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The Guangxi Zhuang Autonomous Region in southern China is one of the most typical karst relief areas with various forms, and tiankeng is one of the most typical karst relief forms of the Quaternary Period. In this work, accurate measurements of tiankeng exposure ages were made. The exposure ages of carbonate rocks from the five largest tiankengs in the world, the DaShiwei, HuangJing, ChuanDong, DaTuo, and DaCao tiankengs, were determined by accelerator mass spectrometry to be at least 20–400 thousand years, which provides significant proof for activity of new tectonic movement of the Eurasian continent in the Quaternary.

Tiankeng, a typical Karst relief of the Late Quaternary Period, in the south of China, plays an important role when researching the surface shape and evolution of the Karst relief. The accumulation of Chlorine-36 (T1/2 = 301 ka) through the interaction of cosmic ray particles with Ca, K and Cl in rocks allow it to be used as the ideal nuclide for determination of the exposure age and erosion rate of limestone. In this work, an improved 36Cl sample preparation method for Tiankeng limestone was presented. The Isotope Dilution-AMS technique allows for the simultaneous measurement of 36Cl and Cl with a single AMS sample preparation. The barium introduced during the sample preparation was removed to avoid ionizer poisoning and attain a higher and more stable beam current. The method is particularly suitable for limestone samples, as well as for soil, sediment and water samples.

To better understand the reported paleoclimate features and underlying mechanisms in the lowest-latitude region (~28°N to 29°30′N), where 12 major river gorges cross the Himalayas, of the southern Tibetan Plateau, we aim to elucidate the major sources and behavior of modern monsoon air masses in the region based on spatial variations in the δ18O and δ2H of stream water and precipitation, and vegetation during the summer monsoon season. Our main findings were following: The river gorges, high mountain ranges bearing extensive dense vegetation, and stronger solar insolation characteristic of the lowest-latitude region may have functioned for an extended period as the essential geological settings for strongly drawing significant amounts of moisture from the Indian Ocean toward the region without passing through the Yarlung Zangbo basin. The combination of such geological settings specific to this region may have caused its earlier response to the climate amelioration after a cold/dry event, such as the Younger Dryas and Heinrich-1, compared to other regions on the Plateau. Furthermore, gorge-derived monsoon air masses that blew through the lowest-latitude region are highly likely to have more significantly influenced the onset of the climate amelioration after a cold/dry event even in the southwestern, south-central, and southeastern regions, rather than the Yarlung Zangbo-derived monsoon air masses. Therefore, this caused the subsequent expansion of the Indian summer monsoon (ISM) over the Plateau. Thus, with its unique geological setting, the lowest-latitude region has presumably played a critical role as the key region, i.e. the initiator, for the early evolution of the ISM on the Tibetan Plateau by responding to climate amelioration after cold/dry events more rapidly than any other region and drawing gorge-derived monsoon air masses strongly toward the region.

Concentrations of phase-partitioning 13 polycyclic aromatic hydrocarbons (PAHs) in seawater were investigated in the Tsukumo Bay, Noto Peninsula, Japan, during 2014&ndash, 2018, to improve the understanding of the environmental behavior of PAHs in the coastal areas of the Japan Sea. Total PAH (particulate plus dissolved) concentrations in surface seawater were in the range 0.24&ndash, 2.20 ng L&minus, 1 (mean 0.89 ng L&minus, 1), an order of magnitude lower than the mean values observed in the Japan Sea in 2008 and 2010. Although the PAH contamination levels during 2014&ndash, 2018 were significantly lower than those in the East China Sea, the levels increased from 2014 to 2017 and were maintained at the higher level during 2017&ndash, 2018. The main sources of particulate and dissolved PAHs during 2014&ndash, 2018 were combustion products, of which the former were more influenced by liquid fossil-fuel combustion and the latter by biomass or coal combustion. The increase in particulate PAH concentrations in October&ndash, December during 2014&ndash, 2018 was due to the impact of PAH-rich airmasses transported from the East Asian landmass in the northwesterly winter monsoon winds. The increase in dissolved PAH levels during July&ndash, September in 2014, 2016, 2017, and 2018 indicates that the Tsukumo Bay is possibly impacted by the PAH-rich summer continental shelf water transported by the Coastal Branch of the Tsushima Warm Current, which flows into the Japan Sea from the East China Sea.

