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

Abstract

Abstract. The mid-Piacenzian Warm 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.

Production of diverse brGDGTs by Acidobacterium Solibacter usitatus in response to temperature, pH, and O2 provides a culturing perspective on brGDGT proxies and biosynthesis

“…Growth rate was similarly observed to be temperature‐dependent in lacustrine microcosm incubations (Martínez‐Sosa et al, 2020 ). Taken together, these observations suggest that the observed warm‐season bias in empirical calibrations (e.g., Dearing Crampton‐Flood et al, 2020 ) may originate from seasonal differences in bacterial growth rates with increased production of brGDGTs in warm summer months, a result that may help to guide future proxy calibration approaches.…”

Sclerochronological evidence of pronounced seasonality from the late Pliocene of the southern North Sea basin and its implications

“…It would be possible to obtain a more accurate estimate of regional mean ASST for comparison with model outputs by combining temperatures from a summer proxy with those from a winter proxy if such existed. Dearing Crampton-Flood et al (2020) obtained TEX 86 estimates about 6 • C lower than from alkenones for sea temperature during the MPWP in the Netherlands. They argued from several lines of evidence that the former data reflect surface conditions during winter, when the source organisms (archaea) of the lipids concerned may have bloomed.…”

“…2 and Sect. 6.1.2 that seasonal variation in shell δ 18 O is unlikely to have been enhanced by variation in water δ 18 O, and it can be added here that fluvial input (the means by which variation in water δ 18 O might have been brought about) may have been less in the Pliocene than now due to a smaller catchment area of the Rhine-Meuse-Scheldt system (Dearing Crampton-Flood et al, 2020), making enhancement of shell δ 18 O variation by water δ 18 O variation even more improbable. Notwithstanding these arguments, actual evidence of water δ 18 O would be very welcome, both as a check on the stability of values through the year and as a means of deriving accurate absolute temperatures.…”

The Pliocene Lillo, Poederlee, Merksplas, Mol and Kieseloolite Formations in northern Belgium: a synthesis

“…During the Pliocene the North Sea Basin was a semi-enclosed basin and connection with the Atlantic Ocean existed only via the North (Ziegler, 1990) since the southern connection was impeded by the Weald-Artois Axis. However, Dearing Crampton-Flood et al (2020) advance the concept that during high sea levels temporary connections may have existed, deduced from palaeontological data (Funnel, 1996) and sealevel evolution (Gibbard & Lewin, 2016). The Pliocene North Sea Basin was a shallow shelf sea with depths not exceeding 100 m (Overeem et al, 2001).…”