Snowball Earth climate dynamics and Cryogenian geology-geobiology

Paul F. Hoffman (1) , Dorian S. Abbot (2) , Yosef Ashkenazy (3) , Douglas I. Benn (4) , Jochen J. Brocks (5) , Phoebe A. Cohen (6) , Grant M. Cox (7) , Jessica R. Creveling (8) , Yannick Donnadieu (9, 10, 11) , Douglas H. Erwin (12) , Ian J. Fairchild (13) , David Ferreira (14) , Jason C. Goodman (15) , Galen P. Halverson (16) , Malte F. Jansen (2) , Guillaume Le Hir (17) , Gordon D. Love (18) , Francis A. Macdonald (1) , Adam C. Maloof (19) , Camille A. Partin (20) , Gilles Ramstein (10, 11) , Brian E. J. Rose (21) , Catherine V. Rose (22) , Peter M. Sadler (18) , Eli Tziperman (1) , Aiko Voigt (23) , Stephen G. Warren (24)

1 Harvard University
2 University of Chicago
3 BGU - Ben-Gurion University of the Negev
4 University of St Andrews [Scotland]
5 ANU - Australian National University
6 Williams College [Williamstown]
7 University of South Australia [Adelaide]
8 OSU - Oregon State University
9 CEREGE - Centre européen de recherche et d'enseignement des géosciences de l'environnement
10 LSCE - Laboratoire des Sciences du Climat et de l'Environnement [Gif-sur-Yvette]
11 CLIM - Modélisation du climat
12 Smithsonian Institution
13 University of Birmingham [Birmingham]
14 UOR - University of Reading
15 Wheaton College [Norton]
16 McGill University = Université McGill [Montréal, Canada]
17 IPGP - Institut de Physique du Globe de Paris
18 UC Riverside - University of California [Riverside]
19 Princeton University
20 U of S - University of Saskatchewan [Saskatoon]
21 University at Albany [SUNY]
22 Trinity College Dublin
23 INT - Institute of Nanotechnology [Karlsruhe]
24 University of Washington [Seattle]

Geological evidence indicates that grounded ice sheets reached sea level at all latitudes during two long-lived Cryogenian (58 and >= 5 My) glaciations. Combined uranium-lead and rhenium-osmium dating suggests that the older (Sturtian) glacial onset and both terminations were globally synchronous. Geochemical data imply that CO$_2$ was 10$^2$ PAL (present atmospheric level) at the younger termination, consistent with a global ice cover. Sturtian glaciation followed breakup of a tropical supercontinent, and its onset coincided with the equatorial emplacement of a large igneous province. Modeling shows that the small thermal inertia of a globally frozen surface reverses the annual mean tropical atmospheric circulation, producing an equatorial desert and net snow and frost accumulation elsewhere. Oceanic ice thickens, forming a sea glacier that flows gravitationally toward the equator, sustained by the hydrologic cycle and by basal freezing and melting. Tropical ice sheets flow faster as CO$_2$ rises but lose mass and become sensitive to orbital changes. Equatorial dust accumulation engenders supraglacial oligotrophic meltwater ecosystems, favorable for cyanobacteria and certain eukaryotes. Meltwater flushing through cracks enables organic burial and submarine deposition of airborne volcanic ash. The subglacial ocean is turbulent and well mixed, in response to geothermal heating and heat loss through the ice cover, increasing with latitude. Terminal carbonate deposits, unique to Cryogenian glaciations, are products of intense weathering and ocean stratification. Whole-ocean warming and collapsing peripheral bulges allow marine coastal flooding to continue long after ice-sheet disappearance. The evolutionary legacy of Snowball Earth is perceptible in fossils and living organisms.

Domaines: Sciences de la Terre

Paul F. Hoffman, Dorian S. Abbot, Yosef Ashkenazy, Douglas I. Benn, Jochen J. Brocks, et al.. Snowball Earth climate dynamics and Cryogenian geology-geobiology. Science Advances , 2017, 3 (11), pp.e1600983. ⟨10.1126/sciadv.1600983⟩. ⟨hal-01765604⟩