Iron limitation of kelp growth may prevent ocean afforestation.

Carbon dioxide removal (CDR) and emissions reduction are essential to alleviate climate change. Ocean macroalgal afforestation (OMA) is a CDR method already undergoing field trials where nearshore kelps, on rafts, are purposefully grown offshore at scale. Dissolved iron (dFe) supply often limits oceanic phytoplankton growth, however this potentially rate-limiting factor is being overlooked in OMA discussions. Here, we determine the limiting dFe concentrations for growth and key physiological functions of a representative kelp species, Macrocystis pyrifera, considered as a promising candidate for OMA. dFe additions to oceanic seawater ranging 0.01-20.2 nM Fe' ‒ Fe' being the sum of dissolved inorganic Fe(III) species ‒ result in impaired physiological functions and kelp mortality. Kelp growth cannot be sustained at oceanic dFe concentrations, which are 1000-fold lower than required by M. pyrifera. OMA may require additional perturbation of offshore waters via dFe fertilisation.

Chasing iron bioavailability in the Southern Ocean: Insights from Phaeocystis antarctica and iron speciation.

Dissolved iron (dFe) availability limits the uptake of atmospheric CO2 by the Southern Ocean (SO) biological pump. Hence, any change in bioavailable dFe in this region can directly influence climate. On the basis of Fe uptake experiments with Phaeocystis antarctica, we show that the range of dFe bioavailability in natural samples is wider (<1 to ~200% compared to free inorganic Fe') than previously thought, with higher bioavailability found near glacial sources. The degree of bioavailability varied regardless of in situ dFe concentration and depth, challenging the consensus that sole dFe concentrations can be used to predict Fe uptake in modeling studies. Further, our data suggest a disproportionately major role of biologically mediated ligands and encourage revisiting the role of humic substances in influencing marine Fe biogeochemical cycling in the SO. Last, we describe a linkage between in situ dFe bioavailability and isotopic signatures that, we anticipate, will stimulate future research.

Giant Virus Infection Signatures Are Modulated by Euphotic Zone Depth Strata and Iron Regimes of the Subantarctic Southern Ocean.

Viruses can alter the abundance, evolution, and metabolism of microorganisms in the ocean, playing a key role in water column biogeochemistry and global carbon cycles. Large efforts to measure the contribution of eukaryotic microorganisms (e.g., protists) to the marine food web have been made, yet the in situ activities of the ecologically relevant viruses that infect these organisms are not well characterized. Viruses within the phylum Nucleocytoviricota ("giant viruses") are known to infect a diverse range of ecologically relevant marine protists, yet how these viruses are influenced by environmental conditions remains under-characterized. By employing metatranscriptomic analyses of in situ microbial communities along a temporal and depth-resolved gradient, we describe the diversity of giant viruses at the Southern Ocean Time Series (SOTS), a site within the subpolar Southern Ocean. Using a phylogeny-guided taxonomic assessment of detected giant virus genomes and metagenome-assembled genomes, we observed depth-dependent structuring of divergent giant virus families mirroring dynamic physicochemical gradients in the stratified euphotic zone. Analyses of transcribed metabolic genes from giant viruses suggest viral metabolic reprogramming of hosts from the surface to a 200-m depth. Lastly, using on-deck incubations reflecting a gradient of iron availability, we show that modulating iron regimes influences the activity of giant viruses in the field. Specifically, we show enhanced infection signatures of giant viruses under both iron-replete and iron-limited conditions. Collectively, these results expand our understanding of how the water column's vertical biogeography and chemical surroundings affect an important group of viruses within the Southern Ocean. IMPORTANCE The biology and ecology of marine microbial eukaryotes is known to be constrained by oceanic conditions. In contrast, how viruses that infect this important group of organisms respond to environmental change is less well known, despite viruses being recognized as key microbial community members. Here, we address this gap in our understanding by characterizing the diversity and activity of "giant" viruses within an important region in the sub-Antarctic Southern Ocean. Giant viruses are double-stranded DNA (dsDNA) viruses of the phylum Nucleocytoviricota and are known to infect a wide range of eukaryotic hosts. By employing a metatranscriptomics approach using both in situ samples and microcosm manipulations, we illuminated both the vertical biogeography and how changing iron availability affects this primarily uncultivated group of protist-infecting viruses. These results serve as a foundation for our understanding of how the open ocean water column structures the viral community, which can be used to guide models of the viral impact on marine and global biogeochemical cycling.

