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Taiwan is particularly sensitive to changes in monsoonal precipitation and to typhoon-induced heavy precipitation events, however, rainfall variability in Taiwan on centennial and millennial time scales during the Holocene has not been well understood. This study describes mid-Holocene rainfall features of Taiwan based on pollen, total organic carbon (TOC), total nitrogen (TN), and C/N ratio records of core MD05-2908. The step-wise increase in sedimentation rate, fern spore percentage and concentration, TOC content, and C/N ratio suggests an increasing terrestrial material supply due to the intensified rainfall in Taiwan since 6800 cal. yr BP. This rainfall pattern shows an inverse pattern to the decreasing East Asian summer monsoon (EASM) strength represented by the multi-proxy records from North China. Variation of the East Asian summer circulation and associated moisture transport may account for the long-term rainfall changes in Taiwan. Superimposed on this trend, we interpreted three prominent rainfall changes, which focus on the periods of 6800–6600, 1090–880 and 490–190 cal. yr BP. These centennial time scale rainfall variations in our records are linked to the intensity of El-Nino Southern Oscillations.

•Chennai (India) received the highest rainfall of 490 mm on 1 Dec 2015.•This study looked at NOAA/NESDIS global analysis of SST anomaly (°C).•Revival of 769 km long Buckingham Canal essential for flood mitigation.•Renovating canals, ponds, and lakes crucial for flood prevention.•India needs better strategies to adapt to future extreme weather situations.

Geological sequestration of atmospheric carbon dioxide (CO2) can be achieved by the erosion of organic carbon (OC) from the terrestrial biosphere and its burial in long-lived marine sediments. Rivers on mountain islands of Oceania in the western Pacific have very high rates of OC export to the ocean, yet its preservation offshore remains poorly constrained. Here we use the OC content (Corg, %), radiocarbon (Δ 14Corg) and stable isotope (δ13Corg) composition of sediments offshore Taiwan to assess the fate of terrestrial OC, using surface, sub-surface and Holocene sediments. We account for rock-derived OC to assess the preservation of OC eroded from the terrestrial biosphere and the associated CO2 sink during flood discharges (hyperpycnal river plumes) and when river inputs are dispersed more widely (hypopycnal). The Corg, Δ14Corg and δ 13Corg of marine sediment traps and cores indicate that during flood discharges, terrestrial OC can be transferred efficiently down submarine canyons to the deep ocean and accumulates offshore with little evidence for terrestrial OC loss. In marine sediments fed by dispersive river inputs, the Corg, Δ14Corg and δ 13Corg are consistent with mixing of terrestrial OC with marine OC and suggest that efficient preservation of terrestrial OC (>70%) is also associated with hypopycnal delivery. Sub-surface and Holocene sediments indicate that this preservation is long-lived on millennial timescales. Re-burial of rock-derived OC is pervasive. Our findings from Taiwan suggest that erosion and offshore burial of OC from the terrestrial biosphere may sequester >8 TgC yr−1 across Oceania, a significant geological CO2 sink which requires better constraint. We postulate that mountain islands of Oceania provide a strong link between tectonic uplift and the carbon cycle, one moderated by the climatic variability which controls terrestrial OC delivery to the ocean.

