Neoproterozoic Snowball Earth Events Research Articles

Response of the Snowball Earth Climate to Orbital Forcing at a High CO2 Level

Abstract 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 it 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 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.

Mg and Sr Isotopes in Cap Dolostone: Implications for Oceanic Mixing after a Neoproterozoic Snowball Earth Event

The snowball Earth (SBE) describes a state of the Earth’s climate with global or near-global ice cover. The cap dolostone at the base of the Ediacaran successions serves as useful archives for studying environmental change during the Marinoan Snowball Earth deglaciation in Neoproterozoic. The characteristic compositions in dolomite provide critical information on continental weathering and coastal water mixing after glacial retreat. However, valid methods for pristine dolomite separation remain challenging. In this study, four selected cap dolostone samples from the base of the Ediacaran Lantian Formation were used for establishing a new 3-step leaching method, to remove the secondary calcite and other impurities before determination of δ26Mg and 87Sr/86Sr in dolomite. Non-destructive Raman, X-ray diffractometer (XRD) and scanning electron microscopy (SEM) were used to examine the distribution of dolomite and minor calcite/silicate in each sample. Micro-drill powders before each extraction procedure were examined in weight loss and mineralogical compositions, as well as the chemicals in the leaching solutions. Potential diagenetic artifacts were evaluated using Sr/Ca, Mn/Sr, 87Sr/86Sr and δ26Mg in solutions. By applying a simple two-end member mixing between the seawater and the silicate sources (R2 = 0.48, n = 23), the down-core variations of δ26Mg and 87Sr/86Sr in cap dolostone can be used to gain a better understand of the temporal weathering intensity changes, as well as the coastal oceanic mixing processes, after the Marinoan deglaciation.

Sea-glacier retreating rate and climate evolution during the marine deglaciation of a snowball Earth

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 CO 2 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 CO 2 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. • The sea-glacier retreating of snowball Earth is studied using a climate model • The complete ablation of the thick marine ice takes at most ~300 yr to 1500 yr • The elapsed time is longer if the sea-ice albedo is lowered, e.g., by dust • A fresh water lid of hundreds of meters thick would form upon completion

Snowball Earth, population bottleneck and Prochlorococcus evolution.

Prochlorococcus are the most abundant photosynthetic organisms in the modern ocean. A massive DNA loss event occurred in their early evolutionary history, leading to highly reduced genomes in nearly all lineages, as well as enhanced efficiency in both nutrient uptake and light absorption. The environmental landscape that shaped this ancient genome reduction, however, remained unknown. Through careful molecular clock analyses, we established that this Prochlorococcus genome reduction occurred during the Neoproterozoic Snowball Earth climate catastrophe. The lethally low temperature and exceedingly dim light during the Snowball Earth event would have inhibited Prochlorococcus growth and proliferation, and caused severe population bottlenecks. These bottlenecks are recorded as an excess of deleterious mutations accumulated across genomic regions and inherited by descendant lineages. Prochlorococcus adaptation to extreme environmental conditions during Snowball Earth intervals can be inferred by tracing the evolutionary paths of genes that encode key metabolic potential. Key metabolic innovation includes modified lipopolysaccharide structure, strengthened peptidoglycan biosynthesis, the replacement of a sophisticated circadian clock with an hourglass-like mechanism that resets daily for dim light adaption and the adoption of ammonia diffusion as an efficient membrane transporter-independent mode of nitrogen acquisition. In this way, the Neoproterozoic Snowball Earth event may have altered the physiological characters of Prochlorococcus, shaping their ecologically vital role as the most abundant primary producers in the modern oceans.

Influence of Dust on the Initiation of Neoproterozoic Snowball Earth Events

AbstractIt has been demonstrated previously that atmospheric dust loading during the Precambrian could have been an order of magnitude higher than in the present day and could have cooled the global climate by more than 10 °C. Here, using the fully coupled atmosphere-ocean general circulation model CESM1.2.2, we determine whether such dust loading could have facilitated the formation of Neoproterozoic snowball Earth events. Our results indicate global dust emission decreases as atmospheric CO2 concentration (pCO2) decreases due to increasing snow coverage, but atmospheric dust loading does not change or even increases due to decreasing precipitation and strengthening June-July-August (JJA) Hadley circulation. The latter lifts more dust particles to high altitude and thus increases the lifetime of these particles. As the climate becomes colder and the surface albedo higher, the cooling effect of dust becomes weaker; when the global mean surface temperature is approximately -13 °C, dust has negligible cooling effect. The threshold pCO2 at which Earth enters a snowball state is between 280 to 140 ppmv when there is no dust, and is similar when there is relatively light dust loading (~4.4 times present-day value). However, the threshold pCO2 decreases dramatically to between 70 to 35 ppmv when there is heavy dust loading (~33 times present-day value), due to the decrease in planetary albedo which increases the energy input into the climate system. Therefore, dust makes it more difficult for Earth to enter a snowball state.

