| 1. |
- Berggren, Ann-Marie, 1969-, et al.
(författare)
-
A 600-year annual 10Be record from the NGRIP ice core, Greenland
- 2009
-
Ingår i: Geophysical Research Letters. - 0094-8276 .- 1944-8007. ; 36, s. L11801-
-
Tidskriftsartikel (refereegranskat)abstract
- Despite the extensive use of 10Be as the most significant information source on past solar activity, there has been only one record (Dye-3, Greenland) providing annual resolution over several centuries. Here we report a new annual resolution 10Be record spanning the period 1389-1994 AD, measured in an ice core from the NGRIP site in Greenland. NGRIP and Dye-3 10Be exhibits similar long-term variability, although occasional short term differences between the two sites indicate that at least two high resolution 10Be records are needed to assess local variations and to confidently reconstruct past solar activity. A comparison with sunspot and neutron records confirms that ice core 10Be reflects solar Schwabe cycle variations, and continued 10Be variability suggests cyclic solar activity throughout the Maunder and Spörer grand solar activity minima. Recent 10Be values are low; however, they do not indicate unusually high recent solar activity compared to the last 600 years.
|
|
| 2. |
- Dehnert, Andreas, et al.
(författare)
-
Cosmogenic isotope burial dating of fluvial sediments from the Lower Rhine Embayment, Germany
- 2011
-
Ingår i: Quaternary Geochronology. - 1871-1014 .- 1878-0350.
-
Tidskriftsartikel (refereegranskat)abstract
- Cosmogenic isotope burial dating, using 10Be and 26Al, was applied to PlioePleistocene fluvial successionsfrom the Lower Rhine Embayment, Germany. The approach consists of three principal steps: (1)measurement of cosmogenic nuclides in depth profiles, (2) modelling of hypothetical nuclide concentrationsbased on a first-order conceptualisation of the geological context and the principal succession ofdepositions and subsequent erosional and burial phases, and (3) using parameter estimation to identifyvalues for the a priori unknown model parameters (burial age, initial nuclide concentrations, terraceerosion rates) that result in minimal disagreement between hypothetical and measured nuclideconcentrations.
|
|
| 3. |
- Harrison, Stephan, et al.
(författare)
-
Glaciar Leon, Chilean Patagonia: late-Holocene chronology and geomorphology
- 2008
-
Ingår i: Holocene. - : SAGE Publications. - 0959-6836. ; 18:4, s. 643-652
-
Tidskriftsartikel (refereegranskat)abstract
- Glaciar Leon is a temperate, grounded outlet of the eastern North Patagonian Icefield (NPI). It terminates at an active calving margin in Lago Leones, a 10 km long proglacial lake. We take a multidisciplinary approach to its description and use ASTER imagery and clast sedimentology to describe the geomorphology of the glacier and its associated moraines. We date periods of glacier retreat over the last 2500 years using a combination of lichenometric, dendrochronological, cosmogenic and optically stimulated luminescence techniques and show that the glacier receded from a large terminal moraine complex some 2500 years ago and underwent further significant recession from nineteenth-century moraine limits. The moraine dates indicate varying retreat rates, in conjunction with significant downwasting. The bathymetry of Lago Leones is characterized by distinct ridges interpreted as moraine ridges that dissect the lake into several basins, with water depths reaching 360 m. The fluctuations of Glaciar Leon appear to have been controlled by the interplay between climatic forcing and calving dynamics.
|
|
| 4. |
- Ljung, Karl, et al.
(författare)
-
Variable Be-10 fluxes in lacustrine sediments from Tristan da Cunha, South Atlantic: a solar record?
