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1. How do intermittency and simultaneous processes obfuscate the Arctic influence on midlatitude winter extreme weather events?

   https://doi.org/https://doi.org/10.1088/1748-9326/abdb5d  

   Overland, J. E. ( March 2021 , Environmental research letters)

   null (Ed.)

   Pronounced changes in the Arctic environment add a new potential driver of anomalous weather patterns in midlatitudes that affect billions of people. Recent studies of these Arctic/midlatitude weather linkages, however, state inconsistent conclusions. A source of uncertainty arises from the chaotic nature of the atmosphere. Thermodynamic forcing by a rapidly warming Arctic contributes to weather events through changing surface heat fluxes and large-scale temperature and pressure gradients. But internal shifts in atmospheric dynamics—the variability of the location, strength, and character of the jet stream, blocking, and stratospheric polar vortex (SPV)—obscure the direct causes and effects. It is important to understand these associated processes to differentiate Arctic-forced variability from natural variability. For example in early winter, reduced Barents/Kara Seas sea-ice coverage may reinforce existing atmospheric teleconnections between the North Atlantic/Arctic and central Asia, and affect downstream weather in East Asia. Reduced sea ice in the Chukchi Sea can amplify atmospheric ridging of high pressure near Alaska, influencing downstream weather across North America. In late winter southward displacement of the SPV, coupled to the troposphere, leads to weather extremes in Eurasia and North America. Combined tropical and sea ice conditions can modulate the variability of the SPV. Observational evidence for Arctic/midlatitude weather linkages continues to accumulate, along with understanding of connections with pre-existing climate states. Relative to natural atmospheric variability, sea-ice loss alone has played a secondary role in Arctic/midlatitude weather linkages; the full influence of Arctic amplification remains uncertain. 

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2. A stable isotope record of late Quaternary hydrologic change in the northwestern Brooks Range, Alaska (eastern Beringia)

   https://doi.org/10.1002/jqs.3368  

   King, Amanda L. ; Anderson, Lesleigh ; Abbott, Mark ; Edwards, Mary ; Finkenbinder, Matthew S. ; Finney, Bruce ; Wooller, Matthew J. ( September 2021 , Journal of Quaternary Science)

   A submillennial‐resolution record of lake water oxygen isotope composition (δ¹⁸O) from chironomid head capsules is presented from Burial Lake, northwest Alaska. The record spans the Last Glacial Maximum (LGM; ~20–16k cal abp) to the present and shows a series of large lake δ¹⁸O shifts (~5‰). Relatively low δ¹⁸O values occurred during a period covering the LGM, when the lake was a shallow, closed‐basin pond. Higher values characterize deglaciation (~16–11.5k cal abp) when the lake was still closed but lake levels were higher. A rapid decline between ~11 and 10.5k cal abpindicates that lake levels rose to overflowing. Lake δ¹⁸O values are interpreted to reflect the combined effects of changes in lake hydrology, growing season temperature and meteoric source water as well as large‐scale environmental changes impacting this site, including opening of the Bering Strait and shifts in atmospheric circulation patterns related to ice‐sheet dynamics. The results indicate significant shifts in precipitation minus evaporation across the late Pleistocene to early Holocene transition, which are consistent with temporal patterns of vegetation change and paludification. This study provides new perspectives on the paleohydrology of eastern Beringia concomitant with human migration and major turnover in megafaunal assemblages.

    

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3. Late Quaternary changes in sediment composition on the NE Greenland margin (~73° N) with a focus on the fjords and shelf

   https://doi.org/10.1111/bor.12169  

   Andrews, John T. ; Stein, Rüdiger ; Moros, Matthias ; Perner, Kerstin ( February 2016 , Boreas)

