18O
amplitude changes are possibly underestimated here.The aragonite content
record (in wt%) shows regular cycles that follow the oxygen isotope pattern (Fig.
2, Fig. 3). This trend in the
Bahamian area has been previously described in Droxler et al. (1983, 1988) and
Reijmer et al. (1988). During sea-level highstands, the platform sheds
fine-grained material into a basin consisting mainly of the metastable mineral
aragonite. Site 1006 was drilled on the leeward side of the Great Bahama Bank in
658 m of water, well above the depth of dissolution of aragonite (Droxler et
al., 1991). Thus the aragonite content curve can be interpreted as the sole
result of aragonite input (Boardman and Neumann, 1984). Maximum input of
aragonite occurs consistently during the sea-level highstands. The carbonate
fraction is clearly dominated by aragonite during interglacial periods (up to 85
wt%), while LMC and HMC prevail during glacial periods at 41 and 5 wt%,
respectively (Rendle et al., Chap.
6, this volume). However, platform delivery was not entirely switched
off during the lowstands, resulting in increased total sediment input during the
highstands compared to the lowstands. Therefore, our sample density in the
glacial intervals is low (normal pelagic sedimentation vs. elevated rates by
platform input during interglacial periods); this explains the spikiness in the
oxygen isotope and aragonite content records, and indicates that the true
glacial-interglacial 18O
amplitude changes are possibly underestimated here.
The fact that aragonite fluctuations at Site 1006 are entirely controlled by input from the platform and not by dissolution on the seafloor, coupled with the record's completeness, makes this site ideal for use as a standard site in studying dissolution patterns at other deeper sites. However, that is beyond the scope of this paper. Rendle et al. (Chap. 6, this volume) use Site 1006 as the most distal site of the Leg 166 transect to study the sedimentation patterns along the flank of the Great Bahama Bank.
