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Orbitally forced ice sheet fluctuations during the Marinoan Snowball Earth glaciation



Two global glaciations occurred during the Neoproterozoic. Snowball Earth theory posits that these were terminated after millions of years of frigidity when initial warming from rising atmospheric CO2concentrations was amplified by the reduction of ice cover and hence a reduction in planetary albedo. This scenario implies that most of the geological record of ice cover was deposited in a brief period of melt-back. However, deposits in low palaeo-latitudes show evidence of glacial-interglacial cycles. Here we analyse the sedimentology and oxygen and sulphur isotopic signatures of Marinoan Snowball glaciation deposits from Svalbard, in the Norwegian High Arctic. The deposits preserve a record of oscillations in glacier extent and hydrologic conditions under uniformly high atmospheric CO2concentrations. We use simulations from a coupled three-dimensional ice sheet and atmospheric general circulation model to show that such oscillations can be explained by orbital forcing in the late stages of a Snowball glaciation. The simulations suggest that while atmospheric CO2concentrations were rising, but not yet at the threshold required for complete melt-back, the ice sheets would have been sensitive to orbital forcing. We conclude that a similar dynamic can potentially explain the complex successions observed at other localities.
PUBLISHED ONLINE: 24 AUGUST 2015 | DOI: 10.1038/NGEO2502
Orbitally forced ice sheet fluctuations during the
Marinoan Snowball Earth glaciation
Douglas I. Benn1,2*, Guillaume Le Hir3, Huiming Bao4, Yannick Donnadieu5, Christophe Dumas5,
Edward J. Fleming1,6, Michael J. Hambrey7, Emily A. McMillan6, Michael S. Petronis8,
Gilles Ramstein5, Carl T. E. Stevenson6, Peter M. Wynn9and Ian J. Fairchild6
Two global glaciations occurred during the Neoproterozoic.
Snowball Earth theory posits that these were terminated
after millions of years of frigidity when initial warming from
rising atmospheric CO2concentrations was amplified by the
reduction of ice cover and hence a reduction in planetary
albedo1,2. This scenario implies that most of the geological
record of ice cover was deposited in a brief period of
melt-back3. However, deposits in low palaeo-latitudes show
evidence of glacial–interglacial cycles4–6. Here we analyse the
sedimentology and oxygen and sulphur isotopic signatures
of Marinoan Snowball glaciation deposits from Svalbard, in
the Norwegian High Arctic. The deposits preserve a record
of oscillations in glacier extent and hydrologic conditions
under uniformly high atmospheric CO2concentrations. We
use simulations from a coupled three-dimensional ice sheet
and atmospheric general circulation model to show that such
oscillations can be explained by orbital forcing in the late stages
of a Snowball glaciation. The simulations suggest that while
atmospheric CO2concentrations were rising, but not yet at
the threshold required for complete melt-back, the ice sheets
would have been sensitive to orbital forcing. We conclude
that a similar dynamic can potentially explain the complex
successions observed at other localities.
The Wilsonbreen Formation in northeast Svalbard contains a
detailed record of environmental change during the Marinoan, the
second of the major Cryogenian glaciations (650–635 Ma; refs 7,8).
At this time, Svalbard was located in the Tropics on the eastern
side of Rodinia9,10. The <180 m thick Wilsonbreen Formation was
deposited within a long-lived intracratonic sedimentary basin11. It
is subdivided into three members (W1, W2 and W3) based on
the relative abundance of diamictite and carbonate beds7,8 (Fig. 1
and Supplementary Figs 1 and 2). The occurrence throughout the
succession of lacustrine sediments containing both precipitated car-
bonate and ice-rafted detritus, and intermittent evaporative carbon-
ates and fluvial deposits, indicates that the basin remained isolated
from the sea, consistent with eustatic sea-level fall of several hundred
metres and limited local isostatic depression (Supplementary Infor-
mation; ref. 12). This makes it ideal for investigating environmental
change within a Neoproterozoic panglaciation, as it provides direct
evidence of subaerial environments and climatic conditions.
We made detailed sedimentary logs at ten known and new
localities extending over 60 km of strike (Fig. 1 and Supplemen-
tary Fig. 1; see Methods). Seven sediment facies associations were
identified, recording distinct depositional environments that varied
in spatial extent through time (Supplementary Fig. 3 and Supple-
mentary Information). These are: FA1: subglacial, recording di-
rect presence of glacier ice; FA2: fluvial channels; FA3: dolomitic
floodplain, recording episodic flooding, evaporation and microbial
communities; FA4: carbonate lake margin, including evidence of
wave action; FA5: carbonate lacustrine, including annual rhythmites
and intermittent ice-rafted debris; FA6: glacilacustrine, consisting
of ice-proximal grounding-line fans (FA6-G) and ice-distal rainout
deposits (FA6-D); and FA7: periglacial, recording cold, non-glacial
conditions. Further descriptions are provided in the Supplementary
Information. The vertical and horizontal distribution of these facies
associations (Fig. 1) allows the sequence of environmental changes
to be reconstructed in detail:
(1) The base of the Wilsonbreen Formation is a well-marked
periglacially weathered horizon with thin wind-blown sands
(Supplementary Fig. 4a,b). This surface records very limited
sediment cycling in cold, arid conditions.
(2) At all localities, the weathering horizon is overlain by fluvial
channel facies (FA2) and mudstones, marking the appearance
of flowing water in the basin and implying positive air temper-
atures for at least part of the time (Supplementary Fig. 5a).
