Successful applications to the first RAPID funding round: Project Abstracts

Processes controlling dense water formation and transport on Arctic continental shelves

Professor A Willmott, Keele University; Dr J Holt, NERC Proudman Oceanographic Laboratory (POL); Dr R Proctor, POL; Professor V Shira, Keele University

The Barents Sea is an important site for the production of dense intermediate water. Up to one half of this intermediate water flows into the North Atlantic over the Scotland-Greenland Ridge, constituting an important branch of the global thermohaline circulation. The presence of numerous coastal polynyas and the relatively low river input into the Barents Sea explain why this region is a significant site for water for water mass transformation. Parameterisations for dense water production in polynyas for application in non-polynya resolving ocean circulation models, will be developed and tested in a coupled sea ice-shelf sea model of the Barents Sea. The latter will be used to study present day water mass transformation processes and to predict how they will change in a warmer climate.

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The Role of Air-Sea Forcing in Causing Rapid Changes in the North Atlantic Thermohaline Circulation

Dr S Josey, Southampton Oceanographic Centre (SOC)

The main aims of this proposal are to determine the role that surface forcing variability plays in causing rapid changes in the ocean circulation and to examine the effect of such changes on climate. We will address these issues through a combined analysis of coupled model output and observational datasets. The focus of the analysis will be the North Atlantic thermohaline circulation (THC) although the results will be interpreted in the broader context of the global climate system. Variations in the air-sea fluxes of surface heat and freshwater have the potential to cause rapid changes in the ocean circulation eg through their influence on deep convection. However, the relationship between surface forcing variability and rapid changes in the ocean remains to be properly determined; our goal is to significantly improve understanding of this area.

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High resolution anatomy of rapid climate transitions in the last glacial period from a Greenland ice core

Dr E Wolff, NERC British Antarctic Survey (BAS); Dr R Mulvaney, BAS

We will investigate with unprecedented time resolution the sequence of events at the start and end of two rapid climate events observed in Greenland ice cores. Using techniques to minimise sample volumes we will analyse chemically (using GRIP/NGRIP ice cores) a sub-seasonal resolution the transitions into and out of Dansgaard-Oeschger event 8 (glacial period) and the 8.2 kyr event (Holocene). We will revisit other transitions at lower resolution. Our analyses will show the pattern of change in temperature, accumulation rate, salt and dust transport: the true rate of change, the phasing between these different aspects of climate, and the seasonality of the change will be compared with the prediction of GCM output for freshwater forcing. This will give a critical insight into the mechanisms of rapid climate change, and a strong test of model ability to simulate such changes.

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Hydrographic and flow changes at sharp climate transitions in the North Atlantic MOC, 0-16ka BP

Professor IN McCave, University of Cambridge; Professor H Elderfield, University of Cambridge; Dr I Hall, Cardiff University; Dr R Rickaby, Oxford University

Changes in hydrographic structure and flow of water masses along the Scotland-Labrador boundary of the N. Atlantic through late Glacial and Holocene rapid climate changes will be documented. Leads and lags in water temperature, salinity, nutrient structure of the water column and flow speed will provide a key to assessing possible outcomes to changes in these parameters observable today. Target sites for this investigation are South Iceland Rise and Eirik Drift. The Sortable Silt grain size and AMSus flow speed proxies will be calibrated using surface sediments from long-term current meter sites in the region.

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The role of sloping topography in the overturning circulation of the North Atlantic

Dr R Williams, University of Liverpool; Dr C Hughes, POL; Professor J Huthnance, POL

The role of sloping topography in controlling the overturning of the North Atlantic will be examined using a hierarchy of isopycnic model experiments with realistic topography for idealised and realistic forcing. The study will focus on how sloping topography affects where water masses are formed, the communication of overturning signals via wave propagation, as well as the transport, recirculation and evolution of dense, water masses. The study will provide a context to interpret monitoring signals from RAPID identifying how overturning signals are communicated from high to low latitudes along sloping western boundaries. A tied studentship will examine how the circulation of North Atlantic Deep Water alters in a glacial environment, the separate effect of forcing and sea level changes, and the large-scale consequences for atmospheric CO2 uptake.

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Quantitative applications of high-resolution late Holocene proxy data sets: estimating climate sensitivity and thermohaline circulation influences

Professor K Briffa, University of East Anglia; Professor P Jones, University of East Anglia

Output from state-of-the-art coupled climate models will be analysed in conjunction with very long instrumental climate data and an extensive archive of annual- and selected decadal-resolution palaeoclimate data to study climate changes during the past millennium. Actual and model-derived synthetic networks of palaeoclimate data will be used to estimate the extent to which (i) variations in Atlantic meridional overturning circulation strength; (ii) variations in the North Atlantic Oscillation; and (iii) the sensitivity of climate to external forcing changes can be reconstructed from different networks of palaeoclimate data, making assumptions about coverage, seasonality of response and reliability of expressed climate signal.

