Browsing by Subject "proxy"
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Hydrological changes in subarctic Russian peatlands during the last millennia due to climate change (2021)Abstract: Northern boreal peatlands form one of the biggest carbon pools in the biosphere, thus having great potential to cause major changes to the global carbon cycle. The ongoing recent warming may affect the carbon dynamics though factors, such as, vegetation, hydrology and permafrost balance. As the future is still uncertain there are no definitive answers on how the peatlands will react in the future. Fortunately, moisture sensitive organisms such as, bryophytes and testate amoeba is preserved in the peat and can therefore be used to reconstruct past climatic shifts. In this thesis I studied palaeohydrology and peat accumulation over the last two millennia, from three peat cores originating in a permafrost peatland in Rogovaya, Russia. I used testate amoeba as a proxy of past moisture conditions and plotted the taxa composition of each core against 14C and 210Pb dated samples, to reconstruct past moisture shifts. The results were also supplemented by plant macrofossil and carbon accumulation data for more robust results. Of the three cores, Rog11 provided the oldest testate amoeba dataset by reaching the Dark Ages Cold Period. During this period there were indications of dry moisture conditions followed by a wet Medieval Warm Period. The Little Ice Age gave indications of a drying trend, while toward the end of the LIA Rog8 indicated opposite moisture conditions. From the end of the LIA onwards a general trend of drying and increased carbon accumulated is noted. Yet, during the last decade the trend has turned. The wet shift might indicate that the threshold for the peatland has been reached and the amount of melting permafrost has exceeded the evapotranspiration rate. As a conclusion my result indicates that the dynamics of both hydrology and carbon are complicated processes affected by both autogenic and allogenic factors, therefore causing large variability even on a local scale. The absence of widely spread observations of the most recent wet shift also indicates that the response of the peatland to the recent warming might be unequal. To rectify this situation, continued research is crucial, so that we can increase our understanding of climate-peatland interactions.
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(2024)For a better understanding of global climate change we need evidence allowing us to track changes in the environment. Pollen is geologically stable, making it a key option as a potential proxy for tracing historic environmental changes. To quantify past environmental changes, it is necessary to test proxies under today’s climate. The amount of UV-B radiation reaching the surface of the Earth has varied throughout the Earth’s history. These variations are ecologically important because changes in UV-B radiation impact plant regulation, growth, defense, and decomposition. The availability of fossil pollen and spores has resulted in significant interest in the potential of using the relationship between UV-B radiation and the accumulation of phenolic sunscreens as a proxy to trace past changes in UV-B radiation. Fossil pollen from Pinus sylvestris is readily available and proven techniques exist to quantify levels of UV-B absorbing compounds from both fossil and extant pollen. We investigated how levels of UV-B-absorbing compounds in Pinus sylvestris pollen change after strobili developed under UV attenuating filters. Fifteen Pinus sylvestris trees were selected from a seed orchard of trees in Nurmijärvi, Finland. The treatments used were Rosco 226 film – filtering solar UV-A and UV-B light, polyester film – filtering solar UV-B, polyethylene film – acting as a transparent control, and an open control condition with no filter. The filters were installed in April 2022 and 2023 and remained in place each year beyond dehiscence towards the end of May. The pollen was analysed using Fourier-transform infrared spectroscopy. Principal component analyses and linear regression models were used to simplify the multivariate data and then describe the levels of UV-B absorbing compounds in the different treatment groups. A sample of needles from underneath the filters was used to verify the effectiveness of UV treatments across the experimental design by analysing their epidermal flavonol content. Our results found no clear link between UV-B exposure and accumulation of UV-B absorbing compounds in Pinus sylvestris pollen. However, we did find statistically significant differences in concentrations of UV-B absorbing compounds in pollen between the different trees. The needle analyses verified that the experimental design had the potential to affect the biochemistry of these branches by revealing significant differences in relative absorbance by epidermal flavonols due to UV treatment type. Multifactorial drivers affect the concentrations of UV-B-absorbing compounds in plants, and viewing the response of these compounds to a single driver may be an oversimplification complicating their use as a proxy. We argue that methodologies used in previous research have inconsistencies which fail to account for environmental factors that either covary with UV radiation or diverge from it. This may explain why our results go against the trend. Finally, we examine our own research experimental design and suggest improvements and avenues by which this research can move forward.
Now showing items 1-2 of 2