Reconstructing climates of the past relies on a variety of evidence from a large number of sites to capture the varied features of climate and the spatial heterogeneity of climate change. This review ...summarizes available information from diverse Holocene paleoenvironmental records across eastern Beringia (Alaska, westernmost Canada and adjacent seas), and it quantifies the primary trends of temperature- and moisture-sensitive records based in part on midges, pollen, and biogeochemical indicators (compiled in the recently published Arctic Holocene database, and updated here to v2.1). The composite time series from these proxy records are compared with new summaries of mountain-glacier and lake-level fluctuations, terrestrial water-isotope records, sea-ice and sea-surface-temperature analyses, and peatland and thaw-lake initiation frequencies to clarify multi-centennial- to millennial-scale trends in Holocene climate change. To focus the synthesis, the paleo data are used to frame specific questions that can be addressed with simulations by Earth system models to investigate the causes and dynamics of past and future climate change. This systematic review shows that, during the early Holocene (11.7–8.2 ka; 1 ka = 1000 cal yr BP), rather than a prominent thermal maximum as suggested previously, temperatures were highly variable, at times both higher and lower than present (approximate mid-20th-century average), with no clear spatial pattern. Composited pollen, midge and other proxy records average out the variability and show the overall lowest summer and mean-annual temperatures across the study region during the earliest Holocene, followed by warming over the early Holocene. The sparse data available on early Holocene glaciation show that glaciers in southern Alaska were as extensive then as they were during the late Holocene. Early Holocene lake levels were low in interior Alaska, but moisture indicators show pronounced differences across the region. The highest frequency of both peatland and thaw-lake initiation ages also occurred during the early Holocene. During the middle Holocene (8.2–4.2 ka), glaciers retreated as the regional average temperature increased to a maximum between 7 and 5 ka, as reflected in most proxy types. Following the middle Holocene thermal maximum, temperatures decreased starting between 4 and 3 ka, signaling the onset of Neoglacial cooling. Glaciers in the Brooks and Alaska Ranges advanced to their maximum Holocene extent as lakes generally rose to modern levels. Temperature differences for averaged 500-year time steps typically ranged by 1–2 °C for individual records in the Arctic Holocene database, with a transition to a cooler late Holocene that was neither abrupt nor spatially coherent. The longest and highest-resolution terrestrial water isotope records previously interpreted to represent changes in the Aleutian low-pressure system around this time are here shown to be largely contradictory. Furthermore, there are too few records with sufficient resolution to identify sub-centennial-scale climate anomalies, such as the 8.2 ka event. The review concludes by suggesting some priorities for future paleoclimate research in the region.
•We summarize diverse Holocene paleoclimate records from Alaska and NW Canada.•Proxy types include midges, pollen, biogeochemistry, glaciers, isotopes, lake levels.•Early Holocene (11.5–8.0 ka) temperatures were highly variable, but cold on average.•Regional average temperature increased to a maximum between 7 and 5 ka.•Priorities for future paleoclimate research in the region are suggested.
Dating of ancient permafrost is essential for understanding long-term permafrost stability and interpreting palaeoenvironmental conditions but presents substantial challenges to geochronology. Here, ...we apply four methods to permafrost from the megaslump at Batagay, east Siberia: (1) optically stimulated luminescence (OSL) dating of quartz, (2) post-infrared infrared-stimulated luminescence (pIRIR) dating of K-feldspar, (3) radiocarbon dating of organic material, and (4) 36Cl/Cl dating of ice wedges. All four chronometers produce stratigraphically consistent and comparable ages. However, OSL appears to date Marine Isotope Stage (MIS) 3 to MIS 2 deposits more reliably than pIRIR, whereas the latter is more consistent with 36Cl/Cl ages for older deposits. The lower ice complex developed at least 650 ka, potentially during MIS 16, and represents the oldest dated permafrost in western Beringia and the second-oldest known ice in the Northern Hemisphere. It has survived multiple interglaciations, including the super-interglaciation MIS 11c, though a thaw unconformity and erosional surface indicate at least one episode of permafrost thaw and erosion occurred sometime between MIS 16 and 6. The upper ice complex formed from at least 60 to 30 ka during late MIS 4 to 3. The sand unit above the upper ice complex is dated to MIS 3–2, whereas the sand unit below formed at some time between MIS 4 and 16.
