The oxygen isotopic composition of phosphate as an effective tracer for phosphate sources in Hongfeng Lake

In order to characterize the oxygen isotopic composition of internal phosphate and explore the possibility of using these data to identify phosphate sources, we measured oxygen isotopic compositions of phosphate(δ^(18)O_p) in sediment pore water in Hongfeng Lake, a typical deep-water lake in a mountainous area. These data, in combination with δ^(18)O_p in surface water samples and water column samples, were successfully used to identify phosphate sources. The δ^(18)O_p value of sediment pore water ranged from 15.2% to 15.8%, with an average value of 15.5%—the δ^(18)O_p value of internal phosphate. The δ^(18)O_p values decreased gradually through the water column from 19.4% in surface water to 16.4% in deeper water, implying that internal phosphate had more negative δ^(18)O_p values than external phosphate. This finding was substantiated by horizontal variations in δ^(18)O_p values, which decreased with increasing distance from inflowing rivers. All collected evidence suggests that external and internal phosphate have distinctly different isotopic signatures and that these signatures have not been considerably altered by biological mediation in Hongfeng Lake. Therefore, δ^(18)O_p can be used to distinguish phosphate sources. A two-endmember mixing model showed that internal phosphate had an average contribution of 40%, highlighting the influence of internal phosphorus loading on aqueous phosphate and eutrophication. This study illustrates the need to reduce the internal phosphorus load from sediment and provides guidance for nutrient management and in-lake restoration treatment in Hongfeng Lake. The data presented here are limited, but serve to highlight the great potential of δ^(18)O_p as an effective tracer for identifying phosphate sources. Systematic investigations of the oxygen isotopic compositions of external phosphate, internal phosphate, and phosphate through the water column, in combination with in-lake P biogeochemical cycle study, would be desirable in further research.

大高加索山南部大气降水氧同位素的气候意义

大高加索山脉位于黑海和里海之间,是欧洲与亚洲的分界线,该区域气候受到北大西洋涛动(North Atlantic Oscillation,NAO)的强烈影响。为了对该区域的大气降水δ^18O(δ^18OP)与NAO的关系有更加深入的认识,本文利用大高加索山以南6个全球降水同位素监测网(Global Network of Isotope in Precipitation,GNIP)站点的δ^18OP数据,分析该区域δ^18OP的季节变化规律,以及δ^18OP与温度和降水量等气象要素及大气环流之间的关系。得到以下主要认识:①在月时间尺度上,δ^18OP与月平均温度之间有着显著的正相关关系(p<0.01),表明该区域δ^18OP主要受当地温度控制,表现出“温度效应”。②北大西洋涛动通过改变西风的强度和位置从而影响δ^18OP的变化:当NAO呈现负相位时,此时西风输送较弱,使得来自地中海的富含18O的水汽能够达到大高加索山以南,该地区δ^18OP偏正。而当NAO正相位时,西风急流输送较强,从北大西洋穿越黑海带来更多的δ^18OP偏轻的降水。因此,NAO所导致的水汽输送路径的变化可能是影响大高加索山以南地区δ^18OP的重要因素,这一研究结果为利用该地区地质记录中的δ^18O记录来重建过去的NAO变化提供了前提。

天山地区大气降水氧同位素的影响因素及其对西风环流变化的指示意义

利用全球降水同位素观测网（GNIP）提供的乌鲁木齐大气降水氧同位素（δ^18Op）观测数据（1986-2003年）,结合和田δ^18Op数据及天山冰芯δ^18O记录,分析了天山地区δ^18Op在年内和年际尺度上的变化特征,及其与主要气候要素（温度和降水量）的关系。结果表明,年内尺度上,δ^18Op与月均温和月降水量均为显著正相关,表现出明显的＂温度效应＂;年际尺度上,加权平均年δ^18Op与年均温度却呈现负相关关系,与降水量仍为正相关。近40-50年的天山地区4支冰芯的δ^18O具有整体偏负的变化趋势,与研究区逐步升高的温度呈反向变化,说明在年际至年代际尺度上,这一区域δ^18Op与温度之间的负相关关系是客观存在的。进一步对研究区水汽来源路径的对比分析发现：δ^18Op值偏负的高温年份（1997年）的暖季水汽相对更多来源于远源的高纬度区域,而δ^18Op值偏正的低温年份（1988年）则相对更多来自近源的中、低纬度区域;同时,研究区上风方向的欧亚大陆14个GNIP站点1997年和1988年的暖季加权平均δ^18Op值存在高纬度区域偏负而中、低纬度区域偏正的特征;这些结果说明年际至年代际尺度上,天山地区δ^18Op与温度之间的负相关,本质上指示了西风环流南北摆动所引起的水汽来源变化,可以作为西风环流变化的指示器。

天山地区大气降水氧同位素的影响因素及其对西风环流变化的指示意义（英文）

Proxy records of the oxygen isotopic composition of meteorological precipitation （δ^18Op） preserved in archives such as ice cores, lacustrine carbonates and stalagmite calcite are important for paleoclimatic studies. Therefore, knowledge of the variations and controlling mechanisms of modern δ^18Op on different time scales is necessary. Here, we investigate the linear correlations between δ^18Op and corresponding temperature and precipitation on monthly and inter-annual timescales, using data from the Urumqi （1986-2003） and Hotan stations of the Global Network of Isotopes in Precipitation （GNIP）, and δ^18O data from 4 ice cores in the adjacent Tianshan Mountains. Consistent with previous reported results, modern δ^18Op variations on a seasonal time scale in the Tianshan region are mainly controlled by a ＇temperature effect＇ （indicated by a significant positive correlation between δ^18Op and temperature）, with more positive δ^18Op values occurring in summer. However, on an inter-annual timescale, there is a weak inverse correlation between weighted average annual δ^18Op and annual average temperature at Urumqi station. This finding is supported by the inversely varying trends of δ^18Op data from 4 ice cores in the central and eastern Tianshan Mountains compared to annual average temperatures in the same region during the past 40-50 years. The data from Urumqi station and the 4 ice cores demonstrate that there is inverse correlation between δ^18Op and temperature on inter-annual to decadal time scales. Analysis of water vapor sources and pathways for the warm year of 1997 and the cold year of 1988 reveal that relatively more water vapor for the Tianshan region was derived from long-distance transport from high-latitude sources than during the warm year of 1997; and that more water vapor was transported from more proximal sources from mid- to low-latitude areas during the cold year of 1988. In addition, the δ^18Op values are more negative in the high latitude areas than those in mid- to low-latitude areas in the Eurasian continent at the upper wind direction of Tianshan Mountains region, according to the weighted averaged warm season （May to September）δ^18Op values for 14 GNIP stations in the years 1997 and 1988. Due to the distribution of δ^18Op within the Eurasian continent, the relative shift of water vapor sources between warm and cold years convincingly explains the observed variations of δ^18Op in the Tianshan Mountains region. Therefore, we conclude that variations in 518OD in this region are mainly controlled by changes in water vapor sources which are ultimately caused by northward and southward shifts in the Westerly circulation.