Measurement of O(1D) formation by ozone photolysis in the troposphere

An actinometric method to determine the rate constantk _1D of O(¹D) formation by ozone photolysis in the troposphere and at higher altitudes is presented. N₂O is used as a scavenger gas for O(¹D), and the molecular nitrogen product measured after gas chromatographic separation. First results of the method for ground level and for 26 km altitude are reported and compared with theoretical estimates ofk _1D for these levels.     

D/H and O/O ratios of water in the crater lake at Kusatsu-Shirane volcano, Japan

The D/H and ¹⁸O/¹⁶O ratios of water in the active crater lake situated on the Kusatsu-Shirane volcano, Japan are about 20 and 6‰, respectively, higher than local meteoric water. The ratios show seasonal variations superimposed on a gradual change over nine years. The isotopic ratios started to increase in early 1990 and decrease in the spring of 1995. The seasonal variation which is high in winter and low in summer correlates with the temperature difference between lake water and ambient air. The large temperature difference in winter enhances the evaporation of lake water and produces the enriched isotopic ratios relative to the ratios in summer. The accumulation of snow and the decrease in the flux of meteoric water into the lake strengthens the winter-time isotopic enrichment. The enriched isotopic ratios of the lake water over a long time result from the addition of an end member with heavy isotopic ratios contained in a thermal fluid supplied to the lake. Considering the water balance in the lake, the isotopic ratios of the thermal fluid were found to be close to the lake water itself, suggesting the circulation of the lake water seeping through lake floor. Based on the correlation between Cl⁻concentration and the isotopic ratios, the contribution by the heavy end member was estimated to be 25–36% relative to the enrichment by evaporation. The heavy end member could be a liquid phase evolved from a parental fluid, which is a mixture of local meteoric water and a magmatic fluid as found in high-temperature volcanic gases.     

Water uptake of riparian plants in the lower Lhasa River Basin,South Tibetan Plateau using stable water isotopes

Riparian plants can adapt their water uptake strategies based on climatic and hydrological conditions within a river basin. The response of cold-alpine riparian trees to changes in water availability is poorly understood. The Lhasa River is a representative cold-alpine river in South Tibet and an under-studied environment. Therefore, a 96 km section of the lower Lhasa River was selected for a study on the water-use patterns of riparian plants. Plant water, soil water, groundwater and river water were measured at three sites for δ¹⁸O and δ²H values during the warm-wet and cold-dry periods in 2018. Soil profiles differed in isotope values between seasons and with the distance along the river. During the cold-dry period, the upper parts of the soil profiles were significantly affected by evaporation. During the warm-wet period, the soil profile was influenced by precipitation infiltration in the upper reaches of the study area and by various water sources in the lower reaches. Calculations using the IsoSource model indicated that the mature salix and birch trees (Salix cheilophila Schneid. and Betula platyphylla Suk.) accessed water from multiple sources during the cold-dry period, whereas they sourced more than 70% of their requirement from the upper 60–80 cm of the soil profile during the warm-wet period. The model indicated that the immature rose willow tree (Tamarix ramosissima Ledeb) accessed 66% of its water from the surface soil during the cold-dry period, but used the deeper layers during the warm-wet period. The plant type was not the dominant factor driving water uptake patterns in mature plants. Our findings can contribute to strategies for the sustainable development of cold-alpine riparian ecosystems. It is recommended that reducing plantation density and collocating plants with different rooting depths would be conducive to optimal plant growth in this environment.     

鄱阳湖湿地典型植被群落地下水—土壤—植被—大气系统界面水分通量及水源组成

地下水-土壤-植被-大气系统(GSPAC)界面水分传输是湿地生态水文过程研究的关键.本文选取鄱阳湖湿地高位滩地的2种典型植被群落:茵陈蒿(Artemisia capillaris)和芦苇(Phragmites australis)群落为研究对象,运用HYDRUS-1D垂向一维数值模拟,量化了湿地GSPAC系统界面水分通量,阐明了典型丰水年(2012年)和枯水年(2013年)鄱阳湖湿地植被群落的蒸腾用水规律和水源组成.结果表明:(1)茵陈蒿和芦苇群落土壤-大气界面的年降水入渗量为1570~1600 mm,主要集中在雨季4-6月,占年总量的60%;植物-大气界面的年蒸腾总量分别为346~470 mm和926~1057 mm,其中7-8月植被生长旺季最大,占年总量的40%~46%;地下水-根区土壤界面的向上补给水量受不同水文年水位变化的影响显著,地下水年补给量分别为15~513 mm和277~616 mm,主要发生在蒸散发作用强烈和地下水埋深较浅的时段.(2)植被蒸腾用水分为生长初期(4-6月)和生长旺季(7-10月)2个阶段,丰水年植被的整个生长期蒸腾用水充足,枯水年植被生长旺季的蒸腾用水受到严重水分胁迫,实际蒸腾量仅为潜在蒸腾量的一半左右.(3)不同水文年湿地植被生长旺季的水源贡献不同:丰水年茵陈蒿群落以地下水补给为主,芦苇群落以湖水和地下水补给为主;枯水年茵陈蒿群落以降水和前期土壤水储量为主,芦苇群落以地下水补给为主.本研究结果有助于揭示湿地植被的水分利用策略,为阐明湖泊水情变化与植被演替的作用机理提供参考依据.     

Chronology of Early to Mid-Pleistocene sediments in the northern North Sea: New evidence from amino acid and strontium isotope analyses

Sediments deposited during glacial-interglacial cycles through the Early to Mid-Pleistocene in the North Sea are chronologically poorly constrained. To contribute to the chronology of these units, amino acid racemization (AAR) and strontium (Sr) isotope analyses have been performed on samples from four shallow borings and one oil well along a transect in the northern North Sea. D/L Asp (aspartic acid) values obtained through reverse-phase liquid chromatography in the benthic foraminiferal species Elphidium excavatum is focused on because of consistent results and a good stratigraphic distribution of this benthic species. For the Early Pleistocene, an age model for the well 16/1–8, from the central part of the northern North Sea based on Sr ages allows for dating of the prograding wedges filling the pre-Quaternary central basin. A regional calibration curve for the racemization of Asp in Elphidium excavatum is developed using published ages of radiocarbon-dated samples and samples associated with the previously identified Bruhnes/Matuyama (B/M) paleomagnetic boundary and a Sr age from this study. Based on all the available geochronological evidence, samples were assigned to marine oxygen isotope stages (MIS) with uncertainties on the order of 10–70 ka.Sr ages suggest a hiatus of <2 million years (Ma) possibly due to non-deposition or low sedimentation between the Utsira Formation (Pliocene) and the Early Pleistocene. An increase in sedimentation rates around 1.5 ± 0.07 Ma (∼MIS 51) may partly be due to sediment supply from rivers from the south-east and partly due to the extension of ice sheet around 1.36 ± 0.07 Ma from the Norwegian coast to the central North Sea. A possible basin-wide glaciation occurred around 1.1 Ma (∼ MIS 32) (upper regional unconformity/top of unit Q4 in this study), resulting in erosion and regional unconformity. Two interglacials in the Norwegian Channel have been dated: the Radøy Interglacial to 1.07 ± 0.01 Ma (possibly MIS 31, the ‘super interglacial’), and the Norwegian Trench Interglacial to 0.50 ± 0.02 Ma (possibly MIS 13). A massive till unit identified at the same stratigraphic level in all shallow borings may partly represent an extensive MIS 12 glaciation. This study shows that the combined use of amino acid racemization data and Sr isotope chronology can refine the chronological ambiguities of Quaternary North Sea sediments related partly to the impact of glacial processes.