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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2009.06.002 Byline: Matthias Lankhorst (a)(d), David Fratantoni (b), Michel Ollitrault (c), Philip Richardson (b), Uwe Send (a)(d), Walter Zenk (a) Abstract: A comprehensive analysis of velocity data from subsurface floats in the northwestern tropical Atlantic at two depth layers is presented: one representing the Antarctic Intermediate Water (AAIW, pressure range 600-1050dbar), the other the upper North Atlantic Deep Water (uNADW, pressure range 1200-2050dbar). New data from three independent research programs are combined with previously available data to achieve blanket coverage in space for the AAIW layer, while coverage in the uNADW remains more intermittent. Results from the AAIW mainly confirm previous studies on the mean flow, namely the equatorial zonal and the boundary currents, but clarify details on pathways, mostly by virtue of the spatial data coverage that sets float observations apart from e.g. shipborne or mooring observations. Mean transports in each of five zonal equatorial current bands is found to be between 2.7 and 4.5Sv. Pathways carrying AAIW northward beyond the North Brazil Undercurrent are clearly visible in the mean velocity field, in particular a northward transport of 3.7Sv across 16[degrees]N between the Antilles islands and the Mid-Atlantic Ridge. New maps of Lagrangian eddy kinetic energy and integral time scales are presented to quantify mesoscale activity. For the uNADW, mean flow and mesoscale properties are discussed as data availability allows. Trajectories in the uNADW east of the Lesser Antilles reveal interactions between the Deep Western Boundary Current (DWBC) and the basin interior, which can explain recent hydrographic observations of changes in composition of DWBC water along its southward flow. Author Affiliation: (a) Leibniz-Institut fur Meereswissenschaften (IFM-GEOMAR), Kiel, Germany (b) Woods Hole Oceanographic Institution (WHOI), Woods Hole, MA, USA (c) Institut francais de recherche pour l'exploitation de la mer (Ifremer), Plouzane, France (d) Scripps Institution of Oceanography (SIO), 9500 Gilman Drive, Mail code 0230, La Jolla, CA 92093-0230, USA Article History: Received 29 April 2008; Revised 29 May 2009; Accepted 2 June 2009

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2005.12.007 Byline: Torsten Kanzow (a)(b), Uwe Send (a)(c), Walter Zenk (a), Alan D. Chave (d), Monika Rhein (e) Keywords: Geostrophic transport; Time series; Bottom pressure; Density; Meridional overturning circulation Abstract: As a component of the meridional overturning variability experiment in the tropical North Atlantic, a four-year-long time series of meridional transport of North Atlantic deep water has been obtained from moored end point measurements of density and bottom pressure. This study presents a quality assessment of the measurement elements. Rigorous pre- and post- deployment in situ calibration of the density sensors and subsequent data processing establish an accuracy of O(1.5Sv) in internal transport in the 1200-5000dbar range at subinertial time scales. A similar accuracy is reached in the bottom pressure-derived external transport fluctuations. However, for pressure, variability with periods longer than a deployment's duration (presently about one year) is not measurable. This effect is demonstrated using numerical simulations and a possible solution for detecting long-term external transport changes is presented. Author Affiliation: (a) Leibniz-Institut fur Meereswissenschaften, Dusternbrooker Weg 20, 24105 Kiel, Germany (b) National Oceanography Centre, Empress Dock, Southampton, SO14 3ZH, UK (c) Scripps Institution of Oceanography, University of California San Diego, La Jolla, CA 92093-0230, USA (d) Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA (e) Institut fur Umweltphysik, Otto Hahn Allee NW1, 28334 Bremen, Germany Article History: Received 7 September 2004; Revised 1 November 2005; Accepted 27 December 2005

Tests are conducted to determine the comparative performance and accuracy of Sippican Inc.'s eXpendable Conductivity Temperature Depth (XCTD) probes as opposed to CTD sondes. As previously seen in the THETIS-I experiment, errors that occurred due to experimental conditions are segregated from errors caused by the equipment. Results show the relative accuracy of XCTD sensors based on the manufacturer's specifications.