Phytoplankton Responses to Bacterially Regenerated Iron in a Southern Ocean Eddy.

In the Subantarctic sector of the Southern Ocean, vertical entrainment of iron (Fe) triggers the seasonal productivity cycle but diminishing physical supply during the spring to summer transition forces microbial assemblages to rapidly acclimate. Here, we tested how phytoplankton and bacteria within an isolated eddy respond to different dissolved Fe (DFe)/ligand inputs. We used three treatments: one that mimicked the entrainment of new DFe (Fe-NEW), another in which DFe was supplied from bacterial regeneration of particles (Fe-REG), and a control with no addition of DFe (Fe-NO). After 6 days, 3.5 (Fe-NO, Fe-NEW) to 5-fold (Fe-REG) increases in Chlorophyll a were observed. These responses of the phytoplankton community were best explained by the differences between the treatments in the amount of DFe recycled during the incubation (Fe-REG, 15% recycled c.f. 40% Fe-NEW, 60% Fe-NO). This additional recycling was more likely mediated by bacteria. By day 6, bacterial production was comparable between Fe-NO and Fe-NEW but was approximately two-fold higher in Fe-REG. A preferential response of phytoplankton (haptophyte-dominated) relative to high nucleic acid (HNA) bacteria was also found in the Fe-REG treatment while the relative proportion of diatoms increased faster in the Fe-NEW and Fe-NO treatments. Comparisons between light and dark incubations further confirmed the competition between picophytoplankton and HNA for DFe. Overall, our results demonstrate great versatility by microorganisms to use different Fe sources that results in highly efficient Fe recycling within surface waters. This study also encourages future research to further investigate the interactions between functional groups of microbes (e.g. HNA and cyanobacteria) to better constraint modeling in Fe and carbon biogeochemical cycles.

Bioavailable iron titrations reveal oceanic Synechococcus ecotypes optimized for different iron availabilities.

The trace metal iron (Fe) controls the diversity and activity of phytoplankton across the surface oceans, a paradigm established through decades of in situ and mesocosm experimental studies. Despite widespread Fe-limitation within high-nutrient, low chlorophyll (HNLC) waters, significant contributions of the cyanobacterium Synechococcus to the phytoplankton stock can be found. Correlations among differing strains of Synechococcus across different Fe-regimes have suggested the existence of Fe-adapted ecotypes. However, experimental evidence of high- versus low-Fe adapted strains of Synechococcus is lacking, and so we investigated the transcriptional responses of microbial communities inhabiting the HNLC, sub-Antarctic region of the Southern Ocean during the Spring of 2018. Analysis of metatranscriptomes generated from on-deck incubation experiments reflecting a gradient of Fe-availabilities reveal transcriptomic signatures indicative of co-occurring Synechococcus ecotypes adapted to differing Fe-regimes. Functional analyses comparing low-Fe and high-Fe conditions point to various Fe-acquisition mechanisms that may allow persistence of low-Fe adapted Synechococcus under Fe-limitation. Comparison of in situ surface conditions to the Fe-titrations indicate ecological relevance of these mechanisms as well as persistence of both putative ecotypes within this region. This Fe-titration approach, combined with transcriptomics, highlights the short-term responses of the in situ phytoplankton community to Fe-availability that are often overlooked by examining genomic content or bulk physiological responses alone. These findings expand our knowledge about how phytoplankton in HNLC Southern Ocean waters adapt and respond to changing Fe supply.

Distinct iron cycling in a Southern Ocean eddy.

Mesoscale eddies are ubiquitous in the iron-limited Southern Ocean, controlling ocean-atmosphere exchange processes, however their influence on phytoplankton productivity remains unknown. Here we probed the biogeochemical cycling of iron (Fe) in a cold-core eddy. In-eddy surface dissolved Fe (dFe) concentrations and phytoplankton productivity were exceedingly low relative to external waters. In-eddy phytoplankton Fe-to-carbon uptake ratios were elevated 2-6 fold, indicating upregulated intracellular Fe acquisition resulting in a dFe residence time of ~1 day. Heavy dFe isotope values were measured for in-eddy surface waters highlighting extensive trafficking of dFe by cells. Below the euphotic zone, dFe isotope values were lighter and coincident with peaks in recycled nutrients and cell abundance, indicating enhanced microbially-mediated Fe recycling. Our measurements show that the isolated nature of Southern Ocean eddies can produce distinctly different Fe biogeochemistry compared to surrounding waters with cells upregulating iron uptake and using recycling processes to sustain themselves.

