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  • 1
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    The global biological microplastic particle sink (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: Every year, about four percent of the plastic waste generated worldwide ends up in the ocean. What happens to the plastic there is poorly understood, though a growing body of evidence suggests it is rapidly spreading throughout the global ocean. The mechanisms of this spread are straightforward for buoyant larger plastics that can be accurately modelled using Lagrangian particle models. But the fate of the smallest size fractions (the microplastics) are less straightforward, in part because they can aggregate in sinking marine snow and faecal pellets. This biologically-mediated pathway is suspected to be a primary surface microplastic removal mechanism, but exactly how it might work in the real ocean is unknown. We search the parameter space of a new microplastic model embedded in an earth system model to show that biological uptake can significantly shape global microplastic inventory and distributions and even account for the budgetary “missing” fraction of surface microplastic, despite being an inefficient removal mechanism. While a lack of observational data hampers our ability to choose a set of “best” model parameters, our effort represents a first tool for quantitatively assessing hypotheses for microplastic interaction with ocean biology at the global scale.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    A critical examination of the role of marine snow and zooplankton faecal pellets in removing ocean surface microplastic (2020)
    Frontiers
    Details
    Publication Date: 2023-02-08
    Description: Numerical simulations and emissions estimates of plastic in and to the ocean consistently over-predict the surface inventory, particularly in the case of microplastic (MP), i.e. fragments less than 5 mm in length. Sequestration in the sediments has been both predicted and, to a limited extent, observed. It has been hypothesized that biology may be exporting a significant fraction of surface MP by way of marine snow aggregation and zooplankton faecal pellets. We apply previously published data on MP concentrations in the surface ocean to an earth system model of intermediate complexity to produce a first estimate of the potential global sequestration of MP by marine aggregates, including faecal pellets. We find a MP seafloor export potential of between 7.3E3-4.2E5 metric tons per year, or about 0.06-8.8% of estimated total annual plastic ocean pollution rates. We find that presently, aggregates alone would have the potential to remove most existing surface ocean MP to the seafloor within less than 2 years if pollution ceases. However, the observed accumulation of MP in the surface ocean, despite this high potential rate of removal, suggests that detrital export is an ineffective pathway for permanent MP removal. We theorize a prominent role of MP biological fouling and de-fouling in the rapid recycling of aggregate-associated MP in the upper ocean. We also present an estimate of how the potential detrital MP sink might change into the future, as climate change (and projected increasing MP pollution) alters the marine habitat. The polar regions, and the Arctic in particular, are projected to experience increasing removal rates as export production increases faster than MP pollution. Northern hemisphere subtropical gyres are projected to experience slowing removal rates as stratification and warming decrease export production, and MP pollution increases. However, significant uncertainty accompanies these results.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Mixed layer depth dominates over upwelling in regulating the seasonality of ecosystem functioning in the Peruvian Upwelling System (2022)
    Copernicus Publications (EGU)
    Details
    Publication Date: 2024-02-07
    Description: The Peruvian Upwelling System hosts an extremely high productive marine ecosystem. Observations show that the Peruvian Upwelling System is the only Eastern Boundary Upwelling Systems (EBUS) with an out-of-phase relationship of seasonal surface chlorophyll concentrations and upwelling intensity. This "seasonal paradox" triggers the questions: (1) what is the uniqueness of the Peruvian Upwelling System compared with other EBUS that leads to the out of phase relationship; (2) how does this uniqueness lead to low phytoplankton biomass in austral winter despite strong upwelling and ample nutrients? Using observational climatologies for four EBUS we diagnose that the Peruvian Upwelling System is unique in that intense upwelling coincides with deep mixed layers. We then apply a coupled regional ocean circulation-biogeochemical model (CROCO-BioEBUS) to assess how the interplay between mixed layer and upwelling is regulating the seasonality of surface chlorophyll in the Peruvian Upwelling System. The model recreates the "seasonal paradox" within 200 km off the Peruvian coast. We confirm previous findings that deep mixed layers, which cause vertical dilution and stronger light limitation, mostly drive the diametrical seasonality of chlorophyll relative to upwelling. In contrast to previous studies, reduced phytoplankton growth due to enhanced upwelling of cold waters and lateral advection are second-order drivers of low surface chlorophyll concentrations. This impact of deep mixed layers and upwelling propagates up the ecosystem, from primary production to export efficiency. Our findings emphasize the crucial role of the interplay of the mixed layer and upwelling and suggest that surface chlorophyll may increase along with a weakened seasonal paradox in response to shoaling mixed layers under climate change.