Liang-Jian Shiau

500 000-Year records of carbonate, organic carbon, and foraminiferal sea-surface temperature from the southeastern South China Sea (near Palawan Island)

High-resolution records of planktic foraminifer sea-surface temperature (SST) and biogenic sediment components of carbonate and total organic carbon (TOC) concentrations were determined in an IMAGES giant piston core spanning Vthe last 500 000 years, taken near the western slope of Palawan Island in the southeastern South China Sea (SCS). The records provide information of paleoceanographic and paleoclimatological variations linked to East Asian monsoon systems in the SCS, the largest marginal sea of the western Pacific. Constrained by planktic foraminifer (Globigerinoides ruber) oxygen isotope stratigraphies, the records show a lowering of faunal SSTby V3‡C during glacial stages, indicating significant cooling in the glacial western Pacific climate. In general, they show lowfrequency patterns with high SSTs, high carbonate content, and low TOC content during interglacial periods, and exhibit low SSTs, low carbonate content, and high TOC content during glacial periods. The carbonate content variations indicate that the sediment composition is mostly controlled by terrigenous inputs, which are associated with sea-level fluctuations in the SCS during past glacial^interglacial stages. The low SST and high TOC content indicate cooling and high productivity conditions in the surface oceans of the SCS, which also reflect a condition of intensified winter monsoon winds associated with glacial boundary conditions. Some rapid, high-frequency oscillations of the SSTand T OC found in the records are coincident with intervals of intensified winter or summer monsoons from the Arabian Sea, implying that the Asian monsoon systems had wider regional effects than previously assumed. Timeseries analyses reveal that variations in the SST, carbonate and TOC contents of this record contain statistically significant concentrations of variance at orbital frequency bands, namely 100 kyr 31 , 41 kyr 31 , and 23 kyr 31 , suggesting that both ice volume and orbital solar insolation changes are potential mechanisms for the SCS monsoon variations.

Increased precipitation during the Little Ice Age in northern Taiwan inferred from diatoms and geochemistry in a sediment core from a subalpine lake

We studied diatoms in a 55.5-cm-long sediment core from a subalpine lake in northern Taiwan, Tsuifong Lake (TFL), to investigate environmental changes from AD 490 to present. Diatom assemblages of the last century were dominated by acidophilous species, whereas alkaliphilous taxa dominated the record between AD 1480 and 1910. Over the studied time frame, four decadal periods with high precipitation were inferred from evidence of elevated soil input from the watershed, supported by the stable isotope signatures (δ15N, δ13C) of organic matter and magnetic susceptibility of the sediments. We compared the inferred changes in pH of TFL to values obtained from three other Taiwanese subalpine lakes. The present study revealed that elevated precipitation was associated with increased solar irradiance over the last five centuries, with a stable dry period between AD 490 and 1450. Acidification of TFL in the last ~100xa0years was a consequence of deforestation and acid rain.

Factors controlling temporal and spatial variations of atmospheric deposition of 7Be and 210Pb in northern Taiwan

(1) Fluxes of 7 Be and 210 Pb monitored at two contrasting sites in northern Taiwan were studied along with meteorological data to elucidate factors controlling their temporal and spatial variations. The 9 year time series of both nuclides at Nankang in the Taipei Basin show dependence on wet precipitation and follow an annual cycle regulated by typhoons, monsoons, and mei-yu¨. Superimposed on the annual cycle are interannual variation caused by El Nino-Southern Oscillation and intraseasonal oscillations due to the passage or invasion of fronts, cold surges, dust storms, and the Pacific high-pressure system. The observed 7 Be/ 210 Pb ratios are indicative of the source regions of the fallout nuclides, with higher ratios from high-altitude rain and lower ratios from dry fallout and low-altitude rain. The 2 year time series at Yangminshan shows that 7 Be and 210 Pb fluxes at the mountainous site are in phase with those at Nankang. However, nuclide fluxes at Yangminshan are 4-5 times those at Nankang. After combining results from this and other ancillary studies at Yangminshan, we suggest that (1) in applying fallout nuclides to study the Earths surface processes, the assumption of constant flux should be made judicially according to the timescales involved, and that (2) the application of fallout nuclides to study soil erosion in hilly areas must consider not only control by wet and dry precipitation but also by direct contact and interaction of clouds with soils enhancing nuclide fluxes.

Warm pool hydrological and terrestrial variability near southern Papua New Guinea over the past 50k

Here,we presenta 50k archiveof U37′ seasurface temperature (SST), planktic foraminifera oxygen isotopes, and terrestrial input indicators including branched and isoprenoid tetraether (BIT) biomarkers, 232 Th activity, and non‐biogenic sediment components recorded in core MD052928 from the WPWP (near southern Papua New Guinea, PNG). The planktic foraminifer oxygen isotopes in the core show millennial‐scale changes indicating fresher seawater during the NH cold periods (i.e., Heinrich Events, HEs) and suggesting hydrological changes that are most likely linked to the strength of the boreal winter Asian‐Australian monsoon (AAM). Our observations are corroborated by evidence from the same core that indicates increased terrestrial input caused by higher precipitation on land and more river runoff from southern PNG during the cold periods. Consistent with other nearby hydrological records from land, our study indicates persistent millennial‐scale hydrological changes within the past 50k in the western tropical Pacific and Southeast Asia. The timing of the millennial‐scale changes appears to have been determined by the latitudinal displacement of the Intertropical ConvergenceZone(ITCZ)thatreflectsahistoryofheattrans

Marine records of East Asian monsoon variability over the past 5 Ma

Abstract Marine sedimentary cores retrieved from the western Pacific provide important clues for deciphering how the East Asian Monsoon (EAM) system has evolved during the past 5 Ma. Here we briefly review some recent progress on the reconstructions of the EAM based on marine SST (sea surface temperature), SSS (sea surface salinity), and productivity records from the SCS (South China Sea) and ECS (East China Sea) and their implications for EAM evolution and variability on tectonic, orbital and millennial timescales. This review highlights the importance of high resolution sampling on giant marine cores (such as cores collected with the International Marine Past Global Change, IMAGES program) that provide opportunities for better defining the timing and amplitude of the EAM variability expressed in marine records. We also discuss possible future directions of EAM palaeoclimatic and palaeoceanographic studies that require development of multiple new marine EAM proxies and a comparison of the marine records with the stalagmite records on land.