Advective Loss Research Articles

The Application of a Non-Intrusive Methodology to Estimate Particle Egress Rate and Advective Heat Losses of a Falling Particle Receiver During On-Sun Tests

Abstract The direct measurement of particle temperatures and advective losses from solid particle receiver has been a topic of necessary interest to de-risk the technology and improve its performance. Due to the flow's transient and stochastic nature, it has presented a challenge to traditional thermometry and metrology methods. In this work, a simplified quantitative non-intrusive imaging methodology previously developed is applied to Sandia's falling particle receiver during on-sun tests to collect image sets, which could help estimate the average particle temperature and particle egress rate from the system. Further additions to the technique are presented to permit the estimation of the plume (air and particles) egress rate and total advective heat losses during on-sun operation. The falling particle receiver testing campaign in 2020 and 2021 allowed the team to capture multiple flow configurations and environmental conditions used to build a large database of data captures with different characteristics. Finally, the results captured were used to complete a regression study to gain further insight into the factors which impact the particle egress and the receiver's efficiency. Particle temperature, receiver flow configuration, and wind speed were found to be the most impactful factors in the study.

Evaluation of the environmental exposure risks of pesticides used in vegetable production in Türkiye

In this study, first, a list of pesticides that can potentially pose environmental exposure risks was compiled by analyzing the recent literature on residue levels in fresh vegetables produced in Türkiye. Then, by using the fundamental environmental partitioning properties of these pesticides, their potential multi-media environmental distributions were assessed. Acetamiprid, chlorpyrifos, and pyridaben were among the pesticides that frequently exceeded the residual limit values. Multi-media environmental modeling was conducted for these three pesticides using an evaluative four-compartment (air, soil, water, sediment) model. Compartmental distributions, inter-compartmental mass transfer rates, advective, and reactive losses were estimated for the selected pesticides after their simulated application to soil. The ranking of overall persistence among the pesticides was found to be pyridaben > chlorpyrifos > acetamiprid. The percentage mass distribution of acetamiprid in water was higher due to its low volatility and high solubility. The overall persistence of chlorpyrifos was limited by its higher partitioning to air although it is more persistent than pyridaben in other compartments. To investigate the residue dynamics of the three pesticides in tomato crops, temporal changes in harvest fractions were compared using the regression equations of the crop model dynamiCROP. Acetamiprid was estimated to be taken up at higher rates in tomatoes after initial application. The residue dynamics of chlorpyrifos and pyridaben were found to be similar. The quantitative methods in this study can be used to assess the environmental risks associated with commonly used pesticides in Türkiye and to address the issue of exceeding residue limits in agricultural products.

Design Optimization of a Horizontal Particle Receiver for a Modular Beam Down Receiver CSP

CSP research is focused on increasing the economic competitiveness of this technology as compared to conventional and emerging energy generators. Higher temperature operation conditions represent a pathway toward cost reductions since they enable a relatively smaller solar field area (typically ~40-50% of the plant cost) for the same electrical output. For example, supercritical CO2 power cycles with solid particles as the HTF could enable >600°C operations and a ~50% power bloc cycle efficiency (considerably higher than steam cycles, <40%). Additionally, small modular systems could increase competitiveness through reduced financial risk, increased system flexibility, and the value of additional services that a modular CSP could offer to the electricity grid (frequency control, peaking supply, etc.). This study investigates the Beam Down Receiver (BDR) configuration as a design that could be well-suited to meet these goals while also overcoming some of issues with particle receivers, such as particle attrition, advective losses, and operation control. In particular, this work introduces a novel horizontal particle receiver (HPR) and analyzes the main design parameters, including tower height, BDR size, radiation flux on the receiver, and receiver nominal power. The analysis shows that tower heights between 35m to 60m are ideal for high temperature receiver capacities of 8-15 MWth, and that this configuration can achieve a minimized LCOH of ~24 USD/MWth. These results suggest that BDRs combined with particle mediums could represent a viable high temperature, high efficiency CSP alternative.