Influence of Dust on the Initiation of Neoproterozoic Snowball Earth Events

Influence of Dust on the Initiation of Neoproterozoic Snowball Earth Events

Neoproterozoic Blaini Formation of Lesser Himalaya, India: Fiction and Fact

AbstractThe long-conceived idea of the glacial origin of Blaini diamictite of Lesser Himalayan Neoproterozoic succession reached its maxima when the diamictites and capping pink limestone were attributed to the Neoproterozoic Snowball Earth event and its aftermath, respectively. Occurrences of diamictite-limestone association in two different levels have also been correlated with the Sturtian and Marinoan glaciations. Critical review, however, reveals that the interpretations of the glacial origin of diamictites are not well founded. The diamictite-limestone association, which occurs at the lower part of a thick, light brown shale unit and laterally grades into light brown shale, primarily indicates episodic surge events in an otherwise tranquil condition favorable for hemipelagic sedimentation. The lithology, bed geometry, internal organization, and disposition of the diamictite bodies suggest deposition of debris flow fan lobes along fault scarps in a rift setting. Emplacement of subaqueous debris flows is indicated by the associated deposits of entrained turbidity currents. The limestone also bears the signature of claciturbidites. The appearance of diamictite bodies and associated limestone in two distinct levels is not a stratigraphic disposition; on the contrary, the deposits were dislocated and repeated by two successive regional thrust faults. The Chemical Index of Alteration (CIA) values of the light brown shale and the matrix of the diamictites indicate that these sediments formed through prolonged subaerial weathering. The events leading up to development of the rift system and evidence of prolonged weathering within the basin-fill sediments are consistent with supercontinental break up, the prologue of Snowball Earth.

Large true polar wander in a sea level model with application to the Neoproterozoic snowball Earth events

A sea level model which is normally used to calculate sea level changes during glacial-interglacial cycles is modified to solve the approximate nonlinear Liouvelle equation, in order to calculate ‘large’ true polar wander (TPW) that may be induced by ice sheet loading. The purpose is to understand when the TPW will be too large to be solved properly by the linear model, and to properly calculate the TPW induced by snowball Earth events. It is found that the relative error for TPW calculated with a linear model will be >10% when the TPW exceeds ∼2° for ice sheets that develop near the poles, but remains <10% when the TPW exceeds 20° for ice sheets centered at between 45° and 60° latitude. To ensure the relative error for TPW speed to be <10%, the TPW should not exceed 1° and 10° for ice sheets near the poles and 50° latitude, respectively. Because the hypothesized ice sheets during the Neoproterozoic snowball Earth events were located near 55°S for one of the continental configuration, and not much lower than 45°S for the other, the TPW calculated with the linear model in a previous study is overall correct even though its magnitude could be >10° for certain viscosity profiles of the Earth.

Did the transition to plate tectonics cause Neoproterozoic Snowball Earth?

AbstractWhen Earth's tectonic style transitioned from stagnant lid (single plate) to the modern episode of plate tectonics is important but unresolved, and all lines of evidence should be considered, including the climate record. The transition should have disturbed the oceans and atmosphere by redistributing continents, increasing explosive arc volcanism, stimulating mantle plumes and disrupting climate equilibrium established by the previous balance of silicate‐weathering greenhouse gas feedbacks. Formation of subduction zones would redistribute mass sufficiently to cause true polar wander if the subducted slabs were added in the upper mantle at intermediate to high latitudes. The Neoproterozoic Snowball Earth climate crisis may reflect this transition. The transition to plate tectonics is compatible with nearly all proposed geodynamic and oceanographic triggers for Neoproterozoic Snowball Earth events, and could also have contributed to biological triggers. Only extraterrestrial triggers cannot be reconciled with the hypothesis that the Neoproterozoic climate crisis was caused by a prolonged (200–250 m.y.) transition to plate tectonics.

