Recent Variability in Ocean Climate in the Scotia-Maine and Adjacent Regions Brian Petrie, Roger Pettipas, Charles Hannah Bedford Institute of Oceanography Fisheries and Oceans Canada

General Circulation General 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 Surface Temperature Quest: Find coherent regional patterns in the SST variability. Process: Take all SST from 1985 to 2008; Define 23 sampling areas covering shelf regions Do an EOF analisys of the resulting time series

Sea Surface Temperature Longest east coast series Blue 5 year running mean obs; red 5y rmf model Trend Halifax none St Andrews +1 o C/century

100 year Air Temperature Trends North ~ 0 o C South – rise of 1 o C 1 Iqaluit, Cartwright, Sable <100y

Can Air Temperature predict SST? Observed SST Stat Model SST=f(Air T) Model captures main features but smoothes them; Underestimates anomalies = 0.76*Obs R 2 = 0.76

Are predictions acceptable for periods other than ? Avalon Channel predicted SST versus Station 27 observations: Predicted = 0.84*Observation, underestimates anomaly R 2 = 0.66, captures variability well Other areas: CSS 0.55*Obs, R 2 =0.44; Fundy 0.39*Obs, R 2 = 0.40.

If Air T were to rise by 2 o C Representative Annual SST rise ~ 1 o C based on air temperature projections for 2050

Depth-Averaged T/S Bay of Fundy Temperature shows trend towards higher values at 1.2 o C/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

Is the variation of integrated water temperature related to the local air temperature (a proxy for heat flux)?

Is salinity also connected strongly to local forcing as represented by the Saint John River outflow?

Stratification 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

Other Areas From 1950 to 2009, trends represent changes in density difference of for Hamilton Bank, for Stn 27 Avalon Chn, for Magdalen Shallows, for Georges Basin

 S(0)  0.18 S(0)  0.33 S(0)  0.49 T(0)  0.51 S(0)  0.30 T(0)  0.31 S(0) a) Direction of change between 1950 and 2009: b) Magnitude of change in density difference between 50 m and the surface. c) Series accounting for most of the variance: T(0), T(50), S(0), S(50) Background is sea surface temperature for April 2000 Changes in surface stratification between 1950 and 2009 a b c

Biological Impact of Stratification Greenness strongly correlated with stratification with last 15 years featuring high values of both Correlation is not causation. However production models suggest a 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

Ice Volume Nfld Labrador Ice volume shows a weak decreasing trend (270 km 3 /century); ice volume is highly correlated with ocean temperature (r 2 = 0.74, T increasing) and amount of subzero water (CIL) over northeast Nfld Shelf (r 2 = 0.61, CIL area decreasing).

Summary Long (90 y) record indicates +1 o C/century at St. Andrews; upper 90 m warming at same rate and freshening. Air temperature in southern half of region has been rising for last century (~1 o C); shelf SST can be constructed and hindcast well. Stratification shows increasing trends south of Labrador with surface salinity dominating until the Gulf of Maine. Declining ice volumes. Bottom 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 warmest.

Causes Salinity (Freshwater) has had the largest impact in the region Model projections indicate decreased freshwater inflow from St. Lawrence

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

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 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 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 warmest LabradorScotian Shelf Gulf of St. Lawrence

Summary Long (90 y) record indicates +1 o C/century at St. Andrews; upper 90 m warming at same rate and freshening Air temperature in southern half of region rising for last century (~1 o C); shelf SST can be constructed and hindcast well. Btm T responds coherently to NAO forcing with Nfld-Lab-GSL opposite to SSGoM Stratification shows increasing trends south of Labrador with surface salinity dominating until the Gulf of Maine. Declining ice volumes. Pentadal, decadal T/S are dominated by interannual variability but 8 of 16 areas show warmest.

Ocean Temperature and Salinity The oceans are warming globally by about 0.1 o C ( ), m; there has been considerable interannual and interdecadal variability. IPCC assessment shows 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. Here we assess the changes in the Atlantic region.