Absorption coefficient spectra (median) of phytoplankton during POLARSTERN cruise PS93.2
Absorption coefficients by phytoplankton (aph) were measured on water samples collected from underway AC-S flow-through system outflow and CTD. Measurements were performed using a dual-beam UV/VIS spectrophotometer as described in Liu et al. (2018) and Liu et al. (2019).
- About sampling:
a) underway samples were collected from unfiltered AC-S outflow (depth: 11m); CTD samples with 5-6 depths were collected on upcast.
b) vacuum pressure for filtration: maximum 200 hPa
c) samples were shock frozen in liquid nitrogen and then stored in -80°C until measurement after cruise.
d) blank filters were collected by soaking them in 0.2um filtered seawater.
e) replicates were not collected.
- About measurements:
a) Instrument: dual-beam UV/VIS Spectrophotometer (Cary 4000, Varian Inc., Palo Alto, CA, USA) equipped with a 150 mm integrating sphere (external DRA-900, Varian, Inc. and Labsphere Inc., made from Spectralon (TM)).
b) wavelength range of scan and resolution: 300-850 nm, 1 nm.
c) slit band width: 2 nm.
d) scan speed: 150 nm min−1
e) Sample filters were extracted with 95% methanol for the absorption measurement of NAP.
f) The baseline of the spectrophotometer was set with a dry piece of a blank filter. Filters were wetted with purified water and measured regularly after every fifth sample filter served as references.
- About data analysis:
a) interpolated wavelength range and resolution: 350-750 nm, 1nm.
b) pathlength amplification factor (beta correction factor): 4.5 (Röttgers and Gehnke 2012; Röttgers et al., 2014).
c) Null-point scattering correction at 750 nm is applied.
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