Additional reading: Stewart Ch. 6, Tomczak Ch. 5 SIO 210 Typical distributions of water properties (2 lectures) Fall 2014 Reading: DPO Chapter 4 Additional reading: Stewart Ch. 6, Tomczak Ch. 5 First problem set: due Oct. 11 (Friday) First lecture 1. Review of surface properties 2. Definitions - structures 3. Concepts 4. Water masses 5. 4-layer structure Second lecture 1. Upper layer 2. Intermediate layer 3. Deep and bottom layers 4. Time scales Talley SIO210 (2014)

1. Review: Surface temperature: note where the 4°C isotherm occurs (most ocean volume is colder than this) DPO Figure 4.1: Winter data from Levitus and Boyer (1994) Talley SIO210 (2014)

1. Review: Surface salinity Surface salinity (psu) in winter (January, February, and March north of the equator; July, August, and September south of the equator) based on averaged (climatological) data from Levitus et al. (1994b). DPO Fig. 4.15 Talley SIO210 (2014)

1. Review: Surface density (winter) Surface density sq (kg m–3) in winter (January, February, and March north of the equator; July, August, and September south of the equator) based on averaged (climatological) data from Levitus and Boyer (1994) and Levitus et al. (1994b). DPO Figure 4.19 Talley SIO210 (2014)

2. Definitions: structures Example: Pacific potential temperature section thermocline DPO Fig. 4.12a Talley SIO210 (2014)

2. Definitions: vertical structures (temperature) Mixed layer Thermocline Thermostad Dichothermal layer (T minimum) Typical North Pacific profiles DPO Figure 4.2 Talley SIO210 (2014)

Pacific potential temperature section Mixed layer Thermostad Thermocline thermocline Dichothermal layer (T minimum) DPO Fig. 4.12a Talley SIO210 (2014)

2. Definitions: Mixed layer depth Typically 20 to 200 m (late winter) Thicker (> 500) in some special locations, notably in (1) band in the Southern Ocean and (2) northern North Atlantic Using delta T = 0.2°C DPO Fig. 4.4c from Holte et al. Talley SIO210 (2014)

2. Definitions: Thermostads (pycnostads) Location of thermostads - coordinated structures, derived from thick winter mixed layers that are capped at the top by spring-summer warming, then spread into the interior along isopycnals Hanawa and Talley (2001); DPO 14.12 Talley SIO210 (2014)

2. Definitions: Pacific salinity vertical section Salinity minimum layers - intermediate waters (Antarctic and North Pacific I.W.) Salinity maximum layers DPO Fig. 4.12b Talley SIO210 (2014)

2. Definitions: Salinity X X X X Halocline Salinity minimum Talley SIO210 (2014)

2. Definitions: Shallow salinity maximum layer Vertical sections of (a) salinity and (b) oxygen (mmol/kg) with selected potential density contours, along approximately 25°W in the Atlantic Ocean. (c) Salinity at sq = 25.0 kg/m3. 2. Definitions: Shallow salinity maximum layer FIGURE S9.28 Talley SIO210 (2014)

2. Definitions: Intermediate water masses (salinity extrema) Low salinity intermediate layers (salinity minimum layers) High salinity intermediate layers (salinity maximum layers) DPO Fig. 14.13 Talley SIO210 (2014)

Pacific section of potential densit(ies) DPO Fig. 4.12 Talley SIO210 (2014)

2. Definitions: Typical potential density structure Pycnocline: Where density changes rapidly (large vertical gradient) Pycnostad: Where density changes slowly (small vertical gradient), generally refers to being embedded in the pycnocline, hence in the upper ocean. DPO Figure 4.20 Talley SIO210 (2014)

