Except for the profile from Site 1050, pore-water strontium concentration increases linearly with depth (Table T1; Fig. F2A). However, the rate of the strontium concentration increase varies with depth along the Leg 171B transect (Fig. F1). Site 1049 shows the smallest increase with depth (from 7.2 to 8.4 ppm). The maximum measured concentration (~146 ppm) was at Site 1052, the site farthest away from the platform edge. In general, the strontium concentration gradient increases as the distance from the platform edge increases. At Site 1050 strontium concentration increases approximately linearly to a subsurface maximum at 386 meters below seafloor (mbsf). Below this level the concentration profile decreases slightly.
87Sr/86Sr values decrease with depth at all Sites (Table T1; Fig. F3). In the shallowest samples the 87Sr/86Sr values are slightly less than our measurements of modern seawater (0.709175; Paull et al., 1995).
The depth profiles define a simple convex upward curvature in the three deeper holes (Sites 1050, 1051, and 1052). Strontium isotope values at these sites become nearly asymptotic to constant strontium isotopic values (Fig. F3). The profiles from Sites 1050 and 1051 are similar and both converge to basal 87Sr/86Sr values of 0.707775. The profile at Site 1052, which is farthest from the escarpment edge, converges on a slightly different basal value of 0.707400.
The isotope profile from Site 1049, nearest to the escarpment edge, is nearly linear and the values change less rapidly with depth compared to the other four sites. Drilling penetrated to only 183.3 mbsf at Site 1053, but the data from this site closely correspond with those from the upper portion of the adjacent Site 1052.
The strontium isotopic
composition of acid-leached sediment squeeze cakes from Site 1050 (Table T1;
Fig. F3) correspond
closely with the strontium isotopic composition predicted using biostratigraphy
and the strontium seawater curve of Howarth and McArthur (1997). Figure F3
shows that 15 out of 25 predicted strontium isotopic compositions fall within 2 
of the measured value (typically 0.000018), and no predicted 87Sr/86Sr
value differed by more than 0.000094 (<7
of measurement at 502.72 mbsf). The differences between predicted and measured
strontium isotopic values are not only the result of analytical errors but
include the more subjective determination of biostratigraphic age.
