Abstract and Figures

Established theories ascribe much of the observed long-term Cenozoic climate cooling to atmospheric carbon consumption by erosion and weathering of tectonically uplifted terrains, but climatic effects due to changes in magmatism and carbon degassing are also involved. At timescales comparable to those of Milankovitch cycles, late Cenozoic building/melting of continental ice-sheets, erosion and sea level changes can affect magmatism, which provides an opportunity to explore possible feedbacks between climate and volcanic changes. Existing data show that extinction of Neo-Tethyan volcanic arcs is largely synchronous with phases of atmospheric carbon reduction, suggesting waning degassing as a possible contribution to climate cooling throughout the early to middle Cenozoic. In addition, the increase in atmospheric CO2 concentrations during the last deglaciation may be ascribed to enhanced volcanism and carbon emissions due to unloading of active magmatic provinces on continents. The deglacial rise in atmospheric CO2 points to a mutual feedback between climate and volcanism mediated by the redistribution of surface masses and carbon emissions. This may explain the progression to higher amplitude and increasingly asymmetric cycles of late Cenozoic climate oscillations. Unifying theories relating tectonic, erosional, climatic, and magmatic changes across timescales via the carbon cycle offers an opportunity for future research into the coupling between surface and deep Earth processes.
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Magmatic Forcing of Cenozoic Climate?
Pietro Sternai
2
, Luca Caricchi
1
, Claudia Pasquero
2
, Eduardo Garzanti
2
,
Douwe J. J. van Hinsbergen
3
, and Sébastien Castelltort
1
1
Department of Earth Sciences, University of Geneva, Geneva, Switzerland,
2
Department of Earth and Environmental
Sciences, University of MilanoBicocca, Milan, Italy,
3
Department of Earth Sciences, Utrecht University, Utrecht,
Netherlands
Abstract Established theories ascribe much of the observed longterm Cenozoic climate cooling to
atmospheric carbon consumption by erosion and weathering of tectonically uplifted terrains, but climatic
effects due to changes in magmatism and carbon degassing are also involved. At timescales comparable
to those of Milankovitch cycles, late Cenozoic building/melting of continental ice sheets, erosion, and sea
level changes can affect magmatism, which provides an opportunity to explore possible feedbacks between
climate and volcanic changes. Existing data show that extinction of NeoTethyan volcanic arcs is largely
synchronous with phases of atmospheric carbon reduction, suggesting waning degassing as a possible
contribution to climate cooling throughout the early to middle Cenozoic. In addition, the increase in
atmospheric CO
2
concentrations during the last deglaciation may be ascribed to enhanced volcanism and
carbon emissions due to unloading of active magmatic provinces on continents. The deglacial rise in
atmospheric CO
2
points to a mutual feedback between climate and volcanism mediated by the redistribution
of surface masses and carbon emissions. This may explain the progression to higher amplitude and
increasingly asymmetric cycles of late Cenozoic climate oscillations. Unifying theories relating tectonic,
erosional, climatic, and magmatic changes across timescales via the carbon cycle offer an opportunity for
future research into the coupling between surface and deep Earth processes.
Plain Language Summary Among the most fascinating contemporary developments in the
Earth Sciences is the idea that plate tectonics and climate changes are coupled through complex cycles.
More than four decades of study have revealed tantalizing examples of relationships between processes near
the Earth's surface and deeper within. Accounting for such a surfacedeep Earth process coupling has
improved our understanding of major climate and tectonic events for virtually all timescales. So far,
however, the role of magmatism was overlooked. Magmatism exerts a strong inuence on the amount of
greenhouse gasses in the atmosphere because of volcanic outgassing. In turn, tectonic and climatic changes
control the transfer of rocks, water, and ice masses at the Earth surface and within the Earth's interior,
thereby affecting the production, transfer, and eruption of magmas. Unravelling the interactions between
surface and deep Earth processes accounting for magmatism will help managing natural resources and
mitigating natural hazards. Even more importantly, understanding how climate is naturally related to plate
tectonics and magmatism will allow scientists to assess the anthropogenic perturbations to the Earth system
and anticipate ongoing and future climate changes.
1. Rationale: Coupling Surface and Deep Earth Processes
Mountain ranges, sedimentary basins, subduction zones, volcanic arcs, oceanic ridges, and nearly all major
geological features testify uxes of geological materials occurring at and across the Earth's surface.
Interactions between the solid Earth (i.e., our planet's solid surface and its interior) and the uid Earth
(i.e., our planet's wet or icy surface and the atmosphere) are thus ubiquitous and occur across timescales
(e.g., Broecker, 2018). Correspondences between global climatic and tectonic changes throughout the
Cenozoic fostered our understanding of the evolution of mountain ranges (e.g., Molnar & England, 1990),
rock exhumation (Ruddiman, 1997), and the geological carbon cycle (e.g., Raymo & Ruddiman, 1992).
The main logical link to relate past climate and tectonic changes is their synchronicity. However, limited
temporal resolution in the geological archives prevents a clear recognition of the causative relationships
behind such changes. Which mechanisms control the coupling between surface and deep Earth processes?
Which are the characteristic timescales and magnitudes of the feedbacks involved? Answering these ques-
tions is still a challenge in the Earth Sciences (e.g., NAP, 2012; Frontiers, Media, 2015; Huntington et al.,
©2019. American Geophysical Union.
All Rights Reserved.
FEATURE ARTICLE
10.1029/2018JB016460
Key Points:
Waning volcanic degassing along
the southern Eurasian margin is a
possible cause of the longterm
Cenozoic climate cooling
A climate changevolcanism
feedback during glacialinterglacial
cycles explains the change in shape
of late Cenozoic climate oscillations
Correspondence to:
P. Sternai,
pietro.sternai@unimib.it
Citation:
Sternai, P., Caricchi, L., Pasquero, C.,
Garzanti, E., van Hinsbergen, D. J. J., &
Castelltort, S. (2020). Magmatic forcing
of Cenozoic climate? Journal of
Geophysical Research: Solid Earth,125,
e2018JB016460. https://doi.org/
10.1029/2018JB016460
Received 23 MAR 2019
Accepted 9 NOV 2019
Accepted article online 20 DEC 2019
STERNAI ET AL. 1of22
2017). A continuously growing body of observational constraints and advances in coupled processes
modeling increases opportunities to progress in this research.
Here, we focus on the Cenozoic (last ~65 Myr), which includes several welldocumented natural experi-
ments reporting on the coupling between solid and uid Earth processes (e.g., Miller et al., 1987; Zachos
et al., 2008). In section 2, we address processes occurring at multimillion years timescales. First, we review
an ongoing debate on causal relationships between the IndiaEurasia convergence and collision history and
climate cooling in the NeogeneQuaternary via erosion and weathering of tectonically uplifted terrains. We
then develop the debate supporting the hypothesis that variations in volcanic degassing due to extinction of
NeoTethyan volcanic arcs may have contributed to climate cooling since the Eocene. In section 3, we
address the coupling between surface and deep processes at timescales comparable to those of
Milankovitch cycles. Previous studies suggested that the waxing and waning of continental ice sheets, ero-
sion, and sea level changes during climate oscillations affect the volcanic activity. Here, a simple model of
radiative equilibrium is used to evaluate whether estimated variations of atmospheric CO
2
concentrations
due to volcanic changes induced by the surface mass redistribution throughout glacialinterglacial cycles
may affect the amplitude and symmetry of Pleistocene climate oscillations consistently with observations. In
section 4, we outline open questions and opportunities for research focused on the coupling between surface
and deep Earth processes. Quantifying feedbacks between climate and tectonics accounting for magmatism
is a compelling challenge to progress our understanding of the coupling between surface and deep Earth pro-
cesses, toward a holistic understanding of the functioning of the Earth system.
2. Solid Earth Control on Cenozoic Climate Cooling
The oxygen isotope composition of ocean sediments is sensitive to ocean temperature and ice volumes and
shows unsteady but continuous increase in δ
18
O values since ~50 Ma (Figure 1a). This implies longterm glo-
bal cooling following the late Paleoceneearly Eocene (~6050 Ma) climate warming (e.g., Zachos et al.,
2001). Antarctica was ice free until about ~30 Ma (e.g., Barrett et al., 1987; DeConto & Pollard, 2003;
Pagani et al., 2011), and glaciation of the Northern Hemisphere only started during the PlioQuaternary (last
~5 Myr; e.g., Raymo, 1994; Willeit et al., 2015). Thus, early Cenozoic δ
18
O trends are driven primarily by tem-
perature changes. The variability of the δ
18
O record increased after ~30 Ma and became even larger in the
last ~3 Myr, suggesting an increasingly dominant coupling with ice cover (e.g., Zachos et al., 2001; see
section 3). Enhanced differentiation of the midlatitude continents into areas of wetter and drier climates
is also inferred from the terrestrial fossil record and abundant glacial detritus blanketing middletohigh lati-
tudes worldwide (e.g., Ruddiman et al., 1989). For more than a century, scientists have been searching for
explanations for the Cenozoic climate evolution (e.g., Broecker, 2018; Chamberlin, 1899), often alluding
to a dominant, but still elusive, role of plate tectonics.
2.1. Tectonic Inuence on the Ocean and Atmosphere Circulation Patterns
Paleogeographic changes, involving the formation and destruction of oceanic corridors and orographic bar-
riers, are a straightforward mechanism through which plate tectonics may affect climate. Overall, global
temperatures decrease when increasing portions of energyabsorbing oceans at the tropics are replaced by
energyreective continental land (e.g., Crowley et al., 1987). However, continental migration toward the
tropics over the past 100 Myr is limited and unlikely to explain Cenozoic cooling (e.g., Barron, 1985;
Goddéris et al., 2014). Thermal insulation due to the development of the circumAntarctic currents, when
Antarctica separated from Australia in the middle to late Oligocene (e.g., Barrett et al., 1987; Kennett
et al., 1974), has also been invoked to explain synchronous cooling of Antarctica (e.g., DeConto & Pollard,
2003; Pagani et al., 2011). However, models suggest that this event would also reduce precipitation in the
polar region, in turn inhibiting the onset of glaciation (e.g., Oglesby, 1989). A longstanding idea is that
the emergence of the Isthmus of Panama in the late Pliocene may have triggered the onset of Northern
Hemisphere glaciations (e.g., Bartoli et al., 2005; Haug & Tiedemann, 1998; Raymo, 1994). However, numer-
ical simulations suggest that highlatitude cooling may also occur without the closure of the Panama gate-
way (e.g., MaierReimer et al., 1990; Murdock et al., 1997). An additional hypothesis is that Cenozoic true
polar wanderthe rotation of the Earth and mantle relative to the spin axis in response to change in solid
Earth density distributionsmay have preconditioned the northern Atlantic for glaciation (Steinberger
et al., 2015).
