Dust is produced primarily in desert regions and transported long distances through the atmosphere to the oceans. Upon deposition of dust, its dissolution can provide an important source of a range ...of nutrients, particularly iron, to microbes living in open ocean surface waters. The dust supply is greatest nearest to deserts, hence in the Northern Hemisphere. The Southern Ocean region is farthest from these dust sources and shows clear evidence that phytoplankton primary production is limited, at least in part, by the rate of supply of iron. Iron is also essential for nitrogen fixation. In regions of high atmospheric iron supply, such as the tropical North Atlantic, stimulation of nitrogen fixation drives the phytoplankton population toward a state in which phosphorus supply rates limit primary production. Atmospheric deposition is also an important source of nitrogen to the low latitude ocean, where it stimulates primary production. In this review we consider the sources, transport, and deposition of atmospheric dust iron and nitrogen to the oceans and their impacts on plankton systems. In conclusion, we suggest key areas for future research.
Abstract
Nutrient availability limits phytoplankton growth throughout much of the global ocean. Here we synthesize available experimental data to identify three dominant nutrient limitation regimes: ...nitrogen is limiting in the stratified subtropical gyres and in the summertime Arctic Ocean, iron is most commonly limiting in upwelling regions, and both nutrients are frequently co-limiting in regions in between the nitrogen and iron limited systems. Manganese can be co-limiting with iron in parts of the Southern Ocean, whilst phosphate and cobalt can be co-/serially limiting in some settings. Overall, an analysis of experimental responses showed that phytoplankton net growth can be significantly enhanced through increasing the number of different nutrients supplied, regardless of latitude, temperature, or trophic status, implying surface seawaters are often approaching nutrient co-limitation. Assessments of nutrient deficiency based on seawater nutrient concentrations and nutrient stress diagnosed via molecular biomarkers showed good agreement with experimentally-assessed nutrient limitation, validating conceptual and theoretical links between nutrient stoichiometry and microbial ecophysiology.
The long-term efficacy and safety of mepolizumab for treatment of severe eosinophilic asthma are well established. Here, we examine the clinical impact of stopping mepolizumab after long-term use.
...COMET (NCT02555371) was a randomised, double-blind, placebo-controlled, parallel-group, multicentre study. Patients who had completed COLUMBA (NCT01691859) or COSMEX (NCT02135692) and received continuous mepolizumab treatment for ≥3 years were randomised 1:1 to stop (switch to placebo) or continue subcutaneous mepolizumab 100 mg every 4 weeks for 52 weeks. Primary end-point: time to first clinically significant exacerbation; secondary end-points: time to first exacerbation requiring hospitalisation/emergency department visit, time to decrease in asthma control (≥0.5-point increase in Asthma Control Questionnaire-5 score from COMET baseline) and blood eosinophil count ratio to COMET baseline. Safety was assessed.
Patients stopping (n=151)
continuing (n=144) mepolizumab had significantly shorter times to first clinically significant exacerbation (hazard ratio 1.61, 95% CI 1.17-2.22; p=0.004) and decrease in asthma control (hazard ratio 1.52, 95% CI 1.13-2.02; p=0.005), and higher blood eosinophil counts at week 52 (270
40 cells·µL
; ratio (stopping
continuing) 6.19, 95% CI 4.89-7.83; p<0.001). Differences in efficacy outcomes between groups were observed when assessed from week 12 (16 weeks after last mepolizumab dose). Exacerbations requiring hospitalisation/emergency department visit were rare. Adverse events in patients continuing mepolizumab were consistent with previous studies. For patients who stopped mepolizumab, the safety profile was consistent with other eosinophilic asthma populations.
Patients who stopped mepolizumab had an increase in exacerbations and reduced asthma control
those who continued.
