Georges Bank Stratification Study

1992 Data Report

ALBATROSS IV 92-04 AND 92-05

27 April - 29 May 1992

December 8, 2004

J. Manning

T. Holzwarth-Davis

M. Taylor

T. Rotunno

D. Mountain

G. Lough

Funding provided by NOAA's Climate and Global Change Program under the Marine Ecosystem Response Program

Table of Contents

Acknowlegements	iii

List of Figures	iv

INTRODUCTION	1

SAMPLING SYSTEMS	1

ShipBoard	1

Mooring	2

Drifting	2

METHODS	3

Sampling Operations

3

Processing Operations	5

RESULTS	8

Physical Oceanography	8

Biology	9

DISCUSSION	11

Scotian Shelf Washover	11

May 25 Wind Event	11

Small Scale Fluorescence Structure	11

CONCLUSIONS	12

REFERENCES	13

Table 1. Brief Listing of Events	14

Table 2. Mooring statistics	15

Table 3. Listing of MOCNESS hauls by site.	16

Table 4. MOCNESS physical data/station information.	17

Table 5. Summary of samples taken for biochemistry/molecular biology	24

APPENDIX 1. Detailed Event Log	25

APPENDIX 2. Transect Log.	30

APPENDIX 3. Grid Log.	31

APPENDIX 4. Naming Conventions and archive access	32

APPENDIX 5. Personnel	33

Acknowlegements

We thank the personnel at the Atlantic Marine Center, Dennis Shields in particular, for the development and installation of the Scientific Computing System on board the ALBATROSS, Art Allen at USCG R&D center for lending us Loran_C Marker Buoys, Dr. Jim Irish for lending us holey sock drogues, Sean Kerry and Matt Gould for advice on mooring design, and, finally, the officers and crew of the RV/ALBATROSS IV for providing expert and friendly assistance on this first of many MER/GLOBEC experiments.

List of Figures Appended

Figure 1a. Station map of operations on AL9205

Figure 1b. A 3-d prospective of Figure 1a.

Figure 2. Drifter and mooring instrument configuration.

Figure 3. Time series of wind and detided current.

Figure 4. Time series of temperature as measured on mooring.

Figure 5. Time series of salinity as measured on mooring.

Figure 6. Evolution of water column structure and time series of wind.

Figure 7. Drifter track .

Figure 8. Trajectory of the drifter, VACM, and model simulation.

Figure 9 Model simulation (tidal residual) given a 15m release at site S.

Figure 10a. Station Positions on AL9204 according to operation.

Figure 10b. CTD positions on AL9204 with station numbers posted

Figure 11. Surface and bottom temperature measured on AL9204.

Figure 12. Surface and bottom salinity measured on AL9204.

Figure 13. Surface temperature anomaly and surface temperature anomaly normalized.

Figures 14-18. AL9204 cross sections

Figure 19. Station Positions on cruise AL9205.

Figure 20. Surface and bottom temperature measured on AL9205.

Figure 21. Surface temperature anomaly.and surface temperature anomaly normalized.

Figure 22. Surface and bottom salinity measured on AL9205.

Figures 23-39. Al9205 cross-sections.

Figure 40. Cross-sections at the drifter site.

Figure 41. Summary of the grid operations.

Figure 42. Grid paths in both geographic and Lagrangian.

Figure 43-44 Grid cross-sections

Figure 45. Satellite figures for May 6 and 21, 1992.

Figure 46. Length frequencies and #fish per haul.

Figure 47. Relative catch per tow on AL9205 Bongo survey.

Figure 48. MOCNESS length frequency distributions.

Figure 49. AL9205- egg distribution at the mixed site.

Figure 50. AL9205- cod distribution at the mixed site.

Figure 51. AL9205- haddock distribution at the mixed site.

Figure 52. AL9205- egg distribution at the stratified site.

Figure 53. AL9205- cod distribution at the stratified site.

Figure 54. AL9205- haddock distribution at the stratified site.

Figure 55. AL9205- egg distribution by stage at the site S.

Figure 56. AL9205- egg distribution at the drifter site.

Figure 57. AL9205- cod distribution at the drifter site.

Figure 58. AL9205- haddock distribution at the drifter site.

Figure 59. AL9205- egg distribution by stage at the drifter site.

