Three objectives were proposed to achieve the main goal of Noceanic: (1) estimating POM fluxes in anoxic OMZs and the Black Sea; (2) linking variability in POM fluxes to externally-forced primary productivity and the secondary source of POM; and (3) quantifying N release rates in anoxic OMZs and the Black Sea.
The work performed to achieve each objective is summarised below.
Objective 1. Data collected by BGC-Argo floats were quality controlled and exploited to estimate fluxes of POM of different sizes in OMZs over time series ranging between 1-4 years. For the latter task, I used three independent novel approaches based on optical properties and images of POM. I also developed a new metric to estimate the attenuation rates of POM fluxes within water layers. These outputs allowed me to assess how the fluxes of POM linked to a given range of size are reinforced and/or attenuated within water layers of OMZs. This information is fundamental to understand if the OMZs indeed reinforce the efficiency of the oceans in sequestering atmospheric CO2 by exporting surface POM to the abyss (1000 m).
Objective 2. I used quality controlled data recorded by BGC-Argo floats to model the production of POM in the surface (1-100 m) and sub-surface (>100-180 m) in the eastern tropical north Pacific OMZ. In addition, I exploited satellite data to assess how atmospheric forcing (i.e. wind and rain) can partially modulate the production and accumulation of POM mainly in the surface. For the latter purpose, I also developed a metric to assess how atmospheric forcing can in part foster the formation and accumulation of POM of a given range of sizes. These findings allowed me to partially identify and quantify the predominant mechanisms that drive the formation, accumulation, and eventual export of surface-POM to the abyss over a given period of the year.
Objective 3. N2 release rates have been indirectly estimated from the attenuation rates of the POM fluxes and the coefficients of the reactions involved. In addition, (1) I developed a novel combined approach based on oxygen (O2) and optical backscattering (bbp) recorded by the float’s sensors to better delineate the section with maxima release rates of N2, and (2) I am developing an innovative method to model N2 release rates from NO3- measurements recorded by the floats. The novel insights provided by these methods are allowing me to validate the intrinsic relationship between POM fluxes and N2 release rates, to explain this correlation in terms of temporal changes in the injection of POM from the two POM sources to the anoxic section (100-500 m, O2 ≤ 1 µM), and to better constrain N2 release rates and potential uncertainties in the current estimations.
Noceanic impacted a myriad of groups that include the general public, kids and international scientific communities because its outputs were disseminated by multiple ways. These multiple ways included: (1) disseminating the results and associated field activities by social media (i.e. twitter), (2) communicating the activities and basic knowledge acquired to young people through the educational project "adopt a float initiative" led by the Laboratoire d’Oceanographie de Villefranche, (3) delivering formal seminars in the LOV, Europe, and USA (most of them were conducted by video conferences), and (4) publishing in high-impact scientific journals (i.e. Global Biogeochemical Cycles, and Biogeosciences) and guaranteeing open access to articles to maximise their diffusion.
