Canadian Data Report Of Hydrography and Ocean Sciences

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Rapport statistique canadien sur ,

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Canadian Data Report of Hydrography and Ocean Sciences 143

STATE OF THE GULF OF ST. LAWRENCE: OCEANOGRAPHIC CONDITIONS IN 1994

D. ~ilbert ' , B. pettigrewl, D. swain2 and M. couture1

1 Division de la Productivité des Océans Ministère des Pêches et des Océans

Institut Maurice-Lamontagne C.P. 1000, Mont-Joli, Qukbec, G5H 32%

Department of Fisheries and Oceans Science Branch P.O. Box 5030

Moncton, N.B., E1C 9B6

O Minister of Supply and Services Canada 1996 Cat. No. Fs 97- 161143E ISSN 07 11-6721

Correct citation for t h publication:

Gilbert, D., B. Pettigrew, D. Swain and M. Couture. 1996. State of the Gulf of St. Lawrence: oceanographic conditions in 1994. Cm. Data Rep. Hydrogr. Ocean Sci 143: xi + 85pp.

111

TABLE OF CONTENTS

LIST OF TABLES ................................................................................................................ v

LIST OF FIGURES ............................................................................................................... vi

ABSTRACT~ÉSUMÉ ...........................................................................................................

1 . INTRODUCTION ............................................................................................................. 1

2 . AIR TEMPERATURE ...................................................................................................... 1

3 . SEA ICE ............................................................................................................................ 2

.................................................................... 4 . FRESHWATER DISCHARGE (RIVSUM) 2

5 . NORTHWEST GULF METEOROLOGICAL BUOY .................................................... 2

............................. 6 . LAYER-AVERAGED TEMPERATURE AND SALINITY FIELDS 3

...................................................................................................................... 6.1 Methods 3

6.2 O to 30 m layer ............................................................................................................ 4

........................................................................................................ 6.3 30 to 100 m layer 4

.................................. 6.4 100 to 200 m layer ; ................................................................... 4

...................................................................................................... 6.5 200 to 300 m layer 4

................................... 6.6 1985-1994 layer-averaged temperatures for the entire Gulf 5

................. 7 . SEPTEMBER BOTTOM TEMPERATURE IN THE SOUTHERN GULF 5

7.1 Methods ...................................................................................................................... 5

8 . COLD INTERMEDIATE LAYER (CIL) ....................................................................... 7

9 . AVERAGE TEMPERATURE OF THE 200-300 m LAYER AT CABOT ................................................................................................................................. STRAIT 7

TABLE OF CONTENTS (cont.)

10. SUMMARY ..................................................................................................................... 7

11. ACKNOWLEDGEMENTS ............................................................................................ 8

12. ABBREVIATIONS USED IN THE TEXT ..................................... .............................. 8

REFERENCES ...................................................................................................................... 9

APPENDIX A: LAYER-AVERAGED TEMPERATURES AND SALINITIES FOR THE GULF OF ST. LAWRENCE IN AUGUST-SEPTEMBER 1994, DIFFERENCES WITH 1993, AND ANOMALIES RELATIVE TO THE LONG-TERM MEANS OF PETRIE (1990) ....................................................................................................................... 44

APPENDIX B: LAYER-AVERAGED TEMPERATURES AND SALINITIES FOR THE GULF OF ST. LAWRENCE, CALCULATED FROM THE 1915-1987 CLIMATOLOGICAL ATLAS OF PETRIE (1990) ................................................................. 69

LIST OF TABLES

Table 1. August-September 1994 layer-averaged temperatures in eighteen subareas of the Gulf of St. Lawrence. .................................................................................................. 10

Table 2. August-September 1993 layer-averaged temperatures in eighteen subareas of the Gulf of St. Lawrence. ................................................................................................. 1 1

Table 3. August-September 1994 layer-averaged salinities in eighteen subareas of the Gulf of St. Lawrence. .................................................................................................. 12

Table 4. August-September 1993 layer-averaged salinities in eighteen subareas of the Gulf of St. Lawrence. ................................................................................................. 1 3

Table 5. Gulf-wide layer-averaged temperatures ( O C ) from 1985 to 1994, calculated from CTD and XBT data collected during the shrimp and groundfish stock assessment surveys in the southern and northern Gulf of St. Lawrence. ......................................... 14

LIST OF FIGURES

Figure 1. Map of the Gulfof St. Lawrence, with the 50 m and 200 m isobaths, showing Petrie's (1990) boxes, the coastal weather stations mentioned in the text, and the location of the meteorological buoy. ............................................................................ -15

Figure 2. Map of the Gulfof St. Lawrence showing the locations of the August-September 1994 CTD casts fiom the shrimp and groundfish survey, together with the 50 m and

......................................................................................................... 200 m isobaths.. .16

Figure 3. Monthly air temperature anomalies (OC) for (a) Mont-Joli, (b) sept-Îles, (c) Charlottetown and (d) Îles de la Madeleine, fiom September 1993 to December 1994. ......................................................................................................................... 17

Figure 4. Monthly air temperature anomalies (OC) for (a) Stephenville, (b) Daniel's Harbour, and (c) Cartwright (Labrador), fiom September 1993 to December 1994.. ...................... 18

Figure 5. Wmter air temperature anomalies at sept-Îles, calculated fiom the average of the ......................................................... December, January and February monthly means. .19

Figure 6. Spring air temperature anomalies at sept-Îles, calculated fiom the average of the March, April and May monthly means. ........................................................................ -20

Figure 7. Summer air temperature anomalies at sept-Îles, calculated fiom the average of the June, July and August monthly means.. ........................................................................ .2 1

Figure 8. FaU air temperature anomalies at sept-Îles, calculated fiom the average of the ..................................................... September, October and November monthly means. .22

Figure 9a. Location of the 1994 ice edge together with the 1962-1987 minimum, median and maximum ice edge positions (Côté, 1989) for December 3 1, 1993 and January 15,

