SIO 210 Typical distributions (2 lectures) Fall 2014 Reading:
DPO Chapter 4 Chapter S7 (or 7) sections 7.4.1, 7.8.5, 7.10.1,
7.10.2 First lecture 1. Definitions - structures 2. Concepts 3.
Water masses 4. 4-layer structure Second lecture 1. Upper layer 2.
Intermediate layer 3. Deep and bottom layers 4. Time scales Talley
SIO210 (2014)
Slide 2
The approximately layered structure of the top-to-bottom ocean:
Now in more detail 1.Upper ocean (down through the permanent
pycnocline) a. Surface mixed layer b. Pycnocline/thermocline c.
Pycnostad/thermostad embedded in pycnocline (mode water)
2.Intermediate layer 3.Deep layer 4.Bottom layer Talley SIO210
(2014)
Slide 3
Mixed layers Surface layer of the ocean is almost always
vertically mixed to some degree In summer, calm, warm conditions,
the mixed layer might be very thin (several meters) At the end of
winter, after the full season of cooling and storms, mixed layers
reach their maximum thickness Mixed layers are created by Wind
stirring (max. depth of such a mixed layer is around 100 m) Cooling
and evaporation (increasing the density of the surface water),
which creates vertical convection. Max. depth of these mixed layers
can range up to about 1000 m, but is mainly 200-300 m. Talley
SIO210 (2014)
Slide 4
Maximum mixed layer depth (mainly late winter in each location)
DPO Fig. 4.4c from Holte et alUsing delta T = 0.2C Typically 20 to
200 m Thicker (> 500) in some special locations, notably in (1)
band in the Southern Ocean and (2) northern North Atlantic Talley
SIO210 (2014)
Slide 5
Mixed layer development Large, McWilliams and Doney (Rev.
Geophys 1994) Winter development of mixed layer: Wind stirring and
cooling erode stratification, gradually deepening the mixed layer
to maximum depth at the end of winter (Feb. to April depending on
location) Summer restratification: Warming at the top adds
stratified layer at surface, usually leaves remnant of winter mixed
layer below. DPO Figure 4.8 Talley SIO210 (2014)
Slide 6
Mixed layer development Winter development of mixed layer: Wind
stirring and cooling erode stratification, gradually deepening the
mixed layer to maximum depth at the end of winter (Feb. to April
depending on location) Summer restratification: Warming at the top
adds stratified layer at surface, usually leaves remnant of winter
mixed layer below. DPO Figure 7.3 Talley SIO210 (2014)
Slide 7
The approximately layered structure of the top-to-bottom ocean
1.Upper ocean (down through the permanent pycnocline) a. Surface
mixed layer b. Pycnocline/thermocline c. Pycnostad/thermostad
embedded in pycnocline (mode water) 2.Intermediate layer 3.Deep
layer 4.Bottom layer Talley SIO210 (2014)
Slide 8
Thermocline (pycnocline) Two separate physical processes:
1.Vertical balance: mixing between warm, light surface waters and
cold, dense deep waters, plus upwelling (diffusive process)
2.Circulation of denser surface waters down into interior and thus
beneath the lower density surface layers (subduction) (advective
process) DPO Fig. 4.5 (1) Talley SIO210 (2014)
Slide 9
Thermocline (pycnocline) Two separate physical processes:
1.Vertical balance: mixing between warm, light surface waters and
cold, dense deep waters, plus upwelling (diffusive process)
2.Circulation of denser surface waters down into interior and thus
beneath the lower density surface layers (subduction) (advective
process) DPO Fig. 7.15 (2) Talley SIO210 (2014)
Slide 10
Creation of the thermocline through subduction Iselin (1939):
equivalence of surface properties on transect through N. Atlantic
with properties on a vertical profile in the subtropical gyre
--> hypothesized that properties are advected into the interior
from the sea surface Circles: section 1 Squares: section 2
Continuous plots: vertical profiles xx Talley SIO210 (2014)
Slide 11
The approximately layered structure of the top-to-bottom ocean
