Physical Variability Atlantic Shelves, Coastal Areas

Variables

• Background, general circulation

• Sea Level

• Ocean temperature/salinity

• Stratification

• Sea Ice

Circulation over Continental Shelf

Transport of heat and freshwater by ocean currents have an important effect on Atlantic regional atmospheric and ocean climate.

Life in the sea is dependent on the biogeochemical status of the ocean and is influenced by the mean and variable physical state and circulation

General CirculationGeneral north to south currents with major impact on region

Built on hydrographic surveys, current meter/drift bottles/buoy data, …, plankton distributions, chemical tracers …modelling

Sea Level

Global mean sea level has been rising by ~2 mm/year (0.2 m/century)

Sea level change varies substantially from area to area on a global scale, rising more rapidly than the mean in some regions, falling in others.

Sea Level in Atlantic Canada

Relative sea level is measured, ocean surface relative to a reference point on land.

For many issues, coastal erosion, storm surges, … RSL is the important variable.

Changes to RSL due to:

Crustal loading – post glacial rebound at Halifax has the land sinking at ~0.23 m/century; rising in the northern Gulf of St. Lawrence

Absolute sea level changes – changing ocean properties (temperature, fresh water content), currents, atmospheric pressure, winds.

Observed Trends of Relative Sea Level: over the last 100 years

Observed Trends of Relative Sea Level: over the last 100 years

• Sea Levels are generally increasing, with Halifax typical of the region for trend and variability

Halifax Sea Level

0.7

0.8

0.9

1

1.1

1890 1910 1930 1950 1970 1990 2010

An

nu

al S

ea

Le

ve

l Ha

lifa

x

Post-Glacial Rebound

Annual MSLLinear fit 1920ff

Overall trend 1920-present, rise of 0.32 m/century

RSL exceeds post-glacial rebound by 0.08 m over 90 y.

Two periods, 1920-70 & 1970-present, exhibit different long term trends.

1920-70 0.4 m/century

1970-present 0.19 m/century (<PGR model result of 0.23 cm/century)

How widespread?

-0.4

-0.3

-0.2

-0.1

0

0.1

0.2

1880 1900 1920 1940 1960 1980 2000 2020

Se

a L

ev

el

(m)

Halifax Saint John St. John's Charlottetown Rimouski

Portland Boston New York Atlantic City

-0.25

0

0.25

0.5

NJ

NY RI

Ma

Me

St

J

Hfx

Ch

rltw

n

Rim

SJ

's

Se

a L

ev

el T

ren

d (

m/c

en

tury

) <1970 1970ff Diffrnce

Decreasing sea level trend 1970-present, centered on Scotian Shelf-Eastern Gulf of Maine, moderating to the south along US East Coast and to the northeast into the Gulf of St. Lawrence and onto the Newfoundland Shelf.

Projected sea level trends

Used 1920-2009 Halifax sea level stats (-PGR) to project sea level to 2099 in 100 simulations (+PGR);

Used range of IPCC projections to construct 2009-2099 sea level rise.

0.4 m

0.6

0.8

1

1.2

1.4

1.6

1.8

1900 1950 2000 2050 2100

Sea

Lev

el

Observed

Projected

Range IPCC projections

Ocean Temperature and Salinity

The oceans are warming globally by about 0.1oC (1961-2003), 0-700 m; there has been considerable interannual and interdecadal variability.

IPCC assessment shows 1961-2003 cooling trend for deep ocean areas Lab-Nfld region, warming trend for NS region.

Large scale trends of salinity are seen globally with freshening characterizing subpolar latitudes. Data are not good enough to assess global average changes.

Atlantic region: 1. SST data, model; 2. Btm T vs NAO; . 3. Depth-averaged T/S

Sea Surface Temperature

Longest east coast series

Blue 5 year running mean obs;

red 5y rmf model

Trend

Halifax none

St Andrews +1oC/century

-2

-1

0

1

2

1920 1940 1960 1980 2000

An

nu

al T

em

pe

ratu

re A

no

ma

ly Halifax SST

-2

-1

0

1

2

1920 1940 1960 1980 2000

An

nu

al T

em

pe

ratu

re A

no

ma

ly St. Andrews SST

100 year Air Temperature Trends 1909-20091

+1

0

-1

North ~ 0oC

South – rise of 1oC

1Iqaluit, Cartwright, Sable <100y

Can Air Temperature predict SST?

