| 1. |
- Menkveld, Albert J., et al.
(författare)
-
Nonstandard Errors
- 2024
-
Ingår i: JOURNAL OF FINANCE. - : Wiley-Blackwell. - 0022-1082 .- 1540-6261. ; 79:3, s. 2339-2390
-
Tidskriftsartikel (refereegranskat)abstract
- In statistics, samples are drawn from a population in a data-generating process (DGP). Standard errors measure the uncertainty in estimates of population parameters. In science, evidence is generated to test hypotheses in an evidence-generating process (EGP). We claim that EGP variation across researchers adds uncertainty-nonstandard errors (NSEs). We study NSEs by letting 164 teams test the same hypotheses on the same data. NSEs turn out to be sizable, but smaller for more reproducible or higher rated research. Adding peer-review stages reduces NSEs. We further find that this type of uncertainty is underestimated by participants.
|
|
| 2. |
- Muller, Joanne, et al.
(författare)
-
The use of principle component analyses in characterising trace and major elemental distribution in a 55 kyr peat deposit in tropical Australia: Implications to paleoclimate
- 2008
-
Ingår i: Geochimicia et Cosmochimica Acta. ; 72, s. 449-463
-
Tidskriftsartikel (refereegranskat)abstract
- The Lynch's Crater peat deposit in NE-Australia is a sensitive environmental archive located in the tropical Southern Hemisphere. This unique deposit illustrates that local and regional changes had a profound effect on the local Australian ecosystem over the past 55 kyr. To obtain a proxy of past climate changes, trace and major element geochemistry analyses were applied to a 13 m peat core from the crater. Principle component analysis (PCA) was used to identify the main factors that control elemental distribution in the peat and to add interpretative strength to the geochemical behavior of selected major and trace elements. For example, Sc, Al, Cu, and Pb were found to be related to increased erosion of the basin soils, and from this, several periods of significant flux from atmospheric input and/or terrigenous run-off were identified. Geochemically mobile elements during rock weathering and pedogenesis, such as Mg, Ca, and Sr helped to identify the peat ombrotrophic-minerotrophic boundary at ~1.5 m depth and offered important information about fluxes of these nutrients to the mire and their dynamics within the deposit. Arsenic and V comparisons between the peat record (high concentrations in some peat sections) and in local basin rocks (very low concentrations), suggested the presence of a long range, atmospheric dust source early in the formation of the mire. The Lynch's Crater peat record presents a continuous record of environmental change in tropical Australia and contributes new understanding to geochemical processes in peatlands.
|
|
| 3. |
- Chi Fru, Ernest, et al.
(författare)
-
Cu isotopes in marine black shales record the Great Oxidation Event
- 2016
-
Ingår i: Proceedings of the National Academy of Sciences of the United States of America. - : Proceedings of the National Academy of Sciences. - 0027-8424 .- 1091-6490. ; 113:18, s. 4941-4946
-
Tidskriftsartikel (refereegranskat)abstract
- The oxygenation of the atmosphere similar to 2.45-2.32 billion years ago (Ga) is one of the most significant geological events to have affected Earth's redox history. Our understanding of the timing and processes surrounding this key transition is largely dependent on the development of redox-sensitive proxies, many of which remain unexplored. Here we report a shift from negative to positive copper isotopic compositions (delta Cu-65(ERM-AE633)) in organic carbon-rich shales spanning the period 2.66-2.08 Ga. We suggest that, before 2.3 Ga, a muted oxidative supply of weathering-derived copper enriched in Cu-65, along with the preferential removal of Cu-65 by iron oxides, left seawater and marine biomass depleted in Cu-65 but enriched in Cu-63. As banded iron formation deposition waned and continentally sourced Cu became more important, biomass sampled a dissolved Cu reservoir that was progressively less fractionated relative to the continental pool. This evolution toward heavy delta Cu-65 values coincides with a shift to negative sedimentary delta Fe-56 values and increased marine sulfate after the Great Oxidation Event (GOE), and is traceable through Phanerozoic shales to modern marine settings, where marine dissolved and sedimentary delta Cu-65 values are universally positive. Our finding of an important shift in sedimentary Cu isotope compositions across the GOE provides new insights into the Precambrian marine cycling of this critical micronutrient, and demonstrates the proxy potential for sedimentary Cu isotope compositions in the study of biogeochemical cycles and oceanic redox balance in the past.
|
|
| 4. |
|
|
| 5. |
- Kylander, Malin E., et al.