1.Upper ocean (down through the permanent pycnocline) a. Surface
mixed layer b. Pycnocline/thermocline c. Pycnostad/thermostad
embedded in pycnocline (mode water) 2.Intermediate layer 3.Deep
layer 4.Bottom layer Talley SIO210 (2014)
Slide 12
Thermostad development: Subtropical Mode Water (Eighteen Degree
Water) Section across Gulf Stream Thickening of
isotherms/isopycnals is the thermostad/pycnostad Forms at surface
as a thick mixed layer near Gulf Stream in late winter. Circulates
into the interior south of the Gulf Stream along isopycnals WHP
Atlas Atlantic Pot. Temp. Neutral density Talley SIO210 (2014)
Slide 13
Mode water: definition, location and development
Pycnostads/thermostads embedded in the pycnocline occur in
identifiable regions They usually occur on the warm (low density)
side of strong currents Example (previous slide): Gulf Stream has a
pycnostad/thermostad at about 18C on its south (warm) side. Because
a pycnostad has a large volume of water in a given
temperature-salinity interval, these waters were termed Mode
Waters, to indicate that the the mode of the distribution of volume
in T/S space occurs in these particular T/S ranges. Talley SIO210
(2014)
Slide 14
Mode Waters Location of especially strong, permanent
thermostads/pycnostads - derived from thick winter mixed layers
that then spread into the interior along isopycnals (subduct)
Hanawa and Talley (2001); DPO 14.12 Gulf Streams Eighteen Degree
Water (Subtropical Mode Water of the North Atlantic) from previous
slide Talley SIO210 (2014)
Slide 15
Chlorofluorocarbon (CFC) water column inventory (conservative
anthropogenic tracer) Importance of mode waters for dissolved gas
inventories Willey et al. (GRL 2004) Talley SIO210 (2014)
Slide 16
Anthropogenic CO2 Importance of mode waters for dissolved gas
inventories Khatiwala et al. (Biogeosciences 2013) Talley SIO210
(2014)
Slide 17
The approximately layered structure of the top-to-bottom ocean
We are using four layers to describe the worlds oceans. 1.Upper
ocean (down through the permanent pycnocline) 2.Intermediate layer
3.Deep layer 4.Bottom layer Talley SIO210 (2014)
Slide 18
Pacific intermediate waters DPO Fig. 4.12 North Pacific
Intermediate Water (NPIW) Antarctic Intermediate Water (AAIW)
Intermediate depth (500-2000 m), vertical salinity minima Talley
SIO210 (2014)
Slide 19
Intermediate water production sites Intermediate water masses
Labrador Sea Water: salinity minimum, deep convection in Labrador
Sea Mediterranean Overflow Water: salinity maximum, evaporation and
cooling in Mediterranean Sea, overflow Antarctic Intermediate
Water: salinity minimum, medium convection in Drake Passage region
Red Sea Overflow Water: salinity maximum, evaporation in Red Sea,
overflow North Pacific Intermediate Water (Okhotsk Sea): salinity
minimum, brine rejection in the Okhotsk Sea DPO Fig. 14.13 Pacific
intermediate waters from previous slide Talley SIO210 (2014)
Slide 20
Atlantic intermediate waters DPO Fig. 4.11 Labrador Sea Water
(LSW) Mediterranean Water (MW) Antarctic Intermediate Water (AAIW)
Intermediate depth (500-2000 m), vertical salinity minima AND
maximum Talley SIO210 (2014)
Slide 21
Intermediate water production sites Intermediate water masses
Labrador Sea Water: salinity minimum, deep convection in Labrador
Sea Mediterranean Overflow Water: salinity maximum, evaporation and
cooling in Mediterranean Sea, overflow Antarctic Intermediate
Water: salinity minimum, medium convection in Drake Passage region
Red Sea Overflow Water: salinity maximum, evaporation in Red Sea,
overflow North Pacific Intermediate Water (Okhotsk Sea): salinity
minimum, brine rejection in the Okhotsk Sea DPO Fig. 14.13 Atlantic
intermediate waters from previous slide Talley SIO210 (2014)
Slide 22
Atlantic intermediate waters viewed in Potential
temperature-salinity Mediterranean Overflow Water Labrador Sea
