scholarly journals Ooids forming in situ within microbial mats (Kiritimati atoll, central Pacific)

PalZ ◽  
2021 ◽  
Author(s):  
Pablo Suarez-Gonzalez ◽  
Joachim Reitner

AbstractOoids (subspherical particles with a laminated cortex growing around a nucleus) are ubiquitous in the geological record since the Archean and have been widely studied for more than two centuries. However, various questions about them remain open, particularly about the role of microbial communities and organic matter in their formation and development. Although ooids typically occur rolling around in agitated waters, here, we describe for the first time aragonite ooids forming statically within microbial mats from hypersaline ponds of Kiritimati (Kiribati, central Pacific). Subspherical particles had been previously observed in these mats and classified as spherulites, but these particles grow around autochthonous micritic nuclei, and many of them have laminated cortices, with alternating radial fibrous laminae and micritic laminae. Thus, they are compatible with the definition of the term ‘ooid’ and are in fact very similar to many modern and fossil examples. Kiritimati ooids are more abundant and developed in some ponds and in some particular layers of the microbial mats, which leads to the discussion and interpretation of their formation processes as product of mat evolution, through a combination of organic and environmental factors. Radial fibrous laminae are formed during periods of increased supersaturation, either by metabolic or environmental processes. Micritic laminae are formed in closer association with the mat exopolymer (EPS) matrix, probably during periods of lower supersaturation and/or stronger EPS degradation. Therefore, this study represents a step forward in the understanding of ooid development as influenced by microbial communities, providing a useful analogue for explaining similar fossil ooids.

2018 ◽  
Vol 11 (4) ◽  
pp. 935-959 ◽  
Author(s):  
Mehrdad Sarhadi ◽  
Saied Yousefi ◽  
Amin Zamani

PurposeThe purpose of this paper is to understand the philosophical changes which underpin research and practices in project management. This study is an attempt to challenge previous studies that have tried to explain this change in order to provide a better explanation.Design/methodology/approachThe authors adopt a critical review research method to challenge previous explanations of the paradigm change and definition of communication. For this purpose, philosophical and social theories and concepts have been used.FindingsThis paper proposed changing the paradigm from modernism to postmodernism and the paradigm shift, which happens from postmodernism to participation, as a better explanation for the paradigmatic change in project management. Furthermore, the important role of communication has been illustrated in the participation paradigm.Originality/valueFor the first time in project management, the authors attempt to clarify the role of power in this paradigmatic shift, especially because this concept is an axial concept in postmodern philosophy and a neglected concept in project management literature. In addition, communicative action theory has been used with the aim of pursuing the influence of informal power in the participation paradigm and paving the way for confronting its emerging challenges in future studies.


2021 ◽  
Vol 50 (2) ◽  
pp. 121-135
Author(s):  
Joeri Kaal ◽  
Virginia Martínez-Pillado ◽  
Antonio Martínez Cortizas ◽  
Jorge Sanjurjo Sánchez ◽  
Arantza Aranburu ◽  
...  

Speleothems are a recognized source of paleoclimatic information, but their value as a source of signals from human activities in caves with an archaeological record has rarely been explored. Previous studies of speleothems in the Sierra de Atapuerca karst system (Burgos, northern Spain) revealed an important human fossil record, provided information about human activities in and around these caves, and the impacts on their natural environment. The present study reports the results of molecular characterization of dark-colored laminae from the stalagmites Ilargi (Galería de las Estatuas) and GS1, GS2, and GS3 (Galería del Silo), by pyrolysis-GC-MS (Py-GC-MS) and thermally assisted hydrolysis and methylation (THM-GC-MS). The features of the organic matter demonstrate the presence of (1) a dominant aliphatic fraction probably from in situ bacterial and ex situ plant-derived lipids, (2) black carbon (from soot and/or charcoal), (3) polysaccharides and N-rich moieties (probably from bat guano and microbial sources), and (4) a signal of terpenoid derivatives that may originate from the overlying limestone (kerogen) and extant gymnosperm resin (soils) or cyanobacteria (cave). Some plant-derived lignin may be present as well but was not identified unambiguously. It is concluded that this approach allows identifying multiple general sources of organic matter which can help understand speleothem formation processes, and evidence of soot deposition could be clearly linked to human activities.