(3) Glacilacustrine deposits (FA6-D) record flooding of the basin
and delivery of sediment by ice rafting (Supplementary
Fig. 4c,d). Far-travelled clasts are common, indicating transport
by a large, continental ice sheet.
(4) Warm-based, active ice advanced into the basin, indicated by
traction tills and glacitectonic shearing (FA1; Supplementary
Fig. 4e–g). (1–4 make up Member W1).
(5) Ice retreat is recorded by a second periglacial weathering
surface (FA7). This is overlain by fluvial channel, flood-
plain, lake-margin and carbonate lacustrine sediments of
W2 (FA2-5; Supplementary Fig. 5), recording a shifting mo-
saic of playa lakes and ephemeral streams. Lakes and river
channels supported microbial communities. Millimetre-scale
carbonate-siliciclastic rhythmites indicate seasonal cycles of
1Department of Geology, The University Centre in Svalbard (UNIS), N-9171 Longyearbyen, Norway. 2School of Geography and Geosciences, University of
St Andrews, St Andrews KY16 8YA, UK. 3Institut de Physique du Globe de Paris, 75238 Paris, France. 4Department of Geology and Geophysics, E235
Howe-Russell Complex, Louisiana State University, Baton Rouge, Louisiana 70803, USA. 5Laboratoire des Sciences du Climat et de l’Environnement,
CNRS-CEA, 91190 Gif-sur-Yvette, France. 6School of Geography, Earth and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK.
7Institute of Geography and Earth Sciences, Aberystwyth University, Aberystwyth SY23 3DB, UK. 8Natural Resource Management, Environmental
Geology, New Mexico Highlands University, Las Vegas, New Mexico 87701, USA. 9Lancaster Environment Centre, University of Lancaster, Lancaster
LA1 4YQ, UK. Present address: CASP, West Building, 181A Huntingdon Road, Cambridge CB3 0DH, UK. *e-mail:
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20 30 40 50 60
Marine carbonate FA1: subglacial (till) FA2: fluvial
FA6: (proximal)
FA7: periglacial
FA6: glacilacustrine (distal)FA1: (glacitectonite)
FA2-5: (carbonate) fluvial and lacustrine
Figure 1 | Sedimentary architecture and palaeoenvironments of the
Wilsonbreen Formation. Regional correlation of facies associations and
members W1, W2 and W3 across northeast Svalbard. From north to south,
study locations are: DRA, Dracoisen; DIT, Ditlovtoppen; AND, East
Andromedafjellet; REIN, Reinsryggen (informal name); KLO, Klofjellet;
McD, MacDonaldryggen; BAC, Backlundtoppen–Kvitfjellet ridge; PIN,
Pinnsvinryggen (informal name); SLA, Slangen and ORM, Ormen.
photosynthesis. The environment seems to have been closely
similar to that of the present-day McMurdo Dry Valleys in
Antarctica, although with less extreme seasonality owing to its
low latitude13.
(6) Water levels and glacier extent underwent a series of oscil-
lations, recorded by switches between glacilacustrine diamic-
tite (FA6-D) and fluvial, lacustrine and lake-margin sediments
(FA2-5) in W2. Sedimentation rates inferred from annual
rhythmites in W2 suggest that each retreat phase may have
lasted 104years.
(7) A second major ice advance marks the base of W3, with
widespread deposition of subglacial tills and glacitectonism of
underlying sediments. Basal tills are absent from the northern-
most locality, but close proximity of glacier ice is recorded by
grounding-line fans (FA6-G; Supplementary Fig. 4h,i).
(8) Ice retreated while the basin remained flooded and glaci-
genic sediment continued to be delivered to the lake by
ice rafting. Thin laminated carbonates (FA5) in W3 indi-
cate periods of reduced glacigenic sedimentation, indicative
of minor climatic fluctuations over timescales of 103years
(Supplementary Fig. 5g).
(9) A sharp contact with overlying laminated ‘cap’ carbonate
(Supplementary Fig. 2) records the transition to post-glacial
conditions. At some localities, basal conglomerates provide ev-
idence of subaerial exposure, followed by marine transgression.
The cap carbonate closely resembles basal Ediacaran carbonates
elsewhere, and marks global deglaciation, eustatic sea-level rise
and connection of the basin to the sea1,12,14.
Environmental and atmospheric conditions during deposition
of W2 and W3 can be further elucidated by isotopic data from
carbonate-associated sulphate in lacustrine limestones (Fig. 2
and Supplementary Fig. 6). These exhibit negative to extremely
negative 117O values, with consistent linear co-variation with δ34S,
indicating mixing of pre-glacial sulphate and isotopically light
sulphate formed in a CO2-enriched atmosphere15,16. The observed
y = 0.106x − 3.37
Towards light
r2 = 0.59
W2 limestones, existing data
W2 limestones, new data
W3 limestones, all new data
CAS δ34S (% )
CAS Δ17O (% )
Figure 2 | Co-variation of 117O and δ34S from carbonate-associated
sulphate in W2 and W3. ‘Existing data’ (ref. 16) and new data define a
mixing line between pre-glacial sulphate (top) and an isotopically light
sulphate formed by oxidation of pyrite including incorporation of a
light-117O signature from a CO2-enriched atmosphere. Data from W2 and
W3 lie on closely similar trend lines, indicating no detectable change in
pCO2between deposition of the two members.
values could reflect non-unique combinations of pCO2,pO2, O2
residence time and other factors, but a box model17 indicates pCO2
was most likely 10 to 100 mbar (1 mbar =1,000 ppmv).
