Variable aging and storage of dissolved black carbon in the ocean.

During wildfires and fossil fuel combustion, biomass is converted to black carbon (BC) via incomplete combustion. BC enters the ocean by rivers and atmospheric deposition contributing to the marine dissolved organic carbon (DOC) pool. The fate of BC is considered to reside in the marine DOC pool, where the oldest BC 14C ages have been measured (>20,000 14C y), implying long-term storage. DOC is the largest exchangeable pool of organic carbon in the oceans, yet most DOC (>80%) remains molecularly uncharacterized. Here, we report 14C measurements on size-fractionated dissolved BC (DBC) obtained using benzene polycarboxylic acids as molecular tracers to constrain the sources and cycling of DBC and its contributions to refractory DOC (RDOC) in a site in the North Pacific Ocean. Our results reveal that the cycling of DBC is more dynamic and heterogeneous than previously believed though it does not comprise a single, uniformly "old" 14C age. Instead, both semilabile and refractory DBC components are distributed among size fractions of DOC. We report that DBC cycles within DOC as a component of RDOC, exhibiting turnover in the ocean on millennia timescales. DBC within the low-molecular-weight DOC pool is large, environmentally persistent and constitutes the size fraction that is responsible for long-term DBC storage. We speculate that sea surface processes, including bacterial remineralization (via the coupling of photooxidation of surface DBC and bacterial co-metabolism), sorption onto sinking particles and surface photochemical oxidation, modify DBC composition and turnover, ultimately controlling the fate of DBC and RDOC in the ocean.

Incidence and risk factors for unplanned readmission after colorectal surgery: A meta-analysis.

BACKGROUND: Unplanned readmissions (URs) after colorectal surgery (CRS) are common, expensive, and result from failure to progress in postoperative recovery. These are considered preventable, although the true extent is yet to be defined. In addition, their successful prediction remains elusive due to significant heterogeneity in this field of research. This systematic review and meta-analysis of observational studies aimed to identify the clinically relevant predictors of UR after colorectal surgery. METHODS: A systematic review was conducted using indexed sources (The Cochrane Database of Systematic Reviews, MEDLINE, and Embase) to search for published studies in English between 1996 and 2022. The search strategy returned 625 studies for screening of which, 150 were duplicates, and 305 were excluded for irrelevance. An additional 150 studies were excluded based on methodology and definition criteria. Twenty studies met the inclusion criteria and for the meta-analysis. Independent meta-extraction was conducted by multiple reviewers (JD & SR) in accordance with PRISMA guidelines. The primary outcome was defined as UR within 30 days of index discharge after colorectal surgery. Data were pooled using a random-effects model. Risk of bias was assessed using the Quality in Prognosis Studies tool. RESULTS: The reported 30-day UR rate ranged from 6% to 22.8%. Increased comorbidity was the strongest preoperative risk factor for UR (OR 1.39, 95% CI 1.28-1.51). Stoma formation was the strongest operative risk factor (OR 1.54, 95% CI 1.38-1.72). The occurrence of postoperative complications was the strongest postoperative and overall risk factor for UR (OR 3.03, 95% CI 1.21-7.61). CONCLUSIONS: Increased comorbidity, stoma formation, and postoperative complications are clinically relevant predictors of UR after CRS. These risk factors are readily identifiable before discharge and serve as clinically relevant targets for readmission risk-reducing strategies. Successful readmission prediction may facilitate the efficient allocation of healthcare resources.

A special issue preface: Radiocarbon in the Anthropocene.

The Anthropocene is defined by marked acceleration in human-induced perturbations to the Earth system. Anthropogenic emissions of CO2 and other greenhouse gases to the atmosphere and attendant changes to the global carbon cycle are among the most profound and pervasive of these perturbations. Determining the magnitude, nature and pace of these carbon cycle changes is crucial for understanding the future climate that ecosystems and humanity will experience and need to respond to. This special issue illustrates the value of radiocarbon as a tool to shed important light on the nature, magnitude and pace of carbon cycle change. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

Radiocarbon signatures of carbon phases exported by Swiss rivers in the Anthropocene.

