Comparison of field data with theories on ice cover progression in large rivers

1984 ◽  
Vol 11 (4) ◽  
pp. 798-814 ◽  
Author(s):  
Bernard Michel
Keyword(s):  
Quantitative Determination ◽  
Key Words ◽  
Field Data ◽  
Ice Cover ◽  
Large Rivers ◽  
Ice Dynamics ◽  
Physical Mechanisms ◽  
Flow Parameters ◽  
Existing Data ◽  
St Lawrence River

There are many theories pertaining to the progression of ice covers in rivers fed by frazil slush and floes but very few have been examined critically by comparing them with field data. In this paper the existing theories on dynamic ice cover progression are reviewed, an additional one is proposed, and they are classified according to the physical mechanisms that are involved. Finally, they are compared with some existing field data for large rivers. The data are extremely scarce and difficult to obtain because of the costs involved and the dangers in traveling over thin ice when the ice cover is being formed.It is usually easier to get only the critical values of parameters giving the limits of ice cover progression. In this paper, complete data were taken from the St. Lawrence River, the Beauharnois Canal, and the La Grande Rivière where the ice thicknesses along with the flow parameters have been measured.In these cases the existing data are adequate, so they could be grouped to explain the various mechanisms involved and to obtain numerical values for their quantitative determination. Key words: glaciology, river ice, ice dynamics, fluvial processes, ice hydraulics.

CARACTÉRISTIQUES DES SOLS SULFATÉS ACIDES DE LA SÉRIE DE L'ANSE EN MILIEU ESTUARIEN (QUÉBEC)

1988 ◽  
Vol 68 (3) ◽  
pp. 577-592
Author(s):  
C. R. DE KIMPE ◽  
M. R. LAVERDIERE ◽  
R. W. BARIL
Keyword(s):  
Key Words ◽  
Lower Limit ◽  
Marine Sediments ◽  
Acid Sulfate Soils ◽  
Acid Sulfate ◽  
Organic C ◽  
South Shore ◽  
Sulfate Soils ◽  
Sulfate Leaching ◽  
St Lawrence River

Acid sulfate soils were sampled according to the transect method in four bays along the south shore of the St. Lawrence river to determine their properties in their area of distribution. In each bay, six profiles of cultivated soils were sampled along a transect perpendicular to the river. One non-cultivated profile was also sampled at l'Isle-Verte. The lower limit of the B horizons, between 79 and 89 cm, suggested a homogeneous development of these soils across the area. Most profiles contained jarosite in the lower Bg and, sometimes, in the C horizons; this mineral was absent in the upper part of the profiles of soils that had been limed prior to cultivation. Total S content increased with depth, but only a few horizons had a content > 0.75% presumably because of sulfate leaching once the soils were drained. Organic C content in the de l'Anse soils decreased less rapidly with depth than in other gleysolic soils, because vegetation grew while sediments were being deposited. Key words: Acid sulfate soils, total S, recent marine sediments, jarosite

In situ creep of frozen soil, Fenghuo Shan, Tibet Plateau, China

1995 ◽  
Vol 32 (3) ◽  
pp. 545-552 ◽  
Author(s):  
B. Wang ◽  
Hugh M. French
Keyword(s):  
Key Words ◽  
Power Flow ◽  
Field Data ◽  
Field Measurements ◽  
Frozen Soil ◽  
Tibet Plateau ◽  
Soil Creep ◽  
Extreme Variability ◽  
The Mean

Field measurements of frozen soil creep in the upper 3.0 m of permafrost indicate that creep occurs in both winter and summer. Between 1992 and 1993, the mean rate of creep ranged from 0.44 cm at 1.6 m depth to 0.16 cm at 2.8 m depth but there was extreme variability. Creep parameters n and A, as defined by the power flow law, were calculated from field data. Parameter n ranged between 1.96 and 2.29 and increased with depth, while A decreased with depth. Comparisons of creep rates for different permafrost environments suggest that ground temperature largely controls the magnitude of permafrost creep. Key words : permafrost, creep parameters, Tibet Plateau.

Thlaspi sylvestre Jord. (= T. caerulescens J. & C. Presl), update on the localities and sites of a rare species in the flora of Slovenia / Thlaspi sylvestre Jord. (= T. caerulescens J. & C. Presl), dopolnjena vednost o razširjenosti in rastiščih redke ...

