Marine diatoms rose to prominence about 100 million years ago and today generate most of the organic matter that serves as food for life in the sea. They exist in a dilute world where compounds essential for growth are recycled and shared, and they greatly influence global climate, atmospheric carbon dioxide concentration and marine ecosystem function. How these essential organisms will respond to the rapidly changing conditions in today's oceans is critical for the health of the environment and is being uncovered by studies of their genomes.

https://moritz.botany.ut.ee/~olli/aldoc/Life_of_diatoms_in_the_world_oceans.pdf

The life of diatoms in the world's oceans

This chapter presents a general overview of the major controls of trace metals in seawater, developed from the extensive research on trace metals over the last few decades. The reader should be given a first-order understanding and insight into trace metal biogeochemistry in the oceans, rather than presented with a comprehensive review of the distribution of each trace metal. Each of the trace metals discussed will undoubtedly prove to have unique characteristics and subtle differences from this version, yet the comparison with these characteristics will serve as a good springboard to a more complete understanding.

Controls of Trace Metals in Seawater

The nitrogen-isotope record preserved in Southern Ocean sediments, along with several geochemical tracers for the settling fluxes of biogenic matter, reveals patterns of past nutrient supply to phytoplankton and surface-water stratification in this oceanic region. Areal averaging of these spatial patterns indicates that reduction of the CO2 ‘leak’ from ocean to atmosphere by increased surface-water stratification south of the Polar Front made a greater contribution to the lowering of atmospheric CO2 concentration during the Last Glacial Maximum than did the increased export of organic carbon from surface to deep waters occurring further north.

Contribution of Southern Ocean surface-water stratification to low atmospheric CO 2 concentrations during the last glacial period

The accumulation of inorganic carbon from seawater by eukaryotic marine phytoplankton is limited by the diffusion of carbon dioxide (CO2) in water and the dehydration kinetics of bicarbonate to CO2 and by ribulose-1,5-bisphosphate carboxylase/oxygenase's (RubisCO) low affinity for its inorganic carbon substrate, CO2. Nearly all marine phytoplankton have adapted to these limitations and evolved inorganic carbon (or CO2) concentrating mechanisms (CCMs) to support photosynthetic carbon fixation at the concentrations of CO2 present in ocean surface waters (< 10-30 microM). The biophysics and biochemistry of CCMs vary within and among the three dominant groups of eukaryotic marine phytoplankton and may involve the activity of external or intracellular carbonic anhydrase, HCO3- transport, and perhaps a C4 carbon pump. In general, coccolithophores have low-efficiency CCMs, and diatoms and the haptophyte genus Phaeocystis have high-efficiency CCMs. Dinoflagellates appear to possess moderately efficient CCMs, which may be necessitated by the very low CO2 affinity of their form II RubisCO. The energetic and nutrient costs of CCMs may modulate how variable CO2 affects primary production, element composition, and species composition of phytoplankton in the ocean.

Carbon Concentrating Mechanisms in Eukaryotic Marine Phytoplankton

https://darchive.mblwhoilibrary.org/bitstream/handle/1912/5118/1-s2.0-S1568988311001533-main.pdf

Pseudo-nitzschia physiological ecology, phylogeny, toxicity, monitoring and impacts on ecosystem health

We quantified and compared physiological parameters and iron requirements of several oceanic Pseudonitzschia spp., newly isolated from the high-nitrate, low-chlorophyll waters of the northeast subarctic Pacific, with coastal Pseudo-nitzschia spp. and the oceanic centric diatom Thalassiosira oceanica at a range of iron concentrations. In iron-replete conditions, the iron (Fe) : carbon (C) ratios in the six Pseudo-nitzschia isolates ranged from 157 mmol Fe mol C21 to 248 mmol Fe mol C21, with no apparent differences between oceanic and coastal isolates. In low iron conditions, all Pseudo-nitzschia spp. exhibited marked reductions in photosynthetic efficiency, whereas the extent of the reductions in specific growth rates varied among species. When iron-limited, the Fe : C ratios decreased significantly in all oceanic Pseudo-nitzschia species, with the lowest ratios ranging from 2.8 mmol Fe mol C 21 to 3.7 mmol Fe mol C 21 . Combined with faster growth rates, lower Fe : C ratios in oceanic isolates of Pseudo-nitzschia resulted in significantly higher iron-use efficiencies relative to their coastal congeners and T. oceanica. The wide range between iron-replete (Fe-Qhigh) and iron-limited (Fe-Qlow) quotas indicates that oceanic Pseudo-nitzschia spp. have an extensive plasticity in iron contents relative to other diatoms grown at similar iron concentrations reported in the literature; the Fe-Qhigh : Fe-Qlow ratios for oceanic species were 46 to 67, whereas for coastal Pseudo-nitzschia species they were 16 and 43. We suggest that the ability of oceanic Pseudo-nitzschia species to exhibit an extensive growth response to iron enrichment events may, in part, be a result of their extraordinary capacity to accumulate and potentially store large amounts of intracellular iron when iron concentrations are high, yet substantially reduce their iron requirements to sustain fast growth rates well after external iron concentrations are depleted.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2006.51.5.2092

