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

Halifax Sea Level Overall trend 1920-present, rise of 0.32 m/century RSL exceeds post-glacial rebound by 0.08 m over 90 y. Two periods, & present, exhibit different long term trends m/century 1970-present 0.19 m/century (<PGR model result of 0.23 cm/century)

How widespread? 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 Halifax sea level stats (-PGR) to project sea level to 2099 in 100 simulations (+PGR); Used range of IPCC projections to construct sea level rise. 0.4 m

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. 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 +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

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 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

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

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

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

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

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

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 Sea level increasing but since 1970 at ~PGR rate; coherent regional response 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 Pentadal, decadal T/S are dominated by interannual variability but 8 of 16 areas show warmest. Stratification shows increasing trends south of Labrador with salinity dominating. Projected trends in forcing- air T increasing, (precipitation- evaporation)/runoff decreasing, NAO increasing