Based on collections of Koryak geobotanical expeditions of the Komarov Botanical Institute, 23 species of lichens and four lichenicolous fungi are reported as new to Koryakia, nine of them are also ...new to Kamchatka. Ephebe hispidula, Lambiella impavida, Rhizocarpon simillimum, Rhizoplaca opiniconensis, and Vestergrenopsis isidiata are new to the Russian Far East. Altogether 529 species of lichens and allied fungi are currently known for Koryakia.
Genetic history of Native AmericansSeveral theories have been put forth as to the origin and timing of when Native American ancestors entered the Americas. To clarify this controversy, Raghavan et ...al. examined the genomic variation among ancient and modern individuals from Asia and the Americas. There is no evidence for multiple waves of entry or recurrent gene flow with Asians in northern populations. The earliest migrations occurred no earlier than 23,000 years ago from Siberian ancestors. Amerindians and Athabascans originated from a single population, splitting approximately 13,000 years ago.Science, this issue 10.1126/science.aab3884 How and when the Americas were populated remains contentious. Using ancient and modern genome-wide data, we found that the ancestors of all present-day Native Americans, including Athabascans and Amerindians, entered the Americas as a single migration wave from Siberia no earlier than 23 thousand years ago (ka) and after no more than an 8000-year isolation period in Beringia. After their arrival to the Americas, ancestral Native Americans diversified into two basal genetic branches around 13 ka, one that is now dispersed across North and South America and the other restricted to North America. Subsequent gene flow resulted in some Native Americans sharing ancestry with present-day East Asians (including Siberians) and, more distantly, Australo-Melanesians. Putative "Paleoamerican" relict populations, including the historical Mexican Pericues and South American Fuego-Patagonians, are not directly related to modern Australo-Melanesians as suggested by the Paleoamerican Model.
Display omitted
•Aphylogenyis presented for the beesubfamily Andreninae based on UCE sequences.•The Eastern Mediterranean subgenus Cubiandrena is sister to all remaining Andrena.•Many Andrena ...subgenera exhibit paraphyly or polyphyly, requiring recircumscription.•At least 11 Old World–New World exchange events have occurred within Andrena.
The mining bee subfamily Andreninae (Hymenoptera: Andrenidae) is a widely distributed and diverse group of ground-nesting solitary bees, including numerous species known to be important pollinators. Most of the species diversity of Andreninae is concentrated in the mainly Holarctic genus Andrena, comprising ca. 1550 described species. The subfamily and especially the genus have remained relatively neglected by recent molecular phylogenetic studies, with current classifications relying largely on morphological characters. We sampled ultraconserved element (UCE) sequences from 235 taxa, including all andrenine genera and 98 out of 104 currently recognized Andrena subgenera. Using 419,858 aligned nucleotide sites from 1009 UCE loci, we present a comprehensive molecular phylogenetic analysis of the subfamily. Our analysis supports the recognition of seven distinct genera in the Andreninae: Alocandrena, Ancylandrena, Andrena, Cubiandrena, Euherbstia, Megandrena, and Orphana. Within the genus Andrena, present-day subgeneric concepts revealed high degrees of paraphyly and polyphyly, due to strong homoplasy of morphological characters, necessitating a thorough, extensive revision of the higher classification of the genus. Based on our findings, we place the subgenus Calcarandrena in synonymy with Andrena (Lepidandrena); Hyperandrena, Nemandrena, Scoliandrena, Tylandrena and Zonandrena with A. (Melandrena); Distandrena, Fumandrena and Proxiandrena with A. (Micrandrena); Carandrena with A. (Notandrena); Agandrena with A. (Plastandrena); Geandrena and Xanthandrena with A. (Ptilandrena); Xiphandrena with A. (Scrapteropsis); and Platygalandrena and Poliandrena with A. (Ulandrena) (new synonymies). We additionally reestablish the groups known as Opandrena and Truncandrena as valid subgenera of Andrena. Our results also show that the MRCA of Andrena + Cubiandrena dispersed from the New World to the Palaearctic probably during the Eocene–early Oligocene, followed by 10–14 Neogene dispersal events from the Palaearctic to the Nearctic and 1–6 Neogene dispersals back into the Palaearctic, all within the genus Andrena.
