The Polar Front j Cold-Core Rings — 



Effects on Abundance and Distribution of Phytoplankton 



January 1979 



The dramatic CZCS pigment image of the central Drake Passage and 

 western Scotia Sea taken on 6 January (99-2) and the corresponding 

 locator map (99-1) show the extensive geographical variability of near- 

 surface distributions of phytoplankton pigments in these icy waters. This 

 is in sharp contrast to the relatively smooth pattern of pigment 

 distribution obtained from shipboard observations made in this region. 

 The image shows generally low pigment values in the polar front region 

 (0.05 mg chl m"3). However, there is, within the polar front, a region of 

 relatively high pigment concentration squeezed between bands of low 

 pigment concentration. Pigment values north of the polar front are also 

 generally low, but isolated regions of concentrations in excess of 

 0. 1 mg chl m"3 are observed. The highest pigment values occur to the south 

 of the polar front. The reasons for these enhanced concentrations are 

 unknown. The general pattern and values of the pigments shown in the 

 image are in agreement with shipboard observations made in this region of 

 the Southern Ocean (El-Sayed et al., 1964; El-Sayed, 1967). 



The meandering nature of the polar front is apparent in the CZCS 

 image. Also apparent are cold-core rings which form from meanders in the 

 polar front (Joyce and Patterson, 1977; Joyce et al., 1981; Peterson et al., 

 1982; Hofmann et al., 1984). Like their counterparts in the Gulf Stream 

 and Agulhas Current, these rings retain their physical and probably 

 biological characteristics for long periods. Peterson et al. (1982) suggest 

 that these rings are an important component of the heat and salt budgets of 

 the Southern Ocean. It has been shown that within Gulf Stream cold-core 

 rings, the structure of the planktonic community is conserved (Wiebe 

 et al., 1976). Furthermore, Wiebe and Boyd (1978) suggest that these cold- 

 core rings are capable of transporting zooplankton communities a long 

 distance from their usual habitat. Similarly, cold-core rings in the 

 Southern Ocean may also transport biological and chemical properties 

 across the Antarctic Circumpolar Current. 



It is unfortunate that this region of the Southern Ocean is often covered 

 by clouds. This makes it difficult to obtain a sequence of CZCS images 

 from which the time development of phytoplankton blooms and water 

 movement can be studied. However, the available images do provide 

 synoptic observations in a region in which logistical constraints make a 

 comprehensive field study difficult. 



References 



El-Sayed. S. Z., 1967: On the productivity of the Southwest Atlantic Ocean and the waters 



west of the Antarctic Peninsula, Antarctic Research Series. In Biology of the 



Antarctic Seas III, 11. edited by Waldo Schmitt and George Llano, American 



Geophysical Union, Washington, D.C., 15-47. 

 , 1972: Primary productivity and standing crop of phytoplankton. In Chemistry, 



Primary Productivity, and Benlhic Marine Algae of the Gulf of Mexico, Serial Atlas of 



the Marine Environment. Folio 22, edited by V. C. Bushnell, American Geographical 



Society, 8-13. 

 El-Sayed, S. Z., E. F. Mandelli, and Y. Sugimura, 1964: Primary organic production in the 



Drake Passage and Bransfield Strait. In Biology of the Antarctic Seas I. 1, edited by 



M. O. Lee, American Geophysical Union, Washington, D.C.. 1-110. 

 Hofmann, E., T. Whitworth III. and D. Nowlin, Jr., 1984: Mesoscale flow variability at 



Drake Passage. J. Geophys. Res., submitted. 

 Joyce, T. M.,andS. L. Patterson, 1977: Cyclonic ring formation at the polar front in Drake 



Passage. Nature, 265, 131-133. 

 Joyce, T. M., S. L. Patterson, and R. C. Millard, Jr., 1981: Anatomy of a cyclonic ring in 



Drake Passage. Deep-Sea Res.. 28, 1265-1289. 

 Peterson, R. G., W. D. Nowlin, Jr.. and T. Whitworth III, 1982: Generation and evolution 



of a cyclonic ring at Drake Passage in early 1979. / Phys. Oceanogr.. 12, 1\1-1\9. 

 Wiebe, P. H., and S. H. Boyd, 1978: Limits of Nematoscelismegalops in the Northwestern 



Atlantic in relation to Gulf Stream and cold-core rings. I. Horizontal and vertical 



distributors. J. Marine Res., 36, 119-142. 

 Wiebe, P. H., E. M. Halburt, E. J. Carpenter, A, E. Jahn, G. P. Knapp III, S. H. Boyd, 



P. B. Ortner, and J. L. Cox, 1976: Gulf Stream cold-core rings: Large-scale interaction 



sites for open ocean plankton communities. Deep-Sea Res., 23, 695-710. 



