Camille Contoux

Sea Surface Temperature of the mid-Piacenzian Ocean: A Data-Model Comparison

The mid-Piacenzian climate represents the most geologically recent interval of long-term average warmth relative to the last million years, and shares similarities with the climate projected for the end of the 21st century. As such, it represents a natural experiment from which we can gain insight into potential climate change impacts, enabling more informed policy decisions for mitigation and adaptation. Here, we present the first systematic comparison of Pliocene sea surface temperature (SST) between an ensemble of eight climate model simulations produced as part of PlioMIP (Pliocene Model Intercomparison Project) with the PRISM (Pliocene Research, Interpretation and Synoptic Mapping) Project mean annual SST field. Our results highlight key regional and dynamic situations where there is discord between the palaeoenvironmental reconstruction and the climate model simulations. These differences have led to improved strategies for both experimental design and temporal refinement of the palaeoenvironmental reconstruction.

Modelling the mid-Pliocene Warm Period climate with the IPSL coupled model and its atmospheric component LMDZ5A

Abstract. This paper describes the experimental design and model results of the climate simulations of the mid-Pliocene Warm Period (mPWP, ca. 3.3–3 Ma) using the Institut Pierre Simon Laplace model (IPSLCM5A), in the framework of the Pliocene Model Intercomparison Project (PlioMIP). We use the IPSL atmosphere ocean general circulation model (AOGCM), and its atmospheric component alone (AGCM), to simulate the climate of the mPWP. Boundary conditions such as sea surface temperatures (SSTs), topography, ice-sheet extent and vegetation are derived from the ones imposed by the Pliocene Model Intercomparison Project (PlioMIP), described in Haywood et al. (2010, 2011). We first describe the IPSL model main features, and then give a full description of the boundary conditions used for atmospheric model and coupled model experiments. The climatic outputs of the mPWP simulations are detailed and compared to the corresponding control simulations. The simulated warming relative to the control simulation is 1.94 °C in the atmospheric and 2.07 °C in the coupled model experiments. In both experiments, warming is larger at high latitudes. Mechanisms governing the simulated precipitation patterns are different in the coupled model than in the atmospheric model alone, because of the reduced gradients in imposed SSTs, which impacts the Hadley and Walker circulations. In addition, a sensitivity test to the change of land-sea mask in the atmospheric model, representing a sea-level change from present-day to 25 m higher during the mid-Pliocene, is described. We find that surface temperature differences can be large (several degrees Celsius) but are restricted to the areas that were changed from ocean to land or vice versa. In terms of precipitation, impact on polar regions is minor although the change in land-sea mask is significant in these areas.

The late Pliocene Benguela upwelling status revisited by means of multiple temperature proxies

As compared to the late Pleistocene, Alkenone-based sea surface temperature (SST) in the Benguela region revealed relatively warm and stable SST recorded between approximate to 3.5 and 2.0 Ma, and coincide with a period of increasing biological productivity as revealed by increasing deposition of biogenic opal. We assess how the hydrological patterns recorded in SST proxies are embedded in the geological record by performing a proxy-proxy comparison. We used Laser-Ablation Inductively Coupled Plasma-Mass Spectrometry to measure the Mg/Ca on the planktonic foraminifera species Globigerina bulloides, allowing in situ measurements of Mg/Ca on individual foraminiferal tests. Mg/Ca-derived temperatures provide much colder temperatures than alkenone-derived SST by up to 10 degrees C. We build a scenario involving contrasting sensitivities of paleothermometers upon the annual cycle, namely alkenones preferentially capturing SST when the surface ocean is warmer than the mean-annual average SST, and G. bulloides capturing SST when upwelling intensifies. Multichamber analysis also suggests that G. bulloides migrates below the sea surface while calcifying its last chambers prior to gametogenesis, allowing the extraction of both surface and subsurface temperature from Mg/Ca measured on different chambers. The range of temperatures recorded between our multiple SST proxies is supported by the range of temperatures simulated with a general circulation model when different seasons, different water depth and different orbital configurations occurring during the late Pliocene are considered. A greater seasonal cycle in SST during the Pliocene can account for alkenone and Mg/Ca-derived temperature contrast, pointing to a radically different mode of upwelling activity in the Benguela region compared to today.

Drivers and mechanisms for enhanced summer monsoon precipitation over East Asia during the mid-Pliocene in the IPSL-CM5A

A comparative analysis of East Asian summer monsoon (EASM) precipitation is performed to reveal the drivers and mechanisms controlling the similarities of the mid-Pliocene EASM precipitation changes compared to the corresponding pre-industrial (PI) experiments derived from atmosphere-only (i.e. AGCM) and fully coupled (i.e. CGCM) simulations, as well as the large simulated differences in the mid-Pliocene EASM precipitation between the two simulations. The area-averaged precipitation over the EASM domain is enhanced in the mid-Pliocene compared to the corresponding PI experiments performed by both the AGCM (LMDZ5A) and the CGCM (IPSL-CM5A). Moisture budget analysis reveals that it is the surface warming over East Asia that drives the area-averaged EASM precipitation increase in the mid-Pliocene in both simulations. The surface warming increases the atmospheric moisture content, as revealed by an increase in the thermodynamic component of vertical moisture advection, resulting in enhanced mid-Pliocene EASM precipitation compared to PI in both simulations. Moist static energy diagnosis identifies the combined effect of enhanced zonal thermal contrast and column-integrated meridional stationary eddy velocity

Challenges in quantifying Pliocene terrestrial warming revealed by data-model discord

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Mid-pliocene Atlantic Meridional Overturning Circulation not unlike modern

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Mid-Pliocene East Asian monsoon climate simulated in the PlioMIP

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