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1. Efficient zinc/cobalt inter‐replacement in northeast Pacific diatoms and relationship to high surface dissolved Co : Zn ratios

   https://doi.org/10.1002/lno.11471  

   Kellogg, Riss M.; McIlvin, Matthew R.; Vedamati, Jagruti; Twining, Benjamin S.; Moffett, James W.; Marchetti, Adrian; Moran, Dawn M.; Saito, Mak A. (June 2020, Limnology and Oceanography)

   Abstract The importance of zinc (Zn) as a nutrient and its ability to be substituted for by cobalt (Co) have been characterized in model marine diatoms. However, the extent to which this substitution capability is distributed among diatom taxa is unknown. Zn/Co metabolic substitution was assayed in four diatom species as measured by the effect of free ion concentrations of Zn²⁺and Co²⁺on specific growth rate. Analysis of growth responses found substitution of these metals can occur within the northwest Atlantic isolateThalassiosira pseudonanaCCMP1335, the northeast Atlantic isolatePhaeodactylum tricornutumCCMP632, and within the northeast Pacific isolatesPseudo‐nitzschia delicatissimaUNC1205 andThalassiosirasp. UNC1203. Metabolic substitution of Co in place of Zn in the Atlantic diatoms supports their growth in media lacking added Zn, but at the cost of reduced growth rates. In contrast, highly efficient Zn/Co substitution that supported growth even in media lacking added Zn was observed in the northeast Pacific diatoms. We also present new data from the northeast Pacific Line P transect that revealed dissolved Co and Zn ratios (dCo : dZn) as high as 3.52 : 1 at surface (0–100 m) depths. We posit that the enhanced ability of the NE Pacific diatoms to grow using Co is an adaptation to these high surface dCo : dZn ratios. Particulate metal data and single‐cell metal quotas also suggest a high Zn demand in diatoms that may be partially compensated for by Co. 

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2. Antarctic glaciers export carbon-stabilised iron(II)-rich particles to the surface Southern Ocean

   https://doi.org/10.1038/s41467-025-59981-y  

   Jones, Rhiannon L; Hawkings, Jon R; Meredith, Michael P; Lohan, Maeve C; Moore, Oliver W; Sherrell, Robert M; Fitzsimmons, Jessica N; Kazemian, Majid; Araki, Tohru; Kaulich, Burkhard; et al (December 2025, Nature Communications)

   Abstract Iron is an essential micronutrient for phytoplankton and plays an integral role in the marine carbon cycle. The supply and bioavailability of iron are therefore important modulators of climate over glacial-interglacial cycles. Inputs of iron from the Antarctic continental shelf alleviate iron limitation in the Southern Ocean, driving hotspots of productivity. Glacial meltwater fluxes can deliver high volumes of particulate iron. Here, we show that glacier meltwater provides particles rich in iron(II) to the Antarctic shelf surface ocean. Particulate iron(II) is understood to be more bioavailable to phytoplankton, but less stable in oxic seawater, than iron(III). Using x-ray microscopy, we demonstrate co-occurrence of iron and organic carbon-rich phases, suggesting that organic carbon retards the oxidation of potentially-bioavailable iron(II) in oxic seawater. Accelerating meltwater fluxes may provide an increasingly important source of bioavailable iron(II)-rich particles to the Antarctic surface ocean, with implications for the Southern Ocean carbon pump and ecosystem productivity. 

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3. Carbon to Nitrogen Uptake Ratios Observed Across the Southern Ocean by the SOCCOM Profiling Float Array

   https://doi.org/10.1029/2022JC018859  

   Johnson, Kenneth S.; Mazloff, Matthew R.; Bif, Mariana B.; Takeshita, Yuichiro; Jannasch, Hans W.; Maurer, Tanya L.; Plant, Joshua N.; Verdy, Ariane; Walz, Peter M.; Riser, Stephen C.; et al (August 2022, Journal of Geophysical Research: Oceans)