A Temporal Downscaling Model for Gridded Geophysical Data with Enhanced Residual U-Net

Temporal downscaling of gridded geophysical data is essential for improving climate models, weather forecasting, and environmental assessments. However, existing methods often cannot accurately capture multi-scale temporal features, affecting their accuracy and reliability. To address this issue, we introduce an Enhanced Residual U-Net architecture for temporal downscaling. The architecture, which incorporates residual blocks, allows for deeper network structures without the risk of overfitting or vanishing gradients, thus capturing more complex temporal dependencies. The U-Net design inherently can capture multi-scale features, making it ideal for simulating various temporal dynamics. Moreover, we implement a flow regularization technique with advection loss to ensure that the model adheres to physical laws governing geophysical fields. Our experimental results across various variables within the ERA5 dataset demonstrate an improvement in downscaling accuracy, outperforming other methods.

Analysis of the absorptance and emittance in particle curtains by means of a discrete MCRT method

Apparent optical properties, absorptance and emittance, in particle curtains are analyzed by means of a discrete Monte Carlo Ray-Tracing model. The effect of solid volume fraction, particle diameter and curtain thickness on these properties is investigated for two types of particles with different absorptivity and emissivity: sand and CARBO HSP. Absorptance and emittance achieved by curtains made of these particles are greater than the values of absorptivity and emissivity of material. The increase in curtain absorptance/emittance compared to the particle absorptivity/emissivity is higher as the particle property is poorer, such as in sand. Both absorptance and emittance are maximum for opaque curtains, which entails high thicknesses. Assuming opaque curtains, the absorptance and emittance increase as the solid volume fraction decreases. The results obtained with the Monte Carlo Ray-Tracing model are used to estimate particle curtain radiative losses including emission and reflection losses. If material properties absorptivity and emissivity are used instead of the obtained curtain properties absorptance and emittance, sand curtain losses are up to 35 pp and only 9 pp in the case of CARBO HSP. Absorptivity is more important than emissivity, that is, it is preferable having high absorptivity than low emissivity to achieve low radiative losses. Emission losses are less important than reflected losses being very similar in both types of curtains. Sand curtains lose 33% of the incoming power while CARBO curtains lose only 7%. Radiative losses are significantly higher than advection losses in sand curtains. However, in CARBO curtains, advection losses are higher.

Fusion Gain and Triple Product for the Sheared-Flow-Stabilized Z Pinch

Fusion gain Q and triple product nTτ are derived for the sheared-flow-stabilized (SFS) Z pinch by including the input power associated with driving the plasma flow and the additional advective loss of thermal energy. Plasma impurities contribute to radiative power losses and to thermal power losses by increasing the electron population. The presence of impurities increases the required plasma parameters, characterized by the triple product, to achieve fusion gain. The analysis is applied to deuterium-tritium (D-T) fusion, though the methodology can be extended to other reactions. Since D-T fusion produces an alpha particle, the possibility exists of magnetically confining the alpha with sufficiently high magnetic fields, which are self-generated by the plasma pinch current. Confined alpha particles can heat the D-T fusion fuel, reduce the needed input power, and thereby amplify the fusion gain. However, ignition (Q→∞) does not occur since the axial plasma flow must be externally driven. The impacts of alpha heating and impurity losses are considered on the fusion performance of the SFS Z pinch. Requirements, assumptions, and limitations are described that would justify a determination of “D-T equivalent Q=1 conditions” in a D-D plasma. A minimum set of experimental measurements of plasma parameters is specified that can be compared to a plasma parameter map to facilitate a “Q=1” claim, where Q is defined by instantaneous values of fusion power and input power. Corroborating measurements are also discussed that would further support extrapolation of plasma and fusion performance to D-T operation.

Drift Algal Accumulation in Ice Scour Pits Provides an Underestimated Ecological Subsidy in a Novel Antarctic Soft-Sediment Habitat.

