Atmospherically produced beryllium-10 in annually laminated late-glacial sediments of the North American Varve Chronology

Abstract. We attempt to synchronize the North American Varve Chronology (NAVC) with the calendar year time scale by comparing records of atmospherically produced Be-10 fallout in the NAVC and in ice cores. The North American Varve Chronology (NAVC) is a sequence of 5659 varves deposited in a series of proglacial lakes adjacent to the southeast margin of the retreating Laurentide Ice Sheet between approximately 18,200–12,500 years before present. Because properties of NAVC varves are related to climate, the NAVC is also a climate proxy record with annual resolution, and our overall goal is to place the NAVC and ice core records on the same time scale to facilitate high-resolution correlation of climate events. Total Be-10 concentrations in NAVC sediments are within the range of those observed in other lacustrine records of Be-10 fallout, but Be-9 and Be-10 concentrations considered together show that the majority of Be-10 is present in glacial sediment when it enters the lake, and only a minority of total Be-10 derives from atmospheric fallout at the time of sediment deposition. Because of this, an initial strategy to determine whether or not Be-10 fallout variations were recorded in NAVC sediments by attempting to observe the characteristic 11-year solar cycle in high-resolution sections of varve sequences was inconclusive: observed short-period variations at the expected magnitude of this cycle were not distinguishable from measurement scatter. On the other hand, we did observe centennial-period variations in Be-10 fallout that are replicated between separate varve sections and have similar magnitude and frequency as coeval Be-10 fallout variations recorded in ice core records. These are most prominent in glacial sections of the NAVC that were deposited in proglacial lakes, but are suppressed in paraglacial sections of the NAVC deposited in lakes lacking direct glacial sediment input, which leads us to conclude that proglacial lakes whose watershed likely includes a large portion of the ablation area of an ice sheet can effectively record Be-10 fallout. We matched observed centennial-scale Be-10 fallout variations in two segments of the NAVC to ice core Be-10 fallout records. Although the calibration of the NAVC to the calendar year time scale implied by these matches is similar to that proposed previously in independent calibrations based on radiocarbon data and correlation of climate events, matches for the two different segments disagree with each other and with the independent calibrations by 50–200 years. One of these matches is not consistent with independent evidence and is probably not valid, but the other is consistent with most, although not all, evidence and may be valid. This leaves several remaining ambiguities in whether or not Be-10 fallout variations can, in fact, be used for synchronizing NAVC and ice core timescales, but these could likely be resolved by higher-resolution and replicate Be-10 measurements on targeted sections of the NAVC.

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Glacial and early postglacial lacustrine environment of a portion of northeastern Lake Ontario

Canadian Journal of Earth Sciences ◽

10.1139/e92-008 ◽

1992 ◽

Vol 29 (1) ◽

pp. 63-75 ◽

Cited By ~ 12

Author(s):

Robert Gilbert ◽

John Shaw

Keyword(s):

Lake Ontario ◽

Late Glacial ◽

High Energy ◽

Upper Great Lakes ◽

Glacial Sediments ◽

The North ◽

Large Channel ◽

Acoustic Facies ◽

Short Time ◽

Subglacial Meltwater

A deep channel in bedrock extending to more than 25 m below sea level occurs along the north shore of the otherwise uniformly shallow Kingston basin of Lake Ontario. Bathymetric and subbottom acoustic data are used to map the topography of the channel and to reconstruct its late glacial and postglacial sedimentary history. The results are interpreted as showing that the large channel and smaller channels nearby were created by high-velocity subglacial meltwater flow. Acoustic facies assemblages of sediments deposited in the channels record patchy deposition, or deposition followed by partial erosion, of glacial sediments on the bedrock of the channel floor, followed by deposition and episodic erosion of glaciolacustrine sediment in a high-energy, ice-proximal lake. Palaeoslope analysis confirms that the early Holocene low-water phase of Lake Ontario resulted in the development of a fluvial system in part of the channel. Water level was controlled by a sill at Kingston. Kingston basin, the Bay of Quinte, and possibly, for a short time, a much larger area of the upper Great Lakes drained through the channel. However, for most of the period, until it was flooded by the rising waters of Lake Ontario, the channel was occupied by a small river on a wide floodplain or it was flanked by broad marshes.

