Sedimentary challenge to Snowball Earth

Allen, Philip A.; Etienne, James L.

doi:10.1038/ngeo355

Cited by 202 publications

(121 citation statements)

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“…Consequently, a smaller glacial volume would be needed to match the 18 O carbonate excursions in the isotope record. The amount of glacial ice during the Shuram-Wonoka event is poorly constrained, but the event is within an ice-age-prone time interval (30,31), and there is some indication of glacial diamictites correlating to the Shuram-Wonoka anomaly (37). Finally, the temperature in the extratropics may have increased by 50% more than the global mean temperature increase (38) (thin dashed line, Fig.…”

Section: Resultsmentioning

confidence: 99%

“…It is important for our modeling that the methane concentration is high enough and its lifetime long enough to elevate temperature for sufficient CO 2 removal by weathering, and to generate the observed timing of the isotope signal in the DIC reservoir. We initialize the model with reservoir sizes as shown in Table S1, and weathering and burial fluxes as estimated for the earliest Phanerozoic (7) modified to result in a relatively cooler climate the ice-age-prone late Neoproterozoic time interval (30,31). The total preevent CH 4 flux to the atmosphere is assumed to be the same as the modern preanthropogenic flux.…”

Section: Modelmentioning

confidence: 99%

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Towards a quantitative understanding of the late Neoproterozoic carbon cycle

Bjerrum

Canfield

2011

Proc. Natl. Acad. Sci. U.S.A.

128

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The cycles of carbon and oxygen at the Earth surface are intimately linked, where the burial of organic carbon into sediments represents a source of oxygen to the surface environment. This coupling is typically quantified through the isotope records of organic and inorganic carbon. Yet, the late Neoproterozoic Eon, the time when animals first evolved, experienced wild isotope fluctuations which do not conform to our normal understanding of the carbon cycle and carbon-oxygen coupling. We interpret these fluctuations with a new carbon cycle model and demonstrate that all of the main features of the carbonate and organic carbon isotope record can be explained by the release of methane hydrates from an anoxic dissolved organic carbon-rich ocean into an atmosphere containing oxygen levels considerably less than today.carbon isotope excursion | carbon monoxide | Shuram-Wonoka anomaly | earth evolution | atmospheric chemistry T he Neoproterozoic Eon was one of the most dynamic, yet enigmatic, times in Earth history. The Eon saw the breakup of super continent Rodinia and was punctuated by several glacial episodes, some of which were global in extent (1). The Eon saw the evolution and expansion of the first animals on Earth (2), as well as a rise in atmospheric oxygen and a major oxygenation of the deep ocean (3, 4). The isotopic composition* of carbonate (δ 13 C IC ) in sedimentary rocks reveals some of the largest isotope fluctuations in marine dissolved inorganic carbon (DIC) in Earth history (e.g., 4-6). Such isotope fluctuations are considered to reflect dynamics in the carbon cycle, and they have been used to reconstruct the history of atmospheric oxygen (e.g., 7, 8).The Neoproterozoic δ 13 C IC record, however, reveals excursions to less than mantle values (< − 5‰), and the assumed input value to the oceans (5, 9) ( Fig. 1). Prolonged negative δ 13 C IC excursions such as these cannot be explained by our normal understanding of the carbon cycle (e.g., 10, 11). While a diagenetic origin has been advocated to explain these excursions (12, 13), we will show that the major features of the carbon isotope records are consistent with a seawater origin through the action of the carbon cycle.Indeed, a nondiagenetic origin for the carbon isotope excursion is supported by the fact that in individual regions, an excursion may be observed over 100's of kilometers, mappable to the same stratigraphic horizon, and with isotope trends independent of sediment lithology (e.g., 14-16). The lateral extent and stratigraphic consistency of these excursions is difficult to reconcile with a diagenetic origin. Furthermore, modeling shows that the extent of isotopic alteration during diagenesis is highly dependant on the mineralogy of both the initial and the altered sediment (12). Isotope trends, however, transcend these differences (e.g., 6, 14, 17), further arguing against a diagenetic origin for the isotope signals.Many of the large Neoproterozoic isotope excursions display a relationship between the 18 O and 13 C of carbonate, which is...

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Section: Resultsmentioning

confidence: 99%

Section: Modelmentioning

confidence: 99%

Towards a quantitative understanding of the late Neoproterozoic carbon cycle

Bjerrum

Canfield

2011

Proc. Natl. Acad. Sci. U.S.A.

128

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“…Temperatures would be too cold for fluvial activity and modification of continental shelf sediments by tidal and wave action would be greatly attenuated (Hoffman and Schrag, 2002). Models that do not require deeply frozen temperatures allow a wider range of sedimentary environments associated with an active hydrologic cycle and open oceans to be active throughout the glaciation and, in certain localities, such sedimentary environments have been highlighted as counter evidence to the presence of a snowball Earth during the Cryogenian (Allen and Etienne, 2008).…”

Section: Introductionmentioning

confidence: 99%

“…The origin and significance of these glaciogenic deposits has been debated for nearly a century (see review in Harland, 2007), but the (Evans and Raub, 2011;Schmidt et al, 2009;Sohl et al, 1999;Sumner et al, 1987). global climate, significant differences in the environment are expected depending on the temperature of Earth's surface. For example, at the temperatures expected by the end-member model of a snowball Earth, the range of active sedimentary processes during the peak glacial periods would be limited (Allen and Etienne, 2008). Wind-blown sediments may be made unavailable for transport because of ice burial or ice cementation.…”