........................................................................................................................ 1994. .23

Figure 9b. Location of the 1994 ice edge together with the 1962-1987 minimum, median and maximum ice edge positions (Côté, 1989) for February 0 1 and March 0 1, 1994.. ........... .24

Figure 9c. Location of the 1994 ice edge together with the 1962- 1987 minimum, median and maximum ice edge positions (Côté, 1989) for April 0 1 and May 0 1, 1994. ..................... .25

Figure 10. Monthly mean values of the RTVSUM index (solid he) , dehed as the sum of the discharges of the St. Lawrence River at Cornwall, the Ottawa River at Carillon, and the Saguenay River at the Isle Maligne dam, fiom October 1993 to November

....................................................................................................................... 1994.. .26

Figure 1 1. Yearly-averaged anomalies of the RIVSUM index, relative to the 196 1 - 1990 3 ............................................................................... clirnatological mean (1 074 1 m 1s). .27

LIST OF FIGURES (cont.)

Figure 12. Wmter anomalies of the RIVSUM index, relative to the 196 1 - 1990 climatological mean (9782 m3/s), calculated from the average of the December, January and

........................................................................................... February river discharges. .28

Figure 13. Spring anomalies of the RIVSUM index, relative to the 196 1 - 1990 climatological mean (1 1894 m3/s), calculated from the average of the March, April and May river

................................................................................................................ discharges. .29

Figure 14. S u m e r anomalies of the RIVSUM index, relative to the 196 1 - 1990 climatological mean (10918 m3/s), calculated from the average of the June, July and August river

................................................................................................................ discharges. .3 O

Figure 15. Fall anomalies of the RIVSUM index, relative to the 196 1 - 1990 climatological mean (1 0372 m3/s), calculated from the average of the September, October and

........................................................................................ November river discharges. 3 1

Figure 16. Monthly mean air temperature (solid line), and surface water temperature (dotted line) at the AES meteorological buoy (see Fig. 1 for location), from 1991 to 1994. ......... .32

Figure 17. Monthly mean air temperature (solid line), and surface water temperature (dotted line and black circles) at the AES meteorological buoy in the northwest Gulf, from

........................................................................................... Aprd to November 1994.. .3 3

Figure 18. Surface water temperature (OC) from the sept-Îles coastal thermograph, during the summer of 1993 (upper panel), and during the surnrner of 1 994 (middle panel). .............. .3 4

Figure 19. Temperature anomalies averaged over the whole Gulfof St. Lawrence for the 0- 30m, 30-100 m, 100-200 m, and 200-300 m layers relative to the long-term means of Petrie (1990), usiig XBT and CTD data Eom the late surnrner groundfish

..................................................... surveys on the Lady Harnrnond and M e d Needler. . 3 5

Figure 20. Variogram for bottom temperature in the southern Gulfof St. Lawrence, for ........................................................................................................ September 1 994. .3 6

Figure 21. Bottom temperature in the southern Gulfof St. Lawrence, for September 1994. ............. .37

Figure 22. Area of the southern Gulfof St. Lawrence (excluding strata 415,425 and 439) with .......................................... bottom temperature below 0°C or 1 OC, Eom 1971 to 1994. .3 8

Figure 23. Mid-summer composite index of CIL core temperature anomaly for the Gulfof St. ............................................................. Lawrence (Eom Gilbert and Pettigrew, 1996). .3 9

Figure 24. Thickness (in meters) of the cold intermediate layer (CIL), defïned here as the layer with waters colder than O°C, during the August-September 1994 shrimp and

..................................................................................................... groundfish survey.. .40

LIST OF FIGURES (cont.)

Figure 25. DBerence between the thickness of the 1994 and 1993 cold intermediate layer (CIL), defined here as the layer with waters colder than O°C, as measured during the August-September shrimp and groundfish surveys.. ....................................................... 41

Figure 26. Depths of the upper and lower 0°C isotherms of the cold intermediate layer (CIL), fiomday117(April27)today314 (November 10)of1994 .......................................... 42

Figure 27. Average temperature of the 200-300 m layer at the standard Cabot Strait section.. .......... .43

Figure A - 1. Average temperature (OC) of the 0-30 m layer, as measured during the August- September 1994 shrimp and groundfish survey.. ........................................................... .45

Figure A-2. DBerence in the temperature of the 0-30 m layer between 1994 and 1993 (August-September 1994 minus 1993). ....................................................................... .46

Figure A - 3. Temperature anomalies in the 0-30 m layer relative to Petrie's (1 990) long-term means, as measured during the August-September 1994 shrimp and groundfish survey. ...................................................................................................................... .47

Figure A - 4. Average salinity of the 0-30 m layer, as measured during the August-September 1994 shrimp and groundfish survey. ............................................................................ .48

Figure A-5. Difference in the salinity of the 0-3 0 m layer between 1994 and 1993 (August- ..................................................................................... September 1994 minus 1993). .49

Figure A - 6. Salinity anomalies in the 0-30 m layer relative to Petrie's (1990) long-term means, as measured during the August-September 1994 shrimp and groundfish survey. .............. 50

Figure A - 7. Average temperature ("C) of the 30-100 m layer, as measured during the August- September 1994 shrimp and groundfish survey. ............................................................ .5 1

Figure A - 8. Difference in the temperature of the 3 0- 100 m layer between 1994 and 1 993 (August-September 1994 minus 1993). ....................................................................... .52

Figure A - 9. Temperature anomalies in the 30-100 m layer relative to Petrie's (1990) long-term means, as measured during the August-September 1994 shrimp and groundfish survey. ...................................................................................................................... .5 3

Figure A - 10. Average salinity of the 3 0- 100 m layer, as measured during the August- ........................................................... September 1994 shrimp and groundfish survey.. .54

Figure A - 1 1. DEerence in the salinity of the 30- 100 m layer between 1994 and 1993 (August- ..................................................................................... September 1994 minus 1993). .55

LIST OF FIGURES (cont.)

