Basal Water Flow Research Articles

A Theoretical Model of Drumlin Formation Based on Observations at Múlajökull, Iceland

AbstractThe drumlin field at the surge‐type glacier, Múlajökull, provides an unusual opportunity to build a model of drumlin formation based on field observations in a modern drumlin‐forming environment. These observations indicate that surges deposit till layers that drape the glacier forefield, conform to drumlin surfaces, and are deposited in shear. Observations also indicate that erosion helps create drumlin relief, effective stresses in subglacial till are highest between drumlins, and during quiescent flow, crevasses on the glacier surface overlie drumlins while subglacial channels occupy intervening swales. In the model, we consider gentle undulations on the bed bounded by subglacial channels at low water pressure. During quiescent flow, slip of temperate ice across these undulations and basal water flow toward bounding channels create an effective stress distribution that maximizes till entrainment in ice on the heads and flanks of drumlins. Crevasses amplify this effect but are not necessary for it. During surges, effective stresses are uniformly low, and the bed shears pervasively. Vigorous basal melting during surges releases debris from ice and deposits it on the bed, with deposition augmented by transport in the deforming bed. As surge cycles progress, drumlins migrate downglacier and grow at increasing rates, due to positive feedbacks that depend on drumlin height. Drumlin growth can be accompanied by either net aggradation or erosion of the bed, and drumlin heights and stratigraphy generally correspond with observations. This model highlights that drumlin growth can reflect instabilities other than those of bed shear instability models, which require heuristic till transport assumptions.

Eurasian ice-sheet dynamics and sensitivity to subglacial hydrology

ABSTRACTIce-stream dynamics are strongly controlled by processes taking place at the ice/bed interface where subglacial water both lubricates the base and saturates any existing, underlying sediment. Large parts of the former Eurasian ice sheet were underlain by thick sequences of soft, marine sediments and many areas are imprinted with geomorphological features indicative of fast flow and wet basal conditions. Here, we study the effect of subglacial water on past Eurasian ice-sheet dynamics by incorporating a thin-film model of basal water flow into the ice-sheet model SICOPOLIS and use it to better represent flow in temperate areas. The adjunction of subglacial hydrology results in a smaller ice-sheet building up over time and generally faster ice velocities, which consequently reduces the total area fraction of temperate basal ice and ice streaming areas. Minima in the hydraulic pressure potential, governing water flow, are used as indicators for potential locations of past subglacial lakes and a probability distribution of lake existence is presented based on estimated lake depth and longevity.

Evolution of subglacial overdeepenings in response to sediment redistribution and glaciohydraulic supercooling

AbstractGlaciers erode bedrock rapidly, but evacuation of sediments requires efficient subglacial drainage networks. If glaciers erode more rapidly than evacuation proceeds, a protective subglacial till layer can form to armor the bed. Where glaciers cross overdeepenings, local closed depressions, the bed slope opposes the ice surface and lowers the hydraulic potential gradient that drives water flow. Here, we present results of a dynamic, distributed model of coupled basal water flow and sediment transport to show how overdeepenings evolve over the course of a melt season. We use steady‐state calculations as well as numerical simulations to understand how alluvial bed erosion alters overdeepenings. Numerical results from a modified form of the Spring‐Hutter equations show behaviors that cannot be inferred from either local or steady‐state calculations. In general, opposition of surface and bed slopes lessens sediment transport regardless of ice accretion from glaciohydraulic supercooling. Drainage efficiency strongly affects erosion and deposition rates. Results show characteristic behaviors of flow through overdeepenings such as overpressured water systems and accretion rates compatible with field measurements. Simulations that start with overdeepened glacier configurations progress out of a freezing regime where glaciohydraulic supercooling occurs. This progression indicates that glacier hydrology is more strongly affected by erosion and deposition than by freezing from glaciohydraulic supercooling. We discuss how this outcome affects glacier erosion and sediment transport under modern and past ice sheets.

Effect of a dynein inhibitor on vasopressin action in toad urinary bladder.