These values are far too high to permit formation of low-
latitude ice sheets in the Neoproterozoic, but they are consistent
with a late-stage Snowball Earth. For an ice-free Neoproterozoic
Earth, model studies indicate mean terrestrial temperatures in the
range 30–50 C for pCO2=10 to 100 mbar (ref. 18). Formation of
low-latitude ice sheets requires much lower pCO2, on the order of
0.1–1 mbar (refs 2,19,20). Once formed, however, ice sheets can
persist despite rising CO2from volcanic outgassing, as a result of
a high planetary albedo. This hysteresis in the relationship between
pCO2and planetary temperature is a key element of Snowball Earth
theory. It implies that W2 and W3 were deposited relatively late in
the Marinoan, after volcanic outgassing had raised pCO2from 0.1 or
1 mbar to 10 or 100 mbar. Modelled silicate weathering and volcanic
outgassing rates indicate that this would require 106to 107years21.
The consistent co-variation of 117O and δ34S in lacustrine
limestones in both W2 and W3 suggests no detectable rise in
atmospheric pCO2, as this would alter the slope of the mixing
line (Fig. 2). This implies that the glacier oscillations recorded
in W2 and W3 occurred during a relatively short time interval
(<105years21) towards the end of the Marinoan. In turn, this implies
that the remainder of the Wilsonbreen Formation (including the
basal weathering horizon) represents many millions of years, during
which pCO2built up from the low values necessary for inception
of low-latitude glaciation to those indicated by the geochemical
evidence. The weathering horizon provides direct evidence of cold,
arid conditions during this interval, before the appearance of fluvial
and glacilacustrine sediments in the basin.
The evidence for ice sheet advance/retreat cycles at low latitudes
in a CO2-enriched atmosphere motivated a series of numerical
simulations to test the hypothesis that these cycles were linked
to Milankovitch orbital variations. We employed asynchronous
coupling of a three-dimensional ice sheet model and an atmospheric
general circulation model using the continental configuration of
ref. 22. We first ran simulations with a modern orbital configuration
to examine ice sheet behaviour through a large range of pCO2
values from 0.1 to 100 mbar (ref. 23; Supplementary Figs 7–10).
Consistently with previous results2,20, at low pCO2(0.1 mbar), global
ice volume reaches 170 ×106km3, but substantial tropical land
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Surface NH
Surface SH
Land ice surface
(×1013 m2)
Ice thickness (CSO, 30 kyr of simulation)Ice thickness (WSO, 20 kyr of simulation)
Ice thickness (WSO minus CSO)
20° N
20° S
40° N
40° S
60° S
20° N
20° S
40° N
40° S
60° S
20° N
20° S
40° N
40° S
60° S
0 10,000 20,000
Time (yr)
30,000 40,000
Figure 3 | Modelled ice sheet oscillations in response to orbital forcing. a,b, Shaded contours show land ice thickness obtained with 20 mbar of carbon
dioxide in response to changes of orbital forcing (WSO (a)) and CSO (b), warm/cold summer orbit for the northern hemisphere) over the course of two
precession cycles (40kyr of simulation). In the light brown continental areas without ice, the white line is used to represent the old ice sheet extension
(WSO case). The Svalbard area is indicated by a red circle. c, Ice thickness variation in 10 kyr (WSO case after 20 kyr minus CSO case after 30kyr of
simulation). In acthe continental outline is shown by the 0.5m elevation contour. d, Surface of hemisphere covered by ice (m2) through time ([WSO] and
[CSO] indicate which orbital configuration is used).
areas remain ice free as a result of sublimation exceeding snowfall
(Supplementary Fig. 10a). Ice volume remains relatively constant
for pCO2=0.1 to 20 mbar (Supplementary Fig. 10b), owing to an
increase in accumulation that compensates for higher ablation rates
(Supplementary Fig. 13). In contrast, above 20 mbar, ice extent in the
eastern Tropics significantly decreases (Supplementary Fig. 10c). At
pCO2=100 mbar, most of the continental ice cover disappears, except
for remnants over mountain ranges (Supplementary Fig. 10d).
To test the sensitivity of the tropical ice sheets to Milankovitch
forcing, experiments with changing orbital parameters were initial-
ized using the steady-state ice sheets for pCO2=20 mbar. Although
obliquity has been invoked as a possible cause of Neoproterozoic
glaciations24, this mechanism remains problematical and cannot
account for significant climatic oscillations at low latitudes25,26 . We
therefore focused on precession as a possible driver, and used two
opposite orbital configurations, favouring cold and warm summers,
respectively, over the northern tropics (CSO: cold summer orbit
and WSO: warm summer orbit; Supplementary Fig. 14). Switch-
ing between these configurations causes tropical ice sheets to ad-
vance/retreat over several hundred kilometres in 10 kyr (Supple-
mentary Movie 1), with strong asymmetry between hemispheres
(Fig. 3). Shifting from WSO to CSO causes ice retreat in the South-
ern Hemisphere and ice sheet expansion in the Northern Hemi-
sphere (Supplementary Fig. 14c,d). Significant ice volume changes
occur between 30N and S, but are less apparent at higher lati-
tudes. This reflects higher ablation rates in the warmer low lati-
tudes (Supplementary Fig. 14e,h), and higher ice sheet sensitivity
to shifting patterns of melt. Larger greenhouse forcing at the end of
the Snowball event implies increasing ice sheet sensitivity to subtle
insolation changes. Given a strong diurnal cycle23, our simulations
also predict a significant number of days above 0C in the tropics
(Supplementary Fig. 15), consistent with geological evidence for
ice rafting, liquid water in lakes and rivers, and photosynthetic
microbial communities.
