Fig. 1: Sampling stations, water temperature and microbial richness in the epi- and mesopelagic between subantarctic and subarctic waters of the Pacific Ocean.

A Stations between 52°S and 59°N. The colour code of the stations refers to their affiliation to biogeographic provinces according to Longurst [32]. BERS Bering Sea, PSAG Pacific subarctic gyre, NPPF north Pacific polar frontal region, NPST north Pacific subtropical gyre, NPTG north Pacific tropical gyre, PNEQ Pacific north equatorial counter current, PEQD Pacific equatorial divergence, SPSG south Pacific subtropical gyre, SSTC south subtropical convergence; NEWZ, New Zealand coastal province, SANT subantarctic province. Stations are overlaid on a map of the Pacific Ocean with annual mean concentrations of chlorophyll a at the surface (https://oceandata.sci.gsfc.nasa.gov). B Contour graph of water temperature along the transect based on continuous measurements by a temperature probe at each station between the surface and 600 m depth. Black dots indicate the depth of sampling. C Effective number of species (here ASV; inverse Simpson index) richness of the free-living (0.2–3 µm), small (3–8 µm) and large particle-associated (>8 µm) prokaryotic and eukaryotic microbial communities at the stations in epipelagic (20–100 m) and mesopelagic waters (200–500 m) at the stations along the transect. Single data points at the depths and stations and loess fit and its 95% confidence interval for the epi- and mesopelagic are given.