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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. [ABSTRACT FROM AUTHOR]

Abstract: The degree of methylation and cyclization of bacteria-derived branched glycerol dialkyl glycerol tetraether (GDGT) membrane lipids in soils depends on temperature and soil pH. Expressed in the methylation index of branched tetraethers (MBT) and cyclization ratio of branched tetraethers (CBT), these relationships are used to reconstruct past annual mean air temperature (MAT) based on the distribution of branched GDGTs in ancient sediments; the MBT–CBT proxy. Although it was shown that the best correlation of this proxy is with annual MAT, it remains unknown whether a seasonal bias in temperature reconstructions could occur, such as towards a seasonal period of ‘optimal growth’ of the, as yet, unidentified soil bacteria which produce branched GDGTs. To investigate this possibility, soils were sampled from eight different plots in the USA (Minnesota and Ohio), The Netherlands (Texel) and the UK (Devon) in time series over 1year and analyzed for their branched GDGT content. Further analyses of the branched GDGTs present as core lipids (CLs; the presumed fossil pool) and intact polar lipids (IPLs; the presumed extant pool) were undertaken for two of the investigated soil plots. The amount of IPL-derived branched GDGTs is low relative to the branched GDGT CLs, i.e. only 6–9% of the total branched GDGT pool. In all soils, no clear change was apparent in the distribution of branched GDGT lipids (either core or IPL-derived) with seasonal temperature change; the MBT–CBT temperature proxy gave similar temperature estimates year-round, which generally matched the mean annual soil temperature. In addition to a lack of coherent changes in relative distributions, concentrations of the branched GDGTs did not show clear changes over the seasons. For IPL-derived GDGTs these results suggest that their turnover time in soils is in the order of 1year or more. Thus, our study does not provide evidence for seasonal effects on the distribution of branched GDGTs in soils, at least at mid-latitudes, and therefore, no direct evidence for a bias of MBT–CBT reconstructed temperatures towards a certain season of optimal growth of the source bacteria. If, however, there is a slight seasonal preference of branched GDGT production, which can easily be obscured by natural variability due to the heterogeneity of soils, then a seasonal bias may potentially still develop over time due to the long turnover time of branched GDGTs. [Copyright &y& Elsevier]