Dissolved Thorium Isotope Evidence for Export Productivity in the Subtropical North Pacific During the Late Quaternary

2020 ◽  
Vol 47 (11) ◽  
Author(s):  
Ruolin Liu ◽  
Maoyu Wang ◽  
Weiqiang Li ◽  
Xuefa Shi ◽  
Tianyu Chen
Keyword(s):  
North Pacific ◽  
Late Quaternary ◽  
Thorium Isotope ◽  
Isotope Evidence ◽  
Export Productivity

scholarly journals Toward a global calibration for quantifying past oxygenation in oxygen minimum zones using benthic Foraminifera

2021 ◽  
Author(s):  
Martin Tetard ◽  
Laetitia Licari ◽  
Kazuyo Tachikawa ◽  
Ekaterina Ovsepyan ◽  
Luc Beaufort
Keyword(s):  
North Pacific ◽  
Transfer Functions ◽  
Late Quaternary ◽  
Global Climate ◽  
Single Species ◽  
Pore Waters ◽  
Oxygen Minimum Zones ◽  
Global Calibration ◽  
Circularity Index ◽  
Oxygen Minimum

Abstract. Oxygen Minimum Zones (OMZs) are oceanic areas largely depleted in dissolved oxygen, nowadays considered in expansion in the face of global warming. Their ecological and economic consequences are being debated. The investigation of past OMZ conditions allows us to better understand biological and physical mechanisms responsible for their variability with regards to climate change, carbon pump and carbonate system. To investigate the relationship between OMZ expansion and global climate changes during the late Quaternary, quantitative oxygen reconstructions are needed, but are still in their early development. Here, past bottom water oxygenation (BWO) was quantitatively assessed through a new, fast, semi-automated, and taxonfree morphometric analysis of benthic foraminiferal tests, developed and calibrated using Eastern North Pacific (ENP) and the Eastern South Pacific (ESP) OMZs samples. This new approach is based on an average size and circularity index for each sample. This method, as well as two already published micropalaeontological approaches based on benthic foraminiferal assemblages variability and porosity investigation of a single species, were here calibrated based on availability of new data from 23 core tops recovered along an oxygen gradient (from 0.03 to 1.79 mL.L−1) from the ENP, ESP, AS (Arabian Sea) and WNP (Western North Pacific, including its marginal seas) OMZs. Global calibrated transfer functions are thus herein proposed for each of these methods. These micropalaeontological reconstruction approaches were then applied on a paleorecord from the ENP OMZ to examine the consistency and limits of these methods, as well as the relative influence of bottom and pore waters on these micropalaeontological tools. Both the assemblages and morphometric approaches (that is also ultimately based on the ecological response of the complete assemblage and faunal succession according to BWO) gave similar and consistent past BWO reconstructions, while the porosity approach (based on a single species and its unique response to a mixed signal of bottom and pore waters) shown ambiguous estimations.

scholarly journals Thorium isotope evidence for melting of the mafic oceanic crust beneath the Izu arc

2016 ◽  
Vol 186 ◽  
pp. 49-70 ◽  
Author(s):  
Heye Freymuth ◽  
Ben Ivko ◽  
James B. Gill ◽  
Yoshihiko Tamura ◽  
Tim Elliott
Keyword(s):  
Oceanic Crust ◽  
Thorium Isotope ◽  
Isotope Evidence

Phytolith and Carbon Isotope Evidence for Late Quaternary Vegetation and Climate Change in the Southern Black Hills, South Dakota

1997 ◽  
Vol 47 (2) ◽  
pp. 206-217 ◽  
Author(s):  
Glen G. Fredlund ◽  
Larry L. Tieszen
Keyword(s):  
South Dakota ◽  
Late Holocene ◽  
Late Quaternary ◽  
Isotope Analysis ◽  
Fire Frequency ◽  
Soil Development ◽  
Black Hills ◽  
Isotope Evidence ◽  
Mixed Grasslands ◽  
Vegetation And Climate

Analyses of phytoliths and carbon isotopes document change in late Quaternary grasslands in the Red Valley of the southern Black Hills. Late Pleistocene grassland composition was equivalent to the C3grass parklands of modern central Alberta. The rise of mixed grassland occurred rapidly between 11,000 and 9000 yr B.P. Early Holocene mixed grasslands included both short and tall C4grasses. A mid-Holocene erosional unconformity (ca. 8000 to 4500 yr B.P.) precludes phytolith or isotope analysis, but suggests lack of vegetation and landscape denudation caused by a drier climatic. Basin-wide stability and soil development followed the erosional episode (ca. 4500 to 3600 yr B.P.). Mesic-adapted C4panicoid grasses increased during this period of soil development. Low-magnitude fluctuation in the C4-dominated mixed grassland occurred throughout the late Holocene (3600 yr B.P. to present). Rise in δ13C values during the last 1000 yr without corresponding change in phytoliths may indicate a decrease in woodlands caused by increased fire frequency.

Late-Quaternary climatic change on the American North Pacific Coast

Nature ◽  
1985 ◽  
Vol 315 (6019) ◽  
pp. 485-487 ◽  
Author(s):  
C. J. Heusser ◽  
L. E. Heusser ◽  
D. M. Peteet
Keyword(s):  
Climatic Change ◽  
North Pacific ◽  
Pacific Coast ◽  
Late Quaternary

Uranium/Thorium isotope evidence for ground-water history in the Eastern Desert of Egypt

2002 ◽  
Vol 50 (2) ◽  
pp. 343-357 ◽  
Author(s):  
Adel A. Dabous ◽  
J.K. Osmond ◽  
Yehia H. Dawood
Keyword(s):  
Ground Water ◽  
Eastern Desert ◽  
Water History ◽  
Thorium Isotope ◽  
Isotope Evidence
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