白令海陆架区夏季水文分布特征及年际变化

On the basis of the CTD data obtained within the Bering Sea shelf by the Second to Sixth Chinese National Arctic Research Expedition in the summers of 2003, 2008, 2010, 2012 and 2014, the classification and interannual variation of water masses on the central Bering Sea shelf and the northern Bering Sea shelf are analyzed. The results indicate that there are both connection and difference between two regions in hydrological features. On the central Bering Sea shelf, there are mainly four types of water masses distribute orderly from the slope to the coast of Alaska: Bering Slope Current Water(BSCW), MW(Mixed Water), Bering Shelf Water(BSW) and Alaska Coastal Water(ACW). In summer, BSW can be divided into Bering Shelf Surface Water(BSW_S) and Bering Shelf Cold Water(BSW_C). On the northern Bering Sea shelf near the Bering Strait,it contains Anadyr Water(AW), BSW and ACW from west to east. But the spatial-temporal features are also remarkable in each region. On the central shelf, the BSCW is saltiest and occupies the west of 177°W, which has the highest salinity in 2014. The BSW_C is the coldest water mass and warmest in 2014; the ACW is freshest and mainly occupies the east of 170°W, which has the highest temperature and salinity in 2012. On the northern Bering Sea shelf near the Bering Strait, the AW is saltiest with temperature decreasing sharply compared with BSCW on the central shelf. In the process of moving northward to the Bering Strait, the AW demonstrates a trend of eastward expansion. The ACW is freshest but saltier than the ACW on the central shelf,which is usually located above the BSW and is saltiest in 2014. The BSW distributes between the AW and the ACW and coldest in 2012, but the cold water of the BSW_C on the central shelf, whose temperature less than 0°C, does not exist on the northern shelf. Although there are so many changes, the respond to a climate change is synchronized in the both regions, which can be divided into the warm years(2003 and 2014) and cold years(2008, 2010 and 2012). The year of 2014 may be a new beginning of warm period.     

北极地区深海微生物研究进展及对策

对北极地区深海微生物研究进展进行了综述和展望分析,并提出强化我国北极深海微生物研究的对策,以期为相关研究和决策提供参考。综述表明北极深海微生物具有丰富的多样性,是数量巨大的遗传基因资源承载者,群落结构表现出显著的空间分布差异,在北极深海食物链中可能发挥着基础性作用。展望分析提出聚焦北极深海这一特殊的极端环境,开展微生物多样性和地理分布特征研究、新颖遗传生化功能挖掘以及多尺度生态系统下微生物与环境变化的研究具有重要意义和价值。建议我国顶层布局、构建北极深海微生物协同研究体系,提升专用配套仪器装备保障能力,全面推进相关研究工作。     

Assessing the effects of forest biomass reductions on forest health and streamflow

Forest biomass reductions in overgrown forests have the potential to provide hydrologic benefits in the form of improved forest health and increased streamflow production in water-limited systems. Biomass reductions may also alter evaporation. These changes are generated when water that previously would have been transpired or evaporated from the canopy of the removed vegetation is transferred to transpiration of the remaining vegetation, streamflow, and/or non-canopy evaporation. In this study, we combined a new vegetation-change water-balance approach with lumped hydrologic modelling outputs to examine the effects of forest biomass reductions on transpiration of the remaining vegetation and streamflow in California's Sierra Nevada. We found that on average, 102 mm and 263 mm (8.0% and 20.6% of mean annual precipitation [MAP]) of water were made available following 20% and 50% forest biomass-reduction scenarios, respectively. This water was then partitioned to both streamflow and transpiration of the remaining forest, but to varying degrees depending on post-biomass-reduction precipitation levels and forest biomass-reduction intensity. During dry periods, most of the water (approximately 200 mm [15.7% on MAP] for the 50% biomass-reduction scenario) was partitioned to transpiration of the remaining trees, while less than 50 mm (3.9% on MAP) was partitioned to streamflow. This increase in transpiration during dry periods would likely help trees maintain forest productivity and resistance to drought. During wet periods, the hydrologic benefits of forest biomass reductions shifted to streamflow (200 mm [15.7% on MAP]) and away from transpiration (less than 150 mm [11.8% on MAP]) as the remaining trees became less water stressed. We also found that streamflow benefits per unit of forest biomass reduction increased with biomass-reduction intensity, whereas transpiration benefits decreased. By accounting for changes in vegetation, the vegetation-change water balance developed in this study provided an improved assessment of watershed-scale forest health benefits associated with forest biomass reductions.     