Lateral carbon transport through the land-to-ocean-aquatic-continuum (LOAC) represents a key component of the global carbon cycle. This LOAC involves complex processes, many of which are prone to anthropogenic perturbation, yet the influence of natural and human-induced drivers remains poorly constrained. This study examines the radiocarbon (14C) signatures of particulate and dissolved organic carbon (POC, DOC) and dissolved inorganic carbon (DIC) transported by Swiss rivers to assess controls on sources and cycling of carbon within their watersheds. Twenty-one rivers were selected and sampled during high-flow conditions in summer 2021, a year of exceptionally high rainfall. Δ14C values of POC range from -446‰ to -158‰, while corresponding ranges of Δ14C values for DOC and DIC are -377‰ to -43‰ and -301‰ to -40‰, respectively, indicating the prevalence of pre-aged carbon. Region-specific agricultural practices seem to have an influential effect on all three carbon phases in rivers draining the Swiss Plateau. Based on Multivariate Regression Analysis, mean basin elevation correlated negatively with Δ14C values of all three carbon phases. These contrasts between alpine terrain and the lowlands reflect the importance of overriding ecoregional controls on riverine carbon dynamics within Switzerland, despite high spatial variability in catchment properties. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

Multi-molecular 14C evidence for mineral control on terrestrial carbon storage and export.

Compound- and compound class-specific radiocarbon analysis of source-diagnostic 'biomarker' molecules has emerged as a powerful tool to gain insights into terrestrial carbon cycling. While most studies thus far have focused on higher plant biomarkers (i.e. plant leaf-wax n-alkanoic acids and n-alkanes, lignin-derived phenols), tracing paedogenic carbon is crucial given the pivotal role of soils in modulating ecosystem carbon turnover and organic carbon (OC) export. Here, we determine the radiocarbon (14C) ages of glycerol dialkyl glycerol tetraethers (GDGTs) in riverine sediments and compare them to those of higher plant biomarkers as well as markers of pyrogenic (fire-derived) carbon (benzene polycarboxylic acids, BPCAs) to assess their potential as tracers of soil turnover and export. GDGT Δ14C follows similar relationships with basin properties as vegetation-derived lignin phenols and leaf-wax n-alkanoic acids, suggesting that the radiocarbon ages of these compounds are significantly impacted by intermittent soil storage. Systematic radiocarbon age offsets are observable between the studied biomarkers, which are likely caused by different mobilization pathways and/or stabilization by mineral association. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

Making the case for an International Decade of Radiocarbon.

Radiocarbon (14C) is a critical tool for understanding the global carbon cycle. During the Anthropocene, two new processes influenced 14C in atmospheric, land and ocean carbon reservoirs. First, 14C-free carbon derived from fossil fuel burning has diluted 14C, at rates that have accelerated with time. Second, 'bomb' 14C produced by atmospheric nuclear weapon tests in the mid-twentieth century provided a global isotope tracer that is used to constrain rates of air-sea gas exchange, carbon turnover, large-scale atmospheric and ocean transport, and other key C cycle processes. As we write, the 14C/12C ratio of atmospheric CO2 is dropping below pre-industrial levels, and the rate of decline in the future will depend on global fossil fuel use and net exchange of bomb 14C between the atmosphere, ocean and land. This milestone coincides with a rapid increase in 14C measurement capacity worldwide. Leveraging future 14C measurements to understand processes and test models requires coordinated international effort-a 'decade of radiocarbon' with multiple goals: (i) filling observational gaps using archives, (ii) building and sustaining observation networks to increase measurement density across carbon reservoirs, (iii) developing databases, synthesis and modelling tools and (iv) establishing metrics for identifying and verifying changes in carbon sources and sinks. This article is part of the Theo Murphy meeting issue 'Radiocarbon in the Anthropocene'.

Readmission prediction after colorectal cancer surgery: A derivation and validation study.

