Seminar 2

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Seminar 2
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Halocarbons, anthropogenic tracers Generally
chlorofluorocarbons (CFCs) CFC-11, CFC-12 and
CFC-113 and carbon tetrachloride (CCl4) or common
coolants in refrigerators and transformators,
propellants for spray cans and dry cleaning
fluid. The are released into the atmosphere and
can dissolve in seawater. Due to industrial
developments their atmospheric concentrations
increased and mutual ratio changed.
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Halocarbons can be used as tracer for recently
(100 year) ventilated water. Also as clock
tracer, because of changing mutual atmospheric
mixing ratios MRa, but Montreal Protocol, 1987
MR reconstructed atmospheric mixing
ratioCi seawater concentration of component i
Fi solubility function of component ICompare MR
with the known MRa and the ägeof the seawater is
known
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Equatorial upper NADW core. Formation in 1965,
based on CFC-11/CFC-12 mixing ratio, but CFC-11
is factor 10 below saturation level.
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Zonal distributions at A03, 36.5N
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Zonal distribution at A10, 30S
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(7) Water mass analysis of the Southern Ocean
10 meridional WOCE sections across the
wind-drivenAntarctic Circumpolar Current
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NADW enters the Southern and Indian Oceans along
the South-African continental margin
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Salinity in the Southern Ocean
NADW
North Atlantic Deep Water
Lower Circumpolar Deep Water
LCDW
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Potential Temperature in the Southern Ocean
NADW
NADW, 2.3C
LCDW, 1-2C, warm part of NADW is missing
LCDW
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AOU in the Southern Ocean
NADW
NADW, high oxygen core
LCDW below low oxygen core of Upper Circumpolar
Deep Water

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CFC-11 (pmol/kg) in the Southern Ocean
NADW
NADW is very low in CFCs (older than 100 year!)
LCDW
Less CFCs in the LCDW from the Weddell Sea to
Drake Passage
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NADW/LCDW is modified flowing from the southern
sector of the Atlantic in the ACC around
Antarctica
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(8) The Indian Ocean
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• Meridional Indian Ocean section I08
• high salinity core (LCDW) and cold AABW enter
  the Indian Ocean from the ACC
• salinitifcation due to Red Sea Water (RSW)
• ageing (high AOU) in ill flushed northern Indian
  Ocean. This NIDW leaves the Indian Ocean at a
  shallower level (gt UCDW)
• deep central Indian Basin ill flushed (low
  d14C). LCDW is relatively young (high d14C)

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• Zonal South Indian Ocean section I05P
• NADW/LCDW with S maximum at 2500 to 3500 m
• Fresher and older AABW below this level
• AAIW with S minimum at 1000 to 1500 m
• inflow of young low AOU NADW/LCDW and AABW in
  western side of basins
• outflow of aged high AOU NIDW along eastern side
  of Indian Ocean basins

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• 2-dimensional frequency distribution in q-S space
• maximum in transition between the IDW/LCDW and
  the AABW cores
• secondary maximum AABW in the Australian-Antarcti
  c Basin
• ridges toward warm and saline RSW and low S AAIW

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(9) The Pacific Ocean
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• Meridional Pacific Ocean section P15
• inflow of high salinity LCDW (1 to 1.5C
• inflow of colder low salinity AABW (lt1C)
• strong mixing of AABW, LCDW and overlying water
  causes near homogenous deep stratification north
  of the equator (Pacific Deep Water, PDW)
• low S AAIW and Pacific Arctic Intermediate water
  (PAIW)
• very low salinity surface water

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ageing along P15 from biogeochemical tracers
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• Ageing in the north Pacific from the clock tracer
  d14C ()
• bottom water is about 950 years older than AABW
  in Southern Ocean, or 650 years relative to LCDW
• water at 2000 m is about 300 years older than
  near the bottom (gt slow upwelling!)

