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Cruise 4: R/V Gyre 05G05

Mechanisms Controlling Hypoxia on the Louisiana Shelf
22-29 March 2005

Port: Galveston, Texas
Mobilization: 22 March 2005
Cruise: 23 - 29 March 2005

Objectives

(a) to deploy one mooring 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

Collecting Data
Personnel

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. Eurico D'Sa -LSU : Bio-optical Measurements and Surface Biology
Dr. Antonietta Quigg-TAMUG- Water-column Biology
*Mr. Bruce Spiering - NASA: Bio-optical Measurements

Technicians
Jorge-GERG: mooring deployment, Marine Tech
Paul Clark-GERG: mooring deployment, ADCP operation, CTD/Electronics Tech
Cris Schmidt: nutrient/oxygen/salt tech, NAS Specialist
Eddie Webb: CTD/electronics tech
Julie Manuel: Geological oceanography, cores TAMUG

Students
Scott Davenport: Master Diver TAMUG (S)
Erin Johnson: microbial structure, water sampler (S)
Sara Keach, Geochemistry (S) TAMUG
Valerie Kiselkova: Physical oceanography, ADCP processing, water sampler (S)
Sudeshna Lahiry: Physical oceanography, water sampler (S)
Shellie Meyer: microbial biology (S) TAMU
Clif Nunnally: benthic productivity, water sampler (S) TAMUG
Derek Schultz: Biology (S) TAMUG
Chihlin Wei: benthic productivity, diver (S) TAMUG
Tara Hans: (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 (aka POGO)(OCNG)
Shipboard PAR (OCNG)
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 (at GERG)
Turner Fluorometer (OCNG) and Chelsea flowthrough (OCNG)
1.5-l bottle for bottom bottle oxygen (Bottle 1 and POGO) (GERG)
0.45 m boxcore (TAMUG)
Freezer bags for core samples: TAMUG (Dellepenna)
Microbial Structure sample supplies (Long)
Shipboard ADCP (GERG)
C14: primary productivity (Quigg)
Digital cameras - All
CDOM filtering supplies, pump, filter, milli-Q water - (D'Sa, LSU)
Bio-optical Package/Radiometer - (Spiering, NASA)
Benthic Respiration Chambers - (Nunnally, TAMUG MARB)
Radio/CD player

Mooring Measurements: (see mooring schematic)
Instrumentation: 1 RCM9, 1 RCM7, 1 NAS-2E, 1 Hydrolab DataSonde traps
Sediment traps (6) (TAMUG-MARB)
Current velocity: 2 depths
Temperature: 2 depths
Salinity: 2 depths
Nitrate: 1 depth
Oxygen: 2 depths
Two witness buoys
Laptop (1) 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, DO (Pogo only), and nutrients
Particulate organic material and Dissolved organic material (tentative)
3-m salinity, temperature, chlorophyll (GERG system and Biggs' fluorometer) and SAIL
Boxcore (refrigerate samples for on-shore analysis): Cifuentes/Dellapenna/Long core samples

Synopsis of sampling and deployments

The clusters of stations in Figure 1 represent the hypothesized three zones of hypoxia. A multi-instrumented mooring will be deployed near the center of Zone C. Diving operations during the deployment include uncapping sediment traps on the mooring and running a tag line from the mooring to the rig nearby. 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. About 70 CTD stations are planned. Depending on the location of the Mississippi River plume (imagery provided by NASA and LSU) some stations in Zone A may be moved east and south of the delta. We will be doing microbial structure and geochemistry at 9 stations. For microbes, we will sample from top, middle, and bottom bottles. The POGO containing four 1.5-l Niskin bottles, CTD, and transmissometer will be deployed at each station. The order of zones will be C followed by B followed by A. On the return to port we will sample along the 20 m isobath. Some stations may be sampled on the run out and on the way back. Nutrients, DO, and salinity will be sampled from all tripped bottles at each station. The number of tripped bottles will depend on the water depth. Multiple bottles will be tripped if demand is high for samples at a particular site.

If there is sufficient time near the end of the cruise, we will stay on station near mooring Site C (29°N, 92°W) for a tidal cycle (roughly 24 hours). CTD/bottle/BOP casts will be performed roughly every hour. The purpose of this sampling is to look for internal waves and associated biological response.

One mooring deployment is planned at Site C near 29°N, 92°W. Two witness buoys will be deployed close by. Divers will uncap sediment traps and run a tag line to a nearby rig. Forest Oil owns the rig; we have full permission from the owner to place this mooring with marker buoys at this site. The marker buoys are equipped with radar reflectors and warning lights.

D'Sa and Spiering will deploy a bio-optical package at selected stations during the cruise. It is anticipated that the bio-optical package (BOP) will be deployed from the CTD area using the boxcore winch. The BOP will be deployed roughly two dozen times. D'Sa will also measure CDOM at selected stations.