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To assess whether the southward deep water flow of the Atlantic meridional overturning circulation can be monitored by measuring the deep western boundary current, the structure and transport of the time-averaged deep western boundary current at 26.5N are estimated from long current meter records deployed in a series of 7 mooring deployments over 11 years from March 1986 to June 1997 east of Abaco Island in the Bahamas. Time-averaged meridional velocities for each current meter record are combined into estimates of mean velocity at 3 to 10 depths at 10 mooring locations extending eastward from the continental slope out to an offshore distance of 580 km. The mean deep western boundary current below 1000 m depth exhibits a core of strong southward velocities above 15 cm s Ϫ1 at an offshore distance of about 55 km and extends out to an offshore distance of about 160 km with an estimated total southward transport of 34.6 Sv. We estimate the error in this time-averaged transport to be 3.7 Sv due to uncertainties in the mean velocities due to temporal variability and up to 4 Sv due to the choice of methods to integrate spatially the time-averaged velocities across the section. Offshore from 160 km out to at least 580 km, there is broad, slow northward flow that recirculates deep water northward. While the mooring array is not sufficient to accurately measure the northward recirculation, a simple spatial average of the time-averaged currents indicates a northward recirculation of about 13 Sv in this offshore region. Daily estimates of the deep western boundary current from two arrays with reasonably complete coverage of the deep western boundary current suggest that the instantaneous boundary current has a width of about 100 km, naturally narrower than the mean boundary current. Daily southward transports vary between 5 and 75 Sv but the array does not fully resolve the boundary current during offshore meander events that occur about 20% of the time. We conclude that it is problematic to monitor the net southward flow of the Atlantic meridional overturning circulation with boundary current measurements at 26.5N because the narrow deep western boundary current transport has substantially larger transport than the net southward flow and the offshore northward recirculation is broad and diffuse so that accurate estimates of the recirculation would require an extensive array of moored instruments.

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We report the results of a set of measurements made within the Charlie-Gibbs Fracture Zone in 1988-1989. The principal dam sources are year-long current meter •rds, 16 in number, and 23 conductivity-temperature-depth stations. The aim was to determine the flux of overflow water passing westward out of the Iceland Basin in the eastern North Atlantic. Within the fracture zone, overflow water is defined either as having salinity greater than 34.94 at the present time or, more generally, as having a potential density c•0 > 27.8 kg/m 3. In 1988-1989 the core salinity had a value equal to that reported in 1981 and 1983 but was fresher by about 0.02 than was found in 1964. The flux was estimated twice per day and was found to fluctuate strongly, with energy spread in a broad band of periods, ranging from 10 to 400 days. No annual signal could be detected. The mean value was 2A + 0.5 Sv, less than all previous estimates based on hydrography alone. It is suggested that hydrography may systematically overestimate transport because diffusion is neglected. Flux estimates from current meter arrays are rarely used in initializing numerical ocean models; consequently measurements, like those reported here, are an independent and important means for assessing the performance of such models. At the deepest levels, water enters the two wansform valleys of the fracture zone from the west. In the northern valley the flow is periodically flushed out by energetic bursts of overflow water. A critical value of an inverse Froude number is shown to define the flushing threshold. Introduction Under the impact of severe winter cooling, the Norwegian-Greenland-Iceland Seas produce dense water which overflows the shallow ridge in the northern North Atlantic lying between Greenland, Iceland and Scotland [Swi•, 1984]. As recent moored current meter measurements show, in two locations the overflow is persistent and steady, namely in the Denmark Strait [Dickson et al., 1990] and in the Faeroe Bank Channel [Saunders, 1990]. In contrast, on the Iceland-Faeroe Ridge it is intermittent [Meincke, 1983]. East of Iceland the overflow water follows a path on the eastern flanks of the Reykjanes Ridge as well as filling the deepest levels of the Iceland Basin [Harvey and Theodorou, 1986]. Near 53øN the overflow encounters the Charlie-Gibbs Fracture Zone (CGFZ) where it passes westward into the Irminger and Newfoundland Basins [Worthington and Volkmann, 1965], see Figure 1 (inset). Recently McCartney [1992] has modified the traditional view discussed above by advancing the concept of a Deep Northern Boundary Current, of which the northern overflow is a constituent, but nevertheless major part. In addition, his deep current contains recirculating Labrador Sea Water and deep water drawn up from midlatitudes. During the past 4 years the author of this paper has been engaged in a field program studying the overflow east of the Mid-Atlantic Ridge. The principal aims of the project are, first, to measure the flux of dense water at source and to determine what fac...

A method is described to relate the parameters appearing in interpolation equations for radiation thermometry directly to the radiometric characteristics of the thermometer itself. It is shown that for sufficiently narrow bandwidths these parameters are independent of the shape of the spectral responsivity and can be expressed solely in terms of its mean wavelength and bandwidth as determined by the variance. This allows the parameters to be determined either by direct measurement of the spectral responsivity, by measurements at fixed points, or by a combination of the two, in effect unifying the ITS-90, interpolation, and absolute thermometry methodologies for determining temperature. The development of high-temperature metal-carbon and metal-carbide-carbon eutectic fixed points means that temperatures up to and exceeding 3500 K may be determined by implementing a single simple interpolation equation in a variety of ways.

An analysis is made of data from 30 Aanderaa recording current meters (RCMs) set on nine moorings located east of Cape Farewell, the southern tip of Greenland. The purpose of the measurements was to allow for the estimation of transport in the deep western boundary current (DWBC) below a depth of about 1500 m. The records commenced in September 2005 and lasted from 9.5 to 11.5 months. After calibration of the raw data, 12-h averages of temperature and current were derived and the latter employed to estimate the flow across and along the array direction. The 9.5-month average transport of water colder than 38C was found to be 7.8 Sv (1 Sv [ 1 3 10 6 m 3 s 21 ) with a standard error of 0.8 Sv. For water denser than s u 5 27.85 kg m 23 , the transport is calculated as 4.5 Sv. Whether either of these values is significantly different from comparable measurements made 500 km upstream cannot be determined. In marked contrast, for s u . 27.8 kg m 23 , the transport is estimated as only 9.0 Sv, smaller than the widely accepted value of 13 Sv for nearby measurements made in 1978. A reevaluation of the calculations and assumptions made then allows one to determine the uncertainty of the earlier estimate and thereby conclude that the difference between the previous and present measurements is significant, that is, that the transport has decreased between 1978 and 2005-06. A weakening of the transport during the 9.5-month period is also observed, along with a warming and an increase in salinity in the core of the DWBC. These latter changes are shown to be consistent with interannual variability rather than a long-term trend.