   In order to document changes in Holocene glacier extent and activity inNEGreenland (~73° N) we study marine sediment records that extend from the fjords (PS2631 andPS2640), across the shelf (PS2623 andPS2641), to the Greenland Sea (JM07‐174GC). The primary bedrock geology of the source areas is the Caledonian sediment outcrop, including Devonian red beds, plus early Neoproterozoic gneisses and early Tertiary volcanics. We examine the variations in colour (CIE*), grain size, and bulk mineralogy (from X‐ray diffraction of the <2 mm sediment fraction). Fjord corePS2640 in Sofia Sund, with a marked red hue, is distinct in grain size, colour and mineralogy from the other fjord and shelf cores. Five distinct grain‐size modes are distinguished of which only one is associated with a coarse ice‐rafting signal – this mode is rare in the mid‐ and late Holocene. A sediment unmixing program (SedUnMixMC) is used to characterize down‐core changes in sediment composition based on the upper late Holocene sediments from coresPS2640 (Sofia Sund),PS2631 (Kaiser Franz Joseph Fjord) andPS2623 (south of Shannon Is), and surface samples from the Kara Sea (as an indicator of transport from the Russian Arctic shelves). Major changes in mineral composition are noted in all cores with possible coeval shifts centredc. 2.5, 4.5 and 7.5 cal. kaBP(±0.5 ka) but are rarely linked with changes in the grain‐size spectra. CoarseIRD(>2 mm) andIRD‐grain‐size spectra are rare in the last 9–10 cal. kaBPand, in contrast with areas farther south (~68° N), there is no distinctIRDsignal at the onset of neoglaciation. Our paper demonstrates the importance of the quantitative analysis of sediment properties in clarifying source to sink changes in glacial marine environments.

    

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4. Northward Shifts in the Polar Front Preceded Bølling and Holocene Warming in Southwestern Scandinavia

   https://doi.org/10.1029/2020GL088153  

   Cowling, O. C. ; Thomas, E. K. ; Svendsen, J. I. ; Mangerud, J. ; Vasskog, K. ; Haflidason, H. ( July 2020 , Geophysical Research Letters)

   The last deglaciation in northern Europe provides an opportunity to study the hydrologic component of abrupt climate shifts in a region with complex interactions between ice sheets and oceanic and atmospheric circulation. We use leaf wax hydrogen isotopes (δ²H) to reconstruct summer precipitation δ²H and aridity in southwestern Norway from 15.8 to 11.5 ka. We identify transitions to a more proximal moisture source before the ends of Heinrich Stadial 1 and the Younger Dryas, prior to local warming and increased primary productivity in both instances. We infer these changes in moisture delivery to southwestern Norway to be a response to northward shifts in the polar front caused by warm water intrusion into the North Atlantic, which preceded abrupt warming in the circum‐North Atlantic. These results suggest that moisture transport pathways shift northward as warm surface ocean water reaches higher latitudes in the North Atlantic.

    

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5. Holocene hydroclimatic variability recorded in sediments from Maddox Lake (northern California Coast Range)

   https://doi.org/10.1017/qua.2023.18  

   Kirby, Matthew ; Barbosa, Jazleen ; Carlin, Joe ; MacDonald, Glen ; Leidelmeijer, Jenifer ; Bonuso, Nicole ; Han, Jiwoo ; Nauman, Benjamin ; Avila, Judith ; Woodward, Alex ; et al ( September 2023 , Quaternary Research)

   Perspectives on past climate using lake sediments are critical for assessing modern and future climate change. These perspectives are especially important for water-stressed regions such as the western United States. One such region is northwestern California (CA), where Holocene-length hydroclimatic records are scarce. Here, we present a 9000-year, relative lake level record from Maddox Lake (CA) using a multi-indicator approach. The Early Holocene is characterized by variably low lake levels with a brief excursion to wetter climates/relative highstand ca. 8.4–8.06 cal ka BP, possibly related to the 8.2 ka cold event and changing Atlantic Meridional Overturning Circulation (AMOC). From 5.2–0.55 cal ka BP, Maddox Lake experienced a long-term regression, tracking changes in summer-winter insolation, tropical and northeast Pacific SSTs, and the southward migration of the ITCZ. This gradual regression culminated in a pronounced relative lowstand during the Medieval Climatic Anomaly (MCA). A marked relative highstand followed the MCA, correlative to the Little Ice Age. The latter reflects a far-field response to North Atlantic volcanism, solar variability, and possibly changes in AMOC and Arctic sea ice extent. Our results further confirm the hydroclimatic sensitivity of northwest California to various forcings including those emanating from the North Atlantic.

    

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