine conditions in the Pliocene southern North Sea basin at a seasonal scale, yielding enhanced insights into imminent western European climate conditions.

Amplified seasonality in western Europe in a warmer world

“…S3]. Preservation of the original shell calcite and aragonite was verified using a combination of scanning electron microscopy (SEM), cathodoluminescence microscopy, electron backscatter diffraction microscopy (EBSD), micro–x-ray fluorescence (μXRF), and x-ray diffraction [XRD; see ( 67 ) and figs. S4 to S12].…”

“…Some samples were replicated more than once, causing multiple replicates to originate from the same location in the shell, and some of these replicate measurements were discarded as outliers during data processing (see below). Measurements from A. benedeni benedeni (SG126 and SG127) include data from ( 67 ) as well as additional analyses on the same specimens carried out for this study. Small (70 to 160 μg) aliquots of each sample were digested in phosphoric acid for 600 s at 70°C in a Kiel IV carbonate preparation device, after which the resultant CO 2 gas was purified using two cold fingers and a Porapak trap ( 69 ) before the clumped isotope composition (Δ 47 ) was analyzed using two Thermo MAT253 mass spectrometers.…”

“… Maps of northwestern Europe showing the present ( A ) and estimated mPWP ( B ) [after ( 35 , 37 , 67 )] SNS bathymetry. The locality of fossil shells (red star), the local modern temperature record (blue star), and the area containing the SNS data integrated from extended reconstructed SST (Extended Reconstructed SST v5), PlioMIP2, and CMIP6 models (black rectangle with orange filling; 51°N to 55°N, 2°E to 4°E; Figs.…”

Tracing timing of growth in cultured molluscs using strontium spiking

“…Secondly, all three species occur naturally in the area (Wadden Sea and North Sea), limiting risk to the success of growth experiments by ensuring optimal growing conditions as well as to the local ecosystem by not introducing invasive taxa to the Wadden Sea, which is a UNESCO World Heritage site (Beukema et al, 2001;Bennema et al, 2020). Thirdly, the species represent similar taxa from the fossil record which are used for paleoclimate and paleoenvironmental reconstructions, driving the need to better understand shell growth using growth experiments (Obelic et al, 1998;Huyghe et al, 2015;Wichern et al, 2022). Finally, all three species are (historically) commercially important, and growth experiments such as the ones described here may aid in understanding their growth to optimize aquaculture practices (Smaal and Lucas, 2000;Kraan et al, 2011;Colsoul et al, 2021).…”

Amplified seasonality in western Europe in a warmer world

“…This approach offers a detailed glimpse of the potential future climate in Europe under a moderate emission scenario. 35,37,40 ) SNS bathymetry. The locality of fossil shells (red star), the local temperature record (blue star) and the area containing the SNS data integrated from extended reconstructed SST (ERSSTv5), PlioMIP2 and CMIP6 models (black rectangle with orange filling; 51-55°N, 2-4°E; Fig.…”