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87:6097 Borehole evidence for a thick layer of basal ice in the central Ronne Ice Shelf
OLR (1987)34 (I I)
A. PhysicalOceanography
87:6097 Engelhardt, Hermann and Jtlrgen Determann, 1987. Borehole evidence for a thick layer of basal ice in the central Ronne k e Shelf. Nature, Lond., 327(6120):318-319.
Extensive radio-echo sounding (RES) revealed reflections at the relatively shallow depth of 100-200 m below surface. Interpretation of these echoes, which varied in strength, was ambiguous, and the possibility of internal reflecting horizons was thoroughly discussed. After surface elevation measurements by radar altimeter from drifting balloons appeared to fit the presence of thin ice, a thickness map of the Ronne Ice Shelf was based on these RES echoes. Direct observational evidence from boreholes that the total ice thickness is much greater than mapped, and that the shallow RES reflections do come from internal horizons is presented. Inst. fur Geophys., Westfalische Wilhelms Univ., Corrensstr. 24, D-4400 Munster, FRG. 87:6098 Lal, D., K. Nishiizumi and J.R. Arnold, 1987. In-situ cosmogenic 3H, 14C, and 1°Be for determining the net accumulation and ablation rates of ice sheets. J. geophys. Res., 92(B6):4947-4952.
Application of aH and l°Be is severely constrained because at deposition, ice contains appreciable amounts of these isotopes from the atmosphere. The case is much more favorable for ~4C, which is not carried with wet precipitations; atmospheric ~4C gets mechanically trapped in the ice during deposition. Cosmogenic ~4C would probably exist as ~4CO in ice. Conditions under which these isotopes can be used to study net accumulation and ablation rates are discussed along with data on 14C and ~°Be on polar ice from accumulation and ablation zones. 3H and t4C should find wide application in studying ice dynamics, and ~°Be only in very special circumstances. Scripps Inst. of Oceanogr., La Jolla, CA 92093, USA. 87:6099 Wake, Akio, Y.-K. Poon and Randy Crissman, 1987. Ice transport by wind, wave, and currents. J. cold Regions Engng, Am. Soc. civ. Engrs, 1(2):89-93.
A simple numerical model is developed for predicting ice floe motion under the influence of unidirectional forces of wind, drift current, and short water waves for the case in which the length of the floe is much longer than that of the winter waves. Model predictions of the transient motion provide only qualitative agreement with the experimental results, but predictions of terminal drift speed are better, with a maximum error of about 15%. The
927
time to reach 95% of the terminal speed is insensitive to the wind speed. The motion is most sensitive to floe thickness. Both terminal speed and tg~ approach asymptotic values when the length-to-thickness ratio exceeds 16. Dept. of Civ. Engng, State Univ. of New York, Buffalo, NY 14260, USA. 87:6100 Zakrzewski, W.P., 1986. On the contribution of sea ice ridges into the mass of ice in the Gulf of Botlmia. Geophysica, 22(1-2):131-144. Dept. of Geogr., Univ. of Alberta, Edmonton, AB, Canada.
A240. Optical properties 87:6101 Siegel, D.A. and T.D. Dickey, 1987. Observations of the vertical structure of the diffuse attenuation coefficient spectrum. Deep-Sea Res., 34(4A):547563.
Profiles of the diffuse attenuation coefficient spectrum for downwelling spectral irradiance (DSI) were determined using data taken during the autumn of 1982 in the eastern North Pacific Ocean. Nearsurface it was consistent with Jerlov water types IA or IB and did not show any significant variations with sun altitude angle or cloud amount, supporting the notion that DSI is a 'quasi-inherent' optical property. The observed depth-wavelength distribution may be divided into a blue-green group (400-500 nm) with a vertical structure similar to the vertical distribution of chlorophyll pigments and a green-yellow group (500-575 nm) with little vertical variation. Robust interrelationships among the total pigment concentration, the in-situ fluorescence and DSI were observed, suggesting that any one of these parameters can be used to ascertain the variability of the others. Dept. of Geolog. Sci., Univ. of Southern Calif., Los Angeles, CA 90089-0741, USA. 87:6102 Zakharov, A.K. and Yu.A. Gol'din, 1986. Monte Carlo calculation of the structure of a narrow nonstationary light beam in seawater at large optical depths. Izv. A tmos. Ocean Phys. (a translation of Fiz. Atmos. Okeana), 22(5):403408.
Attenuation of the peak brightness and spreading of the signal in the geometric zone at optical depths T = 50 are calculated taking into account the actual geometry of the source-receiver system, time response of the equipment, and the scattering properties of seawater. Inst. of Oceanol., Acad. of Sci., USSR.
