Flood and desiccation events reconstructed based on luminescence profiles and palaeobotanical proxies from the High Arctic lake Tenndammen, Svalbard

<p>We present a 700-year reconstruction of the environmental changes in the Colesdalen, Svalbard, inferred from a sediment core retrieved from lake Tenndammen (N 78°06.118; E 15°02.024). A comparison of modern and old maps revealed that the lake was artificially connected to its western tribute that now inputs additional water and sediment into the lake, but earlier lake Tenndammen was mainly fed by discharge and groundwater from the main valley. A multi-proxy approach was applied involving sedimentary ancient DNA (sedaDNA), pollen, spores, plant macrofossils, sedimentology and biogeochemistry. Establishing a chronology for this core was problematic as nine of the fourteen AMS dates were revered. However, core imaging as well as X-ray fluorescence (XRF) demonstrated clear stratification and undisturbed sediment layers. This is supported by the clear and coherent data obtained from the plant palaeo-proxies in terms of vegetation and environmental changes indicated by all proxies at the same core depths. From these observations, we inferred that lake Tenndammen experienced a number of floods which brought older sediments into the lake and produced a high proportion of the reversed dates. In order to test this hypothesis, portable optically stimulated luminescence (pOSL) and infrared stimulated luminescence (pIRSL) was employed. The pIRSL, pOSL and pIRSL/pOSL profiles suggested a series of 15 flooding and 8 drying events occurring at the depths associated with the reversed dates. However, relatively high amount of spheroidal carbonaceous particles (SCP, up to 1300 per gram of dried sediment mass) helped to improve the core chronology through a comparison with the calendar dates of the history of the coal mining and power production in Svalbard. SCP record allowed to find three tie points for the age-depth model at (1) the construction time of the power plant in 1911-1913 in Colesdalen, (2) the abrupt decrease in SCPs associated with the Second World War in 1941-1946, and (3) the highest output of the power plant in Colesdalen in the middle of the 1950s. When combined with the earlier non-reversed dates this provides an age-depth model with the basal age of the core at c. 730 cal. yr. BP and with the upper sediments deposited at c. 1950-1980s. Using this revised age-depth model, four chrono-stratigraphic units were described and, according to the data on luminescence profiling, the most intensive floods were associated with the second unit, which corresponded with the most intensive ice melting in the study area (c. 1670 - 1420 BP). The strongest drying events took place at the end of the second unit and in the first part of the third unit (c.  1655 BP). This was supported by the plant proxies with an abundance of the aquatic and swamp bryophyta <em>Warnstorfia exannulata/Warnstorfia fluitans</em>, algae (i.e. <em>Closterium littorale, Cosmarium botrytis</em> and <em>Staurastrum punctulatum</em>) both in the non-pollen microfossils record and the sedaDNA.  This study shows that a combination of biological proxies, sedimentology and pOSL can detect flood and desiccation events, and that lake Tenndammen was a highly sensitive fluvio-lacustrine systems during the late Holocene/Anthropocene.</p>

Winter atmospheric nutrients and pollutants deposition on West Sayan mountain lakes (Siberia)

The world map of anthropogenic atmospheric nitrogen deposition and its effects on natural ecosystems is not described with equal precision everywhere. In this paper, we report atmospheric nutrient, sulphate and spheroidal carbonaceous particles (SCPs) deposition rates, based on snowpack analyses, of a formerly unexplored Siberian mountain region. Then, we discuss their potential effects on lake phytoplankton biomass limitation. We estimate that the nutrient depositions observed in the late season snowpack (40 ± 16 mg NO3-N × m−2 and 0.58 ± 0.13 mg TP-P · m−2) would correspond to yearly depositions lower than 119 ± 71 mg NO3-N · m−2 · y−1 and higher than 1.71 ± 0.91 mg TP-P · m−2 · y−1. These yearly deposition estimates would approximately fit the predictions of global deposition models and correspond to the very low nutrient deposition range although they are still higher than world background values. In spite of the fact that such low atmospheric nitrogen deposition rate would be enough to induce nitrogen limitation in unproductive mountain lakes, the extremely low phosphorus deposition would have made the bioavailable N : P deposition ratio to be frankly high. In the end, lake phytoplankton appeared to be hanging on the fence between phosphorus and nitrogen limitation, with a trend towards nitrogen limitation. We conclude that slight imbalances in the nutrient deposition might have important effects on the ecology of these lakes under the expected scenario of climate warming, increased winter precipitation, enhanced forest fires and shifts in anthropogenic nitrogen emissions.

