Cross-Frontal Exchange and Scotian Shelf Cross-over Workshops
10-12 October, 2000
Holiday Inn, Falmouth, Massachusetts
Moored Current Meter Array
Physical and Biological Processes at the Tidally Mixed Front on Southern Georges Bank
Ron Schlitz (NMFS)
closely-spaced current array, centered at 60 m isobath across the southern
flank of Georges Bank, was established in March 1999 and recovered in August
1999. There were two settings; first
from ~20 March-20 June and second from ~20 June-1 September. The second setting was moved toward the west
about 8 nm due to opening of Closed Area II for scalloping.
The positions are in Figure 1(below).
All moorings in the array were recovered except tripod 4 from the second setting.
In addition, sampling to examine physical and biological processes in the frontal area was completed on each of three cruises. This included CTD, MOCNESS/VPR, and nutrients. On the March cruise (17 - 25 March) there were 23 MOC/VPR tows and 3 CTD sections with nutrients. On the June cruise (14 - 23 June) there were 19 MOC/VPR tows and 8 CTD sections with nutrients. Finally on the August cruise (25 August - 3 September) there were 8 MOC/VPR tows and 5 CTD sections with nutrients. MOC/VPR tows were primarily designed to provide a time series at the mean position of the front. CTD/nutrient sections were generally closely-spaced along the array.
The structure of currents along the array from March-June 1999 during the unstratified season is dominated by high variability. Alongshelf jets have time scales of days and the spatial scale is ~ 3 km horizontally. There are energetic events in the secondary circulation, i.e. in the across shelf plane, that appear related to the alongshelf structure and wind. Mean currents across the shelf for the first setting are shown in Figure 2. After stratification for the summer became permanent along the southern flank in June, the alongshelf cross-shelf currents showed more stability. An alongshelf jet was found near the northern end of the array, related to the tidally mixed front. The mean currents across the shelf for the second setting, which corresponds well at the start to permanent stratification, are shown in Figure 3.