BACKGROUND: Unplanned readmissions after colorectal cancer (CRC) surgery are common, expensive, and result from failure to progress in postoperative recovery. The context of their preventability and extent of predictability remains undefined. This study aimed to define the 30-day unplanned readmission (UR) rate after CRC surgery, identify risk factors, and develop a prediction model with external validation. METHODS: Consecutive patients who underwent CRC surgery between 2012 and 2017 at Christchurch Hospital were retrospectively identified. The primary outcome was UR within 30 days after index discharge. Statistically significant risk factors were identified and incorporated into a predictive model. The model was then externally evaluated on a prospectively recruited dataset from 2018 to 2019. RESULTS: Of the 701 patients identified, 15.1% were readmitted within 30 days of discharge. Stoma formation (OR 2.45, 95% CI 1.59-3.81), any postoperative complications (PoCs) (OR 2.27, 95% CI 1.48-3.52), high-grade PoCs (OR 2.52, 95% CI 1.18-5.11), and rectal cancer (OR 2.11, 95% CI 1.48-3.52) were statistically significant risk factors for UR. A clinical prediction model comprised of rectal cancer and high-grade PoCs predicted UR with an AUC of 0.64 and 0.62 on internal and external validation, respectively. CONCLUSIONS: URs after CRC surgery are predictable and occur within 2 weeks of discharge. They are driven by PoCs, most of which are of low severity and develop after discharge. Atleast 16% of readmissions are preventable by management in an outpatient setting with appropriate surgical expertise. Targeted outpatient follow-up within two weeks of discharge is therefore the most effective transitional-care strategy for prevention.

Molecular 14 C evidence for contrasting turnover and temperature sensitivity of soil organic matter components.

Climate projection requires an accurate understanding for soil organic carbon (SOC) decomposition and its response to warming. An emergent view considers that environmental constraints rather than chemical structure alone control SOC turnover and its temperature sensitivity (i.e., Q10 ), but direct long-term evidence is lacking. Here, using compound-specific radiocarbon analysis of soil profiles along a 3300-km grassland transect, we provide direct evidence for the rapid turnover of lignin-derived phenols compared with slower-cycling molecular components of SOC (i.e., long-chain lipids and black carbon). Furthermore, in contrast to the slow-cycling components whose turnover is strongly modulated by mineral association and exhibits low Q10 , lignin turnover is mainly regulated by temperature and has a high Q10 . Such contrasts resemble those between fast-cycling (i.e., light) and mineral-associated slow-cycling fractions from globally distributed soils. Collectively, our results suggest that warming may greatly accelerate the decomposition of lignin, especially in soils with relatively weak mineral associations.

Retrospective cohort study of the impact of faecoliths on the natural history of acute appendicitis.

BACKGROUND: Despite acute appendicitis is one of the most common surgical emergencies, its aetiology remains incompletely understood. AIM: This study aimed to assess the rate at which faecoliths were present in acute appendicitis treated with appendicectomy and whether their presence was associated with complicated appendicitis. METHODS: All adult patients who underwent appendicectomy for acute appendicitis in a 2 years period (January 2018 and December 2019) at a single institution were retrospectively reviewed. The presence of a faecolith was identified by at least one of three methods: pre-operative CT scan, intraoperative identification, or histopathology report. Patients were grouped according to the presence or absence of a faecolith and demographics, type of appendicitis and surgical outcomes analysed. Complicated appendicitis was defined as appendicitis with perforation, gangrene and/or periappendicular abscess formation. RESULTS: A total of 1035 appendicectomies were performed with acute appendicitis confirmed in 860 (83%), of which 314 (37%) were classified as complicated appendicitis. Three hundred thirty-nine (35%) of the appendicitis cases had faecoliths (complicated 165/314 cases; 53%; uncomplicated 128/546; 23%, p < 0.001). The presence of a faecolith was associated with higher complications and a subsequent longer post-operative stay. CONCLUSION: The rigorous methodology of this study has demonstrated a higher rate of faecolith presence in acute appendicitis than previously documented. It reinforces the association of faecoliths with a complicated disease course and the importance in prioritising emergency surgery and postoperative monitoring for complications.

Aquatic biomass is a major source to particulate organic matter export in large Arctic rivers.

