The basis for, and use of, fine grain size parameters for inference of paleoflow speeds is reviewed here. The basis resides in data on deposited sediment taken in conjunction with flow speed ...measurements in the field, experimental data on suspended sediment transport and deposition, and theoretical treatments of the generation of size distributions of deposits from suspension controlled by particle settling velocity and flow speed. In the deep sea, sorting events occur under resuspension/deposition events in benthic storms. At flow speeds below 10–15 cm s−1, size in the noncohesive “sortable silt” (10–63 μm) range is controlled by selective deposition, whereas above that range, removal of finer material by winnowing also plays a role. The best particle size instruments to measure a flow speed–related grain size employ the settling velocity method, while laser diffraction sizers can yield misleading results because of particle shape effects. Potential problems, including source effects, downslope supply on continental margins, spatial variability of flow over bedforms, and influence of ice‐rafted detritus, are examined. A number of studies using the sortable silt flow speed proxy are reviewed, and inverse modeling of grain size distributions is examined. Outstanding problems are that corroboration is sparse because almost no studies have yet used the full range of proxies for flow rate and water mass identification and that the sortable silt mean size is not yet properly calibrated in terms of flow speed.
Owing to the lack of absolutely dated oceanographic information before the modern instrumental period, there is currently significant debate as to the role played by North Atlantic Ocean dynamics in ...previous climate transitions (for example, Medieval Climate Anomaly-Little Ice Age, MCA-LIA). Here we present analyses of a millennial-length, annually resolved and absolutely dated marine δ
O archive. We interpret our record of oxygen isotope ratios from the shells of the long-lived marine bivalve Arctica islandica (δ
O-shell), from the North Icelandic shelf, in relation to seawater density variability and demonstrate that solar and volcanic forcing coupled with ocean circulation dynamics are key drivers of climate variability over the last millennium. During the pre-industrial period (AD 1000-1800) variability in the sub-polar North Atlantic leads changes in Northern Hemisphere surface air temperatures at multi-decadal timescales, indicating that North Atlantic Ocean dynamics played an active role in modulating the response of the atmosphere to solar and volcanic forcing.
Increased use of phosphorus (P) fertilizers and detergents and intensified livestock production have more than doubled P inputs to human‐impacted watersheds over pre‐industrial levels. While P ...fertilizer use and manure application help to maximize crop yields, excess P is lost to runoff, leading to eutrophication of downstream waters. Excess P also accumulates across the landscape, leading to legacies that serve as long‐term sources of P to surface waters, even after inputs to the watershed are reduced. Here, we have developed, for the first time, a process‐based model, Exploration of Long‐tErM Nutrient Trajectories‐Phosphorus, designed to capture legacy P accumulation and depletion trajectories along the land‐aquatic continuum. To drive the model, we have developed a more than 100‐year trajectory of watershed P inputs to the Grand River Watershed (GRW), Canada’s largest watershed draining directly to Lake Erie. Our results first show that net P inputs to the watershed approximately tripled between 1900 and the late‐1970s, when P surplus magnitudes peaked at approximately 15 kg ha−1 y−1. During this same period, stream P loads have increased more than fourfold, from 0.11 kg ha−1 y−1 in 1900 to 0.80 kg ha−1 y−1 in the 1970s. Since 1900, the GRW has served as a net P sink, with approximately 96% of net P inputs having been retained within the basin. Future simulations suggest that while 40% reductions in P loading in Lake Erie watersheds are possible under aggressive management scenarios, legacy P will continue to elevate P loads to Lake Erie for many decades to come.
Plain Language Summary
Phosphorus is a major driver of algal blooms and water quality challenges throughout the Great Lakes region. Excess phosphorus from crop and livestock production is a particular problem in agricultural areas, and much of the phosphorus applied to the landscape is accumulating as legacy within our watersheds. We have developed a model demonstrating that watershed phosphorus legacies continue to degrade water quality over many decades and can make it difficult to meet water quality goals. Our modeling results show that we must take legacy phosphorus into account when setting policy goals for water quality improvement. Our results also show that better manure management can provide relatively fast improvements and should therefore be emphasized when implementing conservation measures.
