Analysis of sediment grain size samples from Tvärminne 2007

(Joanna Norkko 17.3.2008, edited by Laura Kauppi for SYNC 12.1.2024)

Samples taken with 2.1 cm diam syringe, sliced off top 5 cm and stored frozen at -20ºC.

NOTE: Be careful with the hydrogen peroxide; use gloves and eye protection, work in fume hood!

 NOTE: Always sieve the sediment through 2 mm sieve and analyze the <2mm fraction in the grain size analyzer. Remember to weigh your fractions to get proper grain size distribution! (See instructions below).

1. Make up 6% H2O2 (200 ml 30% H2O2 and 800 ml water).
2. Move the sample from its snaplock bag to a 250 ml container, remove any large shells.
3. Add enough H2O2 to cover the sediment (about 30 ml) to remove organics by digesting for 2+ days. Stir each day.
4. Sieve your sediment through 2 mm sieve, weigh and label (sample code + sieve size) 2 x 250 ml containers for each sample (1 for >2mm and one for <2 mm). Analyze only the <2mm fraction in the SYNC (this avoids clogging the analyzer). Sieve through 2 mm sieve collecting the water in a 5L bucket. Note: Wet all sieves first
5. Wash sediment from the sieve into appropriate labelled preweighed containers and dry at 60ºC, weigh when dry.
6. Leave water in labelled 5L bucket to settle for ~48hrs (longer if water is not clear). Decant off water and wash fine sediment into preweighed container. Dry at 60ºC, weigh when dry.
7. Calculate the percentage of each sediment fraction.
8. Analyze the under 2 mm fraction / the unsieved sediment with Microtrac SYNC.

Determine fractions to be used - note we will be using sieves in bold only.

Sieves              fraction

> 2 mm           gravel

> 500 µm       coarse sand

> 250 µm       medium sand

(> 125 µm      fine sand)

> 63 µm         very fine sand

(> 31 µm        coarse silt)

< 63 µm         silt & clay

Amendments by SeVa to grain size analysis (version 17.3.2008 by JoNo)

1. move “frozen” sample
2. stir “2 times a” day
3. Sieve through 2mm into a 500um sieve with an empty 5L bucket under. Remove 2mm sand into container. Continue sieving sand through the 500um sieve into the same bucket. Remove 500um sand into container. Sieve all content of bucket through 250um sieve into an empty bucket. Remove 250um sand into container. Sieve all bucket content through 63um sieve into empty bucket. Remove 63um sand into container.
4. leave buckets for 48hrs close to suction pump, use suction sample to remove as much as possible of over lying water with H202 without disturbing sediment at bottom. Wash remaining sediment content into pre-weighed containers. Leave to settle for 48hrs. Use suction pump to remove excess water from smaller containers. Dry at 60C, then weigh.