Eddy transport of Western Mediterranean Intermediate Water to the Alboran Sea

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1 Click Here for Full Article JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 113,, doi: /2007jc004649, 2008 Eddy transport of Western Mediterranean Intermediate Water to the Alboran Sea J. T. Allen, 1 S. C. Painter, 1 and M. Rixen 2 Received 26 November 2007; revised 22 February 2008; accepted 5 March 2008; published 19 April [1] During the second cruise of the EU funded OMEGA project the towed undulating vehicle SeaSoar, was deployed to survey the upper 350 m of the water column in the eastern Alboran Sea and extreme western Algerian basin. With an effective along-track resolution of 4 km, the data sets enabled a detailed description of the different upper ocean water types and the fronts that separate them. The Almeria Oran front forms at the eastern boundary of the Alboran Sea gyre system, in the upper m of the water column, and separates waters of predominantly Atlantic origin from those formed in the Western Mediterranean Sea. Below these surface waters, but above the Levantine Intermediate Water, Western Mediterranean Intermediate Waters, believed to be formed to the north of the Balearic Sea, are normally observed in this region. However, to our knowledge, this is the first time a discrete eddy of Western Mediterranean Intermediate Water, a weddy, has been described in the extreme western Algerian basin. Repeated surveys of the region allowed us to observe the evolution of the eddy over a period of 40 d. A climatological analysis of historical data in the MEDAR/MEDATLAS database provides evidence for the repeatability of this observation and the significance of the estimated transport. Citation: Allen, J. T., S. C. Painter, and M. Rixen (2008), Eddy transport of Western Mediterranean Intermediate Water to the Alboran Sea, J. Geophys. Res., 113,, doi: /2007jc Introduction [2] Western Mediterranean Intermediate Waters (WIW) are formed seasonally through the intense winter cooling of Modified Atlantic Waters (MAW) principally in the northern regions of the Western Mediterranean [Perkins and Pistek, 1990; López-Jurado et al., 1995; Gasparini et al., 1999]. Before cooling, these waters of Atlantic origin have undergone considerable mixing with Levantine Intermediate Water (LIW) and Mediterranean Surface Waters (MSW). Conan and Millot [1995] suggested that this mixing and cooling mechanism for the formation of WIW could occur throughout the Western Mediterranean. [3] Perhaps the most extensive study of WIW is presented in the work of Pinot and Ganachaud [1999] and Pinot et al. [2002]. They discussed the observation of a number of different types of WIW, and their pathways, in the Balearic Sea. Furthermore, they showed how discrete weddies, anticyclonic eddy structures of WIW origin, could become topographically trapped in the southern basin of the Balearic Sea and block water exchange through the Ibiza Channel. [4] Gasparini et al. [1999] published an intensive CTD study of a lens of WIW in the Ligurian Sea. Having shown that the horizontal scale of the lens, although small, was considerably larger than the internal Rossby radius of 1 National Oceanography Centre, Southampton, UK. 2 NATO Undersea Research Centre, La Spezia, Italy. Copyright 2008 by the American Geophysical Union /08/2007JC004649$09.00 deformation, they concluded that the lens was a stable eddy. However, a detailed analysis of vertical density structure and Turner angle indicated that the lens was modified by double diffusive processes in its upper layer and convective instability on its lower boundary. [5] In conjunction, both these papers [Pinot and Ganachaud, 1999; Gasparini et al., 1999] indicated that the spreading mechanisms for WIW are not well understood, indeed Gasparini et al. [1999] make exactly this point early on in their paper. In this paper we will present a data set of repeated surveys (section 2) in which a WIW eddy, or weddy, was observed just east of the Alboran Sea. These data indicate that weddies may be long-lived and may therefore provide a significant mechanism for the transport of WIW over long distances (section 3). A climatological analysis of historical data in the MEDAR/MEDATLAS database provides evidence for the repeatability of this observation and the significance of the estimated transport (section 4). 2. OMEGA2 Data Set [6] The Alboran Sea fills a small and topographically complex region at the western end of the Mediterranean. Atlantic water flows into the Alboran Sea at the surface through the Strait of Gibraltar and generally forces a system of anticyclonic gyres [Viúdez et al., 1998; Allen et al., 2001, Figure 1]. At the eastern boundary of the Alboran Sea gyre system, an intensified front is frequently formed between surface waters of recent Atlantic origin and those of the 1of17

