Abstract
Abstract. Micronekton – small marine pelagic organisms around 1–10 cm in size – are a key component of the ocean ecosystem, as they constitute the main source of forage for all larger predators. Moreover, the mesopelagic component of micronekton that undergoes diel vertical migration (DVM) likely plays a key role in the transfer and storage of CO2 in the deep ocean: this is known as the “biological pump”. SEAPODYM-MTL is a spatially explicit dynamical model of micronekton. It simulates six functional groups of vertically migrant (DVM) and nonmigrant (no DVM) micronekton, in the epipelagic and mesopelagic layers. Coefficients of energy transfer efficiency between primary production and each group are unknown, but they are essential as they control the production of micronekton biomass. Since these coefficients are not directly measurable, a data assimilation method is used to estimate them. In this study, Observing System Simulation Experiments (OSSEs) are used at a global scale to explore the response of oceanic regions regarding energy transfer coefficient estimation. In our experiments, we obtained different results for spatially distinct sampling regions based on their prevailing ocean conditions. According to our study, ideal sampling areas are warm and productive waters associated with weak surface currents like the eastern side of tropical oceans. These regions are found to reduce the error of estimated coefficients by 20 % compared to cold and more dynamic sampling regions.
Highlights
Micronekton organisms are at the midtrophic level of the ocean ecosystem and have a central role, as prey of larger predator species such as tuna, swordfish, turtles, sea birds or marine mammals, and as a potential new resource in the blue economy (St John et al, 2016)
SEAPODYM-MTL provides a parsimonious approach with only a few parameters and a maximum likelihood estimation (MLE) to estimates these parameters from observations
The energy transfer efficiency coefficients are of great importance because they directly control the biomass of micronekton functional groups, including those that undergo Diel vertical migration (DVM) and contribute to the sequestration of carbon dioxide into the deep ocean (Davison et al, 2013; Giering et al, 2014; Ariza et al, 2015)
Summary
Micronekton organisms are at the midtrophic level of the ocean ecosystem and have a central role, as prey of larger predator species such as tuna, swordfish, turtles, sea birds or marine mammals, and as a potential new resource in the blue economy (St John et al, 2016). Diel vertical migration (DVM) characterizes a large biomass of the mesopelagic (inhabiting the twilight zone, 200–1000 m) component of micronekton of the world ocean. This migration of biomass occurs when organisms move up from a deep habitat during daytime to a shallower habitat at night. DVM is generally related to a trade-off between the need for food and predator avoidance (Benoit-Bird et al, 2009) and seems to be triggered by sunlight (Zaret and Suffern, 1976) Through these daily migrations, the mesopelagic micronekton potentially contributes to a substantial transfer of atmospheric CO2 to the deep ocean, after its metabolization by photosynthesis and export through the food chain (Davison et al, 2013).
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