Figure A - 12. Salinity anomalies in the 30- 100 m layer relative to Petrie's (1 990) long-term means, as measured during the August-September 1994 shrimp and groundfish survey. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , , . . . . . . . . , . . . . . . . . . . . . . . . . . . . . . . . . . . .5 6

Figure A-1 3. Average temperature (OC) of the 100-200 m layer, in August-September 1994. . . . . . . . . . . .5 7

Figure A - 14. DEerence in the temperature of the 100-200 m layer between 1994 and 1993 (August-September 1994 minus 1993). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . i. . . . . , . . . .5 8

Figure A - 15. Temperature anomalies in the 100-200 m layer relative to Petrie's (1 990) long- term means, in August-September 1994.. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .59

Figure A-1 6. Average salinity of the 100-200 m layer, in August-September 1994. . . . . . . . . . . . . . . . . . . . . . . . . . .60

Figure A-17. Difference in the salinity of the 100-200 m layer between 1994 and 1993 (August-September 1994 minus 1 993). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . . , . . . . , . . , . . . . . . . .6 1

Figure A-18. Salinity anomalies in the 100-200 m layer relative to Peîrie's (1990) long-term means, in August-September 1994. ................... ..................... ... ....... ....... .... .... . ......, . . ... 62

Figure A - 19. Average temperature (OC) of the 200-300 m layer, in August-September 1994. . . . . . . . . . . .63

Figure A - 20. DEerence in the temperature of the 200-300 m layer between 1994 and 1993 (August-September 1994 minus 1993). ...... ..... .... ...... ......... ..... . .. ... . ... .. . .... . .. . . . .. ..... .. . . . ..64

Figure A O 21. Temperature anomalies in the 200-300 m layer relative to Petrie's (1990) long- term means, in August-September 1994. .: . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . .65

Figure A - 22. Average saIinity of the 200-300 m Iayer, in August-September 1994.. . . . . . . . . . . . . . . . . . . . . . . . . .66

Figure A-23. DEerence in the salinity of the 200-300 m layer between 1994 and 1993 (August-September 1994 minus 1993). .... . .. ... ...... . ........ . . . ...... . .. .. . .... . .. .... . ... .. .. . .. . . . .. , . .. .67

Figure A - 24. Salinity anomalies in the 200-300 m layer relative to Petrie's (1990) long-term means, in August-September 1994. .. ..... .. ... . ..... ... . .. ... . . . . . . ... . . .... . . ... . .. ...... . .... .... . . .. . . .... . ..68

Figure B-1. August average temperature (OC) of the O to 30 m layer, calculated from the climatological atlas of Petne (1 990). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . .70

Figure B 2 . September average temperature (OC) of the O to 30 m layer, calculated from the climatological atlas of Petrie (1 990). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . .7 1

Figure B - 3. October average temperature (OC) of the O to 30 m layer, calculated from the climatological atlas of Petrie (1 990). . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . , . . . . . . . . . . . . . .72

LIST OF FIGURES (cont.)

Figure B 4 . August average temperature (OC) of the 30 to 100 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1990). .73

Figure B-5. September average temperature (OC) of the 30 to 100 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1990). .74

Figure B 6 . October average temperature (OC) of the 30 to 100 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1990). .75

Figure B-7. Yearly-averaged temperature (OC) of the 100 to 200 m layer, calculated fiom the climatological atlas of Petrie (1990). ............................................................................. 76

Figure B 8 . Yearly-averaged temperature (OC) of the 200 to 300 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1990). .77

Figure B 9 . August average salinity of the O to 30 m layer, calculated fiom the climatological ................................................................................................. atlas of Petrie (1 990). .78

Figure B-10. September average salinity of the O to 30 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1990). .79

Figure B-11. October average salinity of the O to 30 m layer, calculated fiom the climatological atlas of Petrie (1990). ................................................................................................. -80

Figure B-12. August average salinity of the 30 to 100 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1 990). .8 1

Figure B - 13. September average salinity of the 30 to 100 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1990). .82

Figure B - 14. October average salinity of the 30 to 100 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1 990). .83

Figure B - 15. Yearly-averaged salinity of the 100 to 200 m layer, calculated fiom the ............................................................................ climatological atlas of Petrie (1 990). .84

Figure B - 16. Yearly-averaged salinity of the 200 to 300 m layer, calculated fiom the ............................................................................ clirnatological atlas of Petrie (1990). .85

ABSTRACT

Gilbert, D., B. Pettigrew, D. Swain and M. Couture. 1996. State of the Gulfof St. Lawrence: oceanographic conditions in 1994. Cm. Data Rep. Hydrogr. ûcean Sci 143: xi + 85pp.

We present an overview of the physical oceanographic conditions in the Gulf of St. Lawrence for 1994, with special emphasis on the temperature and salinity profiles collected during the August- September 1994 shrirnp and groundfish survey. The main highlights for 1994 are that 1) winter air temperatures were below the 1961-1990 normal for the sixth consecutive year, 2) the ice cover was above the 1962-1987 median areal extent, 3) the cold intermediate layer was colder than normal for the ninth consecutive year, 4) intense upwelling occurred dong Québec's north shore during the month of August, as evidenced by the very cold surface temperatures, and 5) the deep layers (100-200 m and 200-300 m) warmed everywhere in the Gulf, except in Cabot Strait where the temperatures dropped by about 0.5OC.

Gilbert, D., B. Pettigrew, D. Swain and M. Couture. 1996. State of the Gulf of St. Lawrence: oceanographic conditions in 1994. Can. Data Rep. Hydrogr. ûcean Sci 143: xi + 85pp.