The interplay between regeneration and scavenging fluxes drives ocean iron cycling.

Despite recent advances in observational data coverage, quantitative constraints on how different physical and biogeochemical processes shape dissolved iron distributions remain elusive, lowering confidence in future projections for iron-limited regions. Here we show that dissolved iron is cycled rapidly in Pacific mode and intermediate water and accumulates at a rate controlled by the strongly opposing fluxes of regeneration and scavenging. Combining new data sets within a watermass framework shows that the multidecadal dissolved iron accumulation is much lower than expected from a meta-analysis of iron regeneration fluxes. This mismatch can only be reconciled by invoking significant rates of iron removal  to balance iron regeneration, which imply generation of authigenic particulate iron pools. Consequently, rapid internal cycling of iron, rather than its physical transport, is the main control on observed iron stocks within intermediate waters globally and upper ocean iron limitation will be strongly sensitive to subtle changes to the internal cycling balance.

Biogeochemical controls of surface ocean phosphate.

Surface ocean phosphate is commonly below the standard analytical detection limits, leading to an incomplete picture of the global variation and biogeochemical role of phosphate. A global compilation of phosphate measured using high-sensitivity methods revealed several previously unrecognized low-phosphate areas and clear regional differences. Both observational climatologies and Earth system models (ESMs) systematically overestimated surface phosphate. Furthermore, ESMs misrepresented the relationships between phosphate, phytoplankton biomass, and primary productivity. Atmospheric iron input and nitrogen fixation are known important controls on surface phosphate, but model simulations showed that differences in the iron-to-macronutrient ratio in the vertical nutrient supply and surface lateral transport are additional drivers of phosphate concentrations. Our study demonstrates the importance of accurately quantifying nutrients for understanding the regulation of ocean ecosystems and biogeochemistry now and under future climate conditions.

Lung Lavage Granulocyte Patterns and Clinical Phenotypes in Children with Severe, Therapy-Resistant Asthma.

BACKGROUND: Children with severe asthma have frequent exacerbations despite guidelines-based treatment with high-dose corticosteroids. The importance of refractory lung inflammation and infectious species as factors contributing to poorly controlled asthma in children is poorly understood. OBJECTIVE: To identify prevalent granulocyte patterns and potential pathogens as targets for revised treatment, 126 children with severe asthma underwent clinically indicated bronchoscopy. METHODS: Diagnostic tests included bronchoalveolar lavage (BAL) for cell count and differential, bacterial and viral studies, spirometry, and measurements of blood eosinophils, total IgE, and allergen-specific IgE. Outcomes were compared among 4 BAL granulocyte patterns. RESULTS: Pauci-granulocytic BAL was the most prevalent granulocyte category (52%), and children with pauci-granulocytic BAL had less postbronchodilator airflow limitation, less blood eosinophilia, and less detection of BAL enterovirus compared with children with mixed granulocytic BAL. Children with isolated neutrophilia BAL were differentiated by less blood eosinophilia than those with mixed granulocytic BAL, but greater prevalence of potential bacterial pathogens compared with those with pauci-granulocytic BAL. Children with isolated eosinophilia BAL had features similar to those with mixed granulocytic BAL. Children with mixed granulocytic BAL took more maintenance prednisone, and had greater blood eosinophilia and allergen sensitization compared with those with pauci-granulocytic BAL. CONCLUSIONS: In children with severe, therapy-resistant asthma, BAL granulocyte patterns and infectious species are associated with novel phenotypic features that can inform pathway-specific revisions in treatment. In 32% of children evaluated, BAL revealed corticosteroid-refractory eosinophilic infiltration amenable to anti-TH2 biological therapies, and in 12%, a treatable bacterial pathogen.

Appraisals of DisAbility Primary and Secondary Scale-Short Form (ADAPSS-sf): Psychometrics and association with mental health among U.S. military veterans with spinal cord injury.