2 Figure 1. (top left) Survey region in context, cruise tracks for Large Scale Surveys (top right) 1 and (bottom left) 2 (LSS1 and LSS2) and (bottom right) an example cruise track for repeated Fine Scale Surveys 1 5. western Mediterranean Sea [Tintoré et al., 1988]. This front is known as the Almeria-Oran front. Water leaving the Almeria-Oran frontal jet is either reentrained into the Alboran Sea gyre system or feeds the Algerian Current, hugging the steep topography of the coast of Algeria [Arnone et al., 1990]. [7] During the 2nd observational phase of OMEGA (partly funded by the European Commission under MAST contract MAS3-CT ) a field experiment was carried out at the eastern end of the Alboran Sea to examine the impact of mesoscale motion on biological distributions [Fielding et al., 2001]. A total of 7 surveys were made of the Almeria-Oran front region (Figure 1) during RRS Discovery cruise 224 [Allen et al., 1997a; Pugh et al.,1997] in December 1996 and January 1997 using the towed undulating CTD instrument, SeaSoar [Pollard, 1986; Allen et al., 1997b]; for ease of reference the survey timing is summarized below. 16:15 GMT 2/12/96 17:15 GMT 5/12/96 Large Scale Survey 1 (LSS1) 17:40 GMT 6/12/96 04:30 GMT 10/12/96 Large Scale Survey 2 (LSS2) 18:30 GMT 11/12/96 10:00 GMT 15/12/96 Fine Scale Survey 1 (FSS1) 21:10 GMT 16/12/96 17:30 GMT 20/12/96 Fine Scale Survey 2 (FSS2) 19:50 GMT 21/12/96 22:15 GMT 24/12/96 Fine Scale Survey 3 (FSS3) 18:10 GMT 26/12/96 21:30 GMT 28/12/96 Algerian Current Survey (not referred to further in this paper) 2of17

3 Figure 2. Potential temperature as a function of salinity for all the SeaSoar data collected during the second large scale survey (black dots). Envelopes of potential temperature as a function of salinity for SeaSoar LSS2 and FSS1-5 of the Almeria-Oran front (colored lines). Lines of constant density are also shown at intervals of 0.1 kg/m 3. Note the relatively fresh surface modified Atlantic waters (MAW) in the eastern Alboran gyre, the warm salty Mediterranean surface waters (MSW), the Levantine water (LIW) and the temperature minimum layer (TML). (Modified from Allen et al. [2001] and included here for clarity). Figure 3. Composite indicating the three-dimensional structure of the upper 350 m of the water column during LSS2. The dotted cruise tracks are colored to show the horizontal salinity distribution at depths of 13 m and 157 m. The vertical contoured section shows temperature along leg PD of the cruise track (Figure 1); the vertical axis has been removed for clarity but the dotted tracks for leg PD on the two horizontal slices are shown in the plane of the vertical section. Only the horizontal planes are annotated. The solid black cartoon lines on the horizontal planes indicate the boundaries between water masses observed at the time of LSS2. (Reproduced from Allen et al. [2001] and included here for clarity). 3of17

4 Figure 4. Contoured (top) temperature and (bottom) salinity sections respectively for leg FB of LSS1 with selected density contour lines overplotted. The core of WIW is clearly apparent at 0.81 W. Port call, Cartagena, Spain 18:00 GMT 30/12/96 14:00 GMT 2/1/97 Fine Scale Survey 4 (FSS4) 08:00 GMT 14/1/97 20:00 GMT 16/1/97 Fine Scale Survey 5 (FSS5). [8] Routine calibration and processing of SeaSoar/CTD hydrographic data and RDI 150 khz VM-ADCP current data are considered sufficient for accuracy in salinity to 0.01 and in absolute current velocity to order 1 cm s 1 [Allen et al., 1997b, 1997c] (see also omega/disco/index.html). [9] In Figure 2 (modified from Allen et al. [2001] and included here for clarity), we present a potential temperature versus salinity (q/s) diagram for the SeaSoar CTD data collected during the second large-scale survey. The transport of surface waters and the dynamic nature of the Almeria Oran front observed in this data set were discussed in detail by Allen et al. [2001]. Thus we will only provide a summary description of these near surface water masses here. The lowest salinity waters, 36.63, are surface waters of recent Atlantic origin and are referred to as Modified Atlantic Water (MAW) [Arnone et al., 1990; Sparnocchia et al., 1994]. Mediterranean Surface Waters (MSW) [Arnone et al., 1990], salinity > 37.5 and temperature > 15.5 C, were found in the NE corner of the LSS2 area. MSW flowed slowly southwestward along the Spanish coast during the period of observation [Allen et al., 2001]. The characteristic q/s of MSW was less well defined (Figure 2) than that of the MAW perhaps as a result of the wide area and variability of its formation; predominantly old MAW that has remained at the surface in the Western Mediterranean [Benzohra and Millot, 1995; Gascard, 1978]. Between these two surface water masses, a large area of lower temperature intermediate 4of17

