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The Arctic, one of the most sensitive components of the Earth's climate system, experienced pronounced climatic fluctuations during the Late Holocene. In order to obtain a detailed record of past environmental and climatic variability, sedimentary cores from two interconnected infilled depositional basins in the Kobbefjord area, southwestern Greenland, were retrieved and subjected to a multi-proxy investigation. The absolute chronostratigraphy was established through radiocarbon (C-14) and short-lived radioisotope (Pb-210, Cs-137) dating. We also analysed magnetic susceptibility, grain size, X-ray fluorescence element composition, total content of carbon, nitrogen and sulphur, biogenic silica and diatom assemblages. The palaeoenvironmental reconstruction presented from the upper basin records similar to 800 years of sedimentation in a former shallow Arctic lake/pond that was modulated by catchment processes and regional hydroclimate. The record is dominated by alternating periods of increased organic and clastic deposition, suggesting warmer/drier and colder/wetter climate, respectively. Comparison of our records with other proxy-based lacustrine, marine and glacier records and instrumental measurements from Greenland and the North Atlantic reveals common climatic trends, consistent with the inferred North Atlantic Oscillation pattern. Periods at similar to 800-600, similar to 320-220 and similar to 140-30 cal. a BP correspond to the main cold phases. The earliest climatic deterioration coincides with the demise of the nearby Norse Western Settlement. The most recent cold period represents the culmination of the Little Ice Age with the maximum Holocene advances of Greenland glaciers. Ameliorated conditions predominated at similar to 550-320 and similar to 220-140 cal. a BP. The evolution of both water bodies is concluded by transition into oligotrophic peat bogs after complete infilling of the basins at similar to 30 cal. a BP. Despite differences in proxy signals between the coring sites, this study endorses the usefulness of shallow lake/pond sediments from infilled basins for environmental reconstructions, as long as local depositional processes do not mask the external driving factors.

Arctic shrubs have a strong potential for climate and environmental reconstructions in the chronically understudied regions of the high northern latitudes. The climate dynamics of these regions are important to understand because of large-scale feedbacks to the global climate system. However, little is known about other factors influencing shrub ring growth, possibly obscuring their climate signal. For example, as of yet we are not able to differentiate between herbivory or climatically induced growth depressions. Here, we use one of the most common Arctic shrubs, Alnus viridis as a test case to address this question. We sampled Alnus in Kobbefjord, Greenland, measured shrub-ring width and cell wall thickness and built site chronologies of each parameter. We analysed climate-growth relationships, tested their stability over time and employed a pointer-year analysis to detect growth depressions. We employed bootstrapped transfer function stability tests (BTFS) to assess the suitability of our shrub chronologies for climate reconstruction. Correlations with climate data showed strong significantly positive and stable correlations between summer temperature and ring-width with the exception of the recent decade. A climate reconstruction model failed stability tests, when the complete period of record was used for calibration and verification. Wood anatomy analysis uncovered the occurrence of unusual cell structure (very thin cell walls) in the exceptionally narrow ring of 2004, a recorded insect outbreak year in other parts of Greenland. When excluding the affected ring and a recovery period, the reconstruction model passed all tests, suggesting that the unusual 2004 ring was not climate driven, but rather the result of an insect attack. When combining anatomical analysis with traditional ring-width measurements, we move a step further in potentially distinguishing small rings caused by insect attacks from small rings formed in climatically challenging years. While this study does not provide unambiguous evidence, it does provide potential useful methodological combinations to enable more robust climate reconstructions in areas where climatic records are extremely sparse.

The Arctic is one of the most sensitive areas worldwide with respect to climate changes, and recent climate change impacts are evident throughout Arctic ecosystems. In order to put current and projected changes in a palaeoclimatic context, exact information of past conditions and therefore detailed knowledge of proxy archives are crucial. Here, we investigated wood anatomical and other growth-related records of the long-lived and widespread Arctic tundra shrub Juniperus communis L. Annual ring-widths and cell anatomical parameters of 20 individuals from south-west Greenland were measured to test for age-related trends in the proxy time series and to correlate them with past climatic conditions. We documented a clear age trend in the investigated growth parameters (ring-widths, conduit-lumen areas, and cell wall thicknesses), which indicates the need for detrending the time series prior to possible climate correlation analyses and climate or environmental reconstructions. Prostrate growth forms of J. communis do not exhibit the general trend of an exponential widening of the conduit-lumen areas during ontogeny, as has been observed for many tree species, but their conduit lumens stop to increase in size at some point. This is possibly caused by a combination of extreme climate and physiological adaptations, which result in a prostrate growth form. Of the tested growth parameters, only detrended cell wall thickness showed stable correlations with summer temperature and the summer standardized precipitation evapotranspiration index (SPEI). The other growth parameters did not pass cross-calibration verification analyses, although for ring-widths we found the strongest climate correlations. Despite the fact that the ecophysiological processes behind our observations (i.e. reduced cell wall thickness combined with wider rings under dry conditions in the vegetation season) yet are not fully understood, we recognize the potential of J. communis for climate reconstructions. To our knowledge, this is the first demonstration of using cell anatomical parameter of J. communis shrubs as palaeoclimatological proxy for the Arctic.

The Arctic is the most sensitive zone to climate changes and the impacts are reflected in local ecosystems. In order to extract information of the past from proxy archives the detailed knowledge of such archive is crucial. The paper summarizes modern approaches of tundra dwarf shrub research for the purposes of paleoclimatology. Dwarf tundra shrubs as still relatively untapped archive are believed to contain valuable proxy data in their annual growth increments. Field sampling, and laboratory work are reviewed in detail. Constraints of dwarf tundra shrub research are discussed as well. The relationship between climate and growth is addressed to find a link between them depending on location and species. Majority of investigations found the strongest relationship between summer temperatures and ring widths, although exceptions are not rare. Dwarf tundra shrubs can fully serve as valuable proxy archive only if those are understood. Finally, the factors influencing the length of dwarf tundra shrub life are studied in order to sample the oldest living individuals in the field. Despite the field collection should aim to sample various sizes and ages of plants to make the dataset robust, the longest living individuals which are important to prolong chronologies are usually inhabiting rather nutrient poor and undisturbed sites close to their survival limits. The paper indicates the most suitable dwarf tundra shrub research designs for the purposes of paleoclimatology. As such it can help to harvest the benefits of dendrochronology from the vast and new territories.