OBJECTIVE: Cognitive appraisals, that is, interpretations of what is observed and the personal relevance attributed to those observations, affect one's behavior and well-being. Despite the centrality of appraisals in the transactional model of stress and coping, the application of spinal cord injury (SCI)-specific appraisals to adjustment is a recent development. This study examined the psychometric properties of a measure of SCI-specific appraisals, the Appraisals of DisAbility Primary and Secondary Scale-Short Form (ADAPSS-sf). METHOD: A retrospective study using clinical data from SCI annual evaluations at a U.S. Department of Veterans Affairs medical center was employed (N = 262). RESULTS: Findings supported the ADAPSS-sf's 2-factor structure of catastrophic negativity and determined resilience. SCI appraisals were associated with mental health concerns, mental disorders, life satisfaction, racial minority status, age, SCI severity (based on the American Spinal Injury Association Impairment Scale [AIS]), and SCI etiology (traumatic or nontraumatic). Counterintuitively, those with less severe injuries (i.e., AIS D) had the greatest catastrophic negativity. Although veterans with SCI were heterogeneous in their appraisals, it is encouraging that they tended to endorse determined resilience and disavow catastrophic negativity. CONCLUSIONS: The ADAPSS-sf demonstrated many desirable characteristics, including brevity, convergent validity, and face-valid content. An implication of this study is that to understand the adjustment experience, one must look beyond injury severity and impairment to the individual's personal and subjective experience of SCI. The ADAPSS-sf offers clinicians and researchers a potentially valuable tool to assess SCI appraisals and personalize treatment. (PsycINFO Database Record

Inter-laboratory study for the certification of trace elements in seawater certified reference materials NASS-7 and CASS-6.

Certification of trace metals in seawater certified reference materials (CRMs) NASS-7 and CASS-6 is described. At the National Research Council Canada (NRC), column separation was performed to remove the seawater matrix prior to the determination of Cd, Cr, Cu, Fe, Pb, Mn, Mo, Ni, U, V, and Zn, whereas As was directly measured in 10-fold diluted seawater samples, and B was directly measured in 200-fold diluted seawater samples. High-resolution inductively coupled plasma mass spectrometry (HR-ICPMS) was used for elemental analyses, with double isotope dilution for the accurate determination of B, Cd, Cr, Cu, Fe, Pb, Mo, Ni, U, and Zn in seawater NASS-7 and CASS-6, and standard addition calibration for As, Co, Mn, and V. In addition, all analytes were measured using standard addition calibration with triple quadrupole (QQQ)-ICPMS to provide a second set of data at NRC. Expert laboratories worldwide were invited to contribute data to the certification of trace metals in NASS-7 and CASS-6. Various analytical methods were employed by participants including column separation, co-precipitation, and simple dilution coupled to ICPMS detection or flow injection analysis coupled to chemiluminescence detection, with use of double isotope dilution calibration, matrix matching external calibration, and standard addition calibration. Results presented in this study show that majority of laboratories have demonstrated their measurement capabilities for the accurate determination of trace metals in seawater. As a result of this comparison, certified/reference values and associated uncertainties were assigned for 14 elements in seawater CRMs NASS-7 and CASS-6, suitable for the validation of methods used for seawater analysis.

Effect of Post-Traumatic Stress Disorder on Cognitive Function and Covert Hepatic Encephalopathy Diagnosis in Cirrhotic Veterans.

BACKGROUND: In veterans, post-traumatic stress disorder (PTSD) is often associated with substance abuse, which in turn can lead to cirrhosis. Cirrhotic patients are prone to cognitive impairment, which is typically due to covert hepatic encephalopathy (CHE), but can also be affected by PTSD. The aim was to define the impact of PTSD on cognitive performance and the diagnosis of CHE in cirrhotic patients. METHODS: Outpatient veterans with cirrhosis underwent two separate modalities for CHE cognitive testing [Psychometric Hepatic Encephalopathy Scale (PHES) and Inhibitory Control Test (ICT)]. ICT tests for inhibitory control and response inhibition, while PHES tests for attention and psychomotor speed. Comparisons were made between patients with/without PTSD. Multivariable logistic regression with CHE on PHES and CHE on ICT as dependent variables including prior OHE, demographics, PTSD and psychotropic medications was performed. RESULTS: Of 402 patients with cirrhosis, 88 had evidence of PTSD. Fifty-five of these were on psychoactive medications, 15 were undergoing psychotherapy, while no specific PTSD-related therapy was found in 28 patients. Cirrhotic patients with/without PTSD were statistically similar on demographics and cirrhosis severity, but cirrhotic subjects with PTSD had a higher frequency of alcoholic cirrhosis etiology and psychotropic drug use. PTSD cirrhosis had higher ICT lure and switching errors (NCT-B response), but on regression, there was no significant impact of PTSD on CHE diagnosis using either the ICT or PHES. CONCLUSIONS: Veterans with cirrhosis and PTSD have a higher frequency of psychotropic drug use and alcoholic cirrhosis etiology. CHE diagnosis using PHES or ICT is not affected by concomitant PTSD.