Our results show that geological evidence for glacial–interglacial
cycles5–7 is consistent with an enriched Snowball Earth theory. Ter-
mination of the Marinoan panglaciation was not a simple switch
from icehouse to greenhouse states, but was characterized by a
climate transition during which glacial cycles could be forced
by Milankovitch orbital variations. The geochemical evidence
presented here implies that at least the upper 60–70% of the
Wilsonbreen Formation was deposited in 105years, on the as-
sumption that a trend in pCO2would be evident over longer
timescales21. Rates of CO2build-up, however, may have slowed in
the later stages of Snowball Earth owing to silicate weathering of
exposed land surfaces, so it is possible that the oscillatory phase was
more prolonged.
Initiation of low-latitude glaciation in the Neoproterozoic re-
quires low pCO2(0.1–1 mbar; refs 2,19,20), implying that the os-
cillatory phase was preceded by a prolonged colder period (106
to 107years) during which pCO2increased gradually as a result of
volcanic outgassing21. This timescale is in agreement with recent
dates indicating the Marinoan lasted 15 million years27. The basal
weathering horizon is consistent with a period of low temperatures
and limited hydrologic cycle before the oscillatory phase2,19 .
Further work is needed to refine the upper and lower limits
of pCO2conducive to climate and ice sheet oscillations in Snow-
ball Earth. Factors not included in the present model, such as
supraglacial dust or areas of ice-free tropical ocean28–30 , can be
expected to make the Earth system more sensitive to orbital forcing.
While many details remain to be investigated, our overall conclu-
sions remain robust.
The Neoproterozoic Snowball Earth was nuanced, varied and
rich. We anticipate that detailed studies of the rock record in other
parts of the world, in conjunction with numerical modelling studies,
will continue to yield insight into the temporal and regional diversity
of this pivotal period in Earth history.
Methods and any associated references are available in the online
version of the paper.
Received 17 February 2015; accepted 8 July 2015;
published online 24 August 2015
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This work was supported by the NERC-funded project GR3/ NE/H004963/1 Glacial
Activity in Neoproterozoic Svalbard (GAINS). Logistical support was provided by the
University Centre in Svalbard. This work was granted access to the HPC resources of
CCRT under allocation 2014-017013 made by GENCI (Grand Equipement National de
Calcul Intensif). We also thank D. Paillard and P. Hoffman for stimulating discussions
and valuable insights.
Author contributions
Field data were collected and analysed by I.J.F., D.I.B., E.J.F., M.J.H., E.A.McM., M.S.P.,
P.M.W. and C.T.E.S. Geochemical analyses were conducted by H.B. and P.M.W. Model
experiments were designed and conducted by G.L.H., Y.D., C.D. and G.R. The
manuscript and figures were drafted by D.I.B., I.J.F. and G.L.H., with contributions from
the other authors.
Additional information
Supplementary information is available in the online version of the paper. Reprints and
permissions information is available online at
Correspondence and requests for materials should be addressed to D.I.B.
Competing financial interests
The authors declare no competing financial interests.
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Sedimentology. Lithofacies were classified based on grain size, internal
sedimentary structures and deformation structures, and bounding surfaces.
Detailed stratigraphic logs were made in the field, supplemented by drawings and
photographs of key features. Samples were taken for polishing and thin sectioning,
to allow detailed examination of microstructures in the laboratory. In addition,
data were collected on clast lithology, shape, surface features and fabric.
Diamictites of the Wilsonbreen Formation are commonly very friable, allowing
included clasts to be removed intact from the surrounding matrix, allowing
measurement of both clast morphology and orientation, using methods developed
for unlithified sediments. Clast morphology (shape, roundness and surface texture)
was measured for samples of 50 clasts to determine transport pathways. Clast fabric
analysis was performed by measuring a-axis orientations of samples of 50 clasts
with a compass-clinometer, and data were summarized using the eigenvalue or
orientation tensor method. Oriented samples for measurement of anisotropy of
magnetic susceptibility (AMS) were collected using a combination of field-drilling
and block sampling. AMS was measured using an AGICO KLY-3 Kappabridge
operating at 875 Hz with a 300 A m1applied field at the University of Birmingham
and an AGICO MFK-1A Kappabridge operating at 976Hz with a 200 A m1
applied field at New Mexico Highlands University.
Geochemistry. Laboratory procedures for extracting, purifying and measuring the
triple oxygen (δ18O and 117O) and sulphur (δ34 S) isotope composition of
carbonate associated sulphate (CAS) in bulk carbonates are detailed in ref. 16.
Briefly, fresh carbonate-bearing rock chips were crushed into fine grains and
powders using mortar and pestle. Rinsing the fines with 18 Mwater revealed little
water-leachable sulphate in any of the Wilsonbreen carbonates. Subsequently,
about 10 to 30 g carbonates were slowly digested in 1–3 M HCl solutions. The
solution was then centrifuged, filtered through a 0.2µm filter, and acidified before
saturated BaCl2droplets were added. BaSO4precipitates were collected after >12 h
and purified using the DDARP method (see Supplementary Information). The
purified BaSO4was then analysed for three different isotope parameters: 117O, by
converting to O2using a CO2-laser fluorination method; δ18O, by converting to CO
through a Thermal Conversion Elemental Analyzer (TCEA) at 1,450C; and δ34 S,
by converting to SO2by combustion in tin capsules in the presence of V2O5
through an Elementar Pyrocube elemental analyser at 1,050 C. The 117O was run
in dual-inlet mode, whereas the δ18O and δ34 S were run in continuous-flow mode.
