A highly miniaturized electron and ion energy spectrometer prototype for the rapid analysis of space plasmas.

MEMS (Micro Electro-Mechanical Systems) plasma analyzers are a promising possibility for future space missions but conventional instrument designs are not necessarily well suited to micro-fabrication. Here, a candidate design for a MEMS-based instrument has been prototyped using electron-discharge machining. The device features 10 electrostatic analyzers that, with a single voltage applied to it, allow five different energies of electron and five different energies of positive ion to be simultaneously sampled. It has been simulated using SIMION and the electron response characteristics tested in an instrument calibration chamber. Small deviations found in the electrode spacing of the as-built prototype were found to have some effect on the electron response characteristics but do not significantly impede its performance

A prototype Cylindrical And Tiny Spectrometer for the rapid energy analysis of space plasmas

Miniaturised space plasma analysers allow for lower cost plasma measurements for space science and for space weather monitoring applications; further miniaturisation will make possible nanosat-scale plasma instruments. Small instruments produced in large numbers are ideal for very-large-scale swarm and constellation missions. The field of MEMS (micro-electro-mechanical systems) potentially enables all these possibilities. This thesis introduces these themes and describes the conception and development of CATS (Cylindrical And Tiny Spectrometer), an instrument designed with MEMS in mind. CATS uses an innovative, highly-miniaturised, concentric cylindrical geometry that is able to measure simultaneously, multiple energies of both electrons and ions in space plasmas. A prototype of a CATS analyser head has been fabricated – the critical electrodes by electron discharge machining – and has been demonstrated with 30 eV to 8 keV electrons in a laboratory environment. A CEM (channel electron multiplier) and a CCD (charge coupled device) have been adapted for use with the prototype. The CCD is a back-illuminated, ion-implanted device that has been used to detect electrons directly—the first known use of such a device in an analyser instrument. The prototype design has also been extensively modelled using SIMION charged particle ray-tracing simulations, run within a tool-kit of specially created and highly sophisticated IDL automation and analysis routines. This has revealed the focussing properties of the design and options for improvements. The experimental results were compared with the simulation results and discrepancies were revealed that suggested deviations from the design specification. These deviations were confirmed, in part, by a visual inspection. Recommendations for future work and possible applications of the instrument are discussed, including the destination of the current CATS prototype and CCD detector: PoleCATS, a student-led, educational project to develop a low-altitude sounding rocket instrument

Using a CCD for the direct detection of electrons in a low energy space plasma spectrometer

An E2V CCD64 back-illuminated, ion-implanted CCD (charge-coupled device) has been used as a direct electron imaging detector with CATS (Conceptual And Tiny Spectrometer), a highly miniaturised prototype plasma analyser head. This is in place of an MCP (microchannel plate) with a position sensing anode which would more conventionally be used as a detector in traditional low energy space plasma analyser instruments. The small size of CATS however makes it well matched to the size of the CCD, and the ion implants reduce the depth of the CCD backside electron potential well making it more sensitive to lower energy electrons than standard untreated silicon. Despite ionisation damage from prolonged exposure to excessively energetic electrons, the CCD has been able to detect electrons with energies above 500eV, at temperatures around room temperature. Using both a long integration 'current measuring' mode and a short integration `electron counting' mode it has been used to image the low energy electrons exiting the analyser, enhancing our understanding of the CATS electrostatic optics. The CCD has been selected as the detector for use with CATS for an instrument on a low-altitude student sounding rocket flight. Although it cannot detect the lowest energy electrons that an MCP can detect, and it is more sensitive to stray light, the low voltages required, the lack of vacuum requirements and its novelty and availability made it the most attractive candidate detector

A miniaturised, nested-cylindrical electrostatic analyser geometry for dual electron and ion, multi-energy measurements

The CATS (Cylindrical And Tiny Spectrometer) electrostatic optics geom- etry features multiple nested cylindrical analysers to simultaneously measure multiple energies of electron and multiple energies of ion in a conguration that is targeted at miniaturisation and MEMS fabrication. In the prototyped model, two congurations of cylindrical analyser were used, featuring terminating side- plates that caused particle trajectories to either converge (C type) or diverge (D type) in the axial direction. Simulations show how these dierent electrode congurations aect the particle focussing and instrument parameters; C-type providing greater throughputs but D-type providing higher resolving powers. The simulations were additionally used to investigate unexpected plate spacing variations in the as-built model, revealing that the K-factors are most sensitive to the width of the inter-electrode spacing at its narrowest point

Optimising environmental monitoring for carbon dioxide sequestered offshore

Carbon Capture and Storage (CCS) provides a mechanism by which CO2 can be removed from the atmosphere and stored in reservoirs. Regulations and stakeholder assurance require monitoring to show storage is robust. The marine environment is heterogeneous and dynamic, and baselines are extremely variable. Hence, distinguishing anomalous CO2 from natural variability is challenging. Monitoring schemes must be designed to identify releases early and with certainty, whilst being cost effective. A key question is how to deploy the smallest number of sensors to ensure effective monitoring? We approached this problem through a 3D hydrodynamic model (FVCOM) coupled to a carbonate system. The unstructured grid resolution ranges from 0.5 km to 3 m and simulates seabed release scenarios ranging from 3 t d−1 to 300 t d−1 using the Goldeneye complex as an exemplar test bed. This configuration allows us to characterise and analyse the fate of CO2 in the water column, with the spatial and temporal CO2 patterns shown to be affected by both tides and seasonal mixing/stratification. A weighted greedy set algorithm is used to identify the positions within the model domain which yield the greatest combined coverage for the smallest number of sampling stations, further limited by selecting only a feasible number of sample sites. The weighted greedy set algorithm incorporates the effect of the variable grid spacing as well as the proximity of the sample locations to the Goldeneye complex. The weighted greedy set can identify releases sooner, with a stronger signal than a regular sampling approach