1. The effect of the dynein inhibitor erythro-9-[3-(2-hydroxynonyl)] adenine (EHNA) on the osmotic water flow response to vasopressin or exogenous cAMP has been investigated in isolated toad urinary bladders. 2. Pretreatment with serosal EHNA had no effect on basal water flow, but inhibited the development and maintenance of the hydrosmotic response to vasopressin (20 mU ml-1) or 8-(4-parachlorophenylthio)-adenosine 3',5'-cyclic monophosphate (8 CPT-cAMP; 0.1 mM). 3. The inhibitory effect of EHNA on vasopressin-induced water flow was dose dependent. Inhibition occurred in the dose range in which EHNA inhibits the ATPase and motor activities of dynein in vitro. 4. EHNA also inhibited the maintenance of the high rate of water flow established by prior exposure to vasopressin. 5. The inhibitory effect of EHNA on the onset phase of the vasopressin response was attenuated after exposure of the tissue to the microtubule-disruptive drug nocodazole but was fully additive with that of cytochalasin B. 6. EHNA inhibited basal and vasopressin-stimulated transepithelial sodium transport. 7. The findings support the view that EHNA inhibits hormone-induced water flow through an action on a cytoplasmic dynein. The results are consistent with the hypothesis that dynein is involved in the microtubule-based delivery of water channel-containing vesicles to the apical membrane of the granular epithelial cells during both the onset and maintenance of the water permeability response to vasopressin.

Hydrological discharges and motion of Fels and Black Rapids Glaciers, Alaska, U.S.A.: implications for the structure of their drainage systems

AbstractCharacteristics of the hydrology and motion of Black Rapids and Fels Glaciers, Alaska, were observed from 1986 to 1989. Hydrological measurements included stage, electrical conductivity and suspended-sediment concentration in the discharge stream of each glacier, and were made at 0.5–1 h intervals continuously through most of the melt seasons. Variations in the glacier speed were monitored through the full year at a number of locations along the length of each glacier using time-lapse photography (1 d time resolution), strain meters (0.5–1 h resolution) and seismometers set up to count acoustic emissions. Both glaciers show similar seasonal, diurnal and short-term event changes in hydrological discharges and ice speed. The hydrological behavior is analyzed in terms of a “fast” sub-system composed of surface streams, moulins and large tunnels with discharge that responds rapidly and a “slow” sub-system composed of heterogeneous small passageways through the ice and distributed over the bed that maintain approximately uniform discharge over a day. The liming and amplitude of water discharge in the diurnal cycle indicate that roughly 10–40% of the water is routed directly into the fast system. The remaining 90–60% of the water enters the slow system. Dilution of the solute discharged from the slow system by the variable discharge in the fast system results in changes in water discharge and solute concentration that are approximately equal in relative amplitude and inversely related. A small time lag from discharge maximum (minimum) to solute minimum (maximum) suggests that the fast system is confined to roughly the lowermost 30–40% of the full glacier length. The residence time of water in the fast system is short compared to 1 d. The slow system contains both short- and long-residence time passages. Characteristics of the diurnal cycles are somewhat variable through the melt season, but no systematic evolutionary patterns were discerned even though large changes in the mean discharges of water and solutes occur, which suggests parallel evolution of the variables that control the response of the fast system. Events were characterized by contemporaneous increases in suspended-sediment concentration in the discharge water and distinct changes in straining on the glaciers. Events caused by-increases in melt or precipitation related to weather and events related to release from reservoirs internal to the glaciers could be distinguished based on the changes in electrical conductivity of the discharge water. The correlated changes in sediment discharge and motion of the glaciers indicate that the events were associated with temporary modifications of the slow passages distributed over the bed that allowed enhanced sliding and access of basal water flow to erosion products. Hydrological differences between Black Rapids and Fels Glaciers can be explained by differences in the size of the glaciers. If there is a difference in bed structure that explains the difference in dynamics (surge — Black Rapids Glacier - versus non-surge - Fels Glacier), it does not affect the hydrological parameters that were observed.