Key Points
More than 95% of surplus phosphorus has been retained within the watershed since 1900
Legacy phosphorus is a major contributor to current watershed phosphorus loads
Reducing manure handling losses can provide substantial reductions in watershed P loads
Synchronised reproduction offers clear benefits to planktonic foraminifera – an important group of marine calcifiers – as it increases the chances of successful gamete fusion. Such synchrony requires ...tuning to an internal or external clock. Evidence exists for lunar reproductive cycles in some species, but its recognition in shell flux time series has proven difficult, raising questions about reproductive strategies. Using spectral analysis of a 4-year time series (mostly at weekly resolution) from the northern Gulf of Mexico, we show that the shell flux of Globorotalia menardii, Globigerinella siphonifera, Orbulina universa, Globigerinoides sacculifer, Globigerinoides ruber (both pink and white varieties), Pulleniatina obliquiloculata, Neogloboquadrina dutertrei, Globigerinella calida and Globigerinita glutinata is characterised by lunar periodicity. However, the lunar rhythm is not present in all size fractions of each species and tends to be more dominant in the flux of larger shells, consistent with reproduction being more prevalent in larger specimens. Lunar periodicity is superimposed on longer term/seasonal changes in the shell fluxes, but accounts for a significant part of the variance in the fluxes. The amplitude of the lunar cycle increases roughly proportional with the magnitude of the flux, demonstrating that most of the population is indeed affected by lunar-phased synchronisation. In most species peak fluxes occur predominantly around, or just after, full moon. Only G. siphonifera and G. calida show a contrasting pattern with peaks concentrated around new moon. Although the exact cause of the synchronisation remains elusive, our data considerably increase the number of species for which lunar synchronised reproduction is reported and suggest that such reproductive behaviour is common in many species of planktonic foraminifera.
Simulations of 21st century climate change for Great Britain predict increased seasonal precipitation that may lead to widespread soil loss by increasing surface runoff. Land use and different ...vegetation cover can respond differently to this scenario, mitigating or enhancing soil erosion. Here, by means of a sensitivity analysis of the PESERA soil erosion model, we test the potential for climate and vegetation to impact soil loss by surface-runoff to three differentiated British catchments. First, to understand general behaviours, we modelled soil erosion adopting regular increments for rainfall and temperature from the baseline values (1961–1990). Then, we tested future climate scenarios adopting projections from UKCP09 (UK Climate Projections) under the IPCC (Intergovernmental Panel on Climate Change) on a defined medium CO2 emissions scenario, SRES-A1B (Nakicenovic et al., 2000), at the horizons 2010–39, 2040–69 and 2070–99. Our results indicate that the model reacts to the changes of the climatic parameters and the three catchments respond differently depending on their land use arrangement. Increases in rainfall produce a rise in soil erosion while higher temperatures tend to lower the process because of the mitigating action of the vegetation. Even under a significantly wetter climate, warmer air temperatures can limit soil erosion by enhancing primary productivity and in turn improving leaf interception, infiltration-capacity, and reducing soil erodibility. Consequently, for specific land uses, the increase in air temperature associated with climate change can modify the rainfall thresholds to generate soil loss, and soil erosion rates could decline by up to about 33% from 2070 to 2099. We deduce that enhanced primary productivity due to climate change can introduce a negative-feedback mechanism limiting soil loss by surface runoff as vegetation-induced impacts on soil hydrology and erodibility offset the effects of increased precipitation. The expansion of permanent vegetation cover could provide an adaptation strategy to reduce climate-driven soil loss.
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•Climate change impacts ecosystems with a repercussion on soil erosion.•We conducted a sensitivity analysis on the PESERA soil erosion model.•We focused on climate and vegetation in three UK catchments.•Vegetation productivity with temperature increases can reduce erosion up to −33%.•Crops can contribute to an increase in erosion of up to about 60.7% from 2070 to 2099.
Post-treatment detection of circulating tumour DNA (ctDNA) in early-stage triple-negative breast cancer (TNBC) patients predicts high risk of relapse. c-TRAK TN assessed the utility of prospective ...ctDNA surveillance in TNBC and the activity of pembrolizumab in patients with ctDNA detected ctDNA positive (ctDNA+).
c-TRAK TN, a multicentre phase II trial, with integrated prospective ctDNA surveillance by digital PCR, enrolled patients with early-stage TNBC and residual disease following neoadjuvant chemotherapy, or stage II/III with adjuvant chemotherapy. ctDNA surveillance comprised three-monthly blood sampling to 12 months (18 months if samples were missed due to coronavirus disease), and ctDNA+ patients were randomised 2 : 1 to intervention : observation. ctDNA results were blinded unless patients were allocated to intervention, when staging scans were done and those free of recurrence were offered pembrolizumab. A protocol amendment (16 September 2020) closed the observation group; all subsequent ctDNA+ patients were allocated to intervention. Co-primary endpoints were (i) ctDNA detection rate and (ii) sustained ctDNA clearance rate on pembrolizumab (NCT03145961).