Sediment core OS03-1 retrieved from the Akademia Nauk Rise in Southern Okhotsk Sea was analyzed for the contents of rare earth elements (REEs) and combined with carbon isotope (δ13C) time series of benthic foraminifera to infer changes in terrigenous accumulation and bottom water ventilation on glacial–interglacial timescales in the study area. The age model of OS03-1 was constructed by a combination of foraminifer δ18O stratigraphy and 14C AMS dating, revealing that the 380 cm long core provides a window on climate change in the southern Okhotsk Sea since ∼180 ka. A grain size-controlled-REE content shows strong glacial–interglacial changes. The Cerium and Europium anomalies vary from 0.89 to 1.32 and from 1.14 to 1.37, respectively. The (La/Yb)N values range between 0.55 to 0.92. Both results suggest a significant contribution of volcanic debris in the core sediments. In addition, the relationships between Sm vs. Nd suggest main contribution origin from the Amur River and sea ice during warm intervals and from the sea ice during cold intervals, indicating that the sea ice played an important role in transporting terrigenous materials to the study site in the southern Okhotsk Sea. During the last 180 ka, the mass accumulation rates (MAR) of ∑REEs are relatively higher during glacials and lower during interglacials with a peak accumulation during the early deglacial period. We infer that an intensified Mongolia High is responsible for the first-order accumulation pattern of ∑REEs in the southern Okhotsk Sea by mediating the dynamic changes in sea ice extent. Furthermore, six δ13C minima are associated with intensified Asian monsoon (AM) precipitation and maximum MARs of ∑REEs, indicating that the dominance of barrier layer effects by high fresh water input through sea ice melting. The maximum MAR of ∑REEs during the Marine Isotope Stage (MIS) 5c coincides with the minimum of benthic foraminiferal δ13C, indicating a major interruption of ventilation in the bottom water in the Okhotsk Sea. The major low ventilation event in the deep water of the Okhotsk Sea appears to be dampened by a cooling condition and a major blooming of surface productivity preceded the event.

We used multi-decadal pollen and diatom records from sediment core TFL-1 from Tsuifong Lake to reconstruct the vegetation dynamics and hydroclimate in northeastern Taiwan during the past 3500 cal BP. Coarse grained sediments in association with higher percentages of wetland pollen (Cyperaceae) and upper conifer pollen (Tsuga and Pinus) in the lower part of the core indicate low lake levels and a relatively cold/dry climate between 3500 and 2030 cal BP, reflecting a decline of the East Asian summer monsoon (EASM). Muddy sediments coupled with reduction of wetland pollen represent the rise of lake levels, implying the re-strengthening of the EASM during the past 2000 years. Paleotemperature was inferred from the variation of pollen origin from the upper and lower mountain forest, indicating the global temperature anomalies of the Medieval Warm Period (MWP) and the Little Ice Age (LIA). In comparison to the main climate forces in the North Pacific, we suggest that the long-term climatic trend in Taiwan was controlled by variations in EASM intensity, while increased precipitation over the past 2000 years may also be linked to warmer sea surface temperature (SST) of the western Pacific Warm Pool (WPWP) and increased El Nino-Southern Oscillation (ENSO) events, which increased typhoon intensity. Higher diatom-inferred pH during 2930–2030 cal BP and the LIA suggest strong hydrological disturbances, reflecting more typhoons passing over Taiwan. The frequent typhoon events could be linked by an abrupt shift of typhoon track, due to the reduction of the WPWP and expansion of the Northwestern Pacific High, which move typhoons in a more westerly direction.

The global export of organic carbon (OC) is intimately linked to the total flux of terrestrial sediment to the ocean, with the continental margins receiving ~ 90% of the sediment generated by erosion on land. Recent studies suggest that a substantial amount of particulate OC (POC) might escape from the shelf and be exported to the continental slope-deep sea sector, although the mechanisms and magnitude of such deep sea POC transfer remain unknown. Here we investigate hyperpycnal flow-associated total suspended matter (TSM) collected from water depths of ~ 3000 m, near the bottom of sea floor, in the Gaoping Submarine Canyon (GSC) off southwestern Taiwan. Elemental (C, N), isotopic (δ 13 C, δ 15 N) and biomarker compositions of TSM were investigated to understand its biogeochemical characteristics. A two end-member δ 13 C mixing model indicates that deep sea TSM contains ~ 90% terrigenous OC, while a similar mixing model using δ 15 N reveals a lower proportion (~ 58%). Organic biomarkers of TSM suggest contributions from a mixture of resuspended, continental-margin derived marine organic matter (OM MAR ) and terrigenous sources, revealing that terrestrial OC likely mixes with nitrogen-rich marine material during rapid transport. This study documents that rapid transfer of terrigenous organic matter (OM TERR ) into the deeper regions of GSC occurred within a week of typhoon Morakot, likely through hyperpycnal injection of sediment-laden, warm freshwater from southern Taiwan. Evidence from this typhoon Morakot-induced hyperpycnal plume event in Taiwan demonstrates that extreme storm events provide an efficient way to export terrigenous OC without oxidation to hitherto unknown water depths of deep sea in the Oceania region.

