 Paper published in December 2000. * Corresponding author. Tel.: 1-831-775-1978, fax: 1-831-775-1652. E-mail address: ryjo@mbari.org (J.P. Ryan).  Now at MBARI, 7700 Sandholdt Road, Moss Landing, CA 95039-0628, USA. Deep-Sea Research II 48 (2001) 159}178 In#uence of a Gulf Stream warm-core ring on water mass and chlorophyll distributions along the southern #ank of Georges Bank  J.P. Ryan*, J.A. Yoder, D.W. Townsend Graduate School of Oceanography, University of Rhode Island, Narragansett, RI 02882, USA School of Marine Sciences, University of Maine, Orono, Maine 04469, USA Received 12 August 1998; received in revised form 16 September 1999; accepted 10 December 1999 Abstract During late spring 1997, a Gulf Stream warm-core ring (WCR) strongly in#uenced water mass and chlorophyll distributions along the southern #ank of Georges Bank. Entrainment of Georges Bank shelf water by the WCR, centered at the central southern #ank, persisted through May. By late May, shelf water encircled nearly the entire WCR, and horizontal convergence toward the central southern #ank was evident. Scotian Shelf water (SSW) extended across Northeast Channel, onto Georges Bank near the northeast peak, and along the southern #ank between the 60-m isobath and the shelfbreak front. SSW extended furthest southwest along the southern #ank shelfbreak. Satellite imagery from the ocean color and temperature sensor (OCTS) showed that by late May, in addition to the high chlorophyll concentrations within the entrained shelf water encircling the WCR, pigment rich bands of chlorophyll developed along the 60- and 100-m isobaths. Where this biological enhancement developed along '100 km of the shelfbreak (100-m isobath), shelf waters extended furthest seaward due to entrainment by the WCR. The enhanced shelfbreak chlorophyll was sampled in situ along two transects separated by +40 km along shelf. Along both transects, the enhanced chlorophyll coincided with divergent cross-shelf #ow, maximum along-shelf #ow and minimum surface temperature. Coincidence of the highest surface chlorophyll and lowest surface temperature with divergent cross-shelf #ow is consistent with upwelling. Coincidence with along-shelf jets and their associated vertical shear is consistent with turbulent vertical mixing. The importance of turbulent vertical mixing was supported. Maximum velocity at the shelfbreak coincided with the subsurface temperature minimum of SSW near 30-m depth. Estimated gradient Richardson numbers (Ri) above the SSW were below critical ((0.25) within the shelfbreak chlorophyll maximum along both transects, and surface chlorophyll was signi"cantly, inversely correlated with Ri along the southern #ank. WCR entrainment of shelf water continued into June as 0967-0645/01/$ - see front matter  2000 Published by Elsevier Science Ltd. PII: S 0 9 6 7 - 0 6 4 5 ( 0 0 ) 0 0 1 1 7 - X