7,281 research outputs found
Microbial nutrient niches in the gut
No full textThe composition and function of the mammalian gut microbiota has been the subject of much research in recent years, but the principles underlying the assembly and structure of this complex community remain incompletely understood. Processes that shape the gut microbiota are thought to be mostly niche-driven, with environmental factors such as the composition of available nutrients largely determining whether or not an organism can establish. The concept that the nutrient landscape dictates which organisms can successfully colonize and persist in the gut was first proposed in Rolf Freter's nutrient niche theory. In a situation where nutrients are perfectly mixed and there is balanced microbial growth, Freter postulated that an organism can only survive if it is able to utilize one or a few limiting nutrients more efficiently than its competitors. Recent experimental work indicates, however, that nutrients in the gut vary in space and time. We propose that in such a scenario, Freter's nutrient niche theory must be expanded to account for the co-existence of microorganisms utilizing the same nutrients but in distinct sites or at different times, and that metabolic flexibility and mixed-substrate utilization are common strategies for survival in the face of ever-present nutrient fluctuations.</p
Surface forcing of the North Atlantic: accuracy and variability
No full textA new methodology to estimate the turbulent air – sea heat and moisture fluxes andtheir uncertainty is developed and assessed using Voluntary Observing Ship (VOS)observations. Whilst important drivers of the global oceanic and atmospheric circulationthese fluxes remain poorly quantified, both in terms of mean value and uncertainty. Thenew methodology addresses both of these issues and is extensible to other data sources.The individual observations are first bias and height adjusted to remove systematicerrors and the impact of changing observing heights. They are then characterised interms of random errors using a semi-variogram analysis and a range of variogrammodels. The data quality and sampling are then taken into account using optimalinterpolation (OI) to grid the observations, producing daily mean fields and uncertaintyestimates. These are then used to estimate the fluxes and flux uncertainty on both dailyand monthly time scales.Comparisons of the mean fields and fluxes to the original input data and toindependent buoy observations show the fields not to be significantly biased. Theadjustments applied before gridding and flux calculation are also shown to improve theagreement with the buoy observations. The uncertainty estimates are assessed using aseries of cross validation experiments and 3-way error analyses to make alternativeestimates of the uncertainty. These alternative estimates are shown to be of the sameorder of magnitude as the OI uncertainty estimates and generally to be within 10 – 20%of the OI estimate. Whilst all three estimates are similar there are some systematicdifferences. The OI uncertainty estimates tend to be lower (higher) than the alternativeestimates in high (low) variability regions.The representation of the variability in the new dataset is examined and shown to beimproved compared to previous VOS based datasets. The adjustments are shown tohave little impact on the temporal trends in temperature and humidity whilst reducingthe wind speed and sensible and latent heat flux trends. These reduced trends arethought to be more realistic. The wind speed trend after adjustment is more similar tothe trends reported in previous studies using reanalysis model output. However, thereare still some differences in the trends, with the VOS based estimates larger, leading touncertainty in trend estimates. The trends in the adjusted latent and sensible heat fluxestimates are similar to those seen in other flux datasets but when compared to changesin the upper ocean heat content may still be too large. This may be due to theoverestimate of the wind speed trend. Overall the uncertainty in the wind speed trendgives the largest uncertainty in the flux trends.Finally, the advances made in developing the new methodology are summarised andthe potential uses of the new dataset identified. Future work and improvements are thensuggested
Assessing the health of the global surface marine observing system
No full textThe in situ surface marine climate observing system includes contributions from several different types of observing platforms. Most observations come from mobile platforms, e.g. ships or surface drifting buoys. Climate applications using marine observations often require fields of environmental parameters to be constructed on regular spatiotemporal grids. User requirements are therefore typically presented in terms of parameter uncertainty at particular space and timescales. It is therefore important to relate the characteristics of marine observations, in terms of their expected quality and sampling distribution, to these requirements. A simple method to estimate the instrumental uncertainty in fields derived from a mixture of observation types is presented. This method enables preliminary assessment of the extent to which the available observations meet the stated user requirements.Example observing system adequacy assessments are presented for two climate variables, sea surface temperature (SST) and marine air temperature (MAT) using in situ data. The method is also applicable to gridded data sets constructed from combined in situ and satellite data. While the global metrics for SST show an improvement in observing system adequacy over time, the adequacy for MAT is declining. The assessments can determine the most efficient approach to improving observing system adequacy. For in situ SST the best approach would be to increase the number of different platforms making observations. For MAT, increasing the number of observations overall, regardless of platform and increasing the geographical coverage is required to reduce the uncertainty.The assessments would be improved by more extensive evaluation of uncertainties associated with each different variable for each platform type. It would also be beneficial to review the completeness of the user requirements: e.g. to include user requirements relating to the stability of averages on large space and timescales required for climate monitoring, or for constructing estimates of air–sea exchange
A new air-sea interaction gridded dataset from ICOADS with uncertainty estimates.