Both the 117O and δ18 O were run on a MAT 253 at Louisiana State University,
whereas the δ34S was determined on an Isoprime 100 continuous-flow mass
spectrometer at the University of Lancaster, UK. The 117O was calculated as
117Oδ017 O0.52×δ018 O in which δ01,000ln (Rsample/Rstandard ) and Ris the
molar ratio of 18O/16 O or 17O/16O. All δvalues are in Vienna Standard Mean Ocean
Water VSMOW and Vienna Canyon Diablo Troilite (VCDT) for sulphate oxygen
and sulphur, respectively. The analytical standard deviation (1σ) for replicate
analysis associated with the 117O, δ18O and δ34 S are ±0.05h,±0.5hand ±0.2h,
respectively. As the CAS is heterogeneous in hand specimens, the standard
deviation is for laboratory procedures. δ34S values were corrected against VCDT
using within-run analyses of international standard NBS-127 (assuming δ34S values
of +21.1h). Within-run standard replication (1 s.d.) was <0.3h. All geochemical
data are included in Supplementary Table 1.
Numerical modelling. Model runs were conducted with a coupled
atmospheric general circulation model (LMDz) and ice sheet model (GRISLI:
GRenoble Ice Shelf and Land Ice model). LMDz (spatial resolution 4in latitude
×5in longitude with 38 vertical levels) was run with prescribed continental ice
to climatic equilibrium. GRISLI has a 40km grid size and is driven with
downscaled climatic fields of surface air temperature, precipitation and
evaporation. To capture ice sheet–climate feedbacks, LMDz is rerun using the new
ice sheet distribution and topography. This procedure was repeated each 10 kyr to
investigate orbital forcing.
Surface mass balance (accumulation minus sublimation and melting) was
computed from monthly mean temperature, precipitation and evaporation rate.
Melt rate is calculated using the positive-degree-day method.
No sea ice dynamics treatment is specified, the sea ice cover is prescribed and a
thickness of 10 m is imposed. Ice albedo is fixed at 0.6, whereas snow albedo varies
from 0.9 from 0.55 as a function of the zenith and ageing process. Land ice/snow
free surface has the characteristic of a bare soil (rocky regolith) with an
albedo of 0.3.
Code availability. Code for the GCM LMDz can be accessed at: Code for the ISM GRISLI (GRenoble Ice Shelf and Land
Ice model) is not available.
Further details of the methods and modelling procedures are provided in the
Supplementary Information in the online version of the paper.
© 2015 Macmillan Publishers Limited. All rights reserved© 2015 Macmillan Publishers Limited. All rights reserved© 2015 Macmillan Publishers Limited. All rights reserved© 2015 Macmillan Publishers Limited. All rights reserved
... Adjusting surface albedo for dust accumulation results in thinner ablation-zone ice (Fig. 7b) and non-steady state pulses of equatorial sea-glacier invasion (Goodman and Strom 2013). (b) Changes in ice-sheet mass balance in response to variable CO 2 radiative forcing in an ice-sheet-atmosphere general circulation model with Marinoan paleogeography and a totally ice covered ocean (Benn et al. 2015). Note the increase in ice-free land area as CO 2 rises, and its concentration in areas where intense Hadley cells generate strong seasonal surface winds and dust plumes (Voigt 2013;Pierrehumbert et al. 2011). ...
... Note the increase in ice-free land area as CO 2 rises, and its concentration in areas where intense Hadley cells generate strong seasonal surface winds and dust plumes (Voigt 2013;Pierrehumbert et al. 2011). (Modified after Hoffman et al. 2017) S reach dynamic steady state within a few 10 5 years (see Benn et al. 2015). This implies that glacial erosion and sedimentation were ongoing through 99% and 96% of the Sturtian and Marinoan epochs, respectively. ...
... Net sea-level falls of 5.10 2 m occur on most continental margins, despite the countervailing effects of ice gravity and isostatic adjustments (Benn et al. 2015, among others). As CO 2 rises, ice-sheet mass balance becomes sensitive to orbital forcing, causing ice-margin migrations of 5.10 5 m on a precessional (2.10 4 year) time scale (Benn et al. 2015). Although ice sheets flow faster as CO 2 rises, their area and mass contract (Fig. 5b), leaving increasingly large fractions of tropical land area free of glacial ice (Benn et al. 2015). ...
... This work focuses on marine deglaciation. The impact of continental deglaciation is not considered in the model simulation as it may not be critically important since the tropical land ice had probably been ablated before the marine deglaciation started according to Benn et al. (Benn et al., 2015). ...
... where T i is the monthly mean surface temperature for the i th month. Although it varies from location to location, it has been found that on average 8 mm of ice can be melted per PDD (Benn et al., 2015). It is often assumed that 50-60% of the meltwater is refrozen to the ice (Tarasov and Peltier, 1997), so 4 mm of net melting of ice per PDD is assumed herein. ...
... The exact location and geographical extent of the ridge are not important as long as it can obstruct the zonal ocean currents in the tropical region. The continental ice sheets in the tropical region might have been ablated at the start of the deglaciation (Benn et al., 2015) and is therefore not considered. ...
