D341: Porcupine Abyssal Plain cruise 2009
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Cruise blog
Tuesday 4 August 2009
PAP – Moorings: Many things lurk beneath
Since 1989 the PAP site in the North East Atlantic (49ºN, 16ºW), has been one of the most frequently studied deep ocean sites. The main reason is that the PAP site is reasonably close to the shore yet it is a deep open ocean site (4840 m) allowing studying oceanic processes along the water column without coastal interferences. The PAP site is currently one of the nine Deep Ocean/Sea observatories which are under the EUROSites project.
Moorings can be equipped with instruments that are able to operate over long periods and produce time series data sets. At the PAP site there are traditionally two mooring sites. The first one is a subsurface mooring (traditionally called PAP3) extending from 3000 m down to the seabed (mooring length: approx. 1800 m). The mooring is equipped with three sediment traps (McLane parflux model: two deployed at 3000m and one 100 meters above the seabed) and two current meters (Aandera RCM) deployed below the first and third sediment trap. The main objective is to collect time series records of sinking particles over a year’s period.
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The second mooring is the PAP 1 Deep Ocean Mooring System (DOMS). Its main purpose is to sustain a suit of sensors, analyzers and samplers. Most of the sensors are deployed at approx. 30 m. Below the sensors frame and down to 1000 m, are a series of Conductivity, Temperature and Depth sensors (Seabird Microcat CTD) installed at various depths. An important feature is that the mooring is equipped with real time telemetry, enabling the monitoring/recording of the deployed sensors. This mooring has had many “interesting” experiences over the past years (e.g. in 2005 the subsurface mooring was lost and there were strong evident supporting that it was “fished”). Recently (23rd May 2009 during cruise JC34T) a surface buoy mooring was deployed bearing a heavily instrumented sensors frame and the telemetry system, which has provided real time high frequency records of nitrates, chlorophyll, temperature – salinity – depth (30, 100, 1000 m). One of the main objectives of cruise D341 on the PAP site is to turn around both PAP3 and PAP1. Especially for PAP 1, more sensors will be added on the frame (CO2, O2, Radiance – Irradiance, Currents), providing a detailed biogeochemical and physical image of the PAP site over extended time periods. Apart from these moorings, during cruise D341 a subsurface mooring extending from 50m down to the seabed was deployed. On the mooring line there are five In situ Oxygen Dynamic Autosamplers– IODA (deployment depths: 50, 300, 600, 1000, 2000 m), which are able to measure oxygen in situ and oxygen dynamics. IODA is a custom made system designed and manufactured in France (collaboration between LMGEM and CPPM in Marseille). On the mooring there are also a zooplankton time series sampler (McLane ZPS), four Microcat CTDs and three Nortek current meters. All the above are deliverables within the EuroSites project. Mooring design, deployment and recovery is a demanding job, which requires a lot of preparation and experience in order for the structure to survive the harsh conditions during its deployment period. The gain though is very valuable as successful moorings provide the base/platform for successful deployment of long term operating instruments. |
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Thanos Gkritzalis – Terry Edwards – Peter Keen – Dominique Lefevre.
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