Grey Matter Perfusion in Clinically Isolated Syndrome and Relapsing-Remitting Multiple Sclerosis

Die vorliegende Studie vergleicht Merkmale der mittels Kernspin-Tomografie bestimmten zerebralen Perfusion in verschiedenen Regionen der Grauen Substanz von Patienten mit klinisch isoliertem Syndrom und Patienten mit schubförmig-remittierender Multipler Sklerose. Als Marker der klinischen Schwere der Erkrankung wurden das normalisierte Hirnvolumen und der erreichte Wert auf der Expanded Disability Status Scale verwendet. In einem simplen Gruppenvergleich findet sich ein keiner der betrachteten Regionen ein Unterschied im Hinblick auf die lokale Perfusion. Die Ergebnisse einer simultanen Korrelationsanalyse suggerieren jedoch, dass es durchaus Unterschiede in der lokalen Perfusion der Grauen Substanz gibt. Die Ergebnisse dieser Studie legen daher nahe, dass einfache Gruppenvergleiche nur schlecht geeignet sind, um Variationen der regionalen Perfusion zu erfassen. Zusammengefassend legt die vorliegende Studie nahe, dass der den hämodynamischen Veränderungen bei Patienten mit klinisch isoliertem Syndrom und schubförmig-remittierender Multipler Sklerose zu Grunde liegende Mechanismus eher diffus als fokal ist und darüber hinaus einer gewissen (zeitlichen) Entwicklung unterliegt.This study compares magnetic resonance imaging-derived cerebral grey matter perfusion characteristics in patients diagnosed with clinically isolated syndrome and patients diagnosed with relapsing-remitting multiple sclerosis. Normalized brain volume and the Expanded Disability Status Scale were used as markers of disease severity. There is no difference between both subject subgroups with respect to perfusion parameters in any of the analysed grey matter regions in a simple group comparison. However, the results from the simultaneous correlation analysis indicate that there is a difference in local perfusion between the two groups of patients. This study therefore suggests that simply group comparisons are not a suitable tool to analyse regional perfusion metrics. In summary, the results of this study suggest that the underlying mechanism responsible for hemodynamic changes in clinically isolated syndrome and relapsing-remitting multiple sclerosis is diffuse rather than focal and is subject to some sort of (temporal) evolution. 2017-10-1

Production and emissions of oceanic nitrous oxide

This study calculates N2O production rates (N2OPR) based on concentration measurements and Transit Time Distribution (TTD) calculations. New parameterisations of N2OPR based on an apparent oxygen consumption rate (AOUR and temperature or depth, respectively, are developed and applied to calculate N2O production the entire ocean. A global annual subsurface N2O production of ~3±1 Tg N and a global annual organic carbon remineralisation rate of 17.6 Pg are estimated. The N2O flux to the mixed layer (F_grad) and the N2O emissions to the atmosphere via gas exchange (F_gasex) are calculated or the central North Atlantic. The mean F_grad is found to be significantly smaller than the mean F_gasex. A possible reason for this is the seasonality of surface pN2O/F_gasex, as a seasonally-resolved, integrated estimate of F_gasex significantly reduces the difference between the two flux estimates. There is no conclusive evidence for a biological N2O source in the mixed layer

Produktion und Emissionen von ozeanischem Distickstoffmonoxid

This study calculates N2O production rates (N2OPR) based on concentration measurements and Transit Time Distribution (TTD) calculations. New parameterisations of N2OPR based on an apparent oxygen consumption rate (AOUR and temperature or depth, respectively, are developed and applied to calculate N2O production the entire ocean. A global annual subsurface N2O production of ~3±1 Tg N and a global annual organic carbon remineralisation rate of 17.6 Pg are estimated. The N2O flux to the mixed layer (F_grad) and the N2O emissions to the atmosphere via gas exchange (F_gasex) are calculated or the central North Atlantic. The mean F_grad is found to be significantly smaller than the mean F_gasex. A possible reason for this is the seasonality of surface pN2O/F_gasex, as a seasonally-resolved, integrated estimate of F_gasex significantly reduces the difference between the two flux estimates. There is no conclusive evidence for a biological N2O source in the mixed layer.In dieser Studie werden, basierend auf Konzentrationsmessungen und Transit Time Distributions (TTD) N2O Produktionsraten (N2OPR) berechnet. Neue Parameterisierungen für N2OPR abhängig von einer Sauerstoffverbrauchsrate (AOUR) und der Temperatur bzw. der Tiefe werden entwickelt und zur Berechnung der N2O-Produktion im Weltozean verwendet. Dabei wird die globale jährliche N2O-Produktion auf ~3±1 Tg N und die jährliche Remineralisationsrate von organischem Kohlenstoff auf 17.6 Pg geschätzt. Der N2O-Fluss in die Mischungsschicht (F_grad) und der N2O-Fluss in die Atmosphäre (F_gasex) werden für den zentralen Nord-Atlantik berechnet. Der mittlere F_grad ist signifikant kleiner als der mittlere F_gasex. Ein möglicher Grund ist der zyklische Jahresgang von pN2O/F_gasex, da eine integrierte Schätzung die Differenz zwischen den verschiedenen Flüssen deutlich reduziert. Es gibt keine zwingenden Hinweise auf biologische N2O-Produktion in der Mischungsschicht

North Atlantic production of nitrous oxide in the context of changing atmospheric levels

