Requiem for the Regolith Hypothesis: Sea-Level and Temperature Reconstructions Provide a New Template for the Middle Pleistocene Transition

The Middle Pleistocene Transition (MPT) has been characterized as the transition in temperature and sea level from low-amplitude, 41-kyr variability to high-amplitude, quasi-100-kyr variability in the absence of any orbital forcing between 1.2 and 0.7 Ma. The regolith hypothesis is one of a class of hypotheses developed to explain the MPT in sea level, which has been largely inferred from d18Obenthic records. Here we use a global array of 130 sea-surface temperature (SST) records based on Mg/Ca, alkenone, and faunal proxies to reconstruct global and regional SST change over the last 4.5 Myr. Average global temperature cooled by ~6.5oC since ~3.5 Ma, with the MPT represented by a significant increase in the rate of cooling between ~1.4 and 0.8 Ma, and a change from dominant 41-kyr to dominant quasi-100-kyr frequencies at ~1.2 Ma that are well correlated with CO2 over the last 800 ka (r2=0.6). Temperature terminations after 1.2 Ma correspond to skipped obliquity beats and, for the last 800 ka, large increases in CO2. We use our global SST reconstruction to remove the temperature signal from the Ahn17 d18Obenthic stack to derive d18Oseawater. Accounting for the influence of changing temperature on the isotopic composition of ice sheets, we use the d18Oseawater record to reconstruct global sea level for the last 4.5 Myr. These results suggest sea-level minima equivalent to or lower than the LGM sea-level low stand (130 m) throughout the Pleistocene. Since inception of Northern Hemisphere glaciation ~3 Ma, sea level varied linearly with obliquity until ~1.2 Ma, when sea-level began to vary nonlinearly with obliquity, with the largest terminations occurring at the same time as temperature terminations that correspond to increasing obliquity and CO2. These results suggest that the MPT is largely a temperature phenomenon likely associated with CO2. The regolith hypothesis other hypotheses developed to explain a transition from low- to high-amplitude sea level variability during the MPT are no longer required, with the MPT change in sea-level response to obliquity likely due to modulation by CO2.

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The Bakken Formation - understanding the sequence stratigraphic record of low-gradient sedimentary systems, shale depositional environments, and sea-level changes in an icehouse world

The Sedimentary Record ◽

10.2110/sedred.2020.4.4 ◽

2020 ◽

Vol 18 (4) ◽

pp. 4-9

Author(s):

Sven O Egenhoff ◽

Neil S Fishman

Keyword(s):

Sea Level ◽

High Amplitude ◽

Depositional Environments ◽

Ice Age ◽

Bakken Formation ◽

Sea Level Changes ◽

Sequence Stratigraphic ◽

Sea Level Fluctuations ◽

Layer Cake ◽

Low Amplitude

The Bakken Formation is a major petroleum producer in the continental US. However, its deposition in an intracratonic, low-gradient setting has often been mistakenly described as “layer-cake”. This contribution is designed to highlight the time-transgressive nature of its main petroleum-producer, the middle Bakken member. Correlation of individual parasequences reveal the subtle nature of otherwise invisible low-angle stratigraphic geometries. Sequence stratigraphically-relevant surfaces occur throughout the unit and subdivide the entire Bakken into 5 third-order sequences; one of them is a hidden sequence at the base of the petroleum-producing middle Bakken indicating both a lowstand and a subsequent transgression. The organic-rich shales above and below the middle Bakken were deposited in an oxygen-deficient environment and show several burrow/fecal string types and indications of active currents during deposition. The Bakken records high amplitude sea-level changes during sequences compared to relative low amplitude sea-level changes of parasequences. This, coupled with a likely mismatch in timing of Bakken deposition relative to world-wide ice-age-induced cyclicity makes it unlikely that the Bakken sea-level fluctuations were dominated by glaciation.

