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  • 1
    Publication Date: 2019-09-23
    Description: Down-core variations in North Atlantic 231Paxs/230Thxs have been interpreted as changes in the strength of the Atlantic meridional overturning circulation (AMOC). This modeling study confirms that hypothetical changes in the AMOC would indeed be recorded as changes in the distribution of sedimentary 231Paxs/230Thxs. At different sites in the North Atlantic the changes in sedimentary 231Pa/230Th that we simulate are diverse and do not reflect a simple tendency for 231Paxs/230Thxs to increase toward the production ratio (0.093) when the AMOC strength reduces but instead are moderated by the particle flux. In its collapsed or reduced state the AMOC does not remove 231Pa from the North Atlantic: Instead, 231Pa is scavenged to the North Atlantic sediment in areas of high particle flux. In this way the North Atlantic 231Paxs/230Thxs during AMOC shutdown follows the same pattern as 231Paxs/230Thxs in modern ocean basins with reduced rates of meridional overturning (i.e., Pacific or Indian oceans). We suggest that mapping the spatial distribution of 231Paxs/230Thxs across several key points in the North Atlantic is an achievable and practical qualitative indicator of the AMOC strength in the short term. Our results indicate that additional North Atlantic sites where down-core observations of 231Paxs/230Thxs would be useful coincide with locations which were maxima in the vertical particle flux during these periods. Reliable estimates of the North Atlantic mean 231Paxs/230Thxs should remain a goal in the longer term. Our results hint at a possible ‘‘seesaw-like’’ behavior in 231Pa/230Th in the South Atlantic.
    Type: Article , PeerReviewed
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  • 2
    Publication Date: 2022-01-31
    Description: Climate model components involve both high-dimensional input and output fields. It is desirable to efficiently generate spatio-temporal outputs of these models for applications in integrated assessment modelling or to assess the statistical relationship between such sets of inputs and outputs, for example, uncertainty analysis. However, the need for efficiency often compromises the fidelity of output through the use of low complexity models. Here, we develop a technique which combines statistical emulation with a dimensionality reduction technique to emulate a wide range of outputs from an atmospheric general circulation model, PLASIM, as functions of the boundary forcing prescribed by the ocean component of a lower complexity climate model, GENIE-1. Although accurate and detailed spatial information on atmospheric variables such as precipitation and wind speed is well beyond the capability of GENIE-1’s energy-moisture balance model of the atmosphere, this study demonstrates that the output of this model is useful in predicting PLASIM’s spatio-temporal fields through multi-level emulation. Meaningful information from the fast model, GENIE-1 was extracted by utilising the correlation between variables of the same type in the two models and between variables of different types in PLASIM. We present here the construction and validation of several PLASIM variable emulators and discuss their potential use in developing a hybrid model with statistical components.
    Type: Article , PeerReviewed
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  • 3
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    Copernicus Publications (EGU)
    In:  Geoscientific Model Development, 12 (12). pp. 5137-5155.
    Publication Date: 2022-01-31
    Description: We describe the development of the “Paleoclimate PLASIM-GENIE emulator” PALEO-PGEM and its application to derive a downscaled high-resolution spatiotemporal description of the climate of the last five million years. The 5-million-year time frame is interesting for a range of paleo-environmental questions, not least because it encompasses the evolution of humans. However, the choice of time-frame was primarily pragmatic; tectonic changes can be neglected to first order, so that it is reasonable to consider climate forcing restricted to the Earth's orbital configuration, ice-sheet state and the concentration of atmosphere CO2. The approach uses the Gaussian process emulation of the singular value decomposition of boundary-condition ensembles of the intermediate complexity atmosphere-ocean GCM PLASIM-GENIE. Spatial fields of bioclimatic variables of surface air temperature (warmest and coolest seasons) and precipitation (wettest and driest seasons) are emulated at 1,000 year intervals, driven by time-series of scalar boundary-condition forcing (CO2, orbit and ice-volume), and assuming the climate is in quasi-equilibrium. Paleoclimate anomalies at climate model resolution are interpolated onto the observed modern climatology to produce a high-resolution spatiotemporal paleoclimate reconstruction of the Pliocene-Pleistocene.
    Type: Article , PeerReviewed
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  • 4
    Publication Date: 2024-02-07
    Description: The newly developed fast Earth system model CLIMBER-X is presented. The climate component of CLIMBER-X consists of a 2.5-D semi-empirical statistical–dynamical atmosphere model, a 3-D frictional–geostrophic ocean model, a dynamic–thermodynamic sea ice model and a land surface model. All the model components are discretized on a regular lat–long grid with a horizontal resolution of . The model has a throughput of ∼ 10 000 simulation years per day on a single node with 16 CPUs on a high-performance computer and is designed to simulate the evolution of the Earth system on temporal scales ranging from decades to 〉100 000 years. A comprehensive evaluation of the model performance for the present day and the historical period shows that CLIMBER-X is capable of realistically reproducing many observed climate characteristics, with results that generally lie within the range of state-of-the-art general circulation models. The analysis of model performance is complemented by a thorough assessment of climate feedbacks and model sensitivities to changes in external forcings and boundary conditions. Limitations and applicability of the model are critically discussed. CLIMBER-X also includes a detailed representation of the global carbon cycle and is coupled to an ice sheet model, which will be described in separate papers. CLIMBER-X is available as open-source code and is expected to be a useful tool for studying past climate changes and for the investigation of the long-term future evolution of the climate.
    Type: Article , PeerReviewed
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