Evaluation of uptake mechanisms of phosphate by Fe(III)(oxyhydr)oxides in Early Proterozoic oceanic conditions

Banded iron formations (BIF) are proxies of global dissolved inorganic phosphate (DIP) content in Precambrian marine waters. Estimates of Precambrian DIP rely on constraining the mechanisms by which Fe(III)(oxyhydr)oxides scavenge DIP in NaCl solutions mimicking elevated Precambrian marine Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are 1) surface attachment on pre-formed Fe(III)(oxyhydr)oxides (adsorption), and 2) incorporation of P into actively growing Fe(III)(oxyhydr)oxides (coprecipitation) during the oxidation of Fe(II) to Fe(III)(oxyhydr)oxides in the presence of DIP. It has been suggested that elevated Si concentrations such as those suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III)(oxyhydr)oxides, however recent coprecipitation experiments show that DIP is scavenged by Fe(III)(oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In this study we show that the DIP uptake onto Fe(III)(oxyhydr)oxides by adsorption is less than 5% of that by coprecipitation. Differences in surface attachment and the possibility of structural capture within the Fe(III)(oxyhydr)oxides are inferred from the robust influence Si has on DIP binding during adsorption, but inhibited for coprecipitation when As(III) and As(V) are present. The data imply that in the Early Proterozoic open oceans, Fe(III)(oxyhydr)oxides precipitated when deep anoxic Fe(II)-rich waters rose and mixed with the first permanently oxygenated ocean surface waters, caused DIP removal from surface waters through coprecipitation rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III)(oxyhydr)oxides, and its partial release into the anoxic bottom waters and in buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters both of which would have most likely decreased the productivity of cyanobacteria and O2 production

Modes of carbon fixation in an arsenic and CO₂-rich shallow hydrothermal ecosystem

Abstract The seafloor sediments of Spathi Bay, Milos Island, Greece, are part of the largest arsenic-CO2-rich shallow submarine hydrothermal ecosystem on Earth. Here, white and brown deposits cap chemically distinct sediments with varying hydrothermal influence. All sediments contain abundant genes for autotrophic carbon fixation used in the Calvin-Benson-Bassham (CBB) and reverse tricaboxylic acid (rTCA) cycles. Both forms of RuBisCO, together with ATP citrate lyase genes in the rTCA cycle, increase with distance from the active hydrothermal centres and decrease with sediment depth. Clustering of RuBisCO Form II with a highly prevalent Zetaproteobacteria 16S rRNA gene density infers that iron-oxidizing bacteria contribute significantly to the sediment CBB cycle gene content. Three clusters form from different microbial guilds, each one encompassing one gene involved in CO2 fixation, aside from sulfate reduction. Our study suggests that the microbially mediated CBB cycle drives carbon fixation in the Spathi Bay sediments that are characterized by diffuse hydrothermal activity, high CO2, As emissions and chemically reduced fluids. This study highlights the breadth of conditions influencing the biogeochemistry in shallow CO2-rich hydrothermal systems and the importance of coupling highly specific process indicators to elucidate the complexity of carbon cycling in these ecosystems

Phosphate and Arsenic Cycling under Experimental Early Proterozoic Marine Conditions

