Paleoceanographic changes during the past one million years in the Central Basin, northwestern Ross Sea

Abstract

The Central Basin is located in the northwestern Ross Sea continental slope and rise. A 11.75 m-long core RS15-LC42 was collected from the southwestern part of the Central Basin (71° 49 S, 178°35.E, 2084 m deep) by the Korean RVIB Araon in 2015. The chronology is established based on paleomagnetism and diatom biostratigraphy. This core covers about 1.3 million years. Ohneize et al. (2019) reported Brunhes-Matuyama reversal (0.78 Ma) at 8.26 mbsf of this core, and according to paleo-intensity records the sedimentation is almost continuous although there is a hiatus near 9.54 mbsf. LC42 core is composed of two distinct sedimentary facies: 1) well-laminated greenish gray diatom-rich silty mud, and 2) massive/bioturbated light gray sandy mud. Well-laminated fac include high content of TOC, opal and carbonate with no IRD (clasts > 2 mm), while massive/bioturbated sandy mud facies show hi MS value and bear clasts IRDs. The laminated silty mud facies has abundance in illite while smectite and kaolinite is relatively rich i sandy mud facies. The chlorite content does not change as a whole. The difference in clay mineral composition between two facies indicates that two facies originated from different sources. The diatom assemblage in LC42 include reworking indicator species (early-Pliocene and Miocene taxa), and the tendency of reworking is evident in the lower part of the boundary between 2.8 and 3.2 mbsf. This result suggest that there was a significant shift in the oceanographic regime in this region around 0.3 Ma.