Oceanography “If everything seems to Lecture 10 be going well, Obviously you’ve a. Density of Seawater overlooked something!” a. Density of Seawater b. TS Diagrams “If Barbie is so popular, c. Density structure of the ocean why do you have to buy her friends! Density: Temperature, Salinity, and Pressure 3 th Density: ! S,T,P = 1.02594 g/cm must be known to the 5 decimal The symbol used to express density is " (sigma). "T (or "#) = (specific gravity – 1) x 1000 Specific gravity = density of a substance/density of water It is the density of a parcel of water of specific T and S that is brought up to the surface (no pressure effect!) "T = ((1.02594/1.0000) – 1) x 1000 = 25.94 No units! T-S Diagram Salinity (‰) 29 31 33 35 37 25 ! t 24.0 ! ! t 23.0 t 25.0 ! t 26.0 20 ! t 27.0 15 10 ! Increasing density t 28.0 Temperature (°C) 5 0 Density: Density Structure of the Oceans: Depth Point D is denser than point B 5°C Warming leads to higher change in density at high T vs. low T The boundary zone between the surface-water and deep-water layers is the pycnocline layer (density gradient): Transition zone where “light” surface water grades into “denser” deep-water layers. Density Structure of the Oceans: Depth Uniformity of Ocean Water? 75% of the total Ocean volume have a ! Temperature: 0-5°C ! Salinity: 34-35‰ Oceans’ depths are filled with cold water (colder than the ~17.5°C average T of the Oceans’ surface waters). Most of this water must have originated in polar latitudes, where it was chilled by losing heat to the frigid air. Uniformity of T and salinity of subsurface seawater from The Ocean can be divided into three structures: Ocean to Ocean suggests that Surface layer; Pycnocline; Deep-layer. Ocean basins are open systems! Pycnocline: Amounts to ~18% of the Oceans volume) Vertical Temperature & Salinity T-S Diagram Temperature vs Depth Salinity vs Depth Salinity (‰) Salinity (‰) Temperature (°C) 34 34.5 35 35.5 36 34 34.5 35 35.5 36 36.5 37 -0.5 4.5 9.5 14.5 19.5 0 0 24 ! 23.0 ! 25.0 t ! 24.0 t t !t 26.0 1000 1000 19 !t 27.0 Potent. T Water is lighter at surface 2000 2000 14 ! Depth (m) 3000 9 t 28.0 3000 Depth (m) 4000 Temperature (°C) 4 4000 Every “bend” represents a In situ T -1 new water mass 5000 5000 Latitudinal Difference in Density Deep water circulation: A model Heavy Caballing: When two water masses merge, the combination of their temperatures and salinities results in densification vertical Light advection of water T has a much greater impact than S on Density! High latitudes (>60ºN and S) Density Structure of the Atlantic Ocean: A model Deep water circulation: A model Density Structure of the Pacific Ocean Density Structure of the Indian Ocean.