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Review of the Early–Middle Pleistocene boundary and Marine Isotope Stage 19

Progress in Earth and Planetary Science ◽

10.1186/s40645-021-00439-2 ◽

2021 ◽

Vol 8 (1) ◽

Author(s):

Martin J. Head

Keyword(s):

North Atlantic ◽

Meridional Overturning Circulation ◽

Middle Pleistocene ◽

Orbital Eccentricity ◽

Middle Pleistocene Transition ◽

Meridional Overturning ◽

Asian Pacific ◽

Low Amplitude ◽

The Antarctic ◽

Insolation Forcing

AbstractThe Global Boundary Stratotype Section and Point (GSSP) defining the base of the Chibanian Stage and Middle Pleistocene Subseries at the Chiba section, Japan, was ratified on January 17, 2020. Although this completed a process initiated by the International Union for Quaternary Research in 1973, the term Middle Pleistocene had been in use since the 1860s. The Chiba GSSP occurs immediately below the top of Marine Isotope Substage (MIS) 19c and has an astronomical age of 774.1 ka. The Matuyama–Brunhes paleomagnetic reversal has a directional midpoint just 1.1 m above the GSSP and serves as the primary guide to the boundary. This reversal lies within the Early–Middle Pleistocene transition and has long been favoured to mark the base of the Middle Pleistocene. MIS 19 occurs within an interval of low-amplitude orbital eccentricity and was triggered by an obliquity cycle. It spans two insolation peaks resulting from precession minima and has a duration of ~ 28 to 33 kyr. MIS 19c begins ~ 791–787.5 ka, includes full interglacial conditions which lasted for ~ 8–12.5 kyr, and ends with glacial inception at ~ 774–777 ka. This inception has left an array of climatostratigraphic signals close to the Early–Middle Pleistocene boundary. MIS 19b–a contains a series of three or four interstadials often with rectangular-shaped waveforms and marked by abrupt (< 200 year) transitions. Intervening stadials including the inception of glaciation are linked to the calving of ice sheets into the northern North Atlantic and consequent disruption of the Atlantic meridional overturning circulation (AMOC), which by means of the thermal bipolar seesaw caused phase-lagged warming events in the Antarctic. The coherence of stadial–interstadial oscillations during MIS 19b–a across the Asian–Pacific and North Atlantic–Mediterranean realms suggests AMOC-originated shifts in the Intertropical Convergence Zone and pacing by equatorial insolation forcing. Low-latitude monsoon dynamics appear to have amplified responses regionally although high-latitude teleconnections may also have played a role.

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The “missing glaciations” of the Middle Pleistocene

Quaternary Research ◽

10.1017/qua.2019.76 ◽

2020 ◽

Vol 96 ◽

pp. 161-183 ◽

Cited By ~ 4

Author(s):

Philip D. Hughes ◽

Philip L. Gibbard ◽

Jürgen Ehlers

Keyword(s):

High Amplitude ◽

Middle Pleistocene ◽

Volume Changes ◽

The West ◽

Feedback Mechanisms ◽

West Antarctic Ice Sheet ◽

Ice Volume ◽

West Antarctic ◽

Middle Pleistocene Transition

AbstractGlobal glaciations have varied in size and magnitude since the Early–Middle Pleistocene transition (~773 ka), despite the apparent regular and high-amplitude 100 ka pacing of glacial–interglacial cycles recorded in marine isotope records. The evidence on land indicates that patterns of glaciation varied dramatically between different glacial–interglacial cycles. For example, Marine Isotope Stages (MIS) 8, 10, and 14 are all noticeably absent from many terrestrial glacial records in North America and Europe. However, globally, the patterns are more complicated, with major glaciations recorded in MIS 8 in Asia and in parts of the Southern Hemisphere, such as Patagonia, for example. This spatial variability in glaciation between glacial–interglacial cycles is likely to be driven by ice volume changes in the West Antarctic Ice Sheet and associated interhemispheric connections through ocean–atmosphere circulatory changes. The weak global glacial imprint in some glacial–interglacial cycles is related to the pattern of global ice buildup. This is caused by feedback mechanisms within glacial systems themselves that partly result from long-term orbital changes driven by eccentricity.