Hydrological discharges and motion of Fels and Black Rapids Glaciers, Alaska, U.S.A.: implications for the structure of their drainage systems

AbstractCharacteristics of the hydrology and motion of Black Rapids and Fels Glaciers, Alaska, were observed from 1986 to 1989. Hydrological measurements included stage, electrical conductivity and suspended-sediment concentration in the discharge stream of each glacier, and were made at 0.5–1 h intervals continuously through most of the melt seasons. Variations in the glacier speed were monitored through the full year at a number of locations along the length of each glacier using time-lapse photography (1 d time resolution), strain meters (0.5–1 h resolution) and seismometers set up to count acoustic emissions. Both glaciers show similar seasonal, diurnal and short-term event changes in hydrological discharges and ice speed. The hydrological behavior is analyzed in terms of a “fast” sub-system composed of surface streams, moulins and large tunnels with discharge that responds rapidly and a “slow” sub-system composed of heterogeneous small passageways through the ice and distributed over the bed that maintain approximately uniform discharge over a day. The liming and amplitude of water discharge in the diurnal cycle indicate that roughly 10–40% of the water is routed directly into the fast system. The remaining 90–60% of the water enters the slow system. Dilution of the solute discharged from the slow system by the variable discharge in the fast system results in changes in water discharge and solute concentration that are approximately equal in relative amplitude and inversely related. A small time lag from discharge maximum (minimum) to solute minimum (maximum) suggests that the fast system is confined to roughly the lowermost 30–40% of the full glacier length. The residence time of water in the fast system is short compared to 1 d. The slow system contains both short- and long-residence time passages. Characteristics of the diurnal cycles are somewhat variable through the melt season, but no systematic evolutionary patterns were discerned even though large changes in the mean discharges of water and solutes occur, which suggests parallel evolution of the variables that control the response of the fast system. Events were characterized by contemporaneous increases in suspended-sediment concentration in the discharge water and distinct changes in straining on the glaciers. Events caused by-increases in melt or precipitation related to weather and events related to release from reservoirs internal to the glaciers could be distinguished based on the changes in electrical conductivity of the discharge water. The correlated changes in sediment discharge and motion of the glaciers indicate that the events were associated with temporary modifications of the slow passages distributed over the bed that allowed enhanced sliding and access of basal water flow to erosion products. Hydrological differences between Black Rapids and Fels Glaciers can be explained by differences in the size of the glaciers. If there is a difference in bed structure that explains the difference in dynamics (surge — Black Rapids Glacier - versus non-surge - Fels Glacier), it does not affect the hydrological parameters that were observed.

Inhibition of the antidiuretic hormone hydroosmotic response by phospholipids and phospholipid metabolites.

Phospholipid metabolities and phospholipids containing arachidonic acid (AA) inhibited the antidiuretic hormone (ADH)-induced increase in transepithelial water flow in the toad urinary bladder, but had no effect on basal water flow when added to the serosal bathing solution. Other fatty acid-substituted phospholipid metabolites had no effect on osmotic water movement in the presence or absence of ADH. Indomethacin attenuated the inhibitory effects of the AA containing phospholipid metabolities (PMAA), suggesting that the PMAA response required AA release and prostaglandin (PG) formation. PMAA increased PGE formation as measured by radioimmunoassay. PG have been reported to inhibit ADH-stimulated water flow by inhibiting adenylcyclase. PGE2 (10(-8) M) had no effect on cyclic AMP-stimulated water flow, whereas exogenous AA and PMAA attenuated the hydroosmotic response to added cyclic AMP. Indomethacin only partially reversed the inhibition by AA of the cyclic AMP-associated water movement, suggesting that the inhibition by AA and PMAA may involve other metabolites of AA than PG. PG and the AA cascade have been implicated as cellular modulators of the ADH hydroosmotic response. The present results offer additional support to the theory that this system may regulate the intracellular events that are transduced following receptor activation by ADH.

Basal Water and High-Pressure Basal Ice

AbstractExpressions are found for the water pressure in channels and cavities under a temperate glacier in a steady state. By steady state is meant that not only is the sliding velocity constant but also the basal water flow as well as the basal water production. The calculations are based on a simplified bimodal obstacle bed. One-size obstacles are of the magnitude of the conventional “controlling” obstacles size. The other obstacle size is several orders of magnitude larger than the controlling size. The large obstacles are introduced in order to investigate the storage of large amounts of water at the bed. The effect of the missing obstacles is mimicked by adding a friction stress whose values decrease linearly with ice–rock separation. It is found that water flow is primarily in a water film if the water flux is below a critical limit. The physical reason for this result is that a minimum water flow must be exceeded in order to keep a water channel open in high ice-pressure regions in front of obstacles. The new ingredient in our analysis of water flow is the explicit account taken of the effect of excess ice pressure (at the up-stream side of obstacles) on the closing of water channels. The excess ice-pressure regions play a critical role in the development of water films. The recognition of the possible importance of high-pressure basal ice regions to the regulation of water flow is the primary result of this paper. It is found that, in steady state, the water pressure is close to the overburden ice pressure provided that water transported through Nye channels is only a minor part of the total. The water flows primarily in a water film. If a large flux of upper-surface melt water descends to the bed, this water could cause a reduction of the water pressure and a channelization of the water flow.

