Salinity distribution in the Oceans Average practical salinity of open ocean waters ≈ 34.72 http://eps.mcgill.ca/~courses/c542/ 1/58 Salinity distribution in the Oceans Factors that control seawater salinity: 1) Evaporation 2) Precipitation (rainfall) 3) Concentration of salts in freezing seawater 4) Dilution with melting ice 5) Continental runoff 6) Transport by ocean currents 7) Mixing 8) Seepage of groundwater 9) Dissolution of ancient evaporite deposits and salt domes Whereas the first five are effective only at the sea surface, at depth, the salinity distribution is governed almost exclusively by 6) and 7). Other factors (e.g., 8) and 9)) are only of local significance. 2/58 Salinity distribution in the Oceans (the balance between evaporation and precipitation) 3/58 Salinity distribution in the Oceans (evaporation and precipitation – atmospheric circulation) Jet stream 4/58 Earth Global Circulation 5/58 The surface currents of the world oceans Pacific Ocean Atlantic Ocean Southern Ocean 6/58 Salinity distribution in the Oceans (ice formation and brine rejection) Brine channels Ice stalactites 7/58 8/58 Salinity distribution in the Oceans (stratified and mixed estuaries) 9/58 10/58 Strait of Belle-Isle LOWER UPPER Cabot Strait RIVER Freshwater discharge = 11,900 m3 s-1 11/58 The St. Lawrence Estuary (a partially stratified estuary) 2 2 1 1 1 2 12/58 Esquiman Channel Anticosti Channel Tadoussac Rimouski Trois-Pistoles Cabot Strait 13/58 The St. Lawrence Estuary, Gulf and continental shelf Belle-Isles Strait Esquiman Anticosti Channel Laurentian Trough Channel Tadoussac Rimouski Cabot Strait Laurentian Trough 14/58 R/V CORIOLIS II 15/58 https://vimeo.com/273233701 16/58 17/58 The St. Lawrence Estuary (a partially stratified estuary) IML2002066 , 07-NOV-2002 14:47:23 0 -100 -200 Depth (m) Depth -300 -400 10 20 30 40 50 60 70 80 90 Oxygen saturation (%) 0 1 2 3 4 5 6 ° Temperature ( C) 28 29 30 31 32 33 34 35 36 Salinity 23 23.5 24 24.5 25 25.5 26 26.5 27 27.5 28 σ -3 Density (kg m ) 18/58 t The St. Lawrence Estuary (a partially stratified estuary) Lower St- Lawrence Atlantic Continental Estuary Gulf of St-Lawrence Shelf 0 Surface Layer 100 Intermediate (Cold) Layer (<0°C) 200 Deep Layer (S= 34.6 T= ~5°C) 300 Depth (m) Depth 400 500 TADOUSSAC CABOT STRAIT 0 200 400 600 800 1000 1200 1400 Distance from Quebec City (km) 19/58 The St. Lawrence Estuary (a partially stratified estuary) Lower St- Lawrence Atlantic Continental Estuary Gulf of St-Lawrence Shelf 0 Surface Layer 100 Intermediate (Cold) Layer (<0°C) 200 Deep Layer (S= 34.6 T= ~5°C) 300 Depth (m) Depth 400 500 TADOUSSAC CABOT STRAIT 0 200 400 600 800 1000 1200 1400 Distance from Quebec City (km) 20/58 21/58 The Saguenay Fjord 22/58 Salinity distribution in the Oceans (ocean currents and circulation) 23/58 Salinity distribution in the Oceans (ocean currents and circulation) Salinity 34.5 1000 T 2000 Depth (m) 3000 24/58 Salinity distribution in the Oceans (ocean currents and circulation) 25/58 Salinity distribution in the Oceans (ocean currents and circulation) 26/58 Salinity distribution in the Oceans (ocean currents and circulation) AAIW AADW AABW AABW – Antarctic Bottom Water AADW – Antarctic Deep Water AAIW – Antarctic Intermediate Water NADW – North Atlantic Deep Water 27/58 Salinity distribution in the Oceans (ocean currents and circulation) AABW 28/58 29/58 The thermohaline circulation 30/58 Salinity distribution in the Oceans (the signature of water masses and T-S diagrams) 31/58 Geochemical tracers of ocean circulation t1/2 = 12.32 yrs t1/2 = 5730 yrs One TU = 1 atom of tritium for every 1018 atoms of hydrogen. 