Nutrient dynamics in the Archean-Paleoproterozoic oceans strongly influenced primary productivity and the rise of atmospheric O2. Reconstructing the cycling of key nutrients such as dissolved inorganic phosphate (DIP) at this time is important for our understanding of the timing, rate and extent of atmospheric oxygenation at this time. Banded iron formations (BIF) can be used as proxies for global DIP content in Precambrian marine waters. Estimating Precambrian DIP requires understanding of the mechanisms by which Fe(III)(oxyhydr)oxides scavenge DIP which has come mainly from experimental studies using NaCl solutions that mimick Precambrian marine conditions with for example, elevated Si and Fe(II) concentrations. The two DIP binding modes suggested for Early Proterozoic marine waters are 1) Adsorption - surface attachment on pre-formed Fe(III) (oxyhydr)oxides, and 2) Coprecipitation - incorporation of P into actively growing Fe(III) (oxyhydr)oxides. It has been suggested that the elevated Si concentrations suggested for Precambrian seawater, strongly inhibit adsorption of DIP in Fe(III)(oxyhydr)oxides. However recent coprecipitation experiments show that DIP is strongly scavenged by Fe(III)(oxyhydr)oxides in the presence of Si, seawater cations and hydrothermal As. In this study we show that the DIP uptake onto Fe(III)(oxyhydr)oxides by adsorption is less than 5% of that by coprecipitation. The data imply that in the Early Proterozoic open oceans, the precipitation of Fe(III)(oxyhydr)oxides during mixing of deep anoxic Fe(II)-rich waters with oxygenated ocean surface waters caused DIP removal from surface waters through coprecipitation rather than adsorption. Local variations in DIP and perhaps even stratification of DIP in the oceans were likely created from the continuous removal of DIP from surface waters by Fe(III)(oxyhydr)oxides, and its partial release into the anoxic bottoms waters and in buried sediments. In addition to a DIP famine, the selectivity for DIP over As(V) may have led to As enrichment in surface waters both of which would have most likely decreased the productivity of Cyanobacteria and O2 production. Näringscirkulationen i haven under arkeikum och paleoproterozoikum påverkade primärproduktionen och uppkomsten av atmosfärisk syrgas (O2). För att förstå när och hur fort koncentrationen av O2 i atmosfären ökade behöver vi rekonstruera hur viktiga näringsämnen, t.ex. löst oorganiskt fosfor (engelska “Dissolved Inorganic Phosphorous”, DIP) cirkulerade. Bandad järnmalm (engelska “Banded Iron Formations”, BIF) kan användas som en markör för DIP i de prekambriska haven. För att kunna använda DIP som markör måste man förstå hur prekambrisk DIP tas upp av järn(III)(oxyhydr)oxider. Hittills har detta studerats med natriumkloridlösningar som ska efterlikna förhållande i de prekambriska haven, med t.ex. förhöjda kisel- och järn(II)-koncentrationer. Ur sådana studier har två bindningsmekanismer föreslagits för paleoproterozoiskt havsvatten 1) Adsorption, d.v.s. DIP binds till ytan på redan bildade kristaller av järn(III)(oxyhydr)oxid, och 2) samutfällning, d.v.s. upptag av fosfor i kristaller av järn(III)(oxyhydr)oxid medan kristallerna bildas. Det har föreslagits att de höga kiselkoncentrationerna som tros ha funnits i de prekambriska havsvattnet hämmade adsorption av DIP på ytan av järn(III) (oxyhydr)oxidkristaller. Men de senaste samutfällningsexperimenten tyder på att järn(III) (oxyhydr)oxid effektivt tar upp DIP även i närvaro av kisel, arsenik från hydrotermala källor och de katjoner som dominerar i havsvatten. I här presenterad studie var mängden DIP som bands till järn(III)(oxyhydr)oxidkristaller genom adsorption mindre än 5 % av den DIP som togs upp av kristallerna via samutfällning. Våra data tyder på att när järn(III) (oxyhydr)oxid fälldes ut i tidiga-proterozoiska hav när järn(II)-rikt djupvatten blandades med syrerikt ytvatten, och att DIP avlägsnades från ytvattnet genom samutfällning snarare än adsorption. Lokala variationer av DIP-koncentrationer i haven, möjligen även skiktning, kan ha orsakats av kontinuerlig utfällning av järn(III)(oxyhydr)oxider ur ytvattnet följt av partiell frigörelse av DIP i syrefria djupvatten och sediment. Kristallisationsprocessen, som gynnar inbindning av DIP och misgynnar inbinding av arsenik (V) kan ha orsakat brist av DIP och anrikning av arsenik i ytvattnet, vilket troligen minskade tillväxten av cyanobakterier med lägre syrgasproduktion som följd.CLAP