2020 ◽  
Vol 61 (2) ◽  
pp. 205-227
Author(s):  
Igor Dakskobler ◽  
Marija Skok ◽  
Gabrijel Seljak ◽  
Jože Lango ◽  
Martina Bačič
Keyword(s):  
World War I ◽  
Key Words ◽  
Rare Species ◽  
Forest Edge ◽  
Thlaspi Caerulescens ◽  
World War ◽  
Rumex Acetosa ◽  
New Localities ◽  
Ranunculus Acris ◽  
Existing Data

In the Čepovan Valley (Čepovan, hamlet Šulgi), on the northwestern rim of the Banjšice Plateau in the villages of Grudnica (in the Tolmin municipality) and near Sveto to the south of the plateau, we found new localities of Thlaspi sylvestre (T. caerulescens), which complement the existing data on the distribution of this species in Slovenia (Srednji Lokovec, Vrata), and surveyed its sites. Thlaspi sylvestre grows on meadows and pastures in the vicinity of human settlements, in hedges, on road banks, on the forest edge and in an open pioneer forest. Its most common companions are Galium mollugo agg. (G. album), Cruciata glabra, Rumex acetosa, Ranunculus acris, Taraxacum sect. Ruderalia and Veronica chamaedrys. Thlaspi sylvestre most frequently occurs in the communities from the class Molinio-Arrhenatheretea. Our findings confirm Tone Wraber’s assumption that it is not indigenous to Slovenia, and was introduced to the Banjšice Plateau as well as to Grudnica and the Čepovan Valley with human assistance (military transport during World War I). Key words: phytogeography, phytosociology, Thlaspi caerulescens, florula castrensis, Čepovan Valley, Grudnica, Banjšice, Slovenia   Izvleček V Čepovanski dolini (Čepovan, zaselek Šulgi), na severovzhodnem robu Banjške planote v vasi Grudnica (občina Tolmin) in pri vasi Sveto v južnem delu te planote smo našli nova nahajališča vrste Thlaspi sylvestre (T. caerules­cens), ki dopolnjujejo njeno do zdaj znano razširjenost v Sloveniji (Srednji Lokovec, Vrata), in popisali njena rastišča. Raste na travnikih in pašnikih v okolici človeških bivališč, v mejicah, na cestnih brežinah, na gozdnem robu in v svetlem pionirskem gozdu. Njene najbolj pogoste spremljevalke so vrste Galium mollugo agg. (G. album), Cruciata glabra, Rumex acetosa, Ranunculus acris, Taraxacum sect. Ruderalia in Veronica chamaedrys. Najpogosteje raste v združbah iz razreda Molinio-Arrhenatheretea. Potrjujemo domnevo Toneta Wraberja, da ta vrsta v Sloveniji ni samonikla in da se je na Banjšice in tudi v Grudnico in Čepovansko dolino priselila s človekovo pomočjo (vojaškimi transporti med prvo svetovno vojno).  Ključne besede: fitogeografija, fitocenologija, Thlaspi caerulescens, florula castrensis, Čepovanska dolina, Grudnica, Banjšice, Slovenija  

The orientation behaviour of multiple chromosome configurations in acridid grasshoppers

Genome ◽  
1987 ◽  
Vol 29 (2) ◽  
pp. 292-308 ◽  
Author(s):  
B. John
Keyword(s):  
Key Words ◽  
Reciprocal Translocation ◽  
Chiasma Frequency ◽  
The Other ◽  
Robertsonian Fusion ◽  
Orientation Behaviour ◽  
Chiasma Distribution ◽  
First Time ◽  
Existing Data ◽  
Combined Data

The existing data on the behaviour of multiple chromosome configurations arising from single interchanges between either metacentric–telocentric or telocentric–telocentric nonhomologues in 10 species of acridid grasshoppers are compared with data from four new cases. Two of these new cases involve metacentric–telocentric exchanges but the other two, for the first time in acridids, deal with a reciprocal translocation between two nonhomologous metacentrics. The combined data are used to evaluate the factors that influence multiple orientation in this family of grasshoppers and reemphasize the importance of chiasma frequency and chiasma distribution for multiple behaviour. This conclusion is reinforced by a consideration of the known cases of chain of three multiples originating from the Robertsonian fusion of nonhomologous telocentrics in acridoids. Key words: acridid grasshoppers, multiple chromosome configurations, chiasma distribution, orientation behaviour.