The paleoclimatic changes in the southern region on the Tibetan Plateau (TP) after the LGM were studied by multi-proxy analysis, including pollen, Ca-carbonates, TOC, δ 13 C TOC , plant macrofossils and sands with sediment cores from Lake Pumoyum Co, close to the east end of the Himalayas. The following paleoclimatic changes characteristic of the southern TP were suggested by comparing with the paleoclimatic records from various regions within the Southwest (SW) monsoon domain on the TP. Soon after the LGM, deglaciation in the southern TP had already started at 18.5 ka BP, and more actively increased after ca. 16.5 ka BP, with the hydrological circulation oscillating in ca. 1200-, 2000- and 4000-year periods. An abrupt increase in humidity under the reduced SW monsoon intensity occurred at 15.0 ka BP as part of further deglaciation processes. Subsequently, the climate amelioration in the southern region started from 15.0 ka BP a few centuries earlier than other regions of the TP and then was further intensified by synchronizing with the Bolling/Allored (B/A) event. Over the B/A period, the SW monsoon intensity in the southern region almost continuously and sharply increased. Unlike many regions on the TP, the southern region experienced almost no or substantially small impact of the Younger Dryas (YD) event and also other major dry/cold reversals, such as Heinrich 1 event, the 8.2 kyr event, and an abrupt spell occurring between 5 and 4 ka BP. The monsoon intensity in the southern region after the YD event started to rapidly increase from 11.4 ka BP and reached a maximum between 10.8 and 10.0 ka BP after the LGM which lagged about 1200 years behind the maximum insolation in the northern hemisphere. From ca. 9.6 ka BP, the gradual decrease in humidity in the southern TP started and continued until 4.2 ka BP. It's aridification trend was characterized by three-stepwise transition observed at 9.6, 7.7 and 5.5 ka BP. However, the aridification in the southern TP was rather weak, and the climatic conditions were sustained fairly humid and comparably stable. The humidity between 4.2 and 2.5 ka BP essentially increased despite the weakened SW monsoon intensity at that time, whereas from 2.5 ka BP to the present, the climatic conditions became most arid and instable during the Holocene. As a consequence, the Holocene climate optimum in the southern region lasted from 11.4 ka BP until 2.5 ka BP and was marked by the earliest start and the latest end timings within the SW monsoon domain on the TP. The comparison of the start timings from various paleoclimatic records indicated that the first SW monsoon on the TP after the YD event generated at 11.4 ka BP in the southern region. Subsequently, according to the degree of the recovery of positive vegetation-albedo feedback system in each region, the monsoon probably extended from the southern TP over the entire TP taking 3000–4000 years. Based on these results, the possible key factors and mechanisms responsible for the paleoclimatic changes in the southern region and also the possible processes as to the evolution of the SW monsoon over the TP are discussed.

Paleoclimatic records from the Tibetan Plateau provide important clues for understanding the Asian monsoon and Asian climate systems. To reconstruct climatic and environmental changes in the southern Tibetan Plateau, a 3.77-m-long sediment core (PY608E–PC) was taken from the southeastern part of Lake Pumoyum Co in August 2006. Because terrestrial plant residues are extremely rare in this core, we performed radiocarbon dating on the total organic carbon fraction. We also estimated the old carbon effect and radiocarbon reservoir age of the total organic carbon fraction. Using these estimates, we propose a new radiocarbon chronology for past climatic changes from ca. 12,500 to 700 cal BP. The linear sedimentation rate of the core was founded to be constant at 32.0 cm/kyr, indicating stable sedimentation conditions in Lake Pumoyum Co from the period of the Younger Dryas to the Holocene.

