Proxy Constraints on a Warm, Fresh Late Cretaceous Arctic Ocean

Abstract:

The warm Late Cretaceous is thought to have been characterized by open Arctic Ocean temperatures upwards of 15°C (Jenkyns et al., 2004). The high temperatures and low equator-to-pole temperature gradient have proven difficult to reproduce in paleoclimate models, with the role of the atmospheric hydrologic cycle in heat transport being particularly uncertain. Here, sediments, coprolites and fish teeth of Santonian-Campanian age from two high-latitude mixed terrestrial and marine sections on Devon Island in the Canadian High Arctic (Chin et al., 2008) were analyzed using a suite of organic and inorganic proxies to evaluate the temperature and salinity of Arctic seawater. Surface temperature estimates were derived from TEX86 estimates of near-shore, shallow (~100 meters depth) marine sediments (Witkowski et al., 2011) and MBT-CBT estimates from terrestrial intervals and both suggest mean annual temperatures of ~20°C, consistent with previous estimates considering the more southerly location of Devon Island. The oxygen isotope composition of non-diagenetic phosphate from vertebrate coprolites and bony fish teeth were then measured, giving values ranging from +13‰ to +19‰. Assuming the TEX86 temperatures are valid and using the temperature calibration of Puceat 2010, the δ¹⁸O values of coprolites imply Arctic Ocean seawater δ¹⁸O values between -4‰ and -10‰, implying very fresh conditions. Lastly, the δD of precipitation will be estimated from the hydrogen isotope composition of higher plant leaf waxes (C-25, C-27, C-29 and C-31 n-alkanes) from both terrestrial and marine intervals. Data are used to model the salinity of seawater and the meteoric relationship between δD and δ¹⁸O, thereby helping to evaluate the northern high-latitude meteoric water line of the Late Cretaceous.