Pollen Diagram from the Nebraska Sandhills and the Age of the Dunes

1985 ◽  
Vol 24 (1) ◽  
pp. 115-120 ◽  
Author(s):  
H. E. Wright ◽  
J. C. Almendinger ◽  
J. Grüger
Keyword(s):  
Sand Dunes ◽  
Dune Sand ◽  
Last Glacial Period ◽  
Pollen Diagram ◽  
Radiocarbon Dates ◽  
The Holocene ◽  
Swan Lake ◽  
Nebraska Sandhills ◽  
Prairie Vegetation ◽  
The Last Glacial

Radiocarbon dates of organic alluvium beneath as much as 40 m of dune sand along the Dismal River have led to the suggestion that the Nebraska Sandhills date from the Holocene rather than the last glacial period. On the other hand, the basal layers of lake and marsh deposits in interdune depressions at three localities date in the range of 9000 to 12,000 yr B.P., implying a pre-Holocene age for the sand dunes. A pollen diagram for one of these sites, Swan Lake, indicates prairie vegetation throughout the last 9000 yr, with no suggestion that the landscape was barren enough to permit the shaping of the massive dunes characterizing the area. Sand was not transported across the site during the Holocene, either during the marsh phase, which lasted until 3700 yr B.P., or during the subsequent lake phase. The sand that buries the alluvium along the Dismal River may represent only local eolian activity, or it may indicate that the younger of the two main dune series identified by H. T. U. Smith (1965, Journal of Geology 73, 557–578) is Holocene in age, and the older one Late Wisconsin in age.

LONG-TERM RATES OF FAULTING DERIVED FROM COSMOGENIC NUCLIDES AND SHORT-TERM VARIATIONS CAUSED BY GLACIAL-INTERGLACIAL VOLUME CHANGES OF GLACIERS AND LAKES

2006 ◽  
Vol 20 (03) ◽  
pp. 261-276 ◽  
Author(s):  
RALF HETZEL ◽  
ANDREA HAMPEL
Keyword(s):  
Slip Rate ◽  
Alluvial Fan ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Slip Rates ◽  
The Holocene ◽  
Last Glacial ◽  
River Terraces ◽  
The Last Glacial

Seismic hazard evaluations on major faults in Earth's crust are based on their slip histories, which reflect the frequency of earthquakes that ruptured a fault in the past. On a 100 000-year timescale, the slip rate of a fault can be determined by dating geomorphic surfaces that are offset by a fault. Application of this method to alluvial fan surfaces and river terraces offset by thrust faults in Tibet yields long-term slip rates of less than 1mm/a. Slip rates on a 10 000-year timescale are derived from paleoseismologic data and document that faults experience considerable slip rate variations on timescales of 100 to 1000 years. In particular, slip rates are often considerable higher in the present interglacial, the Holocene, than during the last glacial period, the Late Pleistocene. The causes of this behavior have remained enigmatic but their assessment is essential for an accurate evaluation of a fault's past and future seismicity. Numerical experiments show that the retreat of lakes and glaciers at the end of the last glacial period can cause an increase in the Holocene slip rate of a fault. Such a correlation between enhanced seismicity and climate-driven mass fluctuations on Earth's surface is best documented for the Wasatch Fault, Utah.

scholarly journals Palaeogeographical And Archaeological Records Of Natural Changes Of The Jordanowo-Niesulice Subglacial Channel Near Lubrza, The Lubusz Lakeland

2015 ◽  
Vol 34 (3) ◽  
pp. 101-116 ◽  
Author(s):  
Magdalena Ratajczak-Szczerba ◽  
Iwona Sobkowiak-Tabaka ◽  
Iwona Okuniewska-Nowaczyk
Keyword(s):  
Late Glacial ◽  
Last Glacial Period ◽  
Geochemical Composition ◽  
Palynological Analysis ◽  
The Holocene ◽  
Ams Radiocarbon Dating ◽  
History Of ◽  
Geomorphological Analysis ◽  
Geological Research ◽  
The Last Glacial

