摘要:

The decade of the 1980s might well have been designated “The Decade for Marginal Ice Zone (MIZ) Research.” These highly energetic regions where air, ice, and water intermingle and interact thermodynamically and dynamically have undergone an unprecedented amount of study during this past decade. Relevant major programs have included the Office of Naval Research‐sponsored Marginal Ice Zone Experiment (MIZEX) West and East experiments, the Coordinated Eastern Arctic Experiment (CEAREX) in the Arctic, and the National Science Foundation‐sponsored Antarctic Marine Ecosystem Research in the Ice Edge Zone (AMERIEZ) program in the Antarctic. There have been a host of smaller experiments

ISSN:0148-0227    

DOI:10.1029/90JC02327

年代:1991

数据来源: WILEY

摘要:

Using a development from the theoretical model presented by Fox and Squire (1990), this paper investigates the strain field generated in shore fast ice by normally incident ocean waves and swell. After a brief description of the model and its convergence, normalized absolute strain (relative to a 1‐m incident wave) is found as a function of distance from the ice edge for various wave periods, ice thicknesses, and water depths. The squared transfer function, giving the relative ability of incident waves of different periods to generate strain in the ice, is calculated, and its consequences are discussed. The ice is then forced with a Pierson‐Moskowitz spectrum, and the consequent strain spectra are plotted as a function of penetration into the ice sheet. Finally, rms strain, computed as the incoherent sum of the strains resulting from energy in the open water spectrum, is found. The results have implications to the breakup of shore fast ice and hence to the floe size distribution of the marginal ice z

ISSN:0148-0227    

DOI:10.1029/90JC02270

年代:1991

数据来源: WILEY

摘要:

The biomass, taxonomy, size, and photosynthesis‐irradiance responses of phytoplankton in the high Arctic (79°N) were investigated in March–April 1987 in the Fram Strait marginal ice zone. Chlorophyllaconcentrations in open water during this period were extremely low, with surface values averaging 0.022 μg L−1. Vertical mixed layers were deep, ranging from 40 to 200 m, and surface incident irradiance was low (average of 44 μumol photons m−2s−1at local noon). The biomass of the microplankton was dominated by three groups: autotrophic flagellates (less than 10 μm), heterotrophic flagellates (less than 10 μm), and heterotrophic dinoflagellates (from 10 to 35 μm ). Detrital carbon contributed the largest fraction (on average 95%) to the particulate carbon pool. Photosynthesis‐irradiance responses indicated that the resident phytoplankton populations were adapted to low irradiance levels, as would be expected after the long periods of darkness encountered during the Arctic winter. Estimates of primary productivity during the March–April period indicate that very little net carbon fixation was occurring (averaging 1.84 mg C m−2d−1with a maximum of 3.3 mg C m−2d−1). Some small increases in surface chlorophyll concentrations (relative to those at the base of the mixed layer) were noted at a few stations, and hence the onset of spring growth may have just begun. However, in view of the biomass and productivity observed during this period, the accumulation of substantial phytoplankton standing stocks, which are often observed at the ice edge, cannot occur until much later in the growing season

ISSN:0148-0227    

DOI:10.1029/90JC01778

年代:1991

数据来源: WILEY

摘要:

Pulse‐limited, airborne radar data taken in June and July 1984 with a 13.8‐GHz altimeter over the Fram Strait marginal ice zone are analyzed with the aid of large‐format aerial photography, airborne synthetic aperture radar data, and surface observations. Variations in the radar return pulse waveforms are quantified and correlated with ice properties recorded during the Marginal Ice Zone Experiment. Results indicate that the wide‐beam altimeter is a flexible instrument, capable of identifying the ice edge with a high degree of accuracy, calculating the ice concentration, and discriminating a number of different ice classes. This suggests that microwave radar altimeters have a sensitivity to sea ice which has not yet been fully exploited. When fused with SSM/I, AVHRR and ERS‐1 synthetic aperture radar imagery, future ERS‐1 altimeter data are expected to provide some missing pieces to the sea ice geophy

ISSN:0148-0227    

DOI:10.1029/90JC01954

年代:1991

数据来源: WILEY

摘要:

