scholarly journals Non-Uniform Occurrence of Short-Term Polarity Fluctuations in the Geomagnetic Field? New Results from Middle to Late Miocene Sediments of the North Atlantic (DSDP Site 608)

2013 ◽  
pp. 161-174 ◽  
Author(s):  
Wout Krijgsman ◽  
Dennis V. Kent
Keyword(s):  
North Atlantic ◽  
Late Miocene ◽  
Geomagnetic Field ◽  
Short Term ◽  
The North ◽  
The North Atlantic ◽  
Dsdp Site

scholarly journals Reinforcing the North Atlantic backbone: revision and extension of the composite splice at ODP Site 982

2017 ◽  
Author(s):  
Anna Joy Drury ◽  
Thomas Westerhold ◽  
David Hodell ◽  
Ursula Röhl
Keyword(s):  
High Resolution ◽  
Stable Isotope ◽  
North Atlantic ◽  
Late Miocene ◽  
Deep Sea ◽  
Equatorial Atlantic ◽  
The North ◽  
Isotope Stratigraphy ◽  
Stable Isotope Stratigraphy ◽  
The North Atlantic

Abstract. Ocean Drilling Programme (ODP) Site 982 represents a key location for understanding the evolution of climate in the North Atlantic over the past 12 Ma. However, concerns exist about the validity and robustness of the underlying stratigraphy and astrochronology, which currently limits the adequacy of this site for high-resolution climate studies. To resolve this uncertainty, we verify and extend the early Pliocene to late Miocene shipboard composite splice at Site 982 using high-resolution XRF core scanning data and establish a robust high-resolution stable isotope stratigraphy and astrochronology between 4.5 and 8.0 Ma. Splice revisions and verifications resulted in ~ 11 m of gaps in the original Site 982 isotope stratigraphy. Our new stratigraphy reveals previously unseen benthic δ18O excursions, particularly prior to 6.65 Ma. The benthic δ18O record displays distinct, asymmetric cycles between 7.7 and 6.65 Ma, confirming that high-latitude climate is a prevalent forcing during this interval. An intensification of the 41-kyr beat in both the benthic δ13C and δ18O is also observed ~ 6.4 Ma, marking a strengthening in the cryosphere-carbon cycle coupling. A large ~ 0.7 ‰ double excursion is revealed ~ 6.4–6.3 Ma, which also marks the onset an interval of average higher δ18O and large precession and obliquity-dominated δ18O excursions between 6.4–5.4 Ma, coincident with the culmination of the late Miocene cooling. The two largest benthic δ18O excursions ~ 6.4–6.3 Ma and TG20/22 coincide with the coolest alkenone-derived SST estimates from Site 982, suggesting a strong connection between the late Miocene global cooling and deep-sea cooling and dynamic ice sheet expansion. The splice revisions and revised astrochronology resolve key stratigraphic issues that have hampered correlation between Site 982, the equatorial Atlantic and the Mediterranean. Comparisons of the revised Site 982 stratigraphy to high-resolution astronomically tuned benthic δ18O stratigraphies from ODP Site 926 (equatorial Atlantic) and Ain el Beida (north western Morocco) show that prior inconsistencies in short-term excursions are now resolved. Our new integrated deep-sea benthic stable isotope stratigraphy and astrochronology from Site 982 will facilitate future high-resolution late Miocene to early Pliocene climate research.

scholarly journals Effect of vegetation on the Late Miocene ocean circulation

2006 ◽  
Vol 2 (4) ◽  
pp. 605-631 ◽  
Author(s):  
G. Lohmann ◽  
M. Butzin ◽  
A. Micheels ◽  
T. Bickert ◽  
V. Mosbrugger
Keyword(s):  
Ocean Circulation ◽  
North Atlantic ◽  
Late Miocene ◽  
Land Surface ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Hydrological Cycle ◽  
Circulation Model ◽  
The North ◽  
The North Atlantic

Abstract. A weak and shallow thermohaline circulation in the North Atlantic Ocean is related to an open Central American gateway and exchange with fresh Pacific waters. We estimate the effect of vegetation on the ocean general circulation using the atmospheric circulation model simulations for the Late Miocene climate. Caused by an increase in net evaporation in the Miocene North Atlantic, the North Atlantic water becomes more saline which enhances the overturning circulation and thus the northward heat transport. This effect reveals a potentially important feedback between the ocean circulation, the hydrological cycle and the land surface cover for Cenozoic climate evolution.

Indian subcontinent hydroclimate and vegetation changes during the last glacial reconstructed by leaf wax stable isotope and pollen analyses on sediments from IODP Site U1446, NW Bay of Bengal

2020 ◽  
Author(s):  
Stefan Lauterbach ◽  
Nils Andersen ◽  
Charlotte Clément ◽  
Stéphanie Desprat ◽  
Coralie Zorzi ◽  
...  
Keyword(s):  
North Atlantic ◽  
Indian Subcontinent ◽  
Vegetation Changes ◽  
Short Term ◽  
Proxy Records ◽  
The North ◽  
Monsoon Variability ◽  
The North Atlantic ◽  
The Last Glacial

