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1. The effects of iron limitation on the small chlorophyte Micromonas from the Northeast Pacific Ocean

   https://doi.org/10.1111/jpy.70079  

   Meyer, Meredith G; White, Vincent J; Torano, Olivia; Hannoush, Heidi; Lankford, Margarita; Marchetti, Adrian (October 2025, Journal of Phycology)

   Abstract Small eukaryotic phytoplankton can account for a considerable amount of biomass and primary production in high nutrient, low chlorophyll (HNLC) regions of the ocean where iron limitation is pronounced. However, the physiological and metabolic strategies these cells invoke to cope under low iron conditions and the extent to which they are responsible for new production (i.e., the fraction of primary production supported by nutrients from outside of the euphotic zone) are unclear. Here, we examined how a representative picoeukaryote—the chlorophyteMicromonassp., recently isolated from the iron‐limited subarctic Northeast Pacific Ocean—responded to iron limitation when grown on nitrate as a nitrogen source. Iron‐limitedMicromonasexhibited reductions in growth rate, cell volume, and elemental quotas along with a restructuring of cellular metabolism. Gene expression and metabolic pathway analyses showed evidence of strategies to mitigate iron limitation with constitutive expression of genes related to nitrogen uptake and utilization. Additionally, cellular carbon and nitrogen quotas were 20–70 fmol C · cell⁻¹and 3.3–20 fmol N · cell⁻¹, respectively, as a function of iron status. Based on the measured cellular quotas, we have estimated that representative picoeukaryotes (<2 μm), such asMicromonas,in HNLC Northeast Pacific waters can account for a significant proportion of new production, supporting the need for a reconsideration of the role small eukaryotic phytoplankton play in the global carbon cycle. 

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2. GEOTRACES: Ironing Out the Details of the Oceanic Iron Sources?

   https://doi.org/10.5670/oceanog.2024.416  

   Conway, Tim; Middag, Rob; Schlitzer, Reiner (January 2024, Oceanography)

   Dissolved iron (dFe) is an essential micronutrient for phytoplankton, with vanishingly low oceanic dissolved concentrations (pico- to nanomoles per kg) known to limit growth—and thus influence primary productivity and carbon cycling—over much of the surface ocean. However, because of the considerable challenges associated with contamination-free sample collection and accurate analysis of such low dFe concentrations, the first reliable dFe measurements came only in the 1980s. Further, by 2003, despite several decades of research, there were only ~25 full-depth oceanic dFe profiles worldwide, with dust considered to be the main oceanic dFe source. Since 2008, facilitated by the extensive field campaign and rigorous intercalibration of the international GEOTRACES program, there has been an “explosion” in the availability of oceanic dFe data, with hundreds of profiles now available. Concurrently, there has been a paradigm shift to a view of the marine Fe cycle where multiple sources contribute, and some forms of dFe can be transported great distances through the intermediate and deep ocean. Here, we showcase the GEOTRACES dFe datasets across the different ocean basins, synthesize our current multi-source view of the oceanic Fe cycle, spotlight sediments as an important dFe source, and look to future directions for constraining oceanic dFe boundary exchange. 

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3. Climate-driven oscillation of phosphorus and iron limitation in the North Pacific Subtropical Gyre

   https://doi.org/10.1073/pnas.1900789116  

   Letelier, Ricardo M.; Björkman, Karin M.; Church, Matthew J.; Hamilton, Douglas S.; Mahowald, Natalie M.; Scanza, Rachel A.; Schneider, Niklas; White, Angelicque E.; Karl, David M. (June 2019, Proceedings of the National Academy of Sciences)

   The supply of nutrients is a fundamental regulator of ocean productivity and carbon sequestration. Nutrient sources, sinks, residence times, and elemental ratios vary over broad scales, including those resulting from climate-driven changes in upper water column stratification, advection, and the deposition of atmospheric dust. These changes can alter the proximate elemental control of ecosystem productivity with cascading ecological effects and impacts on carbon sequestration. Here, we report multidecadal observations revealing that the ecosystem in the eastern region of the North Pacific Subtropical Gyre (NPSG) oscillates on subdecadal scales between inorganic phosphorus (P i ) sufficiency and limitation, when P i concentration in surface waters decreases below 50–60 nmol⋅kg −1 . In situ observations and model simulations suggest that sea-level pressure changes over the northwest Pacific may induce basin-scale variations in the atmospheric transport and deposition of Asian dust-associated iron (Fe), causing the eastern portion of the NPSG ecosystem to shift between states of Fe and P i limitation. Our results highlight the critical need to include both atmospheric and ocean circulation variability when modeling the response of open ocean pelagic ecosystems under future climate change scenarios. 

