Sruise Report, RV ATAIR, Cruise 0671013-1, Bremerhaven - Skagen - Aberdeen, 19 Jul - 11 Aug 2022 | 
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into 3 litre PE bottles. After sampling, the water sample was filtered using a low- pressure 
filtration system. Filtration is done through a glass fibre filter (@ = 47 mm and pore size 0.4um) 
an a glass filter plate. For this purpose, the PE bottle was shaken at first to allow for homo- 
gensosation of the water sample. Then, a measured volume was filled into a filtration tulip, 
which was connected to a suction bottle. The volume to be measured was determined by the 
oreviously recorded Secchi depth, see Table 5.4. The exact sampling depth, the Secchi depth, 
the filtered volume and the room temperature were recorded. After filtration, the glass fibre 
filter with the sample residue was removed from the filtration tulip, folded twice and transferred 
to a PE centrifuge tube with a screw cap. This tube was wrapped in aluminium foil to avoid 
axposure to light. The sample was labelled by assigning a unique sample identification number 
similar to Bedford numbers, which was applied directly to the tube and the aluminium foil. The 
sample was then frozen and stored at -80°C to allow for later analysis in the home laboratory. 
One duplicate sample was analysed per day. On-board filtration was performed as described 
in BSH (2022). Figure 5.6 shows the location of stations with water sampling for subsequent 
chlorophyll-a determination. Corresponding water sampling was carried out on mostly daylight 
stations with Secchi depth measurement. If there was a delay between collecting the water 
from the Niskin bottle and the filtration, the water sample was stored in the dark and cooled in 
the refridgerator. 
Spectrophotometric analysis was carried out in the home laboratory after the cruise to deter- 
mine the total chlorophyll-a content in seawater. The method follows Jeffrey and Humphrey 
(1975). The interlaboratory performance study (QUASIMEME, R2022.1) for the parameter 
chlorophyll-a in seawater during the measuring period in our laboratory was successful. The 
z-scores are 0.5 / 1.2. The mean range for the duplicates (14 samples) taken on this cruise 
was less than 0.06 ug/L CHLA. 
SEN 
Require Volume [ml] for Filtration 
up to 500, onlv for coastal stations 
> 
5-4 U 
ı 0- 
up to 1000 
up to 1500 
up to 3000 
Table 5.4. Secchi depth and corresponding sample volume required for the filtration of chlorophylha 
samples.