1. Temperature and Salinity Variabitlity on the Scotian Shelf and in the Gulf of Maine 1945-1990 BRIAN PETRIE AND KENNETH DRINKWATER

2. 1. Introduction—Earlier Research The region from Middle Atlantic Bight (MAB) to Grand Banks exhibits the highest interannual variability of sea surface temperature (SST) in the North Atlantic Ocean. During 1949 and 1969 the dominant SST low-frequency variation north of 30°N was a cooling trend Before this cooling trend && there was a broad-scale in-phase warming in SST from about 1940s to early 1950s, with its peak in the Gulf of Maine in early 1950s(Weave,1977) The largest variation in 1950s occurred near Nova Scotia (Thompson,1988) In several locations, the subsurface water has same trend as surface water, and speculate the long-term variability might be caused by mix of water masses rather than local weather effect (Lauzier, 1965). Advection influence (water from Gulf of St. Lawrence, Labrador Current) on the climate change (Chapman and Beardsley, 1989)

3. 1 Introduction--Objective extend the prior results by examining temperature and salinity variations throughout the water column extend the prior results by examining temperature and salinity variations throughout the water column investigate the origin of cold SST events compared to Lauzier (1965) ’s speculation. investigate the origin of cold SST events compared to Lauzier (1965) ’s speculation. to determine the likely processes that might contribute to the oceanic forcing. to determine the likely processes that might contribute to the oceanic forcing.

4. 2 Data and Methods--Data

5. 2 Data and Methods– Observation Sites

6. 3 Results- Emerald Basin/temperature/100m  1940s and early 1950s, temperature roses to maximum of above 1°C above the mean in 1952-1953  1940s and early 1950s, temperature roses to maximum of above 1°C above the mean in 1952-1953  temperature declined 3°C for the next 16 years until late 1960s  temperature declined 3°C for the next 16 years until late 1960s  a short-term minimum in 1959(Worthington, 1964). In 1960-1970s there is an increase trend with a maximum variation of over 2°C until late 1970s.  a short-term minimum in 1959(Worthington, 1964). In 1960-1970s there is an increase trend with a maximum variation of over 2°C until late 1970s.

7. 3 Results- Emerald Basin/temperature/all depth  Similar trends are seen at all depth  Similar trends are seen at all depth at surface  less significant due to the high- frequency local effect. at surface  less significant due to the high- frequency local effect. subsurface  has larger amplitude of this variability subsurface  has larger amplitude of this variability

8. 3 Results- Emerald Basin/Temperature change && standard deviation variations of low/high pass temperature anomalies largest (least) variation of 3.9°C (1.6°C) at 150m (0m) largest (least) variation of 3.9°C (1.6°C) at 150m (0m) at depth of less than 50m, high-frequency variation exceeds low- frequency variation, and the opposite is true for subsurface( the low- frequency variation maximum occurs in 100m). at depth of less than 50m, high-frequency variation exceeds low- frequency variation, and the opposite is true for subsurface( the low- frequency variation maximum occurs in 100m).

9. 3 Results- Emerald Basin/temperature/EOF analysis The EOF analysis shows long-term trend of temperature variability (56.6%) in the first mode The EOF analysis shows long-term trend of temperature variability (56.6%) in the first mode  high-frequency variability in the second mode (23.2%).  high-frequency variability in the second mode (23.2%).  the slope water intrusions are at least partly responsible for the long-term temperature variability.  the slope water intrusions are at least partly responsible for the long-term temperature variability.

10. 3 Results- Emerald Basin/Salinity mean salinity decrease (1952-1967) for depth >100m are 0.53psu mean salinity decrease (1952-1967) for depth >100m are 0.53psu T-S diagram supports this joint occurrence of temperature and salinity variation T-S diagram supports this joint occurrence of temperature and salinity variation in the 1950s  Labrador Slope Water (Gatien, 1976) in the 1950s  Labrador Slope Water (Gatien, 1976) in the 1960s  between Labrador Slope Water and Mixed Water (Morgan, 1969). in the 1960s  between Labrador Slope Water and Mixed Water (Morgan, 1969).

11. 3 Results—Halifax Section T  3-4.5°C in 1966 and 8-10°C in 1974 T  3-4.5°C in 1966 and 8-10°C in 1974 S  1psu lower in 1966 S  1psu lower in 1966 The cool and fresh waters in the deep basin in 1966 are found between 50-100m over the slope  long-period anomalies are oceanic in origin The cool and fresh waters in the deep basin in 1966 are found between 50-100m over the slope  long-period anomalies are oceanic in origin

12. 3 Results- Other shelf and slope waters Former researches (Bugden, 1991; Colton, 1968) have found similar long-term variability in Gulf of St. Lawrence and deep basins of the Gulf of Maine. Former researches (Bugden, 1991; Colton, 1968) have found similar long-term variability in Gulf of St. Lawrence and deep basins of the Gulf of Maine. The minimum temperature and salinity (4.5°C, 34.4psu) occurred progressively later from Gulf of St. Lawrence farther into the gulf, indicating an oceanic origin of the anomalies. The minimum temperature and salinity (4.5°C, 34.4psu) occurred progressively later from Gulf of St. Lawrence farther into the gulf, indicating an oceanic origin of the anomalies. After the cold 1960s event, the deep temperature in the gulf rose by 1.5°C in temperature and 0.3psu in salinity. After the cold 1960s event, the deep temperature in the gulf rose by 1.5°C in temperature and 0.3psu in salinity. Some results (Colton, 1968; True and Wiitala, 1990) noticed that the 1960 cold event in the deep basin of Gulf of Maine was due to property exchange with slope water and this deep water event eventually extended upward into top 30m. Some results (Colton, 1968; True and Wiitala, 1990) noticed that the 1960 cold event in the deep basin of Gulf of Maine was due to property exchange with slope water and this deep water event eventually extended upward into top 30m.

