97 research outputs found
The parameterisation of Mediterranean–Atlantic water exchange in the Hadley Centre model HadCM3, and its effect on modelled North Atlantic climate
No full textMultiple palaeo-proxy and modelling studies suggest that Mediterranean Outflow Water (MOW) is an important driver of Atlantic Meridional Overturning Circulation (AMOC), particularly during periods of weak overturning. Here, we employ the HadCM3 ocean–atmosphere General Circulation Model (GCM) to investigate the effect of using different parameterisations of Mediterranean–Atlantic water exchange on global ocean circulation and climate. In HadCM3, simulating flow through the Gibraltar Straits with an ‘open seaway’ rather than a ‘diffusive pipe’ causes a shoaling and strengthening of the MOW plume. This reorganises shallow Atlantic circulation, producing regional surface air temperature anomalies of up to + 11 °C and ?7.5 °C. We conclude that when investigating the influence of MOW on modelled ocean circulation and climate, an accurate parameterisation of Mediterranean–Atlantic exchange is important and should match observed fresh water and salinity flux constraints. This probably cannot be achieved through a simple ‘diffusive pipe’ with depth invariant mixing coefficient
Supplementary: Optimisation of the Nd isotope scheme in the ocean component of the FAMOUS general circulation model
No full text<b>External Organisations</b><br/>University of Leeds; Imperial College London; University of Bern<b>Associated Persons</b><br/>Suzanne Robinson (Creator); Ruza Ivanovic (Creator); Lauren Gregoire (Creator); Tina van de Flierdt (Creator); Yves Plancherel (Creator); Frerk Pöppelmeier (Creator)Supplementary: Optimisation of the Nd isotope scheme in the ocean component of the FAMOUS general circulation mode
The silicon cycle impacted by past ice sheets
No full textGlobally averaged riverine silicon (Si) concentrations and isotope composition (δ30Si) may be affected by the expansion and retreat of large ice sheets during glacial-interglacial cycles. Here we provide evidence of this based on the δ30Si composition of meltwater runoff from a Greenland Ice Sheet catchment. Glacier runoff has the lightest δ30Si measured in running waters (-0.25 ± 0.12‰), significantly lower than non-glacial rivers (1.25 ± 0.68‰), such that the overall decline in glacial runoff since the Last Glacial Maximum (LGM) may explain 0.06-0.17‰ of the observed ocean δ30Si rise (0.5-1.0‰). A marine sediment core proximal to Iceland provides further evidence for transient, low-δ30Si meltwater pulses during glacial termination. Diatom Si uptake during the LGM was likely similar to present day due to an expanded Si inventory, which raises the possibility of a feedback between ice sheet expansion, enhanced Si export to the ocean and reduced CO2 concentration in the atmosphere, because of the importance of diatoms in the biological carbon pump
Public trunk revision 3298 of BISICLES and revision 23085 of Chombo version 3
No full textThis dataset contains archived versions of the model and modelling framework used for the simulations presented in the manuscript "Simulating the Early Holocene demise of the Laurentide Ice Sheet with BISICLES (public trunk revision 3298)". For access to the related manuscript and output data, please refer to the links under 'Related resources' below. Simulating the demise of the Laurentide Ice Sheet covering the Hudson Bay in the early Holocene is important for understanding the role of accelerated changes in ice sheet topography and melt in the '8.2 ka event', a century long cooling of the Northern Hemisphere by several degrees. Freshwater released from the ice sheet through a surface mass balance instability (known as the saddle collapse) has been suggested as a major forcing for the 8.2 ka event, but the temporal evolution of this pulse has not been constrained. Dynamical ice loss and marine interactions could have significantly accelerated the ice sheet demise, but simulating such processes requires computationally expensive models that are difficult to configure and are often impractical for simulating past ice sheets. Here, we developed an ice sheet model setup for studying the Laurentide Ice Sheet's Hudson Bay saddle collapse and the associated meltwater pulse in unprecedented detail using the BISICLES ice sheet model, an efficient marine ice sheet model of the latest generation, capable of refinement to kilometre-scale resolution and higher-order ice flow physics
Modelling Neodymium Isotopes Using a General Circulation Model (FAMOUS): Exploring the Role of a Benthic Flux in Unconservative Behaviour in Paleo Records and Observations
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Common origin for the innominate and left common carotid arteries: A pattern of human aortic branching epicted on multidetector CT
No full textCoexchangeable process modelling for uncertainty quantification in joint climate reconstruction
No full textAny experiment with climate models relies on a potentially large set of
spatio-temporal boundary conditions. These can represent both the initial state
of the system and/or forcings driving the model output throughout the
experiment. Whilst these boundary conditions are typically fixed using
available reconstructions in climate modelling studies, they are highly
uncertain, that uncertainty is unquantified, and the effect on the output of
the experiment can be considerable. We develop efficient quantification of
these uncertainties that combines relevant data from multiple models and
observations. Starting from the coexchangeability model, we develop a
coexchangable process model to capture multiple correlated spatio-temporal
fields of variables. We demonstrate that further exchangeability judgements
over the parameters within this representation lead to a Bayes linear analogy
of a hierarchical model. We use the framework to provide a joint reconstruction
of sea-surface temperature and sea-ice concentration boundary conditions at the
last glacial maximum (19-23 ka) and use it to force an ensemble of ice-sheet
simulations using the FAMOUS-Ice coupled atmosphere and ice-sheet model. We
demonstrate that existing boundary conditions typically used in these
experiments are implausible given our uncertainties and demonstrate the impact
of using more plausible boundary conditions on ice-sheet simulation.Comment: Accepted with major revisions in the Journal of the American
Statistical Association, resubmission is in revie
Abrupt Bølling warming and ice saddle collapse contributions to the Meltwater Pulse 1a rapid sea level rise
No full textElucidating the source(s) of Meltwater Pulse 1a, the largest rapid sea level rise caused by ice melt (14–18 m in less than 340 years, 14,600 years ago), is important for understanding mechanisms of rapid ice melt and the links with abrupt climate change. Here we quantify how much and by what mechanisms the North American ice sheet could have contributed to Meltwater Pulse 1a, by driving an ice sheet model with two transient climate simulations of the last 21,000 years. Ice sheet perturbed physics ensembles were run to account for model uncertainties, constraining ice extent and volume with reconstructions of 21,000 years ago to present. We determine that the North American ice sheet produced 3–4 m global mean sea level rise in 340 years due to the abrupt Bølling warming, but this response is amplified to 5–6 m when it triggers the ice sheet saddle collapse
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