Abstract The region of the Lubusz Lakeland in western Poland where there are a lot of subglacial channels provides opportunity for multi-proxy palaeoenvironmental reconstructions. None of them has not been the object of a specific study. The developmental history of the palaeolakes and their vicinity in the subglacial trough Jordanowo-Niesulice, spanning the Late Glacial and beginning of the Holocene, was investigated using geological research, lithological and geomorphological analysis, geochemical composition, palynological and archaeological research, OSL and AMS-radiocarbon dating. Geological research shows varied morphology of subglacial channel where at least two different reservoirs functioned in the end of the Last Glacial period and at the beginning of the Holocene. Mostly during the Bølling-Allerød interval and at the beginning of the Younger Dryas there took place melting of buried ice-blocks which preserved the analysied course of the Jordanowo-Niesulice trough. The level of water, and especially depth of reservoirs underwent also changes. Palynological analysis shows very diversified course of the Allerød interval.

scholarly journals Geomorphological characteristics of the sand-dune field of the central Kyparissiakos Gulf

2007 ◽  
Vol 40 (4) ◽  
pp. 1530 ◽  
Author(s):  
Th. Karamousalis ◽  
S. Poulos ◽  
H. Maroukian ◽  
G. Ghionis
Keyword(s):  
Sand Dune ◽  
Sand Dunes ◽  
Fine Sand ◽  
Middle Part ◽  
Alluvial Fan ◽  
Last Glacial Period ◽  
Dune Field ◽  
Natural Processes ◽  
Dune Ridge ◽  
The Last Glacial

Sand dunes are sensitive coastal landforms closely related to the evolution (and/or stability) of the beach zone. The present work refers to the central part of the dune field that lies along the middle part of the shoreline of the Kyparissiakos Gulf. The scope of the present investigation is to reveal the geomorphological and sedimentological characteristics of the sand dune field in association with the natural processes contributing to their formation. On the basis of our findings, the dune field of the central Kyparissiakos Gulf consists of four dune ridges, with heights >4.0 m. Their extent indicates the availability of large quantities of sand and the existence of a rather stable wind field. They consist of well sorted medium to fine sand. The alluvial fan of the Zachareiko torrential river has covered the dune field in the area of its mouth and buried the oldest 4th dune ridge to its south. The development of the dune field is estimated to have taken place during the last 3-4 thousand years subsequently to the completion of the rapid sea level rise at the end of the last glacial period.

Causes and climatic influence of centennial-scale denitrification variability in the southeastern Arabian Sea since the last glacial period

2021 ◽  
pp. 1-13
Author(s):  
Sidhesh Nagoji ◽  
Manish Tiwari
Keyword(s):  
Arabian Sea ◽  
Asian Summer Monsoon ◽  
Intermediate Water ◽  
Glacial Period ◽  
South Asian Summer Monsoon ◽  
Last Glacial Period ◽  
The Holocene ◽  
Last Glacial ◽  
Southeastern Arabian Sea ◽  
The Last Glacial

Abstract Denitrification occurring in the oxygen minimum zone of the Arabian Sea produces nitrous oxide, a powerful greenhouse gas. Therefore, it is important to understand the mechanisms controlling denitrification's intensity and evaluate its influence on the global climate at various timescales. We studied multiple geochemical and isotopic proxies in a sediment core from the southeastern Arabian Sea (SEAS) at a high (centennial-scale) resolution. We find that since the last glacial period, both the ventilation and the productivity caused by the South Asian summer monsoon played a major role in controlling the denitrification variability in SEAS. During the Last Glacial Maximum (LGM) and since the Holocene, denitrification increased in SEAS despite reduced monsoon-induced productivity. During the LGM, weakened thermohaline circulation resulted in reduced ventilation of the intermediate waters of SEAS, causing increased denitrification. During the Holocene, the increase in denitrification is caused by an enhanced inflow of oxygen-depleted Red Sea and Persian Gulf waters into the intermediate depth of SEAS owing to a rising sea level that prohibited ventilation by the Antarctic Intermediate Water. We further find millennial-scale synchronicity between denitrification in SEAS, global monsoons, and the North Atlantic climate, implying systematic linkages via greenhouse gases abundance.