Section: Introductionmentioning

confidence: 99%

New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

Ewing

Eisenman

Lamb

et al. 2014

Earth and Planetary Science Letters

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Intense glaciation during the end of Cryogenian time (∼635 million years ago) marks the coldest climate state in Earth history -a time when glacial deposits accumulated at low, tropical paleolatitudes. The leading idea to explain these deposits, the snowball Earth hypothesis, predicts globally frozen surface conditions and subfreezing temperatures, with global climate models placing surface temperatures in the tropics between −20 • C and −60 • C. However, precise paleosurface temperatures based upon geologic constraints have remained elusive and the global severity of the glaciation undetermined. Here we make new geologic observations of tropical periglacial, aeolian and fluvial sedimentary structures formed during the end-Cryogenian, Marinoan glaciation in South Australia; these observations allow us to constrain ancient surface temperatures. We find periglacial sand wedges and associated deformation suggest that ground temperatures were sufficiently warm to allow for ductile deformation of a sandy regolith. The wide range of deformation structures likely indicate the presence of a paleoactive layer that penetrated 2-4 m below the ground surface. These observations, paired with a model of ground temperature forced by solar insolation, constrain the local mean annual surface temperature to within a few degrees of freezing. This temperature constraint matches well with our observations of fluvial deposits, which require temperatures sufficiently warm for surface runoff. Although this estimate coincides with one of the coldest near sea-level tropical temperatures in Earth history, if these structures represent peak Marinaon glacial conditions, they do not support the persistent deep freeze of the snowball Earth hypothesis. Rather, surface temperatures near 0 • C allow for regions of seasonal surface melting, atmosphere-ocean coupling and possible tropical refugia for early metazoans. If instead these structures formed during glacial onset or deglaciation, then they have implications for the timescale and character for the transition into or out of a snowball state.

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“…Geologic and geochemical evidence suggest that glacial/interglacial oscillations are coincident with lower atmospheric CO 2 [5] and are exacerbated by lower solar luminosity [6]. For instance, models indicate overcoming high planetary albedo during Snowball Earth events required greenhouse warming caused by the accumulation of high levels of CO 2 from volcanic outgassing accompanied by decreases in silicate weathering [7,8]. Due to human activity, atmospheric CO 2 is now above 400 ppm [9] and from 1999 to 2010, CO 2 was emitted at a rate 100 times as fast as during the last glacial termination [10].…”

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confidence: 99%

Inorganic carbon addition stimulates snow algae primary productivity

Hamilton

Havig

2018

The ISME Journal

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Earth has experienced glacial/interglacial oscillations accompanied by changes in atmospheric CO 2 throughout much of its history. Today over 15 million square kilometers of Earth's land surface is covered in ice including glaciers, ice caps, and ice sheets. Glaciers are teeming with life and supraglacial snow and ice surfaces are often darkened by the presence of photoautotrophic snow algae, resulting in accelerated melt due to lowered albedo. Few studies report the productivity of snow algal communities and the parameters which constrain their growth on supraglacial surfaces-key factors for quantifying biologically induced albedo effects (bio-albedo). We demonstrate that snow algae primary productivity is stimulated by the addition of inorganic carbon. Our results indicate a positive feedback between increasing CO 2 and snow algal primary productivity, underscoring the need for robust climate models of past and present glacial/interglacial oscillations to include feedbacks between supraglacial primary productivity, albedo, and atmospheric CO 2 .Earth has experienced intervals of glacial and interglacial periods in its history including Snowball Earth events [1,2]. Today, glaciers and ice sheets are integral to the Earth's climate and hydrological system-they influence regional and global climate, are sensitive to climate change, and are the largest freshwater reservoir on Earth [3,4]. Geologic and geochemical evidence suggest that glacial/interglacial oscillations are coincident with lower atmospheric CO 2 [5] and are exacerbated by lower solar luminosity [6]. For instance, models indicate overcoming high planetary albedo during Snowball Earth events required greenhouse warming caused by the accumulation of high levels of CO 2 from volcanic outgassing accompanied by decreases in silicate weathering [7,8]. Due to human activity, atmospheric CO 2 is now above 400 ppm [9] and from 1999 to 2010, CO 2 was emitted at a rate 100 times as fast as during the last glacial termination [10]. Coincident with increasing CO 2 , average global temperatures have increased (~1°C over the past century) leading to glacial retreat and receding snowpack.Glaciers and ice sheets are a host to diverse ecosystems including supraglacial communities that contribute to local and global biogeochemical cycles [11]. Snow algae (eukaryotic photoautotrophs) are key primary producers on supraglacial habitats in the Arctic, and on glaciers and snowfields throughout the world where they thrive in highirradiation environments [12,13]. To overcome this high irradiance, snow algae produce secondary carotenoids resulting in blooms of red algal biomass [14], which darkens snow and ice surfaces. In Sierra Nevada snowfields, snow algae abundance was negatively correlated to surface albedo [15] and a recent study quantified the role of snow algae communities in snowmelt on an icefield in Alaska [16]. Similarly, in the Arctic, red algal blooms darken the snow/ice surface, lowering surface albedo (by as much as 13% over the melt season) [17] and in...

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Sedimentary challenge to Snowball Earth

Cited by 202 publications

References 91 publications

Towards a quantitative understanding of the late Neoproterozoic carbon cycle

Towards a quantitative understanding of the late Neoproterozoic carbon cycle

New constraints on equatorial temperatures during a Late Neoproterozoic snowball Earth glaciation

Inorganic carbon addition stimulates snow algae primary productivity

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