Biogeochemical cycles constitute Earth’s life support system and distinguish our planet from others in this solar system. Microorganisms are the primary drivers of these cycles. Understanding the controls on marine microbial dynamics and how microbes will respond to environmental change is essential for building and assessing model-based forecasts and generating robust projections of climate change impacts on ocean productivit...

The GEOTRACES program has greatly expanded measurements of trace elements, which serve as key nutrients, harmful contaminants, and tracers of ocean processes and past conditions. Many elements tend to associate with particulate matter, and GEOTRACES has been particularly valuable for growing our understanding of this fraction. Focusing on the micronutrient iron as an example, GEOTRACES data demonstrate that the majority of iro...

Climate change scenarios suggest that large‐scale carbon dioxide removal (CDR) will be required to maintain global warming below 2°C, leading to renewed attention on ocean iron fertilization (OIF). Previous OIF modelling has found that while carbon export increases, nutrient transport to lower latitude ecosystems declines, resulting in a modest impact on atmospheric CO 2 . However, the interaction of these CDR responses with o...

Synchrotron instruments are useful for marine studies because they make nondestructive measurements of chemical composition and speciation on small sample volumes and at low concentrations. Synchrotron beamtime is available without cost using a peer-reviewed proposal system. New users do not have to be synchrotron radiation experts to design a good experiment, but some guidance is needed to design and propose appropriate exper...

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 Zn 2+ and Co 2+ on specific growth rate. Analysis of growth res...

While the majority of studies use the environment to describe microbial populations, the high diversity of microbes can conversely be used as a resource to understand subtle environmental variability. Here, we used a high‐resolution spatial and temporal analysis of Prochlorococcus sp. in the Eastern Indian Ocean to determine whether ecotypes and microdiverse taxa can be used to identify fine‐scale biogeochemical regimes in thi...

Summary Frequent blooms of phytoplankton occur in coastal upwelling zones creating hotspots of biological productivity in the ocean. As cold, nutrient‐rich water is brought up to sunlit layers from depth, phytoplankton are also transported upwards to seed surface blooms that are often dominated by diatoms. The physiological response of phytoplankton to this process, commonly referred to as shift‐up, is characterized by increas...

In large regions of the ocean, low iron availability regulates diatom growth and species composition. Diatom species often vary in their physiological response to iron enrichment, with natural and artificial iron additions in iron‐limited regions of the ocean resulting in large blooms of primarily pennate diatoms. The ability of pennate diatoms to proliferate following pulse iron additions has been partly attributed to their a...

Changes in iron (Fe) bioavailability influence diatom physiology and community composition, and thus have a profound impact on primary productivity and ecosystem dynamics. Iron limitation of diatom growth rates has been demonstrated in both oceanic and coastal waters of the Northeast Pacific Ocean and is predicted to become more pervasive in future oceans. However, it is unclear how the strategies utilized by phytoplankton to...

Little is known about the trace metal content of marine prokaryotes, in part due to their co‐occurrence with more abundant particulate phases in the upper ocean, such as phytoplankton and biogenic detritus, lithogenic minerals, and authigenic Mn and Fe oxyhydroxides. We attempt to isolate these biomass signals in particulate data from the US GEOTRACES Eastern Pacific Zonal Transect (cruise GP16) in the Eastern Tropical South P...

The micronutrient iron (Fe) is rapidly cycled in surface waters, and regenerated Fe supports much of the phytoplankton growth in open ocean waters. Meso‐ and microzooplankton grazing are both important mechanisms to regenerate Fe, but the chemical conditions in the respective digestive systems are different and might affect the bioavailability of Fe. We conducted radiotracer grazing experiments with the copepod Acartia tonsa o...

Macronutrients in sinking phytoplankton are typically remineralized at different rates, but less is known about the fate of micronutrient metals associated with sinking cells. Scavenging, the presence of co‐occurring abiotic particles, and inadvertent contamination limit the utility of bulk analytical approaches to study remineralization of trace metals in sinking phytoplankton. We used synchrotron x‐ray fluorescence mapping t...

The quotas of P, S, Mn, Fe, Ni, and Zn in individual Synechococcus cells collected from the surface and deep chlorophyll maximum (DCM) layer of three mesoscale eddies in the Sargasso Sea were measured using synchrotron X‐ray fluorescence microscopy. Cells in a mode‐water eddy had significantly higher P (57 ± 10 amol) and Mn (28 ± 7 zmol) cell quotas than cells collected from a cyclone (22 ±2 amol and 10 ± 1 zmol, respectively)...

Denitrifying bacteria require copper for the synthesis of nitrous oxide reductase. In the absence of sufficient bioavailable Cu, nitrous oxide (N 2 O) may accumulate in natural waters during denitrification. Cultures of Paracoccus denitrificans and natural bacterial assemblages collected from a mesotrophic lake (Linsley Pond) were grown at varying Cu concentrations to determine the Cu speciation that results in elevated N 2 O...

During the Southern Ocean Iron Experiment (SOFeX), we analyzed Si, P, S, Mn, Ni, and Zn in individual diatoms, autotrophic flagellates, and heterotrophic flagellates with synchrotron‐based X‐ray fluorescence (SXRF) and calculated cellular C from measurements of cell size. Element stoichiometries for the different types of protists (normalized to either C, S, or P) were generally in good agreement with prior bulk analyses of na...

Radiotracer techniques were used to quantify the assimilation and subsequent efflux of silver, cadmium, iron, mercury, thallium, and zinc by mesozooplankton fed ciliates, heterotrophic dinoflagellates, or heterotrophic flagellates, and the results were compared with published values measured for phytoplankton prey. The subcellular distribution of the metals within the prey cells was also determined and related to their bioavai...

We tested the hypothesis that rotifer species in the micro‐ and mesozooplankton are a potential food source for zebra mussels. We labeled phytoplankton with 14 C, fed them to two species of rotifers (140–210 µm length) that were previously found abundantly in the Hudson River and had declined following a zebra mussel invasion, and estimated the assimilation of carbon. Assimilation efficiencies were found to be ~37.47–54.0%. Co...

Mysid swarms at benthic coral reef sites disperse into the water column in the evening and reform at the exact same location the following morning, possibly reflecting homing behavior of individual mysids. To facilitate tracking of individual mysids, we radiolabeled part of a swarm of Mysidium gracile with the gamma‐emitting radioisotope 65 Zn and released the labeled animals back to the focal swarm on a reef in Discovery Bay,...