Hydrologic connectivity at the hillslope scale through intra-snowpack flow paths during snowmelt

The seasonal snowmelt period is a critical component of the hydrologic cycle for many mountainous areas. Changes in the timing and rate of snowmelt as a result of physical hydrologic flow paths, such as longitudinal intra-snowpack flow paths, can have strong implications on the partitioning of meltwater amongst streamflow, groundwater recharge, and soil moisture storage. However, intra-snowpack flow paths are highly spatially and temporally variable and thus difficult to observe. This study utilizes new methods to non-destructively observe spatio-temporal changes in the liquid water content of snow in combination with plot experiments to address the research question: What is the scale of influence that intra-snowpack flow paths have on the downslope movement of liquid water during snowmelt across an elevational gradient? This research took place in northern Colorado with study plots spanning from the rain-snow transition zone up to the high alpine. Results indicate an increasing scale of influence from intra-snowpack flow paths with elevation, showing higher hillslope connectivity producing larger intra-snowpack contributing areas for meltwater accumulation, quantified as the upslope contributing area required to produce observed changes in liquid water content from melt rate estimates. The total effective intra-snowpack contributing area of accumulating liquid water was found to be 17, 6, and 0 m² for the above tree line, near tree line, and below tree line plots, respectively. Dye tracer experiments show capillary and permeability barriers result in increased number and thickness of intra-snowpack flow paths at higher elevations. We additionally utilized aerial photogrammetry in combination with ground penetrating radar surveys to investigate the role of this hydrologic process at the small watershed scale. Results here indicate that intra-snowpack flow paths have influence beyond the plot scale, impacting the storage and transmission of liquid water within the snowpack at the small watershed scale.     

Preferential exchange rate effect of isotopic fractionation in a melting snowpack

Stable isotope exchange processes between solid and liquid phases of a natural melting snowpack are investigated in detail by separating the liquid water from snow grains at different depths of the snowpack and collecting the bottom discharge using a lysimeter. In the melting–freezing mass exchange process between the two phases, the theoretical slope of the δD? δ¹⁸O line for newly refrozen ice is calculated to be nearly that of pore water. However, based on observations of the isotopic evolution and snow grain coarsening of the snowpack, it is demonstrated that the slope of the δD? δ¹⁸O line for newly refrozen ice is equal to that of the original ice. This is proved to be due to preferential water flow in the snowpack, which leads to relatively more deuterium and less oxygen‐18 in the mobile water than the immobile water because of the kinetic effect. Higher mass exchange rate in the mobile water region results in excess deuterium in the bulk refrozen ice, compared with the fractionation of uniform fractionation factors and exchange rate. This effect, which is termed the ‘preferential exchange rate effect of isotopic fractionation’, is shown to be larger in the lower part than the upper part of the snowpack. Copyright © 2008 John Wiley & Sons, Ltd.     

Holocene palaeoceanographic changes in Barrow Strait,Canadian Arctic: foraminiferal evidence

Holocene changes in the benthic and planktic foraminiferal fauna (>63 µm) from a marine sediment core (ARC‐3 Canadian Arctic Archipelago, 74° 16.050′ N, 91° 06.380′ W, water depth 347 m) show that significant environmental and palaeoceanographic variations occurred during the last 10 ka. Foraminiferal assemblages are restricted to the ca. 4.5–10 ka interval as younger samples are mostly barren of foraminifera due to intense carbonate dissolution after ca. 4.5 ka. Foraminiferal assemblages in the ca. 4.5–10 ka interval are dominated by the benthic species Islandiella helenae and Cassidulina reniforme (57% of total), with Elphidium clavatum, Cibicides lobatulus and Buccella frigida also being common in this interval. The dominance of these species indicates a seasonal sea ice regime which is consistent with the occurrence of the sea ice diatom‐derived organic geochemical biomarker IP₂₅ throughout the core. The abundances of C. reniforme and E. clavatum decline upcore; consistent with more frequent mixing of the Barrow Strait water column during the early Holocene. It is likely that the influence of CO₂‐rich Arctic surface water masses have caused an increase in bottom water corrosivity after ca. 8.5 ka, and dissolution has been further enhanced by sea ice‐related processes after ca. 6 ka, concomitant with increased IP₂₅ fluxes. Dissolution is strongest when IP₂₅ fluxes are highest, suggesting a link between the sea ice and benthic systems. Copyright © 2010 John Wiley & Sons, Ltd.     

