challenges small internal deformation scale- dynamically wide strait. broad west greenland shelf
DESCRIPTION
. S. Challenges Small internal deformation scale- dynamically wide strait. Broad West Greenland shelf. Ice cover & icebergs. Freshwater moves in thin (~50 m) surface layer. Quantify liquid & ice contributions at monthly to inter-annual time scales. - PowerPoint PPT PresentationTRANSCRIPT
Challenges• Small internal deformation scale-
dynamically wide strait.• Broad West Greenland shelf.• Ice cover & icebergs.• Freshwater moves in thin (~50 m)
surface layer.• Quantify liquid & ice contributions at
monthly to inter-annual time scales.
S
Moorings: Ice draft/velocity, absolute geostrophic velocity, low-mode u, T, S structure, marine mammals (‘06-’08)
Shelf Moorings: Low-cost (~$10k) ICECAT for T-S near ice-ocean interface, upward looking acoustic current profilers and bottom-mounted T-S.
Acoustically-navigated Gliders: Repeated sections (5 km, resolves deformation scale) at O(week) timescales between 500-m isobaths. Samples at ice-ocean interface. Temperature, salinity, dissolved oxygen (other?).
Ship-based Hydrographic Sections: Autumn. Biogeochemical tracers (nutrients, trace metals, TOC, TAlk, CFCs, oxygen isotopes. Spans broad region from S. Baffin Bay to N. Labrador Sea.
Seaglider and Sensors• Hull length: 1.8 m, Wing span: 1.0 m• Mass: 52 kg• Surface to 1000 m.
• Slow: horizontal speed 0.1 - 0.45 m/s (~22 km or 12 nm per day @0.25 m/s)
• Vertical speed 0.06 m/s (minimum)
• Endurance depends on ambient stratification, dive depth and desired speed
• Longest range to date: 3900 km
• Longest endurance to date: 31 weeks
• Sensors: SBE conductivity & tempreature, SBE43 or Aanderaa optode dissolved oxygen. Fluorometers, backscatter, ADCP may be possible.
ICECAT for shallow shelves, moorings• Samples in ice-threatened near-surface
layer.• Shallow element expendable, data logged
below.• Inexpensive (~$10k), deploy many.• 2004(1), 2005(2), 2006(4), 2007 (5)• Contributing this technology to Bering
Strait, other projects.
Operations beneath ice require acoustic navigation (RAFOS), advanced autonomy.
Acoustic data upload desirable for ‘insurance’.
First section beneath ice-covered western Davis Strait in Dec 2006… the system works, but there have also been setbacks associated with platform reliability.
IPY/AON developments include refining under-ice glider system, implementing moored ‘data depot’ for periodic data offload while operating under ice.
Ice
First Glider-based Section Under the Ice:December 2006• Fully navigated using RAFOS array.
• Fully autonomous operation- glider decided where to go, when to attempt to surface, without human intervention.
• Under-ice glider system works, but there have also been setbacks associated with platform reliability.
• Observations to within a few meters of ice-ocean interface, roughly 5 km horizontal resolution. Resolved south-flowing, surface-trapped Arctic outflow from CAA.
REMUS Operations offshore of Barrow
Pacific Water inflow is concentrated in the region between the coast and Barrow Canyon. The center of Barrow Canyon is only about 20 km offshore of Barrow, with maximum depths of about 120 m. These length scales are well suited to the capabilities of REMUS.
• Water mass transformation processes occurring on the Chukchi Shelf (mixing, cooling, and salinity changes due to ice formation and melting) modify the Pacific Water on its way to the Arctic.
• The most important transformations occur during winter, beneath sea ice, and are difficult to observe using conventional techniques.
• The inflow of modified Pacific Water is critical to maintaining the “cold halocline” in the western Arctic.
Plueddemann
The REMUS AUV
REMUS is a relatively small (8” daim x 6’ long), light (100 lb) vehicle capable of ~3.5 kt speed and ~12 hr endurance (~75 km along track) with a payload of navigation aids and oceanographic sensors.
Propulsion and steering
GPS/Iridiumantenna
MSTL 600 kHzSidescan sonar
Wet-Labs ECO-Puck Triplet
Seabird SBE- 49pumped CTD
RDI 1200 kHz ADCP, up-and down-looking
Kearfott T-16Inertial Navigation System
Long-BaseLine(LBL) trackingtransducer
Acoustic modem(operates throughLBL transducer)
Plueddemann
Cross-Shore Transects
The typical cross-shelf hydrography was best characterized by transects from the last mission on 29 August. The warm, fresh surface water (above 20 m) is the Alaskan Coastal Current, which follows the coastal topography after passing through Bering Strait. T/S characteristics below 20 m are consistent with subsurface, summer-water inflow at Bering Strait.