Surface‐based active and passive microwave measurements were made in conjunction with ice property measurements for several distinct ice types in the Fram Strait during March and April 1987. Synthetic aperture radar imagery downlinked from an aircraft was used to select study sites. The surface‐based radar scattering cross section and emissivity spectra generally support previously inferred qualitative relationships between ice types, exhibiting expected separation between young, first‐year and multiyear ice. Gradient ratios, calculated for both active and passive data, appear to allow clear separation of ice types when used jointly. Surface flooding of multiyear floes, resulting from excessive loading and perhaps wave action, causes both active and passive signatures to resemble those of first‐year ice. This effect could possibly cause estimates of ice type percentages in the marginal ice zone to be in error when derived from aircraft‐ or satellite‐bo

ISSN:0148-0227    

DOI:10.1029/90JC02269

年代:1991

数据来源: WILEY

摘要:

A fully prognostic coupled ice‐ocean model is used to examine the importance of interannually variable ocean forcing, on large‐scale monthly simulations of the Arctic ice cover. The model is forced by a prescribed interannually variable atmosphere. Simulations are conducted for a 120‐month period and validated with observed ice concentration data. The model produces very reasonable simulations of the ice edge position, particularly in the Barents and Greenland seas. The use of interannual ocean forcing produces major improvements to the simulation of the ice concentration for both the annual cycle and interannual variations, as compared with simulations in which the ocean forcing is a prescribed mean annual cycle. Vertical ocean heat flux appears to be the dominant mechanism controlling localized ice area anomalies and the overall ice concentration. Consistent errors in simulated ice concentration and thickness remain, including a slightly exaggerated melt‐freeze cycle and insufficient ice thickness. The lack of a nonprognostic mixed layer and the coarse vertical resolution are apparently inadequate to represent the vertical mixing, stratification, and diffusion processes p

ISSN:0148-0227    

DOI:10.1029/90JC02268

年代:1991

数据来源: WILEY

摘要:

In this paper the ocean wave dispersion relation and viscous attenuation by a sea ice cover are studied for waves propagating into the marginal ice zone (MIZ). The derivation of the dispersion relation and the viscous attenuation by an ice sheet are discussed for waves under flexure and pack compression. In the MIZ, the flexure effect is important for short waves. For a fixed wave period the changes in wavelength and group velocity as a function of ice thickness are significant. In turn, the exponential wave attenuation rate shows a rollover at short wave periods, whereby the rapid increase in wave attenuation rate with decreasing wave period slows down or even turns into a decrease. The Labrador Ice Margin Experiment (LIMEX), conducted on the MIZ off the east coast of Newfoundland, Canada, in March 1987, provides us with aircraft synthetic aperture radar (SAR) imagery, wave buoy, and ice property data. On the basis of the wave number spectrum from the SAR data and the concurrent wave frequency spectrum from the ocean buoy data and accelerometer data on the ice during LIMEX '87, the dispersion relation has been estimated and compared with a model. Wave energy attenuation rates are estimated from SAR data and the ice motion package data which were deployed at the ice edge and into the ice pack, and compared with the model. The model‐data comparisons are reasonably good for the ice conditions observed during LIMEX '87. Some previously reported data of wave attenuation in the MIZ are revisited for model compariso

ISSN:0148-0227    

DOI:10.1029/90JC02267

年代:1991

数据来源: WILEY

摘要:

A quasi‐geostrophic, mesoscale eddy‐resolving model is coupled with free‐drifting sea ice to examine mesoscale oceanic structures, which are induced by wind forcing on a nonuniform ice distribution, and redistribution of sea ice. Initial concentration of sea ice has anomalies on the motionless ocean, and the sea ice is suddenly forced by a wind stress. Differences in Ekman transport between the high (low) concentration area and the surrounding area generate dipole eddylike features in the ocean with anticyclonic and cyclonic eddies on the right (left) and left (right), respectively, looking in the downwind direction. Redistribution of ice by the ocean circulation continues after the wind ceases, forming arch or hammer head shapes of ice anomalies. Interactions with the other anomalies can produce various shapes, which could lead to misinterpretation of ocean flow field. It is suggested that to detect ocean flow field in an ice‐covered area (not near the ice edge), trajectories should be used instead of shapes of ic

