Variability of the intensity of the Tsushima Warm Current and bottom water ventilation in western North Pacific marginal seas during the Pleistocene: preliminary results from IODP Expedition 346 (Sites U1427 and U1428) based on ostracod assemblages

Blue posters: no. EGU2015-14259IODP Expedition 346 drilled Sites U1427 and U1428 in ideal locations to monitor changes in (i) the intensity of the influx of the Tsushima Warm Current (TWC), and (ii) the intermediate bottom water ventilation from a few hundred thousand years to over a million years in the western North Pacific marginal seas. Site U1427 is located at 330 m water depth in the marginal sea bordered by the Eurasian continent, the Korean peninsula and the Japanese Islands. This semi-enclosed marginal sea has an average water depth of 1350 m and is connected with other marginal seas in the region by shallow, narrow straits. Site U1428 is located at 724 m in the East China Sea and this region is more influenced by continental freshwater runoff derived from the Yangtze River. Both sites are in the path of the TWC, a branch of the Kuroshio Current, the only warm current flowing into …published_or_final_versio

The abrupt onset of the modern South Asian Monsoon winds

The South Asian Monson (SAM) is one of the most intense climatic elements yet its initiation and variations are not well established. Dating the deposits of SAM wind-driven currents in IODP cores from the Maldives yields an age of 12. 9 Ma indicating an abrupt SAM onset, over a short period of 300 kyrs. This coincided with the Indian Ocean Oxygen Minimum Zone expansion as revealed by geochemical tracers and the onset of upwelling reflected by the sediment's content of particulate organic matter. A weaker 'proto-monsoon' existed between 12.9 and 25 Ma, as mirrored by the sedimentary signature of dust influx. Abrupt SAM initiation favors a strong influence of climate in addition to the tectonic control, and we propose that the post Miocene Climate Optimum cooling, together with increased continentalization and establishment of the bipolar ocean circulation, i.e. the beginning of the modern world, shifted the monsoon over a threshold towards the modern system

A two million year record of low-latitude aridity linked to continental weathering from the Maldives

Indian-Asian monsoon has oscillated between warm/wet interglacial periods and cool/dry glacial periods with periodicities closely linked to variations in Earth’s orbital parameters. However, processes that control wet versus dry, i.e. aridity cyclical periods on the orbital time-scale in the low latitudes of the Indian-Asian continent remain poorly understood because records over millions of years are scarce. The sedimentary record from International Ocean Discovery Program (IODP) Expedition 359 provides a well-preserved, high-resolution, continuous archive of lithogenic input from the Maldives reflecting on low-latitude aridity cycles. Variability within the lithogenic component of sedimentary deposits of the Maldives results from changes in monsoon-controlled sedimentary sources. Here, we present X-ray fluorescence (XRF) core-scanning results from IODP Site U1467 for the past two million years, allowing full investigation of orbital periodicities. We specifically use the Fe/K as a terrestrial climate proxy reflecting on wet versus dry conditions in the source areas of the Indian-Asian landmass, or from further afield. The Fe/K record shows orbitally forced cycles reflecting on changes in the relative importance of aeolian (stronger winter monsoon) during glacial periods versus fluvial supply (stronger summer monsoon) during interglacial periods. For our chronology, we tuned the Fe/K cycles to precessional insolation changes, linking Fe/K maxima/minima to insolation minima/maxima with zero phase lag. Wavelet and spectral analyses of the Fe/K record show increased dominance of the 100 kyr cycles after the Mid Pleistocene Transition (MPT) at 1.25 Ma in tandem with the global ice volume benthic δ 18 O data (LR04 record). In contrast to the LR04 record, the Fe/K profile resolves 100-kyr-like cycles around the 130 kyr frequency band in the interval from 1.25 to 2 million years. These 100-kyr-like cycles likely form by bundling of two or three obliquity cycles, indicating that low-latitude Indian-Asian climate variability reflects on increased tilt sensitivity to regional eccentricity insolation changes (pacing tilt cycles) prior to the MPT. The implication of appearance of the 100 kyr cycles in the LR04 and the Fe/K records since the MPT suggests strengthening of a climate link between the low and high latitudes during this period of climate transition. The Correction to this article has been published in Progress in Earth and Planetary Science 2019 6:21 - https://doi.org/10.1186/s40645-019-0259-

Benthic Biotic Response to Climate Changes over the Last 700,000 Years, the Sea of Japan: Ostracode Assemblages from Site U1427, IODP Expedition 346

