Paleoclimate Proxies 314x314px|Example of a sediment core taken from the Forlorn lakes in Gifford Pinchot National Forest, Washington Paleoclimatology (the study of past climates) uses proxy data in order to relate elements collected in modern-day samples to climatic conditions of the past. In paleolimnology, proxy data refers to preserved or fossilized physical markers which serve as substitutes for direct meteorological measurements. Sediment cores Sediment cores are one of the primary tools for studying paleolimnology because of the role lake and river sediments play in preserving biological information. Paleolimnologists collect sediment cores and observe various proxy indicators in order to reconstruct  past limnology of an area. Such proxy data include geochemical markers and isotope data as well as fossilized pollen, charcoal, diatoms, chironomids, and other organic matter. These proxies show distributions and characteristics that can indicate past limnological conditions. In order to calibrate the proxy data derived from sediment cores, the new core is compared to a group of  around 40 or more calibration lakes. This allows researchers to assess key differences in the limnological conditions of the lake from which the core is taken. Lake-sediment cores in particular facilitate a more comprehensive analysis of an area because of the continual accumulation of sediment as well as other organic matter such as pollen and charcoal. Sediment cores can also be dated quite accurately, often allowing for lake histories to be reconstructed in chronological sequence. Pollen and spores of terrestrial vegetation around a lake are often found within sediment cores and can be analyzed within a lab setting to determine the taxonomy of the pollen grains. Examination of the distribution of these pollen grains can offer insight into the historical distribution of vegetation around the lake. Pollen records derived from paleolimnological assessments also allow researchers to track the distribution and density of different vegetation classes across large periods of time, and allow modeling of the successive ecologies of the surrounding landscape. Several studies have been able to assess transitions in vegetation profiles by examining the relationship between different types of land cover. For instance, an increase in the presence of fern pollen and herbaceous plant pollen coinciding with a decrease in grassland pollen often indicates a major disturbance or significant land clearance. Another trend that can be observed from historical pollen records is rates of soil erosion around the lake, as arboreal pollen rates often increase with soil erosion due to increased pollen levels in surface soils. Vegetation profiles derived from historical pollen analysis are also seen as a key tool in assessing historical climate trends and disturbances. Pollen analysis offers a historical record of vegetation profiles that are sensitive to abrupt changes in climate conditions. Therefore, historical climate events, as well as human-induced climate change, can shift vegetation profiles relatively rapidly compared to natural transitions. For example, the quantity of poplar pollen increased dramatically at the beginning and end of the Younger Dryas period, serving as a biological marker for that time period. Comparing historical vegetation profiles also allows researchers to compare successive changes in vegetation between two specific regions and correlate these differences with the corresponding climates of each region. A recent study conducted at Shudu Lake in the Hengduan Mountains of Yunnan, , southwestern China, was able to correlate changes in temperature and humidity with the development of needleleaf forests, as well as model recent anthropogenic effects on vegetation distribution in the area. Diatoms The taxonomic assemblages of diatoms reflect many aspects of the temperature, chemical, and nutrient environment of a lake. Diatoms are particularly suited to paleolimnology, due to their silica-based frustules, which are preserved in sufficient condition, and in large enough quantities, to be extracted from sediment cores and identified at the species level. Diatoms have also been examined in conjunction with chrysophycean statospores to estimate nutrient conditions of prehistoric temperate lakes. Such estimations can be derived due to the fact that the predominance of either algal group varies depending on the nutrient conditions of their limnic environment. Diatoms show a high degree of success in water with a high nutrient content as opposed to chyrsophytes who are better in water with a lower nutrient content. Certain species of diatoms also demonstrate a preference for specific aquatic pH, which allows researchers to estimate the historical pH conditions of a body of water by analyzing the species of diatoms within a sediment core. This makes diatom samples well suited for determining the impact of acid rain on a specific body of water, as diatom inference techniques are advanced enough to estimate relatively small numeric ranges of nutrient levels and pH values, as well as fluctuations in these measurements over a certain paleolimnological period. Organic matter analysis Examinations of the deposition and makeup of organic matter in the sediments of lakes has often been utilized in paleolimnological assessments. A variety of factors are taken into consideration when examining deposited organic matter, including the quantity, origin, and variety of isotopes and biomarkers. Diagenesis can have significant impacts on these factors, and thus careful consideration of its impacts are required when drawing conclusions from records of organic matter.