(författare)
-
A rapid and reliable method for Pb isotopic analysis of peat and lichens by laser ablation-quadrupole-inductively coupled plasma-mass spectrometry for biomonitoring and sample screening
- 2007
-
Ingår i: Analytica Chimica Acta. - : Elsevier BV. - 0003-2670. ; 582:1, s. 116-124
-
Tidskriftsartikel (populärvet., debatt m.m.)abstract
- An analytical protocol for rapid and reliable laser ablation-quadrupole (LA-Q)- and multi-collector (MC-) inductively coupled plasma-mass spectrometry (ICP-MS) analysis of Pb isotope ratios (207Pb/206Pb and 208Pb/206Pb) in peats and lichens is developed. This technique is applicable to source tracing atmospheric Pb deposition in biomonitoring studies and sample screening. Reference materials and environmental samples were dry ashed and pressed into pellets for introduction by laser ablation. No binder was used to reduce contamination. LA-MC-ICP-MS internal and external precisions were <1.1% and <0.3%, respectively, on both 207Pb/206Pb and 208Pb/206Pb ratios. LA-Q-ICP-MS internal precisions on 207Pb/206Pb and 208Pb/206Pb ratios were lower with values for the different sample sets <14.3% while external precisions were <2.9%. The level of external precision acquired in this study is high enough to distinguish between most modern Pb sources. LA-MC-ICP-MS measurements differed from thermal ionisation mass spectrometry (TIMS) values by 1% or less while the accuracy obtained using LA-Q-ICP-MS compared to solution MC-ICP-MS was 3.1% or better using a run bracketing (RB) mass bias correction method. Sample heterogeneity and detector switching when measuring 208Pb by Q-ICP-MS are identified as sources of reduced analytical performance.
|
|
| 6. |
- Kylander, malin, et al.
(författare)
-
Lead Penetration and Leaching in a Complex Temperate Soil Profile
- 2008
-
Ingår i: Environmental Science & Technology. ; 42:9, s. 3177-3184
-
Tidskriftsartikel (refereegranskat)abstract
- The documented loss of anthropogenic Pb from soil organic horizons and its migration into the mineral soil below has raised several environmental concerns, especially over the leaching of Pb into groundwater aquifers and subsequently into other environmental compartments of the ecosystem. Here, a complex colluvial soil formed over the last 10,000 years in NW Spain is studied. The objective is to evaluate the behavior of Pb in soils, including its migration rates and the potential use of complex soils as archives of atmospheric Pb pollution. To this end, Pb concentrations and Pb isotope ratios for total soil, and for acid-extractable (0.5 M HNO3) and residual fractions were determined. We show that the acid-extractable fraction is more radiogenic than the residual one in most of the soil profile and that this relationship is reversed in the surface layers (
|
|
| 7. |
- Muller, Joanne, et al.
(författare)
-
Possible evidence for wet Heinrich phases in tropical NE Australia: The Lynch's Crater deposit
- 2008
-
Ingår i: Quaternary Science Reviews. ; 27, s. 468-475
-
Tidskriftsartikel (refereegranskat)abstract
- Unarguably, one of the most significant paleoclimatological discoveries of the last two decades has been that of abrupt climate events (Dansgaard-Oeschger cycles and Heinrich events). Most evidence for these events has originated from the high-latitude Northern Hemisphere, with few records documenting the response of the low latitude Southern Hemisphere. Here we present new data from Lynch's Crater, a unique terrestrial record from NE-Australia that may show evidence for southward propagations of the Intertropical Convergence Zone (ITCZ) during abrupt climate perturbations as a result of alteration of the low latitude air masses. Proxies for precipitation/wetness indicate enhanced rainfall in the region during Heinrich events (H events 1-3) and the 8.2 ka Northern Hemisphere cold event. A fully coupled atmosphere/ocean climate model simulating a 1 Sv freshwater influx to the North Atlantic Ocean produces a scenario which agrees with the climate changes shown by the Lynch's Crater record. The model shows precipitation anomalies that include a southward migration of the ITCZ and a zonal shift in mid-latitude storm tracks over the Southern Hemisphere equatorial region. These data indicate large-scale shifts of the austral summer ITCZ position that is known to control monsoonal precipitation in NE Australia. This terrestrial record from Australia may demonstrate the involvement of the tropical western Pacific Ocean in ITCZ migrations during abrupt climate events of the last glacial period. Defining such past migrations offers insight into the importance and role of the equatorial region in global climate dynamics.
