scholarly journals Paleoenvironmental and paleobiological origins of coccolithophorid genusWatznaueriaemergence during the late Aalenian–early Bajocian

Paleobiology ◽  
2015 ◽  
Vol 41 (3) ◽  
pp. 415-435 ◽  
Author(s):  
Baptiste Suchéras-Marx ◽  
Emanuela Mattioli ◽  
Fabienne Giraud ◽  
Gilles Escarguel
Keyword(s):  
Marine Invertebrate ◽  
Time Interval ◽  
Calcareous Nannofossils ◽  
Calcareous Nannoplankton ◽  
Absolute Abundance ◽  
The Pacific ◽  
Relative Abundances ◽  
The Absolute ◽  
Oceanic Plates ◽  
Central Atlantic

AbstractThe latest Aalenian–early Bajocian time interval (ca. 171-169 Ma) is marked by a global reorganization of oceanic plates with the Central Atlantic opening and the formation of the Pacific plate. This time interval is also marked by a global geochemical perturbation of δ13C with a negative excursion at the Aalenian/Bajocian boundary and a positive excursion during the early Bajocian. Evolutionary diversifications of marine invertebrate taxa, namely ammonites, radiolarians, and coccolithophorids, are recorded at that time. Concerning coccolithophorids, this interval witnesses the diversification and expansion of the most successful Mesozoic genus:Watznaueria. In this study, we explore the potential environmental, ecological, and biological forcing at the origin ofWatznaueriadiversification and its effect on the coccolith assemblages through quantification of the absolute and relative abundances of calcareous nannofossils in two Middle Jurassic key sections: Cabo Mondego (Portugal) and Chaudon-Norante (France). In both sections, we find an increase in nannofossil absolute abundance and flux at the beginning of the lower Bajocian, coeval with an increase in absolute and relative abundances ofWatznaueriaspp., followed by a plateau in the middle and upper part of the lower Bajocian. The increase ofWatznaueriaspp. is synchronous with a decrease in relative abundance of other major coccolith taxa, whereas the absolute abundance of these species did not decrease. During the climatically driven early Bajocian eutrophication event,Watznaueriaspp. integrated into the calcareous nannoplankton community in two successive evolutionary steps involving firstW. contractaandW. colaccicchii, and secondW. britannicaandW.aff.manivitiae. Step 1 was driven by an increase in niche carrying capacities linked to the early Bajocian eutrophication. Step 2 was driven by specific adaptation of the newly evolvedWatznaueriaspecies to bloom in nutrient-rich environments not exploited before. These evolutionary events have initiated the 100-Myr reign ofWatznaueriaover the calcareous nannoplankton community.

Biodiversity and the biogeographic relationships of the Amphipoda: Gammaridea on the French coastline

2004 ◽  
Vol 84 (3) ◽  
pp. 621-628 ◽  
Author(s):  
Jean-Claude Dauvin ◽  
Denise Bellan-Santini
Keyword(s):  
Latitudinal Gradient ◽  
Marine Invertebrate ◽  
English Channel ◽  
Latitude Range ◽  
The North ◽  
North Eastern ◽  
Cool Temperate ◽  
Amphipoda Species ◽  
Central Atlantic ◽  
Warm Temperate

A recent inventory of the benthic Gammaridea: Amphipoda species on the French continental coastline catalogued 495 species. An analysis of the biodiversity and the biogeographic relationships that exist between the French Amphipoda: Gammaridea, living on the coastline that extends along 10° latitude range in the temperate region between 41° and 51° North and the other gammaridean faunas living in the north-eastern Atlantic has drawn the pattern of diversity in this marine invertebrate group on a large biogeographical scale. Gammaridean amphipods exhibit a latitudinal gradient over the total number of species, including the continental shelf species and the bathyal species. There are four main fauna groups, which correspond to the biogeographical zones of the north-eastern Atlantic: (1) a cold arctic and cool-temperate Svalbard and Norwegian coastal fauna; (2) a cool-temperate boreal and Boreal–Lusitanian United Kingdom, Irish and English Channel shallow fauna; (3) a warm-temperate Lusitanian Bay of Biscay and subtropical central Atlantic fauna; and (4) a subtropical Mediterranean fauna. The French fauna appears particularly rich, presenting 44% of the 1119 species recorded in the north-eastern Atlantic along the 50° latitude range (30°N–80°N).  This is obviously due to France's intermediate latitudinal location within the Lusitanian temperate biogeographical zone, which produces a biogeographical cross between the boreal fauna in the north and the warm temperate and sub-tropical fauna in the south.