- 2007
-
Ingår i: Quaternary Science Reviews. - : Elsevier BV. - 0277-3791. ; 26:7-8, s. 829-835
-
Tidskriftsartikel (refereegranskat)abstract
- A 650-yr-long sediment sequence from a crater lake on Tristan da Cunha, South Atlantic, was analysed for its Be-10 content. Based on C-14 dating, and sedimentary, geochemical, magnetic and palynological records, the period between 900 and 1450 AD appears to have been unusually stable in terms of sedimentation and vegetation and therefore this period was chosen for analysis of the Be-10 content. During this period of highly organic sedimentation and closed vegetation, the pattern of Be-10 flux variations follows the Be-10 fluctuations from the GRIP ice core and estimated C-14 production rates well. However, before and after this stable period, variable sedimentation rates have to be accounted for to obtain results that are comparable to the established Be-10/C-14 records. Our data show not only the possibility of obtaining detailed enough Be-10 flux data from sedimentary sequences to reconstruct past solar forcing but also how sensitive this type of record is to sedimentary and environmental changes. If suitable archives can be found, they have the potential to improve reconstructions of solar activity far back in time. (c) 2007 Elsevier Ltd. All rights reserved.
|
|
| 5. |
- May, Jan-Henrik, et al.
(författare)
-
Reconstruction of a complex late Quaternary glacial landscape in the Cordillera de Cochabamba (Bolivia) based on a morphostratigraphic and multiple dating approach.
- 2011
-
Ingår i: Quaternary Research. - 0033-5894 .- 1096-0287. ; 76, s. 106-118
-
Tidskriftsartikel (refereegranskat)abstract
- Although glacial landscapes have previously been used for the reconstruction of late Quaternary glaciations inthe Central Andes, only few data exist for the Eastern Cordillera in Bolivia. Here, we present results fromdetailed morphostratigraphic mapping and new data of surface exposure dating (SED), optically stimulatedluminescence (OSL), and radiocarbon dating (14C) from the Huara Loma Valley, Cordillera de Cochabamba(Bolivia). Discrepancies between individual dating methods could be addressed within the context of a solidgeomorphic framework. We identified two major glaciations. The older is not well constrained by theavailable data, whereas the younger glaciation is subdivided into at least four major glacial stages. Regardingthe latter, a first advance dated to ~29–25 ka occurred roughly contemporaneous with the onset of the globallast glacial maximum (LGM) and was followed by a less extensive (re-)advance around 20–18 ka. The locallast glacial maximum (LLGM) in the Huara Loma Valley took place during the humid lateglacial ~17–16 ka,followed by several smaller readvances until ~10–11 ka, and complete deglaciation at the end of the EarlyHolocene.
|
|
| 6. |
- Muscheler, Raimund, et al.
(författare)
-
Changes in the carbon cycle during the last deglaciation as indicated by the comparison of Be-10 and C-14 records
- 2004
-
Ingår i: Earth and Planetary Science Letters. - 1385-013X. ; 219:3-4, s. 325-340
-
Tidskriftsartikel (refereegranskat)abstract
- The variations in atmospheric radiocarbon (C-14) concentration during the last 50 000 years can be attributed to changes in the C-14 production rate (due to changes in solar activity, the geomagnetic field and/or interstellar galactic cosmic ray flux) and to changes in the global carbon cycle. The relative contributions of these processes is the subject of current debate. Although the discrepancies between the various reconstructions of the past atmospheric radiocarbon concentration increase with age, the relatively good agreement over the last 25 000 years allows a quantitative discussion of the causes of the observed C-14 variations for this period. Using Be-10 measurements from Greenland Summit ice cores, we show that, in addition to solar and geomagnetically induced production rate changes, significant changes in the carbon cycle have to be considered to explain the measured C-14 concentrations. There is evidence that these changes are connected to: (1) global deglaciation and (2) climate changes in the North Atlantic region on centennial to millennial time scales related to changes in the ocean circulation. Differences between Be-10 and geomagnetic field records, however, suggest that uncertainties of about 20% still exist in determinations of past changes in the C-14 production rate. (C) 2004 Elsevier B.V. All rights reserved.
|
|
| 7. |
- Scharf, Taryn E., et al.
