Transient climate simulations of the deglaciation 21–9 thousand years before present; PMIP4 Core experiment design and boundary conditions

Abstract

Abstract. The last deglaciation, which marked the transition between the last glacial and present interglacial periods, was punctuated by a series of rapid (centennial and decadal) climate changes. Numerical climate models are useful for investigating mechanisms that underpin the events, especially now that some of the complex models can be run for multiple millennia. We have set up a Paleoclimate Modelling Intercomparison Project (PMIP) working group to coordinate efforts to run transient simulations of the last deglaciation, and to facilitate the dissemination of expertise between modellers and those engaged with reconstructing the climate of the last 21 thousand years. Here, we present the design of a coordinated Core simulation over the period 21–9 thousand years before present (ka) with time varying orbital forcing, greenhouse gases, ice sheets, and other geographical changes. A choice of two ice sheet reconstructions is given, but no ice sheet or iceberg meltwater should be prescribed in the Core simulation. Additional focussed simulations will also be coordinated on an ad-hoc basis by the working group, for example to investigate the effect of ice sheet and iceberg meltwater, and the uncertainty in other forcings. Some of these focussed simulations will focus on shorter durations around specific events to allow the more computationally expensive models to take part.

Variable Stoichiometry Effects on Glacial/Interglacial Ocean Model Biogeochemical Cycles and Carbon Storage

“…However, the difference in VSM biomass-induced mortality changes compared to the Control's changes is larger than the comparative difference in the temperature influences on mortality (Table S4). Further, while the VSMs' recycling rates do decrease and decrease more than the LGM pCO 2 in the VSMs are notably more consistent with ice core data than in the Control (Bereiter et al, 2015;Ivanovic et al, 2016).…”

“…We also identify and quantify the DOC component of biological C storage, which responds similarly to variable stoichiometry as the dissolved inorganic C (DIC) inventory. The resulting LGM climate simulations are closer to reconstruction estimates from observed pCO 2 data than simulations without flexible stoichiometry (Bereiter et al, 2015;Ivanovic et al, 2016;Kageyama et al, 2017). Our results suggest that the LGM biological carbon storage was stronger than previous fixed-stoichiometry simulations suggested and likely contributed to the ocean's…”

Coexchangeable process modelling for uncertainty quantification in joint climate reconstruction

“…Generally, boundary conditions are fixed using a reference run or runs from existing multi-model ensembles (MMEs) that explicitly model the boundary condition's physical process. For example, to run an ice-sheet model over the last glacial maximum (LGM) requires historical climate variables such as temperature, and precipitation (Gregoire et al, 2012) that can be obtained using the Paleoclimate Model Intercomparison Project (PMIP) ensemble of paleo-climate model runs (Ivanovic et al, 2016). MMEs can be biased and do not necessarily span the uncertainty of the physical process.…”