A century of anthropogenic environmental change in tropical Asia: Multi-proxy palaeolimnological evidence from Singapore’s Central Catchment

The environmental ramifications of rapid development on the functioning of warm tropical freshwater ecosystems are poorly understood. Here, a multi-proxy palaeolimnological approach is used to examine the nature and degree of anthropogenic environmental change in a tropical lowland reservoir in Singapore. Singapore has undergone a dramatic transformation over the past century, transitioning from a country with a largely agrarian landscape to one that is highly urbanised. Two radiometrically dated sediment cores were retrieved from one of the country’s oldest reservoirs and analysed for spheroidal carbonaceous particles (SCPs), mercury (Hg), atomic carbon (C) and nitrogen (N), stable C and N isotopes (δ13C and δ15N), and diatoms. The sedimentary data show clear evidence of atmospheric pollution and nutrient enrichment as a result of human activities in Singapore and the region. During the early stages of Singapore’s development (1900s–1960s), the reservoir was minimally impacted and characterised by oligotrophic conditions. As the country began to industrialise and urbanise (1970s–1990s), the SCP data indicate increasing contamination by air pollutants derived from domestic sources of fossil fuel combustion, while the diatom, C/N, δ13C, and δ15N data suggest that the reservoir was becoming more productive, possibly from N depositions arising from an increase in electricity generation and a rapid expansion in transport infrastructure in Singapore. As the pace of development in Singapore slowed down (1990s–the present), the sedimentary data collectively indicate increasing depositions of atmospheric pollutants and nutrient enrichment mediated by a warming climate. A substantial component of increased atmospheric pollution is likely to be of distal, and thus transboundary, origin.

Spheroidal carbonaceous particles in cryoconite sediment on the Russell glacier, Southwest Greenland

In this study, we analysed the organic and inorganic content of the cryoconite holes along the altitudinal gradient at the lower elevations of the Russell glacier ablation zone in Southwest Greenland. We specifically focus on less studied industrial microscopic spheroidal carbonaceous particles (SCP; part of black carbon) to get more insights about their accumulation patterns on the glacier surface. We found no clear SCP distribution pattern, including concentration values. This outcome underlines the complexity of the ice margin zone and draws attention for further research on this topic with the inclusion of multiyear evaluation of SCP concentration at the even wider area that could possibly give results that can be compared to the emission source and long-way air pollution validation. In addition, our results indicate that during the summer of 2016, algae composition was formed of both green algae (Chlamydomonadaceae, Mesotaeniaceae) and cyanobacteria (Oscillatoriaceae). Green algae had a larger relative proportion than cyanobacteria in the cryoconite holes throughout the studied gradient.

The study of atmospherically deposited Spheroidal Carbonaceous Particles (SCP) from the Kongsfjorden, Svalbard

The surface sediment samples of Kongsfjorden were analyzed for the Spheroidal Carbonaceous Particles (SCP) in an attempt to document the SCP in the environment other than previously studied inland lakes and snow and also to understand the probable source of industrial atmospheric pollution. The SCP are derived from the combustion of fossil fuels at high temperatures and are not produced naturally. They are chemically inert in both sediment and water and thus provide the indestructible record of atmospherically deposited pollutants in remote areas and anthropogenic impact on pristine environments. The SCP were recovered from different locations of the fjord and were classified according to their size range (small particles, 5-10 µm – large particles, 20-50 µm). The characterization of the spherical carbonaceous particles (shape, size, morphology, color etc.) was done under the light microscope. The detailed morphological features and chemical composition of SCP were studied using Scanning Electron Microscope equipped with Energy Dispersive X-Ray (SEM-EDX). The result shows that in term of a source of pollution in the area, long-range transportation is the major source of pollution but local sources cannot be ignored. This is a first attempt to study the SCP from the Kongsfjorden.