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Zooplankton grazing of microplastic can accelerate global loss of ocean oxygen (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Global warming has driven a loss of dissolved oxygen in the ocean in recent decades. We demonstrate the potential for an additional anthropogenic driver of deoxygenation, in which zooplankton consumption of microplastic reduces the grazing on primary producers. In regions where primary production is not limited by macronutrient availability, the reduction of grazing pressure on primary producers causes export production to increase. Consequently, organic particle remineralisation in these regions increases. Employing a comprehensive Earth system model of intermediate complexity, we estimate this additional remineralisation could decrease water column oxygen inventory by as much as 10% in the North Pacific and accelerate global oxygen inventory loss by an extra 0.2–0.5% relative to 1960 values by the year 2020. Although significant uncertainty accompanies these estimates, the potential for physical pollution to have a globally significant biogeochemical signal that exacerbates the consequences of climate warming is a novel feedback not yet considered in climate research.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Can top-down controls expand the ecological niche of marine N2 fixers? (2021)
    Frontiers
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    Publication Date: 2024-02-07
    Description: The ability of marine diazotrophs to fix dinitrogen gas (N₂) is one of the most influential yet enigmatic processes in the ocean. With their activity diazotrophs support biological production by fixing about 100-200 Tg N/yr of bioavailable nitrogen (N), an essential limiting nutrient. Despite their important role, the factors that control the distribution of diazotrophs and their ability to fix N₂ are not fully elucidated. We discuss insights that can be gained from the emerging picture of a wide geographical distribution of marine diazotrophs and provide a critical assessment of environmental (bottom-up) versus trophic (top-down) controls. We present a simplified theoretical framework to understand how top-down control affects competition for resources that determine ecological niches. Selective grazing on non-fixing phytoplankton is identified as a critical process that can broaden the ability of diazotrophs to compete for resources in top-down controlled systems and explain an expanded ecological niche for diazotrophy. Our simplified analysis predicts a larger importance of top-down control in nutrient-rich systems where grazing controls the faster growing phytoplankton, allowing the slower growing diazotrophs to become established. However, these predictions require corroboration by experimental and field data, together with the identification of specific traits of organisms and associated trade-offs related to selective top-down control. Elucidation of these factors could greatly improve our predictive capability for marine N2 fixation. The susceptibility of this key biogeochemical process to future changes may not only be determined by changes in environmental conditions but also via changes in the ecological interactions.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 6
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    Modelling approaches for capturing plankton diversity (MODIV), their societal applications and data needs (2022)
    Frontiers
    Details
    Publication Date: 2024-02-07
    Description: Ecosystem models need to capture biodiversity, because it is a fundamental determinant of food web dynamics and consequently of the cycling of energy and matter in ecosystems. In oceanic food webs, the plankton compartment encompasses by far most of the biomass and diversity. Therefore, capturing plankton diversity is paramount for marine ecosystem modelling. In recent years, many models have been developed, each representing different aspects of plankton diversity, but a systematic comparison remains lacking. Here we present established modelling approaches to study plankton ecology and diversity, discussing the limitations and strengths of each approach. We emphasize their different spatial and temporal resolutions and consider the potential of these approaches as tools to address societal challenges. Finally, we make suggestions as to how better integration of field and experimental data with modelling could advance understanding of both plankton biodiversity specifically and more broadly the response of marine ecosystems to environmental change, including climate change.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 7
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    Food web structure and intraguild predation affect ecosystem functioning in an established plankton model (2022)
    ASLO (Association for the Sciences of Limnology and Oceanography) | Wiley
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    Publication Date: 2024-02-07
