Abstract
As both photoautotrophs and calcifiers, coccolithophores play important roles in ecosystems and biogeochemical cycles. Though some species form blooms in high-latitude waters, low-latitude ...communities exhibit high diversity and niche diversification. Despite such diversity, our understanding of the clade relies on knowledge of Emiliana huxleyi. To address this, we examine carbon (C) and nitrogen (N) content of strains (n = 9) from the main families of the calcifying Haptophyceae, as well as allometry and cell size frequency across extant species. Coccolithophore cell size is constrained, with ~71% of 159 species smaller than 10 μm in diameter. Growth rates scale with cell biovolume (μ = 1.83 × cell volume−0.19), with an exponent close to metabolic theory. Organic carbon (C) per cell is lower than for other phytoplankton, providing a coccolithophore-specific relationship between cell organic C content and biovolume (pg C cell−1 = 0.30 × cell volume0.70). Organic C to N ratios (~8.3 mol:mol) are similar to other phytoplankton, implying little additional N cost for calcification and efficient retention and recycling of cell N. Our results support observations that coccolithophores are efficient competitors in low-nutrient conditions, able to photosynthesize, calcify and run the routine metabolic machinery necessary without any additional need for N relative to noncalcifying algae.
•Seasonality and cross shelf distribution of DOM and its optical properties were examined in the Celtic Sea.•Strong cross shelf gradients in humic DOM components with significant negative ...correlations with salinity and DOC.•Variability in labile DOM protein components linked to biological productivity.
The Celtic Sea is a productive temperate sea located on the Northwest European Shelf. It is an important pathway for the delivery of land-derived material to the North Atlantic Ocean, including dissolved organic matter (DOM). The aim of this study was to determine the seasonal and spatial variability in the magnitude, source and composition of DOM at three sites representing on shelf, central shelf and shelf edge regions in the Celtic Sea, using observations collected during the UK Shelf Sea Biogeochemistry (SSB) research programme (November 2014 – August 2015). The concentration of dissolved organic carbon (DOC) alongside DOM absorbance and fluorescence indices were measured and fluorescence Excitation and Emission Matrices (EEMs) combined with Parallel Factor Analysis (PARAFAC) were used to assess DOM composition and lability. The PARAFAC model identified four unique fluorescent components for autumn (November 2014), winter (March 2015), spring (April 2015) and summer (July 2015) consisting of two humic-like components attributed to terrestrial (C1) and marine sources (C2), and two protein components identified as tyrosine-like (C3) and tryptophan-like (C4) attributed to in situ production. DOC varied seasonally and there were strong cross shelf trends. The protein components (C3 and C4) exhibited large seasonal and within season variability particularly during productive periods. In contrast, there were persistent cross shelf gradients in the CDOM absorption coefficient at 305 nm (a305), the UV specific absorbance at 280 nm (SUVA280), the humification index (HIX), and the humic-like fluorescent components (C1 and C2), which were higher in the on shelf region and decreased towards the shelf edge. The humic-like components and the slope ratio (SR) were significantly correlated with salinity throughout all seasons, indicating a strong influence of terrestrially-derived organic matter in the Celtic Sea, with potentially up to 35% of DOC in the central shelf during winter originating from terrestrial inputs. Results from this study illustrate the importance of monitoring DOM quantitatively and qualitatively for a better understanding of the supply, production, cycling and export of this dynamic organic carbon pool in shelf seas.
Global mass balance calculations indicate the majority of particulate organic carbon (POC) exported from shelf seas is transferred via downslope exchange processes. Here we demonstrate the downslope ...flux of POC from the Hebrides Shelf is approximately 3‐ to 5‐fold larger per unit length/area than the global mean. To reach this conclusion, we quantified the offshore transport of particulate and dissolved carbon fractions via the “Ekman Drain,” a strong downwelling feature of the NW European Shelf circulation, and subsequently compared these fluxes to simultaneous regional air‐sea CO2 fluxes and onshore wind‐driven Ekman fluxes to constrain the carbon dynamics of this shelf. Along the shelf break, we estimate a mean offshelf total carbon (dissolved + particulate) flux of 4.2 tonnes C m−1 d−1 compared to an onshelf flux of 4.5 tonnes C m−1 d−1. Organic carbon represented 3.3% of the onshelf carbon flux but 6.4% of the offshelf flux indicating net organic carbon export. Dissolved organic carbon represented 95% and POC 5% of the exported organic carbon pool. When scaled along the shelf break the total offshelf POC flux (0.007 Tg C d−1) was found to be 3 times larger than the regional air‐sea CO2 ingassing flux (0.0021 Tg C d−1), an order of magnitude larger than the particulate inorganic carbon flux (0.0003 Tg C d−1) but far smaller than the DIC (2.03 Tg C d−1) or DOC (0.13 Tg C d−1) fluxes. Significant spatial heterogeneity in the Ekman drain transport confirms that offshelf carbon fluxes via this mechanism are also spatially heterogeneous.
