1.0 Introduction As an extension of the MMS-Funded DeSoto Canyon Eddy Intrusion Study (Hamilton et al., 2000) additional current/temperature measurements were made at the base of the Sigsbee Escarpment in water depths of approximately 2000 m. Deepwater measurements in this specific area, supported by BP, indicated the occurrence of periodic higher speed events that could be of considerable importance to expected oil/gas exploration and development in this deepwater area. In orcer to have available representative and pertinent knowledge of conditions in these development areas, the MMS funded a series of fairly site-specific, deepwater current measurements. In conjunction with MMS support, BP provided support to expand the depth and areal coverage of these measurements in what was a cooperatively government-industry measurement program. 1.1 Background In August 1999, the Minerals Management Service (MMS) funded the deployment of an array of three moorings, clustered near the 2000-m isobath at the base of the continental slope, south of the Mississippi delta (Figure 1-1). This array was designed to study energetic deep currents that had been previously observed by a mooring deployed for BP Exploration Inc. in Block 618 of the Atwater Valley lease area (Hamilton, 1998). Both the previous BP mooring and the MMS array were situated south of a relatively steep slope known as the Sigsbee escarpment which is an extensive geological feature that meanders across the deep northern slope between the Mississippi delta and east Texas. The MMS array consisted of one, extensively instrumented, full depth mooring (I1) and two short bottom moorings (I2 and I3). In order to discover how far up the slope high speed deep currents might extend from the Atwater site, BP contracted with SAIC to deploy another short bottom mooring on a block (Green Canyon 782) north of the escarpment (Figure 1-2). This mooring, denoted J1, was deployed in conjunction with the three MMS moorings. The array of moorings was deployed in August 1999 and J1 was retrieved in August 2000 after one rotation in January 2000. The three MMS moorings were redeployed and after a further rotation in February 2001, finally retrieved in September 2001. The last six months of the I1, I2 and I3 deployments were supplemented additional measurements. BP funded another deep mooring, named I4, on the middle part of the escarpment, just west of I2. Further, three Inverted Echo Sounders, equipped with precision bottom pressure sensors (known as PIES), were deployed at positions equidistant from the main mooring I1. These positions are denoted K1, K2 and K3. These latter were deployed to test the ability of PIES to measure temperature and salinity depth profiles, and through the geostrophic equations combined with bottom currents, absolute velocity profiles in the Gulf of Mexico. The gravest empirical mode (GEM) method is used to convert travel time between the bottom mounted PIES and the surface, and back, to salinity, temperature and density profiles (Tracey and Watts, 19xx). Such derived profiles can be compared to the time series measured at I1. Successful use of PIES would allow economical mapping of low-frequency current, salinity and temperature profiles over larger regions of the deep Gulf of Mexico than might be possible using conventional current meter moorings. PIES have been used successfully, for this purpose, in many regions of the world’s oceans (bunch of references). This report discusses the measurements made at all moorings and PIES over the two-year period. A discussion of the first six months of current measurements is given in Hamilton and Lugo-Fernandez (2001). The first year of bottom currents at I1, I2, I3 and J1 were also analyzed in a report to BP by Hamilton (2000). Observations of the water column over the deeper portions in the Gulf of Mexico basin indicate that there is a basic two-layer structure. Above ~800 to 1200-m depth, the circulation is dominated by the Loop Current (LC) in the east, anticyclonic rings shed from the Loop Current in the central and western basin, and smaller-scale cyclones and anticyclones that are probably generated by the LC rings. This upper layer has vigorous flows that result from eddies, and interactions between eddies. These flows often have strong vertical shears (Kirwan et al., 1984; Elliott, 1982; Hamilton, 1992). Below ~1000 m, eastern Gulf measurements have shown that currents are nearly depth- independent with a tendency for bottom intensification. These lower-layer flows do not appear to have a strong relationship to simultaneous current fluctuations in the upper layer. Hamilton (1990) suggested that these deep motions may result from topographic Rossby waves (TRW) propagating westward across the slope and rise of the basin. Similar kinds of deep motions have been extensively studied in the Mid-Atlantic Bight where there is evidence that they are generated by meanders of the Gulf Stream (Hogg, 1981; Pickart, 1995). In the Gulf, it seems plausible that deep TRW's are generated by Loop Current fluctuations, Loop Current eddy (LCE) shedding events, and the propagation of LCE's across the Gulf. The latter could include the interaction of LCE's with topography and other eddies in the basin. However, the generation mechanisms of TRW's are not presently well understood. Previous analyses of deep current data, from the BP Atwater 618 block (Hamilton, 1998) and the MMS moorings (Hamilton, 2000; Hamilton and Lugo-Fernandez, 2001) were also interpreted in terms of TRW's. However, current magnitudes were exceptional (~ 50 cm/s) and the periods were short (~ 10 days) compared to other regions of the central and western Gulf. There was no obvious source for such short period TRW's. The single extent mooring that made measurements under the LC showed almost no energy at periods shorter than about 15 days (Hamilton, 1990). It was speculated that LC/LCE frontal eddies had space and time scales that matched the observed high-frequency TRW's and therefore could be a source (see Pickart, 1995). In a recent paper, Hogg (2000) has also observed energetic, short period TRW's on the western flanks of the Grand Banks in the North Atlantic. He attributed these TRW's to transient behavior of the Gulf Stream as it passes over the tail of the Grand Banks, though direct evidence of this mechanism was lacking. The analogy with the LC extending over the Mississippi fan is striking, and thus, similar phenomena may be responsible for both the Gulf and North Atlantic TRW motions.