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• q-S frequency distribution
• primary peak, PDW in North Pacific
• secondary peak AABW in South Pacific
• ridge to AAIW and PAIW

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• Zonal section P06 at 35S
• sloping isotherms (isopycnals) suggest deep
  northward inflow through South Pacific Basin
• northward flow of AABW, and LCDW and UCDP
• outflow of aged PDW along South America at
  shallower levels
• freshest AAIW near South America

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• Zonal section P03 at 25N
• difference between distributions of Silicate and
  AOU (and PO4 and NO3) because of different
  biogeochemical cycles.
• Silicate dissolves from biogenic silicium
  (diatom shells), mainly near/at the bottom
• AOU, PO4, and NO3 are influenced by (microbial)
  re-mineralization of soft organic matter (POM and
  DOM) mainly in the water column
• both the AOU maximum and the Si maximum are
  found near the eastern boundary of the North
  Pacific, at shallower levels than bottom layer

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• Data from the Indian and Pacific Oceans suggest
• Deep inflow from the Southern Ocean of AABW and
  LCDW
• Transformation of the deep water mass in the
  ocean basins through mixing, biogeochemical and
  physical ageing
• The oldest water is not found at the bottom, but
  at levels shallower than the inflow
• The oldest water is found along the eastern
  boundary of the ocean basins
• The old water returning to the Southern Ocean on
  the eastern side of the ocean basins has
  properties similar to UCDW
• UCDW in the Southern Ocean contains
  re-circulated deep and bottom water
• Apparently the inflowing water loses density and
  rise to shallower levels in the basins (deep
  upwelling) and then leave for the southern ocean
  after hundreds of years
• The deep water only can lose density if
  turbulent mixing with the overlying less dense
  water takes place! This mixing may be the key
  process, which maintains the THC.

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(10) The return flow

• After the deep upwelling the North Atlantic
  components of the cold abyssal branch have to
  return the their formation regions in the
  northern North Atlantic Ocean. This may occur via
  different routes proposed by Gordon
• From the North Pacific via Bering Strait and the
  Polar Ocean to the North Atlantic Ocean
• Warm Pacific mode waters through the Indonesian
  seas, the Indian Ocean, around South Africa into
  the Atlantic Ocean (the warm water route)
• Colder AAIW (and UCDW) from the southern ocean
  to the Atlantic Ocean (the cold water route)

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Through the shallow Bering Strait (45 m) about
0.8 Sv flows to the Chukchi Sea. This is mainly a
wind-driven transport. During the Ice ages this
route was blocked because of the lower sea level.
There existst hydrographic evidence for this
route.
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The warm Water Route Scheme of the Indonesian
Trough Flow (ITF) route if the water does not
re-circulate around Australia.
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The meridional distribution of salinity along
WOCE section P08 in the western Pacific Ocean.
The gray band shows the depth of the potential
density anomaly interval coinciding with the core
of the ITFW in the Makassar Strait (gq 25.35 to
25.85 kg/m3). The main source for the ITF is in
the North Pacific.
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Meridional section I10, south of Java. The ITF
water is relatively fresh and old.
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In the Indian Ocean the low salinity ITF water in
the South Equatorial current is salinified on its
way westwards
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The development of the salinity minimum in the
isopycnal of the ITF core density layer from the
western tropical Pacific to an Agulhas Ring in
the Atlantic Ocean near South Africa
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ITF water that does not re-circulate in the
Indian subtropical gyre ends in large eddies
(Agulhas rings), which are shed of the Agulhas
Current near South Africa and drift into the
Atlantic Ocean (Agulhas leakage)
S at 150 dbar
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The cold water route There are two cold water
types in the southern Atlantic, which can flow
northwards
S minimum from 50S
Si maximum from 50S
A16 section

• AAIW is formed in the south-eastern Pacific as
  Sub-Antarctic mode water (SAAMW) and enters the
  Atlantic sector via Drake Passage
• UCDW (aged AABW and LCDW) from the Indian and
  Pacific Oceans enters the Atlantic sector also
  via Drake Passage

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AAIW subducts into the subtropical thermocline,
seen on the A12 section near Greenwich meridian
Salinity minimum between g 27.1 to 27.3 kg/m3
potential isopycnals
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Hydrographic properties in S minimum (light blue)
and Si maximum (purple) along A16 section There
is hardly any difference between AAIW and UCDW
north of the equator
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Two cores off French Guyana in the North Brazil
Under Current (52W) on the A20 section
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Hydrographic properties from the Caribbean Slope
Current (green) and Gulf Stream (red) show the
combined AAIW/UCDW core on the A22 section
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RV Tyro section from 1983 between Iceland and the
Shetland Islands
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RV Tyro section from 1983 between Iceland and the
Shetland Islands
Warm Atlantic waters enters the Norwegian Sea