scholarly journals Environmental control on the occurrence of high-coercivity magnetic minerals and formation of iron sulfides in a 640 ka sediment sequence from Lake Ohrid (Balkans)

2016 ◽  
Vol 13 (7) ◽  
pp. 2093-2109 ◽  
Author(s):  
Janna Just ◽  
Norbert R. Nowaczyk ◽  
Leonardo Sagnotti ◽  
Alexander Francke ◽  
Hendrik Vogel ◽  
...  
Keyword(s):  
Environmental Conditions ◽  
Environmental Control ◽  
Magnetic Mineral ◽  
High Coercivity ◽  
Water Volume ◽  
Iron Sulfides ◽  
Lake Ohrid ◽  
Magnetic Minerals ◽  
The Core ◽  
Summer Insolation

Abstract. The bulk magnetic mineral record from Lake Ohrid, spanning the past 637 kyr, reflects large-scale shifts in hydrological conditions, and, superimposed, a strong signal of environmental conditions on glacial–interglacial and millennial timescales. A shift in the formation of early diagenetic ferrimagnetic iron sulfides to siderites is observed around 320 ka. This change is probably associated with variable availability of sulfide in the pore water. We propose that sulfate concentrations were significantly higher before  ∼  320 ka, due to either a higher sulfate flux or lower dilution of lake sulfate due to a smaller water volume. Diagenetic iron minerals appear more abundant during glacials, which are generally characterized by higher Fe / Ca ratios in the sediments. While in the lower part of the core the ferrimagnetic sulfide signal overprints the primary detrital magnetic signal, the upper part of the core is dominated by variable proportions of high- to low-coercivity iron oxides. Glacial sediments are characterized by high concentration of high-coercivity magnetic minerals (hematite, goethite), which relate to enhanced erosion of soils that had formed during preceding interglacials. Superimposed on the glacial–interglacial behavior are millennial-scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Like the processes on glacial–interglacial timescales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both environmental conditions on land and intra-lake processes.

scholarly journals Climatic control on the occurrence of high-coercivity magnetic minerals and preservation of greigite in a 640 ka sediment sequence from Lake Ohrid (Balkans)

2015 ◽  
Vol 12 (16) ◽  
pp. 14215-14243 ◽  
Author(s):  
J. Just ◽  
N. Nowaczyk ◽  
A. Francke ◽  
L. Sagnotti ◽  
B. Wagner
Keyword(s):  
Time Scales ◽  
Environmental Conditions ◽  
Strong Relationship ◽  
Magnetic Mineral ◽  
High Coercivity ◽  
Lake Ohrid ◽  
Magnetic Minerals ◽  
High Concentration ◽  
Magnetic Studies ◽  
Summer Insolation

Abstract. The bulk magnetic mineral record from Lake Ohrid, spanning the past ca. 640 ka, shows a strong relationship to environmental conditions on glacial–interglacial and millennial time scales. During extremely cold glacials, a lower accumulation of organic matter and likely enhanced mixing of the water-column coincides with the presence of greigite, whereas greigite is absent in sediments deposited during less severe glacials. Those "non-greigite" glacial sediments are characterized by high concentration of high-coercivity magnetic minerals, which relates to enhanced erosion of soils that had formed during the preceding interglacials. In contrast, magnetite dominated magnetic mineral assemblages characterize interglacial deposits and most likely originate from detrital particles of physically weathered rocks. Superimposed on the glacial–interglacial behavior are millennial scale oscillations in the magnetic mineral composition that parallel variations in summer insolation. Likewise to the process on glacial–interglacial time-scales, low summer insolation and a retreat in vegetation resulted in enhanced erosion of soil material. Our study highlights that rock-magnetic studies, in concert with geochemical and sedimentological investigations, provide a multi-level contribution to environmental reconstructions, since the magnetic properties can mirror both, environmental conditions on land and intra-lacustrine processes.

Rock magnetic signature as a result of gas hydrate dissociation off southwestern Taiwan

2020 ◽  
Author(s):  
Yin-Sheng Huang ◽  
Chorng-Shern Horng ◽  
Chih-Chieh Su ◽  
Shu-Kun Hsu ◽  
Jing-Yi Lin
Keyword(s):  
Magnetic Susceptibility ◽  
Gas Hydrate ◽  
Magnetic Mineral ◽  
Magnetic Minerals ◽  
Hydrate Dissociation ◽  
Core Sediments ◽  
The Core ◽  
Potential Reservoir ◽  
Core Depth ◽  
Southwestern Taiwan