During the Neoproterozoic snowball Earth events, the climate was cold and the oceans were covered by marine ice of ~1000 m thick (sea glacier). Extremely high CO2 level was required in order to trigger the deglaciation these events. It is unclear how long it would take for the sea-ice cover to be completely ablated after the deglaciation started, and what the physical state of the ocean looked like. Here we use a fully coupled general circulation model, CCSM3, to evaluate the rate of poleward retreating of the marine ice and estimate an upper-bound timescale for the marine deglaciation. It is found that the deglaciation will take at most ~300 to 1500 years, depending on the surface albedo of ice; as the albedo decreases, the deglaciation will be prolonged due to the lower CO2 level required to start the deglaciation. Such fast calving/melting of sea ice allows a fresh water lid of ~800 m to develop at the end of the deglaciation.
... Very few studies on the climatic influence of orbital forcing during a snowball Earth have been carried out, the only one known to the authors being that of Benn et al. (2015). They used an asynchronously coupled climate (LMDZ; Hourdin et al. 2006)-ice sheet model [Grenoble Ice Shelf and Land Ice model (GRISLI); Ritz et al. 2001] with 20-mbar CO 2 to study the fluctuations of continental ice sheets due to orbital forcing during the Marinoan snowball Earth event. ...
... A high pCO 2 is used because this is when a snowball Earth is near its melting point (Abbot et al. 2012), at least for the model used here (Wu et al. 2021). The climate sensitivity to orbital forcing at this point is the most interesting since 1) the sensitivity may be larger than when pCO 2 is high (Benn et al. 2015) and 2) it can help us get a sense of how important orbital configuration might be for the snowball deglaciation. It is found very challenging to extract the mechanisms for the climate response to orbital forcing even in a snowball Earth with no continent. ...
How the climate responded to orbital forcing during the Neoproterozoic Snowball Earth events, the most extreme glaciations on Earth, is still unclear. Here, we investigate this problem using a climate model. To simplify the analysis, continents are removed. The results show that even in this simplified situation, the Snowball Earth climate is sensitive to orbital configurations. The globally averaged annual surface temperature can differ by 2.4 °C and the maximum monthly mean temperature can differ by 3.7 °C under different orbital configurations. Therefore, a Snowball Earth could be deglaciated more easily in some orbital configurations than in others. The climatic effect of a particular orbital parameter is highly dependent on the values of other parameters. For example, the effect of obliquity on tropical surface temperature is generally small (<1°C), but can become large (3.8°C) when eccentricity is large and the northern autumn occurs at perihelion (precession=180°). Surprisingly, the global temperature is generally lower at high eccentricity than at near-zero eccentricity, even though the total insolation received by the Earth is higher in the former than in the latter. Moreover, we find that the Milankovitch hypothesis is valid not only in the extratropical region, but also in the tropics; the snow thickness in the tropical region is inversely proportional to the maximum monthly insolation received in this region.
... This is not the first time periglacial structures have been reported from Cryogenian paleosols, which are widespread in South Australia (Williams, 1986;Retallack et al., 2014), British Isles (Kilburn et al., 1965;Spencer, 1971Spencer, , 1985Johnston, 1993), Sweden (Kumpulainen, 2011), and Mauretania (Deynoux, 1982). Detailed paleoclimatic modelling allows not only limited waterways, but bare rock mountains, sedimentary loess and till plains, and cryoconite dustings of glacial ice during the Cryogenian (Benn et al., 2015;Hoffman et al., 2017). These refugia would have allowed survival of life on land, which was substantial enough to consume CO 2 for biomass and silicate weathering to initiate Snowball Earth in the first place (Retallack, 2021(Retallack, , 2023Retallack et al., 2021a). ...
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Gelisol paleosols with sand wedges and sorted stone stripes are reported from the early Cryogenian (717–659 Ma), Surprise Diamictite Member and Sourdough Limestone Member of the Kingston Peak Formation in Redlands Canyon, western Panamint Range, California. The Surprise Diamictite was thus not entirely marine, although glaciomarine sediments and tectonically induced, mass wasting deposits, may be present in other parts of the Kingston Peak Formation. Sand wedge and stone stripe paleosols are evidence of local ice–free land with frigid continental climate at paleolatitude as low as 8 ± 4º from paleomagnetic studies of the Surprise Diamictite. The Sturt glaciation was a dramatic global cooling, but not a global snowball. Bare ground of landslides, alluvial fans, till and loess with mineral nutrients, and microtopographic shelter for complex life on land would have been important for survival of life on Earth from glacial destruction.
... This hypothesis suggested that accumulation of atmospheric carbon dioxide emitted by volcanic activity, would have resulted in a transformation from the snowball Earth to extreme greenhouse conditions as ice sheets prevented the dissolution of carbon dioxide into seawater during the Marinoan glaciation. However, deposits in low palaeo-latitudes show glacial-interglacial cycles during the Marinoan ice age (Rieu et al., 2007;Allen and Etienne, 2008;Benn et al., 2015) and there was substantial open ocean water for the workings of the global carbon cycle and for the survival and evolution of life (Rieu et al., 2007;Allen and Etienne, 2008), as evidenced by existence of carbonaceous compression fossils from the Marinoan-age Nantuo Formation in South China (Ye et al., 2015). ...
