WHP Line No.: PR6 Last Updated: January 28, 1997 CRUISE REPORT: Repeat Hydrography on Line PR6: WOCE Cruise No. 18DD9512/1 Chief Scientist: Phil Boyd Ship: John P. Tully Ports of Call: none Cruise Dates: August 22 to September 13, 1995 Expedition Designation: 18DD9512/1 Cruise Narrative Our repeat hydrography section was a joint program with Canadian JGOFS. A full CTD survey along Line PR6 to a depth of 3000 m was completed , with CTD casts at 29 stations and rosette/hydro casts at 10 stations. Two additional surveys were conducted: a sawtooth survey to the N and S of Line P (up to 20 miles) from P26 to P19 involving underway sampling only, and a hydrographic survey from P19 to P12 involving both underway and CTD sampling. Salinity, oxygen and nutrients (NO3 & NO2, PO4 and Si) were analyzed onboard ship. A bio-optical mooring was deployed at Stn. PRS1 to assess temporal changes in phytoplankton biomass and production in relation to the mixed layer depth and PAR. The mooring was placed to within 2-3 m of its theoretical position. JGOFS participants collected samples at 5 stations for abundance and activities of bacteria, phytoplankton, micro- and meso-zooplankton and incubated water to measure growth and grazing rates of various groups of plankton. The natural abundance of stable isotopes (15N and 13C) in suspended particulate matter was determined along Line P. Cruise Summary Information Cruise track Line PR6 starts at the mouth of Juan de Fuca Strait on the west coast of Canada, and heads almost due west for 900 n mi. The terminal station is PRS1, formerly designated Ocean Weather Station Papa (50 N, 145 W). Table of Stations by type Sample type: No. stations: Max. depth (m): CTD casts 29 3007 db Rosette/Hydro casts 10 3862 Loop samples 30 5 Mooring 1 Profiling Alace float 1 800 m Floats and Drifters deployed A profiling Alace float was deployed at station PRS1. Principal Investigators Howard Freeland Ocean circulation IOS C.S. Wong Climate chemistry IOS Frank Whitney WOCE coordinator IOS Philip Boyd JGOFS coordinator UBC Preliminary Results A diatom patch was noticed in the vicinity of station P20, eliciting increased sampling in this area. The temperature and salinity structure along Line PR6 define several regions: 1. very near the coast, cooler more saline waters are upwelled as previously described by Freeland and others. 2. two lenses of warm, low salinity water between P4 & 10, and P15 & 18 have different characteristics. The near shore pool with salinity less than 32 psu is restricted to the upper 20 m. Further offshore, fresh water appears to be mixed deeper but the mixed layer is thermally confined to the upper 20 m; 3. beyond P20, salinity increases abruptly by 0.2 psu at the surface and remains fairly uniform out to P26. The mixed layer deepens to 30m. Transmissivity is a good indicator of phytoplankton density (data collected at P2, 4, 12- 20, 24 and 26). Although this data is sparser than T and S, regions with increased biomass can still be defined as: 1. upwelling near the coast which increases nutrient supply; 2. subsurface chlorophyll maximum between P4 and 12, which is formed by a nutricline below the nitrate depleted surface layer (trans. data only at P4 and 12); 3. a break in the subsurface chlorophyll layer coincident with a doming in salinity at P13; 4. a second subsurface chlorophyll layer from P15 to 19, which is also a region where a persistent current from the north (at P16) was notice by the ship as it tried to hold station, and; 5. a region of high surface biomass seen at P20, followed by an increase in transmissivity towards P26. Nitrate is found in surface waters from P18, westward. The two dominant features of biomass distribution apparently are nutrient supply and stratification. Goals Achieved CTD survey of Line PR6. Successful Rosette casts at 10 stations on Line P. Completion of JGOFS sampling for plankton and productivity measurements. A mooring with an optical package and S4 current meter, both in the mixed layer, was deployed. Problems and Goals not Achieved The Alaskan Gyre component of the cruise was canceled in order to study the higher than normal abundance of large diatoms observed at Stn. P20. Cruise Participants & Affiliations Phil Boyd Chief scientist UBC Reg Bigham Watch, mooring IOS John Love Salts, watch IOS Wendy Richardson Oxygen, watch IOS Ron Bellegay Watch, carbonates IOS Janet Barwell-Clarke Nutrients, FD*, prod. expt. IOS