โ Scribed by S. M. Saupe; D. M. Schell; W. B. Griffiths
No coin nor oath required. For personal study only.
Zooplankton from 87 stations in the Bering, Chukchi and Beaufort Seas sampled in 1985, 1986 and 1987 showed a geographic gradient in stable carbon-isotope ratios (613C). The zooplankton most depleted in ~3C were found in the central and eastern Beaufort Sea and those most enriched were from the Bering and Chukchi Seas. Average g~3C values ranged from 20.9 to -26.7%o for copepods and from -19.4 to 25.1%0 for euphausiids. Euphausiids show a minimum of 1.0%0 enrichment relative to copepods throughout the study area. Relative biomasses of the major zooplankton taxa varied significantly across the Alaskan Beaufort Sea in October 1986, with euphausiids dominating in the west and copepods in the east. These differences in taxonomic composition affected the weighted c513C values for "total" zooplankton and may produce an even more pronounced geographic gradient in zooplankton 6~3C than that found within a single taxon. The bowhead whale Balaena rnysticetus migrates between wintering areas in the Bering Sea and summering areas in the Beaufort Sea and feeds over this geographic range. The zooplankton c5~3C gradient is the probable source of 613C oscillations found along the baleen plates of this planktivore. and -2.7%0 for Sagitta elegans. The greatest geographic variation in c513C occurred between Longitude 143 ~ and 149~
Although the causes for these variations remain uncertain, Dunton thought that they might be a consequence of recycling of 13C-depleted (isotopically "light") carbon during upwelling events in the central Beaufort Sea described by Hufford (1974), and the intrusion into the western Beaufort Sea of Bering-Chukchi water having distinct physical and chemical characteristics (Mountain 1974, Aagaard 1984).
The existence of latitudinal gradients in carbon-isotope ratios in plankton from other regions of the world oceans was described by Rau et al. (1982). They found that the latitudinal gradient was steeper in the southern hemisphere than in the northern hemisphere, and they discounted water temperature or inorganic carbon as determining mechanisms. Plankton from 60~ averaged near -22%0, whereas those from 60~ were near-27%0. Two samples of plankton analyzed by Rau et al. from the western Beaufort Sea (150~ yielded values of-21.5 and -22.4%0. The marked difference between these values and those reported by Dunton (1985) from the eastern Alaskan Beaufort Sea indicated that a pronounced regional isotopic gradient might exist.
๐ SIMILAR VOLUMES
The carbon isotope ratio (ฮด^13^C) of vascular plant leaf tissue is determined by isotope discrimination, primarily mediated by stomatal and mesophyll diffusion resistances and by photosynthetic rate. These effects lead to predictable trends in leaf ฮด^13^C across natural gradients of elevation, irrad
Water is usually considered to be the key limiting factor for growth of desert plants, yet there is little information available of the water-use efficiency of species within a desert community. Leaf carbon isotope ratios, an indicator of long-term intercellular carbon dioxide concentrations and thu