Nous présentons un survol des observations d'océanographie physique dans le golfe du Saint-Laurent pour lande 1994, en mettant l'emphase sur les observations de température et salinité recueillies en août et septembre lors de la mission d'évaluation des stocks de crevette et poissons de fond. Les faits saillants sont que 1) pour une 6"" année consééutive, les températures de l'air en hiver ont été inférieures aux normales 1961-1990; 2) la superficie du couvert de glace a étt? supérieure à la normale 1962-1987; 3) la couche intermédiaire froide a été plus goide que la normale pour une 9"" année consécutive; 4) des remontées d'eau intenses sont survenues le long de la côte nord du Québec au cours du mois d'août, tel que rt?vt?lé par des températures de surface très froides 5) les couches profondes (100 à 200 m et 200 à 300 m) se sont réchauffées partout dans le golfe par rapport à 1993, sauf dans le détroit de Cabot où elles se sont refroidies d'environ 0S0C.

1. INTRODUCTION

This report provides an oveniiew of the physical oceanographic conditions in the Gulf of St. Lawrence for 1994, based mostly on the August-September CTD (Conductivity-Temperature-Depth) data fi-om the Needler shrimp and groundfish survey (Figures 1 and 2). The CTD data fi-om the 1991 to 1993 surveys are described by Gratton et al. (1994), who produced the k s t of the present series of annual reports at IML (Institut Maurice-Lamontagne). Many changes have b e n made in this report compared with last year's report. For instance, we removed al1 the large scale meteorological information fiom Climatic Perspectives and other sources. The interested reader is referred to Drinkwater et al. (1995) for a description of the large scale meteorological and sea ice conditions off eastern Canada in 1994.

We more than compensated for the removal of large scale meteorological information by adding new types of oceanographic information to the 1994 report that were not in the 1993 report (Gratton et al. 1994). For example, as a complement to the information contained in the layer-averaged temperature maps, we have presented the corresponding layer-averaged salinity maps. We included thermistor chah data from the meteorological buoy mooring, in the northwest Gulf, as well as surface water temperature data fi-om the sept-Îles coastal thermograph. Several long interannual time series were also added, such as the average temperature of the 200-300 m layer at Cabot Strait, the annual and seasonal mean RIVSUM index, seasonal air temperature anomalies at sept-Îles, a composite index of CIL core temperature for the whole Gulf, and the bottom area with temperatures less than 0°C or 1°C in the southern Gulf. For reference in this and future annual reports on the physical oceanographic conditions of the Gulf of St. Lawrence, we also included maps of the climatological, layer-averaged fields of temperature and salinity, calculated fiom the discrete depth data of Petrie (1990). Other changes pertaining to the methods of data analysis are described in the text itself.

2. AIR TEMPERATURE

Monthly mean air temperatures Fom various weather stations around the Gulf of St. Lawrence were obtained fi-om Environment Canada. In t h section, we will describe the monthly anomalies relative to the 1961-1990 mean temperatures. The monthly anomalies for Mont-Joli, sept-Îles, Îles de la Madeleine (Quebec), and Charlottetown (P.E.I.) are shown on Figure 3, and the anomalies for Stephenville, Daniel's Harbour (Nfld), and Cartwright (Labrador) are shown on Figure 4. In the western Gulf (Mont-Joli, Sept-Îles, and Charlottetown), the strongest negative anomalies (up to -6°C) occurred in January 1994 (Figure 3) whereas in the eastern Gulf (Stephenville and Daniel's Harbour) the strongest negative anomalies (-55°C) occurred in February 1994 (Figure 4). Interannual time series of seasonally averaged air temperature at sept-Îles are shown on Figures 5 to 8. The most striking feature is that the last six consecutive winters have all been well below normal (Figure 5). For the other three seasons, the air temperature at sept-Îles was 1.2"C colder than normal in the sp&g (Figure 6), close to normal in the summer (Figure 7), and 1.5"C warmer than normal in the fall of 1994 (Figure 8).

3. SEA ICE

Ice Central of Environment Canada in Ottawa produces w W y charts that provide information on the location and concentration of sea ice in the Gulf of St. Lawrence. These charts are based on plane surveys and ship-based observations, and may be compared with the minimum, median and maximum ice edge positions for the 1962 to 1987 period (Côtk, 1989). A study of the interannual variability of sea ice cover in the Gulf of St. Lawrence from 1963 to 1990 can also be found in Déry (1992). Figure 9 shows that on December 3 1, 1993 and January 15, 1994 the ice edge was between the 1962-1987 median and maximum ice edge positions. On February 01, 1994, the ice edge was close to the maximum ice edge position, and even exceeded it dong Nova Scotia's eastern shore. On March 01, 1994, the ice edge was again very close to the maximum ice edge position. Finally, during the period of ice retreat (April01 and May 01, 1994), the ice edge was again located between the median and maximum ice edge positions. Overall then, we may say that the 1994 winter was characterized by heavier than average ice conditions, consistent with the colder than average winter air temperatures that prevailed over the Gulf (Figures 3 and 4).

4. FRESHWATER DISCHARGE (RIVSUM)

The October 1993 to November 1994 monthly averaged RIVSUM index is presented on Figure 10, where RIVSUM is de&ed as the sum of the Teshwater discharges of the St. Lawrence River at Cornwall, the Ottawa River at Carillon, and the Saguenay River at the Isle Maligne dam. The 1961- 1990 climatological monthly means are also indicated. We see that the peak freshwater discharge in 1994 was spread over a relatively long three month period (May to July), that the largest deviations Tom the normal occuned in October 1993 and July,1994, and that they were positive. An interannual tirne series of the yearly-averaged RIVSUM index dating back to 1914 is shown on Figure 11, and similar tirne series for winter, spring, surnrner and fall are shown on Figures 12 to 15. Overall, RIVSUM was slightly above normal in 1994 (Figure 11).

