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Zigzagging in the Arctic
Rebecca Woodgate Polar Science Center, University of Washington, Seattle, USA in collaboration with Knut Aagaard (UW), Jim Swift (Scripps), Bill Smethie (LDEO), Kelly Falkner (OSU), Tom Weingartner (UAF) and many others Funded by NSF and ONR With thanks to the crews of USCGC Polar Star, USCGC Healy, RV Helix, CCGS Laurier Be sure to state names
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The Magic of Observations?
CBL cruise, 2002 Be sure to state names Helix cruise, 2004 CBL cruise, 2002 D.G.Barton, 1992
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The Magic of the Arctic Arctic Ocean Basics
Be sure to state names Arctic Ventilation by Pacific Waters – smoking guns in T-S space Tracing Atlantic waters in the Arctic by double diffusive ZigZags
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Where are we in the Global Ocean?
The Great Arctic Ocean Broecker, 1991
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Welcome to the Arctic Ocean
Broad, Shallow Shelves Deep Basins Shallow entrance from the Pacific Medium and Deep connections to the Atlantic Russia Barents Sea From the Atlantic Pacific To the Eurasian Basin Lomonosov R Fram Strait Bering Strait Canadian Basin You are here Greenland Canadian Archipelago About the size of the USA! USA Chart from IBCAO
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What makes the Arctic “hot”?
Decreasing Ice cover What makes the Arctic “hot”? Stroeve et al, 2005, GRL UN Environ Prog Local communities subsistence Arctic Shipping Routes? Oil/Gas Exploration Links to Global Climate Pink= mean minimum NSIDC, 2006
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Arctic Ice Circulation
AMSR, by Agnew, International Arctic Buoy Program, Rigor et al,
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What makes the Arctic FUN?
Russia ICE Weak stratification (away from surface), low energy. Cold Thus – traditionally small terms are important, viz thermobaric, double diffusion etcetctc A Challenge to measure Barents Sea From the Pacific Eurasian Basin Lomonosov R Fram Strait Bering Strait Canadian Basin Greenland USA Chart from IBCAO
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Arctic Ocean Circulation
Surface/Pacific water circulation “similar to ice motion” Atlantic water circum-Arctic Boundary current following topography EDDIES!
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Pacific Water in the Arctic
Rich in Nutrients Source of heat, freshwater, stratification ... and upper ocean ventilation Pathways dependent on atmospheric state Steele et al, 2004
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Pacific and Atlantic Tracers?
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Mixing in T-S Space TEMPERATURE SALINITY Thus, straight lines in TS space suggest mechanical mixing Mechanical mixing in TS space creates straight lines between water masses
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Influence of shelf waters
Along the Chukchi Shelf, upwelling and diapycnal mixing of lower halocline waters and Pacific waters (Note ventilation by polynya waters couldn’t give this T-S structure) Woodgate et al, 2005 Use silicate to track Pacific Water in the Chukchi Borderland Atl Pac Pacific Nutrient Max
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Atlantic layer warming of the 1990s
Karcher et al, 2003 ‘80 ‘84 ‘93 ‘95 ‘87 ‘91 ‘96 ‘99 Follow the warming by tracing the temperature maximum Some suggestions of slight cooling following the warming Mooring and CTD Data, Woodgate etal, 2001; Scicex data, Gunn & Muench, 2001
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The Warming of the 1990s 1993 Larsen deg warmer on the Mendeleev Ridge - inversions in temperature and salinity Carmack et al, ‘95, and McLaughlin et al, ‘96
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Atlantic Water zigzags AOS94
Salinity (psu) Potential Temperature (deg C) Line up/ Nest all through the Arctic Angles of the Zigzags match double diffusive theory Carmack et al, 1997
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Mixing and Double Diffusion in T-S Space
TEMPERATURE SALINITY TEMPERATURE SALINITY In double diffusive processes, heat diffuses faster than salt. So, in TS space resultant waters are not on a straight line between the parent water masses Mechanical mixing in TS space creates straight lines between water masses
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Zigzags - things we know
Line up throughout the Arctic (Carmack et al) NOT isopycnal, but double diffusive Theories for formation, and for growing to a large amplitude steady state (Turner, Ruddick, Toole, Georgi, McDougall, Walsh, Carmack, Rudels, May … ) Salt fingering Regime Warm Salty / Cold Fresh unstable in salt Diffusive Convection Regime Cold Fresh / Warm Salty unstable in temperature
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Warming in the Chukchi Borderland
‘93 ‘97 ‘02 ‘00 ‘99 ‘96 ‘94 ‘98 ‘95 warming progressing through the Chukchi Borderland cf Shimada et al, 2004;Woodgate et al, in press
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Structure in the Atlantic Water core
Pacific Nutrient Max very different T-S structures very sharp fronts 1) The temperature maximum is very dependent on location 2) Why are the structures so different? 3) Can we follow pathways using the T-S structure? Woodgate et al, in press
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Zigzags – what else can they tell us?
NEW?? OLD?? Form within the envelope of the parent water masses? Points of Zigzags contain least altered waters BIG Zigzags - parents different SMALL Zigzags - parents similar
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Zigzags – do tracers agree with this??
NEW?? OLD?? NEW?? OLD?? % Oxygen Saturation CFC-11 Higher Oxygen and CFCs in the warmer, saltier part of the zigzags Temperature Salt Oxygen CFC-11
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Tracking waters with Zigzags
BIG ZIGZAGS - medium Oxygen - middle/low CFCs - Interleaving of boundary current with old basin waters Temperature Oxygen CFC-11
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New boundary current interleaving with recent basin waters
Temperature Oxygen CFC-11 SMALL ZIGZAGS - high Oxygen - high CFCs New boundary current interleaving with recent basin waters
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Relic waters isolated in the Northwind Abyssal Plain
Temp Oxyg CFC-11 RAGGED ZIGZAGS - Low Oxygen - Low CFCs Relic waters isolated in the Northwind Abyssal Plain
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Core of Boundary Current
Temp Oxyg CFC-11 POINT AND BUMP - Medium/high Oxygen - High CFCs Core of Boundary Current
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SMOOTH TEMPERATURE MAXIMUM Shelf-influenced waters
Oxyg CFC-11 SMOOTH TEMPERATURE MAXIMUM - Low Oxygen - Medium CFCs Shelf-influenced waters Woodgate et al, in press
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Chukchi Borderland Atlantic Water Circulation
Only shown Fram Strait Branch Water, but Barents Branch very similar Woodgate et al, in press, JGR
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Arctic from TS-Space NEW OLD Using T-S Zigzags to trace Atlantic Water pathways Pacific/Atlantic diapycnal mixing via upwelling on the Chukchi Shelf
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