Basal Water and High-Pressure Basal Ice

AbstractExpressions are found for the water pressure in channels and cavities under a temperate glacier in a steady state. By steady state is meant that not only is the sliding velocity constant but also the basal water flow as well as the basal water production. The calculations are based on a simplified bimodal obstacle bed. One-size obstacles are of the magnitude of the conventional “controlling” obstacles size. The other obstacle size is several orders of magnitude larger than the controlling size. The large obstacles are introduced in order to investigate the storage of large amounts of water at the bed. The effect of the missing obstacles is mimicked by adding a friction stress whose values decrease linearly with ice–rock separation. It is found that water flow is primarily in a water film if the water flux is below a critical limit. The physical reason for this result is that a minimum water flow must be exceeded in order to keep a water channel open in high ice-pressure regions in front of obstacles. The new ingredient in our analysis of water flow is the explicit account taken of the effect of excess ice pressure (at the up-stream side of obstacles) on the closing of water channels. The excess ice-pressure regions play a critical role in the development of water films. The recognition of the possible importance of high-pressure basal ice regions to the regulation of water flow is the primary result of this paper. It is found that, in steady state, the water pressure is close to the overburden ice pressure provided that water transported through Nye channels is only a minor part of the total. The water flows primarily in a water film. If a large flux of upper-surface melt water descends to the bed, this water could cause a reduction of the water pressure and a channelization of the water flow.

Effects of trifluoperazine and verapamil on the hydro-osmotic response to antidiuretic hormone in the urinary bladder of the toad.

To investigate the role of the intracellular calcium-calmodulin complex in the hydro-osmotic response to antidiuretic hormone (ADH), the effects of trifluoperazine (TFP), a well-established inhibitor of calmodulin-mediated functions, and of verapamil (V), a calcium entry blocker, were examined in the urinary bladder of the toad, a model for the late distal tubule and the collecting duct of the mammalian nephron. Preincubation of the hemibladders with TFP at serosal concentrations of 10(-5) and 10(-4) M was without effect on basal water flow but markedly reduced the maximal hydroosmotic response to ADH (50 mU/ml) in a dose-dependent manner as compared to control hemibladders (23.60 +/- 1.23 vs. 42.17 +/- 4.18 mg/min per hemibladder (10(-5) M TFP) and 5.43 +/- 0.59 vs. 52.50 +/- 4.67 mg/min per hemibladder (10(-4) M TFP). This inhibitory effect of TFP on the ADH-stimulated osmotic water flow persisted in the presence of naproxen (10(-5) M), a known inhibitor of prostaglandin synthesis. The hydro-osmotic response to cyclic adenosine 3',5' monophosphate (cAMP, 10(-3) M) was also significantly reduced in TFP-pretreated tissues (11.68 +/- 1.84 vs. 32.83 +/- 3.14 mg/min per hemibladder), suggesting a post-cAMP inhibitory effect of TFP. V (10(-4) M) had no effect on basal water flow but significantly reduced the hydro-osmotic effect of 50 mU/ml ADH (15.17 +/- 1.05 vs. 38.00 +/- 3.39 mg/min per hemibladder). In contrast, cAMP-stimulated osmotic water flow was significantly stimulated in V-treated tissues (48.07 +/- 1.95 vs. 27.13 +/- 1.50 mg/min per hemibladder).(ABSTRACT TRUNCATED AT 250 WORDS)

Comparative effects of prostaglandin E 2 and prostaglandin E 3 on water flow and cyclic AMP in the urinary bladder of the frog, [formula omitted

