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

1995 Slope Water/Gulf Stream Intrusion Study

EVENTS

AVHRR and the Southern Flank mooring time series show three intrusion events over April-August 1995.

SWI95-1: Was first revealed on 2 May by a sudden rise in surface temperature at NOAA buoy 44011. However, this was principally a near bottom intrusion as indicated by subsequent measurements at the southern flank triad of moorings: SF, ST1 and ST2. The intrusion appeared at these moorings from May 7 through the end of the month. It produced the highest salinities, order 35, near the bottom. Current meter and drifter data indicate an intensification and onbank deflection of the shelf-edge jet due to the intrusion. In recent papers, Manning et al. and Garrison et al. have shown that this intrusion also produced an onbank shift in larval fish populations.

SWI95-2: This intrusion was observed at moorings SF and ST1 over the period of 5-10 July. This was a classic pycnocline intrusion. Observation at ST1 showed the highest salinities at 12 m depth and roughly centered at a sigma-t of 24.5. At SF, the intrusion's maximum salinities appeared somewhat deeper (near 20 m) and at a greater density (25).

SWI95-3: This intrusion was apparent in the SST field to the west of a warm- core ring. It was seen in the ST1 and SF time series from 9 August through the end of the time series (on 24 August). The mooring data show a complex and changing structure of the intrusion. It most often appeared as a subsurface, pycnocline intrusion with maximum salinities centered at roughly 24 sigma-t.

OBJECTIVES

• Describe intrusions of warm, salty water onto the southern flank - spatial/temporal evolution of intrusions, associated flows, influence on biology,..
• Determine if intrusions have any lasting biological (and physical) effects on the southern flank environment.

METHODS

• The subtidal flow in the region of the intrusion can be investigated using the numerous ship-board ADCP sections obtained in 1995. For example, the August intrusion was sampled by seven ADCP transect lines. Preliminary analysis using tidal prediction routines from Flagg's site have produced subtidal current fields which appear reasonable (almost all show a westward jet at the shelf-edge). Further analysis will be done to predict tides via the TRUXTON model applied to the southern flank region of interest only. Given the intensity of Southern Flank current meter and drifter data from 1995, this may produce highly accurate tides.
• The data from the three southern flank moorings (ST1, ST2 and SF) also give a detailed view of the structure and flows of the intruding water. Each intrusion was observed at all moorings allowing for an examination of the alongbank/onbank progression the intruding water, spatial/temporal scales of flow over the intrusions, etc.
• The mooring data also allow for the calculation of cross-bank temperature and salinity fluxes resulting from the intrusions. Preliminary calculations have given statistically significant onshore salt and heat fluxes associated with the May and August intrusions.
• CTD/MOCNESS sampling was done on the southern flank during a) Lough's April and May process cruises, b) the monthly survey cruises. The samples have already been used to examine how the May intrusion influenced larval fish distributions (Manning et al., and Garrison et al.). Durbin and co-workers plan to examine the survey samples for warm- water plankton species associated with the intrusions, and perhaps left in the wake of the intrusions.

References

Manning, J. P., R. G. Lough, J. H. Churchill, A slope water intrusion and shelfbreak jet and their effect on larval advection along the southern flank of Georges Bank, ICES Journal of Marine Science, accepted.

Garrison, L. P., W. Michaels, and W. J. Fogarty, Predation on larval gadids by pelagic fish in the Georges Bank ecosystem: I. Spatial overlap and predations risk associated with hydrographic features. Submitted to Canadian Journal of Fisheries and Aquatic Sciences.