Summer fast ice evolution off Zhongshan Station,Antarctica

Based on the field data acquired in the program of fast ice observation off Zhongshan Station, Prydz Bay, East Antarctica during the austral summer 2005/ 2006, physical properties evolution of fast ice during the ice ablation season is analyzed in detail. Results show that the annual maximum ice thickness in 2005 occurred in later November, and then ice started to reek, and the ablation duration was 62 days; sea water under the ice became warmer synchronously; corresponding to the warming sea ice temperature, a ＂relative cold mid-layer＂ appeared in sea ice; the fast ice marginal line recoiled back to the shore observably, and the recoil distance was 20.9 km from 18 December 2005 through 14 January 2006. In addition, based on the data of sea ice thickness survey along the investigation course of MV Xuelong on December 18 of 2005, the ice thickness distribution paten in the marginal ice zone have been described ： sea ice thickness increased, but the diversity of floe ice thick-ness decreased from open water to fast ice zone distinctly.

Optical properties and surface energy flux of spring fast ice in the Arctic

Over the past decades,sea ice in the polar regions has been significantly affecting local and even hemispheric climate through a positive ice albedo feedback mechanism.The role of fast ice,as opposed to drift ice,has not been well-studied due to its relatively small coverage over the earth.In this paper,the optical properties and surface energy balance of land fast ice in spring are studied using in situ observations in Barrow,Alaska.The results show that the albedo of the fast ice varied between 0.57 and 0.85 while the transmittance increased from 1.3×10-3 to 4.1×10-3 during the observation period.Snowfall and air temperature affected the albedo and absorbance of sea ice,but the transmittance had no obvious relationship with precipitation or snow cover.Net solar shortwave radiation contributes to the surface energy balance with a positive 99.2%of the incident flux,with sensible heat flux for the remaining 0.8%.Meanwhile,the ice surface loses energy through the net longwave radiation by 18.7%of the total emission,while the latent heat flux accounts for only 0.1%.Heat conduction is also an important factor in the overall energy budget of sea ice,contributing 81.2%of the energy loss.Results of the radiative transfer model reveal that the spectral transmittance of the fast ice is determined by the thickness of snow and sea ice as well as the amount of inclusions.As major inclusions,the ice biota and particulates have a significant influence on the magnitude and distribution of the spectral transmittance.Based on the radiative transfer model,concentrations of chlorophyll and particulate in the fast ice are estimated at 5.51 mg/m^(2)and 95.79 g/m^(2),which are typical values in the spring in Barrow.

ECOLOGICAL OBSERVATIONS ON COLOURED LAYER OF COASTAL FAST ICE IN GREAT WALL BAY, KING GEORGE ISLAND, ANTARCTICA

Marine biological and environmental investigations were carried out on the coastatl waters off Great Wall Station (62°13's, 58°58'W) on King George Island, Antarctica, from November 17, 1988, to March 3,1989. Coastal fast ice covered inner part of Great Wall Bay until mid-December 1988, which allowed us to take ice core sampling and observations from mid-November to early December 1988. During this period, ice thickness ranged from 90 to 70cm with baout 20cm of snow cover. About 5cm brown layer occured in the middle part of fast ice core collected on November 20, 1988 at site 2, and two brown layers occured in the interior of ice core collected on November 17,20 and 26, 1988 at site 5.In comparison to the water column, chlorophyll-a concentration in fast ice was higher, which ranged from 2.55 to 56.84mg/m8, and most of them were concentracted in the interior layers of sea ice rather than in the bottom layer often observed in other sea ice areas, such as in Syowa, Davis, Casey Station and McMurdo Sound areas, etc. This might be a result of the difference in structure and formation procese of sea ice.Meanwhile, temperature, transparency, nutrients and chlorophyll-a in water column were measured. Microalgal assemblages both in fast ice and water column of Great Wall Bay were reported.

Observations and modeling of the ice-ocean conditions in the coastal Chukchi and Beaufort Seas

The Chukchi and Beaufort Seas include several important hydrological features： inflow of the Pacific water, Alaska coast current （ ACC ）, the seasonal to perennial sea ice cover, and landfast ice ＇along the Alaskan coast. The dynamics of this coupled ice-ocean system is important for both regional scale oceanography and large-scale global climate change research. A mumber of moorings were deployed in the area by JAMSTEC since 1992, and the data revealed highly variable characteristics of the hydrological environment. A regional high-resolution coupled ice-ocean model of the Chukchi and Beaufort Seas was established to simulate the ice-ocean environment and unique seasonal landfast ice in the coastal Beaufort Sea. The model results reproduced the Beaufort gyre and the ACC. The depthaveraged annual mean ocean currents along the Beaufort Sea coast and shelf hreak compared well with data from four moored ADCPs, but the simulated velocity had smaller standard deviations, which indicate small-scale eddies were frequent in the region. The model resuits captured the sea,real variations of sea ice area as compared with remote sensing data, and the simulated sea ice velocity showed an ahnost stationary area along the Beaufort Sea coast that was similar to the observed landfast ice extent. It is the combined effects of the weak oceanic current near the coast, a prevailing wind with an onshore component, the opposite direction of the ocean current, and the blocking hy the coastline that make the Beaufort Sea coastal areas prone to the formation of landfast ice.

Vertical distribution and seasonal variation in ice algae biomass in coastal sea ice off Zhongshan Station， East Antarctica

the biomass of ice algal communities in coastal sea ice off zhongshan Station, antarctica were monitored from april to december 1992. The maximum Thickness of ice cover was 1. 74 m in november/december and covered-snow was less than35 cm in depth throughout the study period. Brown layers occurred in 2～5 cm of theIce bottom in late april and november, with chlorophyll a peak values of 360. 7 and2810 mg/m3 respectively. The integrated chlorophyll a values ranged from 1. 17 to59. 7 mg/m2 with the peak occurring in november when ice algae bloomed, and theValues never exceeded 6 mg/m2 before mid october except at one site, the highest valueOccurred in april and then decreased nuctuatedly throughout the year. The biomassWas concentrated mainly in the bottom of the ice, and might be also partly concentratedIn the interior sections where autumn bloom had occurred. The dominant diatoms wereComposed of nitzschia lecointei, n. Barkleyi, n. Cylindrus in austral autumn and Amphiphiprora kjellmanii, berkeleya rutilans, nitzschia lecointei in austral spring, andShowed some difference at sites owing to the environmental conditions.