Temperature and Salinity Temperature and Salinity Variabitlity on the Scotian Variabitlity on the Scotian

Shelf and in the Gulf of Shelf and in the Gulf of Maine 1945-1990Maine 1945-1990

BRIAN PETRIE AND BRIAN PETRIE AND KENNETH DRINKWATERKENNETH DRINKWATER

1. Introduction—Earlier ResearchThe 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)

1 Introduction--Objective1 Introduction--Objective

extend the prior results by examining extend the prior results by examining temperature and salinity variations temperature and salinity variations throughout the water columnthroughout the water column

investigate the origin of cold SST investigate the origin of cold SST events compared to Lauzier (1965) ’s events compared to Lauzier (1965) ’s speculation. speculation.

to determine the likely processes that to determine the likely processes that might contribute to the oceanic forcing.might contribute to the oceanic forcing.

2 Data and Methods--Data2 Data and Methods--Data

2 Data and Methods– Observation 2 Data and Methods– Observation SitesSites

3 Results- Emerald 3 Results- Emerald Basin/temperature/100mBasin/temperature/100m

1940s and early 1940s and early 1950s, temperature 1950s, temperature roses to maximum roses to maximum of above 1°C above of above 1°C above the mean in 1952-the mean in 1952-19531953

temperature temperature declined 3°C for the declined 3°C for the next 16 years until next 16 years until late 1960slate 1960s

a short-term a short-term minimum in minimum in 1959(Worthington, 1959(Worthington, 1964). In 1960-1964). In 1960-1970s there is an 1970s there is an increase trend with increase trend with a maximum a maximum variation of over variation of over 2°C until late 2°C until late 1970s.1970s.

3 Results- Emerald 3 Results- Emerald Basin/temperature/all depthBasin/temperature/all depth Similar Similar

trends trends are seen are seen at all at all depth depth

at at surface surface less less significasignificant due to nt due to the high-the high-frequencfrequency local y local effect. effect.

subsurfasubsurface ce has has larger larger amplitudamplitude of this e of this variabilitvariabilityy

3 Results- Emerald Basin/Temperature change && 3 Results- Emerald Basin/Temperature change && standard deviation variations of low/high pass standard deviation variations of low/high pass

temperature anomaliestemperature 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 at depth of less than 50m, high-frequency variation exceeds low-frequency variation, and the opposite is true exceeds low-frequency variation, and the opposite is true for subsurface( the low-frequency variation maximum for subsurface( the low-frequency variation maximum occurs in 100m). occurs in 100m).

3 Results- Emerald 3 Results- Emerald Basin/temperature/EOF analysisBasin/temperature/EOF analysis

The EOF The EOF analysis shows analysis shows long-term trend long-term trend of temperature of temperature variability variability (56.6%) in the (56.6%) in the first mode first mode

high-high-frequency frequency variability in the variability in the second mode second mode (23.2%).(23.2%).

the slope the slope water intrusions water intrusions are at least are at least partly partly responsible for responsible for the long-term the long-term temperature temperature variability. variability.

3 Results- Emerald Basin/Salinity3 Results- Emerald Basin/Salinity

mean salinity decrease (1952-1967) for depth >100m mean salinity decrease (1952-1967) for depth >100m are 0.53psuare 0.53psu

T-S diagram supports this joint occurrence of T-S diagram supports this joint occurrence of temperature and salinity variationtemperature and salinity variation

in the 1950s in the 1950s Labrador Slope Water (Gatien, 1976) Labrador Slope Water (Gatien, 1976) in the 1960s in the 1960s between Labrador Slope Water and Mixed Water between Labrador Slope Water and Mixed Water

(Morgan, 1969).(Morgan, 1969).

3 Results—Halifax Section3 Results—Halifax Section

TT3-4.5°C in 1966 and 8-10°C in 3-4.5°C in 1966 and 8-10°C in 1974 1974

SS1psu lower in 19661psu lower in 1966

The cool and fresh The cool and fresh waters in the deep basin waters in the deep basin in 1966 are found in 1966 are found between 50-100m over between 50-100m over the slopethe slope long-period long-period anomalies are oceanic in anomalies are oceanic in origin origin

3 Results- Other shelf and slope waters3 Results- Other shelf and slope waters

Former researches (Bugden, 1991; Colton, Former researches (Bugden, 1991; Colton, 1968) have found similar long-term variability 1968) have found similar long-term variability in Gulf of St. Lawrence and deep basins of the in Gulf of St. Lawrence and deep basins of the Gulf of Maine. Gulf of Maine.

The minimum temperature and salinity (4.5°C, The minimum temperature and salinity (4.5°C, 34.4psu) occurred progressively later from 34.4psu) occurred progressively later from Gulf of St. Lawrence farther into the gulf, Gulf of St. Lawrence farther into the gulf, indicating an oceanic origin of the anomalies.indicating an oceanic origin of the anomalies.

