Long term trends in deep water properties of BC inlets

The deep waters of inlets, i.e. those waters trapped behind the inlet's sill, are usually quiescent. Isolated from the annual and higher frequency variations present in the near surface waters, the deep waters provide a good sampling location for observing the long term changes in water properties (temperature, salinity and dissolved oxygen). The deep waters chronicle the temperature, salinity and dissolved oxygen properties of the outside waters.

The almost 50 year long time series of water properties from some inlets, more than 60 years in the case of Saanich Inlet, are potentially rich sources of information about our coastal environment and how it has changed in the last half century. This web site presents the time series of deep water properties from the better sampled inlets (Saanich Inlet, Indian Arm, Howe Sound, Jervis Inlet, Bute Inlet, Knight Inlet and Muchalat Inlet). The web site also provides basic physical, hydrologic and oceanographic information for the better sampled inlets.

Background

Dr. George Pickard of the Institute of Oceanography at the University of British Columbia (UBC) initiated in 1951, and conducted for many years, a series of inlet cruises. The inlet cruises, conducted mostly in the summer, were used for studies of the BC fjords and also served as training exercises for oceanography students. Students obtained and analyzed water samples for temperature, salinity and dissolved oxygen in many fjords, straits, passages and channels on the entire BC coast. The data set is a remarkably long (~ 50 years), high quality time series that spans the entire length of the mainland coast and Vancouver Island.

Several other researchers, notably Drs. John Tully and Mike Waldichuk, also conducted sampling programs in several BC inlets. Dr. Tully's work extends back to the 1930's, and Dr. Waldichuk conducted several pollution cruises in the 60's and 70's to inlets where there were pulp mills. In the last 25 years, the fjord research at Institute of Ocean Sciences (IOS) has provided extensive sets of observations from several fjords, in particular Knight, Saanich and Alberni Inlets. All of the IOS data sets and most, but not all, of the early inlet and coastal water surveys are now preserved in digital form in the IOS data archive.

Sampling statistics

One of the first steps in the construction of the time series of deep water properties was to determine which inlets had been sampled most consistently and most often - the sampling statistics for the BC inlets. The IOS electronic data archive was searched for all data holdings in the geographical area corresponding to the major inlets of the BC coast. In some cases smaller but significant inlet areas were also searched. The data holdings from individual inlets were then summarized by time in the form of sampling histograms depicting the length of the time series and number of samples per year. The table below summarizes the sampling statistics for the best sampled inlets, and the diagram that follows depicts geographically the sampling statistics in terms of total number of stations or profiles taken in the different inlets.

Regional descriptions

Georgia Basin inlets (Saanich, Indian Arm, Howe Sound, Jervis, Bute)

• the best sampled inlets of the BC coast

West Coast Vancouver Island Inlets (Alberni, Muchalat, Neroutsos and Rupert-Holberg)

• the inlets of this coast have fragmented times series with long gaps
• in Alberni Inlet, the deep waters have a significant annual signal which obscures long term trends

Central and North Coast inlets (Knight, Douglas - Kitimat, and Observatory)

• with the exception of Knight Inlet, sampling is very sparse
• an appreciable annual signal in the deep waters of Knight inlet may obscure long term trends
• Observatory Inlet and Alice Arm have large number of samples but almost all were takenin a 3 year period

Haida Gwaii

• sampling is very sparse

Table of sampling statistics for the better sampled inlets

Inlet	Number of stations	Length of time series (years)	Comments	Histogram
Saanich Inlet	1560	47	3 year gap in late 50's, earliest measurements in 1930
Jervis Inlet	1000	49	1 and 2 year gap
Indian Arm	1350	45	4 year gap from 1964-67
Howe Sound	860	48	Several 1 or 2 year gaps, half of stations inside sill
Bute Inlet	750	50	Many 2 and 3 year gaps in the 80's and 90's
Knight Inlet	1260	50	Some 1, 2 and 3 year gaps
Muchalat Inet	250	42	Many gaps, one gap is 5 years in length, earliest measurement in 1933
Alberni Inlet	1540	31	Several 1, 2 and 3 year gaps, two main basins, earliest measurements in 1937
Portland and Observatory Inlets and Alice Arm	2200	20	Almost all samples taken in 3 year period from 1981-1983, many gaps

Map of sampling statistics for individual inlets

Related links

• Annual averaged deep water properties for inlets