Estimering av lösta arsenik och fosfor koncentrationer i Prekambriska havsförhållanden

Original estimates of phosphorus (P) concentrations in the Precambrian oceans before 1.9 Ga gave a budget of ~10-25% of modern day levels. This budget was challenged by accounting for high silica (Si) concentrations that were believed to have outcompeted P for binding sites on precipitating iron oxide-hydroxide particles during the chemical oxidation and burial of iron (Fe). Such iron oxide-hydroxide particles are considered as proxies of ancient iron-rich sedimentary rocks, such as banded iron formations, which are often used to infer the dissolved chemistry of trace elements in the ancient oceans. This study raises the question of wether arsenic (As) had an effect of the binding of P to precipitating iron minerals, during the co-precipitation of Iron oxide- hydroxide in elevated Fe and Si concentrations characteristic of the early oceans. This hypothesis is based on the chemical similarities seen between P and As. Results show a more pH dependent competition between P and AsIII, whereby P outcompetes AsIII at a pH <7. The effect decreases as the pH rises until pH ~8 at which the effect cancels out and AsIII becomes somewhat predominant over P. AsV on the other hand, an analogue to P, is outcompeted by P throughout pH 5-10. Distribution coefficients (Kd) of P on iron oxide-hydroxide particles were not affected by the concentration of Si in solution. Average Kd and standard error between concentrations of Si, across the sample pH of 5-10 revealed an average Kd of 0.072 (±0.01) μM-1. This is strikingly similar to another experimental Kd at 0.075 (±0.003) μM-1, when the effects of Si are excluded. The average Kd in this study is also consistent with the average Kd of 0.06 μM-1 from a range of As-rich hydrothermal systems reported in a previous study, supporting the original idea of Precambrian P levels being low. The average Kd between concentrations of Fe revealed a Kd of 0.12 (±0.03) μM-1 although this was not statistically significant from the average Kd between groups of Si. In addition to low levels of P, the Precambrian oceans likely also contained high levels of As, due to the high hydrothermal activity. This scavenging of P from oceanic waters would have become increasingly important as surface oceans became more oxygenated and the presence of AsV would have been greater. Because the availability of Si does not show any great effect on the uptake of P by precipitating iron oxide-hydroxides, Si concentration is likely not a proxy for oceanic P concentrations. It is proposed that low dissolved P levels are consistent with early oceans that w!ere a lot more hydrothermally influenced than the oceans of today. Prekambriska fosfor (P) nivåer var ursprungligen estimerade till ca 10-25% utav koncentrationen funnen i dagens havsvatten. Denna budget blev motsagd i och med att kisel (Si) sades kunna ersätta bundet fosfor på järn oxid-hydroxid partiklar som precipiterade genom kemisk oxidation och sedimentering av järn (Fe). Dessa järn oxid-hydroxid partiklar anses användbara som proxy för formationen av uråldriga järn-rika sedimentära bergarter såsom banded iron formation (BIF), vilka används idag för att bestämma mängden spårämnen i de uråldriga haven. Denna studie ställer frågan huruvida arsenik (As) påverkar mängden P som binder till precipiterande järn mineral under procession av co-precipitering av järn oxid-hydroxid i lösning med förhöjda koncentrationer av Fe och Si, karakteristiska för the uråldriga haven. Denna hypotes är baserad på de kemiska likheter som finns mellan P och As. Resultaten påvisar en pH beroende konkurrens mellan P och AsIII där P utkonkurrerar AsIII vid låg pH. Effekten av denna konkurrans minskar med ökande pH tills effekten blir omvänd omkring pH 8 och P blir istället till viss del utkonkurrerad av AsIII. AsV å andra sedan, en verklig kemisk analog till P, är kontinuerligt utkonkurrerad av P genom alla utförda pH, pH 5-10. Distribueringskoefficienter (Kd) för P på järn oxid-hydroxid partiklar visade ingen påverkan av mängden Si tillgängligt. Medelvärdet av Kd och standard error mellan data av alls pH, grupperat av Si, gav ett värde av 0.072 (±0.01) μM-1. Detta är påfallande nära ett experimentellt framtaget Kd värde av 0.075 (±0.03) μM-1 då effekten av Si är borttagen. Medelvärdet i denna studie är också sammanfallande med det Kd medelvärde man finner idag från olika hydrotemala system av 0.063 (±0.01) μM-1. Detta ger support till den originala idén att de prekambriska haven troligen hade låga halter P tillgängligt. Medelvärdet av Kd mellan koncentrationer av Fe gav ett värde av 0.12 (±0.03) μM-1, dock var detta värde ej statistiskt significant från det Kd utifrån koncentrationer av Si. Förutom de låga nivåer av P i de Prekambriska haven så var det troligen även höga halter av As på grund av utbredd hydrotermal aktivitet. Detta uppfångande av P i de tidiga haven var troligen en alltmer viktigare process då ytvatten blev syrerikare och den oxiderade formen av As, det vill säga AsV hade varit mer vanligt förekommande. Framför allt då den konkurrerande effekten av Si kan bortses när P såväl som As inte påverkas av dess närvaro till den grad man hade trott. Detta gör även att mängden Si troligen inte är en tillförlitlig proxy för att estimera P nivåer i de uråldriga haven. Därmed föreslås det att de prekambriska haven var k!arakteriserade av låga P nivåer, jämfört med idag