Figure 60. AL9205- egg distribution at the Western site.

Figure 61. AL9205- cod distribution at the Western site.

Figure 62. AL9205- haddock distribution at the Western site.

Figure 63. AL9205- egg distribution at the Great South Channel.

Figure 64. AL9205- cod distribution at the Great South Channel.

Figure 65. AL9205- haddock distribution at the GSC site.

Figure 66. Scotian Shelf Water lens thickness contour.

Figure 67. SST as measured at NOAA buoy 44011 in '92 vs long term.

Figure 68. NOAA Buoy Air temperature and seasurface temperature.

Figure 69. Stick plot of the May 24th wind event.

INTRODUCTION

In late spring 1992, three cruises were conducted as part of the NOAA Climate and Global Change, Marine Ecosystem Response Program study entitled: Stratification variability on Georges Bank and its effect on larval fish survival. The study was conducted by researchers from the Northeast Fisheries Science Center (NMFS), the Woods Hole Oceanographic Institution and the Bigelow Laboratory for Ocean Sciences. The field sampling for the study was accomplished by coordinated sampling from two research vessels, ALBATROSS IV (2 legs) and R/V ENDEAVOR.

The objectives of these cruises were to test and intercalibrate a variety of sampling systems for determining the distribution and abundance of larval fish and their planktonic prey in relation to hydrographic conditions. An additional objective was to test and evaluate different sampling strategies that could be used in future field operations. Tissue samples were collected by NMFS scientists from Narragansett, RI to compare biochemical indices of larval growth and condition to the observed prey abundance and hydrographic conditions.

The purpose of this report is to document the data collected by the Woods Hole NMFS scientists on the ALBATROSS cruises AL9204II and AL9205 (Apr 27 - May 7 and May 18 - 29, respectively). It is intended for collaborating scientists as a first step in the process of merging datasets. The sampling systems are described and the data is summarized in the form of basic statistics (tables and graphs). The discussion section is limited to brief notes on the significant unplanned observations of a) the appearance of Scotian Shelf Water, b) a wind event, and c) small small structure of the fluorescence signal. A description of the archived data and the procedure to access that data are included in an appendix.

SAMPLING SYSTEMS

ShipBoard

The primary shipboard sampling systems used during this cruise to accomplish the above objectives were:

MOCNESS: Multiple Opening/Closing Net and Environmental Sensing Systems with 1 m2 (0.333-mm mesh nets) and 1/4 m2 (0.064-mm mesh nets) mouth openings and each equipped with 9 nets and conductivity/temperature/depth measuring packages (identified as MOC1 and MOC1/4, respectively). The MOCNESS systems were deployed on the port side using the boom.

Seabird Electronics Seacat Model 19 CTD (Profiler): a conduc-tivity, temperature, and depth measuring instrument with a sampling rate of 2 observations/second. During a bongo haul, the Profiler was attached above the bongo frame and towed double - obliquely through the water. When a bongo haul was not required, the Profiler was deployed vertically through the water column. The conductivity cell is "free - flushed."

MK5 CTD: a Conductivity/Temperature/Depth measuring system equipped with a fluorometer and rosette water sampler. The MK5 CTD was deployed from the starboard hydrographic A-frame for both vertical profiles while the vessel was stationary and for tow-
yo sampling while the vessel steamed at 2.5 knots. A total of 452 CTD profiles were made (counting down and up casts separately) on AL9205.

Near real time satellite: Satellite derived SST was sent to the ship via radio transmission at 300 baud.

Moored

A physical oceanographic mooring with instruments to measure the temperature, salinity and current in the upper 50 m of the water column was deployed to monitor the vertical structure in the water column during the sampling period.

VACM: Vector Averaging Current Meters were attached at 15m and 45m to record current velocity and temperature 16 times per hour.

RBR Temperature Loggers (TPODS): Single channel temperature loggers (model series XL-105) used in fixed mode of operation as part of the moored array. Temperature observations were recorded every 2 minutes of their deployment. Instruments were attached at 5, 25, and 35 meters.

Seabird Electronics Seacat Model 16: Internally recording temperature / conductivity instruments intended for fixed mooring operations. The conductivity cell is "free - flushed" (i.e. no mechanical pumping of water through the cell). The moored Seacats recorded temperature and conductivity observations every 2 minutes of their deployment. Instruments were attached at 1, 10, 20, 30, 40, and 50 meters.