Four of the five transects were consistent with this relatively simple picture of coastal hydrography
Plueddemann
Gavrilov & Mikhalevsky
Acoustic Paths• TAP (blue)• ACOUS (red)• 20 Hz source• Basin-wide ranging
APLIS
ACOUSSource
Nan
sen Bas
in
Fram
Bas
in
Greenland
RussiaCanada
Spitsbergen
Basin Scale Acoustic Navigation and Communications(?)
Acoustic navigation- GPS analog, critical enabling technology.
Acoustic comms- Iridium analog, less important given decreasing seasonal ice cover?
Transmission loss along ACOUS path at 50 m and 400 m modeled for a broadband signal
0-dB SNR for a 50-Watt (~190 dB) source
Range, km200 400 600 800 1000 1200
30
40
50
60
70
80Depth: 400 m
-120
-115
-110
-100-95
-90
-140
-130
-120
-110
-100
-90
-80
-105
200 400 600 800 1000 1200
30
40
50
60
70
80-135
-130-125
-120
-115
-110
-105
-100
-95
-90
-85
Range, km
Fre
quen
cy,
Hz
Depth: 50 m
-20-dB SNR for a 50-Watt (~190 dB) source
Gavrilov & Mikhalevsky
Cabled/autonomous transceiver nodes
Cabled transceiver nodeswith shore terminals
Autonomous sources Acoustic observation paths
Cable
90E
30
150
60
120
120
60
150
30
1800
GGGrrreeeeeennnlllaaannnddd
RRRuuussssssiiiaaa
CCCaaannnaaadddaaa
4000
500
35002000
500
500
2000
3500
2000
500
ACOUSsource
90W
Notional acoustic network
Gavrilov & Mikhalevsky
1. Weight, power consumption and reliability of low-frequency sources, especially for mobile platforms
Most serious problems
3. Slow communication rate
2. Doppler effect for mobile platforms
4. Accurate timing for mobile platforms
5. Separation of acoustic thermometry/halinometry data from navigational errors.
6,7,… ?
Arctic Species of Interest: most Circumpolar & Subsistence Targets
WHALESBowheadBeluga (white)Narwhal
SEALSRinged, BeardedHarp, HoodedRibbon, Spotted
WALRUSPOLAR BEAR
Sue Moore
Frequency ranges of cetacean calls ~ hearing capability: audiograms available for few spp.
10
100
1000
10000
100000BlueFin GrayBryde's HumpbackMinkeRight (2)Pygmy rightBowheadSei Sperm whaleMonodonts (2)Beaked whales (3)Cephaloryhnchinae (2)River dolphins (3)N. Rt. whale dolphinSteninae (3)Delphininae (14)Pilot whales (2)Porpoises (3)Killer whales (2)
Frequency, Hz
Dolphins
Mysticete whales
??
?
Dave Mellinger and Sara HeimlichOregon State Univ. & NOAA/PMEL
What Should ANCHOR Participants Do?
• Investigate the need for an authorizationLetter of Authorization (LOA)Incidental Harassment Authorization (IHA)
• Specifications of Transmission will be RequiredFrequency & Amplitude (Source Level)Where, When (Duty Cycle) & Transmission LossProximity to marine mammal concentrations & to human subsistence activities (S-P-R Model)
IF low noise levels, short duty cycles & minimum spatial/temporal overlap, seek Finding of No Significant Impact, via memo with NOAA/PR
Sue Moore
Craig Lee, Jason Gobat, Beth Curry, Applied Physics Laboratory, University of WashingtonRichard Moritz, Kate StaffordBrian Petrie Bedford Institution of OceanographyMalene Simon Greenland Nature Institute
An Innovative Observational Network for Critical Arctic Gateways: Understanding Exchanges through Davis (and Fram) Strait
Buoyancy Barrier to Convection (from Bailey, Rhines & Häkkinen)
• 0-500m difference between thermal and haline components of dynamic height (blue: S, red: T)
• Transport and fresh over-capping of the subpolar gyre and Nordic Seas modulates MOC
from Dickson et al, 2005
Fluxes at major ocean gateways
• Understand partitioning between FW exchange west and east of Greenland, impacts on deep water formation and meridional overturning circulation.
• CAA/Davis Strait + Fram Strait captures nearly all of the Arctic FW discharge and primary Atlantic inflow.
Technology development for the Arctic Observing Network
• Ice-capable gliders
• New mooring technologies- ice-ocean interface, shallow shelves, light-weight through-ice (Switchyard).
• Acoustic navigation and communications.
Pacific Water Transformation
Water mass transformation processes occurring on the Chukchi Shelf (mixing, cooling, and salinity changes due to ice formation and melting) modify the Pacific Water on its way to the Arctic.
The most important transformations occur during winter, beneath sea ice, and are difficult to observe using conventional techniques.
The inflow of modified Pacific Water is critical to maintaining the “cold halocline” in the western Arctic.
[ Courtesy of T. Weingartner, U. Alaska ]