How to hedge disclosures? IFRS 7 and Hedge Accounting - A first stocktaking

Background and problem: Financial instruments are often highly complex. An effective financial presentation of the certain risks is therefore vital for the users’, especially for the investors’ understanding of financial reports for their decision-making processes. This is of special importance when it comes to hedge accounting and an understanding of the companies’ risk management policies, and how hedging affects the entities’ financial performances and risk situations. IASBs answer to this issue was the introduction of the IFRS 7 Financial Instruments: Disclosure, an accounting standard with the main goal to improve the quality of disclosed information, compulsory for all annual reports from 1st January 2007 onwards. Purpose: The purpose of this thesis is to explore how Swedish Large Cap entities have disclosed information regarding hedge accounting in their annual reports 2007, after the implementation of IFRS 7. Furthermore this thesis evaluates how the new hedge accounting disclosure requirements are perceived by the financial analysts. Delimitations: The thesis will only focus on that part which is presented in IFRS 7 regarding hegde accounting. The purpose is not to investigate how the companies use hedges, nor the quality of the disclosed information. Moreover, the thesis will only focus on the user’s perspective (investor). Method: A mix between a quantitive and qualitative method have been chosen in order to fulfill the purpose of the thesis. The quantitive method was used by conducting a disclosure study. The secondary data was collected from annual reports 2007. With a qualitative method, primary data was gathered from two telephone interviews with financial analysts and one accounting specialist. Conclusion: The findings and the analysis point out that for fair value hedges approximately 88 percent of the entities’ disclosure information correlated with IFRS 7 hedge accounting requirements. For cash flow hedges and hedges of net investments in foreign operations approximately 63 respective 81 percent of the entities provided information correlating with the requirements Even though, different correlations regarding the standard’s requirements and the information disclosed were identified, the interviewed financial analysts did not perceive those inconsistencies as important issues for their daily work, since hedge accounting disclosure were not considered as vital information sources. Suggestion on further research: It would have been interesting to conduct the same study for financial institutions since hedge accounting is more vital for their business. Furthermore, it would also be useful to evaluate the quality of the disclosed information, besides the quantitative aspects we have tested

Finansanalytikerns oberoende : En beskrivande uppsats om hur finansanalytikerns oberoende inom en investmentbank främjas

