The DOM extraction process is summarised in Figure . Each day, a fresh batch of seawater was collected from the tap into a clean 1000 L HDPE aquarium tank. From there, it was pumped sequentially through three pool filters (5 µm, 0. 5 µm, and 0.5 µm pore size) into a second clean 1000 L HDPE tank, where it was acidified with hydrochloric acid (HCl) to a pH of ~3. This water was pumped through the column for ~ 22 hours each day. On the first day the flow rate was gradually increased from 180 mL min -1 (3.5 bar pressure) to 330 mL min -1 (4.5 bar pressure) over a period of 3 hours. A flow rate of between 320 and 360 mL min -1 and 4 bar pressure was maintained for the rest of the extraction. Accumulated salts were then removed by flushing the column with ~ 2 column volumes (4 L) MilliQ 2.5 L methanol (MeOH). The column was then flushed with a further 4 L acidified MilliQ water. During the elution process, a fresh batch of seawater was filtered and acidified, after which the process was repeated. Eluted MeOH was collected into a series of ashed (4 hours at 550℃) glass Duran bottles and chilled overnight, along with a portion of acidified MilliQ which came through the column on either side of the MeOH (~ 3.5 L total each day). This was done to ensure no MeOH (and by extension, no retained DOM) was missed. A total of 1,500 L seawater was pumped through the column over five days.