Leg 172 Scientific Report


Figure 1. Schematic of circulation patterns in the deep western North Atlantic (updated from Schmitz and McCartney [1993] by M.S. McCartney, pers. comm. to L. Keigwin, 1995). The thin lines represent streamlines of two recirculating gyres with approximate transport in Sverdrups (1 Sv = 106 m3/s). Thick lines represent generalized flow direction of AABW and NADW, which contribute to the Deep Western Boundary Current (DWBC). The stippled pattern marks the region marked by high surface eddy kinetic energy (EKE), deep EKE, and deep suspended sediment. Note that in this scheme the southern recirculating gyre, over the Bermuda Rise, is the mixing zone for northern and southern origin waters and that true "NADW" is formed in that mixing zone.

Figure 2. Map of the western North Atlantic Ocean showing the location of Leg 172 sites on the Carolina Slope (Sites 1054 and 1055), Blake-Bahama Outer Ridge (Sites 1056-1062), northeast Bermuda Rise (Site 1063), and the Sohm Abyssal Plain (Site 1064).

Figure 3. Schematic columnar logs and biomagnetostratigraphic correlations between Sites 1054 through 1063.

Figure 4. Position of Leg 172 sites with respect to water masses in the western subtropical North Atlantic. Water depths are indicated every 500 m along the temperature/salinity (T/S) plot. Sites were chosen so at least one lies within each modern water mass and one lies at the boundary between water masses. This depth distribution of sites is required to monitor the most likely changes in water masses and their boundaries through the late Neogene. U = upper; L = lower. KNORR 140/2 Hydro Sta. 1 refers to the site survey cruise and station number that were used to collect the data.

Figure 5. Comparison of inclination changes of the paleomagnetic field are shown for the Brunhes-Matuyama polarity transition at Sites 1060 and 1063.

Figure 6. Seismic image of mud waves at Site 1062, with sedimentation rate variation vs. depth plotted to the right. The position of the biostratigraphic datums shown in the sedimentation rate are plotted as hollow boxes on the seismic profile. Note how the relative distance between the seafloor and the positions of the datums change from one side of the mud wave to the other, reflecting sedimentation rate variations.

Figure 7. Susceptibility correlation between sites and with the marine oxygen isotopic record.

Figure 8. Seismic record collected by the JOIDES Resolution that shows the high amplitude (100 k.y. cycles?) overlying lower amplitude and more closely spaced reflectors of pre-mid-Pleistocene (40-k.y. cycles?).

Figure 9. Magnetostratigraphy of Site 1063.

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