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4. Drivers of Spatiotemporal Distributions of Macro‐ and Micronutrients (Fe, Ni, Cu, Zn) in the Northern Gulf of Alaska

   https://doi.org/10.1029/2025JC022558  

   Ortega, E_L S; Meier, Ava; Danielson, Seth L; McMonigal, Kay; Aguilar‐Islas, A M (September 2025, Journal of Geophysical Research: Oceans)

   The productive Northern Gulf of Alaska (NGA) ecosystem is impacted by spatiotemporal variability in nutrient distributions and ratios. Due to its advective nature and wide (50–150 km) continental shelf, the NGA may act as a nutrient source to the greater NE Pacific. Using high‐resolution data from 11 seasonal (spring, summer, fall) research cruises (2018–2023), we examined regional drivers of nutrient fields. We found that variable sources of micro‐ and macronutrients influence their distributions and ratios. For example, relative to cellular nutrient quotas for coastal diatoms, surface dissolved Fe (dFe): nitrate (NO₃⁻) ratios indicated an Fe‐replete regime near river outflows throughout the year. In contrast, far from freshwater and subsurface Fe inputs, this ratio indicated potential Fe stress or limitation within outer waters during spring. Near the seafloor, a pool of high dissolved micro‐ and macronutrients highlighted variable nutrient sources (sedimentary and deep offshore waters), and its location indicated its susceptibility to wind forcing. We also observed detachment of bottom boundary layers along shoaling isopycnals within the shelf‐break front that can carry subsurface dFe to depths of ∼100 m: a depth that can be accessed by winter mixing. This represents a potential mechanism to deliver dFe from the shelf to offshore high nutrient low chlorophyll (HNLC) surface waters of the NGA, although shelf‐basin exchange can be diminished by along‐shelf flow (e.g., the Alaskan Stream). This work enhances understanding of nutrient sources in the NGA and adds to a relatively small global repository of seasonally high‐resolution micronutrient data over continental shelves. 

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5. Godzilla mineral dust and La Soufrière volcanic ash fallout immediately stimulate marine microbial phosphate uptake

   https://doi.org/10.3389/fmars.2023.1308689  

   Elliott, Hope Elizabeth; Popendorf, Kimberly J; Blades, Edmund; Royer, Haley M; Pollier, Clément_G L; Oehlert, Amanda M; Kukkadapu, Ravi; Ault, Andrew; Gaston, Cassandra J (January 2024, Frontiers in Marine Science)

   During the “Godzilla” dust storm of June 2020, unusually high fluxes of mineral dust traveled across the Atlantic from the Sahara Desert, reaching the Caribbean Basin, Gulf Coast, and southeastern United States. Additionally, an eruption of the La Soufrière volcano on St. Vincent in April 2021 generated substantial ashfall in the southeastern Caribbean. While many studies have analyzed mineral dust’s ability to relieve nutrient limitation of phosphorus (P) in the P-stressed North Atlantic, less is known about the impact of extreme events and other natural aerosols on fluxes of P into seawater and from seawater into marine microbial cells. We quantified P and iron (Fe) content in mineral dust from the Godzilla dust storm and volcanic ash from the La Soufrière eruption collected at Ragged Point, Barbados. We also performed seawater incubations to assess the marine microbial response to aerosol deposition. Using environmentally-relevant concentrations of atmospheric particles for within the ocean’s mixed layer allowed us to draw realistic conclusions about how these deposition events impacted P cycling in situ. Volcanic ash has lower P content than mineral dust, and P in volcanic ash is far less soluble (~1%) than assumed in current atmospheric deposition models. Adding mineral dust and the volcanic ash leachate in concentrations representing different deposition scenarios increased soluble reactive phosphorus (SRP) concentrations in coastal seawater by ~7-32 nM. Phosphate uptake rate was stimulated in coastal seawater after either mineral dust or volcanic ash deposition at aerosol concentrations relevant to the Godzilla dust event, with ash eliciting the fastest uptake rate. Furthermore, high concentrations of both the mineral dust and volcanic ash led to slightly elevated alkaline phosphatase activity (APA) compared to the relevant controls, indicating higher potential for use of dissolved organic phosphorus (DOP) as a P source. Quantifying these aerosols’ impacts on P cycling is a significant step towards achieving a better understanding of their potential roles in relieving nutrient limitation and fueling the biological carbon pump. 

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