Session: Paleoceanography and Paleoclimatology :PP41E Paleoclimate Variability in the Indo-Pacific Region I - no. PP41E-05The Sea of Japan is a marginal sea, semi-enclosed by the Eurasian Continent, Korean Peninsula, Japanese Islands, and shallow straits (water depth < 130 m). Marginal seas are ideal natural laboratories to study biotic responses to large-scale paleoclimate-ocean mechanisms as they are typically sensitive to glacial/interglacial and stadial/interstadial cycles. The modern oceanographic setting in the Sea of Japan is characterized by the influx of the Tsushima Warm Current (TWC) from the East China Sea, and this setting was formed ~1.7 My ago by tectonic subsidence of the Tsushima Strait. The Sea of Japan, therefore, is an interesting research subject for studying the biotic response to orbital-scale climate changes and benthic faunal development under the influence of TWC. Here we present 700,000-year record of benthic biotic response to the paleoceanographic changes in the southern Sea of Japan based on ostracode assemblage reconstruction at IODP Site U1427. Five local extinction events were caused by extreme bottom conditions (mainly oxygen depletion) during the Ice Age Terminations I, II, IV, V, and VII. Primary and secondary ostracode assemblages were revealed by Q-mode k-means clustering, CABFAC factor analysis, and non-metric multidimensional scaling. The primary ostracode components, characterized by Krithe sawanensis and Cytheropteron hyalinosa, broadly reflect glacial/interglacial and high-latitude insolation cycles. In contrast, a faunal shift determined by the secondary faunal components was driven by the TWC enhancement at ~300 ka

Variability of the Tsushima Warm Current during the Pleistocene and its relationship with the evolution of the East Asian Monsoon. Preliminary results from IODP Expedition 346 (Sites U1427 and U1428/29) based on benthic ostracod assemblages

Abstract no. PP43D-1514The semi-enclosed marginal sea bordered by the Eurasian continent, the Korean peninsula and the Japanese Islands has an average depth of 1350 m and is connected with other marginal seas in the region by shallow and narrow straits. At present, the Tsushima Warm Current (TWC), a branch of the Kuroshio Current, is the only warm current flowing into the marginal sea west of Japan. The TWC carries both subtropical water originating from the North Pacific and fresher runoff water derived from East China Sea continental shelf. The northerly flow of the TWC through the shallow Tsushima Straits is ultimately controlled by relative sea level variations over time. IODP Expedition 346 Sites U1427 and U1428/29 are ideally located to record changes in (i) the intensity of the influx of the TWC, and (ii) the intermediate ventilation of the marginal sea over the last million years. The Japan Sea Intermediate Water (JSIW) corresponds to a vertical salinity minimum, found below the TWC, between 200 and 400-500 m water depth. The JSIW shows a relatively high oxygen concentration, related to the deep water convection in winter and linked to fresh water supply during winter monsoon intervals. Based on recent observations, it is thought during glacial and interglacial conditions, and millennial scale climate cycles the intensity of deep and intermediate water currents varied but the mechanisms of such variations are not fully known. Microfossil faunal proxies can be used for tracking bottom environmental conditions related to variability of the bottom water circulation intensity. Here, we present preliminary results obtained using ostracods (benthic microcrustaceans) that are abundant in the sedimentary sequences recovered at Sites U1427 and U1428/29, and are known to react sensitively to changes in water masses physico-chemical parameters. In particular, the variability of the genus Krithe through time is correlated with the sortable silt (carbonate-free, 10-63 µm sediment size distribution) to infer current speed and bottom water ventilation

Glacial/Interglacial variability of deep-sea benthic fauna in the Japan/East Sea over the last 1 million years: ostracode fossil assemblages from the Site U1427, IODP-Expedition 346

Poster session 4: System Dynamics and Ocean-Ice-Continent Interactions: poster no. P-49

The 'Shackleton Site' (IODP Site U1385) on the Iberian Margin

Nick Shackleton’s research on piston cores from the Iberian margin highlighted the importance of this region for providing high-fidelity records of millennial-scale climate variability, and for correlating climate events from the marine environment to polar ice cores and European terrestrial sequences. During the Integrated Ocean Drilling Program (IODP) Expedition 339, we sought to extend the Iberian margin sediment record by drilling with the D/V JOIDES Resolution. Five holes were cored at Site U1385 using the advanced piston corer (APC) system to a maximum depth of ∼ 155.9 m below sea floor (m b.s.f.). Immediately after the expedition, cores from all holes were analyzed by core scanning X-ray fluorescence (XRF) at 1 cm spatial resolution. Ca/Ti data were used to accurately correlate from hole-to-hole and construct a composite spliced section, containing no gaps or disturbed intervals to 166.5 m composite depth (mcd). A low-resolution (20 cm sample spacing) oxygen isotope record confirms that Site U1385 contains a continuous record of hemipelagic sedimentation from the Holocene to 1.43 Ma (Marine Isotope Stage 46). The sediment profile at Site U1385 extends across the middle Pleistocene transition (MPT) with sedimentation rates averaging ∼ 10 cm kyr−1. Strongprecession cycles in colour and elemental XRF signals provide a powerful tool for developing an orbitally tuned reference timescale. Site U1385 is likely to become an important type section for marine–ice–terrestrial core correlations and the study of orbital- and millennial-scale climate variability