2. Definitions: Summary of terminology for vertical structure Mixed layer Thermocline, halocline, pycnocline: Vertical locations of high gradient (large ΔT/Δz, for thermocline, etc.) Thermostad, halostad, pycnostad: Vertical locations of low gradient, usually embedded in the …cline (small ΔT/Δz, for thermostad, etc.) Vertical extrema sometimes have names: salinity minima, temperature minima or maxima, etc. (e.g. dichothermal layer for very shallow temperature minimum usually in high latitudes Talley SIO210 (2014)

3. Concepts and mechanisms for ocean property distributions Flow is 3-dimensional: east, west, vertical x, y, z in local Cartesian coordinates longitude, latitude, vertical (l, f, z) in geographic coordinates. Also very useful to think of flow relative to isopycnal surfaces, which are not flat: x,y along isopycnals, w diapycnal Talley SIO210 (2014)

3. Concepts and mechanisms for ocean property distributions Ventilation (“breathing”): properties of ocean waters are mostly set initially at the sea surface (heat, freshwater, gas exchange) and modified internally (mixing, biological processes, radioactive decay) Isentropic (isopycnic) flow and mixing is much easier than diapycnal flow and mixing, so water parcels tend to follow isopycnals as they enter the ocean interior. Diapycnal mixing and diapycnal velocity are important for largest scale distributions Ocean tracers: chemical and dynamical properties that allow flow to be traced (from PPSW2 lecture) Talley SIO210 (2014)

3. Concepts: (a) Ventilation (upper ocean) through subduction Subduction: flow from surface mixed layer into interior along isopycnals. DPO Figure 7.15 Talley SIO210 (2014)

3. Concepts: (a) Ventilation of the upper ocean 400 m depth 300 m depth Surface outcrop: source of water for the this shallow isopycnal Water in ocean interior originates at surface outcrops. (There is no interior source of high density.) The water mostly flows into the ocean interior along isopycnals (presuming only weak diapycnal mixing). WOCE Pacific Atlas (2007) Talley SIO210 (2014)

3. Concepts: (a) Ventilation of the deep ocean Localized deep convection or brine rejection at high latitudes, with subsequent local turbulent mixing and then flow mostly along isopycnals DPO Fig. 14.14a Talley SIO210 (2014)

3. Concepts: (a) Ventilation of the deep ocean Low O2 (old water) 4000 m depth High O2 (new water) 3000 m depth Very local high latitude sources of water for the this deep isopycnal (Sources for this deep isopycnal include various sea ice formation regions along Antarctica, and dense water formation in the Nordic Seas, north of the N. Atlantic) WOCE Pacific Atlas (2007) Talley SIO210 (2014)

3. Concepts: (b) isentropic processes Flow and mixing is mostly along isopycnals (isentropes, isoneutral surfaces). Diapycnal flow requires diapycnal mixing, which is very weak (but crucially important at largest scales, even though flow and mixing are dominantly along-isopycnal). Talley SIO210 (2014)

Use tracers to help determine pathways of circulation, age of waters 3. Concepts: (d) Tracers Use tracers to help determine pathways of circulation, age of waters Conservative vs. non-conservative Natural vs. anthropogenic Radioactive vs. stable See and read textbook, Section 3.6, for list and description of commonly used tracers, e.g. oxygen, nutrients, carbon system, chlorofluorocarbons, helium isotopes, oxygen isotopes, carbon isotopes, Talley SIO 210 (2014)

Tracers on isopycnal surfaces Oxygen Chlorofluorocarbons WHP Pacific Atlas (Talley, 2007) Talley SIO 210 (2014)

Tracers on isopycnals 3He 14C WHP Pacific Atlas (Talley, 2007) Talley SIO 210 (2014)

4. Water masses (Tomczak and Godfrey, Ch. 5 definitions) Water mass: “body of water with a common formation history”. Names are capitalized. A water mass has an identifiable property (usually an extremum of some sort) an identifiable formation process Water type: point on a temperature-salinity diagram (or more carefully, point in property-property-property-nthproperthy space) Source water type: water type at the source of water mass In practice, we just name the first, but are always aware that there are specific properties at the sources. Talley SIO210 (2014)

