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Abstract: The Argo array provides nearly 4000 temperature and salinity profiles of the top 2000 meters of the ocean every 10 days. Still, Argo floats will never be able to measure the ocean at all times, everywhere. Optimized Argo float distributions should match the spatial and temporal variability of the many societally important ocean features that they observe. Determining these distributions is challenging because float advection is difficult to predict. Using no external models, transition matrices based on existing Argo trajectories provide statistical inferences about Argo float motion. We use the 24 years of Argo locations to construct an optimal transition matrix that minimizes estimation bias and uncertainty. The optimal array is determined to have a 2°×2° spatial resolution with a 90 day timestep. We then use the transition matrix to predict the probability of future float locations of the Core Argo array, the Global Biogeochemical Array, and the Southern Ocean Carbon and Climate Observations and Modeling (SOCCOM) array. A comparison of transition matrices derived from floats using Argos System and Iridium communication methods shows the impact of surface displacements, which is most apparent near the equator. Additionally, we demonstrate the utility of transition matrices for validating models by comparing the matrix derived from Argo floats with that derived from a particle release experiment in the Southern Ocean State Estimate (SOSE).

North Atlantic subtropical mode water (NASTMW) serves as a major conduit for dissolved carbon to penetrate into the ocean interior by its wintertime outcropping events. Prior research on NASTMW has concentrated on its physical formation and destruction, as well as Lagrangian pathways and timescales of water into and out of NASTMW. In this study, we examine how dissolved inorganic carbon (DIC) concentrations are modified along Lagrangian pathways of NASTMW on subannual timescales. We introduce Lagrangian parcels into a physical‐biogeochemical model and release these parcels annually over two decades. For different pathways into, out of, and within NASTMW, we calculate changes in DIC concentrations along the path (ΔDIC), distinguishing contributions from vertical mixing and biogeochemical processes. The strongest ΔDIC is during subduction of water parcels (+101 μmol L−1 in 1 year), followed by transport out of NASTMW due to increases in density in water parcels (+10 μmol L−1). While the mean ΔDIC for parcels that persist within NASTMW in 1 year is relatively small at +6 μmol L−1, this masks underlying dynamics: individual parcels undergo interspersed DIC depletion and enrichment, spanning several timescales and magnitudes. Most DIC enrichment and depletion regimes span timescales of weeks, related to phytoplankton blooms. However, mixing and biogeochemical processes often oppose one another at short timescales, so the largest net DIC changes occur at timescales of more than 30 days. Our new Lagrangian approach complements bulk Eulerian approaches, which average out this underlying complexity, and is relevant to other biogeochemical studies, for example, on marine carbon dioxide removal. Plain Language Summary: Mode waters are relatively thick water masses with homogeneous properties, such as temperature and salinity. The North Atlantic subtropical mode water (NASTMW), found in the Sargasso Sea, is one such water mass. Lying underneath the ocean surface, it comes into contact with the atmosphere during winter, when the surface layer is vigorously mixed due to strong winds, causing the mixed layer to connect with NASTMW. This way, NASTMW can buffer atmospheric temperature and carbon anomalies during the summer, when there is no surface connection. It is also a conduit for carbon to penetrate beneath the ocean's upper mixed layer, with the potential to sequester it. We study NASTMW from the viewpoint of a water parcel that moves with the currents and see how carbon concentrations in the water parcels change along different NASTMW pathways. For each pathway, the carbon concentration changes due to an interplay of vertical mixing and biogeochemical processes, for example, related to plankton growth and decay. These processes can unfold over different timescales and may counteract or enhance themselves or one another. The largest change in carbon concentration is found when a parcel moves from the upper ocean mixed layer into NASTMW, mostly due to vertical mixing. Key Points: Carbon transformations along pathways of North Atlantic Subtropical Mode Water are split into mixing and biogeochemical contributionsAlong paths into, within, and out of this mode water, mixing and biogeochemistry alter carbon in water parcels over a range of timescalesEnrichment is highest during mixed layer subduction, which few parcels undergo annually; persistence in mode water is the dominant pathway [ABSTRACT FROM AUTHOR]

Numerical simulations of marine surface particle dispersal are a crucial tool for addressing many outstanding issues in physical oceanography with societal relevance, such as marine plastic pollution. However, the quality of these Lagrangian simulations depends on the ability of the underlying numerical model to represent the prevailing ocean circulation features. Here, we investigate how simulated marine surface particle dispersal changes, if the – often omitted or only approximated – impact of wind-generated surface waves on the upper ocean circulation is considered. We use velocity fields from a high-resolution coupled ocean-wave model simulation and a complementary stand-alone ocean model simulation for the Mediterranean Sea to answer the following questions: 1) How does the explicit representation of waves impact the simulated surface particle dispersal, and what is the relative impact of Stokes drift and wave-driven Eulerian currents? 2) How accurately can the wave impact be approximated by the commonly applied approach to advect particles with non wave-driven Eulerian currents and Stokes drift from stand-alone ocean and wave models? We find that the representation of surface waves tends to increase the simulated mean Lagrangian surface drift speed in winter through a dominant impact of Stokes drift, and to decrease the mean Lagrangian surface drift speed in summer through a dominant impact by wave-driven Eulerian currents. Furthermore, simulations that approximate the surface wave impact by including the Stokes drift (but ignoring the wave-driven Eulerian currents) do not necessarily yield a better estimate of the surface particle dispersal patterns with explicit representation of the wave impact than simulations that do not include any surface wave impact. Our results imply that – whenever possible – velocity fields from a coupled ocean-wave model should be used for surface particle dispersal simulations. [ABSTRACT FROM AUTHOR]

How we communicate about climate change affects how others think, feel and act. Therefore, the way climate scientists formulate messages is important. In this study, we assess the effect of personalization, operationalized as writing in a conversational style, as previously done by Ginns and Fraser (2010), and perceived credibility of climate scientists. We exposed hundred participants aged between 18 and 35 to three conditions of a text on the climate impact of train versus plane travel, with varying degree of personalization, and assessed the outcome in their attitude (specifically interest and opinion) towards sustainable travel, as well as the perceived credibility of the climate scientist who wrote the text. Results show that there is a small effect in the degree of happiness after reading the different texts, but little other effects. Our main conclusion is that, although personalization may be well received by readers, it may not be the best mode to influence the attitudes of readers towards sustainable travel, nor how readers come to perceive climate scientists' credibility. [ABSTRACT FROM AUTHOR]

Plastic entering the environment is a growing threat for ecosystems. We estimate the annual mass of known Dutch plastic waste generated and littered and where it ends up. We use two methods: (1) a material flow analysis of plastic waste separately collected from 13 economic sectors (including households, industry and imports) and estimate the amount sent to processing plants or exported and (2) a mismanagement model from observations of litter (on Dutch beaches and riverbanks) plus estimates of inadequately managed exported plastic scraps entering the environment abroad. In 2017 (the most recent complete data set available), an estimate of 1990 (±111) kilotonnes [kt] of plastic waste was separately collected. The top three plastic waste generating sectors (74% of the total) were households, clothing and textiles, and importation. Our mismanagement model estimates that 4.3–21.2 kt enters the environment annually; almost all of which occurs in foreign countries after inadequate management of imported Dutch waste. We highlight unknowns, including the source and/or destination of imported (623 kt) and exported (514 kt) plastics, plastics in non-household mixed waste streams and the plastic fraction of some separately collected waste, for example, e-waste. Our results stress the need for improved monitoring and reporting of plastic waste. Beyond the Netherlands, our recommendations could also help other high-income countries' decision-makers reach their circular economy goals. [ABSTRACT FROM AUTHOR]