<p>Marginal areas off southwestern Taiwan have been widely considered a high potential reservoir of gas hydrates based on several geophysical, geological, and geochemical investigations since the past decades. First gas hydrate sample has been collected on 21 June 2018 during the cruise MD214 at the core site MD18-3542 on the South Yung-An East Ridge. In the study, we focus on magnetic properties of this MD core. The most attractive feature in the magnetic susceptibility is an abrupt drop recorded at about 4 meters core depth. To clarify and identify the dominant magnetic mineral in the core, hysteresis loop parameters were first measured and then presented on the Day Plot, and further the X-ray diffraction analysis was applied to the selected core samples. Based on the magnetic results, the clear drop in the magnetic susceptibility is related to the change of dominant magnetic minerals in core sediments. Before about 4 meters core depth, the dominant magnetic mineral remains detrital magnetite. Below the depth, however, core sediments should have been infected by methane released by gas hydrate dissociation. Authigenic greigite and pyrite have become dominant, and therefore low magnetic susceptibility appears below 4 meters core depth.</p>

Disentangling the role of shared ancestry and the environment on leaf stable isotopes

2019 ◽  
Author(s):  
Marko J. Spasojevic ◽  
Sören Weber1
Keyword(s):  
Stable Isotopes ◽  
Environmental Conditions ◽  
Evolutionary History ◽  
Environmental Control ◽  
Phylogenetic Signal ◽  
Individual Species ◽  
Habitat Types ◽  
Δ13c And Δ15n ◽  
Environmental Controls ◽  
Shared Ancestry

Stable carbon (C) and nitrogen (N) isotopes in plants are important indicators of plant water use efficiency and N acquisition strategies. While often regarded as being under environmental control, there is growing evidence that evolutionary history may also shape variation in stable isotope ratios (δ13C and δ15N) among plant species. Here we examined patterns of foliar δ13C and δ15N in alpine tundra for 59 species in 20 plant families. To assess the importance of environmental controls and evolutionary history, we examined if average δ13C and δ15N predictably differed among habitat types, if individual species exhibited intraspecific trait variation (ITV) in δ13C and δ15N, and if there were a significant phylogenetic signal in δ13C and δ15N. We found that variation among habitat types in both δ13C and δ15N mirrored well-known patterns of water and nitrogen limitation. Conversely, we also found that 40% of species exhibited no ITV in δ13C and 35% of species exhibited no ITV in δ15N, suggesting that some species are under stronger evolutionary control. However, we only found a modest signal of phylogenetic conservatism in δ13C and no phylogenetic signal in δ15N suggesting that shared ancestry is a weaker driver of tundra wide variation in stable isotopes. Together, our results suggest that both evolutionary history and local environmental conditions play a role in determining variation in δ13C and δ15N and that considering both factors can help with interpreting isotope patterns in nature and with predicting which species may be able to respond to rapidly changing environmental conditions.

The Design of ZigBee Wireless Network for the Detection Platform of the Cylinders

2012 ◽  
Vol 241-244 ◽  
pp. 2504-2509
Author(s):  
Yan Li ◽  
Qiao Xiang Gu
Keyword(s):  
Real Time ◽  
Wireless Network ◽  
Environmental Conditions ◽  
Protocol Stack ◽  
The Real ◽  
The Core ◽  
Core Components ◽  
Real Time Detection ◽  
Cable Connection

The equipment, called detection platform of the cylinders, is used for detecting cylinders so that cylinders can be at ease use. In order to transmit the real-time detection data to PC for further processing, the platform should be connected with PC. Cable connection, in some production and environmental conditions, is limited. Under the circumstance, building wireless network is the better choice. Through comparative studying, ZigBee is chosen to be the technology for building wireless network. ZigBee chip and ZigBee2006 protocol stack are the core components in the ZigBee nodes.

Analysis of Strong-Field Hysteresis in High Coercivity Magnetic Minerals

2019 ◽  
pp. 127-142 ◽  
Author(s):  
A. Kosterov ◽  
E. S. Sergienko ◽  
A. G. Iosifidi ◽  
P. V. Kharitonskii ◽  
S. Yu. Yanson
Keyword(s):  
Strong Field ◽  
High Coercivity ◽  
Magnetic Minerals

Paleomagnetic history of the Mealy dykes of Labrador, Canada

1983 ◽  
Vol 20 (12) ◽  
pp. 1818-1833 ◽  
Author(s):  
J. K. Park ◽  
R. F. Emslie
Keyword(s):  
The Other ◽  
Magnetic Mineral ◽  
Magnetic Minerals ◽  
Linear Distribution ◽  
Tectonic Zone ◽  
Magnetic Components ◽  
History Of ◽  
Component C ◽  
A Site