Bakgrund Inom de investmentbanker som idag erbjuder heltäckande tjänster inom värdepappershandel och företagsrelaterade finanstjänster uppstår konflikter som grundar sig på vems intresse som kommer i första hand. I denna process har finansanalytikern en central roll där det finns en risk att hamna i en intressekonflikt med corporate finance avdelningen. Finansanalytikerns oberoende är viktigt då analyserna har påverkan på kursbildningen på värdepappersmarknaden. Syfte Syftet med denna kandidatuppsats är att beskriva hur ett antal svenska investmentbanker arbetar för att främja finansanalytikerns oberoende i sin yrkesroll. För att tydliggöra oberoendet kommer intressekonflikten mellan analysavdelningen och corporate finance avdelningen att beskrivas då problematiken kring finansanalytikerns oberoende här är som tydligast. Metod En kvalitativ ansats har valt för att uppfylla uppsatsens syfte. Tre personliga djupintervjuer genomfördes med investmentbanker och Finansinspektionen. Ytterligare en telefonintervju genomfördes med ett analyshus som marknadsför sig som oberoende. Detta gav sammanlagt tre olika perspektiv på problemet. Slutsats Investmentbankerna främjar finansanalytikerns oberoende genom att skapa förutsättningar för att denne ska kunna ha en hög integritet i sin yrkesroll. Dessa förutsättningar skapas genom att följa lagen och de rekommendationer som Finansinspektionen ger. Tillsammans med interna regler och incitament stärks finansanalytikerns oberoende gentemot corporate finance avdelningen.Background Within today’s full-service investment banks conflicts of interest related to who’s interest that comes first appears. Within this process the equity researcher has a fundamental profession and is exposed to conflicts of interest mainly towards the corporate finance department. The equity researcher’s independence is of importance since the analyses have impact on the determination of prices on the securities market. Purpose The purpose of this bachelor thesis is to describe how a number of Swedish investment banks operate to promote independence in the equity researcher’s profession. To describe the independence, conflicts of interest between the equity research department and the corporate finance department will be described. This situation chosen because of the problematic situation concerning the equity researcher’s independence that appears. Method A qualitative approach has been chosen to fulfil the purpose of the bachelor thesis. Three personal in-depth interviews have been conducted with investment banks as well as the Swedish Financial Supervisory Authority. One additional telephone interview was conducted with a company promoting itself as an independent equity researcher. This together gave us three different perspectives of the problem. Conclusion The investment banks promote the equity researcher’s independence by creating conditions to maintain a high integrity in their profession. These conditions are created by following the law and the recommendations given by the Swedish Financial Supervisory Authority. Together with internal rules and incentives, the equity researcher’s independence towards corporate finance will strengthen

Finansanalytikerns oberoende : En beskrivande uppsats om hur finansanalytikerns oberoende inom en investmentbank främjas

