Metadata Report for BODC Series Reference Number 684743

• Metadata Summary

• Problem Reports

• Data Access Policy

• Narrative Documents

• Project Information

• Data Activity or Cruise Information

• Fixed Station Information

• BODC Quality Flags

• SeaDataNet Quality Flags

Metadata Summary

Problem Reports

No Problem Report Found in the Database

Data Access Policy

Open Data supplied by Natural Environment Research Council (NERC)

You must always use the following attribution statement to acknowledge the source of the information: "Contains data supplied by Natural Environment Research Council."

Narrative Documents

RD Instruments 150kHz Narrow Band Acoustic Doppler Current Profiler

Specifications

RRS Discovery 286 150kHz VMADCP

Deployment and originator's processing

Two RDI Vessel-Mounted Acoustic Doppler Current Profilers (VM-ADCPs) were operated on Discovery 286; the 150kHz VM-ADCP and the 75 kHz Phased Array instrument (Ocean Surveyor) that had been fitted immediately prior to FISHES (Discovery 253, May-June 2001). The 150 kHz ADCP is mounted in the hull 1.75 m to port of the keel, 33 m aft of the bow at the waterline and at an approximate depth of 5 m. The 75 kHz ADCP is mounted in a second well in the hull, but 4.15 m forward and 2.5 m to starboard of the 150 kHz well. The 150kHz RDI ADCP was logged using RDI Data Acquisition Software (DAS) version 2.48 with profiler firmware 17.20. The instrument was configured to sample over 120 second intervals with 96 bins of 4 m thickness, pulse length 4 m and a blank beyond transmit of 4m. The high vertical resolution was chosen to support the remote detection of zooplankton patchiness. Early in the cruise the ADCP was switched to bottom and water track mode over shallow ground to enable calibration. After closely inspecting the data from the two ADCPs without configuring them to synchronise their pings over the ensemble period, it was decided to leave them in this mode as little evidence of interference could be seen. To synchronise the instruments, the 150 kHz instrument has to be set as the master and the 75 as the slave, as recommended by RDI and discussed by Penny Holliday in the D253 cruise report. The result is that each ADCP has only 40 water track pings in the 2 minute period. With no obvious evidence of interference this seemed an unacceptable compromise. Spot gyro heading data were fed into the transducer deck unit where they were incorporated into the individual ping profiles to correct the velocities to earth co-ordinates before being reduced to a 2 minute ensemble. Following advice from RDI, the 150 KHz ADCP on RRS Discovery had been refitted in dry dock, several years ago, to a heading offset of ~45°. This offset was accounted for in the DAS software configuration on D286.The following table describes the setup of the 150kHz ADCP.

A calibration of the 150 kHz ADCP was achieved using bottom tracking data available from our departure across the Agulhas Bank. Using long, straight, steady speed sections of standard two minute ensemble profiles we obtained a calibration of tanØ= -0.0039 (±s.d.= 0.0080), Ø= -0.22° and A =1.0034 (±s.d.= 0.0064)

BODC processing

A total of 37 files were submitted to BODC. The data were supplied in P* binary format. The following variables were transferred to BODC QXF format (a BODC-defined subset of NetCDF and BODC's format for 2 dimensionsal datacycle storage) using transfer process tr339.

Screening and Data quality

The data have been visually screened for obvious problems using the BODC EDSERPLO software. No significant problems were detected.

Project Information

CROZet natural iron bloom EXport experiment (CROZEX)

The multidisciplinary CROZet natural iron bloom EXport experiment (CROZEX) was a major component of the Natural Environment Research Council (NERC) funded core strategic project Biophysical Interactions and Controls over Export Production (BICEP). The project is the first planned natural iron fertilisation experiment to have been conducted in the Southern Ocean.

The overall objective of CROZEX was to examine, from surface to sediment, the structure, causes and consequences of a naturally occurring phytoplankton bloom in the Southern Ocean. The Crozet Plateau was chosen as the study area. This area typically exhibits two phytoplankton blooms a year, a primary bloom in that peaks in October and a secondary bloom in December or January. Specific aims with respect to these were to:

• Determine what limits the primary bloom
• Determine the cause of the secondary bloom

The project was run by the George Deacon Division (GDD), now Ocean Biogeochemistry and Ecosystems (OBE) at the National Oceanography Centre Southampton (NOCS). Participants from five other university departments also contributed to the project.

The project ran from November 2004 to January 2008 with marine data collection between 3^rd November 2004 and 21^st January 2005. There were 2 cruises to the Crozet Islands Plateau, which are summarised in Table 1.

Table 1: Details of the RRS Discovery CROZEX cruises.

The two cruises aimed to survey two areas at different phases of the bloom cycle described above. A control area to the south of the Crozet Islands, which is classified as High Nutrient Low Chorophyll (HNLC), where the blooms do not occur and a second area in the region of the blooms to the north of the Crozet Islands.

Sampling was undertaken at ten major stations (see Pollard et al., 2007) numbered M1 to M10. The following observations/sampling were conducted at each station where possible:

• Several CTD casts sampling:
  • Iron (using a titanium rig)
  • ²³⁴Th
  • Physical parameters (temperature, salinity etc)
  • Oxygen
  • CO₂
  • Nutrients using a stainless steel rig including a Lowered Acoustic Doppler Current Profiller (LADCP)
• At each thorium cast there was an associated Stand Alone Pump System (SAPS) deployment
• At some stations, a drifting PELAGRA trap was deployed for the duration of the work
• Megacoring was undertaken at M5 and M6
• Gravity coring was undertaken at M5, M6 and M10
• Longhurst Hardy Plankton Recorder (LPHR) tows were undertaken at a few major stations

For each of the major stations (M1 to M10), the following were determined:

• Primary productivity
• New Production
• Phytoplankton community composition
• Bacterial activity
• Iron
• Nutrient drawdown
• Thorium export

Sampling between major stations included:

• SeaSoar runs instrumented with:
  • CTD
  • Optical Plankton Counter (OPC)
  • Fast Repetition Rate fluorimeter (FRRf)
• Physics CTD casts on several lines
• Argo float deployments
• Zooplankton nets at nearly every CTD and major station
• Underway and on-station CO₂ measurements
• Underway nutrients and radium sampling
• 5 to 6 day ship-board iron-addition incubation experiments
• Checks against near-real-time satellite and model data
• Mooring deployments based on the satellite imagery in support of the CROZET (Benthic CROZEX) project.

The CROZEX cruises included 6 extra days in support of the CROZET (Benthic CROZEX) project, whose main cruise took place one year after the CROZEX cruises. The CROZET work undertaken during the CROZEX cruises was primarily the moored sediment trap deployments, although some of the coring work is applicable to both projects.

CROZEX produced significant findings in several disciplines, including confirmation that iron from Crozet fertilised the bloom and that phytoplankton production rates and most export flux estimates were much larger in the bloom area than the HNLC area (Pollard et al. 2007). Many of the project results are presented in a special CROZEX issue of Deep-Sea Research II (volume 54, 2007).

References

Pollard R., Sanders R., Lucas M. and Statham P., 2007. The Crozet natural iron bloom and export experiment (CROZEX). Deep-Sea Research II, 54, 1905-1914.

Data Activity or Cruise Information

Cruise

Complete Cruise Metadata Report is available here

Fixed Station Information

No Fixed Station Information held for the Series

BODC Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle:

SeaDataNet Quality Control Flags

The following single character qualifying flags may be associated with one or more individual parameters with a data cycle: