| Summary: | Shallow marine settings comprise invaluable information about the impact of paleoenvironmental change on shelf ecosystems. We measured δ18O and δ13C ratios in fossil fish otoliths to assess temperature and salinity variability in the Ypresian (Ypr., 56.0-47.8 Ma) southern North Sea Basin (sNSB). Well-preserved otoliths were selected representing different environmental facies: the marginal marine Blackheath and Harwich Formations (lower Ypr.) , the outer neritic London and Kortrijk Formations (middle Ypr.) and inner neritic Tielt Formation (middle to upper Ypr.). Otoliths from demersal and presumably non-migratory fish such as ophidiids, bythitids and congrids were used. Bottom water paleotemperatures are determined from outer neritic samples, based on bulk sampling. This facies is composed of fine silts and clays deposited in an offshore environment, unlikely to be influenced by freshwater influx. Mean bulk δ18O values reveal within-horizon consistency among different co-occurring taxa. The horizon means range between -1.9 and -3.4 ‰. This translates to warm, albeit not extreme MAT’s between 21.3 and 28.5 °C during the 54-51.5 Ma interval. Based on incremental sampling, low seasonality of 3-6 °C is observed in the outer neritic facies. By contrast, mean bulk δ18O values from theHarwich and Blackheath Fms. are very negative, ranging from -5 to -7 ‰, indicating substantial mixing with low-salinity waters reduced by 3-4 ‰. Restricted connection of the sNSB with the North Atlantic and an intense global water cycle shortly after the PETM may explain this probably basin-wide freshening. Samples from the inner neritic Tielt Fm. bear values between -3 and -5 ‰ and are thought to be partly influenced by freshwater runoff. All inner neritic facies are characterized by a high intra-annual variability of 3-4 ‰, probably the result of seasonally paced freshwater influx. In summary, otolith stable isotope ratios seem to reliably record paleoenvironmental conditions. status: published
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