Pollen Evidence for Late Pleistocene Bering Land Bridge Environments from Norton Sound, Northeastern Bering Sea, Alaska

Ager, Thomas A.; Phillips, R.L.

doi:10.1657/1523-0430(07-076)[ager]2.0.co;2

Cited by 21 publications

(24 citation statements)

References 47 publications

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“…The plant community appears to have been mostly stable, except for Equisetum peaks that may indicate wetter conditions before the YD and after 690 yr bp . This prostrate shrub‐graminoid tundra is similar to graminoid‐forb tundra found at other glacial‐aged sites in south‐central Beringia (Colinvaux, ; Ager, ; Ager & Phillips, ). The persistence of this dry tundra over the whole period of record may have been facilitated by soils that today are thin and well‐drained, with little paludification and underlain by a volcanic and porous substrate.…”

Section: Discussionmentioning

confidence: 99%

“…Current debates about Beringian vegetation during the LGM centre primarily on the prevalence of mesic shrub tundra versus graminoid-herb tundra (Ager & Phillips, 2008;Elias & Crocker, 2008). One perspective, based on fossil pollen and insect data, holds that mesic shrub tundra was widespread during the LGM, particularly in low-lying and now-submerged portions of Beringia (Elias & Crocker, 2008;Hoffecker et al, 2014), which possibly acted as a biogeographical barrier to steppe-adapted plants and animals (Guthrie, 2001).…”

Section: Introductionmentioning

confidence: 99%

“…One perspective, based on fossil pollen and insect data, holds that mesic shrub tundra was widespread during the LGM, particularly in low-lying and now-submerged portions of Beringia (Elias & Crocker, 2008;Hoffecker et al, 2014), which possibly acted as a biogeographical barrier to steppe-adapted plants and animals (Guthrie, 2001). However, others have argued that graminoid-forb tundra prevailed across Beringia during the LGM, based on fossil pollen, macrofossils and stable isotope analyses in Alaska and on Bering Sea island remnants (Colinvaux, 1981;Ager, 2003;Bigelow et al, 2003;Kaplan et al, 2003;Ager & Phillips, 2008). In the latter interpretation, the graminoid-forb tundra was maintained by dry climates and, perhaps, grazers (Blinnikov et al, 2011), and provided habitat for the diverse Pleistocene megafaunal guilds of Beringia (Willerslev et al, 2014).…”

Section: Introductionmentioning

confidence: 99%

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The southern coastal Beringian land bridge: cryptic refugium or pseudorefugium for woody plants during the Last Glacial Maximum?

Wang

Heintzman

Newsom

et al. 2017

Journal of Biogeography

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Aim The Bering Land Bridge (BLB) connected Asia and North America during glacial periods, supported a diverse ecosystem of now‐vanished megafauna, and is a proposed glacial refugium. This study tests whether southern coastal Beringia was a refugium for woody taxa during the Last Glacial Maximum (LGM) and hypotheses about habitats available on the BLB before and after megafaunal extinction. Location St. Paul Island, Alaska. Methods We analysed sediment cores from the Lake Hill, with a new age model anchored by 18 radiocarbon dates and multiple palaeoecological indicators (sedimentary ancient DNA [sedaDNA], macrobotanical fossils, and pollen) for the presence/absence of four woody genera: Picea, Betula, Alnus and Salix. We reconstructed vegetation history and compare St. Paul tundra composition to mainland counterparts. Results St. Paul has been continuously occupied by graminoid‐forb tundra with prostrate shrubs (Salix, Ericaceae) since 18,000 years before present (yr bp). Fossil pollen of Picea, Pinus, Betula and Alnus is present in the Lake Hill sediments at low relative abundances and accumulation rates, consistent with long‐distance transport. Macrobotanical fossils and sedaDNA analyses do not support Picea, Betula and Alnus presence. The St. Paul modern and fossil pollen assemblages are compositionally unlike mainland counterparts, but most closely resemble Arctic herbaceous tundra. Stratigraphically constrained cluster analysis indicates no major change in the vegetation after woolly mammoth extinction at 5600 yr bp, although Poaceae, Cyperaceae, Equisetum and forb abundances increase. Main conclusions This study strongly indicates that St. Paul and, by implication, southern coastal Beringia were not refugia for woody taxa during the LGM. The persistence of prostrate shrub‐graminoid tundra supports interpretations that herbaceous tundra prevailed on southern Beringia during the LGM, whilst not ruling out the possibility of mesic shrub tundra in the interior. This herbaceous tundra supported an island refugium for woolly mammoth for 8000 years, showing no major vegetation composition changes after extinction.

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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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The southern coastal Beringian land bridge: cryptic refugium or pseudorefugium for woody plants during the Last Glacial Maximum?

