Bathyal records of enhanced silicate erosion and weathering on the exposed Luzon shelf during glacial lowstands and their significance for atmospheric CO₂ sink

Xu, Zhaokai,Li, Tiegang,Clift, Peter D.,Wan, Shiming,Qiu, Xiaohua,Lim, Dhongil Elsevier 2018 Chemical geology Vol.476 No.-

<P><B>Abstract</B></P> <P>We present a new high-resolution multiproxy data set of mass accumulation rates, Sr-Nd isotopes, as well as major and trace elements for the siliciclastic sediment fraction from International Marine Global Change Study Core MD06-3052, located on the continental slope of the western Philippine Sea. We integrate our new data with published grain sizes and sea surface temperatures from the same core, as well as with Equatorial Pacific sea level, and East Asian summer monsoon precipitation, in order to constrain at high-resolution changes in physical erosion and chemical weathering intensities on Luzon, and sediment source-to-sink processes. We assess the potential significance of chemical weathering of arc silicates in regulating global atmospheric CO<SUB>2</SUB> since 156kyr BP. Sr-Nd isotopes show that the siliciclastic sediments were dominantly sourced from volcanic rocks exposed on Luzon (~68–100%), with a lesser contribution from Asian dust (~0–32%). Different indices indicate that stronger physical erosion and chemical weathering occurred during Marine Isotope Stage (MIS) 6 (130–156kyr BP), as well as in the latter stage of MIS 3 and MIS 2 (14–40kyr BP). The large sea-level lowstands and associated significant exposure of continental shelf in the western Philippine Sea during these two cold periods should favor physical erosion and chemical weathering of unconsolidated sediments on the exposed shelf. Furthermore, we notice the relatively good coherence between chemical weathering intensities on Luzon and global atmospheric CO<SUB>2</SUB> concentrations over these cold intervals. We suggest that strengthening of chemical weathering of silicates on Luzon and other tropical arcs (within 20° of the Equator) during the Quaternary glacial sea-level lowstands may significantly contribute to the lowering of atmospheric CO<SUB>2</SUB> concentrations during ice ages. We estimate that a significant fraction, up to ~16% (i.e., ~8ppmv), of all atmospheric CO<SUB>2</SUB> ultimately sequestered by silicate weathering may be processed through an area corresponding to only ~1% of the exorheic drainage area worldwide.</P> <P><B>Highlights</B></P> <P> <UL> <LI> First high-resolution silicate weathering study of the western Philippine Sea. </LI> <LI> Glacial sea-level lowstands favored silicate weathering of sediments on exposed shelf. </LI> <LI> Enhanced weathering on tropical arcs significantly sequestered atmospheric CO2. </LI> </UL> </P>

Geochemical character and material source of sediments in the eastern Philippine Sea

Xu, ZhaoKai,Li, AnChun,Jiang, FuQing,Xu, FangJian Elsevier 2008 Chinese science bulletin Vol.53 No.6

Rare earth elements in bottom sediments of major rivers around the Yellow Sea: implications for sediment provenance

Xu, Zhaokai,Lim, Dhongil,Choi, Jinyong,Yang, Shouye,Jung, Hoisoo Springer-Verlag 2009 Geo-marine letters Vol.29 No.5

Sediment provenance discrimination in northern Okinawa Trough during the last 24 ka and paleoenvironmental implication: rare earth elements evidence

XU, Zhaokai,LI, Tiegang,CHANG, Fengming,CHOI, Jinyong,LIM, Dhongil,XU, Fangjian Elsevier 2012 Journal of rare earths Vol.30 No.11

Elemental and Sr–Nd isotopic compositional disparity of riverine sediments around the Yellow Sea: Constraints from grain-size and chemical partitioning

Lim, Dhongil,Jung, Hoisoo,Xu, Zhaokai,Jeong, Kapsik,Li, Tiegang Elsevier 2015 Applied geochemistry Vol.63 No.-

<P><B>Abstract</B></P> <P>To obtain a better understanding of the source compositions of the river sediments around the Yellow Sea and their relationship with source rocks, elements and strontium-neodymium (Sr–Nd) isotopes of different grain-sizes (silt and clay populations) and chemical (labile and residual phases) fractionations in riverine sediments were studied extensively. These results clearly revealed a systematic compositional disparity between Korean river (KR) and Chinese river (CR) sediments, especially in the residual (detrital) fraction. The geochemical dissimilarity between these might reflect inherited signatures of their source rocks but with minor control from chemical weathering. In particular, the remarkable enrichment of some elements (iron (Fe) and magnesium (Mg)) and the behavior of large ion lithophile elements (e.g., barium (Ba), potassium (K) and Sr) during weathering as well as less-radiogenic Sr isotopic compositions implies that CR sediments might be weathering products of relatively more mafic rocks, with abundant ferromagnesian and plagioclase feldspar minerals, compared with KR sediments derived from silicic granites with relatively higher quartz and potassium feldspar contents. This different petrological rationale is clearly evident in an A–CN–K diagram, which estimated the source rock of CR sediments as granodioritic, a composition that reflects accurately the average composition of weathered continental crust in China. The recognition of such geochemical systematics in two river sediments, especially in grain-size and chemically partitioned data, may contribute to the establishment of provenance tracers for the Yellow Sea and East China Sea sediments with multi-sources as well the dust deposition in the western Pacific.</P> <P><B>Highlights</B></P> <P> <UL> <LI> We solved the compositional linkage between river sediments and their source rocks. </LI> <LI> Sediments were physically and chemically partitioned for element and Sr–Nd compositions. </LI> <LI> Data revealed CR and KR sediments were derived from granodiorite and granites, respectively. </LI> <LI> Especially, estimation of the source rocks is clearly evident in an A–CN–K diagram. </LI> </UL> </P>

