Successful applications to the first 'Monitoring the Atlantic Meridional Overturning Circulation' funding round: Project Abstracts

For more details about these projects, please consult the RAPID MOC monitoring web page

Monitoring the Atlantic Meridional Overturning Circulation at 26.5degN

Professor J Marotzke, Southampton Oceanography Centre; Dr Stuart Cunningham, Southampton Oceanography Centre; Professor H Bryden, University of Southampton;

We propose to observe continuously the meridional overturning circulation (MOC, zonally integrated meridional flow), in Atlantic at 26.5 degrees N). The MOC is the most important dynamical quantity to determine ocean transports of heat, freshwater, carbon and other properties, and is central to all considerations of rapid climate change and the role of the thermohaline circulation. We propose a combination of moored arrays (temperature, salinity, currents and pressure), satellite observations (sea level, winds), the opportunistic use of hydrographic section and float data, and cable measurements (Florida Strait transport), plus modelling to synthesise the observations. The backbone of the observing array will be profiling CTD probes near the end points of the section, allowing us to perform zonally integrated thermal-wind flow calculations quasi-continuously.

Measuring the Meridional Overturning Circulation from space: a feasibility study

Dr D Cromwell, Southampton Oceanography Centre; Mr Peter Challenor, Southampton Oceanography Centre;

Distinguishing the time-mean surface circulation from the marine geoid at spatial scales of a few hundred kilometers and larger will soon be possible with the advent of satellite gravity missions. The missions will allow an estimate of bottom pressure gradients, thus enabling the estimation of deep flow. By combining data from satellites and Argo floats, we should be able to estimate the vertical profile of current and, thus, the meridional overturning circulation in the North Atlantic. The principal objectives of this proposal are to investigate the feasibility of estimating both the zonally-integrated meridional mass/heat transport in the western North Atlantic by combining satellite and in situ data. Secondary objectives include rigorously testing the realism of both ocean and coupled ocean-atmosphere circulation models.

Time series of transient tracers in North Atlantic deep waters

Professor A Watson, University of East Anglia

We will use new sampling technologies and techniques in an international collaboration to collect time-series of transient tracers penetrating the deep branch of the MOC in the northern North Atlantic and its marginal seas, using existing or planned moorings. Tracers will include CFCs, sulphur hexafluoride and Iodine-129, the last two of which have specific sources and rapidly changing signals. These data will give unique information, complementary to standard hydrography and current measurements. They will enable studies of: secular and seasonal change in the source strengths of the deep waters, times of passage between locations, rates of dilution of the "marked" source waters by entrainment, and improved estimates of recirculation of deep waters, e.g. DSOW and LSW in the Labrador sea and upstream of the proposed 24N monitoring array.

A monitoring array along the western margin of the Atlantic

Dr C Hughes, Proudman Oceanographic Laboratory; Dr. David Marshall, University of Reading; Dr. Richard Williams, University of Liverpool

A crucial requirement for a monitoring system of the overturning is the ability to relate integrated changes at low latitudes to their high latitude sources. We propose to deploy an observing system to identify the propagation of overturning signals along the western margin of the North Atlantic. Three lines of bottom pressure recorders, inverted echo-sounders and profiling CTDs will be deployed at depths of 2-4.5 km at 38N, 69W, 42N, 60W and 43N, 52W. The data will identify temporal changes in the Deep Western Boundary Current and reveal how coherent the changes are along the slope. Together with other national and international surveys, this array will assist in assessing the impact of the overturning on the wider climate system.