The remineralization depth of particulate organic carbon (POC) fluxes exported from the surface ocean exerts a major control over atmospheric CO₂ levels. According to a long‐held paradigm most of the POC exported to depth is associated with large particles. However, recent lines of evidence suggest that slow‐sinking POC (SSPOC) may be an important contributor to this flux. Here we assess the circumstances under which this occurs. Our study uses samples collected using the Marine Snow Catcher throughout the Atlantic Ocean, from high latitudes to midlatitudes. We find median SSPOC concentrations of 5.5 μg L−1, 13 times smaller than suspended POC concentrations and 75 times higher than median fast‐sinking POC (FSPOC) concentrations (0.07 μg L−1). Export fluxes of SSPOC generally exceed FSPOC flux, with the exception being during a spring bloom sampled in the Southern Ocean. In the Southern Ocean SSPOC fluxes often increase with depth relative to FSPOC flux, likely due to midwater fragmentation of FSPOC, a process which may contribute to shallow mineralization of POC and hence to reduced carbon storage. Biogeochemical models do not generally reproduce this behavior, meaning that they likely overestimate long‐term ocean carbon storage.

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The biological carbon pump (BCP) stores ∼1,700 Pg C from the atmosphere in the ocean interior, but the magnitude and direction of future changes in carbon sequestration by the BCP are uncertain. We quantify global trends in export production, sinking organic carbon fluxes, and sequestered carbon in the latest Coupled Model Intercomparison Project Phase 6 (CMIP6) future projections, finding a consistent 19 to 48 Pg C increase in carbon sequestration over the 21st century for the SSP3-7.0 scenario, equivalent to 5 to 17% of the total increase of carbon in the ocean by 2100. This is in contrast to a global decrease in export production of –0.15 to –1.44 Pg C y –1 . However, there is significant uncertainty in the modeled future fluxes of organic carbon to the deep ocean associated with a range of different processes resolved across models. We demonstrate that organic carbon fluxes at 1,000 m are a good predictor of long-term carbon sequestration and suggest this is an important metric of the BCP that should be prioritized in future model studies.

The North Atlantic Ocean is a key region for carbon sequestration by the biological carbon pump (BCP). The quantity of organic carbon exported from the surface, the region and depth at which it is remineralized, and the subsequent timescale of ventilation (return of the remineralized carbon back into contact with the atmosphere), control the magnitude of BCP sequestration. Carbon stored in the ocean for >100 years is assumed to be sequestered for climate‐relevant timescales. We apply Lagrangian tracking to an ocean circulation and marine biogeochemistry model to determine the fate of North Atlantic organic carbon export. Organic carbon assumed to undergo remineralization at each of three vertical horizons (500, 1,000, and 2,000 m) is tracked to determine how much remains out of contact with the atmosphere for 100 years. The fraction that remains below the mixed layer for 100 years is defined as the sequestration efficiency (SEff) of remineralized exported carbon. For exported carbon remineralized at the 500, 1,000 and 2,000 m horizons, the SEff is 28%, 66% and 94%, respectively. Calculating the amount of carbon sequestered using depths ≤1,000 m, and not accounting for downstream ventilation, overestimates 100‐year carbon sequestration by at least 39%. This work has implications for the accuracy of future carbon sequestration estimates, which may be overstated, and for carbon management strategies (e.g., oceanic carbon dioxide removal and Blue Carbon schemes) that require long‐term sequestration to be successful.

