POC/PON sampling protocol#

In-house contacts: Anette Wold

Status: To be checked

Sampling#

  • Collect water from Niskin bottles into 1-2L clean containers.

  • Filter 200 - 2000 ml and note exact amount, depending on particle concentration (needs slight coloration on filter), on pre-combusted 25 mm GF/F filters. The filters are combusted at 500°C for 12 hours and stored in aluminium foil.

  • Only use clean tweezers (wash with ethanol) to place filter onto stub, do not touch filter with hands

  • It is important to rinse the filter funnel and measuring cylinder with Milli-Q water in between samples to avoid contamination from one sample to the next which is particularly relevant if a low biomass samples is filtered after a high biomass sample.

  • For each filtration event/station, filter a Milli-Q reference (blank filter) using pre-combusted GF/F filters treated in the same way as the ones used for the samples.

  • After filtration, place each GF/F filter directly into a plastic petri dish or Pall filter slide and dry at 60°C in a drying oven. Make sure drying oven is clean (no dust etc.).

  • Pack Pall slides/petri slides w/ filter in aluminium foil and store at room temperature. Label samples properly.

Analyses#

  • POC/N samples are analyzed with continuous-flow mass spectrometry (CF-IMRS) carried out with a roboprep/tracermass mass spectrometer (Europa Scientific, UK) at the Finnish Environment Institute (SYKE) by Hermanni Kaartokallio.

  • All values have been corrected for instrument drift.

  • Detection limits: 5ug for C and 2-3µg for N

  • The results are given as absolute value [µg PON] & [µg POC] & and as δ15N & δ14C [‰]

Calculation#

  • Calculate concentration POC & PON (µg/L = µg / filtered volume)

  • Correct for blank by subtracting blank filter value. If this is not done use the blank filter value closest in time or average value for the filters from the same batch (filters burned at the same time).

  • In addition, provide concentrations in µmol L-1 (µmol/m3=µg/L divided by atomic mass, N = 14, C= 12)

Result is presented as:

Original values from lab:

  • PON [µg]

  • δ15N [‰]

  • POC [µg]

  • δ13C [‰]

  • C/N

Concentration in gram per volume:

  • PON [µg/L]

  • POC [µg/L]

Concentration in mol per volume:

  • PON [µmol/L]

  • POC [µmol/L]