Arctic rivers provide an integrated signature of the changing landscape and transmit signals of change to the ocean. Here, we use a decade of particulate organic matter (POM) compositional data to deconvolute multiple allochthonous and autochthonous pan-Arctic and watershed-specific sources. Constraints from carbon-to-nitrogen ratios (C:N), δ13C, and Δ14C signatures reveal a large, hitherto overlooked contribution from aquatic biomass. Separation in Δ14C age is enhanced by splitting soil sources into shallow and deep pools (mean ± SD: -228 ± 211 vs. -492 ± 173‰) rather than traditional active layer and permafrost pools (-300 ± 236 vs. -441 ± 215‰) that do not represent permafrost-free Arctic regions. We estimate that 39 to 60% (5 to 95% credible interval) of the annual pan-Arctic POM flux (averaging 4,391 Gg/y particulate organic carbon from 2012 to 2019) comes from aquatic biomass. The remainder is sourced from yedoma, deep soils, shallow soils, petrogenic inputs, and fresh terrestrial production. Climate change-induced warming and increasing CO2 concentrations may enhance both soil destabilization and Arctic river aquatic biomass production, increasing fluxes of POM to the ocean. Younger, autochthonous, and older soil-derived POM likely have different destinies (preferential microbial uptake and processing vs. significant sediment burial, respectively). A small (~7%) increase in aquatic biomass POM flux with warming would be equivalent to a ~30% increase in deep soil POM flux. There is a clear need to better quantify how the balance of endmember fluxes may shift with different ramifications for different endmembers and how this will impact the Arctic system.

Vegetal Undercurrents-Obscured Riverine Dynamics of Plant Debris.

Much attention has been focused on fine-grained sediments carried as suspended load in rivers due to their potential to transport, disperse, and preserve organic carbon (OC), while the transfer and fate of OC associated with coarser-grained sediments in fluvial systems have been less extensively studied. Here, sedimentological, geochemical, and biomolecular characteristics of sediments from river depth profiles reveal distinct hydrodynamic behavior for different pools of OC within the Mackenzie River system. Higher radiocarbon (14C) contents, low N/OC ratios, and elevated plant-derived biomarker loadings suggest a systematic transport of submerged vascular plant debris above the active riverbed in large channels both upstream of and within the delta. Subzero temperatures hinder OC degradation promoting the accumulation and waterlogging of plant detritus within the watershed. Once entrained into a channel, sustained flow strength and buoyancy prevent plant debris from settling and keep it suspended in the water column above the riverbed. Helical flow motions within meandering river segments concentrate lithogenic and organic debris near the inner river bends forming a sediment-laden plume. Moving offshore, we observe a lack of discrete, particulate OC in continental shelf sediments, suggesting preferential trapping of coarse debris within deltaic and neritic environments. The delivery of waterlogged plant detritus transport and high sediment loads during the spring flood may reduce oxygen exposure times and microbial decomposition, leading to enhanced sequestration of biospheric OC. Undercurrents enriched in coarse, relatively fresh plant fragments appear to be reoccurring features, highlighting a poorly understood yet significant mechanism operating within the terrestrial carbon cycle.

Degradation and Aging of Terrestrial Organic Carbon within Estuaries: Biogeochemical and Environmental Implications.

Estuaries are action zones for organic carbon (OC) degradation and aging. These processes influence the nature of terrestrial OC (OCterr) export and the magnitude of OCterr burial in marginal seas, with important environmental implications such as CO2 release and hypoxia. In this study, we determined the contents and carbon isotopic compositions (13C and 14C) of bulk OC and fatty acids (FAs) as well as the sedimentological characteristics of suspended particulate matter (SPM) samples collected from two sites over four seasons and of surface sediment samples from three sites in the Pearl River estuary (PRE) to evaluate processes controlling OCterr degradation and aging along an estuarine gradient. We found that the abundance-weighted average C24-32FA 14C ages increased by an average of ∼1170 years for SPM and by an average of ∼3440 years in PR/PRE sediments, along the ∼60 km PRE transect. These increases in the FA age coincided with an 86% decrease in the corresponding mineral surface area-normalized FA loading along the sediment transport pathway, implying that selective degradation of labile and younger OC resulted in apparent OC aging. These measurements reveal an important shift in the nature of OC, with implications for biogeochemical cycling within estuaries and for regional environmental changes.

Climate control on terrestrial biospheric carbon turnover.

