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  • 1
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    Ocean acidification modifies biomolecule composition in organic matter through complex interactions (2020)
    Nature Research
    Details
    Publication Date: 2023-02-08
    Description: The main source of marine organic carbon (OC) is autotrophic production, while heterotrophic degradation is its main sink. Increased anthropogenic CO2 release leads to ocean acidification and is expected to alter phytoplankton community composition, primary production rates and bacterial degradation processes in the coming decades with potential consequences for dissolved and particulate OC concentration and composition. Here we investigate effects of increased pCO2 on dissolved and particulate amino acids (AA) and carbohydrates (CHO), in arctic and sub-arctic planktonic communities in two large-scale mesocosm experiments. Dissolved AA concentrations responded to pCO2/pH changes during early bloom phases but did not show many changes after nutrient addition. A clear positive correlation in particulate AA was detected in post-bloom phases. Direct responses in CHO concentrations to changing pCO2/pH were lacking, suggesting that observed changes were rather indirect and dependent on the phytoplankton community composition. The relative composition of AA and CHO did not change as a direct consequence of pCO2 increase. Changes between bloom phases were associated with the prevailing nutrient status. Our results suggest that biomolecule composition will change under future ocean conditions but responses are highly complex, and seem to be dependent on many factors including bloom phase and sampling site.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 2
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    Manganese co-limitation of phytoplankton growth and major nutrient drawdown in the Southern Ocean (2021)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Residual macronutrients in the surface Southern Ocean result from restricted biological utilization, caused by low wintertime irradiance, cold temperatures, and insufficient micronutrients. Variability in utilization alters oceanic CO2 sequestration at glacial-interglacial timescales. The role for insufficient iron has been examined in detail, but manganese also has an essential function in photosynthesis and dissolved concentrations in the Southern Ocean can be strongly depleted. However, clear evidence for or against manganese limitation in this system is lacking. Here we present results from ten experiments distributed across Drake Passage. We found manganese (co-)limited phytoplankton growth and macronutrient consumption in central Drake Passage, whilst iron limitation was widespread nearer the South American and Antarctic continental shelves. Spatial patterns were reconciled with the different rates and timescales for removal of each element from seawater. Our results suggest an important role for manganese in modelling Southern Ocean productivity and understanding major nutrient drawdown in glacial periods.
    Type: Article , PeerReviewed
    Format: text
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    Format: other
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 3
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    Persistent equatorial Pacific iron limitation under ENSO forcing (2023)
    Nature Research
    Details
    Publication Date: 2024-02-07
    Description: Projected responses of ocean net primary productivity to climate change are highly uncertain 1. Models suggest that the climate sensitivity of phytoplankton nutrient limitation in the low-latitude Pacific Ocean plays a crucial role 1–3, but this is poorly constrained by observations 4. Here we show that changes in physical forcing drove coherent fluctuations in the strength of equatorial Pacific iron limitation through multiple El Niño/Southern Oscillation (ENSO) cycles, but that this was overestimated twofold by a state-of-the-art climate model. Our assessment was enabled by first using a combination of field nutrient-addition experiments, proteomics and above-water hyperspectral radiometry to show that phytoplankton physiological responses to iron limitation led to approximately threefold changes in chlorophyll-normalized phytoplankton fluorescence. We then exploited the 〉18-year satellite fluorescence record to quantify climate-induced nutrient limitation variability. Such synoptic constraints provide a powerful approach for benchmarking the realism of model projections of net primary productivity to climate changes.
    Type: Article , PeerReviewed
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 4
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    Surface ocean microbiota determine cloud precursors (2021)
    Nature Research
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    Publication Date: 2024-02-07
    Description: One pathway by which the oceans influence climate is via the emission of sea spray that may subsequently influence cloud properties. Sea spray emissions are known to be dependent on atmospheric and oceanic physicochemical parameters, but the potential role of ocean biology on sea spray fluxes remains poorly characterized. Here we show a consistent significant relationship between seawater nanophytoplankton cell abundances and sea-spray derived Cloud Condensation Nuclei (CCN) number fluxes, generated using water from three different oceanic regions. This sensitivity of CCN number fluxes to ocean biology is currently unaccounted for in climate models yet our measurements indicate that it influences fluxes by more than one order of magnitude over the range of phytoplankton investigated.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
  • 5
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    Hypoxia-tolerant zooplankton may reduce biological carbon pump efficiency in the Humboldt current system off Peru (2023)
    Nature Research
    Details
    Publication Date: 2024-02-08
    Description: In the ocean, downward flux of particles produced in sunlit surface waters is the major component of the biological carbon pump, which sequesters atmospheric carbon dioxide and fuels deep-sea ecosystems. The efficiency of downward carbon transfer is expected to be particularly high in tropical upwelling systems where hypoxia occurring beneath the productive surface waters is thought to hamper particle consumption. However, observations of both particle feeders and carbon export in low-oxygen waters are scarce. Here, we provide evidence that hypoxia-tolerant zooplankton feed on sinking particles in the extensive Oxygen Minimum Zone (OMZ) off Peru. Using several arrays of drifting sediment traps and in situ imaging, we show geochemical and morphological transformations of sinking particles and substantial control of carbon export by zooplankton. Our findings challenge the assumption of a consistently efficient biological carbon pump in OMZs and further demonstrate the need to consider mesopelagic organisms when studying oceanic carbon sequestration.
    Type: Article , PeerReviewed , info:eu-repo/semantics/article
    Format: text
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    OceanRep: Article in a Scientific Journal - peer-reviewed
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