Bakgrund Inom de investmentbanker som idag erbjuder heltäckande tjänster inom värdepappershandel och företagsrelaterade finanstjänster uppstår konflikter som grundar sig på vems intresse som kommer i första hand. I denna process har finansanalytikern en central roll där det finns en risk att hamna i en intressekonflikt med corporate finance avdelningen. Finansanalytikerns oberoende är viktigt då analyserna har påverkan på kursbildningen på värdepappersmarknaden. Syfte Syftet med denna kandidatuppsats är att beskriva hur ett antal svenska investmentbanker arbetar för att främja finansanalytikerns oberoende i sin yrkesroll. För att tydliggöra oberoendet kommer intressekonflikten mellan analysavdelningen och corporate finance avdelningen att beskrivas då problematiken kring finansanalytikerns oberoende här är som tydligast. Metod En kvalitativ ansats har valt för att uppfylla uppsatsens syfte. Tre personliga djupintervjuer genomfördes med investmentbanker och Finansinspektionen. Ytterligare en telefonintervju genomfördes med ett analyshus som marknadsför sig som oberoende. Detta gav sammanlagt tre olika perspektiv på problemet. Slutsats Investmentbankerna främjar finansanalytikerns oberoende genom att skapa förutsättningar för att denne ska kunna ha en hög integritet i sin yrkesroll. Dessa förutsättningar skapas genom att följa lagen och de rekommendationer som Finansinspektionen ger. Tillsammans med interna regler och incitament stärks finansanalytikerns oberoende gentemot corporate finance avdelningen.Background Within today’s full-service investment banks conflicts of interest related to who’s interest that comes first appears. Within this process the equity researcher has a fundamental profession and is exposed to conflicts of interest mainly towards the corporate finance department. The equity researcher’s independence is of importance since the analyses have impact on the determination of prices on the securities market. Purpose The purpose of this bachelor thesis is to describe how a number of Swedish investment banks operate to promote independence in the equity researcher’s profession. To describe the independence, conflicts of interest between the equity research department and the corporate finance department will be described. This situation chosen because of the problematic situation concerning the equity researcher’s independence that appears. Method A qualitative approach has been chosen to fulfil the purpose of the bachelor thesis. Three personal in-depth interviews have been conducted with investment banks as well as the Swedish Financial Supervisory Authority. One additional telephone interview was conducted with a company promoting itself as an independent equity researcher. This together gave us three different perspectives of the problem. Conclusion The investment banks promote the equity researcher’s independence by creating conditions to maintain a high integrity in their profession. These conditions are created by following the law and the recommendations given by the Swedish Financial Supervisory Authority. Together with internal rules and incentives, the equity researcher’s independence towards corporate finance will strengthen

Ni isotope fractionation during coprecipitation of Fe(III)(oxyhydr)oxides in Si solutions

The dramatic decline in aqueous Ni concentrations in the Archean oceans during the Great Oxygenation Event is evident in declining solid phase Ni concentrations in Banded Iron Formations (BIFs) at the time. Several experiments have been performed to identify the main removal mechanisms of Ni from seawater into BIFs, whereby adsorption of Ni onto ferrihydrites has shown to be an efficient process. Ni isotopic measurements have shown limited isotopic fraction during this process, however, most experiments have been conducted in simple solutions containing varying proportions of dissolved Fe and Ni as NO3 salts, as opposed to Cl salts which are dominant in seawater. Further, Archean oceans were, before the advent of siliceous eukaryotes, likely saturated with amorphous Si as seen in the interlayered chert layers within BIFs. Despite Si being shown to greatly affect the Ni elemental partitioning onto ferrihydrite solids, no studies have been made on the effects of Si on the Ni isotope fractionation. Here we report results of multiple coprecipitation experiments where ferrihydrite precipitated in mixed solutions with Ni and Si. Ni concentrations in the experiments ranged between 200 and 4000 nM for fixed concentrations of Si at either 0, 0.67 or 2.2 mM. The results show that Si at these concentrations has a limited effect on the Ni isotope fractionation during coprecipitation of ferrihydrite. At 0.67 mM, the saturation concentration of cristobalite, the isotopic fractionation factors between the precipitating solid and experimental fluid are identical to experiments not containing Si (0.34 ± 0.17‰). At 2.2 mM Si, and the saturation concentration of amorphous silica, however, the Ni isotopic composition of the ferrihydrite solids deviate to more negative values and show a larger variation than at low or no Si, and some samples show fractionation of up to 0.5‰. Despite this seemingly more unstable fractionation behaviour, the combined results indicate that even at as high concentrations of Si as 2.2 mM, the δ60Ni values of the forming ferrihydrites does not change much. The results of our study implicate that Si may not be a major factor in fractionating stable Ni isotopes, which would make it easier to interpret future BIF record and reconstruct Archean ocean chemistry

Arsenic-induced phosphate limitation under experimental Early Proterozoic oceanic conditions

