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• OSL ages and GPR data work together to differentiate sand units. • Of particular significance is the KKK1 site, where more than 7 m of eolian sand provided 5 ages within the Younger Dryas Chronozone (YDC). This alignment of YDC-aged dune formation in the Kankakee dunefield with similar findings in other dunefields across the Great Lakes region suggests a prevailing dry climate during the YDC. • While most previous records of the YDC are based on indirect proxy data or pollen analysis, this study provides a tangible example of a visible landscape response—the construction of sand dunes—to the rapid climatic changes that occurred during the YDC. The southern side of the Kankakee River Valley in Illinois and Indiana features an eolain landscape comprising dunes and sand sheets. These dunes are mostly parabolic in shape, ranging in height from 4 to 7 m, occasionally reaching up to 15 m. Due to limited natural exposures and fresh road cuts, three dunes were accessed for sampling through hand auguring for optically stimulated luminescence dating. To enhance our understanding of the subsurface stratigraphy, ground penetrating radar (GPR) surveys were conducted, the results of which revealed that the age variations obtained were consistent with changes from both GPR imagery and field observations. All three sampled sites indicated ages within the Younger Dryas chronozone (YDC, 12.8–11.7 ka). Notably, site KKK1 exhibited about 7 m of eolian sand, with five ages falling within the YDC. This construction of dunes during the YDC coincides with the majority of dune fields in the Great Lakes region, suggesting that the rapid climatic changes during the YDC played a crucial role in the observed dune construction here and the wider Great Lakes region. The regional consistency implies a prevailing dry climate during the YDC. While most previous YDC records are based on proxy data such as fossil pollen and stable isotope data, this study provides a tangible example of visible landscape response, construction of sand dunes, to the rapid climatic change occurring during the YDC. [ABSTRACT FROM AUTHOR]

The Hulunbuir dune field (HLB) is situated near the northern limit of the East Asian summer monsoon (EASM), and vulnerable to climate change. The aeolian sand–paleosol sequences of this region are crucial for understanding the past landform processes in response to climate change, but not yet understood well due to chronological controversies. Here, we presented 20 optically stimulated luminescence (OSL) ages from five aeolian sand–paleosol profiles in the HLB, and reconstructed the aeolian landform processes since 18 ka. The findings of this study suggested that the HLB was probably dominated by mobile dunes before 18 ka, as 10 out of 11 aeolian samples were dated to 18–12 ka. Two strong sandy paleosol layers were found and dated to ∼9 ka and 5–0.5 ka, indicating that strong in situ pedogenic process on the accumulative sand could occur during the Holocene. The OSL ages of samples near the top of three profiles were >9.5 ka, indicating two possible surface processes. First, the land surface was stable since 9.5 ka after stabilization, with no accumulation or erosion. Alternatively, the surface could have been erosive with the eroded sediments feeding downwind active dunes. The latter explanation is consistent with the current local landforms, which has widespread blowout pits, indicators of strong wind erosion. We emphasized that the OSL age of a sand layer sample in fossil dunes implied the onset of mobile dune stabilization, not the age of dune activity, as previously stated. [ABSTRACT FROM AUTHOR]

