Monitoring the Atlantic meridional overturning circulation.

Rayner, Darren, Hirschi, Joël J.-M., Kanzow, Torsten, Johns, William E., Wright, Paul G., Frajka-Williams, Eleanor, Bryden, Harry L., Meinen, Christopher S., Baringer, Molly O., Marotzke, Jochem, Beal, Lisa M. and Cunningham, Stuart A. (2011) Monitoring the Atlantic meridional overturning circulation. Deep-Sea Research Part II-Topical Studies in Oceanography, 58 (17-18). pp. 1744-1753. DOI 10.1016/j.dsr2.2010.10.056.

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Abstract

The rapid climate change programme (RAPID) has established a prototype system to continuously observe the strength and structure of the Atlantic meridional overturning circulation (MOC) at 26.5 degrees N. Here we provide a detailed description of the RAPID-MOC monitoring array and how it has evolved during the first four deployment years, as well as an overview of the main findings so far. The RAPID-MOC monitoring array measures: (1) Gulf Stream transport through Florida Strait by cable and repeat direct velocity measurements; (2) Ekman transports by satellite scatterometer measurements; (3) Deep Western Boundary Currents by direct velocity measurements; (4) the basin wide interior baroclinic circulation from moorings measuring vertical profiles of density at the boundaries and on either side of the Mid-Atlantic Ridge; and (5) barotropic fluctuations using bottom pressure recorders. The array became operational in late March 2004 and is expected to continue until at least 2014. The first 4 years of observations (April 2004-April 2008) have provided an unprecedented insight into the MOC structure and variability. We show that the zonally integrated meridional flow tends to conserve mass, with the fluctuations of the different transport components largely compensating at periods longer than 10 days. We take this as experimental confirmation of the monitoring strategy, which was initially tested in numerical models. The MOC at 26.5 degrees N is characterised by a large variability even on timescales as short as weeks to months. The mean maximum MOC transport for the first 4 years of observations is 18.7 Sv with a standard deviation of 4.8 Sv. The mechanisms causing the MOC variability are not yet fully understood. Part of the observed MOC variability consists of a seasonal cycle, which can be linked to the seasonal variability of the wind stress curl close to the African coast. Close to the western boundary, fluctuations in the Gulf Stream and in the North Atlantic Deep Water (NADW) coincide with bottom pressure variations at the western margin, thus suggesting a barotropic compensation. Ongoing and future research will put these local transport variations into a wider spatial and climatic context. (C) 2011 Elsevier Ltd. All rights reserved.

Document Type: Article
Additional Information: Data availability Data from the RAPID project are logged with the British Oceanographic Data Centre (BODC) on acquisition. Following the NERC data policy for RAPID-WATCH (http://www.bodc.ac.uk/projects/uk/rapid/data_policy/), data are made freely available from the BODC website (http://www.bodc.ac.uk). Timeseries of the overturning and component transports, along with gridded mooring data, are available from the project webpage (http://www.noc.soton.ac.uk/rapidmoc). The Florida Current cable data are made freely available by the Atlantic Oceanographic and Meteorological Laboratory (http://www.aoml.noaa.gov/phod/floridacurrent/) and are funded by the NOAA Office of Climate Observations. The surface layer or Ekman contribution to the MOC is calculated from winds obtained by the QuickSCAT satellite scatterometer (SeaWinds on QuickSCAT. Mission, http://winds.jpl.nasa.gov/missions/quickscat/index.cfm).
Keywords: Physical oceanography; Thermohaline circulation; Ocean circulation; Ocean currents; Mooring systems; Atlantic meridional overturning circulation; WESTERN BOUNDARY CURRENT; TROPICAL NORTH-ATLANTIC; THERMOHALINE CIRCULATION; NORDIC SEAS; OCEAN; VARIABILITY; TRANSPORTS; ARRAY; MODEL; CLIMATE
Research affiliation: OceanRep > GEOMAR > FB1 Ocean Circulation and Climate Dynamics > FB1-PO Physical Oceanography
Refereed: Yes
Open Access Journal?: No
DOI etc.: 10.1016/j.dsr2.2010.10.056
ISSN: 0967-0645
Date Deposited: 11 Jan 2012 14:25
Last Modified: 18 Oct 2016 07:35
URI: http://oceanrep.geomar.de/id/eprint/13409

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