    Description: Understanding how marine microbial food webs and their ecosystem functions are changing is crucial for projections of the future ocean. Often, simplified food web models are employed and their solutions are only evaluated against available observations of plankton biomass. With such an approach, it remains unclear how different underlying trophic interactions affect interpretations of plankton dynamics and functioning. Here, we quantitatively compare four hypothetical food webs to data from an existing mesocosm experiment using a refined version of the Minimum Microbial Food Web model. Food web representations range from separated food chains to complex food webs featuring additional trophic links including intraguild predation (IGP). Optimization against observations and taking into account model complexity ensures a fair comparison of the different food webs. Although the different optimized model food webs capture the observations similarly well, projected ecosystem functions differ depending on the underlying food web structure and the presence or absence of IGP. Mesh-like food webs dominated by the microbial loop yield higher recycling and net primary production (NPP) than models dominated by the classical diatom-copepod food chain. A high degree of microzooplankton IGP increases NPP and organic matter recycling, but decreases trophic transfer efficiency (TTE) to copepods. Copepod production, the trophic role of copepods, and TTE are more sensitive to initial biomass changes in chain-like than in complex food webs. Measurements resolving trophic interactions, in particular those quantifying IGP, remain essential to reduce model uncertainty and allow sound conclusions for ecosystem functioning in plankton ecosystems.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 8
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    Enhanced silica export in a future ocean triggers global diatom decline (2022)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Diatoms account for up to 40% of marine primary production(1,2) and require silicic acid to grow and build their opal shell(3). On the physiological and ecological level, diatoms are thought to be resistant to, or even benefit from, ocean acidification(4-6). Yet, global-scale responses and implications for biogeochemical cycles in the future ocean remain largely unknown. Here we conducted five in situ mesocosm experiments with natural plankton communities in different biomes and find that ocean acidification increases the elemental ratio of silicon (Si) to nitrogen (N) of sinking biogenic matter by 17 +/- 6 per cent under p(CO2) conditions projected for the year 2100. This shift in Si:N seems to be caused by slower chemical dissolution of silica at decreasing seawater pH. We test this finding with global sediment trap data, which confirm a widespread influence of pH on Si:N in the oceanic water column. Earth system model simulations show that a future pH-driven decrease in silica dissolution of sinking material reduces the availability of silicic acid in the surface ocean, triggering a global decline of diatoms by 13-26 per cent due to ocean acidification by the year 2200. This outcome contrasts sharply with the conclusions of previous experimental studies, thereby illustrating how our current understanding of biological impacts of ocean change can be considerably altered at the global scale through unexpected feedback mechanisms in the Earth system.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 9
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    Mixed Layer Depth Promotes Trophic Amplification on a Seasonal Scale (2022)
    AGU (American Geophysical Union) | Wiley
    Details
    Publication Date: 2024-02-07
    Description: The Humboldt Upwelling System is of global interest due to its importance to fisheries, though the origin of its high productivity remains elusive. In regional physical-biogeochemical model simulations, the seasonal amplitude of mesozooplankton net production exceeds that of phytoplankton, indicating “seasonal trophic amplification.” An analytical approach identifies amplification to be driven by a seasonally varying trophic transfer efficiency due to mixed layer variations. The latter alters the vertical distribution of phytoplankton and thus the zooplankton and phytoplankton encounters, with lower encounters occurring in a deeper mixed layer where phytoplankton are diluted. In global model simulations, mixed layer depth appears to affect trophic transfer similarly in other productive regions. Our results highlight the importance of mixed layer depth for trophodynamics on a seasonal scale with potential significant implications, given mixed layer depth changes projected under climate change.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 10
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    The Marine Biodiversity Observation Network Plankton Workshops: Plankton Ecosystem Function, Biodiversity, and Forecasting - Research Requirements and Applications (2022)
    ASLO (Association for the Sciences of Limnology and Oceanography) | Wiley
    Details
    Publication Date: 2023-01-04
    Description: Plankton is a massive and phylogenetically diverse group of thousands of prokaryotes, protists (unicellular eukaryotic organisms), and metazoans (multicellular eukaryotic organisms; Fig. 1). Plankton functional diversity is at the core of various ecological processes, including productivity, carbon cycling and sequestration, nutrient cycling (Falkowski 2012), interspecies interactions, and food web dynamics and structure (D'Alelio et al. 2016). Through these functions, plankton play a critical role in the health of the coastal and open ocean and provide essential ecosystem services. Yet, at present, our understanding of plankton dynamics is insufficient to project how climate change and other human-driven impacts affect the functional diversity of plankton. That limits our ability to predict how critical ecosystem services will change in the future and develop strategies to adapt to these changes.
    Type: Article , PeerReviewed
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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