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Climatic effects have also been linked to late Cenozoic growth of the Tibetan Plateau, the greatest topo-
graphic feature on Earth, which is inferred to have perturbed atmospheric circulation at the scale of the
entire Northern Hemisphere (e.g., Ruddiman & Raymo, 1988; Ruddiman & Kutzbach, 1989; Molnar et al.,
2010). Topography in the Tibetan Plateau was built up in several steps, likely starting well before the colli-
sion between India and Asia (Murphy et al., 1997; Wang et al., 2017). Paleoelevations may have been com-
parable to the present since at least the late Oligocene (DeCelles et al., 2007; DupontNivet et al., 2008; Van
Der Beek et al., 2009), but estimated plateau elevations during the Eocene vary from near sea level to ~5 km
(e.g., Botsyun et al., 2019; Ding et al., 2014; Wei et al., 2016). Normal faulting in Tibet at about 13 Ma suggests
an increase in Plateau elevation at that time (Molnar et al., 1993; Murphy et al., 2009) and may have had cli-
matic effects such as initiation of aeolian accumulation in the main part of the Chinese Loess Plateau and the
onset of intense monsoonal circulation (e.g., Sun et al., 2008, 2014). Numerical models indicate that a low
altitude Tibetan Plateau before the Eocene would have resulted in a trend from equable moist temperate
Figure 1. Compilation of datasets reporting on Cenozoic trends. (a) δ
18
O, surface temperature, and the atmospheric CO
2
concentration required to yield the global
temperature change if climate sensitivity is 0.75 °C/W/m
2
(Hansen et al., 2013; Zachos et al., 2001). Orange dots show the CO
2
proxy records as from Beerling and
Royer (2011) and references therein (error bars are not shown for gure legibility). PETM, EECO and MECO stand for PaleoceneEocoene Thermal Maximum,
EarlyEocene Climate Optimum and MiddleEocene Climate Optimum, respectively. (b) IndiaAsia convergence (van Hinsbergen et al., 2011). (c) Mean Tibetan
Plateau elevation; solid line from Fielding (1996), dashed line from Xu (1981), and diamond from DeCelles et al. (2007). PreOligocene values (dotted line) are
speculative (see text). (d) Global sediment yield (Peizhen et al., 2001). (e) Magmatic activity (nonexhaustive list; see also section 2.2.2 and references therein).
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climates in the early Cenozoic to increased seasonality and regional differentiation of climate in the
Northern Hemisphere today (Ruddiman & Kutzbach, 1989), overall consistent with paleobotanical and
paleoenvironmental records (e.g., Hren et al., 2009; Xu, 1981). However, predictions do not include a
pronounced drop in highlatitude temperatures as the plateau elevations are increased, even when
feedbacks (e.g., snow albedo, sea ice, and mixedlayer ocean temperatures) are taken into account. The
development of high topography and/or the formation of marine sills or gateways alone thus seems
insufcient to drive the longterm Cenozoic evolution. Additional factors such as changes in atmospheric
or ocean composition are required (e.g., Raymo & Ruddiman, 1992).
2.2. Tectonic Inuence on the Geological Carbon Cycle
At timescales of millions to tens of millions of years, the geological carbon cycle modulates the storage of
carbon into rocks and the release of carbon into the ocean and atmosphere (e.g., Sundquist, 1985), thereby
linking the evolution of climate and life to plate tectonics (Figure 2). Variations in the ocean and atmosphere
concentration of radiative gases (particularly CO
2
) can alter the Earth's climate. These express a dynamic
equilibrium between sinks of carbon by chemical weathering of silicate minerals, precipitation/deposition
of carbonates in the ocean and burial of organic matter in sediments (e.g., Galy et al., 2007), and sources
of carbon by volcanic emissions, hydrothermal systems, and metamorphism (e.g., Walker et al., 1981;
Berner & Lasaga, 1989; Berner, 2003). Relevant reactions can be simplied as
CaSiO3þCO2CaCO3þSiO2
Geological proxies suggest decreasing atmospheric CO
2
levels since the Triassic followed by an early
Cenozoic (~6050 Ma) increase in CO
2
values (Figure 1a), including the PaleoceneEocene Thermal
Maximum at ~55.5 Ma and the EarlyEocene Climate Optimum at 52.950.7 Ma (e.g., Anagnostou et al.,
2016; Beerling & Royer, 2011; Hansen et al., 2013; Zachos et al., 2001). Then, two subsequent phases of
reduction of atmospheric CO
2
concentrations occurred. The rst phase lasted until the Oligocene and
included ~500 kyr of climate amelioration, the middle Eocene Climate Optimum, at ~40 Ma (e.g., Sluijs
et al., 2013). The second phase began in the middle Miocene and continues today (although it is currently
outpaced by shortterm natural and anthropogenic emissions). Two endmember hypotheses have been for-
mulated to explain the longterm Cenozoic cooling via a tectoniccontrolled reduction in atmospheric car-
bon levels: Climate cooling may be driven either primarily by an increase in the global weathering rate
(the main sink of surface carbon) on the one hand and by a decrease in the global degassing rate (the main
source of surface carbon) on the other hand. We review these two hypotheses hereafter.
2.2.1. Increase in Global Weathering
Chemical weathering is a function of continental relief (e.g., Raymo et al., 1988; Ruddiman, 1997; Von
Blanckenburg, 2006). During the Cenozoic, the convergence between India and Eurasia resulted in the
deformation, uplift, and erosion of the Indian passive margin in the Himalayas, and in the formation of
Figure 2. Schematic representation of sources and sinks of surface carbon.
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the Tibetan Plateau in Southern Asia. In this region, incident solar heating in summer drives the strong
atmospheric convection and rainfall associated with the Asian monsoon (e.g., Molnar et al., 1993). The pre-
sence of a large elevated plateau in the proximity of a warm ocean leads to very high weathering rates in the
Himalayan region (Pinet & Souriau, 1988). Time constraints on the growth of the Tibetan Plateau to present
day elevations, however, are ambiguous (e.g., Botsyun et al., 2019; van Hinsbergen & Boschman, 2019;
Figures 1b and 1c and section 2.1), which hampers establishing a straightforward correlation between cli-
mate cooling and the reduction of atmospheric CO
2
concentration due to HimalayanTibetan uplift and
associated enhanced weathering. As an alternative or complementary mechanism, Jagoutz et al. (2016) pro-
pose atmospheric CO
2
drawdown due to weathering of mac and ultramac rocks between ~50 and 40 Ma
(see also Macdonald et al., 2019).
The shift toward a cooler and stormier climate may have affected erosion also through a change from uvial
to glacialdominated conditions since the PlioQuaternary (e.g., Molnar & England, 1990). The possible four-
fold to vefold increase in sediment deposition rates in most marine and oceanic basins since ~5 Ma
(Figure 1d) would suggest increased erosion of most orogenic belts worldwide, ascribed to the onset of the
Northern Hemisphere glaciation (e.g., Hay et al., 1988; Donnelly, 1982; Peizhen et al., 2001). Molnar and
England (1990) further proposed that enhanced erosion and valley carving in the PlioQuaternary would
explain inferred synchronous uplift of mountain peaks worldwide (e.g., in the Alps, Pyrenees, and Tibet)
through isostatic rebound of orogens following unloading. This idea provoked ongoing controversies
because a global increase in mountain erosion should increase global weathering and CO
2
consumption
(e.g., Riebe et al., 2004) and thus be the cause rather than the effect of climate cooling. On the one hand,
the global increase in erosion and sedimentation may be related to a preservation bias in the sedimentary
record (i.e., Sadler effect; Willenbring & von Blanckenburg, 2010; Willenbring & Jerolmack, 2016). On
the other hand, the thermochronological record, which should be insensitive to preservation biases, corro-
borates the worldwide acceleration of mountain erosion (Herman et al., 2013). Although the analysis by
Herman et al. (2013) was recently questioned (Schildgen et al., 2018), a number of geochemical proxies
(e.g., Li and Sr isotopes) suggest a change in ocean composition during the late Cenozoic that may be related
to increased worldwide erosion and weathering (e.g., Broecker, 2018; Edmond, 1992; Misra & Froelich,
2012). Assessing the links between mountain uplift, erosion, and weathering has been a major concern of
research regarding the surfacedeep Earth processes coupling. However, it remains unclear whether tec-
tonics controls climate through mountain uplift, erosion, and weathering or rather if climate forces moun-
tain uplift through erosion and isostatic rebound during the late Cenozoic. Despite a lack of consensus, more
than four decades of intense debate suggest that a mutual feedback between tectonic uplift of mountain
ranges and climate cooling via erosion and weathering does exist. Alternatively, or in addition, changes of
global degassing rate following major tectonic events contributed to Cenozoic climate changes (e.g.,
Johnston et al., 2011; McKenzie et al., 2016; Brune et al., 2017; Godderis & Donnadieu, 2017), a possibility
that is examined in more detail below.
2.2.2. Decrease in Global Degassing
Although climate cooling since the Triassic has been shown to correlate with changes in plate boundary
magmatism (e.g., Li & Eldereld, 2013; Van Der Meer et al., 2014), the decrease in global volcanic degassing
hypothesis received less attention compared to the increase in global weathering model of Cenozoic climate
cooling. The overall temporal correspondence between waning of NeoTethyan volcanism and major cli-
mate deterioration throughout the Eocene and early Oligocene suggests a direct causal relationship between
these observations. Yet, as we shall outline hereafter, other major geodynamic events occurred at roughly
the same time and may have conditioned volcanic outgassing and the Cenozoic climate history. In addition,
the extinction of volcanic arcs is inherently related to orogenic processes, which involve changes in erosion
and weathering. Thus, the contributions of magmatic and weathering changes to the Cenozoic climate evo-
lution are related. Our purpose here is to point out the potential climatic implications of magmatic changes
throughout the Cenozoic, while constraining both contributions of magmatism and weathering to Cenozoic
climate changes should be the objective of future research.
2.2.2.1. NeoTethys Closure and Associated Magmatism
Throughout the Mesozoic and into the Eocene, the NeoTethyan seaways extended eastwest for more than
15,000 km (e.g., Seton et al., 2012). In the Late Cretaceous, the NeoTethys Ocean included a composite,
eastwest trending subduction system about 13,000 km long, with associated volcanic arcs along the
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southern continental margin of Eurasia and within the Neotethys ocean (e.g., Dercourt et al., 2000; Stampi
& Borel, 2002; Mafone et al., 2017; Guilmette et al., 2018). A doublesubduction system is unequivocal
between Arabia and Eurasia (e.g., Agard et al., 2007; van Hinsbergen, Mafone, et al., 2019) and was also
proposed to have existed between India and Asia (e.g., Aitchison et al., 2007; Jagoutz et al., 2015), although
the evidence there is debated (e.g., Hu et al., 2016; Huang et al., 2015). In any case, subduction of Indian plate
lithosphere remained active until well after initial collision of the northernmost continental crust of the
Indian plate with Asia (Figure 3). The timing of initial IndiaAsia collision is also controversial, with pro-
posed ages from >60 and <35 Ma (e.g., Molnar & Tapponnier, 1975; Searle et al., 1987; Garzanti et al.,
Figure 3. Paleotectonic maps of the NeoTethyan margin (modied after the paleotectonic reconstructions by the DARIUS program, 2018, http://istep.dgs.jussieu.
fr/darius/maps.html).
