Ice Profiling Sonar:
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Mooring Site - NOAA/DFO Site CH01

       The CH01 site in the northern Chukchi Sea, supported by NOAA and the Canadian Department of Fisheries (DFO), is one in a growing array of sites for continuous monitoring of Arctic sea-ice thickness via sea floor moored upward looking sonar. Sites were first established in the Canadian Beaufort Sea and in Fram Strait almost 20 years ago. The pan-Arctic map (below) shows the status of the Arctic Ice Monitoring (AIM) array during the IPY.



Map of Beaufort Sea ice profiling sonar moorings
Beaufort Sea ice profiling sonar moorings (Courtesy of H. Melling).


       A moored upward looking sonar (ULS) has been positioned at CH01 (see map) to monitor the thickness and movement of pack ice in the region of the Chukchi Plateau since August 2003. The mooring is a collaborative undertaking of the Canadian Institute of Ocean Sciences, the USA Cold Regions Research Engineering Laboratory and the NOAA Arctic Research Office. The effort is jointly supported by NOAA Climate Program Office and the Canadian Department of Fisheries and Oceans.

Status of Observations

        Nine site-years of data from this site are now in hand: one-year records retrieved by USCG Healy in 2004 and by CCGS Sir Wilfrid Laurier in 2005, 2009, 2010 and 2011 and overlapping two-year records (2005-07, 2006-08) retrieved by CCGS Sir Wilfrid Laurier in 2007 and 2008.  The overlapping records from two sites during 2006-07 were a consequence of heavy ice at the original site in October 2006, which caused a 1-year delay in the retrieval of the mooring there and necessitated the deployment of the replacement mooring at a surrogate location 55 km to the south-south-west.

       The data from October 2003 through September 2010 have been processed and are available to the community.  Processing of the data from 2010-11 is presently underway.

     The data from October 2003 through September 2010 have been processed and are availableto the community. Processing fo the data from 2010-2011 is presently underway. Data can be accessed via the Internet from established archives:

Background

         The CH01 monitoring site is supported by NOAA under the umbrella of Russian-American Long-term Census of the Arctic (RUSALCA).  The instruments moored at this site provide year-round measurements of ice thickness and variability (ice profiling sonar), ice drift and ocean current (Doppler sonar), plankton abundance (Doppler sonar), ocean temperature and salinity (T-S recorders) and ambient sound from marine life, human activity and natural processes.   The ice profiling sonar could be upgraded to measure storm waves when ice is not present, as has recently been done at several other sites in the AIM array. The CH01 site provides continuous observations of key variables between the episodic but geographically more extensive RUSALCA cruises.  Data collected from the instruments on the mooring are available for use by other RUSALCA investigators and the broad scientific community.

        The ULS observations provide detailed information on regional ice conditions, important for studies of the marine ecosystem and for the development and validation of high resolution, regionally-focused atmosphere-ice-ocean models.  The data from this site will be used with data from the North Pole Environmental Observatory and other sites to determine changes in the basin-wide mean thickness of the Arctic sea ice cover and for assessment of numerically simulated and Earth-satellite-retrieved fields of ice thickness.   Data are available via the Internet from established archives:

       Since 2003 the mooring has carried instruments to measure ice draft, ice velocity, ocean current, temperature, sea level and sound scatter from zooplankton.

        In 2008 the instrumental suite on the mooring was expanded to include:

       A replacement mooring was deployed at CH01 in 2011 for continued observations during the period October 2011 through September 2012. This mooring again carries the expanded instrumentation suite. There are opportunities for modest expansion of the mooring’s payload, should others be interested.

Results

       The site has been generally covered by first-year ice with occasional multi-year ice incursion. A prolonged invasion occurred in the fall of 2006, when Laurier was unable to reach the site.

      The drift of ice over the site has been generally WNW in the winter and NW in the spring and summer. Drift during 2008-09 was atypical in being north-westerly all year. There are two drift vectors for 2006-07, when two AIM moorings were operational here, 55 km apart. The NORTHWARD movements of sea ice (November through July) have been 400, 600, -150, 750, 700, 1150 and 380 km during seven winters of observation. The length of the NET DISPLACEMENT vector (November through July) has varied almost four-fold, between 500 km in 2005-2006 and 1900 km in 2007-2008.

Ice Drift 2003 - 2004 Ice Drift 2004 - 2005
Ice Drift 2005 - 2006 Ice Drift 2006 - 2007 (Both Sites)
Ice Drift 2007 - 2008 Ice Drift 2008 - 2009
Ice Drift 2009 - 2010

Yearly Ice Drift over Mooring Site CH01
(Click each image above for a full size image of the ice drift plots.)


       In the "old Arctic", the direction of drift in this area was generally in the SW-to-W octant (http://iabp.apl.washington.edu/data_slp.html). The year with net southward drift (2005-06) was the year that brought heavy old ice to the Alaskan coast and onwards to the Bering Strait by February. These conditions stopped the Healy and Klebnikov near Barrow for a couple of weeks in the following July and left multi-year ice floes averaging 8-15 meters in thickness within a few miles of the Alaskan coast in the following September. Actually, this year was different in two ways:

  • A SW push of ice over 500 km during November through mid February, with no analogue during the other three winters, but reminiscent of a similar event during the winter of the first SHEBA year Dec-97 through Feb-98

  • sluggish NW drift the following spring and summer (only 150 km compared with values between 300 and 500 km during the other years).

       The illustration below displays statistical measures (mean, minimum and maximum) of ice draft for 5-day data segments during the first seven years of observation at CH01. There are two sets of data for 2006-07, when two AIM moorings were operational here, 55 km apart. The consistency of the 5-day mean ice drafts at the two locations during the year of overlap is evidence that the accuracy of ice-draft measurement by moored sonar is consistent with our 10-cm estimate of empirical error. Although the record is still relatively short, the data provide little evidence of substantial change in the seasonal ice that dominates this site. This result for seasonal ice is in stark contrast to the dramatic decline in the thickness of multi-year ice in the western Arctic.


       However, this result is consistent with the absence of significant trend in the mean draft of seasonal pack ice at DFO’s AIM site on the Mackenzie Shelf of the Beaufort Sea, 1230 km to the east-south-east. The length of this record is now approaching two decades.

Pack ice draft anomalies Mackenzie shelf 1991 -- 2008
(Click image above for full size image of data plot.)


       The images below show how the ice varies over a period of one year. The plot displays the the ice thickness measurements at CH01 during the 2004-2005 season. The plot shows both the maximum and average ice thickness values based from the ice draft measurements made at CH01. The pictures show what the ice in the area of CH01 (Chukchi Sea) looks like during mid-winter (left image) and mid-summer (right image).


ice thickness plot 2004-2005


Arctic in mid-Winter   Arctic in mid-Summer

Arctic Ice in mid-Winter                                               Arctic Ice in mid-Summer


For more information on the mooring and the mooring data, contact:

Dr. Humfrey Melling
Research Scientist
Fisheries and Oceans Canada, Institute of Ocean Sciences
9860 West Saanich Road PO Box 6000
Sidney, BC Canada V8L 4B2
Phone: 250-363-6552
Fax: 250-363-6746

E-mail: Humfrey.Melling@dfo-mpo.gc.ca
http://www-sci.pac.dfo-mpo.gc.ca/osap/people/melling_e.htm