Comparison of phosphorus concentrations associated with modern hydrothermal Fe(III)(oxyhydr)oxides and ancient Fe(III) oxide-rich iron formations, is used to estimate bioavailable Precambrian marine phosphorus (P) concentrations. This led to the proposition of a low dissolved P budget of ∼10–25% of present-day levels, before ∼1.9 billion years ago. Estimates incorporating ancient marine Si levels ≥0.67mM instead suggested global dissolved P levels greater than today. Here we unite current experimental models that have considered NaCl solutions containing elevated dissolved Fe(II), Si, Ca2+ and Mg2+ ions in the incorporation of P in Precambrian marine Fe(III)(oxyhydr)oxides, in addition to arsenic as a hydrothermal proxy. We show that the coprecipitation of dissolved P and Fe(III)(oxyhydr)oxides from arsenic-rich marine waters produces an average P distribution coefficient of ∼0.072 (±0.01)μM−1 . This is comparable to the ∼0.07μM−1 predicted for Fe(III)(oxyhydr)oxides in modern arsenic-rich, submarine hydrothermal settings, from which the lower Early Proterozoic dissolved marine P concentrations were predicted. As/P molar ratios below modern seawater ratios removed the negative feedback effect high Si impose on P scavenging by Fe(III)(oxyhydr)oxides. The binding of As(III) to Fe(III)(oxyhydr)oxides exhibits a lower competitive influence on P fixation. As(V) that likely became prominent in the surficially oxidized Early Proterozoic oceans induced dissolved P limitation because of preferential P sequestration at the expense of dissolved As(V) enrichment. The control of As on P scavenging by the precipitating Fe(III)(oxyhydr)oxides is strong regardless of common seawater cations (Mg2+ and Ca2+). The data suggest that the application of Si and Fe(III)(oxyhydr)oxides as an ancient seawater P proxy should consider chemical variability between depositional basins, taking into account the rather strong role hydrothermal arsenic has on the distribution of P in Fe(III)(oxyhydr)oxides. We propose that the generalized lower dissolved P budgets estimated from Early Proterozoic iron formations are consistent with oceans thought to be at least 3–4 times more hydrothermally active than at present

Excision and suture in the midline versus Karydakis flap surgery for pilonidal sinus : randomized clinical trial

BACKGROUND: There are several surgical options for the management of pilonidal disease, including midline and off midline closure, but prospective studies are rare. The study hypothesis was that Karydakis flap surgery would result in shorter wound healing and fewer recurrences than excision of pilonidal sinus and suture in the midline. METHODS: A randomized clinical trial was conducted in two hospitals in Sweden between 2006 and 2015 to compare excision and suture in the midline with Karydakis flap surgery. Adult patients with a chronic pilonidal sinus disease were randomized 1:1 at the outpatient clinic without blinding. Power calculation based on recurrence of 2 per cent for Karydakis flap and 10 per cent for excision and primary closure in the midline required 400 patients with 90 per cent statistical power at 5 per cent significance assuming 10 per cent loss during follow-up. Participants were followed up until complete wound healing; late follow-up after 6-13 years was performed by telephone by two blinded assessors. The two co-primary outcomes were time to complete wound healing and recurrence rate. RESULTS: The study was terminated early at a planned interim analysis due slow recruitment and a significant difference in primary outcome. In total, 125 patients were randomized, of whom 116 were available for the present analysis. Median wound healing time was 49 days (95 per cent confidence interval (c.i.) 32 to 66) for excision with suture in the midline and 14 days (95 per cent c.i. 12 to 20) for Karydakis flap surgery (P < 0.001). There were five recurrences in each group, after a median follow-up of 11 years (P = 0.753). CONCLUSION: Karydakis flap surgery for pilonidal sinus disease led to a shorter wound healing time than excision and suture in the midline but no difference in recurrence rates.Registration number: NCT00412659 (http://www.clinicaltrials.gov)