Drifting

Loran-C Buoy Marker Buoy: This instrument, manufactured by Seimac Limited and loaned to us by Art Allen of USCG Research and Development Lab, received Loran radio signals at a user defined setting (we used 30 minutes) and transmitted the time delays via VHF radio to the ship.

The systems listed above and reported on within this report are those used by the NMFS scientist. The other systems deployed during the cruise by Woods Hole Oceanographic scientist are the Greene Bomber (a dual beam acoustic system towed behind the ship) and the BIOSPAR (Bioacoustic Sensing Platform and Relay, a dual-beam biological echo sounder and satlellite and radio commuincations system mounted on a spar buoy).

METHODS

Sampling Operations

In preparation for the subsequent cruise (May 18-29, 1992), the Fisheries Oceanography Investigation conducted four experiments while aboard the ALBATROSS IV from April 27 - May 8, 1992. The first three were instrument tests.

The General Oceanics "Mark5" CTD1, deployed for the first time at sea, worked as expected but cast were limited due to problems associated with the conductive cable and connection to the unit. The second instrument test, that of a SEIMAC Loran-C Marker Buoy, also had a few problems. The high-flyer/drogue that was attached to the instrument tended to drag the unit along causing the antennae to lean away from a vertical position. The Loran-C Canadian chains (#5930) the instrument was receiving were different and probably not as strong as the American chain (#9960) typically used by the ship. Finally, the radar signal from a reflector mounted on the high flyer was not strong enough to be distinguished from background sea clutter.

On three occassions MOCNESS hauls were conducted in order to test recent modifications of hardware and software as well as to provide training sessions for MOCNESS operators. Two hauls were done in the stratified region and one in the mixed region.

The final experiment of AL9204, an oceanographic survey of the temperature and salinity distribution, was successful. An anomalous stream of Scotian Shelf Water (cold 3 C & fresh 31.6 ppt) was observed and tracked along the entire southwestern flank of Georges Bank. A total of 31 Seabird CTD casts, including three cross-bank sections, were conducted.

During the first three days (19-21 May 1992) of the second cruise (AL9205) a survey was conducted to locate cod and haddock larvae on the southern flank of Georges Bank and to provide an initial indication of the hydrographic conditions in the region. A bongo-net (61-cm dia., 0.333-
mm & 0.505-mm nets) equipped with a Seabird CTD profiler was used on 35 stations (5-10 mile spacing) between the 50 and 100 m isobaths.

From the survey information a site was chosen for deployment of the physical oceanographic mooring, the BIOSPAR mooring, and the drifters (Figures 1 and 2). This site (80m bottom depth) was selected to be in the region of the bank which characteristically has a stratified water column. It is identified as the stratified site (S) . A second site (49m bottom depth) was selected in the characteristically well-mixed, shallow portion of the bank nearest to the site S. This site is referred to as the mixed site (M).

The physical oceanographic mooring deployed at site S on May 21 (40° 42.49' N, 67°

52.33 W) and the BIOSPAR mooring was then deployed nearby (40° 42.24 N, 67° 51.47' W), within 0.7 miles of each other. After deployment of the moorings, three drifters were deployed near the site S in an equilateral triangular pattern 2 miles on a side. The drifters consisted of a highflyer with radar reflector and light and a 6m long holey sock drogue tethered to 10m depth. One drifter also had a Loran-C buoy tethered to it (Figure 2a). The vessel had a VHF receiving unit to track the buoy's position. The three drifters formed a third site, the Drifting site (D) which was expected to drift southwest away from the site S during the course of the study.

At the three sites two different sampling schemes were conducted. The first was called a "site transect" which extended from 2 miles south to two miles north of the site (essentially across isobath). A MOC1 tow was made starting at the southern end and towed toward the site. After it was completed the vessel returned to the southern end of the transect and a CTD Tow-Yo was made along the 4 miles section at 2.5 knots with profiles every 5 minutes (approximately 0.2 mile spacing). The Greene Bomber was towed during both MOC1 and Tow-Yo. On some occasions a MOC1/4 tow was made at the completion of the Tow-Yo. Between May 21 to May 24, three site transects were completed at each of the three sites, including day - night comparisons at the sites S and M. Three of the site transects were conducted jointly with R/V ENDEAVOR for intercomparison of systems on the two vessels and for a more complete sampling of the water column by the full suite of available instrument systems.