1980 ◽  
Vol 20 (1) ◽  
pp. 257
Author(s):  
R.W. King

Production platforms required for the development of the North Rankin gas/condensate field will be founded on deep deposits of loose to weakly cemented calcareous material of predominantly marine origin. Although the data base for foundation design in these materials is extremely limited, experience has shown that calcareous sediments exhibit unusual engineering characteristics and that in situ load tests appear to be the most reliable indicator of soil-bearing potential.The foundation investigations performed at North Rankin, in 1978, integrated conventional soil sampling techniques with cone penetrometer testing (CPT), which is a small-scale load test that provides a semicontinuous profile of soil resistance. This being the first time that CPT had been used extensively in calcareous sediments, a series of innovative prototype in situ load tests were performed to provide data for calibration of the core resistance profile.A modified carbonate classification system was introduced into the programme and, together with detailed geological analysis of specimens, it provided an insight into subtle variations in lithology and cementation throughout the profile.These new developments and the comprehensive nature of the investigation produced a large amount of data that are relevant to other locations where similar sediments exist.As a result of these investigations and subsequent studies, Woodside Petroleum Development has been able to progress confidently in the definition of a suitable foundation system and the design of the North Rankin platforms.


2005 ◽  
Vol 52 (7) ◽  
pp. 225-232 ◽  
Author(s):  
S. Okabe ◽  
T. Kindaichi ◽  
Y. Nakamura ◽  
T. Ito

Microautoradiography combined with fluorescent in situ hybridization (MAR-FISH), a powerful tool for linking physiology with identification of individual cells, was applied to investigate microbial interactions between nitrifying bacteria and coexisting heterotrophic bacteria in an autotrophic nitrifying biofilm community fed with only ammonia as the sole energy source and bicarbonate as the sole carbon source. First, nitrifying bacteria were radiolabeled by culturing the biofilm samples with [14C]bicarbonate for 6 h, and then the transfer of radioactivity from nitrifying bacteria to heterotrophic bacteria was monitored by using MAR-FISH. MAR-FISH revealed that the heterotrophic bacterial community was composed of bacteria that were phylogenetically and metabolically diverse. We could obtain direct evidence that organic matter derived from nitrifiers was subsequently utilized by mainly filamentous bacteria belonging to the Chloroflexi (green non-sulfur bacteria) group or CFB group in the biofilm, which was clearly visualized by MAR-FISH at single cell resolution for the first time. On the other hand, the members of the α- and γ-Proteobacteria were specialized to utilize low-molecular-weight organic matter. This community represents functionally integrated units that assure maximum access to and utilization of metabolites of nitrifiers.


2010 ◽  
Vol 7 (8) ◽  
pp. 2419-2432 ◽  
Author(s):  
T. Amaro ◽  
S. Bianchelli ◽  
D. S. M. Billett ◽  
M. R. Cunha ◽  
A. Pusceddu ◽  
...  

Abstract. Megafaunal organisms play a key role in ecosystem functioning in the deep-sea through bioturbation, bioirrigation and organic matter cycling. At 3500 m water depth in the Nazaré Canyon, NE Atlantic, very high abundances of the infaunal holothurian Molpadia musculus were observed. To quantify the role of M. musculus in sediment cycling, sediment samples and holothurians were collected using an ROV and in situ experiments were conducted with incubation chambers. The biochemical composition of the sediment (in terms of proteins, carbohydrates and lipids), the holothurians' gut contents and holothurians' faecal material were analysed. In the sediments, proteins were the dominant organic compound, followed by carbohydrates and lipids. In the holothurian's gut contents, protein concentrations were higher than the other compounds, decreasing significantly as the material passed through the digestive tract. Approximately 33±1% of the proteins were digested by the time sediment reached the mid gut, with a total digestion rate equal to 67±1%. Carbohydrates and lipids were ingested in smaller amounts and digested with lower efficiencies (23±11% and 50±11%, respectively). As a result, the biopolymeric C digestion rate was on average 62±3%. We estimated that the population of M. musculus could remove approximately 0.49±0.13 g biopolymeric C and 0.13±0.03 g N m−2 d−1 from the sediments. These results suggest that M. musculus plays a key role in the benthic tropho-dynamics and biogeochemical processes in the Nazaré Canyon.