scholarly journals Analysis of local AWS and NCEP/NCAR reanalysis data at Lake El'gygtytgyn, and its implications for maintaining multi-year lake-ice covers

2012 ◽  
Vol 8 (2) ◽  
pp. 1443-1483 ◽  
Author(s):  
M. Nolan
Keyword(s):  
Full Range ◽  
Summer Rainfall ◽  
Barometric Pressure ◽  
Ice Cover ◽  
Warming Trend ◽  
Reanalysis Data ◽  
Lake Ice ◽  
Ice Dynamics ◽  
Air Temperatures ◽  
Perennial Ice

Abstract. We compared 7 years of local automated weather station (AWS) data to NCEP/NCAR reanalysis data to characterize the modern environment of Lake El'gygytgyn, in Chukotka Russia. We then used this comparison to estimate the air temperatures required to initiate and maintain multi-year lake-ice covers to aid in paleoclimate reconstructions of the 3.6 M years sediment record recovered from there. We present and describe data from our AWS from 2002–2008, which recorded air temperatures, relative humidity, precipitation, barometric pressure, and wind speed/direction, as well as subsurface soil moisture and temperature. Measured mean annual air temperature (MAAT) over this period was −10.4 °C with a slight warming trend during the measurement period. NCEP/NCAR reanalysis air temperatures compared well to this, with annual means within 0.1 to 2.0 °C of the AWS, with an overall mean 1.1 °C higher than the AWS, and daily temperature trends having a correlation of over 96% and capturing the full range of variation. After correcting for elevation differences, barometric pressure discrepancies occasionally reached as high as 20 mbar higher than the AWS particularly in winter, but the correlation in trends was high at 92%, indicating that synoptic-scale weather patterns driving local weather likely are being captured by the reanalysis data. AWS cumulative summer rainfall measurements ranged between 70–200 mm during the record. NCEP/NCAR reanalysis precipitation failed to predict daily events measured by the AWS, but largely captured the annual trends, though higher by a factor of 2–4. NCEP air temperatures showed a strong trend in MAAT over the 1961–2009 record, rising from a pre-1995 mean of −12.0 °C to a post-1994 mean of −9.8 °C. We found that nearly all of this change could be explained by changes in winter temperatures, with mean winter degree days (DD) rising from −5043 to −4340 after 1994 and a much smaller change in summer DD from +666 to +700. Thus, the NCEP record indicates that nearly all modern change in MAAT is driven by changes in winter (which promotes lake-ice growth) not summer (which promotes lake-ice melt). Whether this sensitivity is representative of paleo-conditions is unclear, but it is clear that the lake was unlikely to have initiated a multi-year ice cover since 1961 based on simple DD models of ice dynamics. Using these models we found that the NCEP/NCAR reanalysis mean MAAT over 1961–2009 would have to be at least 4 °C colder to initiate a multi-year ice cover, but more importantly that multi-year ice covers are largely controlled by summer melt rates at this location. Specifically we found that summer DD would have to drop by more than half the modern mean, from +640 to +280. Given that the reanalysis temperatures appears about 1 °C higher than reality, a MAAT cooling of 3 °C may be sufficient in the real world, but as described in the text we consider a cooling of −4°C ± 0.5 °C a reasonable requirement for multi-year ice covers. Also perhaps relevant to paleo-climate proxy interpretation, at temperatures cold enough to maintain a multi-year ice cover, the summer temperatures could still be sufficient for a two-month long thawing period, including a month at about +5 °C Thus it is likely that many summer biological processes and some lake-water warming and mixing may still have been occurring beneath perennial ice-covers; core proxies have already indicated that such perennial ice-covers may have persisted for tens of thousands of years at various times within the 3.6 M years record.

scholarly journals Sea-ice dynamics strongly promote Snowball Earth initiation and destabilize tropical sea-ice margins

2012 ◽  
Vol 8 (4) ◽  
pp. 2445-2475 ◽  
Author(s):  
A. Voigt ◽  
D. S. Abbot
Keyword(s):  
Sea Ice ◽  
General Circulation ◽  
Climate Models ◽  
Circulation Model ◽  
Hadley Circulation ◽  
Ice Cover ◽  
Ocean General Circulation Model ◽  
Snowball Earth ◽  
Ice Dynamics ◽  
Sea Ice Dynamics

