Approximately half of the freshwater discharged from the Greenland and Antarctic Ice Sheets enters the ocean subsurface as a result of basal ice melt, or runoff draining via the grounding line of a ...deep ice shelf or marine-terminating glacier. Around Antarctica and parts of northern Greenland, this freshwater then experiences prolonged residence times in large cavities beneath floating ice tongues. Due to the inaccessibility of these cavities, it is unclear how they moderate the freshwater associated supply of nutrients such as iron (Fe) to the ocean. Here, we show that subglacial dissolved Fe export from Nioghalvfjerdsbrae (the '79°N Glacier') is decoupled from particulate inputs including freshwater Fe supply, likely due to the prolonged ~162-day residence time of Atlantic water beneath Greenland's largest floating ice-tongue. Our findings indicate that the overturning rate and particle-dissolved phase exchanges in ice cavities exert a dominant control on subglacial nutrient supply to shelf regions.
The Arctic region is undergoing significant changes in climate, with a notable decrease in summertime sea ice coverage over the past three decades. This trend means an increasing proportion of Arctic ...Ocean surface waters can receive direct deposition of material from the atmosphere, potentially influencing marine biogeochemical cycles and delivery of pollutants to the Arctic ecosystem. Here, we present aerosol concentrations of selected trace elements (Al, Ti, V, Mn, Fe, Co, Ni, Cu, Zn, Cd, and Pb) measured during the US GEOTRACES Western Arctic cruise (GN01, also known as HLY1502) in August–October 2015. Concentrations of “lithogenic” elements (Al, Ti, V, Mn, Fe, and Co) were similar to those measured in remote and predominantly marine-influenced air masses in previous studies, reflecting the remoteness of the Arctic Ocean from major dust sources. Concentrations of Ni, Cu, Zn, Pb, and Cd showed significant enrichments over crustal values, and were often of similar magnitude to concentrations measured over the North Atlantic in air masses of North American or European provenance. We use 7Be inventory and flux data from GN01 to estimate a bulk atmospheric deposition velocity during the study period, and combine it with our aerosol concentrations to calculate atmospheric deposition fluxes of the trace elements in the Arctic region during late summer. The resulting estimates for mineral dust and Fe deposition fall at the low end of global estimates and confirm the Arctic Ocean as a low-dust environment during the summer months.
This article is part of a special issue entitled: Conway GEOTRACES - edited by Tim M. Conway, Tristan Horner, Yves Plancherel, and Aridane G. González.
•We report bulk aerosol concentrations of multiple trace elements from the western Arctic Ocean during summer 2015.•Deposition fluxes are calculated using a bulk deposition velocity calculated from aerosol and snow 7Be data.•Summertime atmospheric deposition fluxes of mineral dust and Fe to the Arctic are low relative to other oceanic regions.
Glacier meltwater supplies silicon (Si) and iron (Fe) sourced from weathered bedrock to downstream ecosystems. However, the extent to which these nutrients reach the ocean is regulated by the nature ...of the benthic cycling of dissolved Si and Fe within fjord systems, given the rapid deposition of reactive particulate fractions at fjord heads. Here, we examine the benthic cycling of the two nutrients at four Patagonian fjord heads through geochemical analyses of sediment pore waters, including Si and Fe isotopes (δ30Si and δ56Fe), and reaction‐transport modeling for Si. A high diffusive flux of dissolved Fe from the fjord sediments (up to 0.02 mmol m−2 day−1) compared to open ocean sediments (typically <0.001 mmol m−2 day−1) is supported by both reductive and non‐reductive dissolution of glacially‐sourced reactive Fe phases, as reflected by the range of pore water δ56Fe (−2.7 to +0.8‰). In contrast, the diffusive flux of dissolved Si from the fjord sediments (0.02–0.05 mmol m−2 day−1) is relatively low (typical ocean values are >0.1 mmol m−2 day−1). High pore water δ30Si (up to +3.3‰) observed near the Fe(II)‐Fe(III) redox boundary is likely associated with the removal of dissolved Si by Fe(III) mineral phases, which, together with high sedimentation rates, contribute to the low diffusive flux of Si at the sampled sites. Our results suggest that early diagenesis promotes the release of dissolved Fe, yet suppresses the release of dissolved Si at glaciated fjord heads, which has significant implications for understanding the downstream transport of these nutrients along fjord systems.