Year19851990199520002005A

ZM

P A

rea

BravoHudStrLabShlfHamBankStAnthonyNENfldShlfFlemPassHiberniaAvlnChnSEShoalGreenStPNEGSLNWGSLGSLEstuaryMagShlwCabotStrESSWstrnBnkCSSWSSLurcherGrgesBankBoF

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

Year19851990199520002005

AZ

MP

Are

a

BravoHudStrLabShlfHamBankStAnthonyNENfldShlfFlemPassHiberniaAvlnChnSEShoalGreenStPNEGSLNWGSLGSLEstuaryMagShlwCabotStrESSWstrnBnkCSSWSSLurcherGrgesBankBoF

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 Observed SST Stat Model SST=f(Air T)

-2

-1

0

1

2

-2 -1 0 1 2

Obs Annual T Anomaly

Pre

d A

nn

ua

l T A

no

ma

ly

Model captures main features but smoothes them;

Underestimates anomalies = 0.76*Obs

R2 = 0.76

Are predictions acceptable for periods other than 1985-2008?

-2.0

-1.5

-1.0

-0.5

0.0

0.5

1.0

1.5

2.0

1945 1955 1965 1975 1985 1995 2005

An

nu

al S

urf

ace

T A

no

mal

y

Station 27PredictedStat Model PeriodHindcast Period

Avalon Channel predicted SST versus Station 27 observations:

Predicted = 0.84*Observation, underestimates anomaly

R2 = 0.66, captures variability well

Other areas: CSS 0.55*Obs, R2 =0.44; Fundy 0.39*Obs, R2 = 0.40.

If Air T were to rise by 2oC

0 0.5 1 1.5 2

Bay of FundyGeorges BankLurcher Shoal

WSSCSS

Western BankESS

Cabot StrMagdalen Shlw

GSL EstuaryNW GSLNE GSL

Green-St. PierreFlemish Pass

SE ShoalHibernia

Avalon ChnNE Nfld Shelf

St. AnthonyHamilton Bank

Nain BankHudson Strait

Bravo

An

nu

al S

ST

An

om

aly

Representative Annual SST rise ~ 1oC based on air temperature projections for 2050

NAO = Sea Level Atmospheric Pressure Difference between the Azores and Iceland

Positive NAO leads to severe winters over the Labrador Sea, Shelf and Grand Banks

Negative NAO leads to mild winters over the Labrador Sea, Shelf and Grand Banks

NAO Variability: the dominant meteorological pattern driving North Atlantic ocean climate

NAO Variability: the dominant meteorological pattern driving North Atlantic ocean climate

Negative NAO → warmer than normal bottom temperatures over the Labrador-Newfoundland Shelf, the Gulf of St. Lawrence and the eastern Scotian Shelf;

and

colder than normal conditions over the central and western Scotian Shelf and Gulf of Maine.

The pattern is reversed under positive NAO forcing.

Temperature Anomaly

Impact on Continental Shelf

Bottom temperature is strongly related to NAO

NAO tendencies

Over last 100+ years, the NAO trend has been towards longer periods with the anomalies having the same sign; cold and warm periods tend to last longer.

Model forecasts indicate that the NAO anomalies will tend to be more positive in the future.

NAO influence is more direct on Newfoundland-Labrador than on the Scotian Shelf-Gulf of Maine

Depth-Averaged T/S

4

5

6

7

8

1920

-24

1925

-29

1930

-34

1935

-39

1940

-44

1945

-49

1950

-54

1955

-59

1960

-64

1965

-69

1970

-74

1975

-79

1980

-84

1985

-89

1990

-94

1995

-99

2000

-04

2005

-09

Ave

rag

e A

nn

ual

T 0

-90

m

Bay of Fundy, Prince 5

31.8

31.9

32

32.1

32.2

32.3

32.4

1920

-24

1925

-29

1930

-34

1935

-39

1940

-44

1945

-49

1950

-54

1955

-59

1960

-64

1965

-69

1970

-74

1975

-79

1980

-84

1985

-89

1990

-94

1995

-99

2000

-04

2005

-09

Ave

rag

e A

nn

ual

T 0

-90

m

Bay of Fundy, Prince 5

Bay of Fundy

Temperature shows trend towards higher values at 1.2oC/century

Salinity shows weak trend of -0.18/century, i.e. the Bay is becoming fresher.

Corresponds to 3 weeks of Saint John River inflow

Depth-Averaged T/S

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1950-54 1955-59 1960-64 1965-69 1970-74 1975-79 1980-84 1985-89 1990-94 1995-99 2000-04 2005-09

Ave

rag

e A

nn

ual

T 0

-175

m

Avalon Channel Stn 27

32.35

32.4

32.45

32.5

32.55

32.6

32.65

1950-54 1955-59 1960-64 1965-69 1970-74 1975-79 1980-84 1985-89 1990-94 1995-99 2000-04 2005-09

Avera

ge A

nn

ual S

0-1

75 m

Avalon Channel Stn 27

Avalon Channel Observations illustrate difficulty of discerning trend (~0 for T) against strong interannual variability.

Salinity shows a weak trend of -0.21/century; again not significant against background variability.

