ALBERT

Description: Geochemical and Sr-Nd-Pb isotopic compositions of the detrital sediments from ODP Hole 1202B and Taiwan rivers were measured in this study, aiming to reveal changes in sediment provenance in the southern Okinawa Trough (SOT) since 28 ka, and to examine the weathering and sediment transport processes in response to monsoon climate variability. Large variations in Sr-Nd-Pb isotopic ratios at 11?9 ka suggest changes in detrital sediment provenance in the SOT from a dominance of the paleo-Changjiang (Yangtze River) and/or continental shelf sediment during the late deglaciation and to west Taiwan rivers since 9.5 ka. Volcanic rocks and eastern Taiwan sediments have not significantly contributed to the SOT. The large shift in sediment provenance during the early Holocene marks a major change in oceanic circulation, mainly caused by the intrusion of the Kuroshio Current into the trough. Clay mineral and geochemical proxies suggest that the Taiwan-derived sediments accumulated during the early-mid ?Holocene climate optimum? (ca. 9.5-4 ka) might be tightly related to the reworking of older altered sediments from terraces and floodplains, rather than having experienced more intense silicate weathering than in the late Holocene (~ 4-0 ka). Overall, silicate weathering in Taiwan was greatly inhibited by accelerating sediment production and transfer from land to ocean caused by monsoon intensification in Holocene. Our study illustrates that the radiogenic isotopic and geochemical compositions of fine-grained detrital sediments are sensitive tools for fingerprinting sediment sources and for reconstructing changes in oceanic currents and monsoon climate in river-dominated East Asian continental margin.

Description: Arctic and subarctic regions are sensitive to climate change and, reversely, provide dramatic feedbacks to the global climate. With a focus on discovering paleoclimate and paleoceanographic evolution in the Arctic and Northwest Pacific Oceans during the last 20,000 years, we proposed this German–Sino cooperation program according to the announcement “Federal Ministry of Education and Research (BMBF) of the Federal Republic of Germany for a German–Sino cooperation program in the marine and polar research”. Our proposed program integrates the advantages of the Arctic and Subarctic marine sediment studies in AWI (Alfred Wegener Institute) and FIO (First Institute of Oceanography). For the first time, the collection of sediment cores can cover all climatological key regions in the Arctic and Northwest Pacific Oceans. Furthermore, the climate modeling work at AWI enables a “Data-Model Syntheses”, which are crucial for exploring the underlying mechanisms of observed changes in proxy records.

Description: Quaternary East Asian winter monsoon (EAWM) evolution has long been attributed to high‐latitude Northern Hemisphere climate change. However, it cannot explain the distinct relationships of the EAWM in the northern and southern East Asian marginal sea in paleoclimatic records. Here we present an EAWM record of the northern East China Sea over the past 300 ka and a transient climate simulation with the Kiel Climate Model through the Holocene. Both proxy record and simulation suggest anticorrelated long‐term EAWM evolution between the northern East China Sea and the South China Sea. We suggest that this spatial discrepancy of EAWM can be interpreted as El Niño–Southern Oscillation (ENSO)‐like controlling, which generates cyclonic/anticyclonic wind anomalies in the northern/southern East Asian marginal sea. This research explains much of the controversy in nonorbital scale variability of Quaternary EAWM records in the East Asian marginal sea and supports a potent role of tropical forcing in East Asian winter climate change.

Description: The Pacific hosts the largest oxygen minimum zones (OMZ) in the world ocean, likely to intensify and expand under future climate warming, with consequences for ecosystems, biogeochemical cycles and living resources. Today, better-oxygenated subsurface North Pacific Intermediate Water mitigates OMZ development, but on instrumental time scales, data indicate decreasing NPIW ventilation, induced by surface freshening and increased stratification of seasonal thermocline water. However, longer variations in oceanographic boundary conditions were potentially large and hinder assessment of anthropogenic influences against natural background shifts. We previously provided evidence that modern well-ventilated waters underwent significant millennial-scale variations over the last ca. 12 ka, with a tipping point ca. 4.5 ka before present. Crossing this mid-Holocene threshold led to the Okhotsk Sea losing its modern ventilation source characteristics, although underlying forcing and physical boundary conditions remain largely enigmatic. A combination of sea ice loss, water temperatures, and remineralization rates may have conceivably induced a nonlinear switch into a different mean state in this region. To constrain these factors, we present surface ocean proxy records from Okhotsk Sea key study sites with multi-decadal resolution to assess changes in upper ocean stratification, nutrient characteristics and resulting mid-depth water ventilation. Our results imply that under assumed past warmer- than-present conditions, regional surface temperatures and upper ocean stratification were increased and changed in a nonlinear mode during the last ca. 6,000 years, associated with changing primary productivity patterns and biogeochemical feedback mechanisms. Complementary results from model simulations corroborate our results and provide evidence for close coupling the Okhotsk Sea and the North Pacific Subarctic Gyre, thus exporting marginal sea signals into large oceanic regions.

Description: Strength of Southern Ocean upwelling controls the exchange of carbon dioxide (CO2) between deep ocean reservoirs and atmosphere, as well as the communication of dissolved silicon with the euphotic zone of the Southern Ocean. The silicon supply could limit diatom opal productivity in the high-latitudes of Southern Ocean and the subsequent burial of biogenic opal in underlying sediments. Here we report a record of biogenic opal export off the Prydz Bay south of the polar front of the Southern Ocean, indicating strengthened upwelling during the past five glacial terminations. In all five terminations (Isingle bondV), opal peaks occur in line with Northern Hemisphere summer insolation intensity as well as the existing IRDs, indicating that freshwater injection associated with retreat of the Northern Hemisphere ice sheets could be the cause of enhanced upwelling in the Southern Ocean during terminations. This could in turn promote CO2 outgassing, finally accelerating the completion of the terminations. In addition, the enhanced upwelling could export the Si-rich deep water to low latitudes via Antarctic Intermediate Water (AAIW) and Subantarctic Mode Water (SAMW), potentially leading to deglacial opal peaks in subtropical North Atlantic.

Description: In this study, we investigate light and heavy minerals in sediment core OS03-1 located at the Academy of Sciences Rise of the southern Okhotsk Sea to determine their distributions and sources over the last 180 ka (thousand years). The sediment mainly consists of terrigenous and volcanic detritus. Ubiquitous drop-stones and volcanic detritus throughout the core and high detrital input suggest that sea ice, driven by wind and Kamchatka Current, was the main transport agent of detrital materials to the southern Okhotsk Sea. The ternary diagram of heavy minerals (hornblende-hypersthene-epidote) shows an expansion of detritus provenance from the eastern in cold periods to the northeastern in warm intervals of the Okhotsk Sea. It mainly relates to the shift of Aleutian Low. Combined with previous records, accumulation rates of quartz indicated a maximum extent but not perennial sea ice coverage during the glacial periods.