Quantitative multiproxy assessment of long-term patterns of Holocene environmental change from a small lake near Abisko, northern Sweden

Quantitative reconstructions are made of Holocene changes in climatic and environmental conditions from analyses of pollen, chironomids and diatoms in identical stratigraphic levels of a sediment core from Vuoskkujávri (68°20'43 N, 19°06'00 E, 348 m a.s.l.) near Abisko in northern Sweden (Lapland). Transfer functions, based on regional calibration sets, are applied to reconstruct Holocene patterns in mean July air temperature (using all three indicators), mean January air temperature (pollen), annual precipitation (pollen) and lakewater pH (diatoms). During periods with ‘good’ fit to the modern calibration sets all mean July air-temperature inferences based on the three proxy indicators reveal a general trend of decreasing temperature: pollen-inferred mean July air temperature shows a decrease of c. 1.1°C since 7500 cal. yrs BP; the chironomids show a decrease of c. 1.2°C since the early Holocene; whereas the diatoms show a decrease of c. 1.5°C since 6000 cal. yrs BP. Pollen-inferred mean January air temperature indicates that winters may have been warmer by c. 3.0°C during the early Holocene, followed by a gradual cooling until 8500 cal. yrs BP (c. 1.0°C warmer than today) and a subsequent warming until 7000 cal. yrs BP (c. 2.0°C warmer than today). Since 7000 cal. yrs BP, a gradual cooling towards the present-day values is inferred. According to the pollen, annual precipitation may have been considerably higher during the early Holocene than today (c. +150 mm) and increased until 7000 cal. yrs BP (c. +320 mm). Since 7000 cal. yrs BP, annual precipitation decreased continuously towards present-day values. Diatom-inferred pH trends show that natural acidification of c. 0.5 pH units followed deglaciation; present-day values were reached c. 5000 cal. yrs BP. The early Holocene is identified as a problematic time period for the application of modern calibration sets, as diatoms show ‘poor’ fit to the calibration set from 10 600 to 6000 cal. yrs BP, pollen from 10 600 to 7500 cal. yrs BP, and chironomids from 10 250 to 10 000 cal. yrs BP. Compared with estimates from the COHMAP GCM model, mean July air-temperature inferences based on biological proxies at Vuoskkujávri suggest a more moderate decrease in temperature over the past 9000 years

Interglacial History of a Palaeo-lake and Regional Environment: A Multi-proxy Study of a Permafrost Deposit from Bolshoy Lyakhovsky Island, Arctic Siberia

Chironomid, pollen, and rhizopod records from a permafrost sequence at the Bolshoy Lyakhovsky Island (New Siberian Archipelago) document the evolution of a thermokarst palaeo-lake and environmental conditions in the region during the Last Interglacial (MIS 5e, ca. 130120 ka). Open Poaceae and Artemisia associations dominated vegetation at the beginning of the interglacial period, ca. 130 ka. Rare shrub thickets (Salix, Betula nana, Alnus fruticosa) grew in more protected and wetter places as well. Saalian ice wedges started to melt during this time, resulting in the formation of an initial thermokarst water body. The high percentage of semi-aquatic chironomids suggests that a peatland-pool palaeo-biotope existed at the site, when initial water body started to form. A distinct decrease in semi-aquatic chironomid taxa and an increase in lacustrine ones point to a gradual pooling of water in basin, which could in turn create thaw a permanent pond during the subsequent period. The highest relative abundance of Chironomus and Procladius reflects an existence of unfrozen water remaining under the ice throughout the ice-covered period during the later stage of palaeo-lake development. Chironomid record points to three successive stages during the water body evolution: (1) a peatland pool; (2) a pond (i.e., less deep than the maximum ice-cover thickness); and (3) a shallow lake (i.e., more deep than the maximum ice-cover thickness). The evolutionary trend of palaeo-lake points to intensive thermokarst processes occurring in the region during the Last Interglacial. Shrub tundra communities with Alnus fruticosa, Betula nana dominated the vegetation during the interglacial optimum that is evidenced by pollen record. The climate was relatively moist and warm. The results of this study suggest that quantitative chironomid-based temperature reconstructions from the Arctic thermokarst ponds/lakes may be problematic owing to other key environmental factors, such as prolonged periods of winter anoxia and local hydrological/geomorphological processes, controlling the chironomid assemblage

Geology, Geochronology, Lithogeochemistry and Metamorphism of the Mahatta Creek Area, Northern Vancouver Island

BC Ministry of Energy and Mines, Geoscience Map 2011-3, 1:50 000 scale