Understanding the stability of the early Antarctic ice cap in the
geological past is of societal ... more Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene−Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial−interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions.
Few astronomically calibrated high-resolution (≤5kyr) climate records exist that span the Oligoce... more Few astronomically calibrated high-resolution (≤5kyr) climate records exist that span the Oligocene–Miocene time interval. Notably, available proxy records show responses varying in amplitude at frequencies related to astronomical forcing, and the main pacemakers of global change on astronomical time-scales remain debated. Here we present newly generated X-ray fluorescence core scanning and benthic foraminiferal stable oxygen and carbon isotope records from Ocean Drilling Program Site 1264 (Walvis Ridge, southeastern Atlantic Ocean). Complemented by data from nearby Site 1265, the Site 1264 benthic stable isotope records span a continuous ∼13-Myr interval of the Oligo-Miocene (30.1–17.1Ma) at high resolution (∼3.0 kyr). Spectral analyses in the stratigraphic depth domain indicate that the largest amplitude variability of all proxy records is associated with periods of ∼3.4mand ∼0.9m, which correspond to 405-and ∼110-kyr eccentricity, using a magnetobiostratigraphic age model. Maxima in CaCO3content, δ18O and δ13C are interpreted to coincide with ∼110kyr eccentricity minima. The strong expression of these cycles in combination with the weakness of the precession-and obliquity-related signals allow construction of an astronomical age model that is solely based on tuning the CaCO3content to the nominal (La2011_ecc3L) eccentricity solution. Very long-period eccentricity maxima (∼2.4-Myr) are marked by recurrent episodes of high-amplitude ∼110-kyr δ18O cycles at Walvis Ridge, indicating greater sensitivity of the climate/cryosphere system to short eccentricity modulation of climatic precession. In contrast, the responses of the global (high-latitude) climate system, cryosphere, and carbon cycle to the 405-kyr cycle, as expressed in benthic δ18O and especially δ13C signals, are more pronounced during ∼2.4-Myr minima. The relationship between the recurrent episodes of high-amplitude ∼110-kyr δ18O cycles and the ∼1.2-Myr amplitude modulation of obliquity is not consistent through the Oligo-Miocene. Identification of these recurrent episodes at Walvis Ridge, and their pacing by the ∼2.4-Myr eccentricity cycle, revises the current understanding of the main climate events of the Oligo-Miocene.
Understanding the stability of the early Antarctic ice cap in the
geological past is of societal ... more Understanding the stability of the early Antarctic ice cap in the geological past is of societal interest because present-day atmospheric CO2 concentrations have reached values comparable to those estimated for the Oligocene and the Early Miocene epochs. Here we analyze a new high-resolution deep-sea oxygen isotope (δ18O) record from the South Atlantic Ocean spanning an interval between 30.1 My and 17.1 My ago. The record displays major oscillations in deep-sea temperature and Antarctic ice volume in response to the ∼110-ky eccentricity modulation of precession. Conservative minimum ice volume estimates show that waxing and waning of at least ∼85 to 110% of the volume of the present East Antarctic Ice Sheet is required to explain many of the ∼110-ky cycles. Antarctic ice sheets were typically largest during repeated glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago) and across the Oligocene−Miocene Transition (∼23.0 My ago). However, the high-amplitude glacial−interglacial cycles of the mid-Oligocene are highly symmetrical, indicating a more direct response to eccentricity modulation of precession than their Early Miocene counterparts, which are distinctly asymmetrical—indicative of prolonged ice buildup and delayed, but rapid, glacial terminations. We hypothesize that the long-term transition to a warmer climate state with sawtooth-shaped glacial cycles in the Early Miocene was brought about by subsidence and glacial erosion in West Antarctica during the Late Oligocene and/or a change in the variability of atmospheric CO2 levels on astronomical time scales that is not yet captured in existing proxy reconstructions.