NOAA16卫星积雪识别和参数提取

通过对积雪、地物和云进行光谱分析,指出传统的NOAA-AVHRR可见光和近红外波段进行云雪识别存在困难,而雪在红外波段的低反射性特点是区分云雪的一个可行途径.利用NOAA16气象卫星新增的1.6μm红外波段,对中国北方冬季的卫星积雪图象进行识别,结果显示,云雪可以准确区分.同时,提出了利用AVHRR资料估算积雪面积、积雪深度和积雪时间的方法,并对积雪深度进行了精度检验.     

中国首次北极科学考察沿线气溶胶可溶性成分的分析

中国首次北极科学考察沿线采集的大气气溶胶样品可溶性成分分析表明,大气气溶胶的平均载量为195neq·m^-3,Na⁺和Cl^-的贡献为0%,NH₄⁺和SO₄^2-的贡献为27%,nssSO₄^2-对SO₄^2-的贡献为8%.气溶胶中阴、阳离子总量基本相当,大气环境呈中性.气溶胶中可溶性成分具有较强的纬度变化特征.根据离子的变化态势可将离子分为3大类,即1)Na⁺,Cl^-,SO₄^2-,K⁺,Mg²⁺,Ca²⁺;2)NH₄⁺,NO₃^-;3)MSA.Na⁺和Cl^-具有较好的线性关系,Cl^-/Na⁺的当量浓度比为1.01,小于其在海水中的比值1.1.NH₄⁺和NO₃^-的浓度随纬度的增加呈现减少的趋势,说明在低纬度近海岸地区人类活动的污染相当强烈.MSA的浓度在白令海区出现高值,与Shemya(52°N,174°E)站夏季浓度1.79±0.83neq·m^-3(170±79ng·m^-3)相当.通过与不同海区夏季释放DMS的通量对比,进一步证明了低温有利于DMS向MSA的转化.     

The Nature and Predictability of the East Asian Extreme Cold Events of 2020/21

Three extreme cold events invaded China during the early winter period between December 2020 to mid-January 2021 and caused drastic temperature drops,setting new low-temperature records at many stations during 6?8 January 2021.These cold events occurred under background conditions of low Arctic sea ice extent and a La Ni?a event.This is somewhat expected since the coupled effect of large Arctic sea ice loss in autumn and sea surface temperature cooling in the tropical Pacific usually favors cold event occurrences in Eurasia.Further diagnosis reveals that the first cold event is related to the southward movement of the polar vortex and the second one is related to a continent-wide ridge,while both the southward polar vortex and the Asian blocking are crucial for the third event.Here,we evaluate the forecast skill for these three events utilizing the operational forecasts from the ECMWF model.We find that the third event had the highest predictability since it achieves the best skill in forecasting the East Asian cooling among the three events.Therefore,the predictability of these cold events,as well as their relationships with the atmospheric initial conditions,Arctic sea ice,and La Ni?a deserve further investigation.     

积雪融雪过程中水、热、溶质耦合运移规律的研究进展

大气污染的加剧,形成大量的酸性雨,在冬季则以酸性雪的形式出现.酸性雪对土壤环境、水环境及生态环境的影响已经引起世界性的关注,而对于积雪、融雪过程中水、热、溶质耦合运移规律的研究是评价和预测这些影响的理论基础.在查阅大量中外相关文献的基础上,对该领域的研究历史、发展现状和尚待解决的问题进行了综述.