scholarly journals Geomagnetic secular variation

1989 ◽  
Vol 329 (1606) ◽  
pp. 415-502 ◽  
Keyword(s):  
Steady Flow ◽  
Southern Africa ◽  
Secular Variation ◽  
Static Field ◽  
Time Interval ◽  
The Core ◽  
Flow Maps ◽  
The Pacific ◽  
Construct Maps ◽  
Eighteenth And Nineteenth Centuries

We analyse over 175000 magnetic observations from an interval spanning 1695-1980 to produce a sequence of maps of the magnetic field at the core-mantle boundary; we find that even the earlier data enable us to determine reliable maps. We produce these maps at approximately 60-year intervals through the eighteenth and nineteenth centuries, and at 10-year intervals in the twentieth century. This span of maps is long enough to render straightforward the distinction between static and drifting features in the field: we observe that some features show no sign whatsoever of drift over the entire 285-year time interval, although others drift westwards. In particular, we observe that the secular variation is very low beneath the Pacific ocean, but beneath southern Africa and the South Atlantic ocean we observe rapid secular variation. We interpret the morphology of the static field in terms of a simple model of the dynamo, and conjecture that interactions between the core and the mantle are an important element of the process. As part of the static field we identify four main concentrations of flux, two in each hemisphere, at high latitudes: these features largely account for the Earth’s axial dipole moment. We find unequivocal evidence that magnetic flux has not remained frozen over the time span of our models; much of the diffusive behaviour that we identify is associated with the formation of a pair of flux spots (a ‘core spot’) beneath southern Africa, early in this century. Nevertheless, we are able to construct maps that satisfy a set of necessary conditions for frozen-flux, and use these maps to construct maps of the core surface fluid flow, based on the steady flow hypothesis. Although we find no strong evidence against the steady flow hypothesis, we do find some grounds on which to doubt the validity of the flow maps.

RESPONSE OF CALCAREOUS NANNOPLANKTON TO PALEOCENE–EOCENE THERMAL MAXIMUM IN NORTHERN IRAQ

2020 ◽  
Vol 02 (01) ◽  
pp. 2050001
Author(s):  
RAGHDA SAAD AL-HYALY ◽  
OMAR AHMED AL-BADRANI
Keyword(s):  
Global Warming ◽  
Calcareous Nannofossils ◽  
Calcareous Nannoplankton ◽  
Geological Record ◽  
Northern Iraq ◽  
Thermal Maximum

The Paleocene–Eocene Thermal Maximum (PETM) was an abrupt global warming event in the geological record. Based on calcareous nannofossils from thirteen samples of Aaliji Formation from K-116 well, Northern Iraq, sixty species are identified and can be used to divide the studied section into five biozones. Especially, the transition in the Discoaster multiraditus Biozone (CP8) occurred which is marked by higher speciation for calcareous nannofossils and the occurrences of Discoaster Tan. Such atransition is closely related to global warming during the transition from Paleocene to Eocene.

scholarly journals Five-century record of climate and groundwater recharge variability in southern California

2019 ◽  
Vol 9 (1) ◽  
Author(s):  
F. Manna ◽  
K. M. Walton ◽  
J. A. Cherry ◽  
B. L. Parker
Keyword(s):  
Los Angeles ◽  
Groundwater Recharge ◽  
Southern California ◽  
Surface Soil ◽  
Time Interval ◽  
Chloride Salt ◽  
Freshwater Flow ◽  
The Pacific ◽  
Salt Distribution

AbstractModifications to the rates of water flowing from the surface to groundwater (groundwater recharge) due to climate variability are the most difficult to assess because of the lack of direct long-term observations. Here, we analyze the chloride salt distribution below the surface soil on a plateau near Los Angeles to reconstruct the amount of recharge that occurred in the last five centuries. Over this time interval, periods of major high and low recharge with different duration follow each other and this cyclicity is consistent with long-term atmospheric forcing patterns, such as the Pacific Decadal Oscillation. This study determines the range and the natural variability of recharge to groundwater, which sustains local freshwater flow system, and helps forecast future availability of groundwater resource in southern California, where water scarcity is critical to both local and global populations.