Mental disorder prevalence among U.S. Department of Veterans Affairs outpatients with spinal cord injuries.

OBJECTIVES: Depression and other mental disorders are more prevalent among individuals living with spinal cord injury (SCI) than in the community at large, and have a strong association with quality of life. Yet little is known about the prevalence and predictors of mental disorders among U.S. military Veterans living with SCI. The primary aim of this study was to present an estimate of mental disorder point prevalence in this population. The secondary aim was to examine the relationship of mental disorders to demographics, injury characteristics, and other clinically relevant features such as impairment from mental health problems and life satisfaction. DESIGN: Cross-sectional. SETTING: A SCI & Disorders Center at a U.S. Veterans Affairs Medical Center. PARTICIPANTS/METHODS: Administrative and medical records of 280 Veterans who attended annual comprehensive SCI evaluations were evaluated. Demographics, injury characteristics, self-reported mental and emotional functioning (i.e. SF-8 Health Survey), and clinician-determined mental disorder diagnoses were attained. RESULTS: Overall, 40% of patients received at least one mental disorder diagnosis, most commonly depressive disorders (19%), posttraumatic stress disorder (12%), and substance or alcohol use disorders (11%). Several patient characteristics predicted mental disorders, including age, racial minority identity, non-traumatic SCI etiology, and incomplete (i.e. AIS D) vs. complete injury. Mental disorders were associated with greater impairment from health and mental health-related problems and less satisfaction with life. CONCLUSIONS: Mental disorders are common among outpatients receiving VA specialty care for SCI. These findings highlight the importance of having adequate and effective available mental health services available for Veterans with SCI.

Mindfulness-Based Stress Reduction Therapy Improves Patient and Caregiver-Reported Outcomes in Cirrhosis.

OBJECTIVES: Patient-reported outcomes such as health-related quality of life (HRQOL) are impaired in cirrhosis due to under-treated mood and sleep disorders, which can adversely impact their caregivers. Mindfulness-based stress reduction (MBSR) can improve patient-reported outcomes (PRO) in non-cirrhotic patients but their impact in cirrhosis is unclear. To evaluate the effect of MBSR and supportive group therapy on mood, sleep and HRQOL in cirrhotic patients and their caregivers. METHODS: Cirrhotic outpatients with mild depression (Beck Depression Inventory (BDI)>14) on screening with an adult caregiver were enrolled. At baseline, BDI, sleep (Pittsburgh sleep quality index PSQI, Epworth Sleepiness Scale, ESS), anxiety (Beck Anxiety inventory) and HRQOL (Sickness Impact Profile, SIP) for both patients/caregivers and caregiver burden (Zarit Burden Interview Short-form, ZBI-SF and perceived caregiver burden, PCB) and patient covert HE(CHE) status were measured. Patients who had BDI>14 at baseline, along with their caregivers then underwent a structured MBSR program with four weekly hour-long group sessions interspersed with home practice using CDs. After the last group, all questionnaires were repeated. RESULTS: 20 patient/caregiver dyads were included. All patients were men (60±8 years MELD 12.9±5.7, 14 prior hepatic encephalopathy (HE)) while most caregivers (n=15) were women (55±12 years, 23±14 years of relationship, 65% spouses). There was no change in patient BDI between screening and baseline (20.1±11.2 vs. 19.0±10.6, P=0.81). All dyads were able to complete the four MBSR+supportive group therapy sessions. There was a significant improvement in BDI (19.0±10.6 vs.15.6±8.2 P=0.01), PSQI (7.2±3.7 vs. 5.5±3.7, P<0.001) and overall HRQOL (25.0±13.2 vs. 17.7±14.0,P=0.01) but not in anxiety or CHE rates in patients. Similarly caregiver burden (ZBI-SF13.0±9.0 vs. 9.8±6.9,P=0.04, Perceived burden 72.1±29.9 vs. 63.0±14.5,P=0.05) and depression reduced (BDI 9.1±7.8 vs. 5.9±6.0,P=0.03) while caregiver sleep quality (7.2±3.7 vs. 5.5±3.7,P<0.001) improved. Prior HE did not affect PRO change after MBSR+supportive groups but the ZBI-SF of caregivers taking care of HE patients improved to a greater extent (delta -1.1±6.5 vs. 7.4±5.3 HE, P=0.04). CONCLUSION: A short program of mindfulness and supportive group therapy significantly improves PRO and caregiver burden in cirrhotic patients with depression. This non-pharmacological method could be a promising approach to alleviate psychosocial stress in patients with end-stage liver disease and their caregivers.