5. NORTHWEST GULF METEOROLOGICAL BUOY

A meteorological buoy has been moored in the northwest Gulf of St. Lawrence (see Figure 1) by the Atmospheric Environment Service of Canada, in collaboration with the Department of Fisheries and Oceans and the Canadian Coast Guard. This buoy has been operational for the last four navigation seasons (1991 to 1994). The monthly averaged air and water temperatures for the last four years are presented in Figure 16, and a blowup of the 1994 observations is shown on Figure 17. A cornparison with Petrie's (1990) long-term mean surface water temperatures for this part of the Gulf is also provided in Figure 17. We see that the 1994 surface water temperatures Tom May to July were slightly above normal, but the situation drastically changed in August, when the 1994 temperatures becarne 2S°C colder than normal. We attnbute this rapid decline in surface water temperature fiom

July to August to coastal upwelling dong Québec's north shore. This interpretation is mostly based on satellite pictures of sea surface temperature for the Gulf of St. Lawrence (Pierre Larouche, pers. cornm.). Coastal temperature data recorded at sept-Îles, as part of the Long Term Temperature Monitoring Program (LITMP) for the Gulf of St. Lawrence, are also consistent with our coastal upwelling interpretation of the August 1994 negative temperature anomaly. Figure 18 shows that during mid-August and early September of 1994, the surface (3 m) water temperature at sept-Îles was more than 5OC colder than during the sarne period of 1993.

6. LAYER-AVERAGED TEMPERATURE AND SALINITY FIELDS

6.1 Methods

The CTD data were collected in two parts: between August 15 and September 07 during the northern Gulf shrimp and groundfish survey, and between September 10 and 28 during the southern Gulf groundfish survey. The temperature and salinity data were quality-controlled and put in a standardized format (that of the AFAP database). They were then sorted into the same subregions of the Gulf as in Petrie (1990). There were seventeen ori@ Petrie boxes, and Gratton et al. (1994) added an eighteenth one to cover the Baie des Chaleurs are& Those eighteen boxes are shown on Figure 1, while the locations of thè 1994 profiles within the boxes are shown on Figure 2. For each depth layer (0-30 m, 30-100 m, 100-200 m, 200-300 m) and each Petrie box, a mean value and standard deviation of temperature and salinity was calculated. Note that we only considered the profiles that crossed at least 80% of a given layer thickness in computing these statistics. The mean temperatures and salinities, together with the standard deviations and the number of profiles fi-om which they were computed, are given in Tables 1 to 4 and plotted in appendix A.

To put our layer-averaged results in a historical perspective, we calculated deviations fi-om the long- term averages of Petrie (1990), which we shall refer to as anomalies. Petrie's long-term monthly mean temperature and salinity values, based on historical data collected between 1915 and 1987, are given at standard depths (0, 10, 20, 30, 50, 75, 100, 125, 150, 175, 200, 225, 250, 275, 300 and 400 meters). We calculated layer averages from those discrete depth data, and plotted them in Appendix B. For the 0-30 m and 30-100 m layers, the annual cycle of temperature and salinity was taken into consideration in the calculation of the anomalies, by interpolating the monthly averaged values of Petrie (1990) to the mean date of the 1994 measurements for a given box and depth layer. For the 100-200 m and 200- 300 m layers, the anomalies were calculated relative to Petrie's yearly-averaged values as the annual cycle of temperature and salinity is negligible at those depths (Petrie, 1990). This method of calculating anomalies differs ftom Gratton et al. (1994), who used a comparison with Petrie's (1990) September monthly means to compute anomalies in ali four layers.

It is important to note that the contours shown on the figures of Appendices A and B as well as on Figures 24 and 25 were simply drawn from the Petrie box averages. Those contours are not meant to be an optimal representation of the spatial distribution of temperature or salinity that could have been drawn if we had used data fi-om all the individual profiles. Therefore, in examining these figures, the

Due to equipment problerns, CTD profiles taken September 10-12 Pequently did not closely (within 5 m) approach the bottom. Because the geographic clustering of these missing values could bias 1994 results compared to those of earlier years, we estimated near-bottom temperatures at these sites using data fkom neighbouring sites. An estimate was made if the target and neighbouring sites had similar temperature profiles at shallower depths. This procedure was assessed using trials with the 1993 data with bottom temperatures deleted in geographic and bathymetric patterns sirnilar to those of the 1994 missing values (Swain, 1995). Estimates of the area of cold bottom temperature were closer to the 'true' value (ie., the value obtained using all the data) if the deleted values were predicted Pom neighbouring sites (0.2-1.4% error) than if they were omitted (4.8-7.6% error). Analyses reported here for 1994 used 136 measured and 16 estimated values.

We mapped spatial variation in bottom temperature using ordinary point kriging. Variograms were fitted using GS'. We checked for anisotropy parallel versus perpendicular to the Laurentian ChanneL We found no evidence of anisotropy between the& two directions and fitted an omnidirectional variogram using a spherical mode1 (Figure 20). We estimated bottom temperature on a 41 x 41 grid using the MATLAB program COKRI (Marcotte 1991). Interpolations used the five nearest neighbours. Contours were drawn using SURFER.

To compare the 1994 results to those for 1971-1993, we performed a second analysis omitting stations at depths over 155 m. This was done to avoid bias relative to results for 1984-1988 (when no data were available for these greater depths; see Swain 1993 for details). This analysis used 125 measured and 13 estimated values for 1994. The 41 x 41 grid of interpolated values was smoothed to a 201 x 201 grid using the spline smooth function of SURFER. We used SURFER to estimate Pom these smoothed grids the area within the survey region with bottom temperatures below O°C and 1°C. The survey region used in this analysis omitted strata 415, 425, and 439 (where all stations are deeper than 155 m).

7.2 Results

Bottom temperature in September 1994 was lowest in the central region of the Magdalen Shallows and increased shoreward and with depth dong the Laurentian Channel (Figure 21). Estimated bottom temperature was less than 1 OC over 39% of the survey area (strata 415-439) and less than O°C over 20% of the area. Time series plots of the area within the survey region (excluding strata 415,425, and 439) with estimated bottom temperatures below O°C and 1°C are shown in Figure 22. Subzero bottom temperatures extended over a relatively large area of the southern Gulfin 1994, continiling the period of cold bottom conditions that began in 1990. Conclusions were the same omitting the 13 estimated values. The estimated area of subzero bottom conditions was 15% higher than that shown in Figure 22 if these values were omitted, again leading to the conclusion that 1994, like 1990-1993, was a year of relatively cold bottom conditions in the southern Gulf.