Relative motions between oceanic plates of the Pacific Basin

1984 ◽  
Vol 89 (B12) ◽  
pp. 10291-10310 ◽  
Author(s):  
David C. Engebretson ◽  
Allan Cox ◽  
Richard G. Gordon
Keyword(s):  
Pacific Basin ◽  
The Pacific ◽  
Oceanic Plates ◽  
Relative Motions

On the absolute abundance of calcium in solar flares

1993 ◽  
Vol 404 ◽  
pp. 394 ◽  
Author(s):  
Alphonse C. Sterling ◽  
George A. Doschek ◽  
Uri Feldman
Keyword(s):  
Solar Flares ◽  
Absolute Abundance ◽  
The Absolute

scholarly journals Coccolithophore response to climate and surface hydrography in Santa Barbara Basin, California, AD 1917–2004

2009 ◽  
Vol 6 (10) ◽  
pp. 2025-2039 ◽  
Author(s):  
M. Grelaud ◽  
A. Schimmelmann ◽  
L. Beaufort
Keyword(s):  
Southern Oscillation ◽  
California Current ◽  
Santa Barbara ◽  
Santa Barbara Basin ◽  
Enso Events ◽  
The Pacific ◽  
Hydrographic Conditions ◽  
Shell Carbonate ◽  
Relative Abundances ◽  
Counter Current

Abstract. The varved sedimentary AD 1917–2004 record from the depositional center of the Santa Barbara Basin (SBB, California) was analyzed with monthly to triannual resolution to yield relative abundances of six coccolithophore species representing at least 96% of the coccolithophore assemblage. Seasonal/annual relative abundances respond to climatic and surface hydrographic conditions in the SBB, whereby (i) the three species G. oceanica, H. carteri and F. profunda are characteristic of the strength of the northward flowing warm California Counter Current, (ii) the two species G. ericsonii and G. muellerae are associated with the cold equatorward flowing California Current, (iii) and E. huxleyi appears to be endemic to the SBB. Spectral analyses on relative abundances of these species show that all are influenced by the El Niño Southern Oscillation (ENSO) and/or by the Pacific Decadal Oscillation (PDO). Increased relative abundances of G. oceanica and H. carteri are associated with warm ENSO events, G. muellerae responds to warm PDO events and the abundance of G. ericsonii increases during cold PDO events. Morphometric parameters measured on E. huxleyi, G. muellerae and G. oceanica indicate increasing coccolithophore shell carbonate mass from ~1917 until 2004 concomitant with rising pCO2 and sea surface temperature in the region of the SBB.

Identification of 26-minute Zr-84

1983 ◽  
Vol 61 (4) ◽  
pp. 754-756 ◽  
Author(s):  
Seiichi Shibata ◽  
Paul J. Karol
Keyword(s):  
Cross Sections ◽  
Half Life ◽  
Production Cross ◽  
Isotopic Distribution ◽  
Absolute Abundance ◽  
Spallation Reactions ◽  
Relative Production ◽  
Γ Ray ◽  
The Absolute ◽  
Mev Protons

An unknown γ-ray of energy 112.5 keV was found in zirconium fractions chemically extracted from isotopically enriched molybdenum targets bombarded with 500 and 800 MeV protons. All evidence suggests that the γ-ray is identifiable with the decay of 84Zr to 84Y. A half-life of 25.7 ± 0.5 min was obtained for 84Zr, which is considerably longer than previously reported half-lives. The absolute abundance of the 112.5 keV γ-ray was also determined. Relative production cross sections for 84Zr were calculated using these results and were consistent with the values interpolated from isotopic distribution curves for spallation reactions.

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