douglas g. martinson lamont-doherty earth observatory columbia university [email protected] 12...

Douglas G. MartinsonLamont-Doherty Earth ObservatoryColumbia University

[email protected]

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



Location Map & Grid

--60

BellingshausenSea

An.

Ad.

B.

A.

R.

L.

M.B.SLOPE

SHELF

COAST

Sample region



SHELF

SLOPE COAST

SLOPE

SHELF

COAST Bathymetric Shading:

White ≥ 750 m

750 > light-grey ≥450 m

Dark-grey < 450 m

Background



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



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



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



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)



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



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



Bulk heat flux and Entrainment/diffusive heat flux ratio

FET/FDTFT

W/m2

Shelf heat flux



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.

⎧ ⎨ ⎩



1998 Grid-wide Regime Shift(ubiquitous across physical properties)

Temperature of max

Equivalent ice thickness (m)SDw

FT variability



Modes of ocean heat fluxFT variability



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



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



Backup slides&

More Exciting PO



<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



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



r

SC–

MA+OA

+

NC–

1993-2004 climatology r[z(max), Dynamic Topo]

Delivery to shelf



C.

Delivery to shelfNote: water enters shelf through canyons, consistent with dynamic topo.



Cross-shelf T-anomalies Delivery to shelf



FT Wm-2

Qshelf (x109

J/m2)

Lines 150-650 (average Q-shelf)

r = 0.75

FT variability



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



Year

Lines 150-650 (full shelf and coast stations)Qshelf (x109

J/m2)

All shelf stations

FT variability



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.

douglas g. martinson lamont-doherty earth observatory columbia university [email protected] 12...

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