Plain Language Summary
Through physical grinding and chemical reactions, glaciers are capable of releasing nutrients such as silicon and iron from the underlying rocks. In particular, there is a growing interest in the supply of these glacier‐sourced nutrients to sustain the growth of marine life in high‐latitude estuaries (fjords) and the adjacent coastal ocean. However, a substantial portion of the glacier‐sourced nutrients may be removed by rapid settling of debris (sediments) at the heads of these fjords, before they can be used by marine life. This study analyzes the chemistry of fluids within sediments collected from Patagonian fjord near river and glacial inputs to investigate the fate of glacier‐sourced nutrients (silicon and iron) that have been transferred to the fjord floor. Our laboratory analysis and calculations reveal that biological, chemical and geological processes in these sediments release significant amounts of iron back into the overlying fjord waters, but these high levels of iron chemically bind silicon, restricting its release into fjord waters. The disproportionate release of the two nutrients from fjord sediments found in this study advances our understanding of the modes of supply of glacier‐sourced nutrients to fjords and the coastal ocean.
Schematic shows the coupling of benthic Fe and Si cycling, and the inferred spatial difference in the supply of easily reducible Fe (oxy‐)hydroxides and the intensity of pore water advection between the fjord sites. Adsorption of Si onto Fe (oxy‐)hydroxides and co‐precipitation of amorphous Fe‐Si phases occur under relatively oxic conditions in the upper sediments, while Si is released back to solution following the reductive dissolution of Fe in the ferruginous zone. Circles with brighter colors and solid outlines represent solid‐bound Si and Fe(III) phases, while circles with lighter colors and dashed outlines represent dissolved Si and Fe2+ phases.
Iron (Fe), used as a cofactor in nitrogen fixation and photosynthesis by oceanic microorganisms, has extremely low dissolved concentrations in the surface ocean, leading to widespread limitation of ...phytoplankton growth. Dissolved Fe isotope ratios (δ56Fe) have been shown to be useful in helping to quantify the sources and cycling of Fe in the oceans if Fe source signatures and fractionation processes are well understood. Here, this thesis presents data from GEOTRACES section GA10W, and investigate the isotopic signature of sediment-derived dissolved Fe from the South Atlantic margins. My results show that there are both shallow (δ56Fe of -0.2‰) and deep inputs (δ56Fe of -0.7‰) of dissolved Fe to the water column from sediments on the South American margin. Using a two-component mixing model, the data show that non-reductive sediment dissolution dominates surface inputs of Fe at shelf stations, while reductive release is more important at slope depths (~1250 m). This pattern appears to be driven by the sediment grain size and porosity rather than dissolved oxygen. Near the Uruguayan margin, the influence of a low- salinity plume from the Río de la Plata coincides with a large range in δ56Fe (-1.7 to +0.4‰), highlighting the complexities of Fe cycling in estuarine environments. Farther offshore, from 45°W to 25°W, average surface ocean δ56Fe signatures of +0.1‰ indicate that Fe derived from non-reductive sediment dissolution dominates Fe supply to the western South Atlantic. Farther east, from 20°W to 10°E, heavy δ56Fe in surface waters are linked to in situ surface processes occurring in the Fe-limited waters of the Southern Ocean. Sediment-derived Fe (δ56Fe of -0.5‰) is also observed near the South African margin, but it is not transported far from the shelf. Overall, my results demonstrate the importance of understanding both endmember δ56Fe signatures and in situ processes in order to use δ56Fe to quantify the sources and long-range transport of dissolved Fe.
If there is a genetic predisposition to excessive bleeding, there should be an association in excessive blood loss between multiple cardiac surgeries. We retrospectively determined in 174 patients ...the association of excessive bleeding between 2 cardiac surgeries with cardiopulmonary bypass between January 19, 1990 and June 25, 2002. Excessive bleeding was defined by 2 criteria: (a) postoperating room chest tube blood loss over 24 h more than or equal to 750 mL (chest tube drainage CTD > or = 750) and (b) transfusion of any non-red blood cell (RBC) blood products. Logistic regression was used to estimate the association between excessive bleeding at the first and second cardiac procedures. The logistic regression models for CTD > or = 750 in the second surgery determined that CTD > or = 750 in the first surgery compared to CTD < 750 had an unadjusted odds ratio of 2.18 (P = 0.03) and an odds ratio of 2.42 (P = 0.03) when adjusted for age, sex, body surface area, preoperative anticoagulant use, cardiopulmonary bypass duration, and procedure type at second surgery. The logistic regression model for any non-RBC use in the second surgery determined that any non-RBC use in the first surgery compared with no non-RBC use had an unadjusted odds ratio of 2.32 (P = 0.02) and an odds ratio of 2.55 (P = 0.02) when adjusted for age, sex, body surface area, preoperative anticoagulant use, cardiopulmonary bypass duration, and procedure type at second surgery. We conclude that a history of excessive bleeding during the first operation is associated with more than two times increased risk for excessive bleeding in the second surgery.