Water North Atlantic Deep Water Antarctic Intermediate Water
Antarctic Bottom Water Blue: N. Atlantic > 15N Red: 15S-15N
Green: S. Atlantic < 15S Talley SIO210 (2014)
Slide 23
The approximately layered structure of the top-to-bottom ocean
Four layers to describe the worlds oceans. 1.Upper ocean (down
through the permanent pycnocline) 2.Intermediate layer 3.Deep layer
4.Bottom layer Talley SIO210 (2014)
Slide 24
Bottom properties Potential temperature: high in N. Atlantic
and eastern S. Atlantic (other highs are due to shallower bottom)
Salinity: high in N. Atlantic and Indian DPO 14.14b,c (Mantyla and
Reid, 1983) Talley SIO210 (2014)
Slide 25
Deep and bottom water production sites sites Deep and bottom
water North Atlantic Deep Water: high salinity, high oxygen;
mixture of NSOW, LSW and MOW; formed at sea surface through deep
convection Antarctic Bottom Water: very cold, high oxygen; formed
near sea surface along coast of Antarctica through sea ice
formation- brine rejection Indian and Pacific Deep Waters: low
oxygen, high nutrients; slow upwelling and slow deep mixing of
inflowing NADW and AABW DPO Fig. 14.14a Talley SIO210 (2014)
Slide 26
Atlantic deep and bottom waters Antarctic Bottom Water (AABW)
Cold bottom waters from Antarctic region Talley SIO210 (2014)
Slide 27
Atlantic deep and bottom waters DPO Fig. 4.11 Antarctic Bottom
Water North Atlantic Deep Water (NADW) (high salinity in tropics
and S. Atlantic) Talley SIO210 (2014)
Slide 28
Atlantic deep and bottom waters DPO Fig. 4.11 Antarctic Bottom
Water North Atlantic Deep Water (NADW) (high oxygen) (This very low
O 2 is due to intense biological activity and not age) Labrador Sea
Water Talley SIO210 (2014)
Slide 29
NADW and AABW in the abyssal ocean NADW and AABW both occupy
the deep and bottom layers, although AABW clearly dominates at the
bottom. Maps of the fraction of water at mid-depth and at the
bottom that are NADW or AABW. (Only two water masses were included
in the analysis: these are the surface source waters.) (Johnson et
al., 2008) DPO 14.15 Talley SIO210 (2014)
Slide 30
Atlantic deep/bottom waters viewed in Potential
temperature-salinity Mediterranean Overflow Water Labrador Sea
Water North Atlantic Deep Water Antarctic Intermediate Water
Antarctic Bottom Water Blue: N. Atlantic > 15N Red: 15S-15N
Green: S. Atlantic < 15S Talley SIO210 (2014)
Slide 31
Pacific deep and bottom waters DPO Fig. 4.12 Antarctic Bottom
Water (lower salinity) Remnant NADW (high salinity) Talley SIO210
(2014)
Slide 32
Pacific deep and bottom waters DPO Fig. 4.12 Antarctic Bottom
Water (high oxygen) Pacific Deep Water (low oxygen, old water)
Talley SIO210 (2014)
Slide 33
Pacific deep and bottom waters DPO Fig. 4.24 Pacific Deep Water
(extreme carbon-14, and no CFCs very old water) Talley SIO210
(2014)
Slide 34
Ventilation age (years) based on radiocarbon (Broecker et al.,
2004) Based on difference in radiocarbon age between surface and
deep water. (Taking into account anthropogenic (bomb) radiocarbon
in the surface waters, the actual deep Pacific age should be more
like 1250 years.) (Broecker et al., 2004) Talley SIO210 (2014)
Slide 35
Global deep water potential temperature- salinity Worthington,
1982 4C 0C Pacific Deep Water (or Common Water) Antarctic Bottom
Water Indian Deep Water North Atlantic Deep Water DPO 4.17b Talley
SIO210 (2014)
Slide 36
Deep and bottom water production sites Deep and bottom water
Nordic Seas Overflow Water (contributor to North Atlantic Deep
Water): high oxygen; deep convection in the Greenland Sea, overflow
North Atlantic Deep Water: high salinity, high oxygen; mixture of
NSOW, LSW and MOW Antarctic Bottom Water: very cold, high oxygen;
brine rejection along coast of Antarctica Indian and Pacific Deep
Waters: low oxygen, high nutrients; slow upwelling and slow deep
mixing of inflowing NADW and AABW DPO Fig. 14.14a Talley SIO210
(2014)