<p>Understanding past variability and forcing mechanisms of the Asian monsoon system is of key importance for better forecasting its behaviour under future global warming scenarios and how this may affect modern societies and economies. So far, knowledge about long-term monsoon variability in mainland Asia is mainly based on proxy records from Chinese speleothems, primarily recording changes of the East Asian Summer Monsoon (EASM). These records have provided evidence for orbital-scale monsoon variability, driven by Northern Hemisphere summer insolation changes, but also for centennial- to millennial-scale reductions in monsoon precipitation. These so-called Weak Monsoon Intervals (WMIs) occurred synchronously to cold intervals in the North Atlantic realm, e.g. during Heinrich Events, pointing at a close hemisphere-scale climatic teleconnection between the North Atlantic and Asia. However, the exact mechanisms that control short-term monsoon variability are still elusive. Moreover, long-term palaeomonsoon proxy records from the core zone of the Indian Summer Monsoon (ISM) are still relatively scarce compared to those from the EASM realm. To identify possible short-term changes in ISM intensity and reconstruct related hydroclimate and vegetation changes on the Indian subcontinent during the interval ~6–74 ka BP, sediments from IODP Site U1446 in the NW Bay of Bengal have been analysed. This site, being located within the reach of the Mahanadi River, is characterized by high riverine input of terrestrial organic matter and thus ideal for high-resolution analyses of pollen content and the stable hydrogen (δD) and carbon (δ<sup>13</sup>C) isotope composition of <em>n</em>-alkanes from terrestrial plant leaf waxes. Here we present preliminary results of δD and δ<sup>13</sup>C analyses on odd-numbered long-chain <em>n</em>-alkanes (<em>n</em>-C<sub>27</sub> to <em>n</em>-C<sub>33</sub>,) extracted from the IODP Site U1446 sediments. These indicate several reductions in ISM precipitation during the last glacial, which occurred parallel to cold events in the North Atlantic realm, e.g. during Heinrich events H1, H2, H4, H5 and H6. In combination with pollen and alkenone-based (U<sup>K’</sup><sub>37</sub>) sea surface temperature data from the same sediments, we aim at (1) providing a comprehensive and high-resolution reconstruction of past ISM variability and associated vegetation changes on the Indian subcontinent and (2) understanding the trigger mechanisms of centennial- to millennial-scale WMIs, particularly in relation to changes in Indian Ocean oceanography.</p>

scholarly journals Reinforcing the North Atlantic backbone: revision and extension of the composite splice at ODP Site 982

2018 ◽  
Vol 14 (3) ◽  
pp. 321-338 ◽  
Author(s):  
Anna Joy Drury ◽  
Thomas Westerhold ◽  
David Hodell ◽  
Ursula Röhl
Keyword(s):  
High Resolution ◽  
Stable Isotope ◽  
North Atlantic ◽  
Late Miocene ◽  
Deep Sea ◽  
Equatorial Atlantic ◽  
The North ◽  
Isotope Stratigraphy ◽  
Stable Isotope Stratigraphy ◽  
The North Atlantic

Abstract. Ocean Drilling Program (ODP) Site 982 represents a key location for understanding the evolution of climate in the North Atlantic over the past 12 Ma. However, concerns exist about the validity and robustness of the underlying stratigraphy and astrochronology, which currently limits the adequacy of this site for high-resolution climate studies. To resolve this uncertainty, we verify and extend the early Pliocene to late Miocene shipboard composite splice at Site 982 using high-resolution XRF core scanning data and establish a robust high-resolution benthic foraminiferal stable isotope stratigraphy and astrochronology between 8.0 and 4.5 Ma. Splice revisions and verifications resulted in  ∼  11 m of gaps in the original Site 982 isotope stratigraphy, which were filled with 263 new isotope analyses. This new stratigraphy reveals previously unseen benthic δ18O excursions, particularly prior to 6.65 Ma. The benthic δ18O record displays distinct, asymmetric cycles between 7.7 and 6.65 Ma, confirming that high-latitude climate is a prevalent forcing during this interval. An intensification of the 41 kyr beat in both the benthic δ13C and δ18O is also observed  ∼  6.4 Ma, marking a strengthening in the cryosphere–carbon cycle coupling. A large  ∼  0.7 ‰ double excursion is revealed  ∼  6.4–6.3 Ma, which also marks the onset of an interval of average higher δ18O and large precession and obliquity-dominated δ18O excursions between 6.4 and 5.4 Ma, coincident with the culmination of the late Miocene cooling. The two largest benthic δ18O excursions  ∼  6.4–6.3 Ma and TG20/22 coincide with the coolest alkenone-derived sea surface temperature (SST) estimates from Site 982, suggesting a strong connection between the late Miocene global cooling, and deep-sea cooling and dynamic ice sheet expansion. The splice revisions and revised astrochronology resolve key stratigraphic issues that have hampered correlation between Site 982, the equatorial Atlantic and the Mediterranean. Comparisons of the revised Site 982 stratigraphy to high-resolution astronomically tuned benthic δ18O stratigraphies from ODP Site 926 (equatorial Atlantic) and Ain el Beida (north-western Morocco) show that prior inconsistencies in short-term excursions are now resolved. The identification of key new cycles at Site 982 further highlights the requirement for the current scheme for late Miocene marine isotope stages to be redefined. Our new integrated deep-sea benthic stable isotope stratigraphy and astrochronology from Site 982 will facilitate future high-resolution late Miocene to early Pliocene climate research.

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