2016 ◽  
Vol 3 (3) ◽  
pp. 647-656 ◽  
Author(s):  
Chelsea W. Neil ◽  
Jessica R. Ray ◽  
Byeongdu Lee ◽  
Young-Shin Jun

This study provides for the first timein situobservations of organic matter and arsenic effects on iron(iii) (hydr)oxide precipitation.


2006 ◽  
Vol 3 (1) ◽  
pp. 53-64 ◽  
Author(s):  
H. Biester ◽  
D. Selimović ◽  
S. Hemmerich ◽  
M. Petri

Abstract. Halogens are strongly enriched in peat and peatlands and such they are one of their largest active terrestrial reservoir. The enrichment of halogens in peat is mainly attributed to the formation of organohalogens and climatically controlled humification processes. However, little is known about release of halogens from the peat substrate and the distribution of halogens in the peat pore water. In this study we have investigated the distribution of chlorine, bromine and iodine in pore water of three pristine peat bogs located in the Magellanic Moorlands, southern Chile. Peat pore waters were collected using a sipping technique, which allows in situ sampling down to a depth greater than 6m. Halogens and halogen species in pore water were determined by ion-chromatography (IC) (chlorine) and IC-ICP-MS (bromine and iodine). Results show that halogen concentrations in pore water are 15–30 times higher than in rainwater. Mean concentrations of chlorine, bromine and iodine in pore water were 7–15 mg l−1, 56–123 μg l−1, and 10–20 μg l−1, which correspond to mean proportions of 10–15%, 1–2.3% and 0.5–2.2% of total concentrations in peat, respectively. Organobromine and organoiodine were the predominant species in pore waters, whereas chlorine in pore water was mostly chloride. Advection and diffusion of halogens were found to be generally low and halogen concentrations appear to reflect release from the peat substrate. Release of bromine and iodine from peat depend on the degree of peat degradation, whereas this relationship is weak for chlorine. Relatively higher release of bromine and iodine was observed in less degraded peat sections, where the release of dissolved organic carbon (DOC) was also the most intensive. It has been concluded that the release of halogenated dissolved organic matter (DOM) is the predominant mechanism of iodine and bromine release from peat.


2019 ◽  
Vol 24 (8) ◽  
pp. 536-544 ◽  
Author(s):  
Michael R Narvey ◽  
Seth D Marks

Abstract Hypoglycemia in the first hours to days after birth remains one of the most common conditions facing practitioners across Canada who care for newborns. Many cases represent normal physiologic transition to extrauterine life, but another group experiences hypoglycemia of longer duration. This statement addresses key issues for providers of neonatal care, including the definition of hypoglycemia, risk factors, screening protocols, blood glucose levels requiring intervention, and managing care for this condition. Screening, monitoring, and intervention protocols have been revised to better identify, manage, and treat infants who are at risk for persistent, recurrent, or severe hypoglycemia. The role of dextrose gels in raising glucose levels or preventing more persistent hypoglycemia, and precautions to reduce risk for recurrence after leaving hospital, are also addressed. This statement differentiates between approaches to care for hypoglycemia during the ‘transitional’ phase—the first 72 hours post-birth—and persistent hypoglycemia, which occurs or presents for the first time past that point.


1999 ◽  
Vol 23 (1) ◽  
pp. 57-66 ◽  
Author(s):  
C Keil ◽  
B Husen ◽  
J Giebel ◽  
G Rune ◽  
R Walther

In the present study we demonstrate for the first time the expression of glycodelin mRNA in the female and male genital tracts of rats using non-radioactive in situ hybridisation. Glycodelin fragment 1 (+41 to +141) shares 100% homology with the human gene sequence. In the ovary, glycodelin mRNA was restricted to granulosa cells. In the uterus, glycodelin mRNA was expressed in all epithelial cells of the endometrium. In the male reproductive tract, glycodelin mRNA was distributed in all epithelial cells of the epididymis, the prostate and the seminal vesicle. However, in the testis, glycodelin mRNA was predominantly found in spermatogonia and in spermatocytes of the seminiferous epithelium. The expression in several reproductive organs of rats offers an excellent tool to study further the physiological role of glycodelin, which is so far thought to act as an immunosuppressive factor.


Sign in / Sign up

Export Citation Format

Share Document