scholarly journals EVALUATING SHORT-TERM CLIMATE VARIABILITY IN THE LATE HOLOCENE OF THE NORTHERN GREAT PLAINS

1999 ◽  
Author(s):  
Joseph H. Hartman
Keyword(s):  
Climate Variability ◽  
Great Plains ◽  
Late Holocene ◽  
Northern Great Plains ◽  
Short Term

Siliceous microfossils and mineral magnetic characteristics in a sediment core from Lake Manitoba, Canada: a remnant of glacial Lake Agassiz

1999 ◽  
Vol 36 (8) ◽  
pp. 1299-1314 ◽  
Author(s):  
Jan Risberg ◽  
Per Sandgren ◽  
James T Teller ◽  
William M Last
Keyword(s):  
Great Plains ◽  
Late Holocene ◽  
Climatic Conditions ◽  
Glacial Lake ◽  
Magnetic Characteristics ◽  
Northern Great Plains ◽  
Silty Clay ◽  
Lake Agassiz ◽  
Radiocarbon Dates ◽  
Glacial Lake Agassiz

A 14.2 m long core was recovered from the southern Lake Manitoba basin. The sediment, consisting mainly of silty clay, was studied for siliceous microfossil content and mineral magnetics; 14 new accelerator mass spectrometry (AMS) radiocarbon dates provide chronological control of the paleoenvironmental history of the basin. The basal 5 m contains ice-rafted clasts and is largely barren of siliceous microfossils; these sediments were deposited when the lake was part of glacial Lake Agassiz. Sediments immediately overlying the barren part of the sequence contain AMS dates of 7700-7400 BP and reflect a dramatic change in conditions in the basin. Diatom abundances rise abruptly. Magnetic characteristics change substantially. The presence of freshwater taxa such as Stephanodiscus niagarae, together with brackish water diatoms, indicate that shallow, turbid, high-nutrient conditions with variable salinity occurred during the early part of the middle Holocene. Although climatic conditions throughout the northern Great Plains are known to have become drier and warmer during the mid-Holocene, there is a distinct change in diatom taxa in the Lake Manitoba sequence toward less saline conditions at this time. The presence of the riverine diatom Aulacoseira granulata in this interval supports previous conclusions that these freshwater conditions resulted from the northward diversion of the Assiniboine River into the basin. Following this, diatoms indicate an abrupt increase in salinity to >1500 mg·L-1 total dissolved solids between 4000 and 2600 BP, reflecting the diversion of the fresh waters of the Assiniboine River away from Lake Manitoba. Increasingly cooler and wetter conditions during the late Holocene, combined with differential isostatic rebound, caused a freshening of the lake during the late Holocene.

scholarly journals On the Identification and Characterization of Drought and Aridity in Postglacial Paleoenvironmental Records from the Northern Great Plains

2004 ◽  
Vol 56 (2-3) ◽  
pp. 229-246 ◽  
Author(s):  
Alwynne B. Beaudoin
Keyword(s):  
Global Warming ◽  
High Resolution ◽  
Great Plains ◽  
Northern Great Plains ◽  
Short Term ◽  
Instrumental Data ◽  
Proxy Records ◽  
Identification And Characterization

Abstract The Northern Great Plains region is especially sensitive to drought and is likely to be even more drought-prone under projected global warming. Drought has been invoked as an explanatory factor for changes seen in postglacial paleoenvironmental records. These proxy records may extend drought history derived from instrumental data. Moreover, in the last decade, some paleoenvironmental studies have been expressly undertaken for the examination of long-term drought history. Nevertheless, few such studies explicitly define drought. This makes it difficult to compare results or to understand what the results mean in terms of the operational drought definitions that are used in resource management. Operational drought is defined as usually short-term; longer sustained dry intervals reflect a shift to aridity. Therefore, high resolution paleoenvironmental proxies (annual or subdecadal) are best for the investigation of drought history. Such proxies include tree rings and some lake records. However, most lake-based records are sampled at lower resolution (decadal or subcentury) and are therefore providing aridity signals.

Stratigraphy, sedimentology, and environmental significance of late mid-Holocene dunes, Lauder Sand Hills, glacial Lake Hind Basin, southwestern Manitoba

2005 ◽  
Vol 42 (5) ◽  
pp. 847-863 ◽  
Author(s):  
Karen G Havholm ◽  
Garry L Running IV
Keyword(s):  
Great Plains ◽  
Late Holocene ◽  
Zonal Flow ◽  
Flood Plain ◽  
Glacial Lake ◽  
Northern Great Plains ◽  
Sand Transport ◽  
Transport Direction ◽  
Sand Sheet ◽  
Local Water

Mid-Holocene eolian dune and sand-sheet deposits, rare in the northern Great Plains, are buried under a meter or more of younger sediment in the glacial Lake Hind Basin, southwestern Manitoba. Six facies observed in three cut-bank exposures allow reconstruction of sedimentary processes and resulting landscape at the study site in the basin center around 6100 cal (calibrated) BP. A mosaic of parabolic dunes with interdune and dune-marginal lightly vegetated sand sheets developed in the Souris River flood plain that was least partly covered with woodlands and wetlands. During floods, nearby interdune areas were inundated. Dune foreset orientation and stratification indicate a more easterly sand transport direction, lending support to the hypothesis that more pervasive westerly "zonal" flow contributed to mid-Holocene aridity evident elsewhere in the northern Great Plains. More arid conditions during the mid-Holocene may have helped trigger eolian activity. However, with the exception of a more active eolian component, the flood-plain environment may have been similar to that of the late Holocene. Mid-Holocene Gowen (Mummy Cave Complex) artifacts, the first found in Manitoba, indicate that people inhabited the resource-rich environment where eolian and flood-plain landforms occurred together. Protection of mid-Holocene dune and sand-sheet strata during late Holocene phases of eolian reactivation is attributed to rapid rise in the local water table soon after deposition.

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