4. Water mass Example: Antarctic Intermediate Water - (a) low salinity layer, (b) originating in surface mixed layers near Antarctic Circumpolar Current Talley SIO210 (2014)

5. The (approximately) 4-layered structure of the ocean We can use four layers to describe the world’s oceans. Upper ocean (down through the permanent pycnocline) Intermediate layer Deep layer Bottom layer Talley SIO210 (2014)

5. Atlantic vertical section: overall vertical structure Upper Intermediate Deep 4. Abyssal DPO Fig. 4.11 Talley SIO210 (2014)

5. Atlantic vertical section: overall vertical structure 4 layers Upper Intermediate Deep 4. Abyssal DPO Fig. 4.11 Talley SIO210 (2014)

5. Atlantic vertical section: overall vertical structure, 4 layers Upper Intermediate Deep 4. Abyssal DPO Fig. 4.11 Talley SIO210 (2014)

5. Atlantic vertical section: 4 layers and examples of the named water masses Central Water Antarctic Intermediate Water MediterraneanWater Labrador Sea Water North Atlantic Deep Water Antarctic Bottom Water DPO Fig. 4.11 Talley SIO210 (2014)

5. Four layers: Upper ocean Characterization: Surface mixed layer down through the main pycnocline. Location: In the tropics and subtropics and into the subpolar regions (bounded by the Antarctic Circumpolar Current to the south, and the northern marginal seas to the north) Formation mechanisms: late winter mixed layer properties are “subducted” into the ocean interior (slide down slightly inclined isopycnals from the mixed layer). “Central Water” Mixed layer properties are set by air-sea fluxes, and depth by wind stirring or buoyancy-driven convection Talley SIO210 (2014)

5. Four layers: Intermediate layer Characterization: large-scale salinity maximum and minimum layers. Location: just below the pycnocline in most of the ocean (especially tropics and subtropics), roughly 1000 to 2000 m depth. Originate from very specific sources (“injection sites”) in the Labrador Sea (“Labrador Sea Water”), the Mediterranean Sea (“Mediterranean Water”), the Red Sea (“Red Sea Water”), the Okhotsk Sea (“North Pacific Intermediate Water”), and the Drake Passage region (“Antarctic Intermediate Water”). Formation mechanisms: Deep convection (reaching to about 1500 m); brine rejection; vigorous mixing where boundary currents meet; otherwise nearly-isopycnal spreading Talley SIO210 (2014)

5. Four layers: Deep layer Characterization: This is a thick layer below the intermediate layer and above the bottom waters, characterized by extrema of salinity, oxygen, nutrients. Location: Roughly from 2000 to 4000 m depth. The “North Atlantic Deep Water” originates through deep water formation processes north of the N. Atlantic (joined by Labrador Sea and Mediterranean Sea intermediate waters). It is relatively “new”. The “Pacific Deep Water” originates through slow upwelling of bottom waters in the Pacific, and is the oldest water in the ocean. The “Indian Deep Water” is similar to the PDW. The “Circumpolar Deep Water” is a mixture of these new (NADW) and old (PDW and IDW) waters, plus new deep waters formed in the Antarctic (Weddell Sea etc.). Talley SIO210 (2014)

5. Four layers: Deep layer (continued) Formation mechanisms and history: varied including deep convection (Nordic Seas, Labrador Sea) brine rejection (Antarctic contribution to deep water) upwelling (ocean-wide) vigorous mixing at specific sites (strait overflows) spreading along isopycnals with minimal mixing Talley SIO210 (2014)

5. Four layers: Bottom layer Characterization: Densest, coldest layer Location: ocean bottom, usually connotes very dense water from the Antarctic. Various names: “Antarctic Bottom Water” “Lower Circumpolar Deep Water” Formation mechanism: brine rejection close to Antarctica Talley SIO210 (2014)