Dataset: 16S rRNA gene of microorganisms sampled along the Newport Hydrographic (NH) and Trinidad Head (TR) lines, in OR and CA in 2018 and 2019

Transects ranged from 24 to 86 km in length were sampled along the Newport Hydrographic (NH) line as well as the Trinidad Head (TR) line during the winters (February-March) and summers (July-August) of 2018 and 2019 (winter 2018 transect sample size was n=2 per location due to weather days while summer 2018 – summer 2019, n=4-5). Located off Newport, Oregon, the NH Line has been sampled since 1961 (Peterson and Miller, 1975), while the TR line off northern California has been sampled since 2007.

DNA sampling for microbes was carried out from surface (5-10 meters depth) seawater samples (500-1000 mL, n=2 per station, 6 stations per transect), collected by CTD, that were size fractionated on 47 mm 1.6 µm GF/A filters (Whatman) followed by 47 mm 0.2 µm Supor polyethersulfone filters (Pall Corporation)  using a peristaltic pump. Filter membranes were moved to bead-beater tubes and frozen immediately at -20 ˚C and stored at -80 ˚C. DNA extraction was done using the DNeasy Plant Tissue Mini Kit (Qiagen) with the following modifications. Samples were lysed by bead beating with 0.55 mm and 0.25 mm sterile glass beads at 30 Hz for 2 minutes after addition of lysis buffer, freeze-fractured 3 times, incubated with Proteinase K (VWR Chemicals, Solon, OH, USA) at 20 mg/mL for 1 hour at 55 ˚C, and incubated with RNase A at 100 mg/mL for 10 minutes at 65 ˚C. PCR was performed in triplicate on 1 ng of DNA with the primer pair 515F‐Y/806R amplified the 16S rRNA V4 hypervariable region with conditions as published (Parada et al. 2016) using golay barcodes on the forward primers as in the EMP protocols. Reactions were performed with the QuantaBio 5Prime HotMasterMix (Qiagen Beverly, MA, USA). The Agilent High Sensitivity Kit in the Bioanalyzer (Agilent Technologies, Waldbronn, Germany) confirmed amplicon size. Triplicate PCR reactions from each sample were pooled then purified by magnetic beads. Each final pooled sample was paired-end sequenced with Illumina MiSeq v.3 (Illumina, San Diego, USA).