No full textThe exchange, or flux, of heat between the oceans and atmosphere is an important driver of the global oceanic and atmospheric circulations but remains poorly quantified. Direct measurement of heat flux remains a research activity and so global heat flux datasets are generated using observations of winds, air and sea temperatures and humidity as input to heat flux parameterisations known as "bulk formulae". We remain dependent on the observations from merchant ships in the Voluntary Observing Ships (VOS) program which are archived in the International Comprehensive Ocean-Atmosphere Dataset (ICOADS): measurements from buoys are sparse and satellites cannot accurately recover all the variables required for heat flux calculation. Careful analysis of VOS data is necessary to produce gridded datasets of meteorological variables and fluxes with the accuracy required for climate research. Past in situ flux datasets have averaged observations on monthly timescales in order to reduce random uncertainty. It has therefore been hard to understand the contributions to observed variability from measurement errors, poor sampling or natural variability. The new dataset, which covers the period 1973 to 2006, avoids this problem by first constructing daily mean fields using optimal interpolation. This allows each component of variability to be handled correctly and, for the first time, uncertainty estimates to be produced. New bias adjustments have also been developed and applied. The new dataset is described and a preliminary comparison with flux estimates from moored buoys, satellites and atmospheric reanalysis models is presented.<br/
Air–Sea fluxes from ICOADS: the construction of a new gridded dataset with uncertainty estimates
No full textThe methods used to calculate a new in situ global dataset of air–sea exchanges, called the NOCS Flux Dataset v2.0, are described. The fluxes have been derived from in situ weather reports from Voluntary Observing Ships (VOS) covering the period 1973–2006. The reports have been adjusted for known biases and residual uncertainties estimated. The dataset is constructed using Optimal Interpolation (OI) using new estimates of random uncertainty in the observations. Daily fields have been calculated on a 1° latitude by 1° longitude grid, each grid box and time step have an associated uncertainty estimate. Monthly fields have been calculated from simple averages of the daily fields and monthly uncertainty estimates from the daily uncertainties, using estimates of the autocorrelation between the daily uncertainty estimates. The uncertainties due to the choice of flux parameterisation have not been accounted for. Bias adjustments applied to the data are shown to reduce trends in the data and to improve the consistency of estimates of air temperature, sea surface temperature (SST) and specific humidity. The bias adjustments also improve the agreement of NOCS v2.0 with independent data from research moorings. Cross-validation of the dataset suggests that the uncertainty estimates are realistic, but that the uncertainties are probably underestimated in high variability regions and overestimated in regions with lower variability
A probabilistic approach to ship voyage reconstruction in ICOADS
No full textThe International Comprehensive Ocean-Atmosphere Data Set (ICOADS) provides the main archive for surface marine observations for the past approximately 150 years. ICOADS ship identifier (ID) information is often missing or unusable, preventing the linking of reports to an individual ship. A method for the reconstruction of ship voyages in ICOADS is presented, by which groups of reports can be associated with an individual ship or ship track. The method defines a function representing the probability density function (pdf) of any particular report being associated with a group of reports. The parameters of the pdf are calculated from the ship data themselves, giving the likely variation of a ship report perpendicular to its overall direction of travel. For groups of reports with ID information, the PDF is used to associate reports without ID information with the known-ID track. Reports without ID information are then clustered together to form the most probable track. Results are shown for the period 1855–1969. Both the percentage of reports associated with tracks and the length of those tracks increase substantially following tracking. Initial validation of the results was performed by visual inspection: the model implementation was then refined to improve the results. Confidence in the tracking is increased by a demonstration that the method clusters together reports with similar sea surface temperature characteristics. Issues in the data were found to be one of the main challenges in implementing the tracking technique. Particular problems encountered included the coarse resolution of some position information; reports that were mispositioned in either space or time; unidentified duplicate reports; and the fragmentation of voyages between different ICOADS acquisition sources. Some of these effects could be ameliorated by pre-processing of ICOADS reports, however a full reprocessing of the historical input sources to ICOADS would be required to make further improvements
