Continental weathering intensity during the termination of the Marinoan Snowball Earth: Mg isotope evidence from the basal Doushantuo cap carbonate in South China
Jian LiCuiguo HaoZhihong WangLin DongYiwu WangKang‐Jun HuangXianguo LangTianzheng HuangHonglin YuanChuanming ZhouBing Shen
13
Citation
49
Reference
10
Related Paper
Citation Trend
Keywords:
Snowball Earth
Deglaciation
Carbonate minerals
Deglaciation
Snowball Earth
Ice age
Earth system science
Cite
Citations (43)
Abstract The glacial development of the lower Borgarfjördur region, western Iceland, was investigated with regard to morphology, lithostratigraphy and chronology of glacial events. The maximum glacial situation is outlined, and a synthesis of all available evidence on the deglaciation is proposed. It is concluded that after an initial deglaciation of the coastal lowlands, some time prior to 12,500 BP, glaciers again advanced to the outer coastal areas between 12,000 and 11,700 BP, and, after a minor retreat between 11,700 and 11,000 BP, retained nearly their former positions between 11,000 and 10,300 BP. The marine maximum limit, at 80–90 m a.s.l., was reached in connection with the former advance, and the regional marine limit, at 60–70 m, at the end of the latter advance. A raised beach at 40 m a.s.l. possibly relates to an Early Flandrian glacial episode. These results imply a more extensive glaciation in coastal western Iceland at the end of the Late Weichselian than hitherto assumed. Key Words: Glacial geologychronologyradiocarbon dateslithostratigraphyLate Weichseliandeglaciationsea level changesBorgarfjördurHvalfjördurIceland
Deglaciation
Chronology
Lithostratigraphy
Last Glacial Maximum
Cite
Citations (45)
Formation of melt ponds is pervasive on sea ice and ice shelves prior to their disintegration. Such process should be critical for the deglaciation of a snowball Earth but has never been considered in previous studies. Here we develop a module to explicitly track the initiation, growth and refreezing of melt ponds on ice. Incorporation of the module into a climate model indicates that it provides a strong positive feedback to the climate, and previous studies seriously overestimated the threshold CO2 at which a snowball Earth deglaciates. At CO2 level of 0.1 bar and without the melt pond effect, the annual mean equatorial surface temperature is only -7.7 °C, far from deglaciating. However, this temperature increases to 6.1 °C in a few tens of years once melt pond effect is turned on. The results also demonstrate unambiguously that the deglaciation of snowball Earth should start from the equator, although seasonal melt ponds may appear first in the subtropical regions.
Deglaciation
Snowball Earth
Cite
Citations (1)
Neoproterozoic, and possibly Paleoproterozoic, glaciations represent the most extreme climate events in post‐Hadean Earth, and may link closely with the evolution of the atmosphere and life. According to the Snowball Earth hypothesis, the entire ocean was covered with ice during these events for a few million years, during which time volcanic CO 2 increased enough to cause deglaciation. Geochemical proxy data and model calculations suggest that the maximum CO 2 was 0.01–0.1 by volume, but early climate modeling suggested that deglaciation was not possible at CO 2 = 0.2. We use results from six different general circulation models (GCMs) to show that clouds could warm a Snowball enough to reduce the CO 2 required for deglaciation by a factor of 10–100. Although more work is required to rigorously validate cloud schemes in Snowball‐like conditions, our results suggest that Snowball deglaciation is consistent with observations.
Deglaciation
Snowball Earth
Earth system science
Cite
Citations (76)
Snowball Earth
Ice age
Cite
Citations (118)
Abstract The formation of melt ponds is pervasive on sea ice and ice shelves prior to their disintegration. Such process should be critical for the deglaciation of a snowball Earth but has never been considered in previous studies. Here we develop a module to explicitly track the initiation, growth and refreezing of melt ponds on ice. Incorporation of the module into a climate model indicates that it provides a strong positive feedback to the climate. Deglaciation of a snowball Earth will start when the annual mean equatorial surface temperature is only −7.7°C rather than 0°C. At this point, seasonal melt ponds start to appear in the mid‐latitude region. Its positive feedback induces the appearance of perennial melt ponds within the equatorial region and can increase the annual mean temperature there to 6.1°C in less than 10 years. Thus, our results indicate that the threshold CO 2 required to deglaciate a snowball Earth will be greatly overestimated (by a factor of ∼4 for the model we use) if the annual mean surface temperature reaching 0°C is used as the criteria. The results also demonstrate unambiguously that the deglaciation of snowball Earth should start from the equator. We then speculate on what will happen to the tropical sea glacier after the surface melting starts.
Deglaciation
Snowball Earth
Earth system science
Cite
Citations (7)
Deglaciation
Snowball Earth
Clathrate hydrate
Cite
Citations (0)
The Neoproterozoic is a time of transition between the ancient microbial world and the Phanerozoic, marked by a resumption of extreme carbon isotope fluctuations and glaciation after a billion-year absence. The carbon cycle disruptions are probably accompanied by changes in the stock of oxidants and connect to glaciations via changes in the atmospheric greenhouse gas content. Two of the glaciations reach low latitudes and may have been Snowball events with near-global ice cover. This review deals primarily with the Cryogenian portion of the Neoproterozoic, during which these glaciations occurred. The initiation and deglaciation of Snowball states are discussed in light of a suite of general circulation model simulations designed to facilitate intercomparison between different models. Snow cover and the nature of the frozen surface emerge as key factors governing initiation and deglaciation. The most comprehensive model discussed confirms the possibility of initiating a Snowball event with a plausible reduction of CO 2 . Deglaciation requires a combination of elevated CO 2 and tropical dust accumulation, aided by some cloud warming. The cause of Neoproterozoic biogeochemical turbulence, and its precise connection with Snowball glaciations, remains obscure.
Snowball Earth
Deglaciation
Abrupt climate change
Earth system science
Ice age
Climate state
Paleoclimatology
Cite
Citations (321)
Deglaciation
Snowball Earth
Cite
Citations (0)
Snowball Earth
Diamictite
Deglaciation
Wisconsin glaciation
Cite
Citations (58)