The Cryogenian-Ediacaran transition represents a pivotal geological period in the evolution of global climate, ocean chemistry, and early organisms. The transition is concurrent with the change from Marinoan glacial deposits to overlying cap carbonate/dolomite, which is followed by the appearance of novel animal and algae fossils. Unusual carbon cycling during the deposition of cap carbonate/dolomite is recorded by prominent negative carbonate carbon isotope (δ¹³Ccarb) anomalies. The mechanisms which drove melting of the Marinoan icesheets remain uncertain. To explore the cause of this dramatic climate warming and its effect on oceanic biogeochemical cycles, we measured Hg concentrations and isotopes, along with major and trace elements, of the sedimentary succession across the Cryogenian-Ediacaran boundary at the Jiulongwan and Huajipo sections, South China. Hg concentrations show spikes with a ∼ 2 times increase at the top of the Marinoan Nantuo Formation at both sections, which are likely associated with organic matter drawdown rather than enhanced volcanism as indicated by increased TOC contents and similar Hg isotopic signature as those of background Hg deposition. A conspicuous negative shift in δ²⁰²Hg along with a positive shift in Δ¹⁹⁹Hg are observed in the cap dolomite of the Doushantuo Formation at both sections, which are ascribed to contribution of Hg from anoxic deep water and Hg associated with dissolved organic carbon (Hg-DOC), due to upwelling and oceanic oxygenation after deglaciation. Our Hg data argue against a sudden large igneous province (LIP) event causing Marinoan deglaciation. Results also indicate enhanced upwelling and oceanic oxygenation event during the Cryogenian to Ediacaran transition.
The body fossil and biomarker records hint at an increase in biotic complexity between the two Cryogenian Snowball Earth episodes (ca. 661 million to ≤650 million years ago). Oxygen and nutrient availability can promote biotic complexity, but nutrient (particularly phosphorus) and redox dynamics across this interval remain poorly understood. Here, we present high-resolution paleoredox and phosphorus phase association data from multiple globally distributed drill core records through the non-glacial interval. These data are first correlated regionally by litho- and chemostratigraphy, and then calibrated within a series of global chronostratigraphic frameworks. The combined data show that regional differences in postglacial redox stabilization were partly controlled by the intensity of phosphorus recycling from marine sediments. The apparent increase in biotic complexity followed a global transition to more stable and less reducing conditions in shallow to middepth marine environments and occurred within a tolerable climatic window during progressive cooling after post-Snowball super-greenhouse conditions.
The rapid rise of glacioeustatic change is the most extreme paleoenvironment alteration in the aftermath of Snowball Earth. Although geologists conducted a lot of multi-subdiscipline research on this issue previously, there still exists the potential room for further discussions of the process in detail. For decades, the practice proved that the Fischer plot is a simple and robust tool to illustrate the fluctuations of accommodation patterns v.s. cycle sets or strata depth which could be interpreted as relative sea-level changes. This research simulates the Fischer plot to unravel the sea-level change in the aftermath of Marinoan glaciation by measuring the lower Ediacaran Doushantuo Formation in Shennongjia, South China. The result shows that 131 fifth-order cycles and nine third-order cycles help us propose a completed second-order cycle variation of ice melting-forced sea-level change, i.e., (1) early high-frequency and slow to rapid stepwise rising, and (2) followed by a stable decrease in the latter. In addition, the vertical sedimentary facies of the lower Doushantuo Formation display, in ascending order, (1) intertidal carbonate rock, (2) subtidal clastics with turbidite, and (3) intertidal lagoon fine clastics, indicating the process of the relative waxing and waning of sea-level. Such interpretation of the Fischer plot and the sedimentary facies’ vertical evolution is beneficial for studying the high-frequency sea-level change and paleogeographic reconstruction of post-Marinoan deglaciation.
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The snowball Earth hypothesis predicts globally synchronous glaciations that persisted on a multimillion year time scale. Geochronological tests of this hypothesis have been limited by a dearth of reliable age constraints bracketing these events on multiple cratons. Here we present four new Re-Os geochronology age constraints on Sturtian (717-660 Ma) and Marinoan (635 Ma termination) glacial deposits from three different paleocontinents. A 752.7 ± 5.5 Ma age from the base of the Callison Lake Formation in Yukon, Canada, confirms nonglacial sedimentation on the western margin of Laurentia between ca. 753 and 717 Ma. Coupled with a new 727.3 ± 4.9 Ma age directly below the glacigenic deposits of the Grand Conglomerate on the Congo craton (Africa), these data refute the notion of a global ca. 740 Ma Kaigas glaciation. A 659.0 ± 4.5 Ma age directly above the Maikhan-Uul diamictite in Mongolia confirms previous constraints on a long duration for the 717-660 Ma Sturtian glacial epoch and a relatively short nonglacial interlude. In addition, we provide the first direct radiometric age constraint for the termination of the Marinoan glaciation in Laurentia with an age of 632.3 ± 5.9 Ma from the basal Sheepbed Formation of northwest Canada, which is identical, within uncertainty, to U-Pb zircon ages from China, Australia, and Namibia. Together, these data unite Re-Os and U-Pb geochronological constraints and provide a refined temporal framework for Cryogenian Earth history.
This work presents the detailed geology of Svalbard. It arises from about 50 years of research in many aspects of Svalbard geology by the author, with many colleagues and collaborators. The work is divided into four parts, the first being introductory, setting the scene and outlining the main geological features and the principal geological conventions used throughout. Part two divides Svalbard into eight regions, describing each in a separate chapter. Part three looks at historical events and environments, and part four comprises a summary of the economic aspects of Svalbard geology, plus indexes and reference lists.