Ou-Jin Jeong mooring observer IOS Robert Goldblatt Zooplankton biomass UBC Hugh Maclean Watch, plankton sampling UBC Maureen Soon particulate 13C & 15N UBC Michael Lipsen bacteria enumeration UBC Delphine Thibault Zooplankton excretion Rimouski U. Ken Crocker Zooplankton grazing Memorial U. Jennifer Putland Micro-zooplankton Memorial U. Paul Matthews bacterial productivity Memorial U. Neil Price Fe uptake McGill Maite Maldonado bacteria respiration & production McGill IOS = Institute of Ocean Sciences, Sidney, B.C., Canada. UBC = University of British Columbia, Vancouver, B.C., Canada Measurement Techniques and Calibrations CTD profiles At all stations, a Guildline 8715 CTD coupled with transmissometer was lowered to a maximum 3007 m. Water sampling A rosette holding a Guildline 8737 CTD and 23-10 L polycarbonate Niskin bottles was used for most water sampling. Go-Flo bottles clamped on Kevlar hydro line were used to collect clean water for plankton studies. Each rosette/hydro station consisted of two casts - a down cast and an up cast. The CTD profile is taken from the down cast. The bottles were tripped on the up cast and CTD pressure (dbar) and CTD temperature (uncorrected) recorded from this upcast. At each station, samples for surface chlorophyll, salinity and nutrients were collected from the ship's sea water loop which pumps water from about 5 m continuously into the laboratory. Salinity Samples were collected in glass bottles and analyzed onboard ship using a Guildline Model 8410 Portasal. The Portasal was standardized daily with IAPSO standard sea water. Oxygen An automated titration system (Brinkman Dosimat and Fiber Optic Probe Colorimeter) using the micro-Winkler method (Carpenter, 1965), titrated samples to the iodine end-point. Standards were prepared as outlined in WOCE Report 73/91. Nutrients Samples from hydro casts were collected in polystyrene tubes and refrigerated for a maximum of 12 h before being analyzed. Loop samples (USW) were stored up to 2 days at 4oC before being analyzed. NO3+NO2, PO4 and Si were analyzed using a Technicon Autoanalyzer. NO3+NO2 samples were reduced with Cd/Cu, then complexed with sulfanilamide and N-Naphthylethylene-diamine to form an azo dye (Technicon Method No. 158-71W/B). PO4 produces a molybdenum blue complex in presence of acidic molybdate and ascorbic acid (Technicon Method No. 155-71W). Dissolved Si also forms a molybdenum blue complex and oxalic acid removes PO4 interference (Technicon Method 186-72W). Concentrated standards were freshly prepared the week before the cruise from oven dried reagents. Working standards were made every 1 to 2 days by diluting 1 to 6 mL of various stock solutions to 250 mL with 3.2% NaCl (w/v in double run Milli-Q water). Table. Laboratory temperatures for nutrients. Date Temp (C) Date Temp (C) Aug 24 23.8 Sept. 1 23.5 to 25.9 Aug 27 23.0 to 25.1 Sept. 2 20.0 Aug 28 24.2 Sept. 3 23.4 to 24.3 Aug 31 24.1 to 24.8 Sept. 8 20.6 to 21.8 TCO2, 13C and Alkalinity - a single profile was collected at PRS1. Samples were fixed with HgCl2 and refrigerated. O18/O16 - samples were collected in 60 mL polyethylene bottles and refrigerated. JGOFS sampling - Go-flo bottles were used to collect water for POC/N, DOC/N, chlorophyll, nano- and micro-plankton and incubation experiments. Deck incubations were conducted to measure growth rates of bacteria, phytoplankton and micro- zooplankton. Sp FOR SALINITY, OXYGEN, AND NUTRIENTS Duplicate samples came from Niskin bottles tripped within 1.3 m of each other. Parameter Depth Range (m) Conc. Range Sp Salinity 10 to 3712 32.2 to 34.7 0.0044 (k=23) Oxygen 10 to 3712 63.7 to 280.0 uM/kg 1.09 (k=22) Silicate 10 to 3712 10.0 to 171uM/kg 0.42 (k=16) Nitrate + Nitrite 10 to 3712 0.0 to 41.8 uM/kg 0.22 (k=16) Phosphate 10 to 3712 0.34 to 2.95 0.017 (k=16) Where the standard deviation of pairs Sp = {(sum d2)2k}1/2, d is the difference between pairs, and k is the number of pairs. References Carpenter, J.H. 1965. The Chesapeake Bay Institute technique for the Winkler dissolved oxygen method. Limnol. Oceanogr., 10: 141-143. Technicon Industrial Method No. 155-71W. 1973. Orthophosphate in water and seawater. Technicon Industrial Method No. 158-71W/A. 1977. Nitrate and nitrite in water and seawater. Technicon Industrial Method No. 186-72W/B. 1977. Silicates in water and seawater. WOCE Report 73/91. 1991. A comparison of methods for the determination of dissolved oxygen in seawater.