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1987; Aitchison et al., 2007; Bouilhol et al., 2013; Orme et al., 2015; Garzanti, 2008), partly depending on the
assumed denition of continental collision (e.g., the end of marine sedimentation versus the end of ocean
continent subduction) or the method used to constrain the age of collision (e.g., stratigraphy,
sedimentology, and style of deformation). The arrival of the edge of the Indian continental margin at the
trench adjacent to southern Tibet (Beck et al., 1996) has been recently constrained as 59 ± 1 Ma (Decelles
et al., 2014; Wu et al., 2014; Hu et al., 2015).
The climax of arc magmatism, however, trailed initial collision by some 7 Myr and is followed by progressive
demise. Evidence of extensive Late Cretaceous to Paleogene volcanic activity is widespread along the south-
ern margin of Eurasia (Figure 3). In southern Tibet, the Gangdese volcanic arc was voluminous until early
Eocene times (e.g., Dewey et al., 1988; Treolar et al., 1996; Yin & Harrison, 2000) and recorded an ignimbrite
areup stage around 52 Ma (e.g., Ji et al., 2009; Zhu et al., 2015), followed by return to background activity
and slow extinction lasting until the late Eocene (e.g., Sanchez et al., 2013). The shortlived magmatic are
up is in striking coincidence with the EarlyEocene Climate Optimum, suggesting a causeeffect relationship
between the magmatic and climatic event, a possibility that was only marginally investigated thus far.
Subduction of the carbonaterich Indian passive margin succession in the middle Paleocene may have
enhanced carbon recycling at the Transhimalayan volcanic arc (e.g., Kent & Muttoni, 2008; van
Hinsbergen et al., 2019; Hoareau et al., 2015). Hoareau et al. (2015) modeled the volume of subducted mate-
rials and the amount of CO
2
emitted along the northern Tethyan margin and the effects of estimated CO
2
uxes on global climate. Enhanced CO
2
degassing due to subduction of thicker Indian continental margin
sediments after ~60 Ma would raise surface temperatures to some extent, consistently with the observed
early Eocene climate warming. Similarly, Kerrick and Caldeira (1994) suggested that carbon degassing
due to metamorphism of Indian margin rocks along the Himalayan belt enhanced paleoatmospheric carbon
levels, although revised estimates point to a minor contribution to early Eocene warming (Kerrick &
Caldeira, 1998). A reduction of carbon dioxide emissions is inferred between ~50 and 40 Ma, synchronous
with the observed phase of climate cooling, when Tibetan arc volcanism was waning after collision between
India and Eurasia (Hoareau et al., 2015; Jagoutz et al., 2016; Figure 1).
Between ~50 and ~35 Ma there has been the demise of a highly productive magmatic arc/backarc system
across much of Iran and adjacent areas (e.g., Agard et al., 2011; Schleiffarth et al., 2018). This magmatism
was a net source of atmospheric CO
2
. Peak magmatism along the ArabiaEurasia margin between ~45
and 40 Ma (e.g., Kazmin et al., 1986; Alpaslan et al., 2004; Arslan & Aslan, 2006; Vincent et al., 2005;
Figure 1e) could have promoted a rise in atmospheric carbon concentrations during the middle Eocene cli-
mate optimum (Allen & Armstrong, 2008), which was previously attributed to an unspecied rise in igneous
activity (Bohaty & Zachos, 2003). Only limited volcanic activity persisted into the Oligocene in Iran, though
minor and sporadic magmatic events continue until the present (e.g., Pearce et al., 1990). Waning arc mag-
matism during the late Eocene in Iran and Anatolia is consistent with synchronous compressional deforma-
tion and topographic uplift (e.g., Allen & Armstrong, 2008; Gürer & van Hinsbergen, 2019; Vincent et al.,
2005). The reduction in arc magmatism would have diminished carbon degassing into the atmosphere,
and consequently global temperatures, consistently with observations (Figures 1e and 3).
2.2.2.2. Examples of Other Major Geodynamic Events and Associated Magmatic Changes
Obviously, this is not to dismiss the possible contribution of magmatic activity from igneous provinces other
than the Southern Eurasian margin to early or middle Cenozoic climate changes. For instance, propagation
of the Atlantic midocean spreading between Eurasia and Greenland along the Reykjanes Ridge occurred by
~58 Ma (e.g., Seton et al., 2012; Figure 4) and the associated release of carbon likely contributed to the early
Eocene climate amelioration. In the Caribbean region, there was continental underthrusting and ophiolite
emplacement between 50 and 40 Ma on Cuba and Hispaniola (e.g., Boschman et al., 2014; IturraldeVinent
et al., 2008), which may have contributed to waning global outgassing. Starting at ~39 Ma, large volumes of
magmas were erupted from several volcanic centers in the Basin and Range, where magmatism ended by
~33 Ma (Gans, 1989), in remarkable synchronicity with the nal phases of latest Eocene climate cooling.
Ophiolite emplacement on Kamchatka and the Kuriles and the subsequent onset of subduction along the
Aleutian and the Kuril trenches following arccontinent collision in Kamchatka and, farther south, along
the IzuBoninMarianas trench over a length comparable to that of the NeoTethyan margin occurred
around ~50 Ma (e.g., Konstantinovskaia, 2001; Ishizuka et al., 2011; Domeier et al., 2017; Vaes et al., 2019;
Figure 4). However, intraoceanic subduction zones commonly involve small amounts of carbon emissions
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because few carbonate sediments are subducted (e.g., Johnston et al., 2011), either due to the distance from
the continents or because intraoceanic trenches are typically deeper than the carbonate compensation
depth. Tertiary volcanism in the Great Basin of western United States began in the Eocene with predomi-
nantly effusive and explosive volcanism and ended with late Oligocene and Miocene (~2615 Ma) ignimbrite
eruptions (Gans, 1987). Similarly, increased convergence rate normal to the Chilean Andes at ~25 Ma was
followed by broadening of the volcanic arc into adjacent portions of Bolivia and Argentina (Pilger, 1984).
The number of volcanic ash layers and volumetric estimates of igneous rocks erupted in the circum
Pacic region suggest increased volcanism in the Miocene (e.g., Donnelly, 1973; Kennett et al., 1977).
These events may well have contributed to early and middle Miocene climate warming through enhanced
carbon degassing (Kashiwagi & Shikazono, 2003). Although a number of previous global analyses show clear
temporal correlations between volcanism and climate changes in the Paleozoic and Mesozoic (e.g., Lee et al.,
Figure 4. Global plate reconstruction at ~60 and ~40 Ma (modied after Seton et al., 2012). Blue and red lines show major subduction zones or thrusts and oceanic
ridges or transform, respectively. The green line in the upper panel shows the position of India as suggested from the sedimentary and stratigraphic record
(e.g., Hu et al., 2015), instead of the seaoor spreading history and global plate motion reconstruction (Seton et al., 2012). Yellow arrows point to major modi-
cations of plate boundaries involving potentially signicant magmatic changes: Demise of the NeoTethyan volcanic arc, onset of the IzuBoninMarianas sub-
duction, and propagation of ocean spreading between Greenland and Eurasia. Black arrows show the direction of motion of tectonic plates.
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2013; McKenzie et al., 2016; Van Der Meer et al., 2014), these correlations
have been barely tested for the entire Cenozoic.
2.3. Modeling Climatic Effects of NeoTethyan Arc Extinction
A globalscale analysis is required to assess thoroughly the potential mag-
matic control of Cenozoic climate changes. However, we emphasize here
the role played by progressive extinction of NeoTethyan volcanic arcs
during the Eocene (i.e., until ~35 Ma; Figures 1 and 3) and of the conse-
quent reduction in global carbon emissions, which must have contributed
at least to some extent to longterm Cenozoic climate cooling. To evaluate
the climatic effects of the extinction of NeoTethyan volcanic arcs, it is
necessary to translate uxes of erupted magma into carbon uxes. We
have calibrated this relationship using the Indonesian arc as a modern
analogue of the early Cenozoic NeoTethyan arc, because (i) it lies along
the same plate margin, (ii) it shared a similar preCenozoic and early
Cenozoic tectonic and paleogeographic evolution, and (iii) it measures
about the same length as the eastern NeoTethyan margin (preIndia
Eurasia collision) and western NeoTethyan margin (preArabiaEurasia
collision; e.g., Ricou, 1994; Hall, 2002).
According to Burton et al. (2013, and references therein), estimated mod-
ern carbon emissions from the Indonesian volcanic arc contribute to glo-
bal natural volcanic emissions by 110%. If these reference values are used
as forcing terms for GEOCARB III models of the atmospheric pCO
2
and
temperature evolution (Archer et al., 2009; Berner & Kothavala, 2001)
and all other variables are kept constant, then predictions show cooling
trends consistent in magnitude and timescale with that observed between,
for example, 50 and 45 Ma (Figures 1 and 5). These rstorder estimates
are consistent with previous modeling efforts (e.g., Kashiwagi &
Shikazono, 2003) and suggest that a causal link between extinction of the NeoTethyan volcanic arcs and cli-
mate cooling throughout the EoceneOligocene is plausible.
We hope that these considerations may stimulate more thorough and systematic globalscale research efforts
focused at constraining the relationships between magmatism and climate changes throughout the
Cenozoic. We particularly stress that even though orogenic processes and the arrest of arc volcanism asso-
ciated with continental subduction/collision are considered to produce effects on climate through enhanced
erosion/weathering and reduced outgassing, respectively, the relationships between continental
subduction/collision and magmatic activity are to date particularly poorly constrained.
3. Mutual Feedback Between Quaternary Climate and Volcanism
If climate changes are related to variations of the magmatic activity at long and intermediate timescales, then
climate and magmatism may be even more tightly linked at short timescales such as those of Milankovitch
cycles. Over the late Pliocene and Quaternary, benthic δ
18
O values of deepsea sediments and the Antarctic
ice core records (see upper panels in Figure 6) show global temperature and ice volume oscillations, both
expressions of glacialinterglacial cycles (e.g., Lisiecky & Raymo, 2007). Variations of insolation (i.e., solar
energy received on the Earth's surface) and atmospheric CO
2
concentrations are primary drivers of climate
oscillations and associated glacialinterglacial cycles (e.g., Bereiter et al., 2015; Imbrie, 1984). These show a
puzzling progressive increase in amplitude and shift toward longer cooling than warming trends over the
late Pleistocene (e.g., Lisiecky & Raymo, 2007). Because the parameters of the Earth's orbit vary within rela-
tively stable boundaries at systematic Milankovitch periodicities and the solar radiation is constant at Myr
timescales, it is safe to assume that the insolation curve maintained its amplitude and symmetry throughout
at least the Quaternary (e.g., Broecker & Donk, 1970). Therefore, the change in shape of late Pleistocene cli-
mate oscillations must be driven by dynamics internal to the Earth system (e.g., Ashkenazy & Tziperman,
2004; Huybers, 2007; Liu & Herbert, 2004; Raymo, 1992). We hereby evaluate the possibility that such
dynamics involve a feedback loop between glacialinterglacial cycles and volcanism via the
Figure 5. Estimated surface temperature change using the GEOCARB III
model (http://climatemodels.uchicago.edu/geocarb/) imposing a decrease
in global CO
2
degassing rate by 1% (dashed line) and 10% (solid line) from a
spinup CO
2
degassing rate of 10 × 10
12
mol/a. The reader is referred to
Berner and Kothavala (2001), specially Appendix 1, and Archer et al. (2009)
for the relevant equations in GEOCARB III. Imposed boundary conditions
are shown on the plot.