8. COLD INTERMEDIATE LAYER (CIL)

As irnplied by the word "intermediate", the cold intermediate layer (CIL) is a layer of cold water sandwiched by warmer water both above and below it. Although Gilbert and Pettigrew (1996) defined the CIL as the layer with T < 3OC waters, we will define it here as the layer of water with temperatures l e s than O°C, as in Gratton et al. (1994). We can use this definition because the last five years, fiom 1990 to 1994, have been exceptionally cold (Figure 23). The map of CIL thickness for August- September 1994 is presented on Figure 24. We see that the maximum thickness is found in the northeast Gulf, as in 1991 to 1993 (Gratton et al., 1994), while the srnallest thicknesses are found in the Cabot Strait region and in the Estuary (Figure 24). The largest decrease in CIL thickness relative to 1993 occurred in Cabot Strait (Figure 25). To illustrate the fact that the CIL thickness, as most other oceanographic variables, is extremely variable, we also show temperature data Tom the thermistor chain of a mooring near the meteorological buoy in the Northwest Gulf (Figure 26). Figure 26 shows that the upper and lower depth limits of the CIL can undergo very large changes (up to about 30 m) on relatively short time scales ( les than a week). There are even short periods of time when the CIL (T c 0°C) completely vanishes but reappears later, due to the passage of water masses with different temperature profiles at the mooring site.

9. AVERAGE TEMPERATURE OF THE 200-300 m LAYER AT CABOT STRAIT

We now show what has become a classical time series for the deep waters of the Laurentian Channel, at the entrance of the Gulf of St. Lawrence. An update of Bugden's (1991) average temperature of the 200 to 300 m layer at the standard Cabot Strait section (Figure 27) shows that extremely low temperatures occurred in the mid-sixties, followed by relatively warm conditions right until about 1988. Rapid cooling then occurred until 199 1, followed by very warm conditions in 1993. The most recent value Tom the November 1994 Cabot Strait section, collected during the ice forecast cm&, was 0.5OC colder than in November 1993.

10. SUMMARY

In 1994, winter air temmratures were well below normal for a sixth consecutive year over the enthe Gulf of St. Lawrence, causing a larger than usual areal extent of the ice cover. For the other seasons, air temperature at sept-Îles was 1.2OC colder than normal in the spring, close to normal in the surnmer, and 1.5OC above normal in the fa11 of 1994. The cold intermediate layer (CO,), a relic of winter cooling, was &O colder than normal in the sumrner of 1994. Its core temperature has been below normal for the 1st nine years, with 1990 to 1994 being the coldest years. Since bottom depths coincide with the depth range of the CIL over much of the southern Gulf of St. Lawrence, subzero bottom temweratures extended over a larger than normal area of the southern Gulf in 1994, continuing the period of cold bottom conditions that began in 1990. In the O to 30 m laver, the August 1994 temperatures were colder than in 1993, particularly dong Qukbec's north shore due to intense coastal

Table 1. August-September 1994 layer-averaged temperatures in eighteen subareas of the Gulf of St. Lawrence. For each layer, we give the mean plus or minus one standard deviation; the number of profiles from which those statistics were calculated is written in parentheses. The coordinates of the first seventeen subareas (or boxes) are the same as in Petrie (1990), and the eighteenth box is the Baie des Chaleurs.

Box # 1994 TEMPERA- ( O C )

Table 2. August-September 1993 layer-averaged temperatures in eighteen subareas of the Gulf of St. Lawrence. For each layer, we give the mean plus or minus one standard deviation; the number of profiles from which those statistics were calculated is written in parentheses. The coordinates of the fîrst seventeen subareas (or boxes) are the same as in Petrie (1990), and the eighteenth box is the Baie des Chaleurs.

Box # 1993 TEMPEIIATURE (OC)

Table 3. August-September 1994 layer-averaged salinities in eighteen subareas of the Gulf of St, Lawrence. For each layer, we give the mean plus or minus one standard deviation; the number of profiles from which those statistics were calculated is written in parentheses. The coordinates of the first seventeen subareas (or boxes) are the same as in Petrie (1990), and the eighteenth box is the Baie des Chaleurs.

Box # 1994 S A L m

Table 4. August-September 1993 layer-averaged salinities in eighteen subareas of the Gulf of St. Lawrence. For each layer, we give the mean plus or minus one standard deviation; the number of profiles from which those statistics were calculated is written in parentheses. The coordinates of the fust seventeen subareas (or boxes) are the same as in Petrie (1990), and the eighteenth box is the Baie des Chaleurs.

Table 5. Gulf-wide layer-averaged temperatures (OC) from 1985 to 1994, calculated from CTD and XBT data collected during the shrimp and groundfish stock assessment surveys in the southern and northem Gulf of St. Lawrence. The anomalies relative to the long-tenn mean temperatures of Petrie (1990) are given in parentheses.

Layer 1 0-30 m 30- 100 m 100-200 m 200-300

a) computed from the monthly averages of Petrie boxes 1 to 17. b) computed from the mmthly averages of boxes 1 to 10,l l and 16. c) computed from the yearly averages of Petrie boxes 1 to 10 d) computed from the yearly averages of boxes 1,2,3,6,7,8,9,10. e) averaged from boxes 1,6,8,9,10. f) averaged from boxes 1,4,5,6,8,10.

Mean Temperature ffom Petrie (1990)

10.54" Aug. 1.31b Aug. 10.33" Sep. 1.63~ Sep. 2.50" 4. 8od 10.44" A-S 1.47~ A-S

Figure 1. Map of the Gulf of St. Lawrence, with the 50 m and 200 m isobaths, showing Petrie's (1990) boxes, the coastal weather stations mentioned in the text, and the location of the meteorological buoy.