We obtained three sediment cores from a high-altitude lake (Lake Pumoyum Co; altitude, ~ 5020 m asl) on the southern Tibetan plateau for reconstruction of environmental changes during the last glacial–Holocene transition. In this study, we established the first reliable chronology for sediment cores from Lake Pumoyum Co, ca. 18.5 cal ka BP at the bottom, by 14C analyses of terrestrial plant residue concentrates (PRC, > 125 μm) and aquatic plant residues. The calibrated ages of the PRC fraction in the surface sediment were nearly modern (0.1 ± 0.1 cal ka BP), and the δ13C values (− 22‰ to − 24‰) were agreed well with those of modern terrestrial C3 plants. In addition, we estimated 14C reservoir ages of macrophyte remains from changes in their δ13C values. The major climate boundary layers in the cores (transitions to Bolling–Allerod, 14.5 ± 0.5 cal ka BP; Younger Dryas, 12.8 ± 0.1 cal ka BP; and Preboreal, ~ 11.6 cal ka BP) were confirmed by our new 14C chronology. The transition to the Bolling–Allerod warm phase from the last glacial (14.5 ± 0.5 cal ka BP) coincided with an obvious lithologic boundary (a rapid decrease in the abundance of the macrophyte remains) in the Lake Pumoyum Co sediment cores.

Further discussion about the limnological features of Lake Puma Yum Co, South Tibet, China, is provided based on the results of several investigations. By using depth data from all over the lake, the whole submarine topography has been compiled. Horizontal analysis of the water's physicochemical features indicates that compared with the relatively uniform water features at other lake areas, apparent spatial heterogeneity exists in the water of the subaquatic alluvial fan induced by the Jiaqu River, the biggest inflow. Vertical analysis of water characteristics using two-factor analysis of variance with no re-experiment indicates that temperature, dissolved oxygen, and pH of the water vary with water depth rhythmically, whereas other parameters demonstrate no evident vertical variation, which shows that chemical stratification is not obvious. But this does not exclude slightly higher concentrations of Ca2+ induced by lower pH at the bottom of deep lake water. The hydrochemistry difference between inflow water and lake water reveals the loss of Ca2+ in lake water, which indicates calcite deposition may be an important characteristic of lake sediment.

A new continuous sediment core (PY608W-PC; 3.8 m length) for reconstruction of climatic and environmental changes in the southeastern Tibetan Plateau was taken from the eastern part of Lake Pumoyum Co in August 2006. Sediment layers of the lower part of PY608W-PC (380–300 cm depth) were composed mainly of relatively large plant residues (up to ∼3 cm in length) with an admixture of fine sand and sandy silt. The large plant residues disappeared at ∼300–290 cm depth in core PY608W-PC and were replaced by silt-silty clay. The large plant residues from the lower part of PY608W-PC could be aquatic, because the plant residues were extremely enriched in 13C (up to –3.0‰, −5.6 ± 2.3‰ on average). On the other hand, the plant residue concentrates (PRC fractions) from the upper part of the core (290–0 cm in depth) could be terrestrial C3 plants (δ13C = –21.8 ± 1.7‰ on average). Radiocarbon dating was performed on the large plant residues and PRC fractions from the PY608W-PC sediment core, which represented the chronology from ∼19,000 cal BP to present.

Soil samples from an 85-cm-long continuous section (PY608ES) were collected from an island in Lake Pumoyum Co (southeastern Tibetan Plateau, ∼5020 m asl) in August 2006. To estimate past environmental conditions of Lake Pumoyum Co during the Holocene, we analyzed radiocarbon ages, stable carbon isotope compositions, and total organic carbon/total nitrogen (TOC/TN) atomic ratios of the soil samples. The 14C measurements were performed with the Tandetron accelerator mass spectrometry system at the Center for Chronological Research, Nagoya University. The 14C concentration in the surface layer (101 pMC; 5–10 cm soil depth) was nearly modern. A 14C chronology of the sequence indicated that continuous soil development began on the island in Lake Pumoyum Co at ∼5800 cal BP (at 63 cm soil depth, the top of a gravel layer). These results may reflect a decrease in the lake level in the middle Holocene. The age of the obvious lithologic boundary (∼5800 cal BP) corresponds to the end of Holocene climate optimum.