Diagnosing oceanic nutrient deficiency Moore, C. Mark
Philosophical transactions of the Royal Society of London. Series A: Mathematical, physical, and engineering sciences,
11/2016, Letnik:
374, Številka:
2081
Journal Article
Recenzirano
Odprti dostop
The supply of a range of nutrient elements to surface waters is an important driver of oceanic production and the subsequent linked cycling of the nutrients and carbon. Relative deficiencies of ...different nutrients with respect to biological requirements, within both surface and internal water masses, can be both a key indicator and driver of the potential for these nutrients to become limiting for the production of new organic material in the upper ocean. The availability of high-quality, full-depth and global-scale datasets on the concentrations of a wide range of both macro- and micro-nutrients produced through the international GEOTRACES programme provides the potential for estimation of multi-element deficiencies at unprecedented scales. Resultant coherent large-scale patterns in diagnosed deficiency can be linked to the interacting physical-chemical-biological processes which drive upper ocean nutrient biogeochemistry. Calculations of ranked deficiencies across multiple elements further highlight important remaining uncertainties in the stoichiometric plasticity of nutrient ratios within oceanic microbial systems and caveats with regards to linkages to upper ocean nutrient limitation.
This article is part of the themed issue ‘Biological and climatic impacts of ocean trace element chemistry’.
Nutrient limitation of oceanic primary production exerts a fundamental control on marine food webs and the flux of carbon into the deep ocean. The extensive boundaries of the oligotrophic ...sub-tropical gyres collectively define the most extreme transition in ocean productivity, but little is known about nutrient limitation in these zones. Here we present the results of full-factorial nutrient amendment experiments conducted at the eastern boundary of the South Atlantic gyre. We find extensive regions in which the addition of nitrogen or iron individually resulted in no significant phytoplankton growth over 48 hours. However, the addition of both nitrogen and iron increased concentrations of chlorophyll a by up to approximately 40-fold, led to diatom proliferation, and reduced community diversity. Once nitrogen-iron co-limitation had been alleviated, the addition of cobalt or cobalt-containing vitamin B
could further enhance chlorophyll a yields by up to threefold. Our results suggest that nitrogen-iron co-limitation is pervasive in the ocean, with other micronutrients also approaching co-deficiency. Such multi-nutrient limitations potentially increase phytoplankton community diversity.
Inorganic nitrogen depletion restricts productivity in much of the low-latitude oceans, generating a selective advantage for diazotrophic organisms capable of fixing atmospheric dinitrogen (N2). ...However, the abundance and activity of diazotrophs can in turn be controlled by the availability of other potentially limiting nutrients, including phosphorus (P) and iron (Fe). Here we present high-resolution data (∼0.3°) for dissolved iron, aluminum, and inorganic phosphorus that confirm the existence of a sharp north—south biogeochemical boundary in the surface nutrient concentrations of the (sub)tropical Atlantic Ocean. Combining satellite-based precipitation data with results from a previous study, we here demonstrate that wet deposition in the region of the intertropical convergence zone acts as the major dissolved iron source to surface waters. Moreover, corresponding observations of N2 fixation and the distribution of diazotrophic Trichodesmium spp. indicate that movement in the region of elevated dissolved iron as a result of the seasonal migration of the intertropical convergence zone drives a shift in the latitudinal distribution of diazotrophy and corresponding dissolved inorganic phosphorus depletion. These conclusions are consistent with the results of an idealized numerical model of the system. The boundary between the distinct biogeochemical systems of the (sub)tropical Atlantic thus appears to be defined by the diazotrophic response to spatial—temporal variability in external Fe inputs. Consequently, in addition to demonstrating a unique seasonal cycle forced by atmospheric nutrient inputs, we suggest that the underlying biogeochemical mechanisms would likely characterize the response of oligotrophic systems to altered environmental forcing over longer timescales.
Despite advances in care of critically ill neonates, extended mechanical ventilation and tracheostomy are sometimes required. Few studies focus on complications and clinical outcomes. Our aim was to ...provide long-term outcomes for a cohort of infants who required tracheostomy.
This study is a retrospective review of 165 infants born between January 1, 2000 and December 31, 2010 who required tracheostomy and ventilator support. Children with complex congenital heart disease were excluded.
