MechanismsControlling Hypoxia on the LouisianaShelf 6 April - 11 April 2010 Port: LUMCON, Cocodrie, Louisiana  (a) to conduct 24-hour microbial, zooplankton, phytoplankton,DOC/POC, and biomarker process measurements at 3 stations; Personnel Scientists  National Oceanic and Atmospheric Administration (NOAA), Centerfor Sponsored Coastal Ocean Research. ParticipatingInstitutions TAMU – College Station,Dept. of Oceanography Project Website: Data Collection Instrumentation and Equipment (LUMCON): 12-bottle Rosette (with bottle 1 (5 L) General ProcessMeasurements:
ResearchGroup Measurements: Bianchi: Niskin bottlesamples: From the water column (Niskin bottles) we will sample one or twodepths in the upper layer, and one or two depths in the lower sub-pycnoclinelayer. We will close multiple bottles at each depth depending on water needs. AllPOM and DOM duplicate samples will be collected from CTD/rosette casts at 0, 6,12, 18, 24 hr during each 24 hr station = 5 cycles per 24 hr. Anticipated water needs are: Dagg/Quigg: We would sample at0, 6, 12, 18, 24 hr during each 24 hr station = 5 cycles per 24 hr station). Ateach station we would like CTD/rosette casts every 6 hr to determine watercolumn structure (including the depth of the pycnocline – we assume there willbe a two layer water column). We will take water for preserving and forexperiments. Niskin bottle samples: From the water column (Niskin bottles) wewill sample one or two depths in the upper layer, and one or two depths in thelower sub-pycnocline layer. We will close multiple bottles at each depthdepending on water needs. Anticipated water needs are: Fennel: No measurements inparticular. Graduate student Robin Wilson is participating in the cruise togain seagoing experience (a graduate program requirement he has to fulfill). Heis willing to help with anything as needed. Mills: Active microbialpopulations in water column and sediment; sediment geochemical profiles (SO42-,H2S, Fe(II), Fe(III), TRS, Cl, TOC)  Figure 1. Locations at 3 anchor process stations along the 20 m isobath. Ignore the locations indicated by the red circle. Cruise Synopsis This cruise will examine short-term biogeochemical processes at 3 stations located on the inner Louisiana shelf and how they with relate to physical processes. This is the first time in the history of the MCH program that such an emphasis will be made on the biogeochemical flux and rate measurements. The main objective of this research is to investigate the mechanisms that control the onset hypoxia, which occurs off of coastal Louisiana each summer, by examining dissolved and particulate organic matter (DOM and POM) cycling rates and sources in the region between the Atchafalaya and Mississippi River Plumes. The methods include deployment of real-time reporting instrument systems, an extensive coupled biological/physical/sediment numerical modeling effort, and shipboard process studies (to complement the real-time observations). Sampling on this cruise will consist of CTD/bottle casts and box-cores. Depending on time and weather considerations, we have planned biogeochemical sampling for 24-hour at each of the 3 anchored stations. A test station will be done on the transit to the first CTD station to train graduate students on CTD and rosette sampling and test scientific apparatus. The ship's flow-through system will be run for the duration of the cruise. Bucket nutrients and salinity may be done between planned stations to best locate the river plume. A bottom-tripped frame containing 5 L Niskin bottles, CTD, and transmissometer will be deployed at each station in addition to the 12-bottle rosette. An RDCP current profiler and short-term sediment trap will be deployed at the start of the station. A shipboard 600-kHz ADCP will run throughout the cruise. We will also conduct a number of additional complementary and related experiments during the course of this cruise. These experiments involve the collection of additional water and sediment samples for analysis both at sea and on shore. Prokaryotic community ecology: A combined molecular and geochemical approach will provide a better understanding of the prokaryotic community ecology. Building upon data from previous cruises, sediment associated prokaryotic activity will be assessed by observing transitions in sulfur and iron valence states and concentrations. Supporting anion and cation measurements will provide a more complete view of the potential nutrient cycling. The inorganic chemistry will be compared to the organic chemistry and the physical sediment characteristics. The focal point of the sediment biogeochemistry will be high-resolution sampling and sequencing of the active prokaryotic populations (i.e., Bacteria and Archaea domains). Structural and functional gene targets will be used to determine active metabolic processes within the sediment. Data collected on this cruise will be compared to previous cruises to identify potential trends in population distribution and activity. For the first time on an MCH cruise, the water column prokaryotic populations will also be subjected comprehensive molecular analysis. Focus will shift from sulfur and iron to nitriogen related populations and processes. Again, active populations will be observed through both structure and function based comparisons. Geochemistry obtained via shipboard operation will be used to support molecular analysis. Data collected will provide baseline assessment of water column prokaryotic ecology prior to the onset of summer hypoxia.
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