Stratigraphy and timing of eolianite deposition on Rottnest Island, Western Australia

2003 ◽  
Vol 60 (2) ◽  
pp. 211-222 ◽  
Author(s):  
Paul J. Hearty
Keyword(s):  
North Atlantic ◽  
Late Quaternary ◽  
The West ◽  
Oxygen Isotope Stage ◽  
Amino Acid Racemization ◽  
Marine Deposits ◽  
The North ◽  
The North Atlantic ◽  
Radiometric Ages ◽  
Mis 5E

AbstractOver 100 whole-rock amino acid racemization (AAR) ratios from outcrops around Rottnest Island (32.0° S Latitude near Perth) indicate distinct pulses of eolian deposition during the late Quaternary. Whole-rock d-alloisoleucine/l-isoleucine (A/I) ratios from bioclastic carbonate deposits fall into three distinct modal classes or “aminozones.” The oldest, Aminozone E, averages 0.33 ± 0.04 (n = 21). Red palaeosol and thick calcrete generally cap the Aminozone E deposits. A younger Aminozone C averages 0.22 ± 0.03 (n = 63); comprising two submodes at 0.26 ± 0.01 (n = 14) and 0.21 ± 0.02 (n = 49). Multiple dune sets of this interval are interrupted by relatively weak, brown to tan “protosols.” A dense, dark brown rendzina palaeosol caps the Aminozone C succession. Ratios from Holocene dune and marine deposits (“Aminozone A”) center on 0.11 ± 0.02 (n = 15), comprising submodes of 0.13 ± 0.01 (9) and 0.09 ± 0.01 (6). Calibration of A/I averages from Aminozones E and A are provided by U/Th and 14C radiometric ages of 125,000 yr (marine oxygen isotope stage (MIS) 5e and 2000–6000 14C yr B.P. (MIS 1), respectively. The whole-rock A/I results support periodic deposition initiated during MIS 5e, continuing through MIS 5c, and then peaking at the end of MIS 5a, about 70,000–80,000 yr ago. Oceanographic evidence indicates the area was subjected to much colder conditions during MIS 2–4 (10,000 to 70,000 yr ago), greatly slowing the epimerization rate. Eolianite deposition resumed in the mid Holocene (∼6000 yr ago) up to the present. The A/I epimerization pathway constructed from Rottnest Island shows remarkable similarity to that of Bermuda in the North Atlantic (32° N Latitude). These findings suggest that, like Bermuda, the eolian activity on Rottnest occurred primarily during or shortly after interglacial highstands when the shoreline was near the present datum, rather than during glacial lowstands when the coastline was positioned 10–20 km to the west.

scholarly journals The Combined Effects of SST and the North Atlantic Subtropical High-Pressure System on the Atlantic Basin Tropical Cyclone Interannual Variability

Atmosphere ◽  
2021 ◽  
Vol 12 (3) ◽  
pp. 329
Author(s):  
Albenis Pérez-Alarcón ◽  
José C. Fernández-Alvarez ◽  
Rogert Sorí ◽  
Raquel Nieto ◽  
Luis Gimeno
Keyword(s):  
High Pressure ◽  
Interannual Variability ◽  
Central America ◽  
North Atlantic ◽  
The West ◽  
The Bahamas ◽  
Pressure System ◽  
North Atlantic Subtropical High ◽  
The North ◽  
The North Atlantic

The combined effect of the sea surface temperature (SST) and the North Atlantic subtropical high-pressure system (NASH) in the interannual variability of the genesis of tropical cyclones (TCs) and landfalling in the period 1980–2019 is explored in this study. The SST was extracted from the Centennial Time Scale dataset from the National Oceanic and Atmospheric Administration (NOAA), and TC records were obtained from the Atlantic Hurricane Database of the NOAA/National Hurricane Center. The genesis and landfalling regions were objectively clustered for this analysis. Seven regions of TC genesis and five for landfalling were identified. Intercluster differences were observed in the monthly frequency distribution and annual variability, both for genesis and landfalling. From the generalized least square multiple regression model, SST and NASH (intensity and position) covariates can explain 22.7% of the variance of the frequency of TC genesis, but it is only statistically significant (p < 0.1) for the NASH center latitude. The SST mostly modulates the frequency of TCs formed near the West African coast, and the NASH latitudinal variation affects those originated in the Lesser Antilles arc. For landfalling, both covariates explain 38.7% of the variance; however, significant differences are observed in the comparison between each region. With a statistical significance higher than 90%, SST and NASH explain 33.4% of the landfalling variability in the archipelago of the Bahamas and central–eastern region of Cuba. Besides, landfalls in the Gulf of Mexico and Central America seem to be modulated by SST. It was also found there was no statistically significant relationship between the frequency of genesis and landfalling with the NASH intensity. However, the NASH structure modulates the probability density of the TCs trajectory that make landfall once or several times in their lifetime. Thus, the NASH variability throughout a hurricane season affects the TCs trajectory in the North Atlantic basin. Moreover, we found that the landfalling frequency of TCs formed near the West Africa coast and the central North Atlantic is relatively low. Furthermore, the SST and NASH longitude center explains 31.6% (p < 0.05) of the variance of the landfalling intensity in the archipelago of the Bahamas, while the SST explains 26.4% (p < 0.05) in Central America. Furthermore, the 5-year moving average filter revealed decadal and multidecadal variability in both genesis and landfalling by region. Our findings confirm the complexity of the atmospheric processes involved in the TC genesis and landfalling.