Median gestational age was 27 weeks (range 22-43), and birth weight was 820 g (range 360-4860). The number of male (53.9%) and female (46.1%) infants was similar (P = .312). Infants were divided into 2 groups based on birth weight ≤1000 g (A) and >1000 g (B). Group A: 87 (57.6%) infants; group B 64 (42.4%). Overall tracheostomy rate was 6.9% (87/1345) for group A versus 0.9% (64/6818) for B (P <.001). Group A had a longer time from intubation to positive pressure ventilation independence, 505 days (range 62-1287) vs 372 days (range 15-1270; P = .011). Infants who had >1 reason for tracheostomy comprised 78.8% of the sample; 69.1% of infants were discharged on ventilators. Birth weight did not affect time from tracheostomy to decannulation (P = .323). More group A infants were decannulated (P = .023). laryngotracheal reconstruction rate was 35.8%. Five-year survival was 89%. Group B had higher mortality (P = .033). 64.2% of infants had developmental delays; 74.2% had ≥2 comorbidities.
Tracheostomy rates were higher for extremely low birth weight infants than previously reported rates for all infants. Decannulation rates and laryngotracheal reconstruction rates were consistent with previous studies. Survival rates were high, but developmental delay and comorbidities were frequent.
Marine phytoplankton account for about 50% of all global net primary productivity (NPP). Active fluorometry, mainly Fast Repetition Rate fluorometry (FRRf), has been advocated as means of providing ...high resolution estimates of NPP. However, not measuring CO2-fixation directly, FRRf instead provides photosynthetic quantum efficiency estimates from which electron transfer rates (ETR) and ultimately CO2-fixation rates can be derived. Consequently, conversions of ETRs to CO2-fixation requires knowledge of the electron requirement for carbon fixation (Φe,C, ETR/CO2 uptake rate) and its dependence on environmental gradients. Such knowledge is critical for large scale implementation of active fluorescence to better characterise CO2-uptake. Here we examine the variability of experimentally determined Φe,C values in relation to key environmental variables with the aim of developing new working algorithms for the calculation of Φe,C from environmental variables. Coincident FRRf and (14)C-uptake and environmental data from 14 studies covering 12 marine regions were analysed via a meta-analytical, non-parametric, multivariate approach. Combining all studies, Φe,C varied between 1.15 and 54.2 mol e(-) (mol C)(-1) with a mean of 10.9 ± 6.91 mol e(-) mol C)(-1). Although variability of Φe,C was related to environmental gradients at global scales, region-specific analyses provided far improved predictive capability. However, use of regional Φ e,C algorithms requires objective means of defining regions of interest, which remains challenging. Considering individual studies and specific small-scale regions, temperature, nutrient and light availability were correlated with Φ e,C albeit to varying degrees and depending on the study/region and the composition of the extant phytoplankton community. At the level of large biogeographic regions and distinct water masses, Φ e,C was related to nutrient availability, chlorophyll, as well as temperature and/or salinity in most regions, while light availability was also important in Baltic Sea and shelf waters. The novel Φ e,C algorithms provide a major step forward for widespread fluorometry-based NPP estimates and highlight the need for further studying the natural variability of Φe,C to verify and develop algorithms with improved accuracy.
Most of the Southern Ocean is a high‐nutrient, low‐chlorophyll (HNLC) area. There are exceptions to this situation downstream of some of the islands, where iron from the islands or surrounding ...shallow plateau fertilizes the mixed layer and causes a phytoplankton bloom in spring and summer. The main locations where this occurs are downstream of the South Georgia, Crozet, and Kerguelen islands. Data on mixed layer depths from Argo float profiles together with Sea‐viewing Wide Field‐of‐view Sensor chlorophyll a (chl a) and photosynthetically available radiation from these high‐nutrient, high‐chlorophyll (HNHC) areas are combined to study the effects of mixed layer‐averaged light availability on phytoplankton concentrations in areas where iron limitation has been lifted. The results of this analysis are then transferred to HNLC areas to assess the potential importance of light limitation through the year. We conclude that light limitation does not significantly constrain the annual integrated standing stock of chl a in the HNLC Southern Ocean.
PDF
