HR: 1340h
AN: PP43B-0674    [Abstracts]
TI: Alkenone-SST and Nitrogen Isotope Records in the Three Piston Cores in the Eastern Equatorial Pacific During the Past 150 ky
AU: * Horikawa, K
EM: horikawa@ees.hokudai.ac.jp
AF: Graduate School of Environmental Earth Science, Hokkaido University, N10W5, Kita-ku, Sapporo, Hokkaido, 060-0810 Japan
AU: Murayama, M
EM: murayama@cc.kochi-u.ac.jp
AF: Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku city, Kochi, 783-8502 Japan
AU: Asahi, H
EM: hiroasa@cc.kochi-u.ac.jp
AF: Center for Advanced Marine Core Research, Kochi University, B200 Monobe, Nankoku city, Kochi, 783-8502 Japan
AU: Kato, Y
EM: ykato@scc.u-tokai.ac.jp
AF: School of Marine Science and Technology, Tokai University, Orito 3-20-1, Shimizu-ku, Shizuoka city, Shizu, 424-8610 Japan
AU: Minagawa, M
EM: mas@ees.hokudai.ac.jp
AF: Graduate School of Environmental Earth Science, Hokkaido University, N10W5, Kita-ku, Sapporo, Hokkaido, 060-0810 Japan
AB: We collected three piston cores on a south-north transect crossing the equator in the eastern equatorial Pacific (EEP) to reconstruct paleoceanographic environments (e.g., SST, nutrient state, productivity, etc) in the EEP. We have generated organic carbon and bulk nitrogen stable isotopic compositions and alkenone-derived SST records at HY04, HY06, and HY08B sites during the last 150 k.y. The SST at the HY04 site (4 01'N, 95 03'W, 3563m water depth) was lowest (25.8 degrees) at 25ka and highest (27.2 degrees) at 127ka, documenting a small SST variation (~1.4 degrees) over the last glacial-interglacial cycle (G-IG cycle). On the other hand, HY06 core, located at the equator (0 01'N, 95 26'W, 3242m), was lowest (22.4 degrees) at ~30ka and highest (26.1 degrees) at 125ka, with a SST amplitude in ~3.7 degrees during the last G-IG cycle. HY08 core (5 57'S, 94 55'W, 3867m) shows a range from 25.6 to 23.8 degrees over the past 30 k.y. Assuming the alkenone-SSTs in the EEP reflect a mean annual SST, the SSTs comparison among the three sites at the LGM showed the HY06 SST was lower compared to those of HY04 and HY08. Therefore, we interpret that the ITCZ shifted towards the equator (away from its current position in the northern hemisphere) and thereby the HY06 site was influenced by equatorial divergence upwelling at the time. Nitrogen isotopic compositions of HY04 core varied from 9 to 12 per mil, and the amplitude and timing of d15N variations were very similar to that of the Mexican margin in the Eastern Tropical North Pacific (ETNP). These findings indicate that thermocline nitrate originated from the ETNP have been advected and brought into the euphotic zone, and then almost utilized by phytoplankton at the HY04 site. Furthermore, because denitrification in the ETNP causes a significant loss of nitrate from the ocean during warm periods, the HY04 site would also incur decreases in nitrate that phytoplankton utilizes. Indeed, alkenone concentrations at warm periods were significantly decreased less than half that of cold periods. On the other hand, d15N at the HY06 site were different from that of HY04, which are characterized by the increase-decrease pattern during Termination II (5.2-7 per mil) and the long-term increase from MIS3 to the present (4.8-8.2 per mil), possibly reflecting changes in both nitrate substrate value and relative nitrate utilization at the HY06.
DE: 4845 Nutrients and nutrient cycling (0470, 1050)
DE: 4954 Sea surface temperature
SC: Paleoceanography and Paleoclimatology [PP]
MN: Fall Meeting 2005