Terrestrial vegetation and soils hold three times more carbon than the atmosphere. Much debate concerns how anthropogenic activity will perturb these surface reservoirs, potentially exacerbating ongoing changes to the climate system. Uncertainties specifically persist in extrapolating point-source observations to ecosystem-scale budgets and fluxes, which require consideration of vertical and lateral processes on multiple temporal and spatial scales. To explore controls on organic carbon (OC) turnover at the river basin scale, we present radiocarbon (14C) ages on two groups of molecular tracers of plant-derived carbon-leaf-wax lipids and lignin phenols-from a globally distributed suite of rivers. We find significant negative relationships between the 14C age of these biomarkers and mean annual temperature and precipitation. Moreover, riverine biospheric-carbon ages scale proportionally with basin-wide soil carbon turnover times and soil 14C ages, implicating OC cycling within soils as a primary control on exported biomarker ages and revealing a broad distribution of soil OC reactivities. The ubiquitous occurrence of a long-lived soil OC pool suggests soil OC is globally vulnerable to perturbations by future temperature and precipitation increase. Scaling of riverine biospheric-carbon ages with soil OC turnover shows the former can constrain the sensitivity of carbon dynamics to environmental controls on broad spatial scales. Extracting this information from fluvially dominated sedimentary sequences may inform past variations in soil OC turnover in response to anthropogenic and/or climate perturbations. In turn, monitoring riverine OC composition may help detect future climate-change-induced perturbations of soil OC turnover and stocks.

Surgical outcomes following colorectal cancer resections in patients aged 80 years and over: results from the Australia and New Zealand Binational Colorectal Cancer Audit.

AIM: The primary aim was to compare the 30-day morbidity and mortality in patients aged ≥80 years undergoing surgery for colorectal cancer with those aged <80 years. The secondary aim was to identify independent outcome predictors. METHOD: This was a retrospective study of patients undergoing surgery for colorectal cancer between January 2007 and February 2018. Patients were divided into those <80 years and those ≥80 years at the time of surgery. Data had been collected prospectively by the Australasian Binational Colorectal Cancer Audit and included patient demographics, site and stage of tumour, comorbidity, operative details, American Society of Anesthesiologists score (ASA), pathological staging, 30-day mortality and morbidity (medical and surgical). Univariate and multivariate analyses were used to identify predictors of 30-day morbidity and mortality. RESULTS: During the study period, 4600 out of 20 463 (22.5%) patients were ≥80 years. They had a greater 30-day mortality after both colonic (97/2975 [3.3%] vs. 66/7010 [0.9%], P < 0.001) and rectal resections (50/1625 [3.1%] vs. 36/9006 [0.4%], P < 0.001) compared with younger patients. They also had an increased length of stay (colon cancer, 9 vs. 7 days; rectal cancer, 10 vs. 8 days; P < 0.001) and medical complications (colon cancer, 23.5% vs. 12.7%; rectal cancer, 25.2% vs. 11.2%; P < 0.001). Surgical complications were equivalent. Age ≥80 years was not an independent predictor of 30-day morbidity or mortality. Patients ≥80 years who were ASA 2/3 and had rectal cancer seemed to fare worse in terms of 30-day mortality (ASA 2, 22%, 95% CI 9%-36%, P < 0.001; ASA 3, 11%, 95% CI 4%-19%, P< 0.001). CONCLUSIONS: Postoperative morbidity and mortality are significantly greater in patients ≥80 years undergoing colorectal cancer surgery. Any recommendation for surgery in this age group should take into account patient comorbidity and not be based on age alone.

An Abrupt Aging of Dissolved Organic Carbon in Large Arctic Rivers.

Permafrost thaw in Arctic watersheds threatens to mobilize hitherto sequestered carbon. We examine the radiocarbon activity (F14C) of dissolved organic carbon (DOC) in the northern Mackenzie River basin. From 2003-2017, DOC-F14C signatures (1.00 ± 0.04; n = 39) tracked atmospheric 14CO2, indicating export of "modern" carbon. This trend was interrupted in June 2018 by the widespread release of aged DOC (0.85 ± 0.16, n = 28) measured across three separate catchment areas. Increased nitrate concentrations in June 2018 lead us to attribute this pulse of 14C-depleted DOC to mobilization of previously frozen soil organic matter. We propose export through lateral perennial thaw zones that occurred at the base of the active layer weakened by preceding warm summer and winter seasons. Although we are not yet able to ascertain the broader significance of this "anomalous" mobilization event, it highlights the potential for rapid and large-scale release of aged carbon from permafrost.

