Luckily, we found a reference to measure size-fractioned absorption coefficients of phytoplankton (Ciotti et al., 2002, please see attach file for detials). We design our experiment consistent with Ciotti et al.(2002) as follow:

1. Pass 0.5L or 1L sea water to GF/F 0.7μm poresize filter to obtain total paticulate absorption coefficient (ap).

2. Pass 0.5L or 1L sea water to 20μm filter (Millipore), and than pass the filtrate to GF/F 0.7μm poresize filter to obtain Nano+Pico of ap.

3. Pass 0.5L or 1L sea water to 3μm or 2μm filter (Millipore), and than pass the filtrate to GF/F 0.7μm poresize filter to obtain Pico of ap.

4. Micro of ap is obtained by subtracting Nano+Pico of ap from total ap.

Dear Lin,

For details on best practices for measuring particle absorption (size fractionated or otherwise) on a filter pad, please see: http://ioccg.org/wp-content/uploads/2015/10/absorption_protocol_forcommunitydistribution-sept2017-2.pdf. To use the method you described above, the whole sample and filtered samples should be compared to a blank or baseline sample of the same volume.

You may also find these resources helpful: http://www.oceanopticsbook.info/view/absorption/__level_2/benchtop_spectrophotometry_of_solutions_tmode and http://misclab.umeoce.maine.edu/OceanOpticsClass2019/schedule/ (see Lab 3).

Best of luck!

Sasha