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A stalactite record of four relative sea-level highstands during the Middle Pleistocene Transition

Quaternary Science Reviews ◽

10.1016/j.quascirev.2017.08.008 ◽

2017 ◽

Vol 173 ◽

pp. 92-100 ◽

Cited By ~ 3

Author(s):

Paolo Stocchi ◽

Fabrizio Antonioli ◽

Paolo Montagna ◽

Fabrizio Pepe ◽

Valeria Lo Presti ◽

...

Keyword(s):

Sea Level ◽

Middle Pleistocene ◽

Relative Sea Level ◽

Middle Pleistocene Transition

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New findings on palynofacies characteristics of semi-enclosed deep-sea environments in the East Sea over 2 million years

Scientific Reports ◽

10.1038/s41598-020-73493-3 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Yongmi Kim ◽

Sangheon Yi ◽

Chang-Pyo Jun ◽

Eunmi Lee ◽

Gil Young Kim

Keyword(s):

Sea Level ◽

Late Quaternary ◽

Source Area ◽

High Amplitude ◽

East Sea ◽

Coarse Grained ◽

Sea Level Changes ◽

Inorganic Particles ◽

New Findings ◽

Global Sea Level

Abstract Phytoclasts in the form of plant debris in terrestrial sediments can be transported by water to distant areas because they are lighter than inorganic particles. The semi-enclosed East Sea, which is connected by narrow straits to other seas, is adjacent to continental shelves that are the source area of terrestrial sediment flowing into the East Sea. These shelves alternated repeatedly between terrestrial and marine environments as a result of eustatic sea-level changes during the Late Quaternary. Palynofacies analyses of the IODP Exp. 346 U1430 core, located in the Eastern South Korea Plateau (ESKP) of the East Sea, have revealed changes in the size and concentration of phytoclasts associated with glacial–interglacial cycles. These changes are generally negatively correlated with the global sea-level curve, and their anti-phase cycles with high amplitude are clearly evident during the last ca. 750 ka with the geotectonic stabilization period. In particular, several coarse-grained phytoclasts were observed during the glacial period, including the Last Glacial Maximum (LGM). These findings suggest that the concentration and size of phytoclasts flowing into the East Sea were influenced by changes in the distance of the source area, depending on the water depth of the strait and nearby shelves owing to sea-level changes in tandem with glacial–interglacial cycles and geotectonic events.

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The role of orbital forcing in the Early Middle Pleistocene Transition

Quaternary International ◽

10.1016/j.quaint.2015.01.047 ◽

2015 ◽

Vol 389 ◽

pp. 47-55 ◽

Cited By ~ 38

Author(s):

Mark A. Maslin ◽

Christopher M. Brierley

Keyword(s):

Middle Pleistocene ◽

Orbital Forcing ◽

Middle Pleistocene Transition

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Reconstructions of Global and Regional Temperature Change for the Last 5 Myr

10.5194/egusphere-egu2020-12928 ◽

2020 ◽

Author(s):

Peter U. Clark ◽

Jeremy Shakun ◽

Yair Rosenthal ◽

Patrick Bartlein ◽

Peter Koehler ◽

...

Keyword(s):

Temperature Change ◽

Global Climate ◽

Sea Surface ◽

Orbital Forcing ◽

Average Global Temperature ◽

Climate Evolution ◽

Age Model ◽

Regional Temperature ◽

Global Reconstruction ◽

Global Sea Level

We use a global array of ~120 sea-surface temperature (SST) records based on Mg/Ca, alkenone, and faunal proxies to reconstruct global and regional temperature change over the last 5 Myr. All records are placed on the LR04 age model. Here we report the reconstructions and discuss their implications for characterizing global climate evolution (frequency, variance, transitions) over this interval and its relationship to changes in CO2, orbital forcing, and mean ocean temperature. Average global temperature has cooled by ~6.5oC since 5 Ma, with significant breakpoints tentatively identified at ~3.38 Ma, 1.34 Ma, and 0.88 Ma. We also invert the global reconstruction to reconstruct global sea level for the last 5 Myr.

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