Intraspecific variability in Phaeocystis antarctica's response to iron and light stress.

Phaeocystis antarctica is an abundant phytoplankton species in the Southern Ocean, where growth is frequently limited by iron and light. Being able to grow under low iron conditions is essential to the species' success, but there have been hints that this ability differs among clones. Here, we compare the growth, cell size and chlorophyll a concentrations of four P. antarctica clones cultured under different iron and light conditions. Iron was provided either as unchelated iron (Fe') or bound to the bacterial siderophore desferrioxamine B, representing, respectively, the most and least bioavailable forms of iron which phytoplankton encounter in the marine environment. The growth rate data demonstrate that the clones vary in their ability to grow using organically bound iron, and that this ability is not related to their ability to grow at low inorganic iron concentrations. These results are consistent at low and high light. Physiologically, only three of the four clones shrink or decrease the concentration of chlorophyll a in response to iron limitation, and only one clone decreases colony formation. Together, our data show that P. antarctica clones 1) respond to the same degree of iron limitation using different acclimation strategies, and 2) vary in their ability to grow under the same external iron and light conditions. This physiological diversity is surprisingly large for isolates of a single phytoplankton species.

Iron stable isotopes track pelagic iron cycling during a subtropical phytoplankton bloom.

The supply and bioavailability of dissolved iron sets the magnitude of surface productivity for ∼ 40% of the global ocean. The redox state, organic complexation, and phase (dissolved versus particulate) of iron are key determinants of iron bioavailability in the marine realm, although the mechanisms facilitating exchange between iron species (inorganic and organic) and phases are poorly constrained. Here we use the isotope fingerprint of dissolved and particulate iron to reveal distinct isotopic signatures for biological uptake of iron during a GEOTRACES process study focused on a temperate spring phytoplankton bloom in subtropical waters. At the onset of the bloom, dissolved iron within the mixed layer was isotopically light relative to particulate iron. The isotopically light dissolved iron pool likely results from the reduction of particulate iron via photochemical and (to a lesser extent) biologically mediated reduction processes. As the bloom develops, dissolved iron within the surface mixed layer becomes isotopically heavy, reflecting the dominance of biological processing of iron as it is removed from solution, while scavenging appears to play a minor role. As stable isotopes have shown for major elements like nitrogen, iron isotopes offer a new window into our understanding of the biogeochemical cycling of iron, thereby allowing us to disentangle a suite of concurrent biotic and abiotic transformations of this key biolimiting element.

A solvent extraction technique for the isotopic measurement of dissolved copper in seawater.

Stable copper (Cu) isotope geochemistry provides a new perspective for investigating and understanding Cu speciation and biogeochemical Cu cycling in seawater. In this work, sample preparation for isotopic analysis employed solvent-extraction with amino pyrollidine dithiocarbamate/diethyl dithiocarbamate (APDC/DDC), coupled with a nitric acid back-extraction, to concentrate Cu from seawater. This was followed by Cu-purification using anion-exchange. This straightforward technique is high yielding and fractionation free for Cu and allows precise measurement of the seawater Cu isotopic composition using multi-collector inductively coupled plasma mass-spectrometry. A deep-sea profile measured in the oligotrophic north Tasman Sea shows fractionation in the Cu isotopic signature in the photic zone but is relatively homogenised at depth. A minima in the Cu isotopic profile correlates with the chlorophyll a maximum at the site. These results indicate that a range of processes are likely to fractionate stable Cu isotopes in seawater.

Production of viruses during a spring phytoplankton bloom in the South Pacific Ocean near of New Zealand.