13. 3 Results- Other shelf and slope waters/temperature Similar trend is also found in Emerald Bank, the continental slope and Georges Basin. Similar trend is also found in Emerald Bank, the continental slope and Georges Basin. The largest cooling trend occurs in the Slope Water between 30 and 125m, where it exceeds 4°C. In Georges Basin the cooling was about 2.5°C. The largest cooling trend occurs in the Slope Water between 30 and 125m, where it exceeds 4°C. In Georges Basin the cooling was about 2.5°C. The occurrence again indicates a subsurface, oceanic origin The occurrence again indicates a subsurface, oceanic origin

14. 3 Results- Other shelf and slope waters T  the reduced trend near the end of Scotian Shelf implies that the outflow from the Gulf of St. Lawrence was not a primary cause. T  the reduced trend near the end of Scotian Shelf implies that the outflow from the Gulf of St. Lawrence was not a primary cause. S  decrease trend generally; Sydney Bight/Banquereau Bank surface increase( decrease of the inflow) S  decrease trend generally; Sydney Bight/Banquereau Bank surface increase( decrease of the inflow)

15. 3 Results- Lightship Observations The Lurcher and Sambro lightship temperature observations The time series show similar trend (-2.24,-2.56,-4.21,-2.73 respectively for surface and 90m Lurcher and Sambro, respectively) as indicated in Emerald Basin. The larger trend for surface in Sambro is mainly due to the coastal upwelling. The time series show similar trend (-2.24,-2.56,-4.21,-2.73 respectively for surface and 90m Lurcher and Sambro, respectively) as indicated in Emerald Basin. The larger trend for surface in Sambro is mainly due to the coastal upwelling. The lagged correlation from the two data lends some support to the subsurface and westerly origin of the cooling trend. The lagged correlation from the two data lends some support to the subsurface and westerly origin of the cooling trend.

16. 3 Results—Coastal SST stations For Prince5 station (near Bay of Fundy), the trends for SST is -2.12 and -2.37, higher than those found at St. Andrews. For Prince5 station (near Bay of Fundy), the trends for SST is -2.12 and -2.37, higher than those found at St. Andrews. the salinity at Prince5 doesn’t show significant trend the salinity at Prince5 doesn’t show significant trend  inflow/ mixing by tides  inflow/ mixing by tides General decrease trend before 1945 General decrease trend before 1945 The trends for Halifax, St. Andrews and Boothbay Harbor during 1952-1967 are -1.23, -1.84 and -3.23 The trends for Halifax, St. Andrews and Boothbay Harbor during 1952-1967 are -1.23, -1.84 and -3.23

17. 3 Results—Coastal SST stations Observations from Entry Island SST and station 27 surface and subsurface SST as well as salinity show no trends similar to those discussed above This indicates that this anomaly didn’t originate in the Gulf of St. Lawrence nor from the inshore region of Newfoundland shelf.

18. 4 Lauzier’s hypothesis—Labrador Current Water between 1934 and 1941, both T and S are increasing. between 1934 and 1941, both T and S are increasing. From late 1940s to mid- 1960s, the temperatures generally were positive anomalies, From late 1940s to mid- 1960s, the temperatures generally were positive anomalies,  opposite to Lauzier’s hypothesis. Explanation for the mechanism? Explanation for the mechanism?

19. 4 Lauzier’s hypothesis—Geostrophic transport A3/A4 increase from 1Sv to 4Sv from early 1950s to late 1960s increase from 1Sv to 4Sv from early 1950s to late 1960s The increase is greater for A3  flow may have turned eastward before reaching A4. The increase is greater for A3  flow may have turned eastward before reaching A4.

20. 4 Lauzier’s hypothesis—Simple model the increase of Labrador Current inflow could contribute significantly to the T-S property fluctuations. the increase of Labrador Current inflow could contribute significantly to the T-S property fluctuations. Agree well with observations at Laurentian Channel, Emerald Basin and South of Georges Bank Agree well with observations at Laurentian Channel, Emerald Basin and South of Georges Bank T: circle; S: Square T: circle; S: Square

21. 5 Conclusions (1)The examination of temperature and salinity data from the Scotian Shelf and adjacent continental slopes shows that the dominant low-frequency events during the last 45 years was a cooling and subsurface freshening of the water masses from 1952- 1967s, followed by a reversal of these trends. The largest variation of temperature and salinity is 4.6°C and 0.7psu respectively, which occurred at 100m over the slope. (2) Exchanges with shelf waters and vertical mixing are responsible for enhancing of this event. The Labrador Current low-frequency variability of temperature and salinity are opposite to that of the Scotian Shelf, but the transport increase leads to the cooling and freshening of trend during the cold 1960s (3) The westward transport of Labrador Current is found to increase significantly from 1Sv in 1950s to 4Sv in 1960s. Using a simple model, the increase of Labrador Current inflow could contribute significantly to the T-S property fluctuations.

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