Available reports of dissolved oxygen, δ15N of nitrate (δ 15NNO3) and δ15N of total nitrogen (δ15Nbulk) for trap material and surface/downcore sediments from the Arabian Sea (AS) were synthesized to explore the AS' past nitrogen dynamics. Based on 25 μmol kg−1 dissolved oxygen isopleth at a depth of 150 m, we classified all reported data into northern and southern groups. By using δ15Nbulk of the sediments, we obtained geographically distinctive bottom-depth effects for the northern and southern AS at different climate stages. After eliminating the bias caused by bottom depth, the modern-day sedimentary δ15Nbulk values largely reflect the δ15NNO3 supply from the bottom of the euphotic zone. Additionally to the data set, nitrogen and carbon contents vs. their isotopic compositions of a sediment core (SK177/11) collected from the most southeastern part of the AS were measured for comparison. We found a one-step increase in δ15Nbulk starting at the deglaciation with a corresponding decrease in δ13CTOC similar to reports elsewhere revealing a global coherence. By synthesizing and reanalyzing all reported down core δ15Nbulk, we derived bottom-depth correction factors at different climate stages, respectively, for the northern and southern AS. The diffusive sedimentary δ15Nbulk values in compiled cores became confined after bias correction revealing a more consistent pattern except recent 6 ka. Such high similarity to the global temporal pattern indicates that the nitrogen cycle in the entire AS had responded to open-ocean changes until 6 ka BP. Since 6 ka BP, further enhanced denitrification (i.e., increase in δ15Nbulk) in the northern AS had occurred and was likely driven by monsoon, while, in the southern AS, we observed a synchronous reduction in δ15Nbulk, implying that nitrogen fixation was promoted correspondingly as the intensification of local denitrification at the northern AS basin.

Increasing interest in global climate change has led to attempts to understand and quantify the relationship between chemical weathering processes and environmental conditions, especially climate. This interest necessitates the identification of new climate proxies for the reconstruction of two important Earth surface processes: physical erosion and chemical weathering. In this study, an AMS C-14-dated 2.8-m-long sediment core, GH09B1, from Lake Gonghai in north-central China was subjected to detailed geochemical analyses to evaluate the intensity of chemical weathering conditions in the catchment. Multivariate statistical analysis of major and trace elemental data of 139 subsamples revealed that the first principal component axis PCA1 explained approximate to 53% of the variance in the assemblage of elements/oxides with significant positive correlations between PCA1 scores and the separation of mobile and soluble elements/oxides from the immobile and resistant elements/oxides, which is thus able to indicate the chemical weathering in the catchment. These results are supported by the down-core trends of other major and trace elemental ratios of chemical weathering intensity as well as by pollen data from the same core. Variations in PCA1, chemical index of alteration (CIA), Rb/Sr ratio and other oxides ratios indicate stronger chemical weathering due to a wet climate during the Medieval Warm Period (MWP). However, the MWP was interrupted by an interval of relatively weaker chemical weathering conditions from AD 940-1070. Weak chemical weathering under a dry climate occurred during the Little Ice Age (LIA), and increased chemical weathering intensity during the Current Warm Period (CWP). Our proxy records of chemical weathering over the last millennium correlate well with the available proxy records of precipitation from Gonghai Lake as well as with the speleothem oxygen isotope record from Wanxiang Cave, but do not show a significant correlation with the temperature record in N China, suggesting that the chemical weathering intensity in the study area was mainly controlled by the amount of rainfall rather than by temperature. We conclude that high resolution lacustrine sediment geochemical parameters can be used as reliable proxies for climate variations at centennial-decadal time scales.