Nearshore Zone Dynamics Determine Pathway of Organic Carbon From Eroding Permafrost Coasts.

Collapse of permafrost coasts delivers large quantities of particulate organic carbon (POC) to Arctic coastal areas. With rapidly changing environmental conditions, sediment and organic carbon (OC) mobilization and transport pathways are also changing. Here, we assess the sources and sinks of POC in the highly dynamic nearshore zone of Herschel Island-Qikiqtaruk (Yukon, Canada). Our results show that POC concentrations sharply decrease, from 15.9 to 0.3 mg L-1, within the first 100-300 m offshore. Simultaneously, radiocarbon ages of POC drop from 16,400 to 3,600 14C years, indicating rapid settling of old permafrost POC to underlying sediments. This suggests that permafrost OC is, apart from a very narrow resuspension zone (<5 m water depth), predominantly deposited in nearshore sediments. While long-term storage of permafrost OC in marine sediments potentially limits biodegradation and its subsequent release as greenhouse gas, resuspension of fine-grained, OC-rich sediments in the nearshore zone potentially enhances OC turnover.

Particulate Organic Matter Dynamics in a Permafrost Headwater Stream and the Kolyma River Mainstem.

Ongoing rapid arctic warming leads to extensive permafrost thaw, which in turn increases the hydrologic connectivity of the landscape by opening up subsurface flow paths. Suspended particulate organic matter (POM) has proven useful to trace permafrost thaw signals in arctic rivers, which may experience higher organic matter loads in the future due to expansion and increasing intensity of thaw processes such as thermokarst and river bank erosion. Here we focus on the Kolyma River watershed in Northeast Siberia, the world's largest watershed entirely underlain by continuous permafrost. To evaluate and characterize the present-day fluvial release of POM from permafrost thaw, we collected water samples every 4-7 days during the 4-month open water season in 2013 and 2015 from the lower Kolyma River mainstem and from a small nearby headwater stream (Y3) draining an area completely underlain by Yedoma permafrost (Pleistocene ice- and organic-rich deposits). Concentrations of particulate organic carbon generally followed the hydrograph with the highest concentrations during the spring flood in late May/early June. For the Kolyma River, concentrations of dissolved organic carbon showed a similar behavior, in contrast to the headwater stream, where dissolved organic carbon values were generally higher and particulate organic carbon concentrations lower than for Kolyma. Carbon isotope analysis (δ13C, Δ14C) suggested Kolyma-POM to stem from both contemporary and older permafrost sources, while Y3-POM was more strongly influenced by in-stream production and recent vegetation. Lipid biomarker concentrations (high-molecular-weight n-alkanoic acids and n-alkanes) did not display clear seasonal patterns, yet implied Y3-POM to be more degraded than Kolyma-POM.

Surveillance for dysplasia in patients with inflammatory bowel disease: an updated national survey of colonoscopic practice in New Zealand.

BACKGROUND: Patients with inflammatory bowel disease (IBD) undergo surveillance for an increased risk of colorectal cancer. Advances in endoscopy have rendered most previously invisible dysplasia visible, leading to changes in guidelines around surveillance and management of dysplasia. This study aims to assess New Zealand endoscopists' (i) understanding of current guidelines, (ii) uptake of advanced techniques and (iii) management of dysplasia. METHODS: A digital survey of New Zealand endoscopists was undertaken. Invitations were sent to members of New Zealand gastroenterology and surgical societies. Questions were asked regarding demographics, surveillance interval, risk stratification, endoscopic technique and dysplasia management. RESULTS: Fifty of the 322 invitees completed the survey (15.5%). Over 80% used techniques meeting the guideline recommendations. The majority (77%) of endoscopists take random biopsies in addition to targeted. Endoscopically resectable polypoid low-grade dysplasia was typically managed with surveillance (93%) but this dropped to less than half for high-grade dysplasia and less than a third for non-polypoid high-grade dysplasia (inconsistent with guidelines). CONCLUSIONS: Current New Zealand endoscopists' practice appears to be aligned with international guidelines in terms of screening interval, risk stratification and technique. However, New Zealand endoscopists are less likely to offer a patient surveillance for endoscopically resectable dysplasia.