The Last Glacial Maximum in northern Baffin Bay

2021 ◽  
Author(s):  
Karen Søby Özdemir ◽  
Henrieka Detlef ◽  
Linda Lambertucci ◽  
Christof Pearce
Keyword(s):  
Last Glacial Maximum ◽  
Glacial Maximum ◽  
Ice Shelf ◽  
Radiocarbon Dates ◽  
The Holocene ◽  
Baffin Bay ◽  
Last Glacial ◽  
The Core ◽  
The Last Glacial Maximum ◽  
The Last Glacial

<p>Little is known about climate and ocean conditions during the Last Glacial Maximum in Baffin Bay, Greenland. This is partly due to the dissolution of biogenic carbonates in the central Baffin Bay, preventing reliable <sup>14</sup>C-chronologies. We present the results from a transect of gravity cores retrieved during the 2019 BIOS cruise on the HDMS Lauge Koch in the northern Baffin Bay. Core LK19-ST8-14G has been analyzed for grain size variations, sea-ice biomarkers, XRF, and color spectrophotometry. A preliminary chronology based on radiocarbon dates from foraminifera show that the bottom of the core is approximately 35.000 cal. years BP while the top sediments are of Late Holocene age. The sediment archive thus covers the full extent of the LGM and the last deglaciation. High-resolution photography and CT scans allowed the identification of distinctly different lithofacies in the sediment archive. The lower sections of the core are characterized by laminated mud with no IRD and absence of microfossils indicating a sub ice-shelf environment during the glacial period. The laminated sequence is interrupted by several coarser, detrital-carbonate (DC) rich layers which are interpreted as episodes of glacial retreat or ice-shelf collapse. The youngest of these DC layers immediately precedes the Holocene, which is represented by approximately 40 cm of bioturbated sediments with some IRD. This interpretation is supported by the concentrations of HBIs and sterols throughout the core, which indicate near perennial ice cover in the glacial northern Baffin Bay and more open water conditions during the Holocene.</p>

Stable isotope and 14C study of biogenic calcrete in a termite mound, Western Cape, South Africa, and its palaeoenvironmental significance

2009 ◽  
Vol 72 (2) ◽  
pp. 258-264 ◽  
Author(s):  
Alastair J. Potts ◽  
Jeremy J. Midgley ◽  
Chris Harris
Keyword(s):  
South Africa ◽  
Arid Zone ◽  
Late Quaternary ◽  
Western Cape ◽  
Cam Plants ◽  
Termite Mounds ◽  
Last Glacial Period ◽  
Radiocarbon Dates ◽  
Progressive Decline ◽  
The Last Glacial

AbstractLate Quaternary terrestrial climate records from the semi-arid zone of the Western Cape of South Africa are rare. However, palaeoenvironmental information may be inferred from ancient termite mounds of the region. Calcrete lenses in these mounds have δ13C and δ18O values that show systematic changes with radiocarbon dates, which range from 33,629–36,709 to 21,676–23,256 cal yr BP. These dates confirm that these heuweltjies had been present in the landscape since the last glacial period. The decrease in δ13C and δ18O from 33,629–36,709 to 21,676–23,256 cal yr BP indicates that climate information is recorded by the calcretes. It is suggested that a progressive decline in air temperature and an increase in moisture availability, and a decline in abundance of C4 or CAM plants, occurred in the region during the time heuweltjie calcite precipitated.

scholarly journals Abrupt sea surface pH change at the end of the Younger Dryas in the central sub-equatorial Pacific inferred from boron isotope abundance in corals (<i>Porites</i>)