Two hundred and eight patients registered between 30 January 2018 and 06 December 2019, 185 had tumour sequenced, 171 (92.4%) had trackable mutations, and 161 entered ctDNA surveillance. Rate of ctDNA detection by 12 months was 27.3% (44/161, 95% confidence interval 20.6% to 34.9%). Seven patients relapsed without prior ctDNA detection. Forty-five patients entered the therapeutic component (intervention n = 31; observation n = 14; one observation patient was re-allocated to intervention following protocol amendment). Of patients allocated to intervention, 72% (23/32) had metastases on staging at the time of ctDNA+, and 4 patients declined pembrolizumab. Of the five patients who commenced pembrolizumab, none achieved sustained ctDNA clearance.
c-TRAK TN is the first prospective study to assess whether ctDNA assays have clinical utility in guiding therapy in TNBC. Patients had a high rate of metastatic disease on ctDNA detection. Findings have implications for future trial design, emphasising the importance of commencing ctDNA testing early, with more sensitive and/or frequent ctDNA testing regimes.
•We report the first study to prospectively assess ctDNA for molecular residual disease (MRD) detection in breast cancer.•Implementation of MRD detection with personalised assays was clinically achievable.•The rapid relapsing nature of high-risk TNBC challenged implementation of MRD detection.•Treatment with pembrolizumab did not result in ctDNA clearance, although assessment was limited by small number of patients.•Recommendations for implementation of MRD detection in future studies are given.
Sea ice and associated feedback mechanisms play an important role for both long- and short-term climate change. Our ability to predict future sea ice extent, however, hinges on a greater ...understanding of past sea ice dynamics. Here we investigate sea ice changes in the eastern Bering Sea prior to, across, and after the Mid-Pleistocene transition (MPT). The sea ice record, based on the Arctic sea ice biomarker IP
and related open water proxies from the International Ocean Discovery Program Site U1343, shows a substantial increase in sea ice extent across the MPT. The occurrence of late-glacial/deglacial sea ice maxima are consistent with sea ice/land ice hysteresis and land-glacier retreat via the temperature-precipitation feedback. We also identify interactions of sea ice with phytoplankton growth and ocean circulation patterns, which have important implications for glacial North Pacific Intermediate Water formation and potentially North Pacific abyssal carbon storage.
Background: Rheumatoid arthritis (RA) is associated with increased cardiovascular mortality for reasons which are insufficiently understood. Chronic inflammation may impair vascular function and lead ...to an increase of arterial stiffness, an important determinant of cardiovascular risk. Objective: To investigate the augmentation index (AIx) as a measure of arterial stiffness in patients with RA, free of cardiovascular disease or risk factors, by means of a matched cohort pilot study. Method: Patients with a diagnosis of RA, aged 50 years or younger, were screened for the absence of clinical cardiovascular disease and risk factors, such as smoking, hypercholesterolaemia, hypertension, and excessive systemic steroid use. Suitable subjects were assessed by non-invasive radial pulse wave analysis to determine their AIx. These data were compared with those from healthy controls, matched closely for sex, age, mean peripheral blood pressure, heart rate, and height. Results: 14 suitable patients (11 female; mean (SD) age 42 (6) years, mean RA duration 11 (6) years; mean C reactive protein 19 (15) mg/l, no clinical systemic rheumatoid vasculitis) and matched controls were identified. The RA group had a higher mean (SD) AIx and mean (SD) central blood pressure (BP) than the control group: AIx 26.2 (6.7) v 18.9 (10.8)%, p=0.028; mean central BP 91.3 (7.8) v 88.2 (8.9) mm Hg, p<0.0001, by two tailed, paired t test. Conclusions: This preliminary study suggests that RA is associated with increased arterial stiffness and central BP, independently of clinically manifest cardiovascular disease or risk factors. This may contribute to the increased cardiovascular mortality in RA.
A decadal resolution time series of sea surface temperature (SST) spanning the last two millennia is reconstructed by combining a proxy record from a new sediment sequence with previously published ...data from core MD99–2275, north of Iceland. The alkenone based SST reconstruction is validated with historic observational data and compared to a new similar temporal resolution reconstruction obtained from sediment core RAPiD21–3K, in the subpolar North Atlantic. The two SST paleorecords show consistent multidecadal scale coolings throughout the interval and similar expressions during the contrasted climatic periods ‘colloquially known’ as the Medieval Climatic Anomaly (MCA) and Little Ice Age (LIA). In order to further understand the temporal and spatial SST variations and investigate the influence of natural forcings on the observed SST changes during the last millennium, we compare our time series to simulations using the Institut Pierre‐Simon Laplace IPSLCM4‐v2 climate model. This comparison highlights the potential importance of volcanism as a natural forcing driving coherent abrupt cooling events captured in the subpolar North Atlantic records.
Key Points
Comparative analysis of marine paleo proxy data to simulation of the last 1000 years
The impact of volcanism on ocean variability
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