A. PhysicalOceanography
87:6097 Engelhardt, Hermann and Jtlrgen Determann, 1987. Borehole evidence for a thick layer of basal ice in the central Ronne k e Shelf. Nature, Lond., 327(6120):318-319.
Extensive radio-echo sounding (RES) revealed reflections at the relatively shallow depth of 100-200 m below surface. Interpretation of these echoes, which varied in strength, was ambiguous, and the possibility of internal reflecting horizons was thoroughly discussed. After surface elevation measurements by radar altimeter from drifting balloons appeared to fit the presence of thin ice, a thickness map of the Ronne Ice Shelf was based on these RES echoes. Direct observational evidence from boreholes that the total ice thickness is much greater than mapped, and that the shallow RES reflections do come from internal horizons is presented. Inst. fur Geophys., Westfalische Wilhelms Univ., Corrensstr. 24, D-4400 Munster, FRG. 87:6098 Lal, D., K. Nishiizumi and J.R. Arnold, 1987. In-situ cosmogenic 3H, 14C, and 1°Be for determining the net accumulation and ablation rates of ice sheets. J. geophys. Res., 92(B6):4947-4952.
Application of aH and l°Be is severely constrained because at deposition, ice contains appreciable amounts of these isotopes from the atmosphere. The case is much more favorable for ~4C, which is not carried with wet precipitations; atmospheric ~4C gets mechanically trapped in the ice during deposition. Cosmogenic ~4C would probably exist as ~4CO in ice. Conditions under which these isotopes can be used to study net accumulation and ablation rates are discussed along with data on 14C and ~°Be on polar ice from accumulation and ablation zones. 3H and t4C should find wide application in studying ice dynamics, and ~°Be only in very special circumstances. Scripps Inst. of Oceanogr., La Jolla, CA 92093, USA. 87:6099 Wake, Akio, Y.-K. Poon and Randy Crissman, 1987. Ice transport by wind, wave, and currents. J. cold Regions Engng, Am. Soc. civ. Engrs, 1(2):89-93.
A simple numerical model is developed for predicting ice floe motion under the influence of unidirectional forces of wind, drift current, and short water waves for the case in which the length of the floe is much longer than that of the winter waves. Model predictions of the transient motion provide only qualitative agreement with the experimental results, but predictions of terminal drift speed are better, with a maximum error of about 15%. The
927
time to reach 95% of the terminal speed is insensitive to the wind speed. The motion is most sensitive to floe thickness. Both terminal speed and tg~ approach asymptotic values when the length-to-thickness ratio exceeds 16. Dept. of Civ. Engng, State Univ. of New York, Buffalo, NY 14260, USA. 87:6100 Zakrzewski, W.P., 1986. On the contribution of sea ice ridges into the mass of ice in the Gulf of Botlmia. Geophysica, 22(1-2):131-144. Dept. of Geogr., Univ. of Alberta, Edmonton, AB, Canada.
A240. Optical properties 87:6101 Siegel, D.A. and T.D. Dickey, 1987. Observations of the vertical structure of the diffuse attenuation coefficient spectrum. Deep-Sea Res., 34(4A):547563.
Profiles of the diffuse attenuation coefficient spectrum for downwelling spectral irradiance (DSI) were determined using data taken during the autumn of 1982 in the eastern North Pacific Ocean. Nearsurface it was consistent with Jerlov water types IA or IB and did not show any significant variations with sun altitude angle or cloud amount, supporting the notion that DSI is a 'quasi-inherent' optical property. The observed depth-wavelength distribution may be divided into a blue-green group (400-500 nm) with a vertical structure similar to the vertical distribution of chlorophyll pigments and a green-yellow group (500-575 nm) with little vertical variation. Robust interrelationships among the total pigment concentration, the in-situ fluorescence and DSI were observed, suggesting that any one of these parameters can be used to ascertain the variability of the others. Dept. of Geolog. Sci., Univ. of Southern Calif., Los Angeles, CA 90089-0741, USA. 87:6102 Zakharov, A.K. and Yu.A. Gol'din, 1986. Monte Carlo calculation of the structure of a narrow nonstationary light beam in seawater at large optical depths. Izv. A tmos. Ocean Phys. (a translation of Fiz. Atmos. Okeana), 22(5):403408.
Attenuation of the peak brightness and spreading of the signal in the geometric zone at optical depths T = 50 are calculated taking into account the actual geometry of the source-receiver system, time response of the equipment, and the scattering properties of seawater. Inst. of Oceanol., Acad. of Sci., USSR.