2010 ◽  
Vol 7 (2) ◽  
pp. 1959-1993 ◽  
Author(s):  
E. Douville ◽  
M. Paterne ◽  
G. Cabioch ◽  
P. Louvat ◽  
J. Gaillardet ◽  
...  
Keyword(s):  
Younger Dryas ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Glacial Period ◽  
Ph Change ◽  
Last Glacial Period ◽  
Surface Ph ◽  
The Holocene ◽  
Last Glacial ◽  
The Last Glacial

Abstract. The "δ11B-pH" technique was applied to modern and ancient Porites from the sub-equatorial Pacific areas (Tahiti and Marquesas) spanning a time interval from 0 to 20 720 calendar years to determine the amplitude of pH changes between the Last Glacial Period and the Holocene. Boron isotopes were measured by Multi-Collector-Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) with an external reproducibility of 0.25‰, allowing a precision of ±0.025 pH-units. The boron concentration [B] and isotopic composition of modern samples indicate that the temperature strongly controls the partition coefficient KD for different aragonite species. Modern coral δ11B values and the reconstructed sea surface pH values for different Pacific areas match the measured pH expressed on the Sea Water Scale and confirm the calculation parameters that were previously determined by laboratory calibration exercises. Most ancient sea surface pH reconstructions near Marquesas are higher than modern values. These values range between 8.20 and 8.26 for the Holocene and reached 8.31 at the end of the last glacial period (20.7 kyr BP). At the end of the Younger Dryas (11.50±0.1 kyr BP), the central sub-equatorial Pacific experienced a dramatic drop of up to 0.2 pH-units from the average pH of 8.2 before and after this short event. Using the CO2SYS program, we recalculated the aqueous pCO2 to be 400±24 ppmV at around 11.5 kyr BP for corals at Marquesas and ~500 ppmV near Tahiti where it was assumed that pCO2 in the atmosphere was 250 ppmV. Throughout the Holocene, the difference in pCO2 between the ocean and the atmosphere at Marquesas (ΔpCO2) indicates that the surface waters behave as a moderate CO2 sink (−67 to −11 ppmV) during El Niño-like conditions. In contrast, during the last glacial/interglacial transition, this area was a moderate source of CO2 (−9 to 56 ppmV) for the atmosphere, highlighting predominant La Niña-like conditions. Such conditions were particularly pronounced at the end of the Younger Dryas with a large amount of CO2 released with ΔpCO2 of +140 ppmV. This last finding provides further evidence of the marked changes to the water mass pH and temperature properties in the equatorial Pacific at the Younger Dryas- Holocene transition and the strong impact of oceanic dynamic on the atmospheric CO2 content.

Radiocarbon dates of snow petrel (Pagodroma nivea) nest sites in central Dronning Maud Land, Antarctica

Polar Record ◽  
1997 ◽  
Vol 33 (184) ◽  
pp. 29-38 ◽  
Author(s):  
W.K. Steele ◽  
A. Hiller
Keyword(s):  
Radiocarbon Dating ◽  
Last Glacial Period ◽  
Radiocarbon Dates ◽  
Radiocarbon Age ◽  
Clear Cut ◽  
Nest Sites ◽  
Snow Petrel ◽  
Dronning Maud Land ◽  
Nesting Activity ◽  
The Last Glacial

AbstractThis paper presents the results of a radiocarbon dating study of snow petrel (Pagodroma nivea) nest sites in central Dronning Maud Land, Antarctica. Mumiyo (a sub-fossilized accumulation of regurgitated proventricular oil) samples were collected from 15 snow petrel nest sites at nunataks in the northern Ahlmannryggen, Gjelsvikfjella, and Mühlig-Hofmannfjella.Radiocarbon dating revealed Holocene ages of ca 8500 years and less for all but one of these mumiyo samples. A sample collected at S varthamaren in the Muhlig-Hofmannfjella was dated as old as ca 34,000 a BP, indicating that at least some areas of that mountain escaped the scouring action of glaciers during the last glacial period. Similar pre-Holocene ages have been determined for a small number of mumiyo samples in previous studies. Mumiyo accumulations from some nests indicate periods of occupation as long as 6000 years, whereas the radiocarbon age and volume of other mumiyo samples suggest short periods of frequent nesting activity. As expected, sub-samples extracted from the lower layers of mumiyo pieces generally displayed greater ages than sub-samples from upper layers of the same piece. However, there was no clear-cut correlation between the age of a mumiyo sample and its height above the present ice level. It is suspected that this lack of correlation is due to some of the mumiyo samples being displaced previously through rockfalls.

