Metadata Report for BODC Series Reference Number 2246634

• 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

These data have no specific confidentiality restrictions for users. However, users must acknowledge data sources as it is not ethical to publish data without proper attribution. Any publication or other output resulting from usage of the data should include an acknowledgment.

If the Information Provider does not provide a specific attribution statement, or if you are using Information from several Information Providers and multiple attributions are not practical in your product or application, you may consider using the following:

"Contains public sector information licensed under the Open Government Licence v1.0."

Narrative Documents

Stand Alone Pump (SAP)

A submersible battery powered water pump that sucks water through various filters leaving the materials of interest on the filter for analysis. SAPs are deployed clamped to a hydrographic wire and may be used to sample at depths of up to 6000 m. A SAP can pump thousands of litres of water over a few hours.

Stand Alone Pump (SAP) POC, PON and ²³⁴Th data from RRS Discovery cruise D285/D286

Originator's protocols

The RSS Discovery cruises of D285 and D286 represent two legs of a cruise undertaken as part of the CROZEX project on the Crozet Plateau in the Southwest Indian Ocean. The first leg (D285) took place between 03 November 2004 and 10 December 2004. The second leg (D286) took place between 13 December 2004 and 21 January 2005 with the ship docked in Port Elizabeth between legs. The information below is taken from cruise reports and published journal papers. Where information has been taken from journal papers rather than a cruise report, a citation has been provided. Information lacking a specific citation has been taken from a cruise report. In some cases there are discrepancies between journal papers and cruise reports, and this has been indicated in the text.

Samples for particulate organic carbon (POC), particulate organic nitrogen (PON) and Thorium-234 (²³⁴Th) were collected using a Challenger Oceanic Stand Alone Pump (SAP) deployed at the base of the export layer. The appropriate SAP deployment depth was determined each time based on water temperature, fluorescence and transmissance profiles measured by a CTD unit. The SAP was deployed below the thermal mixed layer, below the bulk of the chlorophyll and below the region where transmission starts to increase, with an additional margin of error of approximately 20 m below these features. This enabled the SAP to collect particles sinking out of the biologically productive surface layers.

The SAP was typically set to pump for 90 mins and filtered approximately 2000 litres of water in that time. A 300 mm diameter 53 µm nylon mesh monofilament screen was inserted into the filter holder of the SAP (Planquette et al., 2009; note that filter details differ slightly in the cruise report). Once the SAP was back on board the filter was removed and rinsed with 1 litre of filtered thorium-free seawater. The sample was then split using a Folsom splitter as follows:

• 6/8^th filtered onto a 142 mm 0.8 µm polycarbonate filter for ²³⁴Th
• 1/16^th filtered onto a pre-weighed GF/F filter for POC and PON analyses
• 1/16^th filtered onto a 20 µm polycarbonate filter for Biogenic Silica
• 1/6^th stored in Lugols and Formalin for microscopy
• 3 x 5 ml of 1/16^th filtered for Chlorophyll
• the remainder of that 1/16^th split filtered for HPLC pigment analysis

Thorium activity

The measurement of total (dissolved + particulate) ²³⁴Th activity in seawater samples is described in Morris et al. (2007) and was based on the MnO₂ precipitation method (Rutgers van der Loeff and Moore, 1999; Turnewitsch and Springer, 2001; and Thomalla et al., 2006). The procedure was scaled to use 10 L samples and all apparatus were washed with a solution of 10 ml of 30% H₂O₂l^-1 of 1 M HCl followed by rinsing with Milli-Q water. Three drops of 25% NH₃ and 125 µl of 60 gl^-1KMnO₄were mixed and added to 10 L aliquots followed by 50 µl of 400 gl^-1MnCl₂.4H₂O. After mixing once more, and thus producing MnO₂ precipitate, the samples were left to stand for 8 hours. The precipitate was then resuspended and filtered onto a 142 mm diameter, 0.8 µm pore polycarbonate, Isopore filter (Millipore product ATTP 142 50). Following filtration, the filters were rinsed with 50 ml of milli-Q water and drained of excess water under vacuum. While the filters were still damp they were folded in half exactly and left to air dry. Once dry, filters were folded with repeatable geometry into 18 x 18 mm squares, wrapped in mylar film and ²³⁴Th activity was determined onboard ship using a DTU Nutech (Riso) GM-25-5A low-level beta Multicounter system.