(författare)
-
Strong rocks sustain ancient postorogenic topography in southern Africa
- 2013
-
Ingår i: Geology. - 0091-7613 .- 1943-2682. ; 41:3, s. 331-334
-
Tidskriftsartikel (refereegranskat)abstract
- The Cape Mountains of southern Africa exhibit an alpine-like topography in conjunction with some of the lowest denudation rates in the world. This presents an exception to the often-cited coupling of topography and denudation rates and suggests that steep slopes alone are not sufficient to incite the high denudation rates with which they are commonly associated. Within the Cape Mountains, slope angles are often in excess of 30 degrees and relief frequently exceeds 1 km, yet Be-10-based catchment-averaged denudation rates vary between 2.32 +/- 0.29 m/m.y. and 7.95 +/- 0.90 m/m.y. We attribute the maintenance of rugged topography and suppression of denudation rates primarily to the presence of physically robust and chemically inert quartzites that constitute the backbone of the mountains. Be-10-based bedrock denudation rates on the interfluves of the mountains vary between 1.98 +/- 0.23 m/m.y. and 4.61 +/- 0.53 m/m.y. The close agreement between the rates of catchment-averaged and interfluve denudation indicates topography in steady state. These low denudation rates, in conjunction with the suggestion of geomorphic stability, are in agreement with the low denudation rates (<20 m/m.y.) estimated for southern Africa during the late Cenozoic by means of cosmogenic nuclide, thermochronology, and offshore sedimentation analyses. Accumulatively, these data suggest that the coastal hinterland of the subcontinent may have experienced relative tectonic stability throughout the Cenozoic.
|
|
| 8. |
|
|
| 9. |
- Sellén, Emma, et al.
(författare)
-
Beryllium Isotope Dating of Sediment Cores From the Alpha Ridge, Arctic Ocean
- 2007
-
Ingår i: Eos, Trans. AGU, 88(52), Fall Meeting.
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- AB: Poor preservation of biogenic calcium carbonate and biosilica in Arctic Ocean sediments has led to large problems regarding the establishment of a reliable chronostratigraphy. There are currently two differing sedimentation rate scenarios proposed for the Arctic Ocean. The first suggests sedimentation rates on the order of mm/ka and is based on cores from the Amerasian Basin, whereas the second suggests sedimentation rates on the order of cm/ka mainly derived from Eurasian Basin cores. Here we present dating results from cores HLY0503-09JPC and HLY0503-14JPC retrieved from the Alpha Ridge during the Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX). These cores have been analyzed for seawater-derived beryllium (Be) isotopes in order to establish a chronostratigraphy. The isotopes 10Be and 9Be were extracted simultaneously from sample aliquots by using a leaching procedure. The decrease of 10Be concentration (half-life = 1.51 Million years) with depth in core provides first order sedimentation rates for the sampled cores. To eliminate the dilution effect of beryllium caused by short-term changes in sedimentation rate and grain size variability, the 10Be concentration was normalized to the stable isotope 9Be. The preliminary results show low downcore 10Be concentrations in both cores from the Alpha Ridge. Plotting 10Be against depth suggests an average sedimentation rate of ~2.9 mm/ka for core HLY0503-09JPC and ~2.3 mm/ka for HLY0503- 14JPC. The calculated 10Be/9Be ratios point to even lower average sedimentation rates of ~1.9 mm/ka for core HLY0503-09JPC and ~1.6 mm/ka for HLY0503-14JPC. However, core HLY0503-14JPC shows a pronounced variability of the 10Be concentration as well as for the 10Be/9Be ratio, which results in a large uncertainty of the calculated sedimentation rates. The 10Be concentrations for this core will be compared with the grain size record in order to reduce the scatter of the data. The preliminary beryllium isotope chronostratigraphy supports lower sedimentation rates in the Amerasian Basin compared to the Eurasian Basin. A long-term solid sea ice cover in the Beaufort Gyre may explain the low 10Be concentrations, but does not explain the calculated low sedimentation rates.
|
|
| 10. |
- Sellén, Emma, et al.