We use transit time distributions calculated from tracer data together with in situ measurements of N(2)O to estimate the concentration of biologically produced N(2)O ([N(2)O](xs)) and N(2)O production rates in the central North Atlantic Ocean. Our approach to estimation of N(2)O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass. We find that previously used approaches overestimate the oceanic equilibrium N(2)O concentrations by 8-13% and thus underestimate the strength of N(2)O sources in large parts of the water column. Thus the quantitative characteristics of the [N(2)O](xs)/AOU relationship used as an indicator of nitrification are distorted. We developed a new parameterization of N(2)O production during nitrification depending linearly on AOU and exponentially on temperature and depth, which can be applied to calculate N(2)O production due to nitrification in the entire ocean including oxygen minimum zones

Estimating changes in ocean ventilation from early 1990s CFC-12 and late 2000s SF6 measurements

Transient tracer measurements can constrain the rates and pathways of ocean ventilation and act as proxies for biogeochemically relevant gases such as CO2 and oxygen. Various techniques have deduced changes in ocean ventilation over decadal timescales using transient tracer measurements made on repeat sections, but these require a priori assumptions about mixing in the ocean interior. Here, we introduce a simple, direct observational method that takes advantage of the similar atmospheric increase rates of chlorofluorocarbon-12 and sulfur hexafluoride, but with a time lag (offset) of 1415 years. Such repeat measurements can be directly compared without prior assumptions about mixing. A difference larger than similar to 2 years between modern sulfur hexafluoride and historical chlorofluorocarbon-12 tracer ages implies a change in ventilation, although lack of difference does not necessarily imply no change. Several tracer data sets are presented, which suggest changes in ventilation in the South Pacific and North Atlantic Oceans

Ventilation versus biology:What is the controlling mechanism of nitrous oxide distribution in the North Atlantic?

The extent to which water mass mixing and ocean ventilation contribute to nitrous oxide (N2O) distribution at the scale of oceanic basins is poorly constrained. We used novel N2O and chlorofluorocarbon measurements along with multiparameter water mass analysis to evaluate the impact of water mass mixing and Atlantic Meridional Overturning Circulation (AMOC) on N2O distribution along the Observatoire de la variabilité interannuelle et décennale en Atlantique Nord (OVIDE) section, extending from Portugal to Greenland. The biological N2O production has a stronger impact on the observed N2O concentrations in the water masses traveling northward in the upper limb of the AMOC than those in recently ventilated cold water masses in the lower limb, where N2O concentrations reflect the colder temperatures. The high N2O tongue, with concentrations as high as 16 nmol kg−1, propagates above the isopycnal surface delimiting the upper and lower AMOC limbs, which extends from the eastern North Atlantic Basin to the Iceland Basin and coincides with the maximum N2O production rates. Water mixing and basin-scale remineralization account for 72% of variation in the observed distribution of N2O. The mixing-corrected stoichiometric ratio N2O:O2 for the North Atlantic Basin of 0.06 nmol/μmol is in agreement with ratios of N2O:O2 for local N2O anomalies, suggesting than up to 28% of N2O production occurs in the temperate and subpolar Atlantic, an overlooked region for N2O cycling. Overall, our results highlight the importance of taking into account mixing, O2 undersaturation when water masses are formed and the increasing atmospheric N2O concentrations when parameterizing N2O:O2 and biological N2O production in the global oceans

Global oceanic production of nitrous oxide

We use transient time distributions calculated from tracer data together with in situ measurements of nitrous oxide (N2O) to estimate the concentration of biologically produced N2O and N2O production rates in the ocean on a global scale. Our approach to estimate the N2O production rates integrates the effects of potentially varying production and decomposition mechanisms along the transport path of a water mass.We estimate that the oceanic N2O production is dominated by nitrification with a contribution of only approximately 7 per cent by denitrification. This indicates that previously used approaches have overestimated the contribution by denitrification. Shelf areas may account for only a negligible fraction of the global production; however, estuarine sources and coastal upwelling of N2O are not taken into account in our study. The largest amount of subsurface N2O is produced in the upper 500 m of the water column. The estimated global annual subsurface N2O production ranges from 3.1+/-0.9 to 3.4+/-0.9 Tg N yr^-1. This is in agreement with estimates of the global N2O emissions to the atmosphere and indicates that a N2O source in the mixed layer is unlikely. The potential future development of the oceanic N2O source in view of the ongoing changes of the ocean environment (deoxygenation, warming, eutrophication and acidification) is discussed

Nitrous oxide production by nitrification and denitrification in the Eastern Tropical South Pacific oxygen minimum zone

The Eastern Tropical South Pacific oxygen minimum zone (ETSP-OMZ) is a site of intense nitrous oxide (N2O) flux to the atmosphere. This flux results from production of N2O by nitrification and denitrification, but the contribution of the two processes is unknown. The rates of these pathways and their distributions were measured directly using 15N tracers. The highest N2O production rates occurred at the depth of peak N2O concentrations at the oxic-anoxic interface above the oxygen deficient zone (ODZ) because slightly oxygenated waters allowed (1) N2O production from both nitrification and denitrification and (2) higher nitrous oxide production yields from nitrification. Within the ODZ proper (i.e., anoxia), the only source of N2O was denitrification (i.e., nitrite and nitrate reduction), the rates of which were reflected in the abundance of nirS genes (encoding nitrite reductase). Overall, denitrification was the dominant pathway contributing the N2O production in the ETSP-OMZ

Nitrous oxide as a function of oxygen and archaeal gene abundance in the North Pacific

Natural Environment Research Council (NERC) (NE/E01559X/1)