Cruise Report for AE2520 on R/V Atlantic Explorer

This is the cruise report for C-CoMP cruise AE2520 on the R/V Atlantic Explorer that took place in September 2025. The goal of the cruise was to compare the microbial dynamics and processes in an oligotrophic region with a more productive region. This cruise is the second of two planned with the same purpose, but to compare the same regions under bloom conditions (spring; AE2504) with more stratified and nutrient-poor conditions (late summer; AE2520). We chose two stations: the Bermuda Atlantic Time-series Study site (BATS) near Bermuda and the southernmost station of the New England Shelf Long-Term Ecological Research (NES-LTER station L11) site west of Connecticut (Figure 1). At each station, we conducted diel sampling near the surface (15m) and placed these samples into context with hydrographic profiles, underway samples, targeted incubations, and large-volume samples from CLIO. We sampled each region within a Lagrangian context, enabled by an SVP drifter deployed at BATS (but not at the LTER site). In contrast to our spring cruise, we had very favorable weather. Consequently, we added a sampling site (the “Eddy”) for 3-4 days along the transect between BATS and NES-LTER-L11. At this site, we surveyed a cyclonic eddy, completing a hydrographic survey of the eddy, and sampling the water column in the eddy center and in a gradient to its outward edges (see below). Versions 1 and 2 of the report characterize the cyclonic eddy as being anticyclonic in the project description. This has been corrected in version 3 of the report.