scholarly journals Climatic implications of the Quaternary fluvial tufa record in the NE Iberian Peninsula over the last 500 ka

2015 ◽  
Vol 84 (3) ◽  
pp. 398-414 ◽  
Author(s):  
Carlos Sancho ◽  
Concha Arenas ◽  
Marta Vázquez-Urbez ◽  
Gonzalo Pardo ◽  
María Victoria Lozano ◽  
...  
Keyword(s):  
Iberian Peninsula ◽  
North Atlantic ◽  
Orbital Forcing ◽  
Precipitation Regime ◽  
Fluvial Systems ◽  
Oxygen Isotope Stage ◽  
Amino Acid Racemization ◽  
River Valleys ◽  
Mis 5E ◽  
Ne Iberian Peninsula

The drainage area of the Iberian Ranges (NE Spain) houses one of the most extensive Quaternary fluvial tufaceous records in Europe. In this study, tufa deposits in the Añamaza, Mesa, Piedra and Ebrón river valleys were mapped, stratigraphically described and chronologically referenced from U/Th disequilibrium series, amino acid racemization and radiocarbon methods. Tufa deposits accumulated in cascades, barrage-cascades and related damming areas developed in stepped fluvial systems. The maximum frequency of tufa deposition was identified at 120 ka (Marine Oxygen Isotope Stage [MIS] 5e), 102 ka (MIS 5c), 85 ka (~ MIS 5a) and 7 ka (MIS 1), probably under warmer and wetter conditions than today. Additional phases of tufa deposition appear at ~ 353 ka (~ end of MIS 11), 258–180 ka (MIS 7) and 171–154 ka (MIS 6). Although most tufa deposition episodes are clearly correlated with interstadial periods, the occurrence of tufa deposits during the penultimate glaciation (MIS 6) is remarkable, indicating that the onset of this stage was climatically favourable in the Iberian Peninsula. Biostatic conditions and the dynamics of karstic systems regulating tufa deposition seem to be sensitive to the precipitation regime, controlled by shifts in the position of North Atlantic atmospheric belts, and summer insolation, regulated by orbital forcing.

Le controle du socle dans l'évolution de la sedimentation en Manche occidentale apres le Paléozoïque

1975 ◽  
Vol 279 (1288) ◽  
pp. 137-143 ◽  
Keyword(s):  
North Atlantic ◽  
Transverse Direction ◽  
Longitudinal Direction ◽  
The West ◽  
The North ◽  
The North Atlantic ◽  
The Difference ◽  
Cenozoic Sediments ◽  
Two Sides

The estimates of the thickness of the Mesozoic and Cenozoic sediments found in the western Channel show that the deposition of these sediments was controlled by two independent processes. (1) In the longitudinal direction, the displacement of maximum sedimentation, from east to west is entirely dependent on the opening of the North Atlantic. (2) In a transverse direction, it is probable that the difference of subsidence between the two sides of the Aurigny—Ouessant fault originated from the fracturing of the original Atlantic rift in the Western Approaches. Transverse compressions and extensions have disturbed the continual depression of the Channel towards the west.

scholarly journals VI.—On the Continental Elevation of the Glacial Period

1898 ◽  
Vol 5 (1) ◽  
pp. 32-38 ◽  
Author(s):  
J. W. Spencer
Keyword(s):  
North Atlantic ◽  
Climatic Changes ◽  
The West ◽  
The North ◽  
Northern Latitudes ◽  
Consequent Reduction ◽  
Glacial Epoch ◽  
The North Atlantic ◽  
Possible Cause ◽  
Glacial Climate