The second sampling operation was the fine scale "grids". These are attempts to survey a square mile of ocean in a Lagrangian sense. In other words, our objective was to map the physical and biological variables relative to the moving water mass assuming a slab like advection over a 3-4 hours of the tidal cycle. The sampling was conducted on nominally 6 transects that were one mile long and 0.2 miles apart. In some cases, R/V ENDEAVOR simultaneously ran grid lines offset by 0.1 miles for the ALBATROSS IV grid so that the combined effort sampled the square mile of water with a transect spacing of 0.1 miles. The movement of the water during the sampling had to be taken into account in order to sample the intended parcel of water. The tidal currents are often greater than 50 cm sec-1 and, over the 4 hours required to conduct the sampling, would displace the parcel of water a distance three to four times greater than the size of the square. To compensate for movement during the sampling, a drifting buoy (with drogue at 15 meters) was used as a reference marker and all grid lines were positioned relative to the drifter at the time the lines were run. The Greene Bomber was deployed on all grid lines. A MOC1 tow was conducted on the first and last lines. A CTD Tow-Yo was conducted on the second through fifth lines with profiles every 3 minutes (for an approximate along-track spacing of 200m). Four grids were completed by ALBATROSS, three of which were conducted with Endeavor (see Appendix 3: Grid Log). The Endeavor conducted one grid alone (Grid #2).

In order to reference the position of samples relative to the moving parcel of water the following procedure, as suggested by Captain Dean Smehil, was used on Grid #'s 4 & 5. The proposed one mile grid pattern was drawn on the ALBATROSS IV radar screen with a grease pen. The ship was simply steered such that the signal from the drifter's reflector traced out the pattern on the screen.

The location of the three sites and a summary of the operations conducted at each site is shown in Figure 1.

Some "longer transects" of observations also were occupied. These included two Tow-Yo transects with the Greene Bomber between the site S and M, with CTD profiles every kilometer. An along isobath transect of CTD stations every 5 miles was occupied from 25 miles northeast to 20 miles southeast of the site S. Transects also were occupied near the western end of Georges Bank and across the eastern side of Great South Channel. These transects included sampling by MOC1, Greene Bomber and the MK5 CTD.

On four occasions the vessel's small boat was used to come alongside BIOSPAR in order to reprogram the instrument's operating system. On two occasions the Greene Bomber was deployed with the vessel drifting near BIOSPAR for an intercomparison between the two systems.

The physical oceanographic mooring and the BIOSPAR mooring were recovered on the morning of May 27. The Loran-C drifting buoy was recovered on the morning of May 28 (40 28.4N, 69 05.9W) . (The other two drifters were recovered on the morning of May 24, after they separated some distance from the Loran-C buoy and could not be easily tracked by themselves.)

A chronological listing of the operations conducted during this cruise, with time and position information, is provided in short form in Table 1 and in detail in Appendix 1. A transect log and grid log are included as Appendix 2 and 3, respectively.

Processing Operations

MOCNESS and most bongo samples have been sorted and identified for fish larvae, eggs, and zooplankton. Fish larvae were measured to the nearest tenth millimeter and all lengths were converted to live lengths using Bolz and Lough (1983) algorithm. All data includes lengths of larval fish specimens taken for biochemical analysis. Copepods and fish eggs from selected MOCNESS hauls have been stages according to life history traits. Depth distributions have been plotted using total numbers, however, means and standard deviations have been calculated for each haul. Weighted mean depth was calculated for fish eggs and larvae using the following formula:

wmd = product/ density

where product = midpoint of depth interval * density of specimens. When more than one depth profile was performed during a haul, each depth profile was considered be be either an up or down haul. Separate sets of analysis were performed for each type of haul (i.e. up or down). Day and night distributions have been calculated for selected MOCNESS hauls at stratified, drifter, and mixed sites. Density distributions of fish eggs and larvae have been calculated using MOCNESS volume data.

Depth distribution of MOCNESS temperature, salinity and sigma-t measurements have been calculated by using the haul start time from the MOCNESS data log and then subsequently adding to it the duration of the time each net was tripped (taken from the MOCNESS computer running time). Raw environmental data from the MOCNESS is missing for MOCNESS hauls 986 and 987.