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Atmospherically produced beryllium-10 in annually laminated late-glacial sediments of the North American Varve Chronology

Geochronology ◽

10.5194/gchron-3-1-2021 ◽

2021 ◽

Vol 3 (1) ◽

pp. 1-33

Author(s):

Greg Balco ◽

Benjamin D. DeJong ◽

John C. Ridge ◽

Paul R. Bierman ◽

Dylan H. Rood

Keyword(s):

High Resolution ◽

North American ◽

Ice Core ◽

Glacial Sediment ◽

Climate Proxy ◽

Varve Chronology ◽

The North ◽

Proglacial Lakes ◽

Short Period ◽

Period Variations

Abstract. We attempt to synchronize the North American Varve Chronology (NAVC) with ice core and calendar year timescales by comparing records of atmospherically produced 10Be fallout in the NAVC and in ice cores. The North American Varve Chronology (NAVC) is a sequence of 5659 varves deposited in a series of proglacial lakes adjacent to the southeast margin of the retreating Laurentide Ice Sheet between approximately 18 200 and 12 500 years before present. Because properties of NAVC varves are related to climate, the NAVC is also a climate proxy record with annual resolution, and our overall goal is to place the NAVC and ice core records on the same timescale to facilitate high-resolution correlation of climate proxy variations in both. Total 10Be concentrations in NAVC sediments are within the range of those observed in other lacustrine records of 10Be fallout, but 9Be and 10Be concentrations considered together show that the majority of 10Be is present in glacial sediment when it enters the lake, and only a minority of total 10Be derives from atmospheric fallout at the time of sediment deposition. Because of this, an initial experiment to determine whether or not 10Be fallout variations were recorded in NAVC sediments by attempting to observe the characteristic 11-year solar cycle in short varve sections sampled at high resolution was inconclusive: short-period variations at the expected magnitude of this cycle were not distinguishable from measurement scatter. On the other hand, longer varve sequences sampled at decadal resolution display centennial-period variations in reconstructed 10Be fallout that have similar properties as coeval 10Be fallout variations recorded in ice core records. These are most prominent in glacial sections of the NAVC that were deposited in proglacial lakes and are suppressed in paraglacial sections of the NAVC that were deposited in lakes lacking direct glacial sediment input. We attribute this difference to the fact that buffering of 10Be fallout by soil adsorption can filter out short-period variations in an entirely deglaciated watershed, but such buffering cannot occur in the ablation zone of an ice sheet. This implies that proglacial lakes whose watershed is mostly glacial may effectively record 10Be fallout variations. We attempted to match centennial-period variations in reconstructed 10Be fallout flux from two segments of the NAVC with ice core fallout records. For both records, it is possible to obtain matches that result in acceptable correlation between NAVC and ice core 10Be fallout records, but the best-fitting matches for the two segments disagree, and only one of them is consistent with independent calendar year calibrations of the NAVC and therefore potentially valid. This leaves several remaining ambiguities in whether or not 10Be fallout variations can, in fact, be used for synchronizing NAVC and ice core timescales, but these could most likely be resolved by higher-resolution and replicate 10Be measurements on targeted sections of the NAVC.

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A palynological investigation of true-moss (Bryidae) spores: morphology and occurrence in modern and late Quaternary lake sediments of Alaska

Canadian Journal of Botany ◽

10.1139/b98-192 ◽

1998 ◽

Vol 76 (12) ◽

pp. 2145-2157 ◽

Cited By ~ 8

Author(s):

L B Brubaker ◽

P M Anderson ◽

B M Murray ◽

D Koon

Keyword(s):

Boreal Forest ◽

Late Quaternary ◽

Late Glacial ◽

North Slope ◽

Wall Structure ◽

Herbarium Specimens ◽

Glacial Sediments ◽

The North ◽

True Moss ◽

Southwestern Alaska

This study describes (i) spore morphology of 121 Alaskan species of true moss (Bryidae) and (ii) percentages of Bryidae and Sphagnum spores in mud-water interface samples from 46 Alaskan lakes and a late-Quaternary sediment core from Idavain Lake in southwestern Alaska. Bryidae spores were collected from herbarium specimens, prepared by standard palynological chemical treatment and described under light microscopy. An identification key based on spore shape, wall structure, and size recognized 11 major morphological groups. Although family, genus, or species identifications were not possible for most groups, spores of a few genera and species were distinctive. Bryidae spores occurred in 80% of the modern sediment samples, representing boreal forest and three areas of tundra (North Slope, Seward Peninsula, and southwestern Alaska). Bryidae and Sphagnum spore percentages showed greatest differences between the North Slope tundra and other vegetation types, whereas pollen percentages distinguished boreal forest from tundra regions as a group. Bryidae spores were present throughout the Idavain Lake record but were most common in late-glacial sediments. Variations in the abundance of Bryidae spores are consistent with or enhance paleoenvironmental interpretations based on pollen and other spore types.Key words: Bryidae, palynology, spores, Alaska, Quaternary, paleoenvironment.

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