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building/melting of ice sheets, erosion, and volcanic CO
2
degassing that affected the shape of late
Pleistocene climate oscillations, as previously hypothesized by, for example, Huybers and Langmuir (2009).
3.1. GlacialInterglacial Cycles and the Forcing on Volcanism
In the past few decades, it has been proposed that climate changes may affect volcanic activity (Kutterolf
et al., 2019, and references therein). Studies of several glaciated regions worldwide (e.g., Sigvaldason et al.,
1992; MacLennan et al., 2002; Nowell et al., 2006; Rawson et al., 2015; Praetories et al., 2016) showed a sig-
nicant increase in subaerial volcanic activity during postglacial warming. Huybers and Langmuir (2009)
analyzed a global record of subaerial volcanic eruptions back to the last glacial period and showed an
increase in eruption frequency of at least 50% during deglaciation. This correspondence is classically
explained by a deglacialtriggering hypothesis (Hall, 1982), according to which the removal of ice caps dur-
ing interglacials and associated continental lithospheric unloading leads to increased subaerial volcanic
activity by reducing the conning pressure within crustal magma chambers (e.g., Sigvaldason et al., 1992;
Jellinek et al., 2004; Pagli & Sigmundsson, 2008) and enhancing mantle melting (e.g., Jull & McKenzie,
1996; Tuffen, 2010). The modeling of Sternai et al. (2016) further indicates that erosion changes during
glacialinterglacial cycles may produce similar unloading effects on magmatism as the melting of continen-
tal ice sheets.
Several authors identied relationships between volcanic cycles and orbital forcing at ~23, ~41, and ~100 kyr
(Milankovitch, cycles). Paterne et al. (1990) recognized ve periods of enhanced volcanic activity of the
Figure 6. (a) Global δ
18
O (Zachos et al., 2001) and temperature (Hansen et al., 2013) curves and tephra frequency in the Northwest Pacic drill (Prueher & Rea,
2001) over the last 5 Ma. The histogram is a threepoint moving average after binning into 100 ka slots (see also Kutterolf et al., 2019). Periods of increased volcanic
activity around the Pacic Ocean are shown in the lower panel (Kennett & Thunell, 1975; Kennett et al., 1977; Hein et al., 1978; Cambray & Cadet, 1994;
Shane et al., 1995; Carey & Sigurdsson, 2000). (b) Global δ
18
O curve (Zachos et al., 2001) and tephra frequency at the Izu Bonin Mariana arc (central panel, using 10
ka binning after Schindlbeck et al., 2018) and the Pacic Ring of Fire (lower panel, using 1 ka binning after Kutterolf et al., 2013). The Middle Pleistocene
Transition leads from dominant ~40 ka periodicity of climate oscillations to dominant ~100 ka cycles. Vertical gray bars mark marine isotope stages (MIS) after
Railsback et al. (2015).
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Campanian province (Italy) with an ~23 kyr periodicity, correlating also with compositional changes in vol-
canic products. McGuire et al. (1997) observed enhanced tephra accumulation in the Mediterranean every
~22 kyr throughout the last ~80 kyr, correlating with the rate of sea level change. Glazner et al. (1999) inves-
tigated the distribution of intraplate volcanic events in eastern California over the last 800 kyr and found a
correlation with glacial maxima. Jellinek et al. (2004) found an ~40 kyr periodicity (and more ambiguous ~17
and 23 kyr periodicities) in the rst 400 kyr of the same data set as that of Glazner et al. (1999) and showed
that periods of fast ice volume reduction anticipate volcanic pulses by ~3 and ~11 kyr for silicic and basaltic
magmas, respectively. Schindlbeck et al. (2018) analyzed the ~1.1 Myr long tephra record of the IzuBonin
arc (within the IODP Hole U1437B) and showed statistically signicant spectral peaks with ~100 kyr periodi-
city (Figure 6), occurring systematically a few thousands of years after glacial maxima over the last ~0.7 Myr.
Kutterolf et al. (2013) compiled a time history of volcanism from around the Pacic Ring of Fire, which
accounts for about half of the global length of active plate subduction, and recognized an ~41 kyr periodicity,
a correlation with the highest rate of decreasing global ice volumes, and a time lag between deglaciation and
volcanic peaks of ~4 kyr. Further largescale magmatic effects are observed in response to major modica-
tions of surface conditions. Cambray et al. (1995) and Prueher and Rea (1998, 2001) emphasize the synchron-
ism between the onset of the Northern Hemisphere glaciation at ~2.5 Ma and intense volcanic activity all
around the North Pacic Ocean possibly due to sea level lowering (Figure 6), a link that was already
hypothesized by Kennett and Thunell (1975). Sternai et al. (2017) proposed a link between sea level drop
during the Messinian salinity crisis and a pulse of magmatic events in Mediterranean igneous provinces.
Melting ice sheets on land has the downstream consequence of raising sea level. This would imply that sub-
marine volcanism may be inhibited by a deeper water column at the same time as subaerial volcanic erup-
tions are enhanced by glacial unloading on land. The seaoor bathymetry, primarily determined by oceanic
crustal thickness, suggests a sensitivity of midocean ridge volcanism to sea level changes on Milankovitch
timescales (e.g., Crowley et al., 2015; Lund & Asimow, 2011; Schindlbeck et al., 2018; Tolstoy, 2015). A peak
of hydrothermal activity ~15 ka after the last glacial maximum on the MidAtlantic Ridge (Middletone et al.,
2016), Juan de Fuca Ridge (Costa et al., 2017), and at the East Pacic Rise (Lund et al., 2016) has been inter-
preted as the delayed melt formation following the hydrostatic pressure minimum.
3.2. Volcanic Forcing on the Shape of GlacialInterglacial Cycles
The solid Earth vents CO
2
into the atmosphere through volcanism and magmatic processes, which appear to
vary in response to the redistribution of the surface ice, water, and rock masses during glacialinterglacial
cycles. Because changes in CO
2
removal rate by chemical weathering have a negligible effect on timescales
comparable to those of glacialinterglacial cycles (e.g., Le Hir et al., 2009; Colbourn et al., 2015), the follow-
ing question arises: Can variations of global CO
2
volcanic degassing driven by glacialinterglacial cycles
affect the shape of climate oscillations? Since glaciation and deglaciation produce anticorrelated variations
in subaerial and submarine volcanism (see section 3.1), the relative magnitude of these effects has to be
quantied to answer the question.
Assuming that emissions are proportional to the frequency of eruptions, Huybers and Langmuir (2009) esti-
mate the global evolution of volcanic CO
2
emissions since 40 ka (Figure 7a). Their model indicates an atmo-
spheric CO
2
reduction by 520 ppm during the last glacial period (~4018 ka), marginally consistent with the
observed ~20 ppm decrease in atmospheric CO
2
data from the Dome C and Taylor Dome Antarctic ice cores
(Indermühle et al., 2000; Monnin et al., 2004). During the initial phase of deglaciation (~1813 ka) their model
suggests a 540 ppm increase in CO
2
concentration, whereas observations show an ~50 ppm increase. During
advanced deglaciation (~137 ka), the reconstruction indicates a 1570 ppm increase in volcanic CO
2
, consis-
tent with the observed ~40 ppm increase. According to their analysis, equilibration with oceanic volcanism
compensates for up to ~20% of the increase in subaerial volcanic CO
2
ux during the deglaciation. The overall
consistency between estimated volcanic emissions by Huybers and Langmuir (2009) and observed atmo-
spheric concentrations of CO
2
suggests that volcanic changes may indeed be primary drivers of the glacial
interglacial climate variability. Huybers and Langmuir (2009) construct their time history of CO
2
uxes using
eruption frequencies rather than unloading histories, and so the potential contribution of erosion to increased
volcanic degassing during the deglaciation (Sternai et al., 2016) is already accounted for. However, the contri-
bution of erosion changes to unloading of active magmatic provinces is not acknowledged in the classic
deglacialtriggering hypothesis of volcanic events (e.g., Hall, 1982; Sigvaldason et al., 1992; Jull &
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McKenzie, 1996; Jellinek et al., 2004; Pagli & Sigmundsson, 2008; Tuffen, 2010). It thus seems important to
remark here that given the density contrast between ice and surface rocks, erosion rate changes by ~1
mm/a or higher during deglaciation unload continents by a similar or greater amount than the melting of
ice sheets (Sternai et al., 2016). Longterm proxies of global sediment efux from mountainous regions
show just such erosion rate variability (e.g., Peizhen et al., 2001; Koppes & Montgomery, 2009; Herman
et al., 2013; Figures 7b and 7c). At secular to millennial timescales, erosional uxes may be even higher
(e.g., Koppes & Montgomery, 2009) and subject to strong variations due to modications of the subglacial
hydraulic system and water supply (e.g., Andrews et al., 2014; Flowers & Clarke, 2002; Herman et al., 2011;
Sternai et al., 2013). The abrupt and highmagnitude magmatic pulses involved by such erosional changes
are likely to force centennialto millennialscale variations of atmospheric greenhouse gases seemingly
unrelated to ocean dynamics (e.g., Marcott et al., 2014). In addition, while reduced submarine volcanism
due to sea level rise during interglacials buffers increased subaerial CO
2
emissions, the erosional forcing on
subaerial emissions is unbalanced because the downstream effect of erosion is depositional loading of
epicontinental or abyssal marine basins mostly located away from oceanic ridges.
Figure 7. (a) CO
2
concentrations from the Dome C and Taylor Dome Antarctic ice cores 4 (dots), and the data smoothed over a 2 ka window (solid line) follow the
left axis. Modeling results by Huybers and Langmuir (2009) constraining the contribution to atmospheric CO
2
from volcanic activity (dashed line) follow the right
axis. The dark and light gray shaded regions represent the 90% condence interval on the modeling estimates and the interglacial period, respectively. (b) Boxes
represent ranges of erosion rates from glaciated catchments or proximal basins including errors in estimations (vertical) and resolved timescale (horizontal;
Brandon et al., 1988; Hallet et al., 1996; Sheaf et al., 2003; Reiners et al., 2003; Koppes et al., 2006; Hebbeln et al., 2007; Geirsdottir et al., 2007; Berger & Spotila, 2008;
Koppes et al., 2009; Cowton et al., 2012; Herman et al., 2013; Herman & Brandon, 2015). AL, Alaska; SA, Southern Andes; GR, Greenland; NO, Norway; PNW,
Pacic Northwest; IC, Iceland. The vertical dashed line represents the approximate time since the LGM (Lisiecky & Raymo, 2007). (c) Estimated continental
unloading rate owing to constant melting of 1,000 m of ice (dotted line for reference) and erosion (assuming a surface rock density of 2,700 kg/m
3
) throughout the
interglacial. (d) Equilibrium change in global mean surface air temperature resulting from increasing atmospheric CO
2
concentrations (see text for detail).