Before the last meeting of the British Association, held in Liverpool, Professor Edward Hull presented a paper upon “Another Possible Cause of the Glacial Epoch.”inthat paper, Professor Hull applied the writer's work on the “Reconstruction of the Antillean Continent,” which brought together evidence of great continental elevation. This elevation and its effects upon the ocean-currents, in diverting them from the West Indian regions, with the consequent reduction of their temperature as they reach the northern latitudes in conjunction with the elevation of the land, were thought by Professor Hull to be sufficient causes for the production of the glacial climate over temperate regions in late geological times. The writer has hitherto never applied his observations on high continental elevation to climatic changes; but in this paper he proposes to extend briefly his researches from the Antillean region to the higher latitudes of America and the North Atlantic regions. Something has also been learned of the date of the great elevation; consequently inferences may be drawn as to climatic changes.

ORIGINS OF THE NORTH AMERICAN EPHEMEROPTERA FAUNA, ESPECIALLY THE LEPTOPHLEBIIDAE

1988 ◽  
Vol 120 (S144) ◽  
pp. 13-24 ◽  
Author(s):  
William L. Peters
Keyword(s):  
North America ◽  
Transition Zone ◽  
Northern Hemisphere ◽  
North Atlantic ◽  
North American ◽  
West Indies ◽  
The West ◽  
The North ◽  
The North Atlantic ◽  
Mexican Transition Zone

AbstractThe complex origins of the North American Ephemeroptera fauna extended from the Lower Permian to the Recent. This paper discusses origins of North American genera of the cosmopolitan family Leptophlebiidae with a few examples from other mayfly families. The two extant subfamilies, Leptophlebiinae and Atalophlebiinae, probably evolved at least by the mid-Cretaceous, or about 100 million years before present. The primitive Leptophlebiinae are distributed throughout most of the Northern Hemisphere and the ancestors of the Leptophlebia–Paraleptophlebia complex within this subfamily dispersed widely by the North Atlantic route as early as the mid-Cretaceous and later probably by northern trans-Pacific dispersals through Beringia. The ancestors of Habrophlebia dispersed through the North Atlantic route at an early time, but the vicariant distribution of Habrophlebiodes in several areas of the Oriental Region and eastern North America correlates with the Arcto-Tertiary forest that covered most of the Northern Hemisphere including Beringia from the Early Tertiary into the Pleistocene. Within the nearly cosmopolitan Atalophlebiinae, Traverella is austral in origin and probably dispersed north through the Mexican Transition Zone during the mid-Tertiary as an ancient dispersal and then dispersed to its northern and eastern limits following the last Pleistocene deglaciation by way of the Missouri River tributaries. Thraulodes and Farrodes are both austral in origin and probably dispersed north through the Mexican Transition Zone during the Early Pleistocene as a relatively recent dispersal. The origins of Choroterpes sensu stricto and Neochoroterpes in North America are unknown. The mayfly fauna of the West Indies is Neotropical in origins, and no affinities between the West Indies and North America through Florida have ever been confirmed.

Understanding Putin: The politics of identity and geopolitics in Russian foreign policy discourse

2017 ◽  
Vol 72 (1) ◽  
pp. 28-55 ◽  
Author(s):  
Kari Roberts
Keyword(s):  
Foreign Policy ◽  
International Relations ◽  
North Atlantic ◽  
Russian Foreign Policy ◽  
Politics Of Identity ◽  
The West ◽  
Security Vulnerabilities ◽  
The North ◽  
Narrow View ◽  
The North Atlantic

Russia’s 2014 annexation of Crimea and the subsequent deterioration in its relations with the West have led many analysts to adopt a narrow view of Vladimir Putin’s foreign policy motivations, chalking them up to old-school geopolitics. This paper makes the case that the traditional structural explanations for Russian foreign policy that are dominant within the discipline of international relations do not adequately consider the influence of identity in Putin’s emerging foreign policy narrative. Putin’s narrative is shaped by, and shapes, a discourse about cultural and historical ties with Russian borderlands, as well as by the cultural and security vulnerabilities generated by the West’s treatment of Russia, evidenced by the expansion of the North Atlantic Treaty Organization (NATO). This discourse has underscored a more militant foreign policy turn under Putin in which he is prepared to protect and defend Russia’s interests at high cost; Russia’s actions in Crimea exemplify this. This connection between identity and foreign policy in Putin’s Russia demands attention if we hope to gain a better grasp of Russian foreign policy under his leadership.

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