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Photosynthesis-irradiance relationships in natural phytoplankton populations of the Barents Sea 总被引：1，自引：0，他引：1
FRANCISCO REY 《Polar research》1991,10(1):105-116
An analysis is made of the photosynthesis-irradiance relationships in natural phytoplankton populations in the Barents Sea. The data set comprises 232 experiments carried out during a 10-year period, both in open and ice-covered waters. The variability on the P-I parameters is discussed and examined in relation to the variation in a variety of environmental conditions. The results suggest that in the Barents Sea, as in other Arctic areas, phytoplankton photosynthesis is mainly controlled by physical variables. However, control of the phytoplankton stock, i.e. by zooplankton grazing, seems also to have a considerable indirect influence on P-I parameters, especially after the spring bloom and the depletion of winter nutrients. 相似文献
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ROLF ZALE REY GLAZOVSKIY JENS-OVE NASLUND 《Boreas: An International Journal of Quaternary Research》1994,23(3):254-258
Seven old, shed caribou ( Rangifer tarandus ) antlers from Alexandra Land, in the high arctic Franz Josef Land archipelago where no caribou are found today, were dated to between 3870 ± 70 and 2245 ± 70 radiocarbon years BP. All were found on the ground above the highest shoreline, thus not transported there by sea-ice. That the ages all fall into a relatively narrow time-span suggests that they originate from a population of caribou that really lived on Alexandra Land. We suggest that they migrated there after the culmination of the Holocene climatic optimum ( c . 6000 to 4500 BP) when the climate again became colder and the sea-ice more persistent. The climate during that period can be compared with that of Nordaustlandet on Svalbard today, where a population of caribou still exists. 相似文献
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The ecology of Lower Cambrian buildups from Zuune Arts, Mongolia: implications for early metazoan reef evolution 总被引：1，自引：0，他引：1
Reefal buildups in western Mongolia of mid-Early Cambrian (late Atdabanian) age flourished during a period when shelf seas were globally widespread. The succession at Zuune Arts records the transition from shallow marine siliciclastic sediments (Bayan Gol Formation) to shallow marine, but still clastic-influenced, carbonates (Salaany Gol Formation). The Salaany Gol Formation is interpreted as having been deposited as a series of shallowing upwards cycles on a shallow, gently inclined shelf in a rapidly subsiding epicontinental sea. Cycles commenced with the growth of subtidal metazoan-calcimicrobe aggregative communities on an open shelf. The resultant buildups were commonly engulfed by extensive, massive microbial stromatolites when they grew in agitated intertidal conditions. Latterly, they were smothered by ooid shoals in response to rapid sea level rise. Four types of reefal buildup are distinguished: (1) green-coloured calcimicrobe (Tarthinia, Epiphyton, Gordonophyton and Renalcis) boundstones; (2) red-or green-coloured Cambrocyathellus-Tarthinia-Epiphyton bafflestones; (3) red-coloured Okulitchicyathus bindstones; and (4) red-coloured radiocyath-archaeocyath-cribricyath bioherms. Each is interpreted as having grown at increasing depths and possibly sedimentation rates. The buildups are commonly enclosed within graded and planar bedded bioclastic grainstones and packstones, and are best developed towards the top of the formation, when sea level was high. Thickets of large, solitary archaeocyaths are also inferred in the deeper interbiohermal areas. These buildups had synoptic relief and constructed porous structures with growth-framework cavities housing diverse coelobiontic communities. Extensive synsedimentary cements are present, including pseudomorphed aragonitic fans and possible pseudomorphed aragontic botryoids. These early reefs thus have geological fabrics similar to later Phanerozoic representatives. It is proposed however, that this ecosystem was largely composed of generalist and opportunistic filter and suspension feeders which were dependent upon a far higher input of nutrients than modern day reefal developments. Bacteria were probably the main primary producers, from both planktic and benthic cyanobacterial communities. The diversity of each buildup assemblage appears to be controlled by primary cavity size, the richest fauna belonging to the highly tiered radiocyath-dominated community inferred to have lived in the deepest waters. The communities at Zuune Arts can be compared with other buildups from the early Cambrian, and with Lower Ordovician receptaculid-calcimicrobe-solitary sponge bioherms known from the USA and Siberia. 相似文献
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