CAROLINA SLOPE HOLE 1054B

At ~1300 m water depth, Site 1054 is at the shallow end-member of the Leg 172 depth transect. This site was defined in part by KNR140 giant gravity core (GGC)-56, which is ~4 miles to the south and 100 m deeper (32°56.339´N, 76°17.738´W; 1400 m). GGC-56 has maximum ¹⁸O of Globigerinoides sacculifera (150-250 mm) in the 450-500 cm range (Fig. F1). However, these results (~0 PDB) are ~0.5 lower than the LGM value at deeper site survey cores, and the mud has no reddish color.

Based on core descriptions, I estimated where the equivalent level would be at Hole 1054B. At this site I analyzed Globigerinoides ruber (white; 150-250 µm), which has the same ¹⁸O as G. sacculifera in many of my site survey cores. At Site 1054, the maximum ¹⁸O is reached at about the same depth downcore as GGC-56, and the value is likewise ~0 (Fig. F1). Below ~530 cm, the ¹⁸O decreases rapidly, suggesting by comparison to GGC-51 (Fig. F2) that this represents the LGM level and that it is a short condensed interval on the Carolina Slope. Oxygen isotope analyses on individual Cibicidoides pachyderma and Cibicidoides wuellerstorfi at Hole 1054B suggest an abrupt increase from deglacial results of ~3 to ~4 (excluding the lowest ¹⁸O result, which might reflect downslope transport of some interglacial foraminifers). The maximum ¹⁸O in benthic and planktonic ¹⁸O also supports the notion that the LGM is ~500 cm in this core. If this interpretation is supported by future ¹⁴C dating, then the lower planktonic ¹⁸O at the shallowest and most shoreward of Leg 172 sites could result from higher sea surface temperature (SST). This makes sense because surface waters at Site 1054 are close to the core of the Gulf Stream. The lack of red sediment during the LGM or other levels at these shallow locations (Fig. F2) may indicate that the shallowest components of the deep western boundary current were deeper than ~1400 m during the LGM.