Enhanced river runoff and permafrost thaw affect Arctic shelf processes

Enhanced river runoff and coastal erosion are causing greater amounts of terrestrial material supply to Arctic shelf waters. Increasing freshwater export of carbon and nutrient loads from land (terr-OM) together with compositional shifts - due to changing hydrologic flow paths and permafrost thaw, can modify shelf water chemistry and biogeochemical processes. Here, we examine how shifts in land-ocean terr-OM supply may alter shelf primary productivity, respiration and ultimately net regional CO2 air–sea fluxes. Unique insights into terr-OM dynamics and composition during transit through riverine, deltaic and shelf waters were collected through multiple field campaigns on the Lena River and Laptev Sea shelf region. Harnessing these field data, we examine the effects of contemporary and future terr-OM supply to shelf waters using newly developed 1-D and 3-D regional biogeochemical models specifically capable of parameterising terr-OM, composition and degradation. In agreement with prior studies, we find that land-derived nutrients could strengthen coastal production sustaining up to ~50% of primary productivity under current terr-OM conditions. However, we also found that additional terr-OM supply caused increased light limitation in coastal waters, offsetting nutrient fertilization effects and stimulating zooplankton grazing. Model experiments indicate that future increases in terr-OM of between 25-50% and/ or shifts to more biologically reactive coastal OM -such as to be expected with permafrost thaw, will reduce net CO2 uptake and lead to positive CO2 feedback from Arctic shelf waters. Our results question the capacity of the coastal Arctic Ocean to serve as a net sink for atmospheric CO2 with future increasing land-ocean connectivity and terr-OM supply

Identifying and protecting macroalgae detritus sinks toward climate change mitigation

Harnessing natural solutions to mitigate climate change requires an understanding of carbon 18 fixation, flux and sequestration across ocean habitats. Recent studies suggest that exported 19 seaweed particulate organic carbon is stored within soft sediment systems. However, very 20 little is known about how seaweed detritus disperses from coastlines, or where it may enter 21 seabed carbon stores, where it could become the target of conservation efforts. Here, focusing 22 on regionally dominant seaweed species, we surveyed environmental DNA (eDNA) of 23 natural coastal sediments, and studied their connectivity to seaweed habitats using a particle 24 tracking model parameterized to reproduce seaweed detritus dispersal behavior based on 25 laboratory observation of seaweed fragment degradation and sinking. Experiments showed Page 1 of 42 Ecological Applications Article 2 26 seaweed detritus density changing over time, differently across species. This, in turn, 27 modified distances travelled by released fragments until they reached the seabed for the first 28 time, during model simulations. Dispersal pathways connected detritus from the shore to the 29 open ocean but, importantly, also to coastal sediments, and this was reflected by field eDNA 30 evidence. Dispersion pathways were also affected by hydrodynamic conditions, varying in 31 space and time. Both the properties and timing of released detritus, individual to each 32 macroalgal population, and short-term near-seabed and medium-term water-column transport 33 pathways, are thus seemingly important in determining the connectivity between seaweed 34 habitats and potential sedimentary sinks. Studies such as this one, supported by further field 35 verification of sedimentary carbon sequestration rates and source partitioning, are still needed 36 to help quantify the role of seaweed in the ocean carbon cycle. Such studies will provide vital 37 evidence to inform on the potential need to develop blue carbon conservation mechanisms, 38 beyond wetlands

Tidal mixing of estuarine and coastal waters in the western English Channel is a control on spatial and temporal variability in seawater CO<sub>2</sub>

Surface ocean carbon dioxide (CO2) measurements are used to compute the oceanic air–sea CO2 flux. The CO2 flux component from rivers and estuaries is uncertain due to the high spatial and seasonal heterogeneity of CO2 in coastal waters. Existing high-quality CO2 instrumentation predominantly utilises showerhead and percolating style equilibrators optimised for open-ocean observations. The intervals between measurements made with such instrumentation make it difficult to resolve the fine-scale spatial variability of surface water CO2 at timescales relevant to the high frequency variability in estuarine and coastal environments. Here we present a novel dataset with unprecedented frequency and spatial resolution transects made at the Western Channel Observatory in the south-west of the UK from June to September 2016, using a fast-response seawater CO2 system. Novel observations were made along the estuarine– coastal continuum at different stages of the tide and reveal distinct spatial patterns in the surface water CO2 fugacity (fCO2) at different stages of the tidal cycle. Changes in salinity and fCO2 were closely correlated at all stages of the tidal cycle and suggest that the mixing of oceanic and riverine endmembers partially determines the variations in fCO2. The correlation between salinity and fCO2 was different in Cawsand Bay, which could be due to enhanced gas exchange or to enhanced biological activity in the region. The observations demonstrate the complex dynamics determining spatial and temporal patterns of salinity and fCO2 in the region. Spatial variations in observed surface salinity were used to validate the output of a regional high-resolution hydrodynamic model. The model enables a novel estimate of the air–sea CO2 flux in the estuarine–coastal zone. Air–sea CO2 flux variability in the estuarine–coastal boundary region is influenced by the state of the tide because of strong CO2 outgassing from the river plume. The observations and model output demonstrate that undersampling the complex tidal and mixing processes characteristic of estuarine and coastal environment biases quantification of air–sea CO2 fluxes in coastal waters. The results provide a mechanism to support critical national and regional policy implementation by reducing uncertainty in carbon budgets