Shipboard calcareous nannofossil datums (Table T1) were used to develop the preliminary biostratigraphically based age model (Fig. F3A). The BIO age model (Fig. F3A) was developed by applying a linear sedimentation rate between calcareous nannofossil datums to the composite Site 1085 MS core data (Fig. F2). Planktonic foraminifer biostratigraphic datums were not used to constrain the ages for this interval mainly because the biostratigraphic resolution of the calcareous nannofossil group is superior in this interval to that of the planktonic foraminifers (see Wefer, Berger, Richter, et al., 1998, for further discussion). One major drop in sedimentation rate is identified using the BIO model at ~103 meters composite depth (mcd) (~93 mbsf, between 2250 and 1950 ka) (Fig. F4). It is associated with a dark greenish gray unit in Hole 1085A (interval 175-1085A-11H-2, 48-100 cm) that maintains a sharp upper contact (91 mbsf) and a gradational lower contact with the light greenish gray unit that dominates this interval (Wefer, Berger, Richter, et al., 1998). The surface at ~103 mcd may be unconformable and, in this model, represents ~200 k.y. of missing time.
When the BIO model is compared to the eccentricity record (Fig. F3B), an ~100-k.y. peak is apparent, although spectral analysis documents that the power spectrum is shifted according to that of the eccentricity (Fig. F5A). The spectral variance of both the BIO age model (Table T3) and the eccentricity record for this interval (5.5-2 Ma) (Fig. F5A) are offset such that the 96- and 128-k.y. eccentricity peaks are centered at 77 and 88 k.y. in the BIO model, and the broad 407-k.y. peak in eccentricity is centered at 291 k.y. in the BIO model (Fig. F5A; Table T3). There is little spectral variance at periods <100 k.y. (Fig. F5A). The similarity in shape of the two curves suggests a strong relationship exists between MS and eccentricity, but tuning is required to confirm it.