We constructed a new age model based on high-time-resolution 14 C data sets from three sediment cores from Academician ridge, Lake Baikal, for reconstruction of environmental and biological changes in southern Siberia during the last ca. 30 kyr. We used 14 C ages of total organic carbon (TOC) for the model, because terrestrial plant residues and biogenic carbonate were not observed in the sediments. For accurate dating and age models based on 14 C ages of TOC, the freshwater 14 C reservoir effect and the effect of dead carbon from land-derived organic materials must be estimated. In this study, we estimated the correction factor for these effects to be 2100 ± 90 yr, on the basis of a key layer, the “ 14 C plateau”, caused by changes in the atmospheric 14 C concentration during the Younger Dryas (YD) cooling event. The new age scale, along with the TOC mass accumulation rate (MAR TOC ) and stable carbon isotope ratio in the sediment cores, clearly indicate a rapid decrease in lake productivity and reduced influx of terrestrial organic materials into the lake during the YD (12.8–11.6 cal ka BP). Productivity was high (MAR TOC , up to 19.7 mg/cm 2 ·kyr) in and around Lake Baikal during 9.3–6.4 cal ka BP (Holocene climate optimum). Moreover, paleoproductivity changes during the last ca. 30 kyr in and around the Lake Baikal were clearly associated with fluctuations in the East Asian monsoon intensity, as inferred from the δ 18 O record from Sanbao and Hulu caves, China, during the late Quaternary (Wang et al., 2008. Nature 451, 1090–1093).

This study investigates the source and flux of particulate 129I in the downstream reaches of the Niida River system in Fukushima. The upper watershed is a relatively highly contaminated zone located 30–40 km northwest of the Fukushima Daiichi Nuclear Power Plant. Samples of total suspended substance (SS) were collected continuously at Haramachi (5.5 km upstream from the river mouth) from December 2012 to January 2014 using a time-integrative SS sampler. Activity of 129I and the 129I/127I ratio in SS were 0.9–4.1 mBq kg−1 and (2.5–4.4) × 10−8, respectively, and were strongly correlated with the total dry weight of SS samples with R2 of 0.79–0.88. High SS 129I activity and 129I/127I ratios were found in March, April, September, and October 2013. SS 129I activity and 129I/127I ratios are considered to reflect the SS source, i.e., the more contaminated upper watershed or the less contaminated downstream area. The flux of particulate 129I at the Haramachi site was estimated to be 7.6–9.0 kBq month−1 during September–October 2013. A relatively high amount of particulate 129I may have been transported from the upstream to the downstream reaches of the Niida River by high rainfall over this period.

Limnological features of Lake Puma Yum Co, a typical alpine lake located at the altitude of 5030 m in the Tibetan Plateau, China, are described based on the findings of the second expedition in September 2004. The lake surface is about 280km2 and maximal depth is 65 m. Total inflow just after the rainy season was estimated to be about 860 000m3 day−1, and the lake water was drained from a newly excavated channel at a rate of 960 000m3 day−1. We may have to expect undesirable lowering of the water level by this new drainage, especially in the dry season. Thermocline developed from 20 to 30 m depth, and the euphotic zone reached the 50 m depth. Dissolved oxygen in surface water was supersaturated as in productive lakes, although there were no large point and nonpoint sources of nutrient in the catchment. Vertical distribution of phytoplankton biomass and primary production suggested the presence of photoinhibition. What should be noted about the flora and fauna is that a Chara zone and a shell zone were distributed at about 30 or 40 m of depth.

Lake Pumoyum Co is on the southeastern Tibetan plateau (altitude, ∼5030 m asl; lake surface area, 281 km2; maximum water depth, 65 m). We obtained 14C dates on total organic carbon (TOC) for three sediment cores from Lake Pumoyum Co, covering the period from the last glacial to the Holocene, and compared them with 14C ages on plant residue concentrates (PRC fraction, mainly terrestrial plant residues) and aquatic plant fragments in the cores. The calibrated ages of TOC were older than those of the PRC fraction in the sediment cores by ca. 0.6–11.3 kyr. The calculated dead carbon fraction (fdead carbon) values for TOC increased during 9.5–5.5 cal ka BP, and fluctuations of fdead carbon paralleled variations in Asian monsoon intensity [Y. Wang et al., Nature 451 (2008) 1090]. One possible explanation for these results is that large amounts of terrestrial organic materials containing old carbon were supplied to the lake (“old carbon effects” from lake terrace, paleosol and/or stratum with dead 14C) when the lake level rose rapidly and its catchment area expanded during the Holocene climate optimum (9.5–5.5 cal ka BP).