Contrasting Patterns in Abrupt Asian Summer Monsoon Changes in the Last Glacial Period and the Holocene

2018 ◽  
Vol 33 (2) ◽  
pp. 214-226 ◽  
Author(s):  
Dianbing Liu ◽  
Yongjin Wang ◽  
Hai Cheng ◽  
R. L. Edwards ◽  
Xinggong Kong ◽  
...  
Keyword(s):  
Summer Monsoon ◽  
Asian Summer Monsoon ◽  
Glacial Period ◽  
Last Glacial Period ◽  
The Holocene ◽  
Last Glacial ◽  
Asian Summer ◽  
The Last Glacial

scholarly journals Abrupt sea surface pH change at the end of the Younger Dryas in the central sub-equatorial Pacific inferred from boron isotope abundance in corals (<i>Porites</i>)

2010 ◽  
Vol 7 (8) ◽  
pp. 2445-2459 ◽  
Author(s):  
E. Douville ◽  
M. Paterne ◽  
G. Cabioch ◽  
P. Louvat ◽  
J. Gaillardet ◽  
...  
Keyword(s):  
Younger Dryas ◽  
Equatorial Pacific ◽  
Sea Surface ◽  
Glacial Period ◽  
Last Glacial Period ◽  
Surface Ph ◽  
The Holocene ◽  
Last Glacial ◽  
Ph Values ◽  
The Last Glacial

Abstract. The "δ11B-pH" technique was applied to modern and ancient corals Porites from the sub-equatorial Pacific areas (Tahiti and Marquesas) spanning a time interval from 0 to 20.720 calendar years to determine the amplitude of pH changes between the Last Glacial Period and the Holocene. Boron isotopes were measured by Multi-Collector – Inductively Coupled Plasma Mass Spectrometry (MC-ICPMS) with an external reproducibility of 0.25‰, allowing a precision of about ±0.03 pH-units for pH values between 8 and 8.3. The boron concentration [B] and isotopic composition of modern samples indicate that the temperature strongly controls the partition coefficient KD for different aragonite species. Modern coral δ11B values and the reconstructed sea surface pH values for different Pacific areas match the measured pH expressed on the seawater scale and confirm the calculation parameters that were previously determined by laboratory calibration exercises. Most ancient sea surface pH reconstructions near Marquesas are higher than modern values. These values range between 8.19 and 8.27 for the Holocene and reached 8.30 at the end of the last glacial period (20.7 kyr BP). At the end of the Younger Dryas (11.50±0.1 kyr BP), the central sub-equatorial Pacific experienced a dramatic drop of up to 0.2 pH-units from the average pH of 8.2 before and after this short event. Using the marine carbonate algorithms, we recalculated the aqueous pCO2 to be 440±25 ppmV at around 11.5 kyr BP for corals at Marquesas and ~500 ppmV near Tahiti where it was assumed that pCO2 in the atmosphere was 250 ppmV. Throughout the Holocene, the difference in pCO2 between the ocean and the atmosphere at Marquesas (ΔpCO2) indicates that the surface waters behave as a moderate CO2 sink or source (−53 to 20 ppmV) during El Niño-like conditions. By contrast, during the last glacial/interglacial transition, this area was a marked source of CO2 (21 to 92 ppmV) for the atmosphere, highlighting predominant La Niña-like conditions. Such conditions were particularly pronounced at the end of the Younger Dryas with a large amount of CO2 released with ΔpCO2 of +185±25 ppmV. This last finding provides further evidence of the marked changes in the surface water pH and temperature in the equatorial Pacific at the Younger Dryas-Holocene transition and the strong impact of oceanic dynamic on the atmospheric CO2 content.

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