Based on elemental geochemical data, we reconstructed the sediment provenance, surface productivity and bottom water redox conditions for the last 48 ka in the Ulleung Basin (Sea of Japan) and inferred the factors controlling them. Al2O3/TiO2 ratio and chemical index of alteration (CIA) suggest that sediment provenance changed during the glacial period (48-18 ka) compared to the deglacial (ca. 18-11 ka) and Holocene. Mass accumulation rates of total organic carbon (TOC), CaCO3, phosphorus, cadmium and excess barium reveal low paleoproductivity during low sea stand. During 18-11 ka, productivity increased due to increasing inflow of nutrient-rich water masses - the Oyashio and the East China Sea coastal water - in tandem with the rising sea level. Maximum productivity occurred during Younger Dryas and Pre-boreal periods when sea level was at �� 60 m and then gradually decreased as the Tsushima Warm Current inflow kicked off at ca. 9.3 ka, consistent with other paleoredox proxies, which reveal the presence of anoxic bottom water during ca. 12-9 ka. With the changes in paleoredox proxies and their ratios (TOC, Mo, U, Mn, C/S ratio and Uauthigenic and Mo contents), we hypothesized that the redox changes were mainly ventilation driven and were superimposed on the influence of circulation-induced productivity changes. The global climate and sea-level changes on a millennial timescale play a major role in enhancing paleoproductivity and restrict bottom water advection, subsequently driving the oxygenation of bottom water in the Ulleung Basin. Copyright # 2012 John Wiley & Sons, Ltd.

National Science Council of Taiwan [NSC 97-2629-M-001-025, NSC 99-2116-M-001-011]; National Science Foundation of China [41176059, 41121091]

Multi-proxy records in two sediment cores (R and Rd) from the subalpine Retreat Lake in NE Taiwan document 5 centennial-scale periods (∼7.3–6.9, 6.35–5.9, 5.8–5.1, 4.5–∼2.1, and 2.0–1.6 ka BP) of relatively reduced summer East Asian monsoon (EAM) precipitation that were superimposed on the long-term decreasing monsoon trend from ∼8 ka BP onwards. The first three intervals of weak summer EAM indicated by low TOC, C/N ratio and water content within the Holocene optimum (∼8.6–4.5 ka BP) correlate with solar activity, revealing that the centennial-scale summer monsoon variations in a warm climate were related to weak solar irradiance. The desiccation of the lake (4.5–∼2.1 ka BP), followed by a weak monsoon event at ∼2.0–1.6 ka BP, may coincide with decreased sea surface temperature in the tropical Pacific. High water content and low dry bulk density in core Rd at ∼7.6, 7.46, 6.8–6.54, 6.1, 5.8, 5.6, and 5.0 ka BP imply a significant increase of summer EAM during these periods, and thus suggest an unstable optimum climate in Taiwan. A possible linkage of weak summer EAM with the tropical Pacific and North Atlantic cooling during these intervals may be driven by coupled ocean–atmosphere interactions, especially reduced heat and moisture transport and enhanced El Nino-Southern Oscillation in the tropical Pacific, as well as solar activity. The centennial-scale reorganizations in the tropical Pacific climate dynamics may have played an important role in the summer EAM instability, particularly during the late Holocene.

Slag material was dumped in two sites off southwestern Taiwan by the China Steel Corporation during 1984-1995. By geochemically analyzing four sediment cores, we investigate the impact of slag on the sediment chemistry. Elemental profiles from the dumping sites show a strong depletion in detrital elements and enrichment in alkaline and redox-sensitive elements, especially for the top ~20 cm of sediments. The relative enrichment factor (EFrel) exhibits wider range for Ca (0.73-13.33), Fe (0.883.03), Mg (0.94-9.58), and Mn (1.22-33.30) due to contamination of sediments by slag. Sediment weathering indicators also show a distinct change with lower values in sediments influenced by dumping due to Ca and Sr addition. Higher EFrel for As, Cd and Pb in the top sections of the cores indicate an additional modern/industrial input of these elements since ~1950. Our study suggests that slag dumping may have a localized effect on biogeochemical processes by inducing the diagenetic remobilization of certain elements.