ISSN:0148-0227    

DOI:10.1029/90JC02266

年代:1991

数据来源: WILEY

摘要:

An ice‐ocean model has been developed by coupling the Hibler ice model to a three‐dimensional ocean model that consists of a turbulent mixed layer model and an inverse geostrophic model. The coupled model has a horizontal grid spacing of 127 km and has 17 vertical levels extending to the ocean bottom. The model is forced with 12‐hourly general circulation model‐derived atmospheric fluxes for the year 1986, for which good quality ice edge analyses and buoy tracks were available for comparisons. The results are presented for the fifth year of a repetitive simulation with the 1986 fluxes, at which time the system has reached a statistical equilibrium. The seasonal and geographical variations of the ice cover and the upper few hundred meters of the ocean have been examined, including the heat and salt budgets. The computed heat fluxes and mixed layer depths (MLDs) fall in the observed seasonal ranges, with winter heat fluxes ranging from 15 W m−2in the central Arctic to about 500 W m−2in the Barents Sea area, and summer fluxes from about 5 W m−2under the ice to about 30 W m−2in the various marginal ice zone (MIZ) edge areas. The corresponding winter MLDs are found to be about 25–75 m in the central Arctic to a deep 800 m in the Greenland Sea; typical summer MLDs are between 5 and 30 m. In all seasons, the MIZ was found to be the center of flux activity for both heat and salt, with the processes of advection, diffusion, atmospheric forcing, and vertical oceanic fluxes having their largest values here, and of comparable magnitudes. Values of the heat flux components in the MIZ exceed those found under the ice by an order of magnitude or more, and those in the open water region by a factor of 2. For salt, the situation is similar except in the summer (June through September), when a lot of salt flux activity takes place under the ice. Comparisons are made with Naval Polar Oceanography Center (NPOC) analyses for ice concentration and ice edge, and with observed Arctic buoy tracks, in the same 1986 time period. The computed ice edge positions have comparable accuracy to previous three‐dimensional coupled ice‐ocean studies, with too much ice growth during the winter in the Barents Sea and too little ice east of Greenland. The ice thickness distributions, however, are much better, with a monotonic increase of the ice thickness from the Siberian coast east toward the Canadian archipelago with maximum winter

ISSN:0148-0227    

DOI:10.1029/90JC02265

年代:1991

数据来源: WILEY

摘要:

Arctic cooling through the fall‐winter transition is calculated from a coupled atmosphere‐sea ice thermal model and compared to temperature soundings and surface measurements made north of Svalbard during the Coordinated Eastern Arctic Experiment (CEAREX). A typical winter, clear‐sky vertical temperature structure of the polar air mass is composed of a surface‐based temperature inversion or an inversion above a very shallow (30–180 m) mechanically mixed boundary layer with temperatures −30° to −35°C, a broad temperature maximum layer of −20° to −25°C between 0.5 and 2 km, and a negative lapse rate aloft. Because the emissivity of the temperature maximum layer is less than that of the snow surface, radiative equilibrium maintains this low level temperature inversion structure. A 90‐day simulation shows that heat flux through the ice is insufficient to maintain a local thermal equilibrium. Northward temperature advection by transient storms is required to balance outward longwave radiation to space. Leads and thin ice (<0.8 m) contribute 12% to the winter tropospheric heat balance in the central Arctic. CEAREX temperature soundings and longwave radiation data taken near 81°N show polar air mass characteristics by early November, but numerous storms interrupted this air mass during December. Snow temperature changes of 15°C occurred in response to changes in downward atmospheric longwave radiation of 90 W m−2between cloud and clear sky. We propose that the strength of boundary layer stability, and thus the degree of air‐ice momentum coupling, is driven by the magnitude of the radiation deficit (downward‐outward longwave) at the surface and the potential temperature of the temperature maximum layer. This concept is of potential benefit in prescribing atmospheric forcing for sea ice models because a surface air temperature‐snow temperature difference field is difficult to obtain and it may be possible to obtain a radiation de

ISSN:0148-0227    

DOI:10.1029/90JC02264

年代:1991

数据来源: WILEY