Iron requirements of the pennate diatom Pseudo‐nitzschia: Comparison of oceanic (high‐nitrate, low‐chlorophyll waters) and coastal species

Effects of iron limitation on intracellular cadmium of cultured phytoplankton: Implications for surface dissolved cadmium to phosphate ratios

We examined substrate-saturated Fe(II) vs. Fe(III) uptake rates of Thalassiosira oceanica preconditioned to varying degrees of Fe limitation. Inorganic Fe(III) uptake rates by Fe-sufficient T. oceanica were 2.4-fold faster than the corresponding inorganic Fe(II) uptake rates. However, when cultures were severely Fe limited, the rate of Fe(II) uptake was upregulated 15-fold, while that of Fe(III) uptake increased only fivefold. The interactions between substrate-saturated uptake rates of inorganic Cd(II) and either Fe(II) or Fe(III) by Fe-limited T. oceanica were also investigated. The addition of equimolar Cd(II) concentration to the Fe(II) uptake media resulted in a ,50% reduction of inorganic Fe(II) uptake rates compared with those in Cd-free media. In turn, Cd uptake rates were inhibited ,36% in the presence of an equimolar Fe(II) concentration. In contrast to Fe(II), Fe(III) transport exhibited no interaction with Cd(II). T. oceanica thus has separate transporters for inorganic Fe(III) and Fe(II). Cadmium(II) and Fe(II) appear to enter the cell through a common putative divalent metal transporter that is upregulated under Fe deficiency. The interaction of Fe(II) and Cd(II) transport under Fe deficiency provides a plausible mechanism to explain some laboratory and field observations of higher Cd quotas in Fe-limited phytoplankton.

https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.2008.53.5.1784

The interaction between inorganic iron and cadmium uptake in the marine diatom Thalassiosira oceanica

This paper discusses the development and results of a new tool used for measuring shifts in students’ perceptions of earth and ocean sciences called the Student Perceptions about Earth Sciences Survey (SPESS). The survey measures where students lie on the novice–expert continuum, and how their perceptions change after taking one or more earth and ocean science course(s). The survey is composed of 29 statements that have been validated with expert responses and student interviews. Factor analysis was used to group statements into seven categories, which provide instructors with valuable information to guide pedagogical change in their classes. Overall student perceptions in earth and ocean sciences show little change over the course of the term, in contrast to novice shifts in perceptions seen in other science disciplines. Students in earth and ocean sciences also do not display any gender differences, unlike those seen in these other disciplines. However, differences are seen between face-to-face and distance education versions of a course, between earth and ocean science majors and nonmajors, and between a community college and a large research institution. The former of each pair are more expert-like. 2012 National Association of Geoscience Teachers. [DOI: 10.5408/10-199.1]

/pdf/spess-a-new-instrument-for-measuring-student-perceptions-in-1cmulmmbhs.pdf

Erin S. Lane

Papers

Iron requirements of the pennate diatom Pseudo‐nitzschia: Comparison of oceanic (high‐nitrate, low‐chlorophyll waters) and coastal species

Effects of iron limitation on intracellular cadmium of cultured phytoplankton: Implications for surface dissolved cadmium to phosphate ratios

The interaction between inorganic iron and cadmium uptake in the marine diatom Thalassiosira oceanica

SPESS: A New Instrument for Measuring Student Perceptions in Earth and Ocean Science