Tides on a Snowball

<p>The severe &#8220;Snowball Earth&#8221; glaciations proposed to have existed during the Cryogenian period (720 to 635 million years ago) coincided with the breakup of one supercontinent (Rodinia) and assembly of another (Pannotia). The presence of extensive continental ice sheets should theoretically lead to a tidally energetic Snowball ocean due to the reduced ocean depth, as was the case during the last glaciations, but the theory of the supertidal cycle suggests that the supercontinent paleogeography should lead to weak tides because the surrounding ocean is too large to host tidal resonances. So which theory is correct? Using an established numerical global tidal model and 22 paleogeographic reconstructions spanning 750-600Ma, we show that the Cryogenian ocean hosted diminished tidal amplitudes and associated energy dissipation rates, reaching 10-50% of today&#8217;s rates, during the Snowball glaciations. In contrast, the tides were more energetic during the ice-free periods, and we propose that the near-absence of Cryogenian tidal processes may have been one contributor to the prolonged glaciations if these were near-global. These results also constrain lunar distance and orbital evolution throughout the Cryogenian and highlight that simulations of past oceans should include explicit tidally driven mixing processes.</p>

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Weak tides during Cryogenian glaciations

Nature Communications ◽

10.1038/s41467-020-20008-3 ◽

2020 ◽

Vol 11 (1) ◽

Author(s):

J. A. Mattias Green ◽

Hannah S. Davies ◽

Joao C. Duarte ◽

Jessica R. Creveling ◽

Christopher Scotese

Keyword(s):

Energy Dissipation ◽

Ice Sheets ◽

Orbital Evolution ◽

Snowball Earth ◽

Mixing Processes ◽

Tidal Model ◽

Dissipation Rates ◽

Tidally Driven ◽

Continental Ice Sheets ◽

Tidal Processes

AbstractThe severe “Snowball Earth” glaciations proposed to have existed during the Cryogenian period (720 to 635 million years ago) coincided with the breakup of one supercontinent and assembly of another. Whereas the presence of extensive continental ice sheets predicts a tidally energetic Snowball ocean due to the reduced ocean depth, the supercontinent palaeogeography predicts weak tides because the surrounding ocean is too large to host tidal resonances. Here we show, using an established numerical global tidal model and paleogeographic reconstructions, that the Cryogenian ocean hosted diminished tidal amplitudes and associated energy dissipation rates, reaching 10–50% of today’s rates, during the Snowball glaciations. We argue that the near-absence of Cryogenian tidal processes may have been one contributor to the prolonged glaciations if these were near-global. These results also constrain lunar distance and orbital evolution throughout the Cryogenian, and highlight that simulations of past oceans should include explicit tidally driven mixing processes.

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On estimating mean and instantaneous turbulent energy dissipation rates with hot wires

Experimental Thermal and Fluid Science ◽

10.1016/s0894-1777(02)00259-5 ◽

2003 ◽

Vol 27 (2) ◽

pp. 151-157 ◽

Cited By ~ 8

Author(s):

R.A. Antonia

Keyword(s):

Energy Dissipation ◽

Turbulent Energy ◽

Dissipation Rates ◽

Hot Wires

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Observations of Small-Scale Turbulence and Energy Dissipation Rates in the Cloudy Boundary Layer

Journal of the Atmospheric Sciences ◽

10.1175/jas3687.1 ◽

2006 ◽

Vol 63 (5) ◽

pp. 1451-1466 ◽

Cited By ~ 75

Author(s):

Holger Siebert ◽

Katrin Lehmann ◽

Manfred Wendisch

Keyword(s):

Boundary Layer ◽

Energy Dissipation ◽

Wind Velocity ◽

Turbulence Theory ◽

Horizontal Wind ◽

Inertial Subrange ◽

Intermittent Flow ◽

Small Scale ◽

Dissipation Rates ◽

Wide Range

Abstract Tethered balloon–borne measurements with a resolution in the order of 10 cm in a cloudy boundary layer are presented. Two examples sampled under different conditions concerning the clouds' stage of life are discussed. The hypothesis tested here is that basic ideas of classical turbulence theory in boundary layer clouds are valid even to the decimeter scale. Power spectral densities S( f ) of air temperature, liquid water content, and wind velocity components show an inertial subrange behavior down to ≈20 cm. The mean energy dissipation rates are ∼10−3 m2 s−3 for both datasets. Estimated Taylor Reynolds numbers (Reλ) are ∼104, which indicates the turbulence is fully developed. The ratios between longitudinal and transversal S( f ) converge to a value close to 4/3, which is predicted by classical turbulence theory for local isotropic conditions. Probability density functions (PDFs) of wind velocity increments Δu are derived. The PDFs show significant deviations from a Gaussian distribution with longer tails typical for an intermittent flow. Local energy dissipation rates ɛτ are derived from subsequences with a duration of τ = 1 s. With a mean horizontal wind velocity of 8 m s−1, τ corresponds to a spatial scale of 8 m. The PDFs of ɛτ can be well approximated with a lognormal distribution that agrees with classical theory. Maximum values of ɛτ ≈ 10−1 m2 s−3 are found in the analyzed clouds. The consequences of this wide range of ɛτ values for particle–turbulence interaction are discussed.

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Last Glacial Maximum and Holocene Climate in CCSM3

Journal of Climate ◽

10.1175/jcli3748.1 ◽

2006 ◽

Vol 19 (11) ◽

pp. 2526-2544 ◽

Cited By ~ 413

Author(s):

Bette L. Otto-Bliesner ◽

Esther C. Brady ◽

Gabriel Clauzet ◽

Robert Tomas ◽

Samuel Levis ◽

...