Initiation of Snowball Earth with volcanic sulfur aerosol emissions

AbstractWe propose that the first Neoproterozoic Snowball Earth event, the Sturtian glaciation, was initiated by the injection of sulfate aerosols into the stratosphere. Geochronological data indicate that the Natkusiak magmatic assemblage of the Franklin large igneous province coincided with onset of the Sturtian glaciation. The Natkusiak was emplaced into an evaporite basin and entrained significant quantities of sulfur, which would have led to extensive SO2 and H2S outgassing in hot convective plumes. The largest of these plumes could have penetrated the tropopause, leading to stratospheric sulfate aerosol formation and an albedo increase sufficient to force a Snowball. Radiative forcing was maximized by the equatorial location of the Franklin and the cool Neoproterozoic background climate, which would have lowered the tropopause height, increasing the rate of stratospheric aerosol injection. Our results have implications for understanding Phanerozoic mass extinction events, exoplanet habitability, and aerosol perturbations to the present‐day climate.

Stable “Waterbelt” climates controlled by tropical ocean heat transport: A nonlinear coupled climate mechanism of relevance to Snowball Earth

AbstractOngoing 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.

Climate simulations of Neoproterozoic snowball Earth events: Similar critical carbon dioxide levels for the Sturtian and Marinoan glaciations

The Sturtian and Marinoan snowball Earth episodes initiated 720 and 650 million years ago, respectively, are among the most dramatic events in Earth's history. The ultimate causes of these events remain obscure, however, and there is still uncertainty about the critical levels of greenhouse gas concentrations at which the snowball transition occurs. Furthermore, earlier modelling results (with incomplete representations of important boundary conditions) provided conflicting indications for differences between the critical carbon dioxide concentrations for the Marinoan and the Sturtian, reporting either the earlier or the later epoch to be more susceptible to global glaciation. Both the absolute values of and possible differences between these glaciation thresholds have profound implications for scenarios of snowball initiations during the Neoproterozoic. Here, we present coupled climate simulations (using an ocean general circulation model with dynamic/thermodynamic sea ice coupled to a fast atmosphere) focusing on the differences between the Neoproterozoic glaciations. For the first time, our simulations use realistic boundary conditions in terms of changes in solar luminosity between the two epochs and the most recent continental reconstructions. In agreement with previous studies with models including ocean and sea-ice dynamics, we report low values for the critical carbon dioxide concentration during the Neoproterozoic. But in contrast to hints from earlier studies we find very similar values of 100–130 ppm for the snowball bifurcation point during the Sturtian and Marinoan. This highlights the importance of realistic boundary conditions for climate simulations of the Neoproterozoic glaciations.

The Laurentian record of Neoproterozoic glaciation, tectonism, and eukaryotic evolution in Death Valley, California

Neoproterozoic strata in Death Valley, California, contain eukaryotic microfossils and glacial deposits that have been used to assess the severity of putative snowball Earth events and the biological response to extreme environmental change. These successions also contain evidence for synsedimentary faulting that has been related to the rifting of Rodinia, and in turn the tectonic context of the onset of snowball Earth. These interpretations hinge on local geological relationships and both regional and global stratigraphic correlations. Here, we present new geological mapping, measured stratigraphic sections, carbon and strontium isotope chemostratigraphy, and micropaleontology from the Neoproterozoic glacial deposits and bounding strata in Death Valley. These new data enable us to refine regional correlations, both across Death Valley and throughout Laurentia, and construct a new age model for glacigenic strata and microfossil assemblages. Particularly, our remapping of the Kingston Peak Formation in the Saddle Peak Hills and near the type locality shows for the first time that glacial deposits of both the Marinoan and Sturtian glaciations can be distinguished in southeastern Death Valley, and that beds containing vase-shaped microfossils are slump blocks derived from the underlying strata. These slump blocks are associated with multiple overlapping unconformities that developed during synsedimentary faulting, which is a common feature of Cyrogenian strata along the margin of Laurentia from California to Alaska. With these data, we conclude that all of the microfossils that have been described to date in Neoproterozoic strata of Death Valley predate the glaciations and do not bear on the severity, extent, or duration of Neoproterozoic snowball Earth events.

