A new age model for the Pliocene of the southern North Sea basin: A multi-proxy climate reconstruction

The mid-PiacenzianWarm Period (mPWP; 3264-3025 ka) represents the most recent interval in Earth's history where atmospheric CO₂ levels were similar to today. The reconstruction of sea surface temperatures (SSTs) and climate modelling studies has shown that global temperatures were 2-4 °C warmer than present. However, detailed reconstructions of marginal seas and/or coastal zones, linking the coastal and continental climate evolution, are lacking. This is in part due to the absence of precise age models for coastal sedimentary successions, as they are generally formed by dynamic depositional systems with varying sediment and freshwater inputs. Here, we present a multi-proxy record of Pliocene climate change in the coastal southern North Sea basin (SNSB) based on the sedimentary record from borehole Hank, the Netherlands. The marginal marine setting of the Hank borehole during the late Pliocene provides an excellent opportunity to correlate marine and terrestrial signals due to continental sediment input mainly derived from the proto-Rhine-Meuse River. We improve the existing low-resolution palynology-based age model for the Hank borehole using stable oxygen and carbon isotope (δ¹⁸O and δ¹³C) measurements of the endobenthic foraminifera species Cassidulina laevigata, integrated with biochrono-and seismostratigraphy. Identification of hiatuses and freshwater effects in the record allows us to isolate glacial-interglacial climate signals in order to tune the endobenthic oxygen stable isotope record to a global benthic δ¹⁸O stack. This results in a tuned age framework for the SNSB for the late Pliocene (∼ 3190-2770 ka). Our multi-proxy climate reconstruction for the interval which covers part of the mPWP (∼ 3190-3000 ka) shows a strong agreement between lipid biomarker and palynology-based terrestrial temperature proxies, which suggest a stable climate, 1-2 °C warmer than present. In the marine realm, however, biomarker-based SSTs show a large range of variation (10 °C). Nevertheless, the fluctuation is comparable to other SST records from the North Atlantic and Nordic Seas, suggesting that a common factor, possibly ocean circulation, exerted a strong influence over SSTs in the North Atlantic and the North Sea at this time.