Impaired viral infection and reduced mortality of diatoms in iron-limited oceanic regions

Diatom primary productivity is tightly coupled with carbon export through the ballasted nature of the silica-based cell wall, linking the oceanic silicon and carbon cycles. However, despite low productivity, iron (Fe)-limited regimes are considered ‘hot spots’ of diatom silica burial with enhanced carbon export efficiency, raising questions about the mechanisms driving the biogeochemistry of these regions. Marine viruses are classically recognized as catalysts of remineralization through host lysis, short-circuiting the trophic transfer of carbon and facilitating the retention of dissolved organic matter and associated elements in the surface ocean. Here we used metatranscriptomic analysis of diatoms and associated viruses, along with a suite of physiological and geochemical metrics, to study the interaction between diatoms and viruses in Fe-limited regimes of the northeast Pacific. We found low cell-associated diatom virus diversity and abundance in a chronically Fe-limited region of the subarctic northeast Pacific. In a coastal upwelling region of the California Current, transient iron limitation also substantially reduced viral replication. These observations were recapitulated in Fe-limited cultures of the bloom-forming, centric diatom, Chaetoceros tenuissimus, which exhibited delayed virus-mediated mortality in addition to reduced viral replication. We suggest Fe-limited diatoms escape viral lysis and subsequent remineralization in the surface ocean, providing an additional mechanism contributing to enhanced carbon export efficiency and silica burial in Fe-limited oceanic regimes

Divergent gene expression among phytoplankton taxa in response to upwelling

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 increases in nitrate assimilation and rapid growth rates. To examine the molecular underpinnings behind this phenomenon, metatranscriptomics was applied to a simulated upwelling experiment using natural phytoplankton communities from the California Upwelling Zone. An increase in diatom growth following 5 days of incubation was attributed to the genera Chaetoceros and Pseudo-nitzschia. Here, we show that certain bloom-forming diatoms exhibit a distinct transcriptional response that coordinates shift-up where diatoms exhibited the greatest transcriptional change following upwelling; however, comparison of co-expressed genes exposed overrepresentation of distinct sets within each of the dominant phytoplankton groups. The analysis revealed that diatoms frontload genes involved in nitrogen assimilation likely in order to outcompete other groups for available nitrogen during upwelling events. We speculate that the evolutionary success of diatoms may be due, in part, to this proactive response to frequently encountered changes in their environment

A Unified Algebraic Approach to Few and Many-Body Correlated Systems

The present article is an extended version of the paper {\it Phys. Rev.} {\bf B 59}, R2490 (1999), where, we have established the equivalence of the Calogero-Sutherland model to decoupled oscillators. Here, we first employ the same approach for finding the eigenstates of a large class of Hamiltonians, dealing with correlated systems. A number of few and many-body interacting models are studied and the relationship between their respective Hilbert spaces, with that of oscillators, is found. This connection is then used to obtain the spectrum generating algebras for these systems and make an algebraic statement about correlated systems. The procedure to generate new solvable interacting models is outlined. We then point out the inadequacies of the present technique and make use of a novel method for solving linear differential equations to diagonalize the Sutherland model and establish a precise connection between this correlated system's wave functions, with those of the free particles on a circle. In the process, we obtain a new expression for the Jack polynomials. In two dimensions, we analyze the Hamiltonian having Laughlin wave function as the ground-state and point out the natural emergence of the underlying linear $W_{1+\infty}$ symmetry in this approach.Comment: 18 pages, Revtex format, To appear in Physical Review

Distal and proximal controls on the silicon stable isotope signature of North Atlantic Deep Water

It has been suggested that the uniquely high ?30Si signature of North Atlantic Deep Water (NADW) results from the contribution of isotopically fractionated silicic acid by mode and intermediate waters that are formed in the Southern Ocean and transported to the North Atlantic within the upper limb of the meridional overturning circulation (MOC). Here, we test this hypothesis in a suite of ocean general circulation models (OGCMs) with widely varying MOCs and related pathways of nutrient supply to the upper ocean. Despite their differing MOC pathways, all models reproduce the observation of a high ?30Si signature in NADW, as well showing a major or dominant (46–62%) contribution from Southern Ocean mode/intermediate waters to its Si inventory. These models thus confirm that the ?30Si signature of NADW does indeed owe its existence primarily to the large-scale transport of a distal fractionation signal created in the surface Southern Ocean. However, we also find that more proximal fractionation of Si upwelled to the surface within the Atlantic Ocean must also play some role, contributing 20–46% of the deep Atlantic ?30Si gradient. Finally, the model suite reveals compensatory effects in the mechanisms contributing to the high ?30Si signature of NADW, whereby less export of high-?30Si mode/intermediate waters to the North Atlantic is compensated by production of a high-?30Si signal during transport to the NADW formation region. This trade-off decouples the ?30Si signature of NADW from the pathways of deep water upwelling associated with the MOC. Thus, whilst our study affirms the importance of cross-equatorial transport of Southern Ocean-sourced Si in producing the unique ?30Si signature of NADW, it also shows that the presence of a deep Atlantic ?30Si gradient does not uniquely constrain the pathways by which deep waters are returned to the upper ocean