Depth-Averaged T/S

-1

-0.5

0

0.5

1

1.5

1950-59 1960-69 1970-79 1980-89 1990-99 2000-09

An

nu

al 0

-150

m T

Ham

ilto

n B

ank Months 6-10

4.8

5

5.2

5.4

5.6

5.8

6

6.2

6.4

1950-59 1960-69 1970-79 1980-89 1990-99 2000-09

An

nu

al 0

-50m

T M

agd

alen

Sh

llo

ws Months 5-11

5.5

6

6.5

7

7.5

8

1950-59 1960-69 1970-79 1980-89 1990-99 2000-09

An

nu

al 0

-250

m T

CS

S

All Months

Trends for southern Labrador Shelf and Gulf of St. Lawrence, and central Scotian Shelf are obscured by decadal variability.

8 of 16 areas from Hamilton Bank to Gulf of Maine 2000-09 warmest

Labrador Scotian Shelf

Gulf of St. Lawrence

Stratification

-0.020

-0.015

-0.010

-0.005

0.000

0.005

0.010

0.015

1940 1945 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010

dr

/dz

(kg

m-3

)/m

Long-term trend of increasing stratification on Scotian Shelf;

Trend equals an increase of density difference from 0-50 m of 0.4 kg m-3

Biological Impact of Stratification

Production models suggest relationship between spring bloom and mixed layer depth; figure compares stratification, a proxy for MLZ, and CPR greenness for 5 year periods

CPR Greenness – measure of chlorophyll concentration from transects of eastern Scotian Shelf; sampling is monthly but in practice the average number of months sampled was 8/y

R2 = 0.94

0

0.2

0.4

0.6

0.8

1

1.2

1.4

1.6

1.8

-0.008 -0.006 -0.004 -0.002 0 0.002 0.004 0.006

StratificationA

nn

ual

CP

R G

ree

nn

ess

96-00

91-95

01-06

71-76 66-70

61-65

No data 1977-90

Other Areas

-0.02

-0.015

-0.01

-0.005

0

0.005

0.01

0.015

0.02

1950 1960 1970 1980 1990 2000 2010

Str

atif

icat

ion

HamBnk Stn 27 Magdln Grgs Bsn

From 1950 to 2009, trends represent change of -0.17 for Hamilton Bank, +0.18 for Stn 27 Avalon Chn, +0.33 for Magdalen Shallows, +0.49 for Georges Basin

CausesSite Ratio S/T Difference

accounting for ρ(50 m)-ρ(0 m)

Series accounting for most ρ(50 m)-ρ(0 m) variance

Hamilton

Bank 3.2

Salinity 0 m

Avalon Channel

1.1 Salinity 0 m

Magdalen Shallows

2.4 Salinity 0 m

Misaine Bank

2.6

Salinity 0 m

Emerald Basin

2.9 Salinity 0 m

Roseway Basin

1.1

Temperature 0 m

Georges Basin

1.6 Temperature 0 m

Salinity (Freshwater) has had the largest impact in the region

Model projections indicate decreased freshwater inflow from St. Lawrence

Ice VolumeNfld Labrador

0

100

200

300

400

500

600

700

1950-54 1955-59 1960-64 1965-69 1970-74 1975-79 1980-84 1985-89 1990-94 1995-99 2000-04 2005-09

Av

era

ge

De

c-J

un

e Ic

e V

olu

me

45 - 55oN

-0.1

0

0.1

0.2

0.3

0.4

0.5

0.6

0.7

0.8

1950-54 1955-59 1960-64 1965-69 1970-74 1975-79 1980-84 1985-89 1990-94 1995-99 2000-04 2005-09

Av

era

ge

An

nu

al T

0-1

75

m

Avalon Channel Stn 27

0

5

10

15

20

25

30

35

40

1950-54 1955-59 1960-64 1965-69 1970-74 1975-79 1980-84 1985-89 1990-94 1995-99 2000-04 2005-09

Av

era

ge

CIL

are

a

Bonavista Section T<0oC

Ice volume shows a weak decreasing trend (270 km3/century);

ice volume is highly correlated with ocean temperature (r2 = 0.74, T increasing)

and

amount of subzero water (CIL) over northeast Nfld Shelf (r2 = 0.61, CIL area decreasing).

Summary

• Sea level increasing but since 1970 at ~PGR rate; coherent regional response

• Long (90 y) record indicates +1oC/century at St. Andrews; upper 90 m warming at same rate and freshening

• Air temperature in southern half of region rising for last century (~1oC); shelf SST can be constructed and hindcast well.

• Btm T responds coherently to NAO forcing with Nfld-Lab-GSL opposite to SSGoM

• Pentadal, decadal T/S are dominated by interannual variability but 8 of 16 areas show 2000-09 warmest.

• Stratification shows increasing trends south of Labrador with salinity dominating.

• Projected trends in forcing- air T increasing, (precipitation-evaporation)/runoff decreasing, NAO increasing