article i nfo Results of clay mineralogy in 140 samples collected in major rivers and lakes in southwestern Taiwan and on the seafloor off Taiwan in the northeastern South China Sea (SCS), combined with clay mineral records of the Pearl River drainage basin, rivers in Luzon, and the South China shelf and slope, are used to semi- quantitatively evaluate the detrital fine-grained sediment contribution of Taiwan to the northern SCS. The clay mineral assemblage of the Taiwan-sourced sediments consists dominantly of illite (average 56%) and chlorite (41%), with very scarce kaolinite and smectite. Their respective distribution from the rivers and lakes to the seafloor off Taiwan does not show obvious basin-wide differences. Linear correlations of illite chemistry index with illite crystallinity and of illite crystallinity with kaolinite (%) present two end-members of provenances, the Pearl River and Taiwan, for the South China shelf and slope. Assuming that kaolinite in the northern SCS is provided completely from the Pearl River, the contribution of Taiwan in clay minerals is evaluated as 29% to the South China shelf and 23% to the South China slope, respectively. Accordingly, the contribution of the Pearl River to the South China shelf and slope is 52% and 31%, respectively. The Luzon Arc accounts for the rest of clay mineral components for the northern SCS mainly by providing smectite. The Bashi Strait-crossed branches of the southward deep North Pacific Deep Water and the northward surface Kuroshio Current in the western Pacific may transport Taiwan-sourced suspended sediments westwards to the northern SCS.

Three sediment cores near the spreading axis in the Andaman backarc basin (ABB) were studied for bulk and clay mineralogy, major, trace and rare earth element (REE) geochemistry in bulk and three selective leaches, to identify sediment sources to this region and to decipher probable hydrothermal contribution. REE and other geochemical data suggest a strong influence of the Irrawaddy River as a major continental source to the ABB sediments. Low carbonate content in the sediments is due to dilution by higher detrital input as well as reduced foraminiferal carbonate contribution because of low sea surface salinity. The contribution from local volcanic sources was identified from the presence of volcanic glass in the sand-sized sediment fraction; higher smectite content in the clay fraction and the trace element data. Mn concentrations in the upper 12 cm are well above those found in pelagic carbonate-free sediments. Mn distribution pattern and oxide nature suggest a hydrothermal source. Other discriminants such as Eu anomaly and Y/Ho ratio also suggest the role of hydrothermal activity. In addition, the association of Mo with Pb, Zn and Cu in the HCl-insoluble residue suggests the presence of sulfidic material probably of hydrothermal origin.

Distribution of 10Be in systematically collected (degree × degree interval at 10 to 16 °S; 73.5 to 76.5 °E) surficial siliceous ooze, siliceous clay and pelagic clay sediments (top 2 cm) from the abyssal Central Indian Basin and the Andaman Sea is used to evaluate sources and to decipher the transport pathways of sediment particles, demarcate sediment depocenters and erosional areas. While 10Be concentrations display a wide variation (0.12–5.56 × 109 atoms g−1) with an average of 3.58 × 109 atoms g−1 in the Central Indian Basin, the values in the Andaman Sea are uniform with an average of 1.49 × 109 atoms g−1. The 10Be/9Be values in the Central Indian Basin sediments range between 0.06 and 2.99 × 10−8 atoms atoms−1 and average to ∼1.56 × 10−8 atoms atoms−1. Correlation of 10Be data with some selected major (Al, Mn, Ti) and trace (Rb and Ba) elements suggest that large part of the isotope has been supplied through direct atmospheric fallout from the water column and minor part from lithogenic detrital flux. Significantly lower 10Be accumulation rates in the Central Indian Basin and an order of magnitude higher in the Andaman Sea sediments compared to the estimated global average production rates indicate removal of the isotopes at the continental margins. Bottom topography seems to exert control on local 10Be variation, where sediments deposited in valleys or topographic depressions contain higher 10Be concentrations in contrast to the probably erosion-dominated areas at the slopes and troughs.