Key Points
Cross‐shelf transports and carbon fluxes are reported for the Hebrides Shelf
The mean Ekman drain downslope transport was 1.81 m2 s−1, but important 4‐fold spatial variability was identified
The Hebrides Shelf may export 5 times more POC per unit area via the Ekman drain than the global mean
The NOMAD Collaboration presents a study of opposite sign dimuon events in the framework of Leading Order QCD. A total of 2714 neutrino- and 115 antineutrino-induced opposite sign dimuon events with
...E
μ1
,
E
μ2
>4.5 GeV, 15<
E
ν
<300 GeV and
Q
2>1
(
GeV/
c)
2
are observed in the Front-Calorimeter of NOMAD during the 1995 and 1996 runs. The analysis yields a value for the charm quark mass of
m
c=1.3
+0.3+0.3
−0.3−0.3
GeV/
c
2
and for the average semileptonic branching ratio of
B
c
=0.095
+0.007+0.014
−0.007−0.013. The ratio of the strange to non-strange sea in the nucleon is measured to be
κ=0.48
+0.09+0.17
−0.07−0.12. The measured rate of charm-induced dimuon relative to single muon, as a function of neutrino energy, is consistent with the slow rescaling hypothesis of heavy quark production.
This paper reports on the charged
K/
π production ratios and on the shape of the
p
T
distributions of
π fluxes measured by the SPY/NA56 experiment for 450 GeV/c proton interactions on beryllium ...targets. The present data cover a secondary momentum range from 7 GeV/c to 135 GeV/c in the forward direction and with
p
T
values up to 600 MeV/c. An experimental accuracy of about 3% has been achieved. These results will reduce the uncertainty on the estimation of the
ν
e
component of neutrino beams.
This paper reports on the charged pion production yields measured by the SPY/NA56 experiment for 450 GeV/c proton interactions on beryllium targets. The present data cover a secondary momentum range ...from 7 GeV/c to 135 GeV/c in the forward direction. An experimental accuracy ranging from 5 to 10%, depending on the beam momentum, has been achieved, limited mainly by the knowledge of the beam acceptance. These results will be relevant in the calculation of neutrino fluxes in present and future neutrino beams.
We carried out a model-independent search for light scalar or pseudoscalar particles
a's (an example of which is the axion) that couple to two photons by using a photon-regeneration method at high ...energies allowing a substantial increase in the sensitivity to eV masses. The experimental set-up is based on elements of the CERN West Area Neutrino Facility (WANF) beam line and the NOMAD neutrino detector. The new particles, if they exist, could be produced through the Primakoff effect in interactions of high energy photons, generated by the 450 GeV protons in the CERN SPS neutrino target, with virtual photons from the WANF horn magnetic field. The particles would penetrate the downstream shielding and would be observed in the NOMAD neutrino detector through their re-conversion into real high energy photons by interacting with the virtual photons from the magnetic field of the NOMAD dipole magnet.
From the analysis of the data collected during the 1996 run with 1.08×10
19 protons on target, 312 candidate events with energy between 5 and 140 GeV were found. This number is in general agreement with the expectation of 272±18 background events from standard neutrino processes. A 90
%
CL
upper limit on the
aγγ-coupling
g
aγγ
< 1.5
×10
−4
GeV
−1
for
a masses up to 40 eV is obtained.
To evaluate extracellular hydrolytic enzymes in an in vivo system, plastic chambers were glued over rabbit dermal BCG lesions in various stages of development, after the central epithelium was ...removed with a scalpel. They were filled with tissue culture medium and left in place 2 days. The following enzymes in the fluid were assayed: collagenase (an enzyme secreted but not stored in macrophages); lysozyme (both secreted and stored); DNase and RNase (released on cell death and possibly regurgitated but not secreted); and, as a control, lactic dehydrogenase (released only on cell death). Tissue sections were prepared and studied histologically for the type of cell infiltrate, for beta-galactosidase (our marker enzyme for macrophage activation), and for necrosis. At 11 and 18 days of age the BCG lesions were largest and the number of activated macrophages in the chamber beds was highest. At this time the levels of the five enzymes assayed in the chamber fluids reached their peaks, tuberculin hypersensitivity was well developed, and the bacilli components would still be plentiful. In general, the chamber fluids from 11- and 18-day BCG lesions contained higher enzyme levels than chamber fluids from tuberculin reactions. Active collagenase was only detected in fluids from such BCG lesions. Evidently, the serum in the chamber fluids was sufficient to inhibit the lower amounts of collagenase probably released from smaller BCG lesions and tuberculin reactions (and from the 2-week polystyrene lesions that were also evaluated). These studies demonstrate that in chronic inflammatory reactions, both acid-acting and neutral-acting hydrolytic enzymes are released extracellularly. Tissue components would be hydrolyzed locally wherever the acid-acting hydrolytic enzymes encounter a drop in pH and wherever the concentration of neutral-acting hydrolytic enzymes exceeds the concentration of their inhibitors.
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