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Cruise 2: R/V Gyre 04G06

Mechanisms Controlling Hypoxia on the Louisiana Shelf
24 June - 1 July 2004

Port: Galveston, Texas
Mobilization: 24 June 2004
Cruise: 25 June - 1 July 2004

Objectives

(a) to recover/service/deploy three moorings containing oxygen, current velocity, and nitrate sensors;
(b) to conduct benthic respiration measurements aboard ship using waters collected near the moorings;
(c) to conduct a hydrographic survey in three hypoxia zones of the Louisiana shelf;
(d) to obtain supplemental biological and geochemical measurements.

Personnel

Scientific Party

Scientists
Dr. Steve DiMarco: Chief Scientist
*Dr. Piers Chapman- LSU: Chemistry leader, nutrients, oxygen, salinity
Dr. Matthew Howard: Hydrographic Data Cop (QA/QC), watch leader
Dr. Ayal Anis: Physical Oceanography, SCAMP, watch leader
Dr. Antonietta Quigg-TAMUG- Water column biology
Dr. Gil Rowe: Benthic biology leader, dive master, ROV
Dr. Les Bender: Deck Engineer, shipboard ADCP

Technicians
Willie Flemings-GERG: mooring deployment, Marine Tech, NAS Specialist
Paul Clark-GERG: mooring deployment, CTD/Electronics Tech
Cris Schmidt: nutrient/oxygen/salt tech, NAS Specialist
Eddie Webb: CTD/electronics tech

Students
Brian Fielder: geochemistry, TAMUG
Gaurav Singhal: Physical oceanography, water sampler (S) TAMUG
Erin Johnson: microbial structure, water sampler (S)
Sudeshna Lahiry: Physical oceanography, water sampler (S)
Mike Lalime: water sampler, assist with NAS (S)
Richard Simons: diver TAMUG
Clif Nunnally: benthic productivity, water sampler (S) TAMUG
Chrissy Stover: geochemistry/microbial, water sampler (S)
Chihlin Wei: benthic productivity, diver (S) TAMUG

Winch
Billy Green-TAMUG: winch operator
Steve Rodriguez-LUMCON: winch operator, RHIB Boat

Data Collection

Instrumentation and equipment:
CTD/12 bottle Rosette (GERG)
CTD/Transmissometer/4 bottle rosette (OCNG)
Shipboard PAR
CTD package (PAR, fluorescence, DO, OBS, T, S) (GERG)
Navigation computers (GERG)
Flow-through system computers (OCNG)
Salinometer and bucket (TAMU)
Autoanalyzer (6-channel) (TAMU)
Winkler Oxygen System (TAMU)
Thermosalinograph flow-through system (GERG)
Pump and filter for flow-through chlorophyll
Sediment traps (GERG)
Turner Fluorometer from Biggs (OCNG) and spare
1.5-l bottle for bottom bottle oxygen (Bottle 1 and bottom tripped frame)
0.45 m boxcore (TAMUG)
Freezer bags for core samples: 1 quart bags
Microbial Structure and TEP sample supplies (Long and Thornton)
Shipboard ADCP (GERG) (Narrowband as backup)
Bottom-tripped frame and bottle (OCNG)
Assorted Coring materials (Smallwood and GERG)
C14: primary productivity (Quigg)
SCAMP: microstructure profiler (Anis)
DI water (Johnson)
Digital cameras
Radio/CD player

Mooring Measurements:
Instrumentation: 2 RCM9, 2 NAS-2E, Hydrolabs Datasonde, 2 sediment traps, 1 acoustic release
Current velocity: 2 depths
Temperature: 2 depths
Salinity: 2 depths
Nitrate: 2 depths
Oxygen: 2 depths
Turbidity, oxygen, downwelling irradiance, pH: near bottom (1 m above release)
Laptops (2) for deployment initialization (GERG)

Survey measurements:
CTD: salinity, temperature, DO, transmission, chlorophyll, PAR (continuous)
Bottle: ammonia, nitrate, nitrite, phosphate, silicate, urea, dissolved oxygen, salinity
Bucket/Pogo salinity and nutrients
Particulate organic material and Dissolved organic material (lipids)
3-m salinity, temperature, chlorophyll (GERG system and Biggs' fluorometer) and SAIL

Boxcore (refrigerate samples for on-shore analysis): Smallwood/Dellapenna core samples


Figure 1. Station map for MCH2 NOAA Hypoxia Cruise 2 24 June - 1 July 2004.


Figure 2. Station plan for MCH2 NOAA Hypoxia Cruise 2 24 June - 1 July 2004.

Synopsis of sampling and deployments

The clusters of stations in Figure 2 represent the hypothesized three zones of hypoxia. A multi-instrumented mooring will be recovered and deployed near the center of each cluster. Benthic respiration will be monitored aboard ship using water samples drawn at each mooring site. Samples will be drawn from the incubation chambers at regular intervals (e.g., 6 hours). The hydrographic survey will consist of CTD/bottle casts, boxcores, and other measurements. Upon survey completion, we will transit to the next zone. A test station will be done on the transit to Zone C from Galveston. Bucket nutrients and salinity will be done between zones to locate the river plume. The ship's flow-through system and shipboard ADCP will be run for the duration of the cruise. Water column primary production will be measured at daytime sights in each zone. We hope for at least 8 sites per zone. Forty-minute incubations are planned, however, 20-minute incubations may be used. 58 CTD stations are planned. Depending on the location of the Mississippi River plume (imagery provided by Nan Walker at LSU) some stations in Zone A may be moved east and south of the delta. We will be doing microbial structure and geochemistry at 15 stations. For microbes, we will sample from top, middle, and bottom bottles. A bottom-tripped frame containing four 1.5-l Niskin bottles, CTD, and transmissometer will be deployed at each station.