Figure 2. Map of the Gulf of St. Lawrence showing the locations of the August-September 1994 CTD casts from the shrimp and groundfish survey, together with the 50 m and 200 m isobaths.

8 a a a a a 4 B d S f 9 t l r d

4.00:

-4.00 - -6.00 i u Sept-Ues ~ 1 1 1 1 1 1 , , 1 1 1 1 1 , 1 1 ,

Figure 3. Monthly air teniperature anomalies (OC) for (a) Mont-Joli, @) sept-Îles, (c) Charlottetom and (d) Îles de la Madeleine, from Septeinber 1993 to December 1994. The anomalies are relative to the 1 % 1 - 1990 climatologieai means.

Figure 4. Monthly air temperature anomalies (OC) for (a) Stephenville, (b) Daniel's Harbour, and (c) Cartwright (Labrador), f?om Septernber 1993 to December 1994. The anomalies are relative to the 1 % 1 - 1990 clirnatological means.

SEPT-ILES I I 1 I I I I I I 1

-4 ' 1 I I I I 1 I l I I I

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Year

Figure 5. Wmter air temperature anomalies at ~e~t-Îks, calculaîed fiom the average of the Decernber, January and Febnülry monthly means. The anomalies are relative to the 1 % 1 - 1990 climatological mean (-12.g°C).

-4 1 I I I I 1 I I 1 I I 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995

Year

Figure 8. FaIl air temperature anomalies a. ~e~t-fies, calcuiaied fiom the average of the Septernber, Wober and Novanber monthly means. The anomalies are relative to the 1961-1 990 climatologicai mean (3.3OC). Data fiom the fhii of 1979 are incoqlete.

Figure 9a. Location of the 1994 ice edge together with the 1962-1987 minimum, median and maximum ice edge positions (Côté, 1989) for December 3 1, 1993 and January 15, 1994.

44" -r' - 44"

Feb. 01,1994 68" 64" 60' 56"

w- Mar. 01,1994

68" 64" 60" 56"

Figure 9b. Location of the 1994 ice edge together with the 1962-1987 minimum, median and maximum ice edge positions (Côté, 1989) for Febmary 01 and March 01, 1994.

44" + - 44"

May 01,1994 68" 64" 60" 56"

Figure 9c. Location of the 1994 ice edge together with the 1962-1987 minimum, median and maximum ice edge positions (Côté, 1989) for April01 and May 01, 1994.

4 Winter RIVSUM Anomaly (December, January, February)

7

X Mean: 9782 MA3/S ('61 - '90) V

191 O 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 12. Wuder anomalies of the RIVSUM index, reiative to the 1961-1990 ciimatological mean (9782 m3/s), caldated fiom the average of the December, January and February river discharges.

1910 1920 1930 1940 1950 1960 1970 1980 1990 2000 Figure 13. Spring anomalies of the RIVSUM index, relative to the 1961-1990 ~Wological mean (1 1894 m3/s), calculated &om the average of the March, Apd and May river discharges.

- - - -

-4.0

u Mean: 1 1894 MA3/S ('61 - '90)

1 \ 1 1 I l I I I I I I I I I I I l I I I l I I I l I I I l I I I I I I

Figure! 16. Monthiy mean air temperature (solid line), and surface water temperature (dotted line) at the AES meteorological buoy (see Fig. 1 for location), fiom 1991 to 1994.

Figure 17. Monthly mean air tempeme (solid h), and surfàce water temperature (dotted line and black circles) at the AES rneteorological buoy in the northwest Ch& fiom April to November 1994. For cornparison, we also show the average of the long-tenn mean surface water temperatures for Petrie's (1990) boxes 6 and 8 (empty circles), for the months with complete data coverage (May to October).

0.00 I may I june I juiy ' augustl sept I oct I nov

0.00 may I june I juiy I au-4 sept I oct I nov

Figure 18. Surface water teanperature (OC) fkom the sept-Îles coastal thermograph, during the summer of 1993 (upper panel), and dunng the summer of 1994 (rniddle panel). The difference between the 1994 and 1993 observations is show on the lower panel.

Figure 19. Temperaîure anomalies averaged over the whole Gulf of St. Lawrence for the 0-30m, 30- 100 m, 100-200 m, and 200-300 m layers relative to the long-term means of Petrie (1990), ushg XBT and CTD data from the late summer groundfish surveys on the Lady Harnrnond and Alfied Needler.

1 O0

Distance (km)

Figure 20. Variogram for bottom temperature in the southern Gulfof St. Lawrence, for September 1994.

Figure 21. Bottom temperature in the southern Gulf of St. Lawrence, for September 1994. The contour interval is 1°C.

75 80 85 90 95

Year

Figure 22. Area of the southem Gulf of St. Lawrence (excluding strata 415,425 and 439) with bottom temperature below 0°C or 1 OC, fiom 197 1 to 1994.

1948-1 994 Guif composite index 1.5 1 I I I I I I I I I I l

a 1 w

>i - E O t a ? 0.5 3 C

2 a>

E- a) C

O O O J -

U O LO 7

X - 3 -0.5 - .)

- 1 I I I I I l l I I l

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 Year

Figure 23. Mid-summer composite index of CIL core tempmme anomaly for the Guif of St. Lawrence (fiom Gilbert and Pettigrew, 19%).

Figure 24. Thickness (in metas) of the fold intermediate layer (CE), defined here as the layer with waters folder than O°C, during the August- Septeinber 1994 shrimp and groundfish survey.

Figure 25. Difference between the thickness of the 1994 and 1993 cold intermediate layer (CIL), defined here as the layer with waters colder than O°C, as measured during the August-September shrimp and groundfish surveys.