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It thus seems plausible that enhanced subaerial volcanic degassing due to combined ice melting and erosion
may account for all of the observed ~90 ppm increase in atmospheric CO
2
concentration during the degla-
ciation, that is, an increase of ~50% with respect to glacial concentrations (Figures 7a and 7d). Arrhenius
law may be used to calculate the resulting radiative forcing, rf, so that rf ¼α·ln C
C0where αis a constant
and C
C0is the relative increase in CO
2
concentration. The equilibrium change in global mean nearsurface
air temperature, T
s
, is then calculated as T
s
=λ·rf, where λis the climate sensitivity. Assuming λequal
to 0.8 K/W/m
2
(e.g., Royer et al., 2007), a T
s
of about 2 °C solely due to volcanic changes throughout
glacialinterglacial cycles should be expected (Figure 7d). This volcanic forcing of temperature oscillations
is concordant and largely in phase with that related to variations of the Earth's albedo during formation
and melting of continental ice caps, producing an additional gain of surface temperatures through glacial
interglacial cycles of comparable magnitudes (e.g., Broccoli & Manabe, 1987; Dickinson et al., 1987;
Meehl & Washington, 1990). A gain of temperature oscillations by up to ~4 °C during the late Pleistocene
with respect to prior the onset of the Northern Hemisphere glaciation is consistent with observations
(Hansen et al., 2013; see top panel in Figure 6a). An increase in the amplitude of temperature oscillations
is also observed after the EoceneOligocene boundary, when the Antarctic ice sheet is established
(Figure 1a). The mutual inuence between volcanism and climate oscillations in the presence of continental
ice sheets, amplied by albedo effects and larger continental ice volumes in the Pleistocene, may thus repre-
sent a primary driver of the late Cenozoic progression toward higheramplitude climate oscillations.
The climatevolcanism feedback during glacialinterglacial cycles would also generate the asymmetric cool-
ing and warming trends of late Pleistocene climate oscillations (e.g., Lisiecky & Raymo, 2007). The main
logic is that inhibition of subaerial eruptions during glacial periods forces accumulation of gasses in mag-
matic reservoirs, which are then released over a few thousands of years during the early interglacials (e.g.,
Jellinek et al., 2004). Assuming that the longterm weathering CO
2
sink is at equilibrium with the steady
state volcanic CO
2
outgassing, the weathering carbon sink slightly dominates over inhibited volcanic carbon
emissions when ice sheets grow, leading to a temporary reduction of atmospheric CO
2
, which sustains cli-
mate cooling. As soon as the orbital forcing of solar radiation overtakes the threshold to trigger the deglacia-
tion, enhanced volcanic carbon outgassing dominates over the weathering carbon sink, in turn fostering
climate warming and bringing the overall atmospheric CO
2
budget back to equilibrium. If, for instance,
enhanced outgassing is extinguished in ~10 ka, then the cooling phase is forced to ~30 ka for early
Pleistocene 40 ka cycles and to ~90 ka for late Pleistocene 100 ka cycles. The ~10 ka time window is chosen
arbitrarily, but the duration of warming of late Pleistocene climate oscillations and the expected response
time of magmatic systems to surface load changes constrain this value (e.g., Jellinek et al., 2004; Lisiecky
& Raymo, 2007). Because both constraints are largely independent on the period of climate oscillations
(i.e., 40 or 100 ka), xing the duration of the phase of enhanced outgassing allows us to speculate that the
longer the period of climate oscillations, the longer the phase of gas accumulation in magmatic reservoirs,
the larger the outgassing rate during the phase of enhanced emissions, and the more pronounced the asym-
metry between warming and cooling trends (Figure 8). This is consistent with the increasing amplitude and
asymmetry of climate oscillations throughout the midPleistocene transition from dominant 40 to 100 ka
cycles (e.g., Lisiecky & Raymo, 2007). We hope that this statement may trigger and motivate further research
on the volcanoclimatic feedback during glacialinterglacial cycles.
4. SurfaceDeep Earth Processes Coupling: Challenges and Opportunities
Once plate tectonics theory became established (e.g., Le Pichon, 1968; McKenzie & Parker, 1967), the corre-
spondences between major geodynamic, magmatic, and climatic changes were readily recognized (e.g.,
Kennett & Thunell, 1975; Kennett et al., 1977; Ziegler et al., 1979; Raymo & Ruddiman, 1992; McKenzie
et al., 2016). Assessing the physical mechanisms and chemical reactions that allow for the surfacedeep
Earth processes coupling has been a major concern of research ever since. Scientists focused on processes
such as mountain building, erosion, and the waxing and waning of continental ice sheets. Disassembling
a complex system of interactions into simpler relationships has been the main approach to progress on this
research, and a broad range of geological data sets were used to develop theories relating mountain building
and erosion, and next erosion and atmospheric CO
2
consumption. However, at the multimillion years time-
scale, besides erosion and weathering of uplifted terrains, mountain building following continental
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collision/subduction involves the closure of oceanic seaways and is typically followed, after a certain time
lapse, by extinction of volcanic arcs, which also impact on climate. Early Cenozoic climate cooling is
widely ascribed to atmospheric carbon consumption due to enhanced erosion and weathering following
initiation of Himalayan growth, but Paleocene closure of NeoTethys and nal waning of arc magmatism
are currently unconstrained factors. In addition, the ~10 Myr long phase of climate warming preceding
the onset of the Cenozoic cooling trend cannot be readily explained by theories referring only to
enhanced weathering following topographic uplift because enhanced weathering involves a reduction of
atmospheric CO
2
and thus climate cooling. Similarly, known effects of surface processes on magmatism
and of magmatism on climate have not been duly considered to assess whether enhanced erosion
following mountain building led to the onset of glaciation in the late Cenozoic or the onset of glaciation
enhanced erosion rates and lithospheric unloading, thereby increasing mountain uplift through isostatic
adjustment. Until the magmatic forcing of Cenozoic climate is quantied, the contribution of
erosion/weathering of uplifted terrains to climate cooling will remain elusive. Continental
collision/subduction and associated orogenesis increase weathering and cause arc demise, and both
processes work in tandem to reduce the atmospheric carbon budget. Discerning between the two
contributions to the Cenozoic climate evolution as indicated by paleoclimate proxies is a major challenge
for future research. The links between surface mass redistribution and volcanism characterized by recent
research focused on PlioQuaternary glacialinterglacial cycles seem to offer an appropriate starting point
for the development of a unifying theory relating tectonics, surface processes, magmatic, and climatic
changes. In this way, we may eventually capture the essence of the surfacedeep Earth processes coupling
and thus gain new insights into the functioning of the Earth system (Figure 9).
The development and validation of such a theory involves a range of disciplines of the Earth Sciences and
will require the conjugation and systematic analyses of global data and modeling. Besides extending the
body of observational constraints reporting on the Cenozoic tectonic and sedimentary uxes, improving data
sets on the timing, magnitude, and chemical composition of major magmatic events is needed. Interpreting
available data will require implementation of current models to account for phase transitions and/or multi-
phase ow in order to investigate the coevolution of geodynamic and magmatic processes. The continuously
Figure 8. Thick lines show modeled atmospheric CO
2
variability associated with normalized sinusoidal radiative forcing
at 40 kyr (thin blue line) and 100 kyr (thin red line). Shaded bars indicate the phase of enhanced outgassing during the
deglaciation lasting for ~10 kyr (see text for detail). Ocean and atmospheric CO
2
are assumed to be in equilibrium, as
their equilibration timescale is much shorter than the timescales considered here (Archer, 2005). Weathering is the
only CO
2
sink considered and the weaterhing rate, W
, is assumed to be constant and equal to 0.1 Gt/a (Gaillardet et al.,
1999; Moon et al., 2014). The volcanic CO
2
emission rate is assigned a glacial value, ė, and an enhanced value, Ė, during
the deglaciation calculated as Ė=2ė(Huybers & Langmuir, 2009). We also assume that the CO
2
budget is balanced over an
entire climate cycle, so that W
(g+d)=Ėd+ėg, where gand dare the duration of the glacial and deglacial periods,
respectively. Thus, for 100 kyr climate cycles with deglaciation lasting for 10 kyr (see text for detail), ė=0.09 Gt/a and
Ė=0.18 Gt/a. For 40 kyr climate cycles with deglaciation lasting for 10 kyr, we adopt ė=0.09 Gt/a, leading to Ė=0.13 Gt/a.
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increasing amount of experimental constraints on rock rheology and pet-
rology and recent improvements in numerical techniques allowed the
development of petrothermomechanical numerical models capable of
handling intense deformation and magmatism (e.g., Bouilhol et al.,
2015; Gerya & Yuen, 2007; Menant et al., 2016; Roche et al., 2018). A com-
ponent of surface processes is often included into recent geodynamic
numerical models (e.g., Ueda et al., 2015) and can benet from a wide
range of continuously growing geomorphological, sedimentological, bios-
tratigraphical, and geophysical observations. Climate models are also con-
tinuously improved in order to account for multiple factors pertaining to
the solid Earth such as variations of the tectonic or sedimentary uxes
(e.g., Archer et al., 2009; Zeebe, 2012). When boundary conditions cannot
be constrained by direct observations, estimates stemming from indepen-
dent petrothermomechanical and/or surface processes modeling results
may be useful. Although challenging, assessing rstorder relationships
between major tectonic and climatic changes accounting for magmatism
seems feasible as of now.
To what extent did the extinction of NeoTethyan volcanic arcs and/or
other major geodynamic events affect global carbon degassing throughout
the Cenozoic? Would associated changes in surface CO
2
concentrations involve a climatic response consis-
tent with paleoclimate proxies? Understanding the post50 Ma climate cooling may rst require understand-
ing the ~6050 Ma climate warming, seemingly unrelated to weathering changes and suggesting a prominent
magmatic forcing on climate. To this aim, we particularly stress the need for accurate and systematic recon-
structions of plate kinematics and magmatic activity at a global scale to be used as observational constraints
for modeling the associated perturbations of the geological carbon cycles. To what extent can the variability of
atmospheric carbon during glacialinterglacial cycles be ascribed to changes in volcanic activity? Do glacia-
tion and associated redistribution of surface masses act as phase locker between volcanic and climatic
changes through a modulation of carbon emissions? Do anticorrelated variations of submarine and subaerial
volcanism throughout glacialinterglacial cycles add up to positive or negative perturbations of the global
longterm carbon degassing and how would these perturbations modulate the shape of Late Quaternary cli-
mate oscillations? Understanding the relationships between PlioQuaternary climate oscillations and volcan-
ism requires accurate quantications of the surface ice water and rock mass redistribution associated with
glaciation and indepth assessments of the response of magmatic systems to perturbations of the surface
loads. In general, any contribution that improves our understanding of carbon recycling at plate margins, vol-
canic arc extinction, surface load variations during glacialinterglacial cycles, and the carbon emission budget
of submarine and subaerial volcanism will help answering these and other outstanding questions regarding
the coupling between surfaceEarth and deepEarth processes.