Paleoclimate proxies 314x314px|Example of a sediment core taken from the Forlorn lakes in Gifford Pinchot National Forest, Washington Paleoclimatology (the study of past climates) uses proxy data in order to relate elements collected in modern-day samples to climatic conditions of the past. In paleolimnology, proxy data refer to preserved or fossilized physical markers which serve as substitutes for direct meteorological measurements. Sediment cores Sediment cores are one of the primary tools for studying paleolimnology because of the role lake and river sediments play in preserving biological information. Paleolimnologists collect sediment cores and observe various proxy indicators in order to reconstruct the past limnology of an area. Such proxy data include geochemical markers and isotope data as well as fossilized pollen, charcoal, diatoms, chironomids, and other organic matter. These proxies show distributions and characteristics that can indicate past limnological conditions. In order to calibrate the proxy data extracted from sediment cores, the new core is compared to a group of those from around 40 or more calibration lakes. This allows researchers to assess key differences in the limnological conditions of the lake from which the core is taken. Lake-sediment cores , in particular, facilitate a more comprehensive analysis of an area because of the continual accumulation of sediment as well as other organic matter such as pollen and charcoal. Sediment cores can also be dated quite accurately, often allowing for lake histories to be reconstructed in chronological sequence. Pollen and spores of terrestrial vegetation around a lake are often found within sediment cores and can be analyzed in a lab setting to determine the taxonomy of the pollen grains. The distribution of these pollen grains can offer insight into the historical distribution of vegetation around the lake. Pollen records derived from paleolimnological assessments also allow researchers to track the distribution and density of different vegetation classes across large periods of time, and allow modeling of the successive ecologies of the surrounding landscape. Several studies have been able to assess transitions in vegetation profiles by examining the relationship between different types of land cover. For instance, an increase in the presence of fern pollen and herbaceous plant pollen coinciding with a decrease in grassland pollen often indicates a major disturbance or significant land clearance. Another trend that can be observed from historical pollen records is rates of soil erosion around the lake, as arboreal pollen rates often increase with soil erosion due to increased pollen levels in surface soils. Vegetation profiles derived from historical pollen analysis are also seen as a key tool in assessing historical climate trends and disturbances. Pollen analysis offers a historical record of vegetation profiles that are sensitive to abrupt changes in climate conditions. Therefore, historical climate events, including human-induced climate change, can shift vegetation profiles relatively rapidly compared to natural transitions. For example, the quantity of poplar pollen increased dramatically at the beginning and end of the Younger Dryas period, serving as a biological marker for that time period. Comparing historical vegetation profiles also allows researchers to compare successive changes in vegetation between two specific regions and correlate these differences with the corresponding climates of each region. A recent study conducted at Shudu Lake in the Hengduan Mountains of Yunnan, , southwestern China, was able to correlate changes in temperature and humidity with the development of needleleaf forests, as well as model recent anthropogenic effects on vegetation distribution in the area. Diatoms The taxonomic assemblages of diatoms reflect many aspects of the temperature, chemical, and nutrient environment of a lake. Diatoms are particularly suited to paleolimnology, due to their silica-based frustules, which are preserved in sufficient condition, and in large enough quantities, to be extracted from sediment cores and identified at the species level. Diatoms have also been examined in conjunction with chrysophycean statospores to estimate nutrient conditions of prehistoric temperate lakes. Such estimations can be derived due to the fact that the predominance of either algal group varies depending on the nutrient conditions of their limnic environment. Diatoms show a high degree of success in water with a high nutrient content as opposed to chyrsophytes , which are better in water with a lower nutrient content. Certain species of diatoms also demonstrate a preference for specific aquatic pH, which allows researchers to estimate the historical pH conditions of a body of water by analyzing the species of diatoms within a sediment core. This makes diatom samples well suited for determining the impact of acid rain on a specific body of water, as diatom inference techniques are advanced enough to estimate relatively small numeric ranges of nutrient levels and pH values, as well as fluctuations in these measurements over a certain paleolimnological period. Organic matter analysis Examinations of the deposition and makeup of organic matter in the sediments of lakes has often been utilized in paleolimnological assessments. A variety of factors are taken into consideration when examining deposited organic matter, including the quantity, origin, and variety of isotopes and biomarkers. Diagenesis can have a significant impact on these factors, and thus careful consideration of such impact is required when drawing conclusions about records of organic matter.
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