|
|
| 8. |
- Rauch, Sebastien, 1971, et al.
(författare)
-
Anthropogenic Forcings on the Surficial Osmium Cycle
- 2010
-
Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 44:3, s. 881-887
-
Tidskriftsartikel (refereegranskat)abstract
- Osmium is among the least abundant elements in the Earth's continental crust. Recent anthropogenic Os contamination of the environment from mining and smelting activities, automotive catalytic converter use, and hospital discharges has been documented. Here we present evidence for anthropogenic overprinting of the natural Os cycle using a ca. 7000-year record of atmospheric Os deposition and isotopic composition from an ombrotrophic peat bog in NW Spain. Preanthropogenic Os accumulation in this area is 0.10 +/- 0.04 ng m(-2) y(-1). The oldest strata showing human influence correspond to early metal mining and processing on the Iberian Peninsula (ca. 4700-2500 cal. BP). Elevated Os accumulation rates are found thereafter with a local maximum of 1.1 ng m(-2) y(-1) during the Roman occupation of the Iberian Peninsula (ca. 1930 cal. BP)and a further increase starting in 1750 AD with Os accumulation reaching 30 ng m(-2) y(-1) in the most recent samples. Osmium isotopic composition (Os-187/Os-188) indicates that recent elevated Os accumulation results from increased input of unradiogenic Os from industrial and automotive sources as well as from enhanced deposition of radiogenic Os through increased fossil fuel combustion and soil erosion. We posit that the rapid increase in catalyst-equipped vehicles, increased fossil fuel combustion, and changes in land-use make the changes observed in NW Spain globally relevant.
|
|
| 9. |
- Weiss, Dominik J., et al.
(författare)
-
The environmental geochemistry of lead
- 2007
-
Ingår i: Advances in Earth Science. - : Imperial College Press. - 9781860947612 ; , s. 344-
-
Bokkapitel (refereegranskat)abstract
- The global biogeochemical cycles of several trace metals are presently dominated by human activities, a result of the nature and magnitude of historical resource consumption. Lead has been mined since ancient times, often as a by-product of silver extraction, and has one of the longest associations with man of all heavy metals [Nriagu, 1983]. As of 1983, human activities accounted for an estimated 97% of the global mass balance of lead [Nriagu and Pacyna, 1988]. At that time as well as today, most of the lead was derived from leaded gasoline [Nriagu, 1990], where it was used as an anti-knock agent.New estimates of anthropogenic sources of lead suggest that the overall burden of anthropogenic lead emissions has decreased but new pollution sources (e.g., China, Mexico) have become important [Pacyna and Pacyna, 2001; Pacyna et al., 1995] leaving anthropogenic Pb emission to remain a global problem and leaded gasoline as the main source. In addition, as metals are not biodegradable, the Pb in the environment has accumulated over the decades and its fate and pathways within the ecosystem need to be investigated.In a manner similar to chlorofluorocarbons and radionuclides derived from atomic testing, the release of lead into the environment represents an inadvertent geochemical tracer experiment, providing new insights into its fate and transport within marine and terrestrial systems. There have been several review papers and books discussing lead, its historical place in society and its impact on human and environmental health [Boutron, 1995; Needleman, 1997; Nriagu, 1983; Nriagu, 1989b; Nriagu, 1990; Reuer and Weiss, 2002; Shotyk and Le Roux, 2005; Weiss et al., 1999] and the reader is encouraged to refer to these works as well.
|
|