Assessing the climatic response to longand shortterm magmatic forcing throughout the Cenozoic will not
only be of scientic relevance but also produce invaluable societal implications. For instance, early Cenozoic
climate changes provide insights into the coupling of climate and the carbon cycle and thus may help to pre-
dict the consequences of current carbon emissions in the future (e.g., Zachos et al., 2008). In addition, gla-
ciers and ice sheets are a primary resource of fresh water and are often used in critical ways, while
geothermal power plants around volcanic contexts worldwide should produce about 140 GWe (~8.3% of total
electricity production) by 2050 (e.g., Bertani, 2016). Because enforced deglaciation since the industrial era
may lead to increased volcanic activity and hazard (e.g., Pagli & Sigmundsson, 2008; Tuffen, 2010), under-
standing the natural joint variability of glaciated and volcanic environments is an urgent action to undertake
in order to improve our ability to manage natural resources and hazards in fastevolving and highpotential/
risk terrains.
5. Boxed Text
The geological carbon cycle regulates the storage of CO
2
into rocks and the release of CO
2
into the ocean and
atmosphere via weathering of surface minerals and volcanic emissions, thereby linking the evolution of
Figure 9. Schematic representation of the surfacedeep Earth processes cou-
pling. Assessing the role of magmatism in setting Cenozoic climate changes
is one of the Grand Challenges for future research on the surfacedeep Earth
processes coupling.
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climate and life to plate tectonics. The last ~60 Myr are characterized by a longterm climate cooling trend,
which may be ascribed to a combination of reduced atmospheric CO
2
due to increased global weathering
and/or progressive reduction of CO
2
emissions following extinction of volcanic arcs. Assessing the magmatic
contribution to the longterm climate evolution is particularly challenging because our knowledge regarding
volcanic carbon emission and the timing and modalities of volcanic arc generation and extinction is still
awed. Major research efforts are thus required and should involve globalscale analyses of available data
and the development of new observational constraints and models.
Climate cooling throughout the Cenozoic Era led to the onset of Northern Hemisphere glaciation in the Plio
Quaternary (~5 Ma to present). Because volcanic emissions affect climate, but the redistribution of surface
ice, water, and rock masses associated with glacialinterglacial cycles affects volcanic activity, a feedback
loop between volcanic and climatic change does exist. Paleoclimate proxies show a progressive increase of
the amplitude and asymmetry of climate oscillations throughout the Late Quaternary, and our preliminary
analysis suggests that the mutual feedback between volcanism and climate during icehouse stages may
explain such observations. However, more thorough quantications of the surface mass redistribution dur-
ing glacialinterglacial cycles and a better understanding of the sensitivity of volcanic systems to surface load
variations are required to assess the variability of subaerial and submarine volcanic carbon degassing and
validate this proposal.
By supporting the view that the Cenozoic climate evolution is largely controlled by changes in magmatic
activity, we put forth a major challenge for future research, because assessing the magmatic forcing on cli-
mate requires globalscale, multidisciplinary investigations. Improving data and modeling regarding the
strain, topographic and magmatic evolution of plate boundaries, and the redistribution of surface mass
across the Earth's surface caused by glacialinterglacial cycles and the associated volcanic response are spe-
cically required to tackle this challenge. Understanding past climate changes will allow us to better assess
ongoing modications and predict future conditions, which in turn should inuence policymakers toward
responsible, conscious, and shared decisions for adaptation and mitigation options. However, the challenge
does not only involve scientists but all individuals that contribute sensitizing the community to the complex
network of interactions that control the Earth's climate. This is an essential step toward increasing aware-
ness of the societal impact on our planet.
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Acknowledgments
Pietro Sternai was supported by the
Swiss NSF (Ambizione Grant
PZ00P2_168113/1) and the Italian
MIUR (Rita Levi Montalcini Grant, DM
69426/2017). This study is also part of
the project MIURDipartimenti di
Eccellenza 20182022, Department of
Earth and Environmental Sciences,
University of MilanoBicocca. Laurent
Jolivet, Marco Malusà, and Andrea
Zanchi are thanked for helpful
suggestions. The manuscript was
signicantly improved based on
revisions by Guilhem Hoareau and an
anonymous reviewer. The data
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... C ooling of Earth's climate during the Cenozoic is broadly thought to have been related to decreasing atmospheric CO 2 concentrations [1][2][3] . The key factors leading to such decreases remain the subject of considerable debate [4][5][6][7][8] . Two hypotheses have been proposed. ...
... The first invokes an increasing rate of CO 2 consumption by silicate weathering during the Cenozoic, caused by the uplift of the Tibetan Plateau 9-12 . The second focuses on a decreasing rate of CO 2 release from Earth's interior in the Cenozoic, attributed to the shutdown of the Neo-Tethyan decarbonation subduction factory during the India-Asia continent collision 7,8,13 . Despite the clear distinction between these two hypotheses, both contain the premise that the India-Asia collision is the ultimate cause of atmospheric CO 2 concentration variations in the Cenozoic. ...
... Several studies [14][15][16][17][18] indicate that Cenozoic magmatism and metamorphism in the Tibetan Plateau are reliable recorders of the evolution of India-Asia collision processes and the formation of the Himalayan-Tibetan orogen. Magmatic and metamorphic degassing, which are fundamentally linked to such plate tectonic processes, are important parts of the Earth's deep carbon cycle on million-year time scales 8,[19][20][21] . Thus, a better understanding of magmatic and metamorphic emissions in Tibet should bring with it the potential for providing critical constraints on explanations of atmospheric CO 2 concentration variations in the Cenozoic. ...
Article
Full-text available
Deep Earth degassing is a critical forcing factor for atmospheric CO2 variations and palaeoclimate changes in Earth’s history. For the Cenozoic, the key driving mechanism of atmospheric CO2 variations remains controversial. Here we analyse three stages of collision-related magmatism in Tibet, which correspond temporally with the three major stages of atmospheric CO2 variations in the Cenozoic and explore the possibility of a causal link between these phenomena. To this end we present geochemical data for the three stages of magmatic rocks in Tibet, which we use to inform a model calculating the continental collision-induced CO2 emission flux associated with the evolving Neo-Tethyan to continental subduction over the Cenozoic. The correlation between our modelled CO2 emission rates and the global atmospheric CO2 curve is consistent with the hypothesis that the India-Asia collision was the primary driver of changes in atmospheric CO2 over the Cenozoic. “Earth degassing is a critical carbon source, but its contribution to Cenozoic atmospheric CO2 variations is not well known. Here, the authors analyse CO2 fluxes on the Tibetan Plateau and suggest that the India-Asia collision was the primary driver of changes in atmospheric CO2 over the past 65 Ma.”
... This proposed mechanism, the reduction of continental runoff (and increased time for water-rock interaction) controlling longterm seawater δ 7 Li, raises questions on how silicate mineral weathering linked to hydrology mediates global climate over the Cenozoic. There are two possibilities: (i) that this led to decreased weathering fluxes; (ii) it led to no change in weathering rate if compensated by an increase in the strength of the silicateweathering climate feedback 32 and/or by changes in CO 2 release from volcanism 81,82 , metamorphism in continental arcs 83 or sedimentary rock weathering 31,[84][85][86] . In terms of the first scenario, based on our dataset from flat lowlands and active mountains, a lower runoff would result in a lower silicate weathering rate (Supplementary Fig. 15c). ...
... Recent studies have suggested global stability of the chemical weathering flux during the Cenozoic 2 , which supports the second scenario. This could come about if declining atmospheric CO 2 was primarily driven by decreasing solid earth degassing rates, as proposed by recent studies [81][82][83] , which would require stable silicate weathering rates while atmospheric CO 2 declined. The release of CO 2 through weathering of sedimentary rocks 31,[84][85][86] could also play a role in net carbon cycle balance. ...
Article
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Seawater lithium isotopes (δ⁷Li) record changes over Earth history, including a ∼9‰ increase during the Cenozoic interpreted as reflecting either a change in continental silicate weathering rate or weathering feedback strength, associated with tectonic uplift. However, mechanisms controlling the dissolved δ⁷Li remain debated. Here we report time-series δ⁷Li measurements from Tibetan and Pamir rivers, and combine them with published seasonal data, covering small (<10² km²) to large rivers (>10⁶ km²). We find seasonal changes in δ⁷Li across all latitudes: dry seasons consistently have higher δ⁷Li than wet seasons, by −0.3‰ to 16.4‰ (mean 5.0 ± 2.5‰). A globally negative correlation between δ⁷Li and annual runoff reflects the hydrological intensity operating in catchments, regulating water residence time and δ⁷Li values. This hydrological control on δ⁷Li is consistent across climate events back to ~445 Ma. We propose that hydrological changes result in shifts in river δ⁷Li and urge reconsideration of its use to examine past weathering intensity and flux, opening a new window to reconstruct hydrological conditions.
... After the EECO, the Earth remained in a warmhouse state, with intermittent bursts of hyperthermal events such as the Middle Eocene Thermal Maximum (METM; Westerhold et al., 2020;Scotese, 2021). Many, if not all hyperthermals were paced by changes in the Earth's orbital parameters (e.g., eccentricity), and the triggering mechanisms of the PETM event are still hotly debated, leading to hypotheses involving the release of methane hydrates (Dickens et al., 1997) or volcanic-gas emissions during emplacement of large igneous provinces (Jones et al., 2019;Sternai et al., 2020). These hyperthermals, and especially the PETM, exerted a profound influence on ecological and sedimentary systems, and caused severe environmental changes including oceanic acidification, sharp modifications of the hydrological cycle, and enhanced storm activity Bowen et al., 2006;Pagani et al., 2006;Hu et al., 2020;Jiang et al., 2021a;Jiang et al., 2021b). ...
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Early Paleogene hyperthermal episodes including the Paleocene-Eocene Thermal Maximum (PETM) have long been viewed as analogues of the Anthropocene global warming. Few studies, however, have analyzed the environmental consequences of such climatic anomalies in deep-water turbidite-rich successions. This integrated sedimentological, biostratigraphic, and stable-isotope study of the Paleogene Pabdeh Formation, deposited along the Arabian continental margin of southwestern Iran, allowed us to document the geological response of hyperthermal events in deep Neo-Tethyan Ocean. The late Thanetian event (Pre-Onset Excursion or long-term late Paleocene climatic perturbation), the Early Eocene Climate Optimum, and the Middle Eocene Thermal Maximum were successfully identified within the Pabdeh Formation. The PETM event could not be documented because the Paleocene/Eocene boundary corresponds to a prolonged non-depositional hiatus marked by a glauco-phosphorite interval. Based on high-resolution microfacies analysis, three different processes in a carbonate slope to basin-margin environment were distinguished including pelagic settling, upwelling-condensation-reworking, and storm-induced turbiditic deposition. Detailed sedimentological analysis revealed an anomalous abundance of storm-induced proximal to distal turbidites represented by packstones with deep-water and reworked shallow-water bioclasts occurring during the hyperthermal intervals. A close causal link between climate warming and tropical storms during the early Paleogene hyperthermal events is thus envisaged. As a principal mechanism, we propose that rapid warming in response to massive carbon release triggered pronounced sedimentological changes along low-latitude tropical margins, leading to generation of storm-induced calciturbidite and re-deposition in the deep sea during hothouse stages.