   Abstract Measurements of pH and nitrate from the Southern Ocean Carbon and Climate Observations and Modeling array of profiling floats were used to assess the ratios of dissolved inorganic carbon (DIC) and nitrate (NO₃) uptake during the spring to summer bloom period throughout the Southern Ocean. Two hundred and forty‐three bloom periods were observed by 115 floats from 30°S to 70°S. Similar calculations were made using the Takahashi surface DIC and nitrate climatology. To separate the effects of atmospheric CO₂exchange and mixing from phytoplankton uptake, the ratios of changes in DIC to nitrate of surface waters (ΔDIC/ΔNO₃) were computed in the Biogeochemical Southern Ocean State Estimate (B‐SOSE) model. Phytoplankton uptake of DIC and nitrate are fixed in B‐SOSE at the Redfield Ratio (RR; 6.6 mol C/mol N). Deviations in the B‐SOSE ΔDIC/ΔNO₃must be due to non‐biological effects of CO₂gas exchange and mixing. ΔDIC/ΔNO₃values observed by floats and in the Takahashi climatology were corrected for the non‐biological effects using B‐SOSE. The corrected, in situ biological uptake ratio (C:N) occurs at values similar to the RR, with two major exceptions. North of 40°S biological DIC uptake is observed with little or no change in nitrate giving high C:N. In the latitude band at 55°S, the Takahashi data give a low C:N value, while floats are high. This may be due to a change in CO₂air‐sea exchange in this region from uptake during the Takahashi reference year of 2005 to outgassing of CO₂during the years sampled by floats. 

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4. Seasonal modulation of phytoplankton biomass in the Southern Ocean

   https://doi.org/10.1038/s41467-020-19157-2  

   Arteaga, Lionel A.; Boss, Emmanuel; Behrenfeld, Michael J.; Westberry, Toby K.; Sarmiento, Jorge L. (December 2020, Nature Communications)

   null (Ed.)

   Abstract Over the last ten years, satellite and geographically constrained in situ observations largely focused on the northern hemisphere have suggested that annual phytoplankton biomass cycles cannot be fully understood from environmental properties controlling phytoplankton division rates (e.g., nutrients and light), as they omit the role of ecological and environmental loss processes (e.g., grazing, viruses, sinking). Here, we use multi-year observations from a very large array of robotic drifting floats in the Southern Ocean to determine key factors governing phytoplankton biomass dynamics over the annual cycle. Our analysis reveals seasonal phytoplankton accumulation (‘blooming’) events occurring during periods of declining modeled division rates, an observation that highlights the importance of loss processes in dictating the evolution of the seasonal cycle in biomass. In the open Southern Ocean, the spring bloom magnitude is found to be greatest in areas with high dissolved iron concentrations, consistent with iron being a well-established primary limiting nutrient in this region. Under ice observations show that biomass starts increasing in early winter, well before sea ice begins to retreat. The average theoretical sensitivity of the Southern Ocean to potential changes in seasonal nutrient and light availability suggests that a 10% change in phytoplankton division rate may be associated with a 50% reduction in mean bloom magnitude and annual primary productivity, assuming simple changes in the seasonal magnitude of phytoplankton division rates. Overall, our results highlight the importance of quantifying and accounting for both division and loss processes when modeling future changes in phytoplankton biomass cycles. 

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5. Adaptive carbon export response to warming in the Sargasso Sea

   https://doi.org/10.1038/s41467-022-28842-3  

   Lomas, Michael W.; Bates, Nicholas R.; Johnson, Rodney J.; Steinberg, Deborah K.; Tanioka, Tatsuro (March 2022, Nature Communications)

   Abstract Ocean ecosystem models predict that warming and increased surface ocean stratification will trigger a series of ecosystem events, reducing the biological export of particulate carbon to the ocean interior. We present a nearly three-decade time series from the open ocean that documents a biological response to ocean warming and nutrient reductions wherein particulate carbon export is maintained, counter to expectations. Carbon export is maintained through a combination of phytoplankton community change to favor cyanobacteria with high cellular carbon-to-phosphorus ratios and enhanced shallow phosphorus recycling leading to increased nutrient use efficiency. These results suggest that surface ocean ecosystems may be more responsive and adapt more rapidly to changes in the hydrographic system than is currently envisioned in earth ecosystem models, with positive consequences for ocean carbon uptake. 

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