Iron and silicic acid concentrations together regulate Si uptake in the equatorial Pacific Ocean

The effects of added Si and Fe on the rate of silicic acid uptake were examined during two cruises to the equatorial Pacific upwelling zone between 110ºW and 140ºW. Maximum uptake rates of Si (Vmax) were highly consistent with a mean of 0.026 ± 0.007 h-1(n = 29), implying maximum diatom growth rates of ~0.6 d-1. Half-saturation constants for Si uptake (KS) also showed little variance, averaging 1.7 ± 0.7 mmol L-1 Si(OH)4. No ecologically significant spatial or temporal patterns for either Vmax or KS were observed. Comparison of Si uptake rates at the ambient silicic acid concentration (Vamb) with Vmax indicated that the ambient [Si(OH)4] restricted Vamb to an average of 63% ± 13% of Vmax. Fe additions also caused significant increases in both Vmax and Vamb, indicating that the rate of Si uptake was also regulated by the ambient [Fe]. Fe additions had a variable effect on KS, but they consistently increased both Vmax and the initial slope of the kinetic curve (Vmax :KS), and thus the diatom assemblages’ ability to take up Si(OH)4 at low concentrations. Added Fe or Si increased Si uptake rates by 87% ± 59% and 69% ± 31%, respectively, indicating nearly equal roles for the two elements in limiting rates of Si uptake in situ. The largest average increase in Si uptake rates, 172% ± 43%, was observed when both Si and Fe were added, implying that together Si and Fe restricted Si uptake rates by almost a factor of three. <br/

Heavy silicon isotopic composition of silicic acid and biogenic silicain arctic waters over the Beaufort shelf and the Canada Basin

Propargylamines are versatile building blocks for the synthesisof various nitrogen-containing heterocyclic compounds,1 andimportant intermediates for the preparation of complex naturalproducts and biologically active molecules.2 Further, somepropargylamines have been clinically used or are currentlytested for the treatment of Parkinson's disease3 and Alzheimer'sdisease.4 Classically, propargylamines are synthesized by thenucleophilic addition of a metal alkynylide to C]N electrophiles,which oen requires stoichiometric amount of highlyactive organometallic reagents such as organolithium,5Grignard reagents,6 and organozinc reagents,7 and hence is lessattractive due to low tolerance of functional groups, harshreaction conditions, and operational complexity. In the pastdecade, transition-metal catalyzed three-component couplingof an aldehyde, an alkyne, and an amine (generally referred asA3-coupling) has received more and more attention due to its atom economy, step efficiency, and high chemical selectivity..

Heavy silicon isotopic composition of silicic acid and biogenic silicain arctic waters over the Beaufort shelf and the Canada Basin

The silicon isotopic composition of silicic acid (δ30Si(OH)4) and biogenic silica (δ30Si‐bSiO2) were measured for the first time in marine Arctic waters from the Mackenzie River delta to the deep Canada Basin in the late summer of 2009. In the upper 100 m of the water column, δ30Si(OH)4 signals (+1.82‰ to +3.08‰) were negatively correlated with the relative contribution of Mackenzie River water. The biogenic Si isotope fractionation factor estimated using an open system model, 30ε = −0.97 ± 0.17‰, agrees well with laboratory and global‐ocean estimates. Nevertheless, the δ30Si dynamics of this region may be better represented by closed system isotope models that yield lower values of 30ε, between −0.33‰ and −0.41‰, depending on how the contribution of sea‐ice diatoms is incorporated. In the upper 400 m, δ30Si‐bSiO2 values were among the heaviest ever measured in marine suspended bSiO2 (+2.03‰ to +3.51‰)..

An inter-laboratory calibration of Si isotope reference materials

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