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The atmospheric water vapour budget and its relevance to the THC

Professor B Hoskins, Reading University; Dr M Blackburn, Reading University

The aim of this research is to increase the understanding of the processes that control the distribution of evaporation and precipitation and their difference in the Atlantic region and in particular that the atmosphere gives a net export of water vapour from that basin. This export is vital to the existence and stability of the oceanic thermohaline circulation in the Atlantic. Contrast will be made with the Pacific Ocean region in which the atmosphere imports water. The research will be pursued through detailed analysis of the new ERA-40 data set, fundamental experimentation with an atmospheric GCM and analysis of data sets from climate change experiments.

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The role of salinity in ocean circulation and climate response to greenhouse gas forcing

Dr E Guilyardi, Reading University; Dr R Sutton, Reading University

Salinity is a major contributor to ocean circulation, stability and variability. Its structure depends on the surface freshwater flux whose distribution is likely to change significantly under global warming, giving rise to the potential for abrupt changes in climate. This project will investigate the mechanisms and feedback loops which govern the salinity distribution in coupled ocean-atmosphere models. Carefully designed experiments where feedbacks are removed will provide a major contribution to understand the role of salinity in the climate response to greenhouse gas forcing. Innovative diagnostics will be developed to assess the salinity/fresh water cycle performance of climate forecast models.

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Improving our ability to predict rapid changes in the El Nino Southern Oscillation climatic phenomenon

Dr A Tudhope, Edinburgh University; Dr M Collins, Reading University; Dr R Ellam, Scottish Universities Environmental Research Centre (SUERC); Professor G Shimmield, Scottish Association for Marine Science (SAMS)

The objective is to use a combination of palaeoclimate reconstruction from annually-banded corals and the fully coupled HadCM3 atmosphere-ocean general circulation model to develop an understanding of the controls on variability in the strength and frequency of ENSO, and to improve our ability to predict the likelihood of future rapid changes in this important element of the climate system. To achieve this, we target three periods:0-2.5 ka: Representative of near-modern climate forcing; will reveal the internal variability in the system.6-9 ka: a period of weak or absent ENSO, and different orbital forcing; a test of the model's ability to capture externally-forced change in ENSO.200-2100 AD: by using the palaeo periods to test and optimise model parameterisation, we will produce a new, improved, prediction of ENSO variability in a warming world.

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Circulation, overflow, and deep convection studies in the Nordic Seas using tracers and models

Professor A Watson, University of East Anglia; Dr D Stevens, University of East Anglia

We will investigate two aspects of the Nordic Seas circulation of importance to the North Atlantic meridional overturning circulation (MOC): (1) Sources of water in the Greenland-Scotland overflows: recent tracer release and transient tracer observations will be used to constrain inverse models of the sources of Denmark Straits and Faroe-Bank channel overflow waters. (2) The initiation of convection and its relation to submesoscale hydrodynamics: very high-resolution non-hydrostatic models for the Central Greenland Sea will be used to model recent observations, which show convection to be intimately related to local sub-mesoscale structure.: The objective will be to develop improved descriptions of convection for use in OGCMs, to more accurately describe how the sinking branch of the MOC will be affected by changes in forcing.

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Atlantic Seaboard Climate Responses including Bounding Errors (ASCRIBE)

Professor I Fairchild, Keele University; Dr T Atkinson, University College London; Dr A Baker, Newcastle-upon-Tyne University; Mr P Dennis, University of East Anglia; Professor C Hawkesworth, Bristol University; Dr D Mattey, Royal Holloway University of London; Dr A Matthews, University of East Anglia

This project will test the influence of thermohaline circulation changes versus other controlling factors on Holocene palaeoclimates. The tests rely on climatic reconstructions of the last 1000 years and the 8.2 ka event from the study of speleothems at sites along the Atlantic seaboard, dated by U-series and annual layer counting. Oxygen isotope compositions of palaeoprecipitation will be determined from fluid inclusions at high resolution. Palaeotemperatures will be derived from these data combined with delta 18 O analysis of speleothems, and climatic data also extracted using annual layer studies, using an enhanced time series statistical methodology. Modelling delta 18 O fractionations in atmospheric moisture will test the convergence of GCM predictions of the magnitude and spatial distribution of palaeoclimates with the evidence from the palaeoclimate record.

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Extending the time series of Atlantic Meridional Overturning backwards in time using historical measurements

Professor H Bryden, University of Southampton

As part of the Rapid Climate Change Thematic Programme, the thermohaline circulation in the Atlantic Ocean at about 25 degrees N will be monitored over the period 2004 to 2007. Using these new measurements and historical measurements made near 25 degrees N, we propose to extend the time series made during 2004-2007 backwards in time to identify longer time scale variability in the thermohaline circulation over the period from at least the 1980's to 2007.