5 Figure 5. (top) Contoured cross track ADCP derived velocities, (middle) geostrophic velocity relative to ADCP velocities at 300 m, and (bottom) the difference between the two for leg FB of LSS1. The zero velocity contour associated with the core of the weddy is highlighted with a dashed line at 0.81 W. Positive velocities (gray shaded) are in a northerly direction across the section. 5of17

6 Figure 6. Contoured salinity sections for legs (top) KL and (bottom) PD of LSS2, with selected density contour lines plotted on top. The thick black dotted line indicates the crossing point of the two legs (Figure 1). salinity water (<15.5 C and psu) was observed at the surface north of the Almeria-Oran front. Following Gascard and Richez [1985], we refer to this as Atlantic- Mediterranean Interface Water (A-MIW). A-MIW is formed through mixing between MAW and intermediate Mediterranean waters either vertically, or horizontally following the upwelling of the latter along the north coast of the Alboran Sea. [10] Below the surface waters, a temperature minimum layer (TML) existed to a depth of generally m. This layer had a salinity around 38.2 and temperature below 13.5 C, indicating significant influence of WIW [Gascard and Richez, 1985; Pinot and Ganachaud, 1999]. Below the TML there was a tight q/s signature of Levantine Intermediate Water (LIW) that forms a distinct salinity maximum (Figure 2) [Sparnocchia et al., 1994; Gascard, 1978]. SeaSoar data were only available to a depth of 370 m and therefore these only just resolved the core of the LIW, 38.5 psu [Gascard and Richez, 1985]. [11] A particularly cold TML water was observed in an anticyclonic eddy at around 36.6 N, 0.9 W (Figure 3, reproduced from Allen et al. [2001] and included here for clarity). This had purer characteristics of WIW as described by Pinot and Ganachaud [1999], temperature <13 C and salinity 38.2 psu. The weddy was observed in the first 6 of the 7 SeaSoar surveys of the Almeria-Oran frontal region (LSS1 and 2, and FSS1 5). By FSS5, the signature of the 6of17

7 Figure 7. (top) Contoured salinity section for leg i of FSS1, with selected density contour lines overplotted. (bottom) ADCP derived current vectors at 150 m depth. eddy had disappeared possibly as a result of wind driven buoyancy loss and vertical mixing; the q/s envelope for FSS5 (Figure 2) shows a marked absence of a clear WIW signature and a significant cooling of surface waters. In the next section we will discuss the observed structure of this eddy in more detail. Comparison with climatological data is 7of17

8 Figure 8. (top and middle) Contoured salinity sections for legs h and i of FSS2, with selected contour lines overplotted. (bottom) ADCP derived current vectors at 150 m depth. 8of17

9 Figure 9. (top) Contoured salinity section for leg h of FSS3 with selected density contour lines overplotted. (bottom) ADCP derived current vectors at 150 m depth. presented in section 4 to provide a wider context to our observations before we provide a summary discussion in section Detailed Analysis of a Weddy 3.1. LSS1 [12] The first observation of the weddy was made on line FB of LSS1 (Figure 4). A core of WIW, 12.9 C and salinity, strongly distorted all isopycnal surfaces from 200 m to below the depth of our hydrographic data (360 m), at 0.81 W ( W). In Figure 5 we see that the ADCP derived cross track velocities and the geostrophic velocities relative to ADCP velocities at 300 m are generally very similar. If we look at the differences between these velocities (also Figure 5), generally these are small and incoherent in nature resulting mainly from the difference between 9of17

10 Figure 10. Contoured (top) temperature and (middle) salinity sections for leg i of FSS4 with selected density contour lines overplotted. (bottom) ADCP derived current vectors at 150 m depth. 10 of 17

