Abstract:
Site 1090 was drilled during Leg 177 and is located in the Subantarctic Zone, north of the present-day Antarctic Polar Front. One goal of ODP Leg 177 (Southern Ocean Paleoceanography) is to determine the effect of the onset of Antarctic glaciation during the Eocene and full continental glaciation during the early Oligocene. This study of Eocene and Oligocene sediments, from a core depth of 215 360 meters below sea floor (32-39 Ma) will address the correlations between phosphorus (P), a nutrient element, and metals during these time intervals. At this site, the Eocene-Oligocene boundary has been placed around 225 mbsf. Sediment was digested using a microwave digestion system and a combination of trace-metal grade HNO (sub 3) , HF, and HCl. Total elemental concentrations for P, Fe, Al, Ti, Mn, Zn, Sr, Ca, and Mg were determined using ICP-AES. Data reveals a strong coupling between P and metals such as Fe and Ti (r>0.74, n = 86). Further, maximum P and metal concentrations appear to correspond to minimum Ca concentrations. Source ratios based on Fe, Al, and Ti are similar to those found at other Southern Ocean sites. Al/Ti (g/g) ratios are low (<12); however, the ratio fluctuates between intervals of higher values (8-12) and lower values (1-5), possibly suggesting changes in terrigenous sources. Fe/Ti (g/g) ratios are extremely constant (average Fe/Ti = 7.0), suggesting Fe and Ti have the same source. Fe/Al and P/Al downcore ratios are almost identical. The ratios are constant and similar to those observed at other Southern Ocean sites, except that intervals of high Fe/Al and P/Al ratios are present. For example, at 245-246 mbsf, the Fe/Al (g/g) ratio jumps from 1 (near crustal) to 18 and the P/Al (g/g) ratios jumps from 0.02 to 0.65. Elevated P/Al ratios suggest higher organic matter deposition or preservation occurred at these time intervals which correspond to intervals of increased Fe input.