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Understanding of past climate variability on millennial to decadal scales are of primary importance in order to assess modern processes and predict future climatic events. Past history of Arctic climate changes is currently receiving increasing attention due to the recent phenomena of rapid sea-ice reduction. In this paper, we thoroughly reviewed the Holocene history of spatiotemporal climatic changes in the western Arctic region in order to better understand recent rapid environmental changes occurring in the Pacific sector of the Arctic, and further to discuss critical issues and new perspectives on the western Arctic in terms of paleoclimate researches. Records of temporal and spatial variations in sea-ice extents as well as marine and terrestrial paleoclimatic proxies show a strong asynchronicity between the western and eastern Arctic throughout the Holocene. The reason for this apparent contradiction across the Arctic may be linked to freshwater discharges over the Arctic shelves and the inflow of the Pacific freshwater into the western Arctic Ocean in coupled with a complex interaction between atmospheric and sea-ice dynamics. Special emphasis is placed on a tentative linkage of the late Holocene paleoclimatic events between the Arctic regions and the northwestern Pacific margin, highlighting the notion that climatic events of the northern Pacific Ocean is closely linked to the global climate system through hydrological dynamics in the western Arctic Ocean. [ABSTRACT FROM AUTHOR]

Marine sediment cores from the Chukchi Plateau are used to demonstrate the efficiency of digital photographic determination of sediment color and lightness, supplemented with the statistically processed data on sediment composition, for lithostratigraphy and paleoreconstructions. Several clusters were established that correspond to brown and gray sediment layers, carbonate-rich beige interlayers and specific segments of unclear lamination and/or lens-like intercalation of brownish and grayish beds. Correlation of the studied cores with other sediment cores from the region with well-established stratigraphy revealed good correspondence (though with certain specific features) to the conventional model of the Late Pleistocene-Holocene sediment accumulation in the offshore Arctic Ocean beyond shelf areas with clearly defined glacial-interglacial cyclicity. It was shown that enhanced red-color component corresponds to the enrichment of the interglacial brown sediment layers with manganese and accompanying elements. Glacial gray layers with enhanced green-color component are enriched in iron, as well as rubidium, vanadium, titanium and yttrium and bear evidence for considerable diagenetic transformations. Blue-color component is related to the high calcium content (carbonate rock fragments) in the carbonate-rich interlayers accumulated during the periods of active disintegration of continental ice sheets and iceberg-rafting of terrigenous lithic fragments. Intermediate values of the studied parameters are likely indicative of specific sedimentation environments. [ABSTRACT FROM AUTHOR]

ABSTRACT In this study, we present new detailed biomarker-based sea ice records from two sediment cores recovered in the Chukchi Sea and the East Siberian Sea. These new biomarker data may provide new insights on processes controlling recent and past sea ice changes. The biomarker proxy records show (i) minimum sea ice extent during the Early Holocene, (ii) a prominent Mid-Holocene short-term high-amplitude variability in sea ice, primary production and Pacific-Water inflow, and (iii) significantly increased sea ice extent during the last ca. 4.5k cal a BP. This Late Holocene trend in sea ice change in the Chukchi and East Siberian Seas seems to be contemporaneous with similar changes in sea ice extent recorded from other Arctic marginal seas. The main factors controlling the millennial variability in sea ice (and surface-water productivity) are probably changes in surface water and heat flow from the Pacific into the Arctic Ocean as well as the long-term decrease in summer insolation. The short-term centennial variability observed in the high-resolution Middle Holocene record is probably related to solar forcing. Our new data on Holocene sea ice variability may contribute to synoptic reconstructions of regional to global Holocene climate change based on terrestrial and marine archives. [ABSTRACT FROM AUTHOR]

Quantitative records of pre-industrial temperature changes are fundamental for understanding long-term natural climate variability. We used visible reflectance spectroscopy to measure chlorophyll content (and its derivatives) in a sediment core from Kurupa Lake, north-central Brooks Range, Alaska, to reconstruct summer temperature and the number of annual non-freezing days over the past 5.7 ka. A calibration-in-time approach was used to convert downcore changes in chlorophyll content to the climate variables, and an ensemble approach was used to integrate age and calibration uncertainties. The strongest correlation (rmedian = 0.69, pmedian = 0.02, RMSEP = 1.9°C) is for summer (June through September) temperature using the 20th Century Reanalysis Project dataset. The chlorophyll-inferred 3-year-mean summer temperature shows that the warmest century (3.0–2.9 ka BP) was about 3.0°C (90% range of the ensemble members = 2.3–4.0°C) higher and that the coldest century (1.4–1.3 ka BP) was about 5.5°C lower (90% range = −7.6°C to −5.0°C) than during the reference period (AD 1961–1990). Century-to-century temperature changes over the past 5.7 ka at Kurupa Lake have been large (90% range = −2.8°C to 3.1°C shifts in centennial mean), including the shift between the 19th and 20th centuries, which was above the 90th percentile of temperature changes across all representations of the reconstruction. In contrast to most Northern Hemisphere temperature reconstructions, Kurupa Lake shows no overall millennial-scale cooling trend. We suggest that increased summer duration (by 4.3 days during the last 6 ka) along with no long-term increase in sea-ice cover over the adjacent Chukchi Sea counter-balanced the influence of decreased insolation intensity on the aquatic productivity in Kurupa Lake. [ABSTRACT FROM PUBLISHER]

Recent geological studies have revealed that the freshwater input to the Arctic Ocean was highly variable during the Holocene. In the present study, the influence of mid-Holocene river runoff on large-scale Arctic ocean/sea-ice dynamics is examined using a general circulation model. A palaeohydrological forcing for the time interval around 6 ka BP (14C timescale) is constructed by compiling data from the available literature. Keeping all other forcing fields and bottom topography of the ocean model at present-day values, the effect of a changed freshwater input to the Arctic Ocean is isolated. The model shows that freshwater supply is vitally important for the polar oceanic circulation. In particular, a close connection between Siberian river runoff and the path of the Transpolar Drift (TPD) is found. Consistent with palaeoceanographic findings of driftwood delivery to the Canadian Arctic Archipelago and Baffin Bay, the model results suggest that enhanced freshwater discharge during the mid-Holocene caused an eastward shift of the TPD with strengthened outflow through Fram Strait. [ABSTRACT FROM AUTHOR]