The sedimentary environment, sediment characteristics and age-depth models of sediment sequences from Arctic lakes Revvatnet and Svartvatnet, located near the Polish Polar Station in Hornsund, southern Svalbard (77°N), were studied with a view to establishing a basis for paleolimnological climate and environmental reconstructions. The results indicate that catchment-to-lake hydroclimatic processes probably affect the transportation, distribution and accumulation of sediments in different parts of lakes Revvatnet and Svartvatnet. Locations with continuous and essentially stable sedimentary environments were found in both lakes between water depths of 9 and 26 m. We used several different dating techniques, including 137Cs, 210Pb, AMS 14C, and paleomagnetic dating, to provide accurate and secured sediment chronologies. Arecovered sequence from the northern basin of Revvatnet spans more than one thousand years long with laminated stratigraphy in the upper part of the sediment. Based on AMS 14C dates, it is possible to suppose that Revvatnet basin was not occupied by a valley glacier during the Little Ice Age. The dates were supported by 137Cs chronologies, but not confirmed with other independent dating methods that extent beyond the last 50 years. A sedimentary sequence from the northern basin of Svartvatnet provides a potential archive for the study of climate and environmental change for the last ca. 5000 years. Based on the stratigraphy and a Bayesian age-depth model of AMS14C and paleosecular variation (PSV) dates, the recovered sediment sections represent a continuous and stable sedimentation for the latter half of the Holocene.

The oxygen isotope composition of chironomid head capsules in a sediment core spanning the past 5500 years from lake Svartvatnet in southern Spitsbergen was used to reconstruct the oxygen isotope composition of lake water (δ 18 Olw) and local precipitation. The δ 18 Olw values display shifts from the baseline variability consistent with the timing of recognized historical climatic episodes, such as the Roman Warm Period, the Dark Ages Cold Period and the Little Ice Age. The highest values of the record, ca. 3‰ above modern δ 18 Olw values, occur at ca. 1900-1800 cal. yr BP. Three negative excursions increasing in intensity toward the present, at 3400-3200, 1250-1100 and 350-50 cal. yr BP, are tentatively linked to roughly synchronous episodes of increased glacier activity and general cold spells around the northern North Atlantic. Their manifestation in the Svartvatnet δ 18 Olw record testify to the sensitivity and potential of high Arctic lacustrine δ 18 Ochir records in tracking terrestrial climate evolution, but also highlight nonlinear dynamics within the northern North Atlantic hydroclimatic system. The Little Ice Age period at 350-50 cal. yr BP displays a remarkable 8-9‰ drop in δ 18 Olw values, construed to predominantly represent significantly decreased winter temperatures during a period of increased seasonal differences and extended sea ice cover inducing changes in moisture source regions.

Existing paleoclimate data are exceedingly sparse from southern Spitsbergen, a High Arctic region predicted to experience significant environmental changes because of amplified warming. We analyzed biotic and isotopic paleolimnological proxies to reconstruct past climate from a lacustrine sediment core, with a basal age of $5500 a BP, in southern Spitsbergen (77˚N). We used fossil Chironomidae assemblages to quantitatively reconstruct past mean July air temperatures and stable oxygen isotope values (d 18 O) of these fossils to estimate changes in mean annual air temperature. These proxy records are strikingly similar and show that the coldest anomaly since the mid-Holocene occurred between 350 and 50 cal a BP, during the 'Little Ice Age', whereas the warmest period in the summer temperature record occurred between 5500-5000 and $2000 cal a BP. Our findings indicate that the natural long-term air temperature dynamics in our study area are most likely connected to solar minima and positive feedback mechanisms from sea-surface temperature maxima. The results also highlight that the recent temperature increase is unprecedented in its rate with a $2˚C increase in the summer temperatures during the past $50 years.