ABSTRACT This paper draws on recent optically stimulated luminescence (OSL) dating to evaluate the long-held assumption that dust accumulation rates in the Loess Plateau and the extent of active aeolian sand in the dunefields to the north have varied together over time, because both are controlled by the strength of the Asian monsoons and also possibly because the dunefields are proximal loess sources. The results show there is little evidence that high rates of loess accumulation coincided with well-dated episodes of extensive dune activity in the Mu Us, Otindag, and Horqin dunefields, at 11-8 ka and 1-0 ka. Explanations for the apparent lack of coupling include local variation in the trapping of dust and post-depositional preservation of the loess and dune sediments, in response to varying local environmental conditions. In addition, a substantial portion of the loess may be transported directly from source areas where dust emission has somewhat different climatic and geomorphic controls than aeolian sand activity within the dunefields. The results of this study cast doubt on the use of loess accumulation rate as a palaeoclimatic proxy at millennial timescale. The dunefield and loess stratigraphic records are interpreted as primarily recording changes in effective moisture at a local scale, but the timing of late Quaternary dune activity, along with a variety of other evidence, indicates that moisture changes in many of the drylands of northern China may not be in phase with precipitation in core regions of the Asian monsoons. Copyright © 2011 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Sand dunes and sand sheets are located along the south side of Kankakee River Valley in Illinois and Indiana, USA, which overlie glaciofluvial outwash, glacial lake sediments and bedrock of Middle Paleozoic shales and carbonates. Dunes are prominent feature of the landscape, and most dunes are 15 to 25 feet high, and some reach 50 feet. Due to the lack of natural exposure and roadcuts, three dunes were sampled by hand augering for OSL (optically stimulated luminescence) dating. Ground penetrating radar (GPR) surveys were conducted for better understanding of the local stratigraphy at the sites of hand augering. Three OSL ages indicate most dune construction occurred during the Younger Dryas chronozone (11.5-12.8 ka). The large error bars of the OSL ages (usually 5-10%, about 900-1200 yrs) usually do not allow for determination of specific climatic events, but multiple ages from multiple sites of these dunes all fall into the range of Younger Dryas. Combined ages using OxCal program reveal that the statistical average of the three is 12.21+/-0.56 ka. Three uppermost ages (<1.3 m in depth) are Holocene. These Holocene OSL ages can be explained by dry climate during Holocene to activate the dunes, but more likely they are attributed to resetting of luminescence signals through near-surface bioturbations in sand. These changes of the ages above and below the Younger Dryas chronozone are consistent with GPR image and lithology changes observed in the field. [ABSTRACT FROM AUTHOR]

Abstract: Reconstructing moisture conditions during the early retreat of the Laurentide Ice Sheet (LIS) may help define the phase relationship of deglacial conditions and atmospheric changes over North America. Here, we report two sediment successions near the concurrent ice margins in the Midwest of the U.S.A. to show that dune formation was active from 17.7 to 14.7 and from 12.8 to 11.8 thousand years ago (ka) and lowland soils formed at 14.7 and wetland sediments developed from 13.5 to 12.8 ka. Our results suggest that moisture conditions in the Midwestern U.S.A. were inversely phased with those in the southwestern U.S.A. During the Heinrich event 1 (H1) and Younger Dryas (YD) stadials, the northern area became drier and southern area became wetter, whereas during the Bølling/Allerød (B/A) interstadials, the northern area became wetter and southern area became drier. This pattern is also observed on phase change levels within the H1 interval. In detail, from 17.7 to 16.5 ka during the H1b phase, major aridity in the Midwest corresponded to wet conditions in the Southwest U.S.A. From 16.5 to 15.0 ka during the H1a phase, climate reversed from dry to wet in the Midwest, whereas conditions went from wet to dry in the Southwest. From 15.0 to 14.7 ka during the transition to the Bølling/Allerød (t-B/A) phase, a return of aridity in the Midwest corresponded to a return of humidity in the Southwest. [Copyright &y& Elsevier]

Abstract: The climatic controls on dune mobility, especially the relative importance of wind strength, remain incompletely understood. This is a key research problem in semi-arid northern China, both for interpreting past dune activity as evidence of paleoclimate and for predicting future environmental change. Potential eolian sand transport, which is approximately proportional to wind power above the threshold for sand entrainment, has decreased across much of northern China since the 1970s. Over the same period, effective moisture (ratio of precipitation to potential evapotranspiration) has not changed significantly. This “natural experiment” provides insight on the relative importance of wind power as a control on dune mobility in three dunefields of northern China (Mu Us, Otindag, and Horqin), although poorly understood and potentially large effects of human land use complicate interpretation. Dune forms in these three regions are consistent with sand transport vectors inferred from weather station data, suggesting that wind directions have remained stable and the stations adequately represent winds that shaped the dunes. The predicted effect of weaker winds since the 1970s would be dune stabilization, with lower sand transport rates allowing vegetation cover to expand. Large portions of all three dunefields remained stabilized by vegetation in the 1970s despite high wind power. Since the 1970s, trends in remotely sensed vegetation greenness and change in mobile dune area inferred from sequential Landsat images do indicate widespread dune stabilization in the eastern Mu Us region. On the other hand, expansion of active dunes took place farther west in the Mu Us dunefield and especially in the central Otindag dunefield, with little overall change in two parts of the Horqin dunes. Better ground truth is needed to validate the remote sensing analyses, but results presented here place limits on the relative importance of wind strength as a control on dune mobility in the study areas. High wind power alone does not completely destabilize these dunes. A large decrease in wind power either has little short-term effect on the dunes, or more likely its effect is sufficiently small that it is obscured by human impacts on dune stability in many parts of the study areas. [Copyright &y& Elsevier]