Creep is an important mode of aeolian sand transport, but it has received little attention in previous studies due to experimental difficulties and insufficient theory. In this study, we conducted 116 groups of experiments with three repeats for each group in a wind tunnel to measure the creeping mass of four different mean grain sizes (152, 257, 321, and 382 µm) over six bed lengths (2.0, 3.5, 5.0, 6.5, 8.0, and 10.0 m) at six different friction velocities (0.23, 0.35, 0.41, 0.47, 0.55, and 0.61 m/s). We attempted to develop a comprehensive model of the aeolian creeping mass by analyzing the effect of wind velocity, the particle size and the sand bed length based on the experimental data. The primary conclusions are as follows: 1) the complex relationship among the wind velocity, the grain size, the length of the bed, and the surface shape determines sand creep. There was no unified formula to express the effect of particle sizes and the sand bed length on aeolian creeping masses, and their effects appeared to depend on each other and wind velocity, whereas the creeping mass increases with increasing wind velocity for any particle size with any length of sand bed. 2) This paper presented a predicting model to determine the aeolian creeping mass, whose calculating results can match to experimental data with correlation coefficients (R2) of 0.94 or higher. 3) The effect of grain size on creeping mass can be classified into three categories: the creeping mass increases with increasing grain size, the creeping mass initially decreases and subsequently increases with increasing grain size, and the creeping mass fluctuates with the grain size. 4) The effect of increasing bed length appears to depend on the grain size. For mean grain sizes of 152, 257, and 321 µm, creep initially increases with increasing bed length before decreasing above a certain value, while for a mean grain size of 382 µm, the creeping mass gradually increased with increasing bed length. The results help to elucidate aeolian creep and provide an intense foundation for advanced study.
The aim of this article is to describe the state of the art of research on the Neoproterozoic atmospheres and glaciation. Using numerical modeling, the authors examine the potential for Earth to have been fully glaciated from the poles to the equator, evaluating the plausibility of a snowball Earth to have occurred. Physical processes and mechanisms suggested for the initiation of a global glaciation are explored and questions asked are as follows: (1) How can climate models that predict a totally ice-capped ocean be reconciled with paleontological evidence that establishes the persistence of photosynthetic activity throughout the snowball event? (2) How can the glacial sequences be explained with the Snowball Earth scenario? (3) What about the melting and the aftermath of the Snowball Earth solution? For each of these questions, 'modeling' solutions that are plausible but may not be definitive are presented, given the extreme severity of these events, which pushes the models to their physical limits. The models, nevertheless, provide important clues and quantitative constraints on the controversial question of whether these catastrophic events could have occurred in their most extreme form.
Geologic evidence of tropical sea level glaciation in the Neoproterozoic is one of the cornerstones of the Snowball Earth hypothesis. However, it is not clear during what part of the Snowball Earth cycle that land-based glaciers or ice sheets could have grown: just before the collapse with tropical oceans still open, or after the collapse with oceans completely covered with sea ice. In the former state, the tropics may still have been too warm to allow flowing ice to reach sea level; in the latter, snowfall minus sublimation may have been too small to build significant ice. These possibilities are tested with a coupled global climate model and dynamic ice sheet model, with two continental configurations (~750 Ma, 540 Ma) and two CO2 levels bracketing the collapse to Snowball Earth (840, 420 ppmv). Prior to collapse large high- latitude ice sheets form at 750 Ma, but with flat continents, no low-latitude ice grows at 750 or 540 Ma. In the absence of reliable knowledge of Neoproterozoic topography, we apply a small-scale “test” profile in the ice sheet model, representing a coastal mountain range on which glaciers can be initiated and flow seaward. Prior to collapse, almost all low-latitude test glaciers fail to reach the coast at 750 Ma, but at 540 Ma many do reach the sea. After the collapse to full Snowball conditions, the hydrologic cycle is greatly reduced, but extensive kilometer-thick ice sheets form slowly on low-latitude continents within a few 100,000 years, both at 750 Ma and 540 Ma.
Ongoing controversy about Neoproterozoic Snowball Earth events motivates a theoretical study of stability and hysteresis properties of very cold climates. A coupled atmosphere–ocean-sea ice general circulation model (GCM) has four stable equilibria ranging from 0% to 100% ice cover, including a “Waterbelt” state with tropical sea ice. All four states are found at present-day insolation and greenhouse gas levels and with two idealized ocean basin configurations. The Waterbelt is stabilized against albedo feedback by intense but narrow wind-driven ocean overturning cells that deliver roughly 100 W m−2 heating to the ice edges. This requires three-way feedback between winds, ocean circulation and ice extent in which circulation is shifted equatorward, following the baroclinicity at the ice margins. The thermocline is much shallower and outcrops in the tropics. Sea ice is snow-covered everywhere and has a minuscule seasonal cycle. The Waterbelt state spans a 46 W m−2 range in solar constant, has a significant hysteresis, and permits near-freezing equatorial surface temperatures. Additional context is provided by a slab ocean GCM and a diffusive energy balance model, both with prescribed ocean heat transport (OHT). Unlike the fully coupled model, these support no more than one stable ice margin, the position of which is slaved to regions of rapid poleward decrease in OHT convergence. Wide ranges of different climates (including the stable Waterbelt) are found by varying the magnitude and spatial structure of OHT in both models. Some thermodynamic arguments for the sensitivity of climate and ice extent to OHT are presented.