Temporal and Spatial Influences of Environmental Factors on the Distribution of Mesopelagic organism in the North Atlantic Ocean

Abstract. Mesopelagic organisms play a critical role in marine ecosystems and the global carbon cycle, acting as key intermediaries between trophic levels through diel (DVM) and seasonal vertical migrations (SVM). However, the seasonal vertical migration patterns of these organisms, and the environmental drivers influencing them, remain insufficiently understood. Here, we analyzed 83,603 backscattering coefficient (b_bp) profiles obtained from 720 BGC-Argo floats deployed in the North Atlantic Ocean from 2010 to 2021. This extensive dataset enabled the identification of spiking layer signals, allowing us to investigate the diurnal and seasonal vertical distributions of mesopelagic organisms, as indicated by these b_bp spikes. Additionally, we examined the horizontal heterogeneity in these distributions and their correlations with key environmental variables. Our findings reveal distinct diurnal migrations, characterized by multilayered aggregations predominantly in the mid-ocean during daylight, with prominent signals at depths around 150 m, 330 m, 650 m, and 780 m. At night, a strong scattering layer forms in the upper ocean, with signals concentrated at depths shallower than 350 m, particularly in the top 100 m. Seasonal analyses shows that in spring and winter, the average b_bp spike intensity is lower in the upper ocean than in the mid-ocean, although the frequency of b_bp spikes is higher in the upper ocean. In contrast, summer and autumn—especially summer—exhibit both higher mean b_bp spike intensity and frequency near the surface. Spatially, mesopelagic organisms migrate deeper in the northeast and remain shallower in the southwest, correlating with higher temperatures and shallower distributions. Random forest analysis identified temperature as the most influential environmental factor affecting the distribution of mesopelagic organisms year-round, with the temperature gradient being particularly critical. Other critical factors include seawater salinity, dissolved oxygen, surface chlorophyll concentration, and latitude, with relative importance of 29.44 %, 15.49 %, 14.85 %, 13.46 %, and 12.35 %, respectively. This study enhances our understanding of the mechanisms driving carbon transfer to the deep ocean and the energy and material cycles within marine ecosystems, providing a basis for future fisheries management in mesopelagic environments.