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Abstract. Acquiring not only field-specific knowledge but also a set of transferable professional skills becomes increasingly important for Early Career Scientists (ECS) in Geosciences and other academic disciplines. Although the need for training in transferable skills adds to the work-load of an individual Early Career Scientist, it is often neglected within the traditional academic environments. International Early Career Networks (ECN) are global voluntary communities of early career scientists aiming (i) to advocate for early stage researchers; and (ii) to advance the careers of their members by raising their profiles and training them in specific transferable skills, such as networking, collaborating and outreach. Accordingly, ECN can be a tool to move beyond institutional barriers and to improve the inclusion of ECS into the international scientific community. In 2019 we conducted three surveys in order to assess ECN from the perspective of its members and regarding the structures of different ECN within a specific discipline and across disciplines. We use the survey results alongside with case studies from well-established and long term networks to elucidate the attributes that make a successful, sustainable ECN. Important characteristics of these international ECN include (1) developing the ECN organizational schemes to promote early career scientists within a specific discipline and across disciplines, (2) scoping for members needs, evaluating the performance of the network, and adapting to feedback, (3) continuity of the organizing committee by ensuring representation of different stages of ECS, and (4) diverse membership to provide strong foundational and personnel support within the network. These characteristics can support the development of best practices for developing ECN successfully, which can guide existing and future networks within Geosciences and other scientific disciplines.

<p>Participation in offshore fieldwork is a frequent pathway into a successful career in marine science due to the unique opportunities for practical skills development provided by such field experiences. However, the ability to participate in scientific research cruises can be hindered for those from certain backgrounds, such as physically disabled scientists with mobility limitations, those with caring responsibilities who cannot spend extended periods of time away from home, and early career researchers from minority groups who may perceive the limited confines of a research ship as a hostile or unwelcoming environment. </p><p>Digital twinning is a new and rapidly developing area that describes how technologies and capabilities, including modelling, remote sensing, and linking shipboard equipment to shore visually in real-time, can be intertwined with traditional offshore operations to promote inclusivity and broaden the diversity of people involved in marine sciences. Here we will present preliminary results from our project that explores whether perceptions of fieldwork as a requirement for a career in marine science exist and whether jobs in marine science explicitly require these skills and experiences. Perceptions of fieldwork were evaluated through a series of questionnaires and semi-structured interviews with prospective marine scientists at undergraduate and PhD level. Additionally, we also conducted a systematic review of advertised vacancies in marine science to determine how perceived requirements for a career in marine science differed from the advertised required skills and experience.  Finally, we collated several case studies of effective use of digital twinning as a tool to enable those who cannot access offshore fieldwork to participate in scientific cruises. We aim to use these case studies to highlight the potential for digital twinning to act as a complimentary route into the field and act as an evidence base for continued investment in, and development of, new technologies to facilitate equitable and inclusive marine science.</p>

<p>Biotic processes in the ocean play a crucial role in driving and mediating natural long-term ocean carbon storage. IPCC assessment exercises find high uncertainty, and therefore low confidence, around the magnitude and sign of change in future ocean carbon storage. This uncertainty is due to a lack of mechanistic understanding of relevant biological processes and/ or a paucity of observational data which limits robust parameterisations in global ocean biogeochemical models. Our study aims to identify and prioritise the processes that have a strong impact on future ocean carbon storage, with tractability from both a modelling and observational perspective. These processes could be the focus of future studies that aim to improve parameterisations in global biogeochemical models used in Earth System Models. We undertook a gap analysis to identify key processes and highlight future research priorities around three areas: net primary production (NPP), interior remineralisation and alkalinity. Here we evaluate CMIP6 model projections to 2100 under the high emissions SSP5-8.5 scenario to determine both the spread and uncertainty in NPP, particulate organic carbon transfer efficiency through the ocean interior and surface salinity-normalised alkalinity. We undertook a model interrogation of which processes are represented, their level of parameterised complexity and the variability in the parameterisation approach. Our analysis shows that CMIP6 models generally agree on the sign of change for transfer efficiency, but display a wide spread for NPP and salinity-normalised alkalinity by the end of the 21st century. Combining our analysis of CMIP6 models and gaps in knowledge allows the potential key processes and uncertainties driving future changes in key biological components of the ocean carbon cycle to be identified. By highlighting the potential gaps that require attention, the representation of biological processes in global ocean biogeochemical models can be improved in future modelling efforts. </p>