Advances in the isolation and sequencing of ancient DNA have begun to reveal the population histories of both people and dogs. Over the last 10,000 y, the genetic signatures of ancient dog remains ...have been linked with known human dispersals in regions such as the Arctic and the remote Pacific. It is suspected, however, that this relationship has a much deeper antiquity, and that the tandem movement of people and dogs may have begun soon after the domestication of the dog from a gray wolf ancestor in the late Pleistocene. Here, by comparing population genetic results of humans and dogs from Siberia, Beringia, and North America, we show that there is a close correlation in the movement and divergences of their respective lineages. This evidence places constraints on when and where dog domestication took place. Most significantly, it suggests that dogs were domesticated in Siberia by ∼23,000 y ago, possibly while both people and wolves were isolated during the harsh climate of the Last Glacial Maximum. Dogs then accompanied the first people into the Americas and traveled with them as humans rapidly dispersed into the continent beginning ∼15,000 y ago.
AIM: I re‐evaluate the specific biogeographical significance of each of the land bridges (Beringia, Thulean and De Geer) in the Northern Hemisphere during the latest Cretaceous–early Cenozoic, ...showing that the Thulean and De Geer routes did not operate contemporaneously. LOCATION: Northern Hemisphere landmasses. METHODS: I review the recent climatic, sea‐level, geotectonic, palaeofloristic, and marine and terrestrial faunal data that have emerged since the establishment in the 1980s of the biogeographical concepts of the early Cenozoic Northern Hemisphere land bridges and present a synthesis supporting a revised scenario for early Cenozoic biogeographical development. RESULTS: Palaeogeographical and geotectonic data, supported by strong floral and faunal evidence, suggest that the palaeogeographical and chronological frames for the formation of all three land bridges are different from those originally proposed. Dispersal events via the causeways seem to have taken place during specific time intervals resulting from fluctuations in sea level and climate. MAIN CONCLUSIONS: The De Geer and Thulean routes were not contemporaneous. The former existed during the latest Cretaceous to the early Palaeocene, joining North America with Eurasia. The Thulean route became established well after the interruption of the De Geer route, offering a southerly connection between western Europe and North America in at least two episodes: c. 57 Ma and c. 56 Ma. The Bering route functioned in two warm periods: 65.5 Ma (coinciding with the De Geer route) and c. 58 Ma, during the Palaeocene (possible Eocene exposures are not considered here). The formation of the De Geer route explains faunal similarities between the Puercan and Torrejonian North American land mammal ages (NALMAs) and the Shanghuan Asian land mammal age (ALMA). The Thulean route explains faunal similarities between the Clarkforkian (Cf1) and Wasatchian (Wa0, 1) NALMAs, and the Cernaysian and Neustrian (PE I, II) European land mammal ages. The Bering route explains faunal similarities between the Gashatan ALMA and the Tiffanian (Ti5) NALMA.
Display omitted
•A phylogeny based on 6 genes and morphology is presented for a large complex of eucerine bees.•A new generic-level classification is proposed for this systematically complex group of ...pollinators.•The evolution of morphological traits is analyzed relative to the molecular phylogeny.•The use of functional traits as diagnostic characters in classifications is critically discussed.•A biogeographic hypothesis explaining the wide distribution of this clade is added.