The Seabird PROFILER (CTD) records were bin-averaged to 1m using Seabird "BINAVG" software. The salinity data was corrected using water samples collected by water bottles and analyzed on an AUTOSAL in the laboratory. Seabird PROFILER data was contoured at sea using Golden Software's SURFER routines in combination with our SURFDR.BAT routine on a 486 machine. The horizontal contour maps presented herein were generated back at the lab using SURFACE3 on the VAX. The vertical sections are SURFER outputs.

The General Oceanics MarkV CTD was deployed 246 times. The General Oceanics software "CTDPOST" was used to generate 1 meter bin averages. A correction of .005 PSU was applied to the CTD salinity data after calibration with Niskin bottle samples. In order to merge position, water depth, and other "header" information with the pressure, temperature, salinity, and fluorometry, several processing steps were developed. Analogous to the "SURFDR.BAT" system for processing SEABIRD data on the PC, we developed a MATLAB routine called "LOOKAT.M" to process/view data on the UNIX machine. This routine conducts the entire process (using several call functions) from merging General Oceanics ".PRS" files with ship position files ("NB2NODC.F") to generating contoured sections ("BARNES.M").

Contouring the Mark V CTD data was done by BARNES.M, a pseudo-objective mapping routine that iteratively grids unequally spaced data (Barnes, 1974). By changing the search radius with each iteration depending on the difference between observed and estimated values, the gridded field is improved. Estimates of error due to the gridding operation could be calculated and are reported along with the figures.

The Lagrangian coordinates for the grid paths were calculated differently for different grids depending on whether we a) were near the mooring, b) were near the drifter, and c) used the "grease pen" technique. Grids #1 and #2 were near the drifter. In these cases we processed the 30 minute position file from the LoranC drifter through two Fortran programs to linearly interpolated to one minute intervals ("interp.exe") and calculate distances (KMs) relative to the start of the grid ("dist.exe"). The "start of the grid" was set to be the time and place the first instrument went over the side of ALBATROSS. This "XYT" file along with that of the ship became input to another fortran routine "LAGRD.EXE" to obtain the back calculated Lagrangian positions. Lagrangian positions for Grid #3 (conducted with the Endeavor near the mooring) were calculated using observations of the VACM at 15m. By running the output of the Buoy Group program "BARRAY.com" through "LAGRIDCM" , the desired result was obtained. For Grids 4 and 5, the "grease pen" method was used. In the the grease pen cases we recorded the ships time and position at the beginning, middle, and end of each leg as well as the drifters range and bearing. This data was input to a routine called "NEWPOS.EXE" which calculated the drifter positions. After interpolation to one minute intervals, calculation of distances relative to the start, and execution of "LAGRD.EXE", the Lagrangian positions were obtained.

The initial processing of the VACM records was done by Fran Hotchkiss at USGS. This including the standard WHOI edited and checking routines (Tarbell et al., 1988). The output was stored in BUOY format on the VAX. The data were transferred to ascii format and post-processed using PC-MATLAB routines. Low-pass filtering was done using a 33-hr 3rd order Butterworth filter. The five moored Seabird SEACAT records and three Branker temperature probe records were hourly averaged. Despiking of the data was unnecessary.

The Loran-C buoy data was automatically stored on disk using a PROCOMM communication software at sea. This file was used to monitor the drifter track. Recorded time delays were simply entered into the Northstar Loran console in order to convert to latitude and longitude. The time delays were also stored continually (and with more reliability) within the instrument. Back at the lab, these values were first hand edited to remove bad points due to radio transmission noise and interference. The clean time delay file was then run through a set of three Fortran programs: 1) PREPLNAV.FOR reformats the data for the standard 2) LORNAV.FOR routine which converts the values to geographic coordinates (latitude and longitude) and 3) BLANK3.FOR converts lat and lon to decimal degrees. The 9960 Loran chains W & Y were used in the lat/lon conversion. The output of these routines were then run through a MATLAB plotting routine (PROVEC.M).

