meth_1.6 Pelagic Water Sampling for Ocean Voyages

Contributor(s): Lev Bodrossy (lev.bodrossy@csiro.au); Jodie van de Kamp (jodie.vandekamp@csiro.au)

Citation:

AM Project ID: Legacy (or list voyages used on?)

Equipment:

1. Seawater sampling bottles (plastic) with screw cap lids × 8
2. Bottle carriers × 2 (each carrier will hold 4 bottles)
3. Peristaltic pump, attached to a (preferably) 8-head pump head
4. Tubing with luer-lock attachment, attached to pump heads
5. 2 µm Sterivex™ filter units with female Luer-lock inlet and male luer lock outlet
6. Small snap-lock bags for storage of individual filter units
7. Larger snap-lock bags for storage of all filter units from a single sampling station
8. Laboratory single-use gloves
9. Sterivex inlet and outlet caps OR Parafilm
10. 50 mL Luer-lock disposable syringes
11. Sampling log sheet (included at end of SOP)
12. 5-10% bleach
13. 70% EtOH

Method:

Pre-sampling preparation

1. Sterivex filter labelling: The preferred Sterivex filter labelling convention would be “CCC-RR-depth” with CCC corresponding to the CTD cast number and RR corresponding to the CTD rosette/Niskin bottle number the sample was taken from. For example, if the sample was taken from CTD cast 1, and niskin bottle number 36, at 100 m depth, the label on the Sterivex filter would be “001-36-100 m”
2. If Sterivex inlet caps were not provided with the sampling box for the voyage, Parafilm should be pre-cut to an appropriate size to seal both ends of the Sterivex filter after filtering.
3. The sampling bottles should be rinsed with MilliQ water before sampling each cast.
4. The tubing (with luer lock attachment) should be flushed with 70% ethanol at least once a day before sampling and flushed with MilliQ water after every filtering procedure before use in subsequent rounds of filtering.

At Sampling Station:

1. Conduct CTD-Niskin bottle casts to pre-determined depths.

 

Samples are usually collected at 6-8 depth points but this is dependant on full depth of water column and CTD cast regime/voyage priorities etc.

 

We are only interested in samples from the same depth that hydrochemistry are conducting analyses.

Surface, deep chlorophyll maximum, mixed layer depth, and max cast depth (bottom depth where possible) are the most important; other samples through the water column we usually aim for are; 500 m, 1000 m, 2000 m, etc. that is, 1000 m intervals till bottom). Ideally these depths will be consistent at all stations but understand there are variations depending on depth at individual stations.

1. While collecting seawater samples from the Niskin bottles, rinse bottle and bottle cap at least once with seawater sample, discard, and fill the bottle with 2 L of seawater. If possible, overfill to the brim before capping and transporting to filtering station.

 

If filtering isn’t occurring immediately, please place bottles (for a maximum of 4 hours) in a cold and dark location (such as refrigerator) to minimize changes.

At Filtering Station:

1. Wearing gloves, place one end of tubing in the bottles and pass tubing through pump head ensuring barb/luer lock fitting is attached to the end of the tubing (but without filter attached).
2. Run ~200 mL (or until the seawater level reaches the 2 L mark on the sampling bottle) seawater to flush the tubing, without filter attached (with pump flow controller set at midpoint).
3. Attached labelled Sterivex filter (labelled according to the guide mentioned in 1. above) to the luer lock fitting, connected to the tubing of the respective bottle of sample.
4. Filter the sample with the pump controller set to midpoint.

 

If filter blocks before 2 L has passed through, stop pump and record volume of water that was filtered in the Comments section of logsheet. Generally, this should not happen with seawater samples collected from open ocean locations.

1. After 2 L has passed through filter, let the pump continue for ~2 min to assist in drying filter.
2. Disconnect each filter from tubing, connect to a 50 mL syringe and purge out as much residual water from inside the filter housing as possible.
3. Cap both ends of filter with the respective inlet/outlet caps place in an individual snap-lock bag

 

If small snap-lock bags are not available, save the wrappers the Sterivex filters came in and use this to store the filters individually after filtering.

 

If inlet/outlet caps are not available, seal the ends of the filter with pre-cut Parafilm mentioned above.

1. Place individually wrapped filters from one sampling station into a larger ziplock bag. Label the large ziplock bag with
   • the CTD cast/sampling station number,
   • date
   • total number of Sterivexes/depths at which samples were collected from that station.

1. Store samples at -80 °C as soon as possible after filtering.
2. Record sample details in the sampling log sheet.
3. To clean the pump tubing after use, run 200 mL 5-10% bleach solution through tubing, followed by 200 mL milliQ or distilled water, and lastly 200 mL 70% EtOH (to dry the tubing and prevent biofilm growth between uses).

Sampling Log Sheet