douglas g. martinson lamont-doherty earth observatory columbia university [email protected] 12...
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Douglas G. MartinsonLamont-Doherty Earth ObservatoryColumbia University
12 years of Palmer LTER: 12 years of Palmer LTER: Physical Oceanography, Physical Oceanography,
Spatiotemporal Variability & Spatiotemporal Variability & Ventilation of Ocean Heat Along Ventilation of Ocean Heat Along the Western Antarctic Peninsulathe Western Antarctic Peninsula
Photo: Dr. R.C. Smith, Sep. 2001
mstecker.com/pages/antsatmap.htm
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Location Map & Grid
--60
BellingshausenSea
An.
Ad.
B.
A.
R.
L.
M.B.SLOPE
SHELF
COAST
Sample region
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
SHELF
SLOPE COAST
SLOPE
SHELF
COAST Bathymetric Shading:
White ≥ 750 m
750 > light-grey ≥450 m
Dark-grey < 450 m
Background
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
0.107˚ C/year Significant at 0.05~5.4x global average
PerennialIce
Western Antarctic Peninsula
Most rapid recent regional winter warming on Earth
Major loss of perennial sea ice
87% of glaciers are in retreat
Motivation
Vaughan et al., 2003
Stammerjohn et al., 2006 Cook et al., 2005
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
1.70˚
2.13˚
34.75
34.54
Source of Winter Heat
ACC-coreUCDW
ANTARCTIC (summer) SURFACE WATERS
(AASW)
WW
PAL LTER Grid (1992-2004)WOCE SP04: WAP ACC (February 1992)
NBP94-04: Bellingshausen Slope (March 1994)
Major global volumetric modes#31
#33
#51
#55
#59
Source of heat
3.5–4˚C
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Bellingshausen Sea
Amundsen Sea
Weddell gyre
Ross gyre
BellingshausenSea
PAL LTERSampling Grid
Proximity of ACC
wAP is unique as only location with ACC directly adjacent to shelf
SLOPE
SHELF
COAST
Antarctic Circumpolar Current
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
r
SC–
MA+OA
+
NC–
1993-2004 climatology r[z(max), Dynamic Topo]
Delivery of UCDW
UCDW pulled onto shelf by upwellingdynamics (likely wind-driven)
Individual years consistent with drifter data (our only absolute velocity obs)
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Seasonal Cycle
Martinson and Takahashi, in prep
CO2D, POD, etc.
TD, SD, D
CO2 Venting
CO2, PO, etc.
Tf, S, winter
Biology
F
CO2D, POD, etc.
TD, SD, D
Tsummer
CO2 Uptake
Ssummer,
w
CO2, PO, etc.
Tf, S, winter
Shelf heat flux
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
FT: Bulk Parameter vs Measured (AnzFlux, 1994)
<FTBP>W = 29.67 Wm2(Martinson & Iannuzzi,
1998)<FT
Obs>W = 27.7 Wm2 (McPhee et al., 1999)
Shelf heat flux
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Bulk heat flux and Entrainment/diffusive heat flux ratio
FET/FDTFT
W/m2
Shelf heat flux
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Slope (~20 km off-shelf) Temperature
Grid line Grid line
Depth (db)
Depth (db)
2000 2001
2002 2003
Temperature (˚C)
Qslope
€
ΔQ(slope −shelf ) = FSΔt S + FwΔt w
€
Q1
M
Qn
⎡
⎣
⎢ ⎢ ⎢ ⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥ ⎥ ⎥ ⎥
=
Δt S1 365 − Δt S1
M M
Δt Sn 365 − Δt Sn
⎡
⎣
⎢ ⎢ ⎢ ⎢ ⎢ ⎢
⎤
⎦
⎥ ⎥ ⎥ ⎥ ⎥ ⎥
< FS >
< Fw >
⎡
⎣ ⎢ ⎢
⎤
⎦ ⎥ ⎥
Shelf heat flux
Temperature section
€
< FS > = 2.1 Wm−2 ΔQ
2.4 Wm−2 kz
⎧ ⎨ ⎩
€
< FW > = 25.3 Wm−2 ΔQ
27.8 Wm−2 B.P.
⎧ ⎨ ⎩
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
1998 Grid-wide Regime Shift(ubiquitous across physical properties)
Temperature of max
Equivalent ice thickness (m)SDw
FT variability
Martinson LDEO/Columbia University
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Modes of ocean heat fluxFT variability
Martinson LDEO/Columbia University
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Ocean heat flux (FT) to atmosphere over WAP shelf shows considerable change in latter part of 1900s (coinciding with increased Tair and glacial melt):
Large step increase in 1990 (+4 Wm-2)
Qshelf & Qslope are proxies for FT
FT shows jump in 1998 by 3 Wm-2 followed by same jump each year thereafter
Contribution to sea level rise and peninsula warming: ocean heat flux FT variability
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
WAP region dominated by circumpolar water masseso ACC/UCDW water along slope delivering heat and nutrients to WAP
continental shelfo UCDW floods shelf from dynamical forcing (likely wind driven upwelling)
o Slope waters enter via canyons in shelf, eventually flood onto shelf floor
WAP bathymetry controls property distributions and stratificationo T–S plot shapes reflect sub-regions and indication of time since renewal
Extreme El Niño of 1998 introduced grid-wise regime shifto Apparent in all physical variables
Ocean heat flux temporal increases on shelf are consistent with strong atmospheric warming and dramatic glacial melt on WAP
o Can continue increasing to what level before internal adjustments regulate?
Conclusions:
Future: Determine WAP glacial melt and commensurate freshwater input Secure funding for moorings to evaluate UCDW flooding episodes
o Monitor excess heat supply from eddies, or other episodic flooding events and tie these events to large scale (satellite observable) mechanistic causes
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Backup slides&
More Exciting PO
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
<Kz> m2/s x10-4
Grid Line (km)
Grid Station (km) Grid Station (km)
m2/s x10-4
€
ΔTww= cpkz∇Tsp +cpkz∇Tpp( )Δt s
hww
^
Shelf heat flux
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
FDT = kzcpT(diffusive heat flux)
= TBw + SDw
(bulk stability)FET = (TBw/FL
(entrainment heat flux)
FL = (Fair - FDT
(latent heat flux)
FT = FDT + FET(total heat flux)
Salinity
Temperature (˚C)
Thermal Barrier (TBw)
Salt Deficit (SDw)
Martinson and Iannuzzi, JGR, 1998
Shelf heat flux
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
r
SC–
MA+OA
+
NC–
1993-2004 climatology r[z(max), Dynamic Topo]
Delivery to shelf
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
C.
Delivery to shelfNote: water enters shelf through canyons, consistent with dynamic topo.
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Cross-shelf T-anomalies Delivery to shelf
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
FT Wm-2
Qshelf (x109
J/m2)
Lines 150-650 (average Q-shelf)
r = 0.75
FT variability
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
YEAR
1990–2004 Average Qslope = (3.83 ± 0.07 )x109
1930–1989 Mean Qslope = (2.98 ± 0.16)x109
~0.7˚ C warming of 300 m column of water below winter mixed layer(+4 W/m2 increased FT for same ΔQshelf)
Qslope (x109 J/m2)
NUMBER OF PROFILES PER AVERAGE
FT variability
rms about
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
Year
Lines 150-650 (full shelf and coast stations)Qshelf (x109
J/m2)
All shelf stations
FT variability
Martinson LDEO/Columbia University
Martinson, 5/15/05; APCV Workshop
The Antarctic Dipole (of which Palmer Station lies at the node point), is the largest response to ENSO events outside of the tropics, displaying a strong tropical-polar teleconnection. It is a major Southern Ocean polar climate mode. It shows a dipole whereby during an El Niño the Weddell gyre is spun up, and becomes colder with more sea ice, while the Amundsen Sea shows the opposite. For La Niña, the opposite relationship is seen.
Two mechanisms are responsible for the formation & maintenance of the Antarctic Dipole: (1) heat fluxes due to the mean meridional circulation of regional Ferrel Cell and (2) anomalous high-pressure center generated by stationary eddies. The changes in the Hadley Cell, the jet stream, and the Rossby Wave train, all associated with El Niño, link the tropical forcing to these high latitude processes.