... The axis of this strip is parallel to the direction of regional magnetic anomalies observed in the CB area [47], [86], [87], a zone characterized by eastwest strike normal fault systems, which mainly affected the basin's basement and preserve remnants of Mesozoic sediments ( Figure 5). Another area with thicknesses greater than 2,000 m, although Ec o p e t r ol [131], in black the global eustatic change curve [93] and the age of the MTCs previously identified [59], [115], [126] . On the right, relative frequency graph of the ages obtained by fission analysis in apatite's (thick black dotted line) and phases of magmatism from other dating methods (blue to red degraded polygons called phases 1 to 4) in the NWCSA, based on the age compilation [33] and the temporal position of the detritic zircons recovered during this study (yellow rhombuses) in the Sinu and San Jacinto mountain ranges (see sample locations in Figs. 9 and 10). ...
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The Colombia basin contains large volumes of sediment accumulated during the last 17 My. The use of isochore maps, exploratory wells, micropaleontological and geochronological dates has enabled us to estimate the volumes of sediment and accumulation rates in this basin. The analysis of source of sediments and exhumation data from the Northern Andes of South America led to the definition of areas and thicknesses of material eroded during the Neogene - Quaternary, to obtain volumes or material eroded from the continent that can be correlated with sediment volumes accumulated in the Colombia Basin. The analyzed sediment volumes suggest that during the last 17 My ~72.06x1015 Tons accumulated in the Colombia Basin, while ~ 7.16x1013 Tons accumulated in the continental catchment areas. The sedimentation in the Colombian Basin has occurred at variable rates, with values ranging from 55 MTons/My to 295 MTons/My, with a peak of 803 MTons/My in the early Pleistocene (between 2.4 and 2.2 Ma). The evaluation between the total volumes of sediment accumulated in the offshore and onshore, suggests that in the continental part of the basin less than 4% of the total volume of eroded sediment is trapped and, therefore, the behavior of the accumulation rates calculated in the offshore directly reflect the relief evolution of South America’s Northern Andes. It seems, at large, that the lithospheric convergence rates and subduction angle (South America vs Nazca and Meso Atlantic opening) have controlled the regional exhumation of the Northern Andes, with the exception of the Pleistocene high sedimentation event, which seems to coincide with local events such as the collision of the Panama Arch against Western Antioquia. It may be concluded that thanks to this collision, drainage systems such as those of the Magdalena and Cauca rivers were modified, which resulted in the formation of the Magdalena Submarine Fan.
... In particular, Crowley et al. (2015) highlighted a correlation between abyssal hill fabrics along mid-ocean ridges and the glacial cycles, suggesting cyclic magmatic response to changes in sea level. In addition, at Milankovitch time scales and longer, it was postulated that magmatic variation could cause climate change via volcanic emissions of greenhouse gases, impacting in turn Earth's surface processes including sea-level changes (Sternai et al., 2020). The interplay between tectonics, climate and Earth's surface processes was also suggested to explain the evolution of mountain building (Pesek et al., 2020). ...
Article
The driving mechanisms of Earth's climate system at a multi-Myr timescale have received considerable attention since the 1980's as they are deemed to control large-amplitude climatic variations that result in severe biogeochemical disruptions, major sea-level variations, and the evolution of Earth's land- and seascapes through geological time. The commonly accepted mechanism for these changes derives from the evolution of Earth's coupled plate-mantle system. Connection between Earth's interior and external climate drivers, e.g., Milankovitch insolation forcing, has not been investigated at multi-Myr timescale, because tectonics and astronomical influences at these longer timescales have long been thought as independent pacemakers in the evolution of the Earth system. Here we have analyzed time-series from multiple geological datasets and found common periodicities of 10 and 35 Myr. Additionally, we have highlighted the modulation in amplitude of the 10 Myr cycle band by the 35 Myr cyclicity in sedimentary sea-level data. We then demonstrate the same physical amplitude modulation relationship between these two cyclicities in astronomical (Milankovitch) variations, and establish correlation between Milankovitch and sea-level variations at these two frequency bands. The 10 and 35 Myr cycles are prominent in the geological records, suggesting either unresolved fundamental Milankovitch periodicities, or reflecting a sedimentary energy-transfer process from higher to lower Milankovitch frequencies, as argued here via amplitude modulation analysis in both astronomical and sea-level data. Finally, we find a coherent correlation, at the 35 Myr cycle band, between Milankovitch, sea-level and geodynamic (plate subduction rate) variations, hinting at a coupling between Earth's interior and surface processes via Milankovitch paced climate. Thus, our findings point to a coupling between Milankovitch and Earth's internal forcings, at 10 to 10s of Myr. The most likely scenario that could link insolation-driven climate change to Earth's interior processes is Earth's interior feedbacks to astro-climatically driven mass changes on Earth's surface. We suggest that Earth's interior processes may drive large-amplitude sea-level changes, especially during greenhouse periods, by resonating to astro-climatically driven Earth's surface perturbations. Keywords Earth's climate Sea level Milankovitch Tectonics Multi-million year timescales
... We expect this recognition to be broadly applicable to other volcanic arcs worldwide and particularly relevant for volcanic arc ore deposits, the exploitation of which is primarily conditioned by the regional topography itself. Because volcanic arcs provide a substantial contribution to the evolution of climate across timescales, this recognition provides an additional evidence of the tight coupling between climate and plate tectonics 46,47 . ...
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Volcanic arcs at convergent plate margins are primary surface expressions of plate tectonics. Although climate affects many of the manifestations of plate tectonics via erosion, the upwelling of magmas and location of volcanic arcs are considered insensitive to climate. In the Southern Andes, subduction of the Nazca oceanic plate below the South American continent generates the Southern Andes Volcanic zone. Orographic interactions with Pacific westerlies lead to high precipitation and erosion on the western slopes of the belt between 42-46°S. At these latitudes, the topographic water divide and the volcanic arc are respectively farther and closer to the subduction trench than at lower latitudes, despite a constant subduction dip angle along strike. Here, we use thermomechanical numerical modeling to investigate how magma upwelling is affected by topographic changes due to orography. We show that a leeward topographic shift may entail a windward asymmetry of crustal structures accommodating the magma upwelling, consistent with the observed trench-ward migration of the Southern Andes Volcanic Zone. A climatic control on the location of volcanic arcs via orography and erosion is thus revealed.
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Although continental weathering intensity has been invoked as a primary control on biogeochemistry, tectonics, and the carbon cycle throughout geologic history, it remains poorly quantified over Earth’s history. As a direct product of continental weathering, paleosols (fossil soils) offer unique insight into past weathering intensity, but they remain underused in efforts to constrain terrestrial weathering patterns over geologic time. Here, we compile the largest terrestrial weathering record to date, comprising 248 paleosol and weathering profiles that span three billion years. We analyze a suite of weathering indices to test common hypotheses around state-changes in terrestrial weathering intensity due to atmospheric changes and terrestrial biosphere expansion. Contrary to commonly invoked assumptions, we find that these weathering indices reflect consistent average terrestrial weathering intensity through time. No unidirectional state changes in average weathering intensity, as have previously been hypothesized, are detectable in the record. However, Phanerozoic paleosols preserve an increase in the total range of Chemical Index of Alteration (CIA) values, with the increased CIA range driven by the appearance of high-CaO paleosols. We compare the paleosol weathering record to weathering intensities recorded by select fluvial sandstones and diamictites. We interpret the overall stability of the continental weathering record as reflecting the baseline level of weathering from which the Earth system deviates during periods of perturbation (i.e., major climate transitions, rapid tectonic activity). With consistent weathering intensity over geologic timescales, the record supports subaerially-emerged continental area as a critical control on total potential erosional flux and nutrient flux to the oceans. The paleosol community should work to build an even more complete database of paleosol geochemistry to allow more nuanced analyses of terrestrial weathering through time.
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Countless continuously interacting processes determine the functioning and evolution of the Earth. Even geodynamic and climate changes, which have been classically studied independently because they pertain to different Earth ‘spheres’, are linked by mutual cause-effect relationships that recent research has just started to recognize and quantify. Modeling, be it analogue or numerical, is a trump card in this research for it allows rigorous integrations and interpretations of multiple observations that report on processes with different characteristic spatial and temporal scales and occurring at the Earth’s surface or deep within its interior. In this solicited chapter, I let my academic journey thus far illustrate the challenges of the study of the feedbacks between internal and external Earth dynamics and its relevance for the Earth Sciences as well as for facing and mitigating ongoing fast and extreme global changes.
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Countless continuously interacting processes determine the functioning and evolution of the Earth. Even geodynamic and climate changes, which have been classically studied independently because they pertain to different Earth 'spheres', are linked by mutual cause-effect relationships that recent research has just started to recognize and quantify. Modeling, be it analogue or numerical, is a trump card in this research for it allows rigorous integrations and interpretations of multiple observations that report on processes with different characteristic spatial and temporal scales and occurring at the Earth's surface or deep within its interior. In this solicited chapter, I let my academic journey thus far illustrate the challenges of the study of the feedbacks between internal and external Earth dynamics and its relevance for the Earth Sciences as well as for facing and mitigating ongoing fast and extreme global changes.
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The multitude of periodicities reported from detrital zircon and related geochemical time-series leads to questions about which cycles should be considered valid, which are byproducts of random noise, and the degree of uncertainty associated with the detected periodicities. To enhance understanding of detrital zircon periodicities, we review existing estimates by assessing both methodological reliability and reproducibility of results. Methods commonly employed include scalograms from wavelet analysis, periodograms from spectral analysis, and correlograms from cross-correlation analysis. This study analyzes possible zircon periodicities ranging from less than 1 million to 1 billion years. We systematically evaluate the capabilities of each approach, and then refine estimates in terms of their reproducibility using seven completely independent to partially independent UPb detrital zircon databases. Periodicities that are consistently found at high confidence levels are considered statistically significant, whereas those that cannot be replicated are considered as spurious. The comparative studies of detrital zircon ages reveal a dominant set of eight period-tripling cycles of ~0.373, 1.12, 3.35, 10.1, 30.2, 90.5, 272, and 815 myr (rounded to three digits). Additionally, a multitude of subordinate cycles are harmonically linked to the main period-tripling sequence. The detected periodicities often correspond to cycles found in large igneous province occurrence, seafloor spreading rates, million-year climatic cycles, mass extinctions, and other natural variation seemingly unrelated to geological processes. The commonality suggests a persistent episodic link between zircon production and other geological and non-geological processes throughout Earth's entire history. As a final step, we review a variety of hypotheses being explored to explain primary, secondary, and tertiary causes of cycles, and then propose tests that should soon be possible to either validate or falsify these diverse ideas.
