Mid-Pliocene NE Atlantic warming: closing the gap between proxy- and model-based sea surface temperature reconstructions

Abstract:

The mid-Pliocene Warm Period (mPWP) (3.025−3.264 Ma) is an important analogue for 21^st Century climate change, with similar continental configurations and atmospheric CO₂ concentrations to present day. Global mPWP sea surface temperature (SST) compilations indicate enhanced warming in the NE Atlantic, with anomalies of +6°C based on alkenone methods (Dowsett et al., 2012). However, this warming far exceeds the more conservative SST estimates (a rise of 2−3°C) predicted by the Pliocene Research, Interpretation and Synoptic Mapping (PRISM) reconstructions and leading climate models (including HadCM3). Here, we present new mid-Pliocene U^K’₃₇ and TEX₈₆ SST data from four regional IODP sites (U1308, 552, 642 and 907) to further examine the magnitude of warming in the NE Atlantic, and evaluate regional discrepancies between proxy and model SST estimates. We demonstrate PRISM-interval SSTs peaked up to 21.5°C and 19.7°C in the NE Atlantic and Nordic Seas, respectively, consistent with existing studies (Robinson et al., 2008; Robinson, 2009). However, we reveal the majority of these SST estimates are derived from GC injections of relatively low total alkenone concentrations (<50 ng/µl), which are susceptible to warming biases caused by chromatographic irreversible adsorption (Grimalt et al., 2001). We subsequently filtered and applied a mathematical correction to our new data to rectify for these warming biases, which results in a reduction in mPWP SSTs, by up to 3.2°C, across all four sites. The corrected (and cooler) U^K’₃₇ data indicate the magnitude of warming in the NE Atlantic may be significantly less than previously thought, helping to reduce and explain regional discrepancies between proxy- and model-based SST reconstructions.