1. 
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.

2. Seaglider and Sensors ICECAT for shallow shelves, moorings
Hull length: 1.8 m, Wing span: 1.0 m
Mass: 52 kg
Surface to 1000 m.
Slow: horizontal speed m/s (~22 km or 12 nm per 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.
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.
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.

3. 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.
In October 2006 we deployed the full six source array indicated by the cyan squares on the map to the right. Seaglider 109 was launched on Oct. 10, Real-time navigation performance through dive 238 is shown in the figure to the left. Based on starting GPS position, glider flight data and a hydrodynamic model we can compute the “known” position of the glider throughout the dive (circles). These positions are compared to the positions calculated onboard the glider from RAFOS receptions (stars). Concurrent positions are matched by color. Over 238 dives the glider was able to calculate 130 acoustic fixes. The mean positioning error of these fixes is 2.4 km. With a revision in the quality filtering this result could be improved to 1.7 km.
Temperature sections across Davis Strait (above left, plotted east-to-west) provide examples of three glider crossings during the 2006 deployment. Because this was the first attempt to operate under the ice, we tried to avoid the complications of working near the rapidly evolving ice edge. Once ice began to form, we held the glider on the ice-free eastern side while waiting for the ice edge to stabilize. This restriction forced us to shorten the November section. The ice edge stabilized in December, at which point we instructed the glider to execute a fully autonomous run beneath the ice, making its own decisions about how to navigate and when to and where to attempt to surface. For this first test, the glider was commanded to occupy a shortened version of its normal section. At approximately 58° W, the glider detected ice and entered its under-ice profiling mode. It completed the westward section to its target at 59° W and back (eastward data not shown) without surfacing, navigating autonomously using RAFOS acoustic navigation. Once east of 58° W, the glider decided that the surface was likely ice-free, surfaced and successfully transmitted its data back to our lab in Seattle. Red hash marks indicate the location of under ice dives. The ice edge at 58° W corresponds well with data from available ice maps from the Canadian Ice Service.

4. 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

5. 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/Iridium
antenna
MSTL 600 kHz
Sidescan sonar
Acoustic modem
(operates through
LBL transducer)
Wet-Labs
ECO-Puck
Triplet
Kearfott T-16
Inertial Navigation
System
Long-BaseLine
(LBL) tracking
transducer
Seabird SBE- 49
pumped CTD
RDI 1200 kHz
ADCP, up-and
down-looking
Plueddemann

6. 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

7. Basin Scale Acoustic Navigation and Communications(?)
Acoustic navigation- GPS analog, critical enabling technology.
Acoustic comms- Iridium analog, less important given decreasing seasonal ice cover?
Acoustic Paths
TAP (blue)
ACOUS (red)
20 Hz source
Basin-wide ranging
Gavrilov & Mikhalevsky

8. Gavrilov & Mikhalevsky
Transmission loss along ACOUS path at 50 m and 400 m modeled for a broadband signal
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
Frequency, Hz
Depth: 50 m
Range, km
200
400
600
800
1000
1200 30 40 50 60 70 80
Depth: 400 m
-120
-115
-110
-100
-95
-90
-140
-130
-80
-105
0-dB SNR for a 50-Watt (~190 dB) source
-20-dB SNR for a 50-Watt (~190 dB) source
Gavrilov & Mikhalevsky

9. Notional acoustic network30
150 60
120
180 G r e n l a d R u s i C 40 00 5 35 20
2000
ACOUS
source
90W
90E
Autonomous sources
Acoustic observation paths
Cabled transceiver nodes
with shore terminals
Cable
Cabled/autonomous transceiver nodes
Gavrilov & Mikhalevsky

10. Most serious problems
Weight, power consumption and reliability of low-frequency sources, especially for mobile platforms
2. Doppler effect for mobile platforms
3. Slow communication rate
4. Accurate timing for mobile platforms
5. Separation of acoustic thermometry/halinometry data from navigational errors.
6,7,… ?

11. Arctic Species of Interest: most Circumpolar & Subsistence Targets
WHALES
Bowhead
Beluga (white)
Narwhal
SEALS
Ringed, Bearded
Harp, Hooded
Ribbon, Spotted
WALRUS
POLAR BEAR
Sue Moore

12. Frequency ranges of cetacean calls ~ hearing capability: audiograms available for few spp.
Dolphins
Mysticete whales ? ? ?
Dave Mellinger and Sara Heimlich
Oregon State Univ. & NOAA/PMEL

14. What Should ANCHOR Participants Do?
Investigate the need for an authorization
Letter of Authorization (LOA)
Incidental Harassment Authorization (IHA)
Specifications of Transmission will be Required
Frequency & Amplitude (Source Level)
Where, When (Duty Cycle) & Transmission Loss
Proximity 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

15. An Innovative Observational Network for Critical Arctic Gateways: Understanding Exchanges through Davis (and Fram) Strait
Craig Lee, Jason Gobat, Beth Curry, Applied Physics Laboratory, University of Washington Richard Moritz, Kate Stafford
Brian Petrie Bedford Institution of Oceanography
Malene Simon Greenland Nature Institute
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
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.
Chart:
4 hydro lines (S. Baffin Bay, Davis Strait mooring line, Ross Mooring line, N. Labrador Sea)
2nd line from north is our moored array. 6 subsurface sites and 8 landers (4 on each shelf)
ICECAT instrument development project- inexpensive float for measuring T-C in ice-threatened near surface layer.
AR is acoustic receiver (for logging navigation signals from mooring)
from Dickson et al, 2005

16. 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 ]