Development of a chironomid-based air temperature inference model for the central Canadian Arctic

Subfossil midge remains were identified in surface sediment recovered from 88 lakes in the central Canadian Arctic. These lakes spanned five vegetation zones, with the southern-most lakes located in boreal forest and the northern-most lakes located in mid-Arctic tundra. The lakes in the calibration are characterized by ranges in depth, summer surface-water temperature (SSWT), average July air temperature (AJAT) and pH of 15.5 m, 10.60°C, 8.40°C and 3.69, respectively. Redundancy analysis (RDA) indicated that maximum depth, pH, AJAT, total nitrogen-unfiltered (TN-UF), Cl and Al capture a large and statistically significant fraction of the overall variance in the midge data. Inference models relating midge abundances and AJAT were developed using different approaches including: weighted averaging (WA), weighted averaging-partial least squares (WA-PLS) and partial least squares (PLS). A chironomid-based inference model, based on a two-component WA-PLS approach, provided robust performance statistics with a high coefficient of determination (r ² = 0.77) and low root mean square error of prediction (RMSEP = 1.03°C) and low maximum bias. The use of a high-resolution gridded climate data set facilitated the development of the midge-based inference model for AJAT in a region with a paucity of meteorological stations and where previously only the development of a SSWT inference model was possible. David Porinchu and Nicolas Rolland contributed equally to the work.     

Sciaridae in lake sediments: indicators of catchment and stream contribution to fossil insect assemblages

The larval head capsules of Sciaridae (black fungus gnats) are transported into lakes from terrestrial habitats, in most cases via streams or rivers, and preserve well in lake sediments. The abundance of sciarid remains can provide information on the importance of terrestrial and running-water input into fossil insect assemblages in lake sediments if examined in relation to the number of fossils of aquatic insects such as the Chironomidae, Thaumaleidae, Ceratopogonidae, or Simuliidae. Here we describe fossil head capsules of sciarid larvae and provide an example of how these remains can be used to constrain past changes in taphonomic processes that influence fossil chironomid records.     

2000—2018年青海湖流域气温和降水量变化趋势空间分布特征

青藏高原是全球气候变化的敏感区,气温和降水量的空间分布及变化趋势是气候变化研究的核心和基础,为开展生态环境变化评估提供基础资料。基于2000—2018年青海湖流域及其周边气象站观测数据,以高程为协变量,结合专业气象插值软件ANUSPLIN对气温和降水量进行空间插值。利用线性回归法分析了青海湖流域2000—2018年气温和降水量的变化趋势;利用双变量空间自相关分析法分析了青海湖流域气温和降水量空间匹配关系。结果表明：（1） 2000—2018年青海湖流域年平均气温呈显著增加趋势,平均增速为0.30 ℃·（10a）^-1,春季增温显著。（2） 降水量呈显著增加趋势,平均增速为73.20 mm·（10a）^-1,春夏季增速显著、秋季变化不明显、冬季趋于变干。（3） 青海湖流域气温和降水量空间匹配差异显著。从年尺度来看,气温和降水量莫兰指数（Moran’s I）为-0.66,表现为显著的负相关,面积比为67.56%,水热组合空间匹配不佳。从季节尺度来看,青海湖流域春季、夏季、秋季和冬季的气温和降水量Moran’s I分别为-0.49、-0.80、-0.32和-0.14,均为空间负相关。春夏季,流域低海拔区域气温逐渐升高,高海拔区域降水量逐渐增多,气温和降水量空间负相关面积逐渐增大,水热组合空间匹配不佳。值得强调的是青海湖巨大水体对环湖区局地气温的调节作用明显,是青海湖流域的“气候调节器”。     

Sensitivity of tropical-African aquatic invertebrates to short-term trends in lake level and salinity: a paleolimnological test at Lake Oloidien,Kenya

Aquatic invertebrates are intrinsically capable of rapid and sensitive response to changes in their lacustrine habitat. Fossil invertebrate assemblages preserved in the sediments of a climate-sensitive lake can thus produce high-resolution proxy records of past climate. In shallow lakes, however, a potential conflict exists between the sensitivity of biota to frequent habitat change in their fluctuating environment and the increased probability of disturbance of selected proxy records by bioturbation and physical mixing of sediments. I investigated this problem with tropical-African aquatic invertebrate faunas in a paleolimnological sensitivity study that incorporates both the response of biota to short-term habitat change and the taphonomic integrity of fossil assemblages in a small, shallow, and hydrologically closed lacustrine basin. Analysis of chironomid, cladoceran, and ostracode remains in a²¹⁰Pb-dated short core from Lake Oloidien (Kenya) indicates that habitat changes accompanying the late 19th- and 20th-century fluctuations in lake level (Z _max range: 3 to 18 m) and salinity (conductivity range:c. 400 toc. 2000–4000 µS cm^–1) were sufficient to drastically alter the composition of local benthic and planktonic invertebrate faunas. This response remained relatively unaffected by taphonomic phenomena during its incorporation into the sediment record. Results indicate that tropical-African aquatic invertebrate faunas in suitable climate-sensitive lakes are a valuable tool to resolve paleoclimatic fluctuations on a timescale of decades.This paper was presented at the VI Palaeolimnology Symposium, held at Canberra in April 1993. Dr. Mark Brenner guest edited this contribution.     

