Message from Liam Antrim (Olympic Coast National Marine Sanctuary)
On Aug 30th, 2012 the Olympic Coast National Marine Sanctuary (OCNMS) crew on the R/V TATOOSH found hypoxic conditions over a large area in the southern portion of the sanctuary. Hypoxic conditions are considered to exist when the dissolved oxygen (DO) is <2 mg/l or <1.43 ml/l. The TATOOSH crew was conducting routine servicing operations on the sanctuary’s oceanographic moorings when hypoxia conditions were found at the 42 meter mooring off Cape Elizabeth, Washington. DO levels were approximately 1.79 mg/l near the seafloor. This finding triggered additional sampling effort to determine the extent of hypoxic conditions. In addition to sampling at the standard mooring locations on the Cape Elizabeth and Kalaloch transects, conductivity, temperature, and DO profiles of the water column were collected on transects off of the Raft River and Hoh Head. A map of the standard mooring sites and positions can be viewed at:
On September 6, 2012 the Olympic Coast National Marine Sanctuary (OCNMS) crew on the R/V TATOOSH set out to monitor the hypoxic conditions originally noted in the southern portion of the sanctuary on August 30th. The TATOOSH crew conducted CTD casts w/DO profiles on the outer stations of four transects, Hoh Head (HH), Kalaloch (KL), Raft River (RR), Cape Elizabeth (CE). Additional stations on an east-west (shallow-deep) transect were added off the Raft River (65, 42, 30, 25 and 20 meter contours) and Cape Elizabeth (42, 65 and 100 meter contours). Hypoxic conditions near the seafloor were observed at all stations except Hoh Head, the northern most station monitored.
On August 30th the hypoxia event appeared to be centered off Kalaloch and extend from just south of Teahwhit Head to the southern border of the OCNMS; waters south of Cape Elizabeth were not sampled. The leading (inshore) edge of the hypoxia was relatively parallel to the shoreline and somewhere between the 42m and 27m contour. Analysis of data from the mooring instruments will reveal when hypoxic conditions moved onto the mid shelf region.
Data collected on September 6th indicates that the center of the hypoxia event off the Washington coast appears to have moved south and inshore. Off the Raft River and south, moderately hypoxic waters have moved inshore toward the 20 meter contour, which lies approximately 4.5 nautical miles from shore at the Raft River. Conditions south of Cape Elizabeth have not been monitored by OCNMS in recent surveys.
The table below shows data from sites monitored on August 30 and September 6, 2012 where moderate hypoxic conditions were identified. A multiplier of 0.7 was used for quick conversion between DO units.
Additional information on OCNMS moorings, including a map of mooring locations, is available at:http://olympiccoast.noaa.gov/science/oceanography/oceanographic_moorings/oceanographic_moorings.html
|Sampling Date||August 30, 2012||September 6, 2012|
|Area||Station||Depth (m)||DO (mg/l)||DO (ml/l)
(multiply by 0.7)
|Depth (m)||DO (mg/l)||DO (ml/l)
(multiply by 0.7)