A data acquisition system called the Scientific Computing System (SCS) developed by engineers at Atlantic Marine Center (AMC) was in its first year of operation on the ALBATROSS IV. It provides the scientists with continuous records of position, ship speed/direction, wind speed/direction, air temperature, and several other variables. This dataset was processed back at the lab in a series of steps including 1) COMPRESS.FOR, 2) READ_COMPRESS.FOR (routines provided by AMC), and SUBSPOSN.FOR (our own). The position data was essential for the CTD Tow-yo operations when the operators record "time of the cast" without position (Lat/Lon). In order to merge the CTD Tow-yo with positions, a subprocess within the "LOOKAT.M" routine, a) creates a ".lis" file for each transect which includes cast number and time, b) accesses the SCS ship position file ("ap2b.dat"), and then c) merges the two.

Satellite SST records as transmitted from shore were run through a ADD_POSN.For routine that merged temperatures with geographic grid points and then contoured with SURFER at sea.

RESULTS

Physical Oceanography:

The physical oceanographic program consisted of 1) deploying a mooring to measure the water column structure during the course of the study, 2) deploying drifters to track for repeated sampling of the same water parcel, and 3) CTD profiles to measure the water column structure in connection with the other sampling programs on the cruise. Results are presented in that order.

1) Mooring

The physical oceanographic mooring is shown in Figure 2b. It contained 2 VACM current meters, 6 SEACAT conductivity/temperature recorders and 3 Branker temperature recorders. The deployment and recovery of the mooring were accomplished successfully except for the loss of one SEACAT recorder2. All the recovered instruments collected good data.

The hourly averaged time series of detided velocity from the two VACM records and the shipmounted anemometer are presented in Figure 3. Concurrent temperature and salinity records are presented in Figure 4 and Figure 5, respectively. The temporal evolution of the water column structure as measured by the mooring is contoured in Figure 6 including resultant wind speed in the top panel.

2) Loran-C Buoy

As depicted in Figure 7 and Figure 8, the quality of the Loran-C Buoy fixes was variable but sufficient for general tracking. The buoy drifted about 100 km to the WSW in 7 days ( 15 cms-1), essentially along the isobaths. This velocity is considerably faster than would be expected for mean conditions in this area during this time of year. Figure 8d represents the estimated track of a water parcel at 15m depth as represented by a 3-d circulation model (Lynch et al., 1992) including wind and residual tide (Figure 9).

3) CTD

The temperature, salinity and fluorescence data collected by the CTD systems showed considerable structure in both the along isobath and cross isobath directions. The SEABIRD station locations and contoured horizontal sections for both cruises AL9204 and AL9205 are presented in Figures 10-13 and 19-22, respectively, including surface and bottom variables. In the case of temperature, anomalies are relative to MARMAP observations (Mountain and Holzwarth, 1989) are included as well. The SEABIRD vertical sections appear in Figures 14-18 and 23-25, respectively. The AL9205 MarkV-CTD vertical sections (transects #5-18, see Transect Log Appendix 2) are included cronologically as Figure 26-39. Figure 40 display these same sections by site when more than two were conducted per site.

Grid study figures begin with a summary of cruise tracks in Figure 41 followed by detailed tracks of each grid in Figure 42. Contoured slices of Grids 1 and 5 are presented in Figures 43 and 44, respectively.

4) Satellite SST

The two images that were received via radio transmission and contoured at sea (May 6 and 21, 1992) are shown in Figure 45.

Biology

During the initial Bongo survey, very few month-old cod were collected in shoal waters on the Southeast Part; however, a broad area of haddock and cod larvae was located on the Southwest Part from the shoals to the 90 m isobath, centered near 68W longitude. The abundance of larvae was relatively low, less than 6 larvae per Bongo-net haul was typical (Figure 46). Larval haddock were about four times as abundant as cod. Most larvae were recently hatched, 4-5 mm SL. Both cod and haddock were a few weeks older, 5-8 mm, and more abundant in the shoal water < 60 m depth (Figure 47). The patch of larvae was located farther to the southwest (40-70 miles) than expected from previous years surveys conducted in the last half of May. Perhaps the cold band of water observed in April that moved onto the southern edge of Georges Bank displaced eggs and larvae southwest and more onto the shoals. The cold water ( <4 °C ) also may have retarded development and induced high mortality of the eggs and larvae.