The longhorn bee tribe Eucerini (Hymenoptera: Apidae) is a diverse, widely distributed group of solitary bees that includes important pollinators of both wild and agricultural plants. About half of the species in the tribe are currently assigned to the genus Eucera and to a few other related genera. In this large genus complex, comprising ca. 390 species, the boundaries between genera remain ambiguous due to morphological intergradation among taxa. Using ca. 6700 aligned nucleotide sites from six gene fragments, 120 morphological characters, and more than 100 taxa, we present the first comprehensive molecular, morphological, and combined phylogenetic analyses of the ‘Eucera complex’. The revised generic classification that we propose is congruent with our phylogeny and maximizes both generic stability and ease of identification. Under this new classification most generic names are synonymized under an expanded genus Eucera. Thus, Tetralonia, Peponapis, Xenoglossa, Cemolobus, and Syntrichalonia are reduced to subgeneric rank within Eucera, and Synhalonia is retained as a subgenus of Eucera. Xenoglossodes is reestablished as a valid subgenus of Eucera while Tetraloniella is synonymized with Tetralonia and Cubitalia with Eucera. In contrast, we suggest that the venusta-group of species, currently placed in the subgenus Synhalonia, should be recognized as a new genus. Our results demonstrate the need to evaluate convergent loss or gain of important diagnostic traits to minimize the use of potentially homoplasious characters when establishing classifications. Lastly, we show that the Eucera complex originated in the Nearctic region in the late Oligocene, and dispersed twice into the Old World. The first dispersal event likely occurred 24.2–16.6 mya at a base of a clade of summer-active bees restricted to warm region of the Old World, and the second 13.9–12.3 mya at the base of a clade of spring-active bees found in cooler regions of the Holarctic. Our results further highlight the role of Beringia as a climate-regulated corridor for bees.
Precipitation isotopes are commonly used for paleothermometry in high latitude regions. Here we present multiple water isotope proxies from the same sedimentary context – perennially frozen loess ...deposits in the Klondike Goldfields in central Yukon, Canada, representing parts of Marine Isotope Stages (MIS) 4, 3 and 2 – allowing us to uniquely corroborate fractionations and temperature conversions during these Late Pleistocene cold stages. We include new and existing proxy data from: relict wedge ice, a direct archive for snowmelt; relict pore ice, an archive for bulk soil water integrating year-round precipitation; and hydrated volcanic glass shards and fossil plant waxes, which are also thought to integrate year-round precipitation but are subject to large fractionations. In some cases, our temperature estimates based on existing proxy data are much cooler than previously estimated due to our use of source water corrections for the glacial ocean, new transfer functions calibrated specifically for northern North America (δDprecip = 3.1‰·°C−1 × T – 155‰; and δ18Oprecip = 0.41‰·°C−1 × T – 20.2‰), and novel insights on the apparent net fractionation correction for Eastern Beringian steppe-tundra plant waxes (εwax/precip = −59 ± 10‰). The snowmelt origin of wedge ice ensures a relatively constrained winter-spring seasonality of contributing precipitation, as supported by the consistency between water isotope measurements from Late Holocene wedge ice and modern winter-spring precipitation. Wedge ice dating to the transitional MIS 3/2 is isotopically depleted relative to modern spring-winter precipitation by an amount that indicates a temperature depression of ∼14 ± 5 °C below modern. The soil water origin of pore ice, and other proxies integrating year-round precipitation from soil water, allows for a more variable precipitation seasonality. The isotopic composition of modern pore ice is consistent with mean annual precipitation. However, the isotopic composition of pore ice during MIS 3/2 converges on wedge ice values, signalling an increase in the ratio of cold-to-warm-season precipitation integrated by pore ice during glacial times, possibly due to drier summers as supported by the fossil record and climate model simulations. In the study region, water isotope proxies integrating year-round precipitation may overestimate annual temperature differences between today and recent cold stages due to transient precipitation seasonality, as detected here, and thus are best interpreted as upper bound estimates. Based on these proxies, we estimate that annual temperatures during MIS 4, 3/2 and 2 were depressed below the modern climate to a maximum of ∼18 °C, 16 °C and 21 °C ± 4–5 °C, respectively. Our study highlights the value of multiple water isotope proxies towards understanding changes in precipitation seasonality and developing robust reconstructions of past climate, and may be particularly important for studies of the major climate transformations over glacial-interglacial timescales.
•Multiple water isotopes proxies are used to constrain fractionations and paleotemperatures.•The water-wax net fractionation for the δDwax of steppe-tundra plants was ∼ −59 ± 10‰.•Relict ice, volcanic glass shards and plant waxes reveal depleted cold stage precipitation.•Winter-spring climates were ∼ 14 ± 5 °C colder than today during the transitional MIS 3/2.•MIS 4 to 2 annual climates were depressed to a maximum of ∼ 16–21 °C ± 5 °C below modern.
PDF