32/58 Geochemical tracers of ocean circulation = ventilation time or age of the water mass 33/58 Geochemical tracers of ocean circulation Atlantic Ocean 34/58 Geochemical tracers of ocean circulation 35/58 The thermohaline circulation 36/58 Salinity distribution in the Oceans (the signature of water masses and T-S diagrams) 37/58 Salinity distribution in the Oceans (mixing and caballing) Tmix ≈ (m1 T1 + m2 T2)/(m1 + m2) Smix = (m1 S1 + m2 S2)/(m1 + m2) 38/58 Long-term mean temperature, salinity and DO saturation estimated on the 27.25 kg m-3 potential density surface. Gilbert et al., Limnol. Oceanogr. (2005) 39/58 Salinity distribution in the Oceans (mixing, caballing and tie lines) 1930 – 72% Labrador/28% WC Atlantic 1985 – 53% Labrador/47% WC Atlantic Gilbert et al., Limnol. Oceanogr. (2005) 40/58 Validity of the law of constant relative proportions 1. Estuarine Mixing 2. Anoxic Basins 3. Freezing 4. Precipitation and Dissolution 5. Evaporation 6. Submarine Volcanism 7. Admixture with Brines 8. Diagenesis 41/58 River compositions Europe Africa Asia 2+ Mg Ca2+ 2+ 2+ 2+ Ca 2+ Ca Mg + Mg K + Na + + Na+ K Na - - Cl SiO Cl - 2 Cl SiO2 2- SiO2 SO 2- - 4 2- - - SO SO4 HCO3 NO 4 - NO3 - 3 HCO HCO3 3 N. America S. America Australia + + K 2+ K 2+ Mg 2+ 2+ Ca Ca Mg 2+ Ca2+ Mg + + + Na - Na Na Cl - K+ Cl SiO2 2- - SO SiO2 Cl 4 SiO2 - 2- 2- HCO 3 - SO4 - SO4 HCO3 HCO3 42/58 Seawater and “mean river” compositions Seawater River Water 2+ 2+ Na+ Ca Mg 2+ 2+ Mg K+ 2- Ca SO4 + K+ Na 2- - SO4 Cl SiO2 - - Cl HCO3 43/58 Anoxic basin Sea River S = 10 S =35 O2 H2S 2- - SO4 + 2 “CH2O” H2S + 2 HCO3 44/58 Anoxic basin (Black Sea) o TEMPERATURE ( C) SIGMA - T 6 8 10 12 14 10 12 14 16 18 0 0 50 50 100 100 150 150 S 200 200 250 250 DEPTH (m) DEPTH DEPTH (m) DEPTH 300 300 t 350 350 400 400 18 19 20 21 22 SALINITY 45/58 Anoxic basin (Black Sea) Mn (µM) Co (nM) Ni (nM) Cu (nM) 0 2 4 6 8 10 0 1 2 3 4 5 0 2 4 6 8 10 12 0 2 4 6 8 0 0 0 0 400 400 400 400 800 800 800 800 1200 1200 1200 1200 DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH 1600 1600 1600 1600 2000 2000 2000 2000 Fe (nM) Pb (pM) Cd (pM) Zn (nM) 0 100 200 300 0 40 80 120 0 50 100 150 200 0 2 4 6 8 10 12 0 0 0 0 400 400 400 400 800 800 800 800 1200 1200 1200 1200 DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH 1600 1600 1600 1600 2000 2000 2000 2000 46/58 Anoxic basin (Framvaren Fjord, Norway) 47/58 Anoxic basin (Framvaren Fjord, Norway) µ Salinity O2 ( M) 12 14 16 18 20 22 24 0 50 100 150 200 250 300 350 0 20 Oxygen 40 60 σt Temp. 80 Salinity 100 DEPTH (m) DEPTH DEPTH (m) DEPTH 120 Sulfide 140 160 180 6 8 10 12 14 16 18 20 0 2 4 6 8 Temperature (oC) and Sigma-T H2S (mM) 2- - SO4 + 2 “CH2O” H2S + 2 HCO3 48/58 Anoxic basin (Framvaren Fjord, Norway) Ni (nM) Cu (nM) Mn (µM) Co (nM) 0 4 8 12 16 0 2 4 6 8 10 0 2 4 6 8 0 2 4 6 0 0 0 0 40 40 40 40 80 80 80 80 120 120 120 120 DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH 160 160 160 160 200 200 200 200 Fe (nM) Pb (pM) Cd (pM) Zn (nM) 0 500 1000 1500 2000 0 200 400 600 0 200 400 600 0 20 40 60 0 0 0 0 40 40 40 40 80 80 80 80 120 120 120 120 DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH DEPTH (m) DEPTH 160 160 160 160 200 200 200 200 49/58 Anoxic basin (Framvaren Fjord, Norway) TCO2 (mM) 0 4 8 12 16 20 24 O , H S (µM) 2 2 pH 0 40 80 120 160 200 240 280 6.6 6.8 7.0 7.2 7.4 7.6 7.8 8.0 8 0 10 20 12 40 Oxygen 14 60 16 80 18 Mn(II) 100 20 TA DEPTH (m) DEPTH 120 22 (m) DEPTH pH 24 140 Fe(II) Sulfide TCO2 26 160 28 180 0 4 8 12 16 20 Mn(II) (µM) 200 0 4 8 12 16 20 0 1 2 3 4 5 TA (mM) Fe(II) (µM) 2- - SO4 + 2 “CH2O” H2S + 2 HCO3 50/58 Anoxic basin (Cariaco Trench) TA (mmol kg-1) 2.3 2.4 2.5 2.6 2.7 2.8 SALINITY [O2] (µM) pH 20 22 24 26 28 30 32 34 36 38 40 0 50 100 150 200 250 7.8 8.0 8.2 8.4 0 0 0 200 Temp. 200 Oxygen 200 400 400 400 TCO2 600 600 600 Sigma-T TA 800 800 800 DEPTH (m) DEPTH Salinity (m) DEPTH DEPTH (m) 1000 1000 Sulfide 1000 pH 1200 1200 1200 1400 1400 15 20 25 30 1400 0 20 40 60 2.0 2.1 2.2 2.3 2.4 2.5 o TEMPERATURE ( C) -1 [H2S] (µM) TCO2 (mmol kg ) 51/58 Freezing (ice formation and brine rejection) Brine channels Besides excluding salts when ice forms, some differential fractionation of the major ions takes place during freezing. For example, sea ice retains proportionally 2- - more sulfate than chloride and, consequently, the SO4 :Cl ratio is lowered in the residual water.