11 Figure 11. Wind speed and direction, averaged over 1-h intervals, for the period of RRS Discovery cruise 224, Julian day referenced to the beginning of the high resolution of the ADCP data and the smoother low resolution of the geostrophically derived velocities. However, across the central core of the eddy (0.75 W 0.90 W), the difference between the ADCP and geostrophic velocities suggest some coherent ageostrophic flow, 5 cms 1, between depths of 100 and 250 m. The core of the weddy was associated with a tangential flow of over 20 cm s 1 near the surface (Figure 5) LSS2 [13] During the second large scale survey, two SeaSoar track legs passed close to the center of the weddy, leg PD (Figure 1) was a repeat of most of leg FB from LSS1, and leg KL which ran in a perpendicular direction to leg PD. Indeed the crossover between legs KL and PD indicates that we missed the center of the weddy by 10 km or less (Figure 6), and therefore we can safely estimate the diameter of the eddy to be around 40 km. By comparing with Figure 4, we can see that the eddy has moved westward 8 km between LSS2 and LSS1. The time between these two observations, along legs FB and PD, was 109 h and thus the advection of the weddy can be estimated at 2 cm s FSS1 [14] During the first of the fine-scale SeaSoar surveys, the weddy was clearly observed at the northern end of leg i (Figure 7). Although both the immediately preceding, h, and proceeding, j, legs of the survey showed small temperature and salinity signatures of the edge of the weddy [Allen et al., 1997b], ADCP velocity vectors at 150 m indicate that leg i passed very close to the center of the weddy (Figure 7). This is consistent with a continued westward propagation, perhaps more west of southwest, of around 9 km in 115 h and thus again 2 cms FSS2 [15] By the second fine scale SeaSoar survey, the weddy was clearly visible on both legs h and i (Figure 8). The vertical structure in contoured temperature (not shown) and salinity (shown) was similar if observed on either leg, indicating that the center of the weddy was now somewhere near halfway between legs h and i of the survey. The ADCP vectors (also shown in Figure 8) confirmed this indication. Once again consistent with a continued west or westsouthwestward propagation at 1.7 cm s FSS3 [16] During the third of the fine scale SeaSoar surveys, the weddy was by now clearly observed at the northern end of leg h (Figure 9). And now both the immediately preceding, g, and proceeding, i, legs of the survey showed small temperature and salinity signatures of the edge of the weddy [Allen et al., 1997b]. ADCP velocity vectors at 150 m indicate that leg h passed very close to the center of the weddy (Figure 9), thus confirming a continued westward propagation of around 2 cm s FSS4 [17] The fourth fine-scale SeaSoar survey followed a survey of the Algerian Current, further east, and a port call 11 of 17

12 Figure 12. Absolute VM-ADCP velocity vectors at 14 m depth (20-min averaged) for (top to bottom) FSS 1 5. Vectors are color coded in intervals of 20 cm s 1 according to the legend above. 12 of 17

13 Figure 13. Colored dots indicating the potential temperature on the density surface (sigma0 = 28.9); each dot is the position of the equivalent CTD station to the SeaSoar data processing, i.e., 4-km spacing and therefore approximately every two SeaSoar undulation cycles [Allen et al., 1997b]. 13 of 17

14 Figure 14. Truncated T/S scatterplots, colored by 2-month period, for the (top) Balearic Sea and (bottom) Alboran Sea, from the MEDAR/MEDATLAS database. in Cartagena; thus there was a gap of 6 d from the end of FSS3. The weddy was now observed back at the northern end of leg i (Figure 10). With little signal of WIW on either the immediately preceding, h, and proceeding, j, legs of the survey [Allen et al., 1997b], we can conclude that leg i passed very close to the center of the weddy. The ADCP velocity vectors at 150 m did not show a strong signature of the circulation of the weddy this time. For the second leg of the cruise, differential GPS navigation was not available and thus the ADCP vectors shown in Figure 10 have had a 20 min moving filter applied to achieve an accuracy of a few cm s 1 [Pugh et al., 1997]. Perhaps more significantly, FSS4 was carried out during a sustained period of significantly higher wind speed (Figure 11), the reduction in depth achieved by the SeaSoar vehicle is testament to the resulting deterioration in sea state. VM-ADCP current vectors at 14 m (Figure 12) showed a breakdown in the Almeria Oran front and by inference the Eastern Alboran Gyre. The resulting generally eastward flow through the region may account for 14 of 17