Paleomagnetic analysis of the Mealy diabase dykes of Labrador reveals magnetizations that predate the Grenville event at about 1000 Ma. These dykes intrude the Mealy Mountains anorthositic complex in the Grenville Structural Province. They are well south of the Grenville Front Tectonic Zone, but were apparently never subjected to temperatures as high as 500 °C during their post-consolidation history.Four distinct magnetic components were uncovered by thermal and alternating field treatments and a fifth remained unresolved. The major magnetic mineral present, titanomagnetite, is thought to record two magnetic directions acquired during cooling from magmatic temperatures. These are B (D = 305°, I = −76°; N = 18 sites; κ = 12; α95 = 11°) and A (D = 095°, I = +52°; N = 20 sites; κ = 46; α95 = 5°). Component B has much within-site dispersion. The other two components, C (D = 274°, I = −47°; N = 10 sites; κ = 15; α95 = 13°) and D (D = 292°, I = −74°; κ = 5; α95 = 31°), probably reside in magnetite and pyrrhotite, respectively. Component C, antiparallel to A, was probably acquired at about the same time as A. We suggest that C and A represent the first stable magnetizations retained by the dykes following an extensive period of cooling and re-equilibration of the magnetic minerals. Components B and D, which agree in direction, represent a later stage of cooling.Component B has a pole at 148°E, 34°S (δp = 18°, δm = 19°) in agreement with regional metamorphic poles from the Grenville; A, however, has a pole at 173°W, 23°S (δp = 5°, δm = 7°), which apparently "sees through" the peak in Grenville activity. The A site poles have a linear distribution along the Keweenawan Track and probably relate to an age between 1000 and 1150 Ma.

The Satiation of Natural Curiosity

2016 ◽  
Vol 5 (2) ◽  
pp. 27-34 ◽  
Author(s):  
Felix Schoeller
Keyword(s):  
Environmental Conditions ◽  
Dynamic Equilibrium ◽  
Human Mind ◽  
Cognitive System ◽  
Accurate Description ◽  
Internal Representations ◽  
The Core ◽  
System A

At the core of this essay is the idea that cognition is best described as a highly developed homeostatic device aiming to maintain a dynamic equilibrium between internal representations and changes in environmental conditions. The author emphasizes the fundamental role played by aesthetics in facilitating an accurate description of the human mind and introduce basic elements of a theory accounting for the influence of art on the cognitive system. A general bibliography is provided for the reader unfamiliar with the notions and desirous to pursue the analysis further.

High-coercivity magnetic minerals in archaeological baked clay and bricks

2020 ◽  
Vol 224 (2) ◽  
pp. 1256-1271
Author(s):  
Andrei Kosterov ◽  
Mary Kovacheva ◽  
Maria Kostadinova-Avramova ◽  
Pavel Minaev ◽  
Natalia Salnaia ◽  
...  
Keyword(s):  
Parent Material ◽  
High Coercivity ◽  
Firing Process ◽  
Magnetic Minerals ◽  
Magnetic Mineralogy ◽  
Archaeological Ceramics ◽  
Mineral Phases ◽  
Initial Magnetic Susceptibility ◽  
Magnetically Hard ◽  
Saturation Remanence

SUMMARY The thorough understanding of magnetic mineralogy is a prerequisite of any successful palaeomagnetic or archaeomagnetic study. Magnetic minerals in archaeological ceramics and baked clay may be inherited from the parent material or, more frequently, formed during the firing process. The resulting magnetic mineralogy may be complex, including ferrimagnetic phases not commonly encountered in rocks. Towards this end, we carried out a detailed rock magnetic study on a representative collection of archaeological ceramics (baked clay from combustion structures and bricks) from Bulgaria and Russia. Experiments included measurement of isothermal remanence acquisition and demagnetization as a function of temperature between 20 and >600 °C. For selected samples, low-temperature measurements of saturation remanence and initial magnetic susceptibility between 1.8 and 300 K have been carried out. All studied samples contain a magnetically soft mineral identified as maghemite probably substituted by Ti, Mn and/or Al. Stoichiometric magnetite has never been observed, as evidenced by the absence of the Verwey phase transition. In addition, one or two magnetically hard mineral phases have been detected, differing sharply in their respective unblocking temperatures. One of these unblocking between 540 and 620 °C is believed to be substituted hematite. Another phase unblocks at much lower temperatures, between 140 and 240 °C, and its magnetic properties correspond to an enigmatic high coercivity, stable, low-unblocking temperature (HCSLT) phase reported earlier. In a few samples, high- and low unblocking temperature, magnetically hard phases appear to coexist; in the others, the HCSLT phase is the only magnetically hard mineral present.

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