J. Churchill (WHOI) and J. Manning (NMFS)
Entrainment into Gulf Stream warm-core rings has been shown to be a dominant agent acting to remove water from the southern flank of Georges Bank and from the shelf of the Middle Atlantic Bight. Present evidence is inconclusive regarding the scope over which water is drawn into a warm-core ring. Examination of hydrographic data by Churchill et al. (1993) and Schlitz (1996) suggests that most of the water entrained into rings originates within the shelf-edge front, and not from the main body of shelf water. However, no researchers have directly measured the transport of shelf water into rings. Defining the scope of warm- core ring entrainment and understanding the mechanisms involved is clearly critical to the study of retention and loss of larvae over Georges Bank. Current planned research of phase-2 of the Georges Bank GLOBEC Project which is directed at the influence of warm-core rings (most notably the SeaSoar surveying of Brink et al.) does not include direct measurements of transport to a ring. In addition, it is limited to two scheduled cruises which may or may not coincide with the presence of a ring. In view of the potential impact of ring entrainment to larval populations, we believe that the phase-2 program should include a study specifically targeting warm-core ring entrainment with a flexible cruise schedule to guarantee (or nearly so) that work be done in the vicinity of a warm-core ring. We propose a drifter-CTD-ADCP study of shelf water transport onshore of a warm-core ring to be carried out from a local fishing vessel. We have contacted two local skippers who will make their vessels available for up to two weeks at short notice. Our effort would include releasing drifters along lines onshore of the rings coupled with ADCP-CTD surveys within the region of these lines. We envision a 10-12 day cruise with 2-3 drifter deployments. We have carried out this type of research from vessels as small as 26'. Ideally, this work would be done as part of one of the major sampling efforts on the bank (given the appearance of a ring). In such case, our plan is to coordinate the drifter deployment and CTD- ADCP surveying with other sampling (especially the SeaSoar surveying). We need the separate vessel due to the requirements of the drifter tracking and to focus the CTD-ADCP surveying in the region of the drifters. In the event that scheduled cruise times are ring-free, we have established an 18-month window over which our cruise can take place to ensure that flow measurements will be acquired in the vicinity of a ring. This type of work was included in our unsuccessful proposal. It was, however, was favorably viewed by all reviewers (objections were raised to other parts of our program).