-30

-35

-40

-45

-50

- E - g -55 al n

-60

-65

-70

-75

-80 120 140 160 180 200 220 240 260 280 300

Day of the year (1994) Figure 26. Depths of the upper and lower O°C isotherms of the cold intermediate layer (CIL), fi-om day 117 (April 27) to day 314 (November 10) of 1994. This tirne series comes i?om the thermistor chah which was deployed underneath the meteorological buoy mooring in the northwest Gul€(see Fig. 1 for location). A twelve hour running mean was used to filter out the semi-diurnal fluctuations.

CABOT STRAIT SECTION, 200-300m layer 7 I I I I 1 l l I 1 I

3.5l I I I I I 1 1 I I l

1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 YEAR

Figure 27. Average temperature of the 200-300 m layer at the standard Cabot Strait section. The dashed line indicates the 1 % 1- 1990 ciimaîological average (5.3 5OC).

LAYER-AVERAGED TEMPERATURES AND SAIL;INITIIES FOR TIBE

GULF OF ST. LAWRENCE IN AUGUSTSEPTEMBER 1994,

DIEFERENCES WITH 1993, AND ANOMALIES RELATIVE TO THE

LONGTERM MEANS OF PETRIE (1990)

Figure A - 1. Average temperature (OC) of the 0-30 m layer, as measured during the August-Septernber 1994 shrimp and groundfish survey.

Figure A 3. Temperature anomalies in the 0-30 m layer relative to Petrie's (1990) long-term meam, as measured during the August- septemb& 1994 shrimp and groundfish survey.

Figure A-4. Average saiinity of the 0-30 m layer, as measured during the August-September 1994 shrimp and pundfish survey.

Figure A - 5. Difference in the salinity of the 0-30 m layer between 1994 and 1993 (August-Septernber 1994 minus 1993).

Figure A 6. Salinity anomalies in the 0-30 m layer relative to Petrie's (1990) long-tem means, as measured during the August-September 1994 shrimp a&d groundfish survey.

Figure A-7. Average temperature (OC) of the 30-100 m layer, as measured during the August-September 1994 shrimp and groundfish survey.

Figure A-9. Temperature anomalies in the 30-100 m layer relative to Petrie's (1990) long-term means, as measured during the August- September 1994 shrimp and groundfish survey.

Figure A - 13. Average temperabire ( O C ) of the 100-200 m layer, in August-September 1994.

Figure A - 15. Temperatme anomalies in the 100-200 rn layer relative to Petrie's (1990) long-term means, in August-September 1994.

Figure A 16. Average saiinity of the 100-200 m layer, in August-September 1994. -

Figure A - 17. Difference in the salinity of the 100-200 m layer between 1994 and 1993 (August-September 1994 minus 1993).

Figure A - 18. Salinity anomalies in the 10-200 m layer relative to Petrie's (1990) long-term means, in August-September 1994.

Figure A-19. Average temperature (OC) of the 200-300 m layer, in August-September 1994.

Figure A - 20. Diierence in the temperature of the 200-300 m layer between 1994 and 1993 (August-Septernber 1994 minus 1993).

Figure A - 21. Temperature anomalies in the 200-300 m layer relative to Petrie's (1990) long-term means, in August-September 1994.

Figure A 22. Average saiinity of the 200-300 m layer, in August-September 1994. -

Figure A - 23. Diffèrence in the sallluty of the 2ûû-30 m layer between 1994 and 1993 (August-Septanber 1994 minus 1993).

Figure A - 24. Saiinity anomalies in the 200-300 m layer relative to Petrie's (1990) long-term means, in August-September 1994.

LAYER-AVERAGED TEMPERATURES AND S-S

FOR THE GULF OF ST. LAWRENCE, CALCULATED FROM THE

1915-1987 CLIMATOLOGXAL ATLAS OF PETRIE (1990)

Figure B - 1. August average temperature (T) of the O to 30 m layer, calailated fi-om the climatological atlas of Petrie (1990).

Figure B-2. September average temperature (OC) of the O to 30 m layer, calculated fiom the climatological atlas of Petrie (1990).

Figure B - 3. October average temperature (OC) of the O to 30 m layer, calculateci &om the chtological atlas of Petrie (1990).

Figure B - 4. Augua average temperature (OC) of the 30 to 100 m layer, caiculated fiom the clirnatological atlas of Petrie (1990).

Figure B - 5. September average temperature ( O C ) of the 30 to 100 m layer, caiculated fiom the climatolo~cai atlas of Petrie (1990).

Figure B - 6. October average temperature (OC) of the 30 to 100 m layer, caldated fian the climatological atlas of Petrie (1990).

Figure B-7. Yeariy-averaged tempture (OC) of the 1ûû to 200 m layer, caidated fiom the climatological atlas of Petrie (1990).

Figure B-8. Yeady-averaged temperature (OC) of the 200 to 300 m layer, chtldated h m the climatological atlas of Petrie (1990).

Figure B-9. August average saiinity of the O to 30 m layer, calculated fiom the clirnatological atlas of Petrie (1990).

Figure B - 10. September average saiinity of the O to 30 m layer, caiculated fi-om the climatological atlas of Petrie (1990).

Figure 8 1 1 . Odober average saiinity of the O to 30 m layer, calailateci fiom the clirnatological atlas of Petrie (1990).

Figure 8 1 2 . August average saünity of the 30 to 100 m layer, calcuiated fiom the cliaatological atlas of Petrie (1990).

Figure B - 13. Septernber average saiinity of the 30 to 1 W m layer, caiailated fiom the climatologicai atlas of Petrie (1 990).

Figure 8 1 4 . Odober average saiinity of the 30 to 100 m layer, caidated fiom the climatological atlas of Petrie (1990).

Figun B - 15. Yeariy-averaged saiinity of the 100 to 200 m layer, uildated fiom the chtologiuil atlas of Petrie (1990).

Figure 8 1 6 . Yeariy-averaged saünity of the 200 to 300 m layer, caldated fiom the ciimato1ogica.i atlas of Petrie (1990).