He led an expedition in 1889 on the steamboat National from Kiel to southern Greenland in the north to as far as near the mouth of the Amazon in Pará, Brazil in the south to study whether plankton can be found more in tropical waters than cold waters.
In 1889, he navigated a steamboat named National from Kiel through northern Greenland and down to the vicinity of the Amazon's mouth near Pará, Brazil, to determine if plankton is more abundant in tropical compared to cold water regions.