Wang

Heintzman

Newsom

et al. 2017

Journal of Biogeography

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“…Willows ( Salix ; Salicaceae), a genus of shrub and tree species, are a significant component of Holarctic ecosystems (Ager & Phillips ; Argus ; Myers‐Smith et al . ).…”

Section: Introductionmentioning

confidence: 99%

Understanding the spectacular failure of DNA barcoding in willows (Salix): Does this result from a trans‐specific selective sweep?

et al. 2014

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Willows (Salix: Salicaceae) form a major ecological component of Holarctic floras and consequently are an obvious target for a DNA-based identification system. We surveyed two to seven plastid genome regions (~3.8 kb; ~3% of the genome) from 71 Salix species across all five subgenera, to assess their performance as DNA barcode markers. Although Salix has a relatively high level of interspecific hybridization, this may not sufficiently explain the near complete failure of barcoding that we observed: only one species had a unique barcode. We recovered 39 unique haplotypes, from more than 500 specimens, that could be partitioned into six major haplotype groups. A unique variant of group I (haplotype 1*) was shared by 53 species in three of five Salix subgenera. This unusual pattern of haplotype sharing across infrageneric taxa is suggestive of either a massive nonrandom coalescence failure (incomplete lineage sorting), or of repeated plastid capture events, possibly including a historical selective sweep of haplotype 1* across taxonomic sections. The former is unlikely as molecular dating indicates that haplotype 1* originated recently and is nested in the oldest major haplotype group in the genus. Further, we detected significant non-neutrality in the frequency spectrum of mutations in group I, but not outside group I, and demonstrated a striking absence of geographical (isolation by distance) effects in the haplotype distributions of this group. The most likely explanation for the patterns we observed involves recent repeated plastid capture events, aided by widespread hybridization and long-range seed dispersal, but primarily propelled by one or more trans-species selective sweeps.

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“…During the Late Wisconsin (Late Glacial), the climate of the BLB was arid and cold. The land was not glaciated because snowfall was extremely light, and predominant vegetation was graminoid-herb-willow tundra (Ager 2003;Ager and Philips 2008). Rising sea levels had began to flood the BLB about 13,500 cal BP (http://www.ncdc.noaa.gov/paleo/parcs/ atlas/beringia/lbridge.html) and climate became wetter with deeper winter snows, and moist, cool summers with dwarf birch-heath-willow-herb tundra vegetation (Ager and Philips 2008).…”

Section: Environmental Changes During Analyzed Time Periodmentioning

confidence: 99%

Frequency Distribution of¹⁴C Ages for Chronostratigraphic Reconstructions: Alaska Region Study Case

Michczyńska

Hajdas

2010

Radiocarbon

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ABSTRACT. In this study, we test the possibility of using databases of radiocarbon ages to estimate boundaries of climatic chronozones. The Alaska region was chosen and compared with chronozones of 2 European countries: Poland and the Netherlands. The study included setting up a database of 14 C ages published for climatic records from Alaska. Some 974 14 C determinations on organic samples were selected and used to establish chronozones for the Late Glacial and the Holocene for the Alaska region. The selected data were calibrated and a summed probability density function (PDF) was calculated. The shape analysis of the constructed frequency distribution of 14 C dates on calendar timescales together with the assumption about preferential sampling seems to be a useful tool for establishing calendar ages for boundaries of climatic periods, i.e. chronozones.

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Pollen Evidence for Late Pleistocene Bering Land Bridge Environments from Norton Sound, Northeastern Bering Sea, Alaska

Cited by 21 publications

References 47 publications

The southern coastal Beringian land bridge: cryptic refugium or pseudorefugium for woody plants during the Last Glacial Maximum?

The southern coastal Beringian land bridge: cryptic refugium or pseudorefugium for woody plants during the Last Glacial Maximum?

Understanding the spectacular failure of DNA barcoding in willows (Salix): Does this result from a trans‐specific selective sweep?

Frequency Distribution of¹⁴C Ages for Chronostratigraphic Reconstructions: Alaska Region Study Case

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Pollen Evidence for Late Pleistocene Bering Land Bridge Environments from Norton Sound, Northeastern Bering Sea, Alaska

Cited by 21 publications

References 47 publications

The southern coastal Beringian land bridge: cryptic refugium or pseudorefugium for woody plants during the Last Glacial Maximum?

The southern coastal Beringian land bridge: cryptic refugium or pseudorefugium for woody plants during the Last Glacial Maximum?

Understanding the spectacular failure of DNA barcoding in willows (Salix): Does this result from a trans‐specific selective sweep?

Frequency Distribution of14C Ages for Chronostratigraphic Reconstructions: Alaska Region Study Case

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Frequency Distribution of¹⁴C Ages for Chronostratigraphic Reconstructions: Alaska Region Study Case