PP53C-2367
Millennial-scale Changes of Surface and Bottom Water Conditions in the Northwest Pacific during the Last Deglacial Period
Friday, 18 December 2015
Poster Hall (Moscone South)
Sunghan Kim1, Boo-Keun Khim1, Ken Ikehara2, Takuya Itaki3, Akihiko Shibahara4 and Masanobu Yamamoto5, (1)Pusan National University, Busan, South Korea, (2)Marine Geology Research Group, Geological Survey of Japan, AIST, Tsukuba, Japan, (3)Geological Survey of Japan, AIST, Tsukuba, Japan, (4)Geological museum office, AIST, Tsukuba, Japan, (5)Faculty of Environmental Earth Science, Hokkaido University, Sapporo, Japan
Abstract:
The last deglacial changes of the water column conditions in the Northwest Pacific were reconstructed using geochemical and isotope proxies (biogenic opal, CaCO3, total organic carbon (TOC), redox sensitive elements, bulk nitrogen isotopes (δ15N), and silicon isotopes (δ30Sidiatom) of diatom frustules) along with the published data (alkenone temperatures and benthic foraminiferal faunas) at core GH02-1030 recovered from the slope off Tokachi. Age model for core GH02-1030 was determined using both planktonic and benthic foraminiferal AMC 14C dates (Ikehara et al., 2006). Alkenone sea surface temperature (SST) shows that biogenic opal productivity was related to the degree of spring-summer mixed layer depth (MLD). Biogenic opal and TOC contents change almost in parallel. δ30Sidiatom values are high (~+1‰) during the Holocene and low (~-0.4‰) during the last glacial maximum. During the Bølling-Allerød (BA) and the Pre-Boreal (PB), silicic acid utilization represented by δ30Sidiatom increased when the biogenic opal productivity and export TOC productivity are high under shoaling of spring-summer MLD. The BA and the PB intervals contain laminated sediment layers, which are characterized by increases of CaCO3 contents, bulk δ15N values, and redox element concentrations (Mo/Al, Cd/Al, and U/Al). All these indicate low dissolved oxygen content of the bottom water during the BA and PB periods, which is supported by the good preservation of dysoxic benthic foraminifera. In addition, compared to the Holocene biogenic opal productivity and related silicic acid utilization, the high δ15N values during the BA and the PB seemed to be attributed more to denitrification through the water column rather than complete utilization of nitrate. Another distinct feature based on benthic foraminiferal assemblage, CaCO3 contents and redox element concentrations is that the dissolved oxygen content in bottom water was lower during the BA than the PB. Because biogenic opal productivity remained comparable during both periods, it implies that intermediate water ventilation was relatively stronger during the PB, which may be related to reopening of the Bering Strait.
References
Ikehara, K., K. Ohkushi, A. Shibahara, and M. Hoshiba (2006), Global Planet. Change 53, 78–91.