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Very long period (VLP) seismic events (with dominant periods of 15 to 40 s), observed from 2007 to 2018 at the summit of K{\=\i}lauea Volcano, Hawai`i, arise from resonant oscillations in the shallow magma plumbing system. Utilizing an oscillation model developed in the companion paper (Liang et al., 2019), we perform Bayesian inversions on seismic data from four representative VLP events separately for the parameters of the shallow conduit-reservoir system, exploring both sphere and crack reservoir geometries. Both sphere and crack geometries are preferentially located $\sim$1-2 km beneath the northeast edge of Halema`uma`u crater and produce similar fits to the data. Considering a reasonable range for reservoir storativity, magma density, and density contrast between the top and bottom of the conduit, we favor a spherical reservoir with a radius of 0.8 to 1.2 km and a short conduit of less than a few hundred meters. For this geometry, buoyancy from density stratification in the conduit provides the dominant restoring force for the VLP oscillation. Viscosity is constrained within an order of magnitude for each event (e.g., approximately 2 to 23 Pa s for one event versus 27 to 513 Pa s for another). Changes in VLP period $T$ and quality factor $Q$ can be explained by changes in viscosity, density stratification, and/or conduit/reservoir geometry. In particular, observed fluctuations in $Q$ over short time intervals (e.g., hours) with minimal changes in $T$ apparently require rapid changes of magma viscosity by over an order of magnitude, assuming geometry remains unchanged, possibly reflecting changes in volatile content, bubble concentration, or conduit flow regime.
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The Eocene (~50‐45 Ma) major absolute plate motion change of the Pacific plate forming the Hawaii‐Emperor bend is thought to result from inception of Pacific plate subduction along one of its modern western trenches. Subduction is suggested to have started either spontaneously, or result from subduction of the Izanagi‐Pacific mid‐ocean ridge, or from subduction polarity reversal after collision of the Olyutorsky arc that was built on the Pacific plate with NE Asia. Here we provide a detailed plate‐kinematic reconstruction of back‐arc basins and accreted terranes in the northwest Pacific region, from Japan to the Bering Sea, since the Late Cretaceous. We present a new tectonic reconstruction of the intra‐oceanic Olyutorsky and Kronotsky arcs, which formed above two adjacent, oppositely‐dipping subduction zones at ~85 Ma within the north Pacific region, during another Pacific‐wide plate reorganization. We use our reconstruction to explain the formation of the submarine Shirshov and Bowers Ridges, and show that if marine magnetic anomalies reported from the Aleutian Basin represent magnetic polarity reversals, its crust most likely formed in an ~85‐60 Ma back‐arc basin behind the Olyutorsky arc. The Olyutorsky arc was then separated from the Pacific plate by a spreading ridge, so that the ~55‐50 Ma subduction polarity reversal that followed upon Olyutorsky‐NE Asia collision initiated subduction of a plate that was not the Pacific. Hence, this polarity reversal may not be a straightforward driver of the Eocene Pacific plate motion change, whose causes remain enigmatic.
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Paleotopographic reconstructions of the Tibetan Plateau based on stable isotope paleoaltimetry methods conclude that most of the Plateau’s current elevation was already reached by the Eocene, ~40 million years ago. However, changes in atmospheric and hydrological dynamics affect oxygen stable isotopes in precipitation and may thus bias such reconstructions. We used an isotope-equipped general circulation model to assess the influence of changing Eocene paleogeography and climate on paleoelevation estimates. Our simulations indicate that stable isotope paleoaltimetry methods are not applicable in Eocene Asia because of a combination of increased convective precipitation, mixture of air masses, and widespread aridity. Rather, a model-data comparison suggests that the Tibetan Plateau only reached low to moderate (less than 3000 meters) elevations during the Eocene, reconciling oxygen isotope data with other proxies.
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This chapter summarizes the available stratigraphic, petrographical and mineralogical evidence from sediments and sedimentary rocks on the evolution of the Himalayan belt and its associated foreland basin. The use of compositional signatures of modern sediments to unravel provenance changes and palaeodrainage evolution through time is hampered by a poor match with detrital modes of ancient strata markedly affected by selective chemical dissolution of unstable minerals during diagenesis. Only semi-quantitative diagnoses can thus be attempted. Volcanic detritus derived from Transhimalayan arcs since India–Asia collision onset at c. 60 Ma was deposited onto the Indian lower plate throughout the Protohimalayan stage, with the exception of the Tansen region of Nepal that is characterized by quartz-arenites yielding orogen-derived zircon grains. During the Eohimalayan stage, begun in the late Eocene when most sedimentation ceased in the Tethys Himalayan domain, low-rank metasedimentary detritus was overwhelming in the central foreland basin, where a widespread unconformity developed spanning locally as much as 20 myr. Volcanic detritus from Transhimalayan arcs remained significant in northern Pakistan. Arrival of higher-rank metamorphic detritus since the earliest Miocene, and the successive occurrence of garnet, staurolite, kyanite and finally sillimanite, characterized the Neohimalayan stage, when repeated compositional changes in the foreland-basin succession document the stepwise propagation of crustal deformation across the Indian Plate margin and widening of the thrust belt with exhumation of progressively more external tectonic units. The correspondence in time between the activity of major thrusts and petrofacies changes indicates a promising approach to accurately reconstruct the geological evolution of the coupled orogen–basin system. Conversely, a poor conceptual framework and the general reliance on ad hoc mechanisms to explain phenomena unpredicted by simplified models represent major factors limiting the robustness of palaeotectonic interpretations. Improved knowledge requires taking into full account the dynamic role played by still poorly understood subduction processes – rather than exclusively the effect of passive loading – as well as the role played by the presence of inherited structures on the downgoing Indian Plate, which control both lateral variability of orogenic deformation and the location of depocentres in the foreland basin.
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Subduction zones are unique to Earth and fundamental in its evolution, yet we still know little about the causes and mechanisms of their initiation. Numerical models show that far-field forcing may cause subduction initiation at weak pre-existing structures, while inferences from modern subduction zones suggest initiation through spontaneous lithospheric gravitational collapse. For both endmembers, the timing of subduction inception corresponds with initial lower plate burial, whereas coeval or delayed extension in the upper plate are diagnostic of spontaneous or forced subduction initiation, respectively. In modern systems, the earliest extension-related upper plate rocks are found in forearcs, but lower plate rocks that recorded initial burial have been subducted and are inaccessible. Here, we investigate a fossil system, the archetypal Semail Ophiolite of Oman, which exposes both lower and upper plate relics of incipient subduction stages. We show with Lu–Hf and U–Pb geochronology of the lower and upper plate material that initial burial of the lower plate occurred before 104 million years ago, predating upper plate extension and the formation of Semail oceanic crust by at least 8 Myr. Such a time lag reveals far-field forced subduction initiation and provides unequivocal, direct evidence for a subduction initiation mechanism in the geological record.
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The archetypal Semail ophiolite of Oman has inspired much thought on the dynamics of initiation of intra-oceanic subduction zones. Current models invoke subduction initiation at a mid-oceanic ridge located sufficiently close to the Arabian passive margin to allow initiation of continental subduction below the ophiolite within ∼10-15 Myr after the 96-95 Ma age of formation of supra-subduction zone crust. Here, we perform an extensive paleomagnetic analysis of sheeted dyke sections across the Semail ophiolite to restore the orientation of the supra-subduction zone ridge during spreading. Our results consistently indicate that the ridge was oriented NNE-SSW, and we infer that the associated trench, close to the modern obduction front, had the same orientation. Our data are consistent with a previously documented ∼150 • clockwise rotation of the ophiolite, and we reconstruct that the original subduction zone was WNW-ward dipping and NNE-SSW striking. Initial subduction likely occurred in the ocean adjacent and parallel to a transform margin of the part of the Arabian continent now underthrust below Iran that originally underpinned the nappes of the Zagros fold-thrust belt. Subduction thus likely initiated along an ancient, continental margin-parallel fracture zone, as also recently inferred from near-coeval ophiolites from the eastern Mediterranean and NW Arabian regions. Subduction initiation was therefore likely induced by (WN)W-(ES)E contraction and this constraint may help the future identification of the dynamic triggers of Neotethyan subduction initiation in the Late Cretaceous.
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On multi-million-year timescales, Earth has experienced warm ice-free and cold glacial climates, but it is unknown if transitions between these background climate states were the result of changes in CO 2 sources or sinks. Low-latitude arc-continent collisions are hypothesized to drive cooling by uplifting and eroding mafic and ultramafic rocks in the warm, wet tropics, thereby increasing Earth’s potential to sequester carbon through chemical weathering. To better constrain global weatherability through time, the paleogeographic position of all major Phanerozoic arc-continent collisions was reconstructed and compared to the latitudinal distribution of ice-sheets. This analysis reveals a strong correlation between the extent of glaciation and arc-continent collisions in the tropics. Earth’s climate state is set primarily by global weatherability, which changes with the latitudinal distribution of arc-continent collisions.
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Paleoaltimetry—the quantitative estimate of the past elevation of land surfaces such as mountain belts—is notoriously difficult to constrain. To estimate past elevation, geologists study sedimentary rocks that accumulated in freshwater lakes in ancient mountain belts. They compare fossils or oxygen stable isotopes (the ratio of which is elevation-dependent) from these rocks with present-day records from elevated areas (1). One region where paleoaltimetry studies are widely conducted is the Tibetan Plateau, which owes its extreme elevation to intense deformation that started at least 70 million years ago during subduction of the Indian plate below Asia. However, elevation estimates for the region—for example, for the Eocene (~40 million years ago)— based on either fossils or stable isotopes differ by kilometers (2, 3). On page 946 of this issue, Botsyun et al. (4) provide an explanation for this discrepancy and bring the two types of estimate nearer to agreement.
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The increase in volcanic activity after the last glacial maximum observed on Iceland has led to one of the most fascinating hypothesis in science in the last decades: that deglaciation may force volcanism. Consequently, tephrostratigraphic records of sufficient length that cover multiple glacial cycles have been used to test whether such relationships hold systematically through the Quaternary. Here we review such tephra records that have been linked with climate proxy records such as δ¹⁸O in marine sediments, which is a measure of sea-level change and which is thought to be orbitally forced, as it exhibits the characteristic Milankovitch periodicities of precession (∼23 kyr), obliquity (∼41 kyr) and eccentricity (∼100 kyr). Statistical analyses have identified these periodicities also in long tephra records from different latitudes and geotectonic settings, as well as in compiled semi-global records. These studies detect Milankovitch periods in their tephra record, and also a phase shift relative to the δ¹⁸O record in such that periods of increased eruption frequencies coincide with the deglaciation period at the glacial/interglacial transition when ice and water loads on the lithosphere change most rapidly. However, there are also disparities in results and interpretations, which may be attributable to the different methods of analysis applied by the studies. We have therefore re-analyzed the four best-characterized tephra records by the same methods. We distinguish between analysis in the frequency domain, a novel approach, and analysis in the time domain, which has been used in previous studies. Analysis in the frequency domain identifies harmonic frequencies that arise from the binary nature of the tephra records and complicate the identification of primary frequencies. However, we show that all four records show spectral density peaks near the main Milankovitch periodicities of 41 and 100 kyr, and that they produce meaningful and significant statistical correlations with each other and the global δ¹⁸O record but not with random time series. Although the time-domain correlations with δ¹⁸O roughly confirm phase shifts implying peak volcanism during deglaciation, correlation coefficients arising from very noisy records are generally too low for precise constraints on the relative timing. These deficiencies presently hamper the recognition of the physical mechanisms through which global climate changes affect volcanism at both, high-latitude glaciated regions and low-latitude non-glaciated regions.