Keyword(s):

Last Glacial Maximum ◽

Ice Sheets ◽

Ocean Model ◽

Arctic Sea Ice ◽

Glacial Maximum ◽

Climate System Model ◽

Last Glacial ◽

Global Cooling ◽

Climate Forcings ◽

Continental Ice Sheets

Abstract The climate sensitivity of the Community Climate System Model version 3 (CCSM3) is studied for two past climate forcings, the Last Glacial Maximum (LGM) and the mid-Holocene. The LGM, approximately 21 000 yr ago, is a glacial period with large changes in the greenhouse gases, sea level, and ice sheets. The mid-Holocene, approximately 6000 yr ago, occurred during the current interglacial with primary changes in the seasonal solar irradiance. The LGM CCSM3 simulation has a global cooling of 4.5°C compared to preindustrial (PI) conditions with amplification of this cooling at high latitudes and over the continental ice sheets present at LGM. Tropical sea surface temperature (SST) cools by 1.7°C and tropical land temperature cools by 2.6°C on average. Simulations with the CCSM3 slab ocean model suggest that about half of the global cooling is explained by the reduced LGM concentration of atmospheric CO2 (∼50% of present-day concentrations). There is an increase in the Antarctic Circumpolar Current and Antarctic Bottom Water formation, and with increased ocean stratification, somewhat weaker and much shallower North Atlantic Deep Water. The mid-Holocene CCSM3 simulation has a global, annual cooling of less than 0.1°C compared to the PI simulation. Much larger and significant changes occur regionally and seasonally, including a more intense northern African summer monsoon, reduced Arctic sea ice in all months, and weaker ENSO variability.

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Distribution of turbulence energy dissipation rates in a Rushton turbine stirred mixer

Experiments in Fluids ◽

10.1007/bf00195789 ◽

1989 ◽

Vol 8 (3-4) ◽

pp. 153-160 ◽

Cited By ~ 30

Author(s):

H. Wu ◽

G. K. Patterson ◽

M. Van Doorn

Keyword(s):

Energy Dissipation ◽

Turbulence Energy ◽

Rushton Turbine ◽

Dissipation Rates ◽

Turbulence Energy Dissipation

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Source, Transportation and Deposition of Debris on Arapaho Glacier, Front Range, Colorado, U.S.A.

Journal of Glaciology ◽

10.1017/s0022143000021936 ◽

1975 ◽

Vol 14 (72) ◽

pp. 407-420 ◽

Cited By ~ 36

Author(s):

Marith Jean Reheis

Keyword(s):

Ice Sheets ◽

Front Range ◽

Denudation Rate ◽

The Past ◽

Glacier Front ◽

Till Fabric ◽

Continental Ice Sheets

This study was undertaken to determine the sources of debris and methods of transportation and deposition in and on a small cirque glacier. Data were collected on the amount of debris, stone roundness, the presence of striations and polish, and till fabric. Lichenometry gave relative ages of the tills, and suggests that the Gannett Peak till is of at least three ages and probably overlies Audubon till.Debris originating from subglacial erosion can be differentiated from that from rockfall or avalanches on stone roundness, polish and striations. A maximum of 70% of the present glacial load derives from subglacial erosion, as compared to 88% during the Gannett Peak stade. Rockfall rates are 35-50 m3/year at present and were 290–485 m3/year during the Gannett Peak stade. Data on present-day processes and on the volume and age of Gannett Peak moraines can be used to make comparisons on present and past rates of denudation. The denudation rate in the cirque at present is 95–165 mm/1 000 year; in the past it was 4 920-8 160 mm/ 1 000 year. The denudation rate and the glacial effects on debris are comparable to rates from other glacial areas and effects on debris carried by valley glaciers and continental ice sheets.

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Erosion by Continental Ice Sheets

Journal of Glaciology ◽

10.1017/s0022143000029981 ◽

1979 ◽

Vol 23 (89) ◽

pp. 401-402

Author(s):

I. M. Whillans

Keyword(s):

Mass Balance ◽

Short Distance ◽

Ice Sheets ◽

Ice Sheet ◽

Present Theory ◽

Frictional Heat ◽

Break Up ◽

Basal Melting ◽

Continental Ice Sheets

Abstract Some of the problems with earlier theories for erosion and transport by ice sheets are discussed, and it is noted that those theories cannot simply account for the often-reported finding that most till is derived from bedrock only a few tens of kilometers up-glacier. Considerations of the mass balance of debris in transport lead to the conclusion that ice sheets are capable of transporting most debris only a short distance. The theory that the break-up of bedrock is mostly a preglacial process is developed. The advancing ice sheet collects the debris and then deposits it after a short travel. As the ice sheet first advances over the regolith, debris is frozen onto the base and is carried until basal melting due to geothermal and frictional heat causes lodgment till deposition. Most debris is deposited during the advance of the ice sheet and is carried only a short distance. A generally small amount of debris is carried at higher levels and is deposited during ice standstill and retreat as melt-out and ablation tills. The present theory makes many predictions, among them, that most till units are not traceable over long distances, that thick till sequences represent unstable glacier margins and not necessarily long periods of glacier occupation, and that lodgment tills are to be interpreted in terms of ice advances and ablation tills in terms of ice retreats. This paper is published in full in Journal of Geology, Vol. 86, No. 4, 1978, p. 516–24.

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