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The Probability of Rapid Climate Change

Mr P Challenor, Southampton Oceanographic Centre (SOC); Professor M Goldstein, Durham University; Professor P Killworth, SOC; Dr J Oakley, Sheffield University; Professor A O'Hagan, Sheffield University

We propose to assess the probability of rapid climate change under future climate scenarios, in particular different greenhouse gas concentration profiles. We will use Bayesian statistical methods to synthesize all sources of uncertainty using expert knowledge, ocean and climate data, and informative runs of coupled ocean/atmosphere models, applying recently developed methodology for the analysis of large slow computer simulators. We will start with an intermediate-complexity model, C-GOLDSTEIN, using this as a stepping-stone to analysing a full climate GCM such as HADCM3.

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Cape Farewell and Eirik Ridge: Interannual to Millenial Thermohaline Circulation Variability

Dr S Bacon, Southampton Oceanographic Centre (SOC); Dr E Rohling, Southampton University; Professor D Stow, Southampton University

Knowledge of the history of the Thermohaline Circulation (THC) is crucial to attempts to forecast it, particularly for model validation. Cape Farewell is one of the few locations in the North Atlantic which can provide a continuous record of the THC from the present day back as far as the Last Glacial Maximum (24,000 yr B.P.). Southward flow in the North Atlantic at 60 degrees N is concentrated in the narrow (~200 km wide) western boundary current system. Also, Eirik Ridge, a contourite drift just south of Cape Farewell, is intimately related to the deep western boundary current (DWBC) there. We propose a novel combination of hydrography and palaeoceanography to determine the variability of the DWBC on timescales from days, years, decades and millennia, to generate modern and palaeo-DWBC flux magnitudes.

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The determination of heat transfer and storage, and their changes in the North Atlantic Ocean

Dr N Wells, Southampton University

Changes in transport of ocean heat transport in the N Atlantic Ocean are intimately connected with changes in the ocean storage and surface heat flux. It is asserted that the ocean storage term can be measured to a depth of 2000m by the ARGO float system, which is providing a good coverage of the North Atlantic Ocean at present. The ARGO data will be used to determine changes in the heat transfer and storage in the N Atlantic over a 8 year period, which will enable seasonal and interannual changes in the heat storage to be determined. This will be compared with surface heat flux measurements to determine relationships between the two components. This methodology will enable the Atlantic components of the heat flux to be determined and provide robust estimates.

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Better Understanding of Open Ocean Deep Convection (OODC) with reference to THC

Dr C Pain, Imperial College; Professor P Killworth, Southampton Oceanography Centre; Dr Cassiano R E de Oliveira, Imperial College

Open-ocean deep convection (OODC) forms one end of the "conveyor belt" of the North Atlantic climate. We shall use the Imperial College Model to gain understanding of the physical basis of OODC and its interaction with topography, and to contribute to the parameterisation of OODC for large-scale models. Specific objectives are: to provide, and to test, the ability to model an ocean basin with small-scale features of a priori unknown location, in great detail; to examine and to understand the interaction of convection with topography and in situ currents; to develop improved parameterizations of convection for use in climate models; to generate reference modeling data sets and to train two PhD students. In providing descriptors for model evaluation and in achieving understanding, features of both Greenland and Labrador seas will be addressed,

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ISOMAP UK: a combined data-modelling investigation of water isotopes and their interpretation during rapid climate change events

Dr J Holmes, University College London; Dr T Atkinson, University College London/ University of East Anglia; Professor K Barber, Southampton University; Dr J Marshall, Liverpool University; Professor F Street-Perrot, University of Wales, Swansea; Professor P Valdes, Bristol University (prev. Reading Uni); Dr E Wolff, NERC British Antarctic Survey

The aims of the proposal are to compare high-resolution isotope records from terrestrial archives in NW Europe with model simulations of isotopes in precipitation in order to investigate the role of different forcing factors in rapid climate change during the late glacial and Holocene and to undertake model validation. The proposal constitutes a UK contribution to the PAGES ISOMAP initiative. A water isotope model will be developed for the UK Hadley centre model HadCM3. Comparisons will be made between simulations of the isotopic composition of precipitation during periods of rapid climatic change and reconstructions from well-dated and well-calibrated palaeo-archives (lake sediments, peat and speleothem) generated in this study and obtained from the literature, in order to investigate the causes and nature of abrupt climatic events.

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The role of the cryosphere on modulating the thermohaline circulation of the North Atlantic

Dr J Bamber, University of Bristol; Dr A Payne, University of Bristol; Professor J Shepherd, Southampton University; Professor P Valdes, Bristol University (prev. Reading Uni)

This project will investigate the role that land ice and, in particular the Greenland ice sheet, and sea ice play on modulating the present day and future thermohaline circulation in the Atlantic under a warming climate. This will be achieved by coupling a suite of sub-models that define the mass balance and behaviour of land and sea ice in the Arctic into a fast Earth model of Intermediate Complexity and a medium resolution fully coupled Atmosphere-Ocean GCM based on HadCM3. The coupled ice-ocean-atmosphere models will be used to investigate, in detail, the interaction of the cryosphere with the rest of the climate system, with particular emphasis on the thermohaline circulation.

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