15 the reversal in the propagation direction of the weddy, eastward between FSS3 and 4 at around 2 cm s FSS5 [18] Little signature of WIW was observed during the fifth fine scale SeaSoar survey (Figure 13), which was conducted 14 d after FSS4. The fate of the weddy is unclear, in the time between FSS4 and 5 it may have been advected out of the domain, or have been mixed into the surrounding water by continued strong winds (Figure 11) destabilizing the thermocline. Following the collapse of the Almeria-Oran front we would expect Mediterranean waters to advect slowly westward in the north of the survey area while Atlantic waters flow eastward in the southern and central part of the area (Figure 12), however we cannot rule out continued eastward advection like that observed between FSS3 and 4. Nevertheless, surface waters were certainly cooler and mixed layers deeper during FSS5 than FSS4 [Allen et al., 1997b]. And, the q/s envelope for FSS5 (Figure 2) does indicate that the MSW were considerably saltier and denser, in addition to being colder, than observed in the previous surveys; indicating mixing with intermediate waters. 4. Climatological Comparisons [19] The MEDAR/MEDATLAS 2002 [Maillard et al., 2005; Rixen et al., 2005] database was used to compare the observed hydrographic conditions in the Omega2 data set with other data sets from the second half of the 20th century. Temperature/salinity (T/S) scatter diagrams for both the Balearic Sea and the Alboran Sea are presented in Figure 14. For clarity these are truncated to show only the lower temperature waters outside the surface layer. The particularly fresh water mass (salinity < 37.9) in March/ April, was observed in two Balearic Sea cruises (1991, 1993). These are shallower waters of recent Atlantic origin within the Gulf of Valencia (M. Marcos and J. L. Lopez- Jurado, personal communication, 2007) and as they are therefore not of relevance here they will not be discussed further. Within the T/S data from the Balearic Sea considerable scatter can be seen in WIW but with a pronounced seasonal signal. Salinities increase significantly during the year from local minimum values of 38.0 during January April and reaching local maximum values of 38.3 by July/ August. A large spread in salinity is seen within A-MIW, suggesting a wide range of source waters are available for winter cooling. Pinot and Ganachaud [1999] identified 5 closely related but subtly distinct types of WIW in the Balearic Sea that differed with location which they suggested was due to mixing with underlying LIW. These observed variations may also reflect the observed spread of thermohaline properties in the A-MIW precursor water mass. WIW reach the Balearic Sea quickly after formation appearing by January/February and remain within the Balearic Sea throughout spring and summer but appear to have fully cleared the region by Sep/Oct (Figure 14, top) leaving little signal of a temperature minimum layer. T/S data for the Alboran Sea reveal that the strongest signal of WIW occurs during late spring and early summer (Figure 14, bottom), and, although a seasonal cycle is visible, a temperature minimum layer (<13.2 C) of WIW origin appears to exist all year round. [20] The MEDAR/MEDATLAS 2002 database was also used to compare our data with climatological conditions during the second half of the 20th century. Climatic monthly temperature and salinity fields on a grid were obtained using the Variational Inverse Method [Brasseur, 1991; Brasseur et al., 1996]. We introduced a Gaussian time correlation function to select the data relevant to each month, which provided a climatological cycle instead of a time series of successive monthly means [Brankart and Pinardi, 2001]. However, this was not able to clearly identify the presence of weddies, possibly as a result of the inevitable smoothing (anonymous reviewer, personal communication, 2007); and while identifying the same seasonal presence of WIW, the analysis added nothing to the analysis of historical T/S profiles above. 5. Discussion [21] We know that WIW reach the Alboran Sea, Viúdez et al. [1998] refer to it as T min water, however its transport there has been unclear. Pinot and Ganachaud [1999] showed that weddies were frequently trapped by topography in the Balearic Sea, nevertheless we have shown that some make it at least as far as the eastern end of the Alboran sea. Pinot et al. [2002] show that the size of the weddy is key to its passage from the Balearic Sea to the Algerian Basin through the Ibiza Channel; those over 50 km in diameter will be significantly restricted by the narrow topography of the channel. Interestingly, Viúdez et al. [1998] may well have discovered a weddy at W, N, in the center of the Alboran Sea but resolved by a single CTD profile they were only able to offer conjecture as to the details of its structure and origin. [22] RRS Discovery cruise 224 occurred during early winter 1996/1997 (December/January) and was thus too early to have observed WIW formed during the 1996/1997 winter period. Typical advection rates for the Northern Current, which carries WIW southward, are estimated to be 10 cm s 1 [Pinot et al., 2002] and WIW is typically first seen in the Ibiza Channel during spring. Crucially, Pinot et al. [2002] and Vargas-Yanez et al. [2005] both identify the 1995/1996 winter period as unusually cold resulting in exceptionally large volumes of WIW reaching the Ibiza Channel. Our observations of an eddy composed of WIW at the western end of the Algerian Basin in December 1996 are consistent with it representing WIW formed during the 1995/1996 winter period (10 12 months previously). Winters following the 1995/1996 period (including the period sampled here) were not as cold and WIW transport through the Ibiza Channel was apparently absent until spring/summer 2000, following another particularly cold winter in 1999/2000 [Vargas-Yanez et al., 2005]. The sporadic appearance of WIW in the Ibiza Channel suggests that the intensity of at least one preceding winter s cooling dictates the volume, if any, of WIW reaching the Alboran Sea. A study by Monserrat et al. [2008] introduces a standardized air-sea temperature anomaly parameter for the key winter period of WIW formation that can be used to infer the presence of WIW within the Balearic region the following spring. The relationship between winter air-sea 15 of 17