Seven MOCNESS hauls were made at the drifter site (D), 8 at the stratified site (S), and 10 hauls at the mixed site (M) (Figure 48 and Table 3). Detailed MOCNESS information is given in Appendix 5. Few cod or haddock larvae were collected at the stratified-water sites; most larvae were collected at the mixed site in water < 50 m bottom depth (Figure 48). The MOCNESS vertical profiles indicated that cod and haddock larvae were distributed broadly through the water column, generally more abundant towards the bottom (Bar Charts Figure 49 - Figure 58). It is important to note that no bars are plotted for depths where there was no net. The figures must be interpreted accordingly. Haddock larvae were collected in greater numbers at depths deeper than 20 m in several hauls. Zooplankton abundance generally appeared to be highest in the upper 40 m of the water column. The copepod Calanus finmarchicus dominated the zooplankton hauls in stratified waters.

Along the transect occupied at the western end of the survey region (68° 20' W) five MOC1 hauls were made simultaneously with the Greene Bomber. Haddock and cod larvae (7-8 mm mode) were collected at the shallowest stations; their abundance and vertical distribution was similar to the previous three site study (Figure 60 - Figure 62). On the transect across the eastern side of the Great South Channel three MOC1 hauls were made from 50-80 m bottom depth. Older haddock and cod larvae (6-11 mm) were collected in all hauls (Figure 63 - Figure 65). The general distribution pattern of larvae observed during the cruise is consistent with the recirculation of some fraction of larvae on the eastern side of the Great South Channel.

Fish larvae were removed from the Bongo and MOC1 nets and preserved in alcohol or frozen for further analysis:

Larval otolith ageing 136 cod, 179 haddock

Biochemical analysis 152 cod, 184 haddock

Isotope analysis 6 cod, 15 haddock

Grazing experiment > 100 live amphipods

A total of 182 cod and 189 haddock larvae were collected with the 1M MOCNESS and frozen for biochemical studies. All but 2 cod and 7 haddock came from the shoal or transect sites. Larvae were sampled from a total of 11 MOC1 hauls representing both day and night tows. Larvae were sampled from both integrated and discrete depth nets. The majority of gadid larvae were frozen on petri dishes in the ships freezer. Other samples were frozen in liquid nitrogen. These samples will be analyzed for RNA and DNA content using an automated fluorescence procedure. We will attempt to sample otoliths from these larvae. Standard length will either be measured directly or estimated from DNA content.

Live amphipods were collected at night at the shoal site (MOC #997, nets 0, 5, 6, 7, and 8, and MOC #1000, 1001, 1004 all nets) for Ted Durbin at URI GSO. Samples of mixed plankton, consisting mostly (>90%) of Calanus, were frozen in liquid nitrogen for isolation of nucleic acids.

DISCUSSION

While most of our cruise went as planned, we were also fortunate to encounter some interesting phenomenon. A very brief description of these unplanned observations are presented in this discussion section. Detailed analysis is expected in forthcoming papers.

Scotian Shelf Washover

The temperature and salinity data on a number of transects indicate the presence of low temperature (<4 °C) and low salinity (<32.00 PSU) in small patches or layers in the water column. This is believed to be a remnant of a large influx of Scotian Shelf Water (SSW) onto eastern Georges Bank which was observed in satellite images from March through June 1992 (Figure 45) and confirmed by shipboard observations on cruise ALB 92-04 in early May. NOAA buoy 44011 SST sensor also recorded unusally cold water from late March through the end of May (Figure 67). The cause of this feature ,as reported by Rusham et. al., 1994 and Bisagni et al., (in prep.), may be the unusally large St. Lawrence River runoff in the spring of 1991. The thickness of the lens as defined by the 32 ppt isohaline varies in both the cross and along-isobath directions (Figure 66). The influx and continued presence of SSW may have important implications for the plankton communities in the bank, both by the unusually cold temperatures and by a westward displacement of the water on the southern flank of the bank.