(författare)
-
Beryllium isotope variations in sediment cores from the Alpha Ridge, Arctic Ocean
- 2008
-
Ingår i: Arctic Palaeoclimate and its Extremes (APEX). ; , s. 92-
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The Healy-Oden Trans-Arctic Expedition 2005 (HOTRAX) recovered cores along a transect across the Arctic Ocean. Here we present results from measurements of seawater-derived beryllium isotopes in cores HLY0503-09JPC and HLY0503-14JPC from the Alpha-Mendeleev Ridge. The intention of measuring beryllium (Be) isotopes is to establish a chronostratigraphy as the decrease of 10Be concentration (half-life = 1.51 Million years) with depth in the cores may provide first order sedimentation rates. The isotopes 10Be and 9Be were extracted simultaneously from sample aliquots by using a leaching procedure. To eliminate the dilution effect of beryllium caused by short-term changes in sedimentation rate and grain size variability, the 10Be concentration was normalized to the stable isotope 9Be. The results show low downcore 10Be concentrations and subsequently sedimentation rates on the order of mm/ka in both cores from the Alpha Ridge. However, we note two indications suggesting that our calculated sedimentation rates from the beryllium results may not be valid and requires further analysis: 1) the decrease of 10Be down core does not follow a well defined trend; 2) a comparison with preliminary results from nannofossil studies of cores HLY0503-14JPC and HLY0503-08JPC located nearby HLY0503-09JPC indicates much higher sedimentation rates than we obtained from the 10Be data (Backman and Fornaciari pers. comm.). The pronounced decrease of 10Be with core depth may imply a stronger effect of sea ice shielding of atmospheric inputs, whereas the 9Be increase with depth may point to a stronger continental input of 9Be.
|
|
| 11. |
- Sellén, Emma, et al.
(författare)
-
Pleistocene variations of beryllium isotopes in central Arctic Ocean sediment cores
- 2009
-
Ingår i: Global and Planetary Change. - : Elsevier BV. - 0921-8181 .- 1872-6364. ; 68:1-2, s. 38-47
-
Tidskriftsartikel (refereegranskat)abstract
- Neogene marine sediments can be dated via decay of the cosmogenic radionuclide 10Be. Two cores from theAlpha and Mendeleev Ridges in the Arctic Ocean have been analyzed for seawater-derived beryllium (Be)isotopes in order to date the sediments and to calculate sedimentation rates. The decrease of 10Be concentrationin the cores was used to calculate first order sedimentation rates. To eliminate the dilution effect of berylliumcaused by short-term changes in sedimentation rate and grain size, the 10Be concentrationswere normalized tothe terrigenous stable isotope 9Be determined in the same sample aliquot. The measured 10Be concentrationsyield low average sedimentation rates for the Alpha and Mendeleev Ridges of 2.3 mm ka−1 and 2.7 mm ka−1,respectively. Sedimentation rates calculated from the 10Be/9Be ratios result in similarly low values, rangingfrom 0.2 to 6.8 mm ka−1 for the Alpha Ridge core and from 1.9 to 6.9 mm ka−1 for the Mendeleev Ridge core.However, amino acid racemization dating for the past 150 ka of a core adjacent to the Mendeleev Ridge corestudied here indicates significantly higher sedimentation rates than calculated from the downcore decreaseof 10Be and 10Be/9Be. If such higher rates also prevailed at the locations of our cores, for which there isbiostratigraphic evidence, either the supply of 10Be was much lower than assumed or that of 9Be was muchhigher. This could imply that the signature of the deepwaters in this part of the Arctic Ocean compared to todaywas largely different for most of the past approximately one million years with a significantly lower 10Be/9Beratio. Our study also addresses the variability of beryllium isotopes in sediment cores across the Arctic Oceanthrough a comparison of previously published results. Calculated 10Be fluxes reveal low values in the AmerasianBasin and highest values in the Eurasian Basin, near the Fram Strait. The decrease of Be isotopes in the twostudied Amerasian Basin cores may thus have been caused by environmental factors such as significantlyreduced inflow of Atlantic waters in the past, reduced input of 10Be and/or increased input of 9Be from theshelves, combined with a more efficient sea ice shielding in this part of the Arctic Ocean.
|
|
