BERMUDA RISE HOLE 1063D

The Bermuda Rise has long been known as a repository of red-colored sediment transported from eastern Canada and as a location where sediment accumulates rapidly enough to resolve surprisingly brief climate events (on the order of centuries to millennia). During shipboard core description, it was noted that the generally dark sediment comprising isotope Stage 6 contained some red layers, and that Stage 6 was well-enough recovered that sampling restrictions could be relaxed. Accordingly, I sampled two intervals continually across the working half of Hole 1063D in the depth ranges of 35.50 to 35.88 mbsf and 38.70 to 40.56 mbsf. These large samples (~35-40 g dry) were sufficient to yield enough G. ruber for stable isotopes (Fig. F5), but benthic foraminifers were too rare and too small to generate a useful stable isotope series. Visual core description identified red intervals between 35.54 mbsf (38.08 mcd)-35.70 mbsf (38.24 mcd) and 38.82 mbsf (41.36 mcd)-38.90 mbsf (41.44 mcd). These intervals do have maximum ¹⁸O, suggesting lower SST, but shipboard spectral reflectance data identify many more red intervals in Stage 6, and there are many maxima in ¹⁸O (Fig. F5). In general, the isotopic maxima coincide with the redder sediment.

Figure F6 shows the Hole 1063D isotopic results in time series with other published G. ruber data from the Bermuda Rise. Whereas GPC-5 data show the Stage 1-3 millennial scale SST variability discussed previously, on this age scale it is difficult to appreciate the Stage 6 variability from Hole 1063D because the samples are so closely spaced. Consider the following. The oldest continuous data, from ~150 ka, represent only ~5 k.y. of accumulation (Fig. F6), yet there are at least three cycles that are evident in Figure F5 between 41 and 43 mcd. Thus, these "cycles" may have a period of ~1500 yr, making them about twice as frequent as those in Stage 3. (An alternative interpretation would be that the age model is off by a factor of two, which seems unlikely.) The amplitude is ~1, as it is in Stage 3, suggesting 4°C SST oscillations, and the coincidence with sediment redness suggests that, as in Stage 3, there may be some connection between SST and deep circulation activity.