Prostaglandins (PGs) modulate osmotic water flow in amphibian urinary bladders. Gas chromatographic analysis of prostaglandin precursors in bladders showed that arachidonic acid represented 13.0 ± 0.6% and eicosapentaenoic acid 4.3 ± 0.1% of the total fatty acid content. The effects of PGE 2 and PGE 3 on basal and arginine vasotocin (AVT) stimulated water flow were compared. Contol water flow (1.1 ± 0.2 mg/min) was increased to 4.6 ± 0.3 mg/min with AVT (10 −6M) present. PGE 2 (10 −6M) inhibited both basal and AVT stimulated water flow. In contrast, PGE 3 (10 −6M) stimulated basal water flow and further increased AVT stimulated water flow. Basal adenylate cyclase activity (ACA, 59 ± 0.3 pmol cyclic AMP/mg protein/10 min) was stimulated by the addition of AVT in the absence or presence of exogenous guanosine 5′ triphosphate (GTP, 10 −5M). Both PGE 2 and PGE 3 stimulated basal ACA in the absence, but not in the presence of GTP. In the absence of exogenous GTP, PGE 2 increased AVT stimulated ACA, whereas PGE 3 decreased it. Both prostaglandins inhibited AVT stimulation when GTP was added. The effects of PGE 2, PGE 3 and AVT on tissue cycilc AMP levels in whole urinary bladders were similar to the effects seen on ACA in the absence of exogenous GTP. The contrasting effects of PGE 2 and PGE 3 on control water flow appear distinct from their similar effects on ACA. However, PGE 2 and PGE 3 may regulate AVT stimulation through mechanisms involving cyclic AMP.

Frogs produce a physiologically active compound from eicosapentaenoic acid

Prostaglandins have been shown to modulate water flow in anuran amphibian urinary bladders. These experiments examined which fatty acid precursor could be metabolized by bladders, and the effect of metabolites on osmotic water flow. Hemibladders were incubated with precursors or prostaglandins (1 μM) and water flow measured. In addition, hemibladders were incubated with 14C-labelled eicosatrienoic, arachidonic, or eicosapentaenoic acid, and products identified by thin layer chromatography. Addition of prostaglandins E 1, E 2 and I 2 inhibited water flow. Eicosatrienoic acid did not affect water flow. Arachidonic acid inhibited basal water flow, an effect which was not completely reversed with the addition of indomethacin. Eicosapentaenoic acid stimulated water flow, and the stimulation was blocked with indomethacin. Frog urinary bladder did not synthesize any prostaglandins from 14C-eicosatrienoic acid. 14C-arachidonic acid was converted into PGE 2 and PGD 2. 14C-eicosapentaenoic acid was synthesized into compounds, presumably PGE 3 and PGD 3, with the opposite physiological effects of two-series prostaglandins. The data suggest that effects of prostaglandins on amphibian bladder depend on the substrate which is metabolized.

Effect of hydrazine on transport on toad urinary bladder.

Vasopressin stimulates osmotic water flow and urea permeability in the toad urinary bladder via separate cAMP-responsive mechanisms. Hydrazine (10--20 MM), added to the bladder's serosal bath, reversibly enhanced the effect of both low and saturating levels of vasopressin on osmotic water flow, without increasing urea permeability. A small increase in basal water flow was also observed. Cyclic AMP-stimulated water flow was not altered by hydrazine, but hydrazine enhanced the effect of both 8-bromo-cyclic AMP and methylisobutylxantine. Hydrazine increased luminal membrane aggregate frequency in vasopressin-treated tissues examined by freeze-fracture electron microscopy. Hydrazine increased both basal and vasopressin-stimulated adenylate cyclase activity. We could measure no effect of hydrazine on cAMP content; however hydrazine did increase the protein kinase activity ratio (-cAMP/+cAMP) in vasopressin-treated tissues, suggesting that the kinase activity ratio is more sensitive than cAMP content as an index of cAMP-related function in the bladder. Further strengthening the relationship between kinase activation and water flow, we found that methohexital, an inhibitor of vasopressin-stimulated water flow and adenylate cyclase, also decreased the kinase activity ratio in the presence of vasopressin. These studies link closely the role of cAMP-dependent kinase and luminal membrane aggregates to the specific mediation of vasopressin-stimulated water flow in the bladder.