Samples were counted as soon as possible after sampling with repeated counting over a six month period covering > 6 ²³⁴Th half lives. This repition was performed to check that the activity decrease followed the expected decay of ²³⁴Th and also allowed a background correction for activity intrinsic to the detector and from other long-lived natural beta emitters. A regression analysis was carried out on the repeated counts to back calculate the ²³⁴Th activity to the time of sampling.

POC/PON determination

POC/PON samples were stored at -20 °C until they were ready for analysis (Morris et al., 2007). Samples were then analysed with the high-temperature combustion technique using a Carlo-Erba NA-1500 Elemental Analyser, following standardisation with acetanilide. See Ehrhardt and Koeve (1999) for further details of the analytical process.

BODC processing

The data were submitted in an Excel spreadsheet and loaded to the BODC database. Station identifiers in the spreadsheet did not match those in the cruise report event logs (tables 1.3 and 1.4), which often list several instrument deployments at the same station, leading to similar identifiers (e.g., 15492, 15492#2 and 15492#3 were CTD, SAP and float deployments, respectively, at station 15492). In the Excel spreadsheet submitted by the originator, only a station identifier was provided (i.e., details such as #2 had been omitted). In addition, the station numbers had been changed on occasion to match those of nearby CTD casts used to collect additional Thorium samples (those data have been loaded separately and are described in a different document). Following discussion with the originators, BODC used the station identifiers from the cruise report event logs rather than those in the data file, as detailed below.

The PON value for the sample from station 15580#2 was later replaced by the value published in Planquette et al. (2007), as it differed from that submitted in the Excel spreadsheet. The matter was raised with the originator but we were unable to establish which value was correct. As a result, the published value was used in the finalised dataset. The original value is given below in the data quality report section.

POC and PON were loaded with no unit conversion, while ²³⁴Th data were converted from the originator's units of decays per minute per litre to milliBecquerels per litre. Using the methodology information provided in Planquette et al. (2009) and Morris et al. (2007), each variable was assigned an appropriate BODC parameter code, as detailed below.

Data quality report

It was noted during BODC processing of the Thorium data that the values were an order of magnitude lower than those obtained from CTD rosette samples collected on the same cruise at similar times, depths and locations, analysed using the same methods and submitted to BODC in the same units (this dataset has been processed separately). The originators were informed but we were unable to establish whether any of the values were suspect.

PON (SFNTCNPK) for the sample from station 15580#2 (BODC station identifier 732102; BODC sample identifier 200718) is flagged as suspect due to different values having been obtained from two sources. The original value was 0.07 µmol l^-1 but this was superseded by the value published in Planquette et al. (2007).

References cited

Ehrhardt, M. and Koeve, W., 1999. Determination of particulate organic carbon and nitrogen, chapter 17. In Grasshoff, K., Kremling, K. and Ehrdhardt, M. (Eds), Methods of Seawater Analysis. Wiley-VCH Weinheim.
Morris, P., Sanders, R., Turnewitsch, R. and Thomalla, S., 2007. ²³⁴Th-derived particulate organic carbon export from an island-induced phytoplankton bloom in the Southern Ocean. Deep-Sea Research II, 54, 2208 - 2232.
Planquette, H., Fones, G.R., Statham, P.J. and Morris, P.J., 2007. Origin of iron and aluminium in large particles (>53 µm) in the Crozet region, Southern Ocean. Marine Chemistry, 115, 31 - 42.
Rutgers van der Loeff, M.M. and Moore, W.S., 1999. Determination of natural radioactive tracers. In Grasshoff, K., Kremling, K. and Ehrhardt, M (Eds), Methods of Seawater Analysis. Wiley-VCH Weinheim (Chapter 13).
Thomalla, S., Turnewitsch, R., Lucas, M. and Poultan, A., 2006. Particulate organic carbon export from the North and South atlantic gyres, the ²³⁴Th/²³⁸U disequilibrium approach. Deep Sea Research II, 53, 1629 - 1648.
Turnewitsch, R. and Springer, B.M., 2001. Do bottom mixed layers influence ²³⁴Th dynamics in the abyssal near-bottom water column? Deep-Sea Research I, 48, 1279 - 1307.

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

Data Activity

BODC Sample Metadata Report for D285_SAP_15543#2

Please note:the supplied parameters may not have been sampled from all the bottle firings described in the table above. Cross-match the Sample Reference Number above against the SAMPRFNM value in the data file to identify the relevant metadata.

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: