Global biogeochemical provinces of the mesopelagic zone

Abstract

Aim Following the biogeographical approach implemented by Longhurst for the epipelagic layer, we propose here to identify a biogeochemical 3‐D partition for the mesopelagic layer. The resulting partition characterizes the main deep environmental biotopes and their vertical boundaries on a global scale, which can be used as a geographical and ecological framework for conservation biology, ecosystem‐based management and for the design of oceanographic investigations. Location The global ocean. Methods Based on the most comprehensive environmental climatology available to date, which is both spatially and vertically resolved (seven environmental parameters), we applied a combination of clustering algorithms (c‐means, k‐means, partition around medoids and agglomerative with Ward's linkage) associated with a nonparametric environmental model to identify the vertical and spatial delineation of the mesopelagic layer. Results First, we show via numerical interpretation that the vertical division of the pelagic zone varies and, hence, is not constant throughout the global ocean. Indeed, a latitudinal gradient is found between the epipelagic–mesopelagic and mesopelagic–bathypelagic vertical limits. Second, the mesopelagic layer is shown here to be composed of 13 distinguishable Biogeochemical Provinces. Each province shows a distinct range of environmental conditions and characteristic 3‐D distributions. Main conclusions The historical definition of the mesopelagic zone is here revisited to define a 3‐D geographical framework and characterize all the deep environmental biotopes of the deep global ocean. According to the numerical interpretation of mesopelagic boundaries, we reveal that the vertical division of the zone is not constant over the global ocean (200–1,000 m) but varies between ocean basin and with latitude. We also provide evidence of biogeochemical division of the mesopelagic zone that is spatially structured in a similar way than the epipelagic in the shallow waters but varies in the deep owing to a change of the environmental driving factors.

Marine DNA Viral Macro- and Microdiversity from Pole to Pole

“…We designated these 5 emergent ecological zones as the Arctic (ARC), Antarctic 235 (ANT), bathypelagic (BATHY), temperate and tropical epipelagic (TT-EPI) and mesopelagic (TT-MES), and used these for further study. Depth ranges overlapped with those previously defined (Reygondeau, et al 2018), with epipelagic, mesopelagic, and bathypelagic being waters of depths 0 to 150 meters, 150 to 1,000 meters, and deeper than 2,000 meters, respectively. Comparison of our virome-inferred ecological zones to those inferred for the oceans in 240 other ways was telling.…”

Mesozooplankton and Micronekton Active Carbon Transport in Contrasting Eddies

“…The planktivorous mesopelagic fishes arguably have the Earth's largest fish biomass, which is likely underestimated by an order of magnitude due in part to the unknown energy transfer through the zooplankton component of pelagic food webs (Irigoien et al, 2014). Energy fluxes between the epipelagic (<200 m) and the mesopelagic (200-1000 m) layers vary globally and play a key role in determining marine productivity and fisheries (Young et al, 2011(Young et al, , 2015Kiko et al, 2017;Reygondeau et al, 2017). The permanent mesopelagic inhabitants (non-vertical migrators) rely on both the passive sinking of epipelagic particles and migratory organisms as a food source, although the proportional importance is still debated (Hannides et al, 2013;Choy et al, 2015).…”

Particulate Rare Earth Element behavior in the North Atlantic (GEOVIDE cruise)

“…The North Atlantic Subtropical (NAST) province is characterized by warm and salty waters 80 Longhurst, 1995;Reygondeau et al, 2018;Zunino et al, 2017). This province is depleted in nutrients, yet under influence of margin inputs, displayed a declining bloom of cyanobacteria during the cruise (Lemaitre et al, 2018).…”