Abstract: The development of a broad-scale array of about 3000 autonomous profiling floats, known as Argo, has been underway since 2000. This array will deliver up to 100,000 vertical profiles of temperature, salinity and other parameters from the surface to depths up to 2000m. While floats are expected to give good measurements of temperature and pressure, salinity measurements sometimes show significant sensor drift with time or offsets. Unless a float is recovered before the battery fails, recalibrations cannot be performed and a remote calibration method is required. Such a quality control system has been set up for the North Atlantic to identify and correct salinity sensor drifts by using historical hydrographic data. An objective mapping method is used that takes the spatial and temporal variations in water mass properties into account. These scales aim to represent the hydrographic structure of the North Atlantic, which follow the large-scale contours of the potential vorticity. The float measurements of each profile are compared to the mapped salinities in potential conductivity space by weighted least-squares, giving one correction for each profile. It is assumed that any conductivity offset changes slowly over time, so that a linear fit of the profile based corrections over the float time series is done. The result is a set of calibrated salinity data with corresponding uncertainties. [Copyright &y& Elsevier]

Investigates the feasibility of using acoustic methods at the Strait of Gibraltar. Number of acoustic transceivers; Measurement of flow and temperature in straits; Effectivity of the reciprocal travel time measurements.

• North Atlantic Current (NAC) is observed with altimetry, floats, moorings, and XBTs. • Decadal NAC variability is traced back to sea level anomalies and density signals. • Uncertainty estimates quantify sensor and sampling errors in NAC observations. • Observed NAC variability is larger than the uncertainty estimates. Large-scale geostrophic flow across an oceanographic section can be computed from in situ density profiles and satellite-borne sea level anomaly measurements at the section endpoints. Here, uncertainties are estimated and compared for observations that span the North Atlantic Current. Out of multi-year mooring records from two sites, Porcupine Abyssal Plain and Central Irminger Sea, 16 months from the 2002–2005 period are available that have sufficient data coverage to observe this current. Transport and uncertainty estimates from these moorings are compared to results from Argo floats and expendable bathythermographs. The latter have longer data sets and provide decadal time series with semiannual resolution in time. Typical uncertainties, which take sensor errors and sub-sampling the eddy field into account, are below 2 Sv of volume transport for the mooring- and float-based estimates and just below 3 Sv for the expendable bathythermographs. Peak-to-peak variability occurs on decadal time scales and is about 11 Sv, well above the observational uncertainty. We can therefore have confidence that the observed signal reflects true changes in the ocean. The time series is further extended to 25 years duration, using solely the altimetry data by proxy. The aim of this study is to add value to such time series by understanding and quantifying the uncertainties and consistency between methods. The methodology is applicable at other locations as well. [ABSTRACT FROM AUTHOR]

This paper is an observational study of small-scale coherent eddies in the Labrador Sea, a region of dense water formation thought to be of considerable importance to the North Atlantic overturning circulation. Numerical studies of deep convection emphasize coherent eddies as a mechanism for the lateral transport of heat, yet their small size has hindered observational progress. A large part of this paper is therefore devoted to developing new methods for identifying and describing coherent eddies in two observational platforms, current meter moorings and satellite altimetry. Details of the current and water mass structure of individual eddy events, as they are swept past by an advecting flow, can then be extracted from the mooring data. A transition is seen during mid-1997, with long-lived boundary current eddies dominating the central Labrador Sea year-round after this time, and convectively formed eddies similar to those seen in deep convection modeling studies apparent prior to this time. The TOPEX / Poseidon altimeter covers the Labrador Sea with a loose “net” of observations, through which coherent eddies can seem to appear and disappear. By concentrating on locating and describing anomalous events in individual altimeter tracks, a portrait of the spatial and temporal variability of the underlying eddy field can be constructed. The altimeter results reveal an annual “pulsation” of energy and of coherent eddies originating during the late fall at a particular location in the boundary current, pinpointing the time and place of the boundary current-type eddy formation. The interannual variability seen at the mooring is reproduced, but the mooring site is found to be within a localized region of greatly enhanced eddy activity. Notably lacking in both the annual cycle and interannual variability is a clear relationship between the eddies or eddy energy and the intensity of wintertime cooling. These eddy observations, as well as hydrographic evidence, suggest an active role for boundary current dynamics in shaping the energetics and water mass properties of the interior region. [Copyright &y& Elsevier]