Abstract. The Snowball Earth bifurcation, or runaway ice-albedo feedback, is defined for particular boundary conditions by a critical CO2 and a critical sea-ice cover (SI), both of which are essential for evaluating hypotheses related to Neoproterozoic glaciations. Previous work has shown that the Snowball Earth bifurcation, denoted as (CO2, SI)*, differs greatly among climate models. Here, we revisit the initiation of a Snowball Earth in the atmosphere-ocean general circulation model ECHAM5/MPI-OM for Marinoan (~630 Ma) continents and solar insolation decreased to 94%. In its standard setup, ECHAM5/MPI-OM initiates a Snowball Earth much more easily than other climate models at (CO2, SI)* ≈ (500 ppm, 55%). Previous work has shown that the Snowball Earth bifurcation can be pushed equatorward if a low bare sea ice albedo is assumed because bare sea ice is exposed by net evaporation in the descent region of the Hadley circulation. Consistent with this, when we replace the model's standard bare sea-ice albedo of 0.75 by a much lower value of 0.45, we find (CO2, SI)* ≈ (204 ppm, 70%). When we additionally disable sea-ice dynamics, we find that the Snowball Earth bifurcation can be pushed even closer to the equator and occurs at a much lower CO2: (CO2, SI)* ≈ (2 ppm, 85%). Therefore, both lowering the bare sea-ice albedo and disabling sea-ice dynamics increase the critical sea-ice cover in ECHAM5/MPI-OM, but sea-ice dynamics have a much larger influence on the critical CO2. For disabled sea-ice dynamics, the state with 85% sea-ice cover is stabilized by the Jormungand mechanism and shares characteristics with the Jormungand climate states. However, there is no Jormungand bifurcation between this Jormungand-like state and states with mid-latitude sea-ice margins. Our results indicate that differences in sea-ice dynamics schemes can be as important as sea ice albedo for causing the spread in climate model's estimates of the location of the Snowball Earth bifurcation.

scholarly journals Robust wavebuoys for the marginal ice zone: Experiences from a large persistent array in the Beaufort Sea

Elem Sci Anth ◽  
2017 ◽  
Vol 5 ◽  
Author(s):  
Martin J. Doble ◽  
Jeremy P. Wilkinson ◽  
Lovro Valcic ◽  
Jeremy Robst ◽  
Andrew Tait ◽  
...  
Keyword(s):  
Sea Ice ◽  
Significant Proportion ◽  
Open Water ◽  
Beaufort Sea ◽  
Ice Cover ◽  
Naval Research ◽  
Ice Dynamics ◽  
Office Of Naval Research ◽  
Marginal Ice Zone ◽  
Sample Frequency

An array of novel directional wavebuoys was designed and deployed into the Beaufort Sea ice cover in March 2014, as part of the Office of Naval Research Marginal Ice Zone experiment. The buoys were designed to drift with the ice throughout the year and monitor the expected breakup and retreat of the ice cover, forced by waves travelling into the ice from open water. Buoys were deployed from fast-and-light air-supported ice camps, based out of Sachs Harbour on Canada’s Banks Island, and drifted westwards with the sea ice over the course of spring, summer and autumn, as the ice melted, broke up and finally re-froze. The buoys transmitted heave, roll and pitch timeseries at 1 Hz sample frequency over the course of up to eight months, surviving both convergent ice dynamics and significant waves-in-ice events. Twelve of the 19 buoys survived until their batteries were finally exhausted during freeze-up in late October/November. Ice impact was found to have contaminated a significant proportion of the Kalman-filter-derived heave records, and these bad records were removed with reference to raw x/y/z accelerations. The quality of magnetometer-derived buoy headings at the very high magnetic field inclinations close to the magnetic pole was found to be generally acceptable, except in the case of four buoys which had probably suffered rough handling during transport to the ice. In general, these new buoys performed as expected, though vigilance as to the veracity of the output is required.

scholarly journals Greater Water Surface Variability Revealed by New Congo River Field Data: Implications for Satellite Altimetry Measurements of Large Rivers

2019 ◽  
Vol 46 (14) ◽  
pp. 8093-8101 ◽  
Author(s):  
Andrew B. Carr ◽  
Mark A. Trigg ◽  
Raphael M. Tshimanga ◽  
Duncan J. Borman ◽  
Mark W. Smith
Keyword(s):  
Water Surface ◽  
Satellite Altimetry ◽  
Field Data ◽  
Large Rivers ◽  
Congo River ◽  
Surface Variability
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