Critical illness often leads to persistent functional impairment among older Intensive Care Unit (ICU) survivors. Identification of high-risk survivors prior to discharge from their ICU ...hospitalization can facilitate targeting for restorative interventions after discharge, potentially improving the likelihood of functional recovery. Our objective was to develop and validate a prediction model for persistent functional impairment among older adults in the year after an ICU hospitalization.
The analytic sample included community-living participants enrolled in the National Health and Aging Trends Study 2011 cohort who survived an ICU hospitalization through December 2017 and had a follow-up interview within 1 year. Persistent functional impairment was defined as failure to recover to the pre-ICU level of function within 12 months of discharge from an ICU hospitalization. We used Bayesian model averaging to identify the final predictors from a comprehensive set of 17 factors. Discrimination and calibration were assessed using area-under-the-curve (AUC) and calibration plots.
The development cohort included 456 ICU admissions (2,654,685 survey-weighted admissions) and the validation cohort included 227 ICU admissions (1,350,082 survey-weighted admissions). In the development cohort, the median age was 81.0 years (interquartile range IQR 76.0, 86.0) and 231 (50.7%) participants were women; demographic characteristics were comparable in the validation cohort. The rates of persistent functional impairment were 49.3% (development) and 50.2% (validation). The final model included age, pre-ICU disability, probable dementia, frailty, prior hospitalizations, vision impairment, depressive symptoms, and hospital length of stay. The model demonstrated good discrimination (AUC 71%, 95% confidence interval CI 0.66-0.76) and good calibration. When applied to the validation cohort, the model demonstrated comparable discrimination (AUC 72%, 95% CI 0.66-0.78) and good calibration.
Application of the model prior to discharge from an ICU hospitalization may identify older adults at the highest risk of persistent functional impairment in the subsequent year, thereby facilitating targeted interventions and follow-up.
The objective of this study was to estimate the incidence and cumulative risk of major surgery in older persons over a 5-year period and evaluate how these estimates differ according to key ...demographic and geriatric characteristics.
As the population of the United States ages, there is considerable interest in ensuring safe, high-quality surgical care for older persons. Yet, valid, generalizable data on the occurrence of major surgery in the geriatric population are sparse.
We evaluated data from a prospective longitudinal study of 5571 community-living fee-for-service Medicare beneficiaries, aged 65 or older, from the National Health and Aging Trends Study from 2011 to 2016. Major surgeries were identified through linkages with Centers for Medicare and Medicaid Services data. Population-based incidence and cumulative risk estimates incorporated National Health and Aging Trends Study analytic sampling weights and cluster and strata variables.
The nationally representative incidence of major surgery per 100 person-years was 8.8, with estimates of 5.2 and 3.7 for elective and nonelec-tive surgeries. The adjusted incidence of major surgery peaked at 10.8 in persons 75 to 79 years, increased from 6.6 in the non-frail group to 10.3 in the frail group, and was similar by sex and dementia. The 5-year cumulative risk of major surgery was 13.8%, representing nearly 5 million unique older persons, including 12.1% in persons 85 to 89 years, 9.1% in those ≥90 years, 12.1% in those with frailty, and 12.4% in those with probable dementia.
Major surgery is a common event in the lives of community-living older persons, including high-risk vulnerable subgroups.
Metabolic diseases are often associated with muscle atrophy and heightened inflammation. The whey bioactive compound, glycomacropeptide (GMP), has been shown to exhibit anti-inflammatory properties ...and therefore may have potential therapeutic efficacy in conditions of skeletal muscle inflammation and atrophy.
The purpose of this study was to determine the role of GMP in preventing lipotoxicity-induced myotube atrophy and inflammation.
C2C12 myoblasts were differentiated to determine the effect of GMP on atrophy and inflammation and to explore its mechanism of action in evaluating various anabolic and catabolic cellular signaling nodes. We also used a lipidomic analysis to evaluate muscle sphingolipid accumulation with the various treatments. Palmitate (0.75 mM) in the presence and absence of GMP (5 μg/mL) was used to induce myotube atrophy and inflammation and cells were collected over a time course of 6–24 h.
After 24 h of treatment, GMP prevented the palmitate-induced decrease in the myotube area and myogenic index and the increase in the TLR4-mediated inflammatory genes tumor necrosis factor-α and interleukin 1β. Moreover, phosphorylation of Erk1/2, and gene expression of myostatin, and the E3 ubiquitin ligases, FBXO32, and MuRF1 were decreased with GMP treatment. GMP did not alter palmitate-induced ceramide or diacylglycerol accumulation, muscle insulin resistance, or protein synthesis.
In summary, GMP prevented palmitate-induced inflammation and atrophy in C2C12 myotubes. The GMP protective mechanism of action in muscle cells during lipotoxic stress may be related to targeting catabolic signaling associated with cellular stress and proteolysis but not protein synthesis.
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