May 25 Wind Event

A slight warming period over a few days from May 22 through mid-May 24 (Figure 68) resulted in a build up in stratification in the vicinity of the mooring site of approximately 4 degC temperature gradient in the top 20 meters of the water column (Figure 6). This was followed by a period of strong northeasterly winds on late May 24 (Figure 69) contributing to mixing of the upper water column (Figure 6) as well as unusually fast westward drift of the surface waters (Figure 8a). This observation supports the hypothesis that the onset of stratification on Georges Bank in late spring is not a steady seasonal process but rather an intermittant addition of the sun's heat interupted by occasional 2-3 day wind events. Examination of the NOAA Buoy 44011 wind record for the entire month of May 1992 reveals at least three other events occurred with magnitudes similar to that observed on May 24th and 25th. Superimposed on these wind-driven cycles are the semi-diurnal advection of both the tidal front and the shelf-slope front. The former advection is clearly evident in the 1992 mooring record as seen by the oscillating isopycnals in the bottom panel of Figure 6 and, as will be demonstated in the 1993 data report (Taylor, et al. in prep), the intrusion of slope water is possible in the lower portion of the southern flank water column.

Small Scale Fluorescence Structure

The structure of the fluorescence, assumed to be an indicator of chlorophyll-a abundance, showed a patchy distribution that in many instances was associated with similar structure in the temperature and salinity distributions. As depicted in the lower right panel of Figures 26-39, there is often a subsurface maximum, especially for the those cast in the stratified area (see, for example, Transect #14 - Figure 35), but there are horizontal gradients as well. Much of the future analysis on this data set will be estimating the lengths scales of these patches. This requires remapping these parameters in a Lagrangian reference frame as done in Figure 43. One such study already in progress (Wiebe et al., 1994) relates the acoustic properties of these patches to other physical and biological parameters.

CONCLUSIONS

While these cruises in the Spring of 1992 were meant to be "pilot studies" and instrument "tests", a large volume of data was collected to allow intercomparison of the net, towed-acoustic, CTD, and moored systems under a variety of conditions. The joint operations with R/V ENDEAVOR also should allow intercomparison with the video, acoustic and pumping systems on that vessel. The ability to determine the three dimensional distribution of the organisms in relation to hydrographic conditions on relatively short space scales is believed to be very important to the objectives of the stratification study. The observations made on these cruises potentially provide a significant contribution to our knowledge of the system. The ability to map a small parcel of water that is being advected by the strong tidal currents on Georges Bank is a enormous challenge but we have made great progress in that effort. The "grid" studies in particular provide for the first time an opportunity to conduct a interdiscinplary investigation sub-mesoscale dynamics on the southern flank of Georges Bank. It is hoped that this report which documents little more than the time, place, and distribution of samples may help in the intergration and synthesis of the GLOBEC field study.

REFERENCES

Barnes, S., 1974, A technique for maximizing details in numerical weather map analysis, Jour. of Applied Meteorology, Vol 3, p.396-409.

Bisagni, J., R. Beardsley, C. Ruhsam, J. Manning, W. Williams, Historical and recent evidence concerning the presence of Scotian Shelf Water on Southern Georges Bank , Deep Sea Research, submitted.

Bolz, G.R. and R.Lough, 1983, Growth of larval Atlantic cod, Gadus morphua, and haddock, Melanogrammus aeglefinus, on Georges Bank, Spring 1981. Fish. Bull. 81(4):827-836.

Lynch, D.R., F.E. Werner, D.A.Greenberg, and J. Loder, 1992, Diagnostic model for baroclinic, wind-driven and tidal circulation in shallow seas, Cont. Shlf. Res., 12(1). pp. 37-64.

Mountain, D.G. and T.J. Holzwarth. 1989. Surface and bottom temperature distributions for the northeast continental shelf. NOAA Tech Mem NMFS-F/NEC-73. 32pp.

Ruhsam, C., J. Bisagni, J. Manning, W. Williams, and R. Beardsley, 1994, Interannual Sea Surface Temperature Variability on the Southern Flank of Georges Bank: Spring 1992 and 1993, EOS 75(3), p.67.

Tarbell, S.A., A. Spencer, and E.T.Montgomery, 1988. The Buoy Group Data Processing System. WHOI Technical Memorandum WHOI-3-88, 207 pp.

Taylor, M. and J. Manning, Georges Bank Stratification Project: 1993 Data Report, NEFSC Lab. Reference Series, Woods Hole, Ma., (in prep).

Wiebe, P.H., D. Mountain, C. Greene, G.Lough, S.Kaarvedt, J.Dawson,LMartin, and N.Copley, Acoustical study of the spatial distribution of plankton on Georges Bank., Deep Sea Res., (in prep.).