Red-and-Black with Unknown Win Probability
No full text1 online resource (PDF, 12 pages)Berry, Donald A.; Heath, David C.; Sudderth, William D.. (1973). Red-and-Black with Unknown Win Probability. Retrieved from the University Digital Conservancy, https://hdl.handle.net/11299/199187
A comparison of SSM/I-derived global marine surface specific humidity datasets
No full textSatellite-based microwave sensors have, since the 1980s, provided a means to retrieve near-surface marine specific humidity (qa), accurate estimation of which is necessary for climate and air–sea interaction applications. Seven satellite measurement-derived monthly mean humidity datasets are compared with one another and with a dataset constructed from in situ measurements. The means, spatial and temporal structures of the datasets are shown to be markedly different, with a range of yearly, global mean qa of ?1?g?kg–1. Comparison of the datasets derived using the same satellite measurements of brightness temperature reveals differences in qa that depend on the source of satellite data; the processing and quality control applied to the data; and the algorithm used to derive qa from the satellite measurements of brightness temperature. Regional differences between satellite-derived qa due to the choice of input data, quality control and retrieval algorithm can all exceed the accuracy requirements for surface flux calculation of ?0.3?g?kg–1 and in some cases can be several g kg–1 in monthly means for some periods and regions
Correcting datasets leads to more homogeneous early-twentieth-century sea surface warming
No full textExisting estimates of sea surface temperatures (SSTs) indicate that, during the early twentieth century, the North Atlantic and northeast Pacific oceans warmed by twice the global average, whereas the northwest Pacific Ocean cooled by an amount equal to the global average1,2,3,4. Such a heterogeneous pattern suggests first-order contributions from regional variations in forcing or in ocean–atmosphere heat fluxes5,6. These older SST estimates are, however, derived from measurements of water temperatures in ship-board buckets, and must be corrected for substantial biases7,8,9. Here we show that correcting for offsets among groups of bucket measurements leads to SST variations that correlate better with nearby land temperatures and are more homogeneous in their pattern of warming. Offsets are identified by systematically comparing nearby SST observations among different groups10. Correcting for offsets in German measurements decreases warming rates in the North Atlantic, whereas correcting for Japanese measurement offsets leads to increased and more uniform warming in the North Pacific. Japanese measurement offsets in the 1930s primarily result from records having been truncated to whole degrees Celsius when the records were digitized in the 1960s. These findings underscore the fact that historical SST records reflect both physical and social dimensions in data collection, and suggest that further opportunities exist for improving the accuracy of historical SST records9,11
Sex Addiction: the Chicken-and-Egg Dilemma of Diagnosis
No full textIn May 2013, the American Psychiatric Association will release the next version of the Diagnostic and Statistical Manual of Mental Disorders (DSM-V). Interestingly, sex addiction, despite significant attention from mainstream media, will be omitted from the manual. This omission presents a challenge to clinicians who treat sex addiction, and researchers aiming to further our understanding of the issue. This commentary outlines some of the reasons sex addiction was not included in the DSM-V, including a ‘chicken-and-egg’ conundrum, which makes it difficult to generate research without a clear diagnosis, and difficult to establish a definitive diagnosis without a supportive body of research
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