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Two Lab-on-Chip sensors, one measuring nitrate + nitrite (here after nitrate) and one measuring silicic acid (here after silicate), were deployed on the Ocean Observing Initiative (OOI) Southern Ocean Array surface mooring at a depth of approximately 12m on the near surface instrument frame in the southeast Pacific Ocean (-54 N, -89W). The nitrate sensor operated as expected for the full deployment period (6/12/2018 to 19/1/2020), collecting daily measurements. The silicate sensor operated as expected for almost ten months (until 1/10/2019), collecting up to four measurements per day. The OOI surface mooring was deployed in December 2018 on research cruise DY096 and recovered in January 2020 on research cruise DY112. The sensors and associated research cruises (DY096 and DY112) were supported by the Natural Environment Research Council (NERC) RoSES Carbon Uptake and Seasonal Trends in Antarctic Remineralisation Depth (CUSTARD) project. This material is based upon work supported by the Ocean Observatories Initiative, which is a major facility fully funded by the National Science Foundation (NSF). 

The ocean plays an essential role in regulating Earth’s climate, influencing weather conditions, providing sustenance for large populations, moderating anthropogenic climate change, encompassing massive biodiversity, and sustaining the global economy. Human activities are changing the oceans, stressing ocean health, threatening the critical services the ocean provides to society, with significant consequences for human well-being and safety, and economic prosperity. Effective and sustainable monitoring of the physical, biogeochemical state and ecosystem structure of the ocean, to enable climate adaptation, carbon management and sustainable marine resource management is urgently needed. The Argo program, a cornerstone of the Global Ocean Observing System (GOOS), has revolutionized ocean observation by providing real-time, freely accessible global temperature and salinity data of the upper 2,000m of the ocean (Core Argo) using cost-effective simple robotics. For the past 25 years, Argo data have underpinned many ocean, climate and weather forecasting services, playing a fundamental role in safeguarding goods and lives. Argo data have enabled clearer assessments of ocean warming, sea level change and underlying driving processes, as well as scientific breakthroughs while supporting public awareness and education. Building on Argo’s success, OneArgo aims to greatly expand Argo’s capabilities by 2030, expanding to full-ocean depth, collecting biogeochemical parameters, and observing the rapidly changing polar regions. Providing a synergistic subsurface and global extension to several key space-based Earth Observation missions and GOOS components, OneArgo will enable biogeochemical and ecosystem forecasting and new long-term climate predictions for which the deep ocean is a key component. Driving forward a revolution in our understanding of marine ecosystems and the poorly-measured polar and deep oceans, OneArgo will be instrumental to assess sea level change, ocean carbon fluxes, acidification and deoxygenation. Emerging OneArgo applications include new views of ocean mixing, ocean bathymetry and sediment transport, and ecosystem resilience assessment. Implementing OneArgo requires about $100 million annually, a significant increase compared to present Argo funding. OneArgo is a strategic and cost-effective investment which will provide decision-makers, in both government and industry, with the critical knowledge needed to navigate the present and future environmental challenges, and safeguard both the ocean and human wellbeing for generations to come. 

Abstract The ocean contributes to regulating atmospheric CO₂levels via the biological carbon pump (BCP). One critical aspect of the BCP is the depth at which sinking particulate organic carbon (POC) remineralizes in the mesopelagic zone (200–1,000 m). In the Southern Ocean, the circulation is such that the products generated from POC remineralization may have drastically different fates depending on (a) the latitude at which sinking particulate material is produced and (b) the depth at which its remineralization occurs. Here, we assess latitudinal and depth variations of POC export marine aggregate abundance and composition in the Southeast Pacific sector of the Southern Ocean. We show changes in flux attenuation depth horizons in the upper mesopelagic in the subantarctic zone. These correspond to rapid particle accumulation below the depth of the euphotic zone followed by abrupt export. We believe that such rapid changes may be linked to diatom life cycles, including resting cell and spore formation and resulting changes in particle sinking velocities rather than attenuation due to heterotrophic degradation or solubilization in the upper mesopelagic zone. We further discuss the occurrence of such features in the Southern Ocean and at the global scale. Our results highlight the importance of alternative flux attenuation processes, such as sudden changes in particles sinking velocities, in explaining variability in organic carbon sequestration by the ocean's BCP.