Slope Water Interaction Workshop

23-24 August, 2000

Clark Laboratory, Woods Hole Oceanographic Institution

Abstract

• Introduction
• Basic Phenmenon
  • May 1999 Slope Water Intrusion (AVHRR)
  • June 1997 Gulf Stream Intrusion (AVHRR)
  • May 1997 Detrainemnt Event (AVHRR)
  • Eddy-Continental Shelf Interaction (Model Results)
  • April 1999 Scotian Shelf Crossover Event (AVHRR)

Overviews

• 1995 Events
• 1997 Events
• 1997 Cruises
• 1999 Events
• 1999 Cruises

Observations and Models

• BIO Moorings
  • June 1997 R/V Parizeau Cruise Track
  • 1997 Southeast Flank Mooring
  • 1999 Northeast Channel Mooring
• Great South Channel Mooring Deployment Cruises
  • Mooring Positions
  • Jan 1997 (OC 296) CTD Stations
  • Aug 1997 (OC 311) CTD Stations
• Eddy Interactions with the Continental Shelf- Model Results
  • No Background Flow
  • Background Shear Flow
• May-June 1997 Detrainment
  • EN301 Cruise Track with AVHRR
• March 1997 SeaSoar- Storm Induced Exchange and Scotian Shelf Crossover
  • Pre-Storm AVHRR
  • Post-Storm AVHRR
  • Survey Chart
• June-July 1997 SeaSoar- Gulf Stream Plume Interactions
  • Survey Chart
  • Early AVHRR (streamer)
  • Mid AVHRR (streamer)
  • Late AVHRR (tendril)
• 1995-1999 Remote Sensing

1997 Slope Water/Gulf Stream Intrusion Study

Events

AVHRR and in-situ measurements show Slope Water intrusions during May and June-July, separate shelf water detrainment events in late May and July, and Scotian Shelf Water cross-over events in March and May.

SWI97-1: Begins about May 12 in AVHRR and depicted in May on Lough's process cruise (http://www.wh.whoi.edu/~jmanning/may97/hadvsig.gif ). Small-scale instabilities along the shelf-slope boundary evidently resulted in parcels of slope-like water intruding on to the mid-shelf region. The distribution of fish larvae was apparently displaced and concentrated near the tidal mixing front (http://www.wh.whoi.edu/~jmanning/may97/surfconv.jpg ).

SWI97-2: Massive intrusion of very warm, salty water onto the southern flank, starting about July 3 (Figure 2). Salinities at SF exceed 34 near-bottom and 36 near-surface for about four days, before a slow return to pre-intrusion levels (~ 32.5) by July 28.

SWD97-1: A shelf water streamer was formed in mid-May by the combined flow of a large WCR and Gulf Stream meander (Figure 3). This detrainment was sampled in late-May/June on Wishner's process cruise.

SWD97-2: A new streamer was formed to the northeast in June, and sampled in late June on Lee's process cruise. SSC97-1: sampled in March by Lee.

SSC97-2: sampled in May by Wishner.

Objectives

Shelf Water Intrusions

• Describe the two intrusions of warm,salty water onto the southern flank - spatial/temporal evolution of intrusions, associated flows, nutrients, biology. In particular, can we successfully detide the observed velocity fields to detect an overall effect of the passing intrusion? Are animals rapidly advected along the front towards the west or are they retained on the shallow portions of the bank?
• Determine if intrusions have any lasting biological (and physical) effects on the southern flank environment.

Detrainment Events

• Describe the two shelf water detrainment events, determining if possible the amount and rate of shelf water and biota exported, and the importance of this loss to the southern flank and Bank ecosystem.

Methods

• April, May, and June BS surveys give before, during, and after SWI97-1 T,S, and species snapshots to compare with the detailed CTD/MOCNESS sampling done on Lough's May cruise.
• The June BS survey provides a before SWI97-2 snapshot, to complement the detailed SeaSoar/VPR sampling of the shelfbreak frontal region on Lee's SWI97-2 (June/July) cruise.
• AVHRR and time series data from the BIO Southeast Flank (SEF) mooring and the Great South Channel recirculation array (GSCA) can be used to place the SWI97-1 event in context. The SEF mooring was recovered in late June, just before the start of SWI97-2. The SF mooring was deployed in early June, thus capturing all of SWI97-2.
• SWD97-1 was sampled using CTD/MOCNESS/ADCP on Wishner's May cruise, while SWD97-2 was sampled using SeaSoar/VPR/ADCP on Lee's June/July cruise. Parallel analysis and comparisons of these two events should help provide a more comprehensive view of the impact of detrainment events on the Bank.