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Zooplankton diel vertical migration (DVM) is a globally ubiquitous phenomenon and a critical component of the ocean's biological pump. During DVM, zooplankton metabolism leads to carbon and nutrient export to mesopelagic depths, where carbon can be sequestered for decades to millennia, while also introducing labile, energy-rich food sources to midwater ecosystems. Three pervasive metabolic pathways allow zooplankton to sequester carbon: fecal pellet egestion, dissolved organic matter excretion, and respiration. Additionally, there are several less well-parameterized sources of DVM transport associated with growth, feeding, reproduction, and mortality. These processes are challenging to measure in situ and difficult to extrapolate from laboratory experiments, making them some of the most poorly constrained factors in assessments and models of the biological pump. In this review, we evaluate and compare observational and modeling approaches to estimate zooplankton DVM and the resulting active carbon flux, highlighting major discrepancies and proposing directions for future research. 

Abstract Oceanic emissions of nitrous oxide (N₂O) account for roughly one‐third of all natural sources to the atmosphere. Hot‐spots of N₂O outgassing occur over oxygen minimum zones (OMZs), where the presence of steep oxygen gradients surrounding anoxic waters leads to enhanced N₂O production from both nitrification and denitrification. However, the relative contributions from these pathways to N₂O production and outgassing in these regions remains poorly constrained, in part due to shared intermediary nitrogen tracers, and the tight coupling of denitrification sources and sinks. To shed light on this problem, we embed a new, mechanistic model of the OMZ nitrogen cycle within a three‐dimensional eddy‐resolving physical‐biogeochemical model of the Eastern Tropical South Pacific (ETSP), tracking contributions from remote advection, atmospheric exchange, and local nitrification and denitrification. The model indicates that net N₂O production from denitrification is approximately one order of magnitude greater than nitrification within the ETSP OMZ. However, only ∼32% of denitrification‐derived N₂O production ultimately outgasses to the atmosphere in this region (contributing ∼36% of the air‐sea N₂O flux on an annual basis), while the remaining is exported out of the domain. Instead, remotely produced N₂O advected into the OMZ region accounts for roughly half (∼57%) of the total N₂O outgassing, with smaller contributions from nitrification (∼7%). Our results suggests that, together with enhanced production by denitrification, upwelling of remotely derived N₂O contributes the most to N₂O outgassing over the ETSP OMZ.