Reanalysis data show an increasing trend in Arctic precipitation over the 20th century, but changes are not homogenous across seasons or space. The observed hydroclimate changes are expected to continue and possibly accelerate in the coming century, not only affecting pan-Arctic natural ecosystems and human activities, but also lower latitudes through the atmospheric and ocean circulations. However, a lack of spatiotemporal observational data makes reliable quantification of Arctic hydroclimate change difficult, especially in a long-term context. To understand Arctic hydroclimate and its variability prior to the instrumental record, climate proxy records are needed. The purpose of this review is to summarise the current understanding of Arctic hydroclimate during the past 2000 years. First, the paper reviews the main natural archives and proxies used to infer past hydroclimate variations in this remote region and outlines the difficulty of disentangling the moisture from the temperature signal in these records. Second, a comparison of two sets of hydroclimate records covering the Common Era from two data-rich regions, North America and Fennoscandia, reveals inter- and intra-regional differences. Third, building on earlier work, this paper shows the potential for providing a high-resolution hydroclimate reconstruction for the Arctic and a comparison with last-millennium simulations from fully coupled climate models. In general, hydroclimate proxies and simulations indicate that the Medieval Climate Anomaly tends to have been wetter than the Little Ice Age (LIA), but there are large regional differences. However, the regional coverage of the proxy data is inadequate, with distinct data gaps in most of Eurasia and parts of North America, making robust assessments for the whole Arctic impossible at present. To fully assess pan-Arctic hydroclimate variability for the last 2 millennia, additional proxy records are required.

Plastics are a recent particulate material in Earth’s history. Because of plastics persistence and wide-range presence, it has a great potential of being a global age marker and correlation tool between sedimentary profiles. In this research, we query whether microplastics can be considered among the array of proxies to delimit the Anthropocene Epoch (starting from the year 1950 and above). We present a study of microplastics deposition history inferred from sediment profiles of lakes in northeastern Europe. The sediments were dated with independent proxies from the present back to the first half of the 18th century. Regardless of the sediment layer age, microplastic particles were found throughout the cores in all sites. Depending on particles’ aspect ratio, less elongated particles were found deeper, while more elongated particles and fibers have reduced mobility. We conclude that interpretation of microplastics distribution in the studied sediment profiles is ambiguous and does not strictly indicate the beginning of the Anthropocene Epoch.

Sediment trapping as a tool to monitor microplastic influx was tested in an urban boreal lake basin. The one-year-long trap monitoring consisted of 5-month and 7-month periods representing growing season and winter season (including the spring flood event), respectively. Sediment accumulation rate (SAR), and organic content were determined, highest SAR - 14.5 g/m2/d - was measured during the winter period. Microplastics were extracted from the sediment applying heavy-liquid density separation method and collected under a microscope for further identification with FTIR spectroscopy. PE was identified as the most abundant synthetic polymer type, while PP and PET are also present. The annual microplastic flux rate is 32 400 pieces/m2/year, and highest accumulation does not coincide with the highest SAR, but occurs during the growing season. Changes in the microplastic accumulation rates are related to seasonal conditions. Highest microplastic concentration with respect to dry sediment weight (10 200 pieces/kg) was observed in a growing season sample, while highest concentration with respect to sediment volume (1800 pieces/l) was observed during winter. This finding underlines the problems related to reporting microplastic concentrations in various units. The results highlight that sediment trap monitoring is an efficient tool for monitoring microplastic accumulation rate in aquatic environments and provides an opportunity to better understand and define processes controlling microplastic accumulation.

Clastic-organic varved sediments from the boreal Lake Kalliojärvi, Central Finland, record changes in snow accumulation for more than 4000 years. The varve record was reconstructed using digital image analysis from 4132 varve yr BP to present with 2.2% counting error and is supported by paleomagnetic data. Two laminae are identified in a typical varve structure: (1) the minerogenic lamina, which accumulates during spring as a result of catchment erosion triggered by spring floods and (2) the organic lamina, which is composed of allochthonous and autochthonous organic matter that accumulates during summer, autumn, and winter. The minerogenic influx is related to variations in snow accumulation and follows the different phases of the North Atlantic Oscillation (NAO). Decreased snow accumulation is related to a weakened NAO phase. Thus, the minerogenic influx record provides additional information about NAO variation. The Fe/Mn ratio is related to changes in redox conditions at the lake floor. The oxygen availability in the lake floor depends on the duration of the ice cover during winter. Strengthened Siberian High (SH) causes colder autumn and winter temperatures and therefore leads to extended duration of ice cover. Fe/Mn can be considered as a proxy for SH. The sediment record suggests pronounced, generally positive but strongly fluctuating NAO phase, from ca. 4100 to 3200 varve yr BP. Periods of strengthened SH are observed at 3900–3600, 1900–1500, and 1200–750 varve yr BP. Our study suggests that NAO and SH operate individually, are not clearly linked, and do not entirely block each other.