Lagrangian studies of virus activity in pelagic environments over extended temporal scales are rare. To address this, viruses and bacteria were examined during the course of a natural phytoplankton bloom in the pelagic South Pacific Ocean east of New Zealand. Daily samples were collected in a mesoscale eddy from year days 263-278 (September 19th-October 4th, 2008). The productive bloom transitioned from a diatom to a pico- and nanoplankton-dominated system, resulting in chlorophyll a concentrations up to 2.43 µg L(-1) . Virus abundances fluctuated c. 10-fold (1.8 × 10(10) -1.3 × 10(11)  L(-1) ) over 16 days. The production rates of virus particles were high compared with those reported in other marine systems, ranging from 1.4 × 10(10) to 2.1 × 10(11)  L(-1)  day(-1) . Our observations suggest viruses contributed significantly to the mortality of bacteria throughout the bloom, with 19-216% of the bacterial standing stock being lysed daily. This mortality released nutrient elements (N, Fe) that likely helped sustain the bloom through the sampling period. Parametric analyses found significant correlations with both biotic (e.g. potential host abundances) and abiotic parameters (e.g. nutrient concentrations, temperature). These observations demonstrate that viruses may be critical in the extended maintenance of regeneration-driven biological production.

Measurement of methyl mercury (I) and mercury (II) in fish tissues and sediments by HPLC-ICPMS and HPLC-HGAAS.

A procedure for the extraction and determination of methyl mercury and mercury (II) in fish muscle tissues and sediment samples is presented. The procedure involves extraction with 5% (v/v) 2-mercaptoethanol, separation and determination of mercury species by HPLC-ICPMS using a Perkin-Elmer 3 µm C8 (33 mm×3 mm) column and a mobile phase 3 containing 0.5% (v/v) 2-mercaptoethanol and 5% (v/v) CH(3)OH (pH 5.5) at a flow rate 1.5 ml min(-1) and a temperature of 25°C. Calibration curves for methyl mercury (I) and mercury (II) standards were linear in the range of 0-100 µgl(-1) (r(2)=0.9990 and r(2)=0.9995 respectively). The lowest measurable mercury was 0.4 µgl(-1) which corresponds to 0.01 µgg(-1) in fish tissues and sediments. Methyl mercury concentrations measured in biological certified reference materials, NRCC DORM - 2 Dogfish muscle (4.4±0.8 µgg(-1)), NRCC Dolt - 3 Dogfish liver (1.55±0.09 µgg(-1)), NIST RM 50 Albacore Tuna (0.89±0.08 µgg(-1)) and IRMM IMEP-20 Tuna fish (3.6±0.6 µgg(-1)) were in agreement with the certified value (4.47±0.32µgg(-1), 1.59±0.12 µgg(-1), 0.87±0.03 µgg(-1), 4.24±0.27 µgg(-1) respectively). For the sediment reference material ERM CC 580, a methyl mercury concentration of 0.070±0.002 µgg(-1) was measured which corresponds to an extraction efficiency of 92±3% of certified values (0.076±0.04 µgg(-1)) but within the range of published values (0.040-0.084 µgg(-1); mean±s.d.: 0.073±0.05 µgg(-1), n=40) for this material. The extraction procedure for the fish tissues was also compared against an enzymatic extraction using Protease type XIV that has been previously published and similar results were obtained. The use of HPLC-HGAAS with a Phenomenox 5 µm Luna C18 (250 mm×4.6 mm) column and a mobile phase containing 0.06 moll(-1) ammonium acetate (Merck Pty Limited, Australia) in 5% (v/v) methanol and 0.1% (w/v) l-cysteine at 25°C was evaluated as a complementary alternative to HPLC-ICPMS for the measurement of mercury species in fish tissues. The lowest measurable mercury concentration was 2 µgl(-1) and this corresponds to 0.1 µgg(-1) in fish tissues. Analysis of enzymatic extracts analysed by HPLC-HGAAS and HPLC-ICPMS gave equivalent results.

Glacial silicic acid concentrations in the Southern Ocean.

Reconstruction of nutrient concentrations in the deep Southern Ocean has produced conflicting results. The cadmium/calcium (Cd/Ca) data set suggests little change in nutrient concentrations during the last glacial period, whereas the carbon isotope data set suggests that nutrient concentrations were higher. We determined the silicon isotope composition of sponge spicules from the Atlantic and Pacific sectors of the Southern Ocean and found higher silicic acid concentrations in the Pacific sector during the last glacial period. We propose that this increase results from changes in the stoichiometric uptake of silicic acid relative to nitrate and phosphate by diatoms, thus facilitating a redistribution of nutrients across the Pacific and Southern Oceans. Our results are consistent with the global Cd/Ca data set and support the silicic acid leakage hypothesis.