Vertical distribution of snow cover and its relation to temperature over the Manasi River Basin of Tianshan Mountains,Northwest China

How snow cover changes in response to climate change at different elevations within a mountainous basin is a less investigated question. In this study we focused on the vertical distribution of snow cover and its relation to elevation and temperature within different elevation zones of distinct climatology, taking the mountainous Manasi River Basin of Xinjiang, Northwest China as a case study. Data sources include MODIS 8-day snow product, MODIS land surface temperature (LST) data from 2001 to 2014, and in situ temperature data observed at three hydrological stations from 2001 to 2012. The results show that: (1) the vertical distribution of snow areal extent (SAE) is sensitive to elevation in low (<2100 m) and high altitude (>3200 m) regions and shows four different seasonal patterns, each pattern is well correspondent to the variation of temperature. (2) The correlation between vertical changes of the SAE and temperature is significant in all seasons except for winter. (3) The correlation between annual changes of the SAE and temperature decreases with increasing elevation, the negative correlation is significant in area below 4000 m. (4) The snow cover days (SCDs) and its long-term change show visible differences in different altitude range. (5) The long-term increasing trend of SCDs and decreasing trend of winter temperature have a strong vertical relation with elevation below 3600 m. The decreasing trend of SCDs is attributed to the increasing trend of summer temperature in the area above 3600 m.     

Chemical stratigraphy of recent sediments from a depth gradient in a meromictic lake, Nordbytjernet, SE Norway, in relation to variable external loading and sedimentary fluxes

Cores of recent sediments were sampled along a depth gradient in a 23 m deep kettle lake with stagnant deep waters containing exceptionally high concentrations of dissolved iron and manganese. Sediment cores were taken on two occasions, in 1978 and 1997, before and after an incidence of full circulation. The aims of this study are to see how oxic and anoxic conditions in the water column influence stratigraphy and sediment focusing and, to compare cores from 1979 and 1998 to see how measured element fluxes and external events are reflected in the chemical stratigraphy. Element analyses show characteristic stratigraphic patterns that depend on the ability to undergo redox transformations, sorptive properties and chemical equilibria in the anoxic deep waters and porewaters. In sediments from the oxic part of the lake Al, Cr, Co, Ni, Zn Cu, Cd, and Pb were well correlated. Positive correlations are seen between elements associated with primary production and sulphur. In the anoxic part of the lake most metals were positively correlated with carbonate. Phosphorus correlated positively with iron in sediments from oxic waters and negatively with manganese and iron deep-water sediments. Porewater analyses indicate that recycling from the deep-water sediments was negligible. The stratigraphy of lead agrees with the historic variation in atmospheric input and is used as a chronological marker. Assessed deposition rates agree with measurements in sediment traps. Most elements more than double their rates of deposition towards the deepest point of the lake, while sulphur, manganese and carbonate had maxima around the depth of the redoxcline in the water. Variations in the external loading and variable redox conditions in the deep waters explain variations in the chemical composition of recent sediments.     

A weighted-averaging regression and calibration model for inferring lakewater salinity from fossil diatom assemblages in saline lakes of the Vestfold Hills: a new tool for interpreting Holocene lake histories in Antarctica

The relationship between surface sediment diatom assemblages and measured limnological variables in thirty-three coastal Antarctic lakes from the Vestfold Hills was examined by constructing a diatom-water chemistry dataset. Previous analysis of this dataset by canonical correspondence analysis revealed that salinity accounted for a significant amount of the variation in the distribution of the diatom assemblages. Weighted-averaging regression and calibration of this diatom-salinity relationship was used to establish a transfer function for the reconstruction of past lakewater salinity from fossil diatom assemblages. Weighted-averaging regression and calibration with classical deshrinking provided the best model for salinity reconstructions and this was applied to the fossil diatom assemblages from one of the saline lakes in the Vestfold Hills in order to assess its potential for palaeosalinity and palaeoclimate reconstruction.