16 temperature anomalies and the presence of WIW within the Ibiza Channel appears robust, providing an early warning of changes to the circulation of the Balearic Sea the following spring. [23] Herbaut et al. [1997] examined the characteristics and pathways of water masses in an atmospherically forced high-resolution (11 km grid) primitive equation model of the Western Mediterranean. The model simulated WIW formation in a number of regions in the North Western Mediterranean. In the spring and early summer the simulated WIW was found to enter the Algerian Basin through the Ibiza Channel with a total transport below 200 m peaking at 0.9 Sv (1 Sverdrup = 10 6 m 3 s 1 ). This transport was found to stop in September. From the extensive observations of the CANALES experiment, Pinot et al. [2002] were able to describe an observed seasonal signal in the total transport of the Northern Current, flowing south down the western side of the Balearic Sea, from 1 to 1.4 Sv in winter to less than 0.5 Sv in summer. The Northern Current brings MSW southward toward the Balearic Channels and also drives the transport of WIW southward [López-Jurado, 2002] from the Gulf of Lion. [24] If we consider our observed weddy to have carried an oblate spheroid of WIW, 20 km radius and 150 m thick (Figures 4 and 6), then it accounted for the transport of m 3 of WIW south and westward from the Ibiza Channel to the western extremity of the Algerian Basin. We can think of this as a lower bound estimate as it takes no account of instability processes releasing WIW to the surrounding water column. Such a quantity is equivalent to 3 4 d of the total transport of waters southward down the western side of the Balearic Sea and through the Ibiza Channel [Herbaut et al., 1997; Pinot et al., 2002]. Initially this does not sound like a large fraction of the WIW produced in the Gulf of Lion. However, there are no published estimates of the maximum volume of WIW produced in the Gulf of Lion or of the transport of WIW flowing south through the Ibiza Channel. However, inspecting Figure 10 of Pinot et al. [2002], it seems reasonable to suggest that at times of maximum transport of WIW, around 50% of the southward transport through the Ibiza Channel may have core WIW characteristics; therefore, our weddy may represent a week or more of WIW transport from the Balearic Sea. With a winter cooling production period of perhaps 2 3 months only, our weddy could therefore have carried around 10% of WIW produced in the winter of 1995/6. However, Pinot et al. [2002] and others have made it clear that WIW are not produced every year and a significant fraction of that produced may circulate round the Balearic Sea before making it through the Ibiza Channel. Interestingly, our first two surveys LSS1 and LSS2 may have passed through a second weddy at their northeast corner (point E and point M, Figures 1 and 13), the VM- ADCP vectors for LSS2 suggest an anticyclonic circulation (not shown). Although we have insufficient data to be conclusive about the second eddy, we feel it is safe to speculate that eddy transport westward toward the Alboran Sea may prove to be the ultimate fate for a significant proportion of WIW. [25] Acknowledgments. We dedicate this paper to the memory of the late Jean-Michel Pinot. We thank the two reviewers and the Associate Editor for their helpful comments and suggestions. We are most grateful to Marta Marcos for her helpful discussions during completion of this manuscript. We thank the Master, crew and scientists on board RRS Discovery cruise 224 for both a comprehensive data set and a splendid Christmas. 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