The Nebula Winter: The united view of the snowball Earth, mass extinctions, and explosive evolution in the late Neoproterozoic and Cambrian periods

Encounters with nebulae, such as supernova remnants and dark clouds in the galaxy, can lead to an environmental catastrophe on the Earth through the negative climate forcings and destruction of the ozone layer by enhanced fluxes of cosmic rays and cosmic dust particles. A resultant reduction in primary productivity leads to mass extinctions through depletion of oxygen and food starvations as well as anoxia in the ocean. The model shows three levels of hierarchical time variations caused by supernova encounters (1–10kyrs), dark cloud encounters (0.1–10Myrs), and starbursts (~100Myrs), respectively. This “Nebula Winter” model can explain the catastrophic phenomena such as snowball Earth events, repeated mass extinctions, and Cambrian explosion of biodiversities which took place in the late Proterozoic era through the Cambrian period. The Late Neoproterozoic snowball Earth event covers a time range of ca. 200Myrs long spanning from 770Ma to the end of Cambrian period (488Ma) with two snowball states called Sturtian and Marinoan events. Mass extinctions occurred at least eight times in this period, synchronized with large fluctuations in δ13C of carbonates in the sediment. Each event is likely to correspond to each nebula encounter. In other words, the late Neoproterozoic snowball Earth and Cambrian explosion are possibly driven by a starburst, which took place around 0.6Ga in the Milky Way Galaxy. The evidences for a Nebula Winter can be obtained from geological records in sediment in the deep oceans at those times.

Ca isotopic compositions of dolomite, phosphorite and the oldest animal embryo fossils from the Neoproterozoic in Weng'an, South China

Deciphering the drastic changes of surface environment and the emergence of animals after the Neoproterozoic Snowball Earth event are important for understanding the changes of surface environment and its influence on the evolution of life through geologic time. Especially, the emergence of two types of Metazoan animals such as animal embryo fossils, cnidarians or sponges, and Ediacaran fauna in the late Neoproterozoic was one of the critical turning points in the biological evolution. Calcium is one of the essential elements for the growth of most animals. In this study, in order to evaluate the Ca cycles in the Neoproterozoic, we have measured Ca isotopic ratios ( 44Ca/ 42Ca and 43Ca/ 42Ca) for phosphorite, dolostone and phosphatic animal embryo fossils with a multiple collector, inductively coupled plasma-mass spectrometer (MC-ICP-MS). The resulting 44Ca/ 42Ca ratio defined by the relative deviation from the ratio of NIST SRM915a ( δ 44/42Ca NIST915) for phosphorite and dolostone ranges from 0.83 to 0.95‰, demonstrating that the fractionation between phosphorite/dolostone and seawater was very small. This evidence indicates that at the emergence of the Weng'an biota seawater was deficient in Ca probably due to mass deposition of phosphorite/dolostone and to the beginning of Ca-biomineralization. Three phosphatic animal embryo fossils have lower δ 44/42Ca values than the phosphorite and dolomite, implying that the precursor of the phosphatic embryo fossils was able to fractionate Ca isotopes through Ca-biomineralization, consistent with marine gastropods.

Variations of sulfur and carbon isotopes in seawater during the Doushantuo stage in late Neoproterozoic

Successive analyses of sulfur and carbon isotopic compositions of carbonates strata in the Doushantuo Formation in the Yangtze area were accomplished through a method of extracting trace sulfate from carbonates. Sulfur and carbon isotopic compositions of coeval seawater were estimated from the samples that show the least diagenetic alteration. A high-resolution age curve of sulfur isotopes in seawater sulfates was obtained in the Doushantuo stage, which reflects the trend of variation in seawater sulfur isotopes after the Neoproterozoic snowball Earth event. Similar characteristics of variation in carbon isotopes were observed in the coeval carbonates. A large positive δ34S excursion over +20‰ occurs in ancient seawater sulfates in the early Doushantuo stage. Simultaneously, the δ13 C values in ancient seawater carbonates exhibit a positive excursion up to 10‰ The maximum δ34S and δ13C values are +46.4‰ and +6.9‰, respectively. In the middle Doushantuo stage, the range of variation in δ34 S values of seawater is relatively narrow, but δ13C values are quite high. Then, δ34S values of seawater become oscillating, and the same occurs in δ13C values. Negative excursions in δ34 S and δ13 C values occur simultaneously at the end of the Doushantuo stage, and the minimum δ34S and δ13C values dropped down to −10.1‰ and –5.7‰, respectively. The characteristics of variations in the sulfur and carbon isotopes of ancient seawater imply strong changes in oceanic environment that became beneficial to inhabitation and propagation of organism. The organic productivity and burial rate of organic carbon once reached a quite high level during the Doushantuo stage. However, the state of environment became unstable after the global glaciation. The global climate and environment possibly were fluctuating and reiterating. The negative excursions in δ34S and δ13C values occurring at the end of the Doushantuo stage may represent a global event, which might be related to oxidation of deep seawater.