A Comprehensive Investigation of Coastal and Shelf Sediment Sources in the South Sea of Korea: A Marginal Sea of the Northwestern Pacific

임동일,조영길,정도현,Jihun Kim,Xu Zhaokai,장태수 한국해양과학기술원 2023 Ocean science journal Vol.58 No.4

To identify and quantify the sediment sources in the South Sea of Korea, a marginal sea of the northwestern Pacific, we analyzed a comprehensive aluminum–magnesium dataset comprising 121 surface sediment samples and two sediment cores. The findings demonstrate pronounced spatial variation in sediment sources, with Korean river sediments dominating in embayment bays and Chinese river sediments prevailing in the shelf area. In the coastal zone, Korean river sediments account for over 60–70%, but their proportion decreased to 10–20% in the shelf zone. This reveals that most of the sediments from Korean rivers are mainly confined to the coastal embayments, with limited transport to the shelf area. Notably, the central South Sea mud (CSSM) deposits are primarily govern by the sediment influx from Chinese rivers (CR), rather than the Seomjin River discharge. The prevalence of CR-sourced sediments in the shelf region is closely linked to the Tsushima Warm Current and Cheju Warm Current, transporting sediments from the East China Sea shelf northwards and the southwestern Korean coastal zone eastwards, respectively. This driving mechanism for the widespread deposition of CR sediments is further supported by an abrupt shift from KR to CR dominance in sediment sources around 8 kyr BP, coinciding with the establishment of the modern current systems in the northwestern Pacific marginal seas. Our study provides a new perspective on the source-to-sink pathways, particularly of Chinese river sediments, in the formation of the Korean coastal mud deposits.

Electrochemical evaluation of La2NiO4+δ -based composite electrodes screen-printed on Ce0.8Sm0.2O1.9 electrolyte

Zhao, Kai,Xu, Qing,Huang, Duan-Ping,Chen, Min,Kim, Bok-Hee Springer-Verlag 2012 Journal of solid state electrochemistry Vol.16 No.8

Performance improvement of inert-substrate-supported tubular single cells via microstructure modification

Zhao, Kai,Kim, Bok-Hee,Xu, Qing,Ahn, Byung-Guk Elsevier 2015 Journal of Power Sources Vol.274 No.-

<P><B>Abstract</B></P> <P>Inert-substrate-supported tubular single cells, with a configuration of porous yttria-stabilized zirconia (YSZ) supporter/Ni anode current collector/Ni–Ce<SUB>0.8</SUB>Sm<SUB>0.2</SUB>O<SUB>1.9</SUB> anode/YSZ/Ce<SUB>0.8</SUB>Sm<SUB>0.2</SUB>O<SUB>1.9</SUB> bi-layer electrolyte/La<SUB>0.6</SUB>Sr<SUB>0.4</SUB>Co<SUB>0.2</SUB>Fe<SUB>0.8</SUB>O<SUB>3−δ</SUB> cathode, have been fabricated. The Ni anode current collector layer is prepared by a dip-coating process, while the cathode layer is produced by drop-coating and dip-coating processes, respectively. The electrochemical performances of the single cells are examined with respect to the microstructures of these two layers. The results indicate a significant effect of the Ni layer thickness on its sheet resistance and the ohmic resistance of the single cells. The preferred dip-coating time of the Ni layer is determined to be four. At 800 °C in hydrogen fuel, the single cell with a Ni layer dip-coated for four times and a drop-coated cathode layer exhibits a maximum power density of 500 mW cm<SUP>−2</SUP>. The electrochemical performance of the single cell is further enhanced by modifying its cathode microstructure. Preparing the cathode layer by dip-coating for four times allows a decrease of the overall electrode polarization by 25% and an increase of the maximum power density to 555 mW cm<SUP>−2</SUP>.</P> <P><B>Highlights</B></P> <P> <UL> <LI> Inert-substrate-supported tubular single cells are prepared. </LI> <LI> The microstructure and electrochemical performance of the cells are investigated. </LI> <LI> Increasing anode current collector thickness renders a lowered ohmic loss. </LI> <LI> Modifying cathode microstructure allows a reduced polarization loss. </LI> <LI> An improvement of MPD up to 555 mW cm<SUP>−2</SUP> is gained at 800 °C in hydrogen. </LI> </UL> </P>