Few astronomically calibrated high-resolution (≤5kyr) climate records exist that span the Oligoce... more Few astronomically calibrated high-resolution (≤5kyr) climate records exist that span the Oligocene–Miocene time interval. Notably, available proxy records show responses varying in amplitude at frequencies related to astronomical forcing, and the main pacemakers of global change on astronomical time-scales remain debated. Here we present newly generated X-ray fluorescence core scanning and benthic foraminiferal stable oxygen and carbon isotope records from Ocean Drilling Program Site 1264 (Walvis Ridge, southeastern Atlantic Ocean). Complemented by data from nearby Site 1265, the Site 1264 benthic stable isotope records span a continuous ∼13-Myr interval of the Oligo-Miocene (30.1–17.1Ma) at high resolution (∼3.0 kyr). Spectral analyses in the stratigraphic depth domain indicate that the largest amplitude variability of all proxy records is associated with periods of ∼3.4mand ∼0.9m, which correspond to 405-and ∼110-kyr eccentricity, using a magnetobiostratigraphic age model. Maxima in CaCO3content, δ18O and δ13C are interpreted to coincide with ∼110kyr eccentricity minima. The strong expression of these cycles in combination with the weakness of the precession-and obliquity-related signals allow construction of an astronomical age model that is solely based on tuning the CaCO3content to the nominal (La2011_ecc3L) eccentricity solution. Very long-period eccentricity maxima (∼2.4-Myr) are marked by recurrent episodes of high-amplitude ∼110-kyr δ18O cycles at Walvis Ridge, indicating greater sensitivity of the climate/cryosphere system to short eccentricity modulation of climatic precession. In contrast, the responses of the global (high-latitude) climate system, cryosphere, and carbon cycle to the 405-kyr cycle, as expressed in benthic δ18O and especially δ13C signals, are more pronounced during ∼2.4-Myr minima. The relationship between the recurrent episodes of high-amplitude ∼110-kyr δ18O cycles and the ∼1.2-Myr amplitude modulation of obliquity is not consistent through the Oligo-Miocene. Identification of these recurrent episodes at Walvis Ridge, and their pacing by the ∼2.4-Myr eccentricity cycle, revises the current understanding of the main climate events of the Oligo-Miocene.
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Papers by A. van Dijk E Dijk
geological past is of societal interest because present-day atmospheric
CO2 concentrations have reached values comparable to
those estimated for the Oligocene and the Early Miocene epochs.
Here we analyze a new high-resolution deep-sea oxygen isotope
(δ18O) record from the South Atlantic Ocean spanning an interval
between 30.1 My and 17.1 My ago. The record displays major
oscillations in deep-sea temperature and Antarctic ice volume in
response to the ∼110-ky eccentricity modulation of precession.
Conservative minimum ice volume estimates show that waxing
and waning of at least ∼85 to 110% of the volume of the present
East Antarctic Ice Sheet is required to explain many of the ∼110-ky
cycles. Antarctic ice sheets were typically largest during repeated
glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago)
and across the Oligocene−Miocene Transition (∼23.0 My ago).
However, the high-amplitude glacial−interglacial cycles of the
mid-Oligocene are highly symmetrical, indicating a more direct response
to eccentricity modulation of precession than their Early
Miocene counterparts, which are distinctly asymmetrical—indicative
of prolonged ice buildup and delayed, but rapid, glacial terminations.
We hypothesize that the long-term transition to a
warmer climate state with sawtooth-shaped glacial cycles in the
Early Miocene was brought about by subsidence and glacial erosion
in West Antarctica during the Late Oligocene and/or a change
in the variability of atmospheric CO2 levels on astronomical time
scales that is not yet captured in existing proxy reconstructions.
geological past is of societal interest because present-day atmospheric
CO2 concentrations have reached values comparable to
those estimated for the Oligocene and the Early Miocene epochs.
Here we analyze a new high-resolution deep-sea oxygen isotope
(δ18O) record from the South Atlantic Ocean spanning an interval
between 30.1 My and 17.1 My ago. The record displays major
oscillations in deep-sea temperature and Antarctic ice volume in
response to the ∼110-ky eccentricity modulation of precession.
Conservative minimum ice volume estimates show that waxing
and waning of at least ∼85 to 110% of the volume of the present
East Antarctic Ice Sheet is required to explain many of the ∼110-ky
cycles. Antarctic ice sheets were typically largest during repeated
glacial cycles of the mid-Oligocene (∼28.0 My to ∼26.3 My ago)
and across the Oligocene−Miocene Transition (∼23.0 My ago).
However, the high-amplitude glacial−interglacial cycles of the
mid-Oligocene are highly symmetrical, indicating a more direct response
to eccentricity modulation of precession than their Early
Miocene counterparts, which are distinctly asymmetrical—indicative
of prolonged ice buildup and delayed, but rapid, glacial terminations.
We hypothesize that the long-term transition to a
warmer climate state with sawtooth-shaped glacial cycles in the
Early Miocene was brought about by subsidence and glacial erosion
in West Antarctica during the Late Oligocene and/or a change
in the variability of atmospheric CO2 levels on astronomical time
scales that is not yet captured in existing proxy reconstructions.