A data-model comparison of shallow marine seasonality during the Mid-Pliocene

Accurate projections of future climate scenarios require a detailed understanding of the behavior of Earth’s climate system under varying radiative forcing scenarios. The mid-Piacenzian Warm Period (mPWP; 3.3 – 3.0 Ma) was characterized by atmospheric CO2 concentrations comparable to present-day values (~400 ppmV), while global mean annual temperatures were roughly 2-3 degrees warmer compared to pre-industrial climate (Haywood et al., 2020). Seasonally resolved climate records from fossil bivalve shells offer a snapshot of short-term variability in temperature and salinity under the mild greenhouse conditions of the mPWP (Wichern et al., 2022).
In this study, we combine a large dataset of clumped isotope measurements incrementally sampled in fossil shells from the North Sea area during the mPWP with climate model simulations for the same time period using the PlioMIP model comparison framework. This combination of data and models allows us to test whether the climate models in PlioMIP can pick up the sub-annual scale variability in temperature and salinity (reconstructed via the oxygen isotope composition of the paleo-seawater). We show that, in contrast to continental reconstructions used in previous PlioMIP data-model comparisons (Tindall et al., 2022), our shallow marine data is reproduced well by PlioMIP models. On average, both model and data show considerably (4-5°C) warmer summer sea surface temperatures during the mPWP while winter temperatures remain relatively close to pre-industrial values. This suggests that the North Sea region can expect warming concentrated in the summer season in response to elevated atmospheric CO2 conditions.