Surface sediment samples collected from the inner shelf region of the Bay of Bengal, were analysed for the major elements and total and acetic acid available trace elements (Al, Ca, Cd, Co, Cr, Cu, Fe, K, Mg, Mn, Na, Ni, P, Pb, Si, Zn) to evaluate geochemical processes influencing their distribution. Major elemental analysis showed that the sediments had high concentrations of Si and relatively low concentrations of Al and Fe. Both major elemental and trace metal concentrations indicated that the sediments represent weathered products of granite and charnockite. Normalization of metals to Al indicated relatively high enrichment factors for Pb, Cd, Zn and Cr. The higher proportions of nondetrital Pb (66%), Cd (41%) and Co (28%) reveal metal contamination due to anthropogenic inputs. Factor analysis (FA) identified six possible types of sedimentological and geochemical associations. The dominant factor accounting for 26.9% of the total variance identifies an anthropogenic input and accumulation of nondetrital Cd, Co, Cr, Ni and Pb. Association of these metals with CaCO3 reveals that shell fragments in the surface sediments are likely act as a carrier phase for nondetrital metals. The results are discussed in the context of the sources and pathways of elements in the Bay of Bengal.

China (973 Program) [2009CB421200]; Program of Introducing Talents of Discipline to Universities [B07034]; Academia Sinica Thematic Program AFOBi, Taiwan [NSC 98-2116-M-001-005]

Sedimentary total organic carbon and carbon-to-nitrogen ratio records from the subalpine Retreat Lake in NE Taiwan reveal four centennial periods (~8–8.3, 5.1–5.7, 4.5–~2.1, and 2–1.6 kyr BP) of relatively reduced summer East Asian monsoon (EAM) precipitation that were superimposed on the insolation-dependent, long-term decreasing monsoon trend during the middle and late Holocene while early Holocene monsoon strength was controlled by glacial boundary conditions. Strikingly, all weak monsoon events correlate with the timings of low sea surface temperature in the tropical Pacific, maxima of hematite stained-grains in the sediments of North Atlantic, reduced formation of North Atlantic Deep Water, and low concentrations of atmospheric methane over Greenland, suggesting a globally well-connected postglacial climate (from ca. 8.6 kyr BP onwards). Persistent linkage of weak summer EAM-tropical Pacific and North Atlantic cooling-reduced global wetland extent during these intervals is believed to be driven by coupled ocean-atmosphere interactions, especially reduced heat and moisture transport and enhanced El Niño-Southern Oscillation in the tropical Pacific, as well as solar activity. Overall similarity of summer EAM with diverse proxy records and their coincidence to abrupt changes witnessed in other paleorecords across the world imply that the centennial-scale reorganizations in the tropical Pacific climate dynamics may have been playing an important role, of course closely in phase with solar variations and North Atlantic climate, in the Holocene summer EAM and, by extension, low-latitude's monsoon instability.

[1] Sedimentary geochemical records from subalpine Retreat Lake, subtropical Taiwan, document the unstable East Asian monsoon (EAM) climate over the past ∼10,300 years, with a weak EAM between ∼10.3 and 8.6 ky B.P., EAM intensity peaks between 8.6 and 7.7 ky B.P., and then gradually decrease in response to summer insolation, heat and moisture transport. Our proxy record reveals several weak monsoon intervals that correlate to low sea surface temperatures in the western tropical Pacific and cold events in the North Atlantic, linking the tropical Pacific, North Atlantic, and Polar climates because weak EAM events at ∼8.2, 5.4 and 4.5–2.1 ky B.P. also correspond to low values of atmospheric methane and periods of reduced North Atlantic Deep Water formation. We therefore suggest that centennial to millennial scale monsoon variability during the Holocene in the northern subtropics is globally-mediated via a sun-ocean-monsoon-North Atlantic linkage.