After the cold 1960s event, the deep After the cold 1960s event, the deep temperature in the gulf rose by 1.5°C in temperature in the gulf rose by 1.5°C in temperature and 0.3psu in salinity. temperature and 0.3psu in salinity.

Some results (Colton, 1968; True and Wiitala, Some results (Colton, 1968; True and Wiitala, 1990) noticed that the 1960 cold event in the 1990) noticed that the 1960 cold event in the deep basin of Gulf of Maine was due to deep basin of Gulf of Maine was due to property exchange with slope water and this property exchange with slope water and this deep water event eventually extended upward deep water event eventually extended upward into top 30m. into top 30m.

3 Results- Other shelf and slope 3 Results- Other shelf and slope waters/temperaturewaters/temperature

Similar trend is also found in Emerald Bank, the Similar trend is also found in Emerald Bank, the continental slope and Georges Basin.continental slope and Georges Basin.

The largest cooling trend occurs in the Slope Water The largest cooling trend occurs in the Slope Water between 30 and 125m, where it exceeds 4°C. In between 30 and 125m, where it exceeds 4°C. In Georges Basin the cooling was about 2.5°C. Georges Basin the cooling was about 2.5°C.

The occurrence again indicates a The occurrence again indicates a subsurface, oceanic originsubsurface, oceanic origin

3 Results- Other shelf and slope waters3 Results- Other shelf and slope waters

TTthe reduced trend near the end of Scotian Shelf implies the reduced trend near the end of Scotian Shelf implies that the outflow from the Gulf of St. Lawrence was not a that the outflow from the Gulf of St. Lawrence was not a primary cause.primary cause.

SS decrease trend generally; Sydney Bight/Banquereau decrease trend generally; Sydney Bight/Banquereau Bank surface increase( decrease of the inflow)Bank surface increase( decrease of the inflow)

3 Results- Lightship Observations The Lurcher 3 Results- Lightship Observations The Lurcher and Sambro lightship temperature observationsand Sambro lightship temperature observations

The time series show similar trend (-2.24,-2.56,-4.21,-The time series show similar trend (-2.24,-2.56,-4.21,-2.73 respectively for surface and 90m Lurcher and 2.73 respectively for surface and 90m Lurcher and Sambro, respectively) as indicated in Emerald Basin. Sambro, respectively) as indicated in Emerald Basin. The larger trend for surface in Sambro is mainly due The larger trend for surface in Sambro is mainly due to the coastal upwelling. to the coastal upwelling.

The lagged correlation from the two data lends some The lagged correlation from the two data lends some support to the subsurface and westerly origin of the support to the subsurface and westerly origin of the cooling trend. cooling trend.

3 Results—Coastal SST stations3 Results—Coastal SST stations

For Prince5 For Prince5 station (near Bay station (near Bay of Fundy), the of Fundy), the trends for SST is trends for SST is -2.12 and -2.37, -2.12 and -2.37, higher than those higher than those found at St. found at St. Andrews.Andrews.

the salinity at the salinity at Prince5 doesn’t Prince5 doesn’t show significant show significant trendtrend

inflow/ mixing inflow/ mixing by tides by tides

General decrease General decrease trend before trend before 19451945

The trends for Halifax, St. Andrews and The trends for Halifax, St. Andrews and Boothbay Harbor during 1952-1967 are -Boothbay Harbor during 1952-1967 are -1.23, -1.84 and -3.231.23, -1.84 and -3.23

3 Results—Coastal SST stations3 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.

4 Lauzier’s hypothesis—Labrador 4 Lauzier’s hypothesis—Labrador Current WaterCurrent Water

between 1934 between 1934 and 1941, both and 1941, both T and S are T and S are increasing.increasing.

From late From late 1940s to mid-1940s to mid-1960s, the 1960s, the temperatures temperatures generally generally were positive were positive anomalies, anomalies,

opposite to opposite to Lauzier’s Lauzier’s hypothesis.hypothesis.

Explanation for Explanation for the the mechanism?mechanism?

4 Lauzier’s hypothesis—Geostrophic 4 Lauzier’s hypothesis—Geostrophic transport A3/A4transport A3/A4

increase increase from 1Sv to from 1Sv to 4Sv from 4Sv from early 1950s early 1950s to late to late 1960s 1960s

The The increase is increase is greater for greater for A3 A3 flow flow may have may have turned turned eastward eastward before before reaching reaching A4.A4.

4 Lauzier’s hypothesis—Simple model4 Lauzier’s hypothesis—Simple model

the increase of Labrador Current inflow could contribute the increase of Labrador Current inflow could contribute significantly to the T-S property fluctuations.significantly to the T-S property fluctuations.

Agree well with observations at Laurentian Channel, Agree well with observations at Laurentian Channel, Emerald Basin and South of Georges BankEmerald Basin and South of Georges Bank

T: circle; S: T: circle; S: SquareSquare

5 Conclusions5 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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