Ice scouring is one of the strongest agents of disturbance in nearshore environments at high latitudes. In depths, less than 20 m, grounding icebergs reshape the soft-sediment seabed by gouging furrows called ice pits. Large amounts of drift algae (up to 5.6 kg/m2) that would otherwise be transported to deeper water accumulate inside these features, representing an underestimated subsidy. Our work documents the distribution and dimensions of ice pits in Fildes Bay, Antarctica, and evaluates their relationship to the biomass and species composition of algae found within them. It also assesses the rates of deposition and advective loss of algae in the pits. The 17 ice pits found in the study area covered only 4.2% of the seabed but contained 98% of drift algal biomass, i.e., 60 times the density (kg/m2) of the surrounding seabed. Larger ice pits had larger and denser algal accumulations than small pits and had different species compositions. The accumulations were stable over time: experimentally cleared pits regained initial biomass levels after one year, and advective loss was less than 15% annually. Further research is needed to understand the impacts of ice scouring and subsequent algal retention on ecosystem functioning in this rapidly changing polar environment.

Toward thermal autarky for large-scale biogas plants: Dynamic energy modeling for energy efficiency in anaerobic digesters with enhanced multimembrane gasholders

Biogas production via anaerobic digestion could approach thermal autarky (less biogas self-consumption and better energy efficiency) using enhanced solutions for thermal insulation based on new multimembrane gasholder configurations, loss avoidance, and heat recovery strategies. In this study, a predictive and configuration-dependent dynamics energy model is developed to daily and seasonally assess the thermal efficiency and heating requirements of industrial biogas plants involving wet digesters with upper multimembrane gasholders. The model is validated using experimental data from a full-scale biogas plant in operation over a one-year period.The energy model involves a set of dynamic energy balances defined for each compartment of the digester and gasholder. All possible heat sources and sinks (ambient air temperature, wind, rain, and solar radiation) and heat exchanges or losses via advection, convection, and conduction, as well as a complete representation of the infrared radiative networks between the surfaces of the digester, are included for each compartment depending on the operating and design parameters. These heat exchanges are subject to fluctuating environmental conditions (e.g., ambient air temperature, wind, rain, and solar radiation).The results indicate that triple-membrane gasholders with a third insulation membrane made of a suitable material and thickness, together with the involvement of heat recovery from the digestate advective heat, are capable of reducing the overall thermal losses by more than 95 % (e.g., −51 % of the gasholder cover loss and − 81 % of the advective digestate loss) and when the waste heat from biogas purification is also valorized, the biogas plant can become thermally self-sufficient.

Irradiation-driven escape of primordial planetary atmospheres

Making use of the publicly available 1D photoionization hydrodynamics code ATES we set out to investigate the combined effects of specific planetary gravitational potential energy (ϕp ≡ GMp/Rp) and stellar X-ray and extreme ultraviolet (XUV) irradiation (FXUV) on the evaporation efficiency (η) of moderately-to-highly irradiated gaseous planets, from sub-Neptunes through hot Jupiters. We show that the (known) existence of a threshold potential above which energy-limited thermal escape (i.e., η ≃ 1) is unattainable can be inferred analytically, by means of a balance between the ion binding energy and the volume-averaged mean excess energy. For log ϕp ≳ log ϕpthr ≈ [12.9 − 13.2] (in cgs units), most of the energy absorption occurs within a region where the average kinetic energy acquired by the ions through photo-electron collisions is insufficient for escape. This causes the evaporation efficiency to plummet with increasing ϕp, by up to 4 orders of magnitude below the energy-limited value. Whether or not planets with ϕp ≲ ϕpthr exhibit energy-limited outflows is primarily regulated by the stellar irradiation level. Specifically, for low-gravity planets, above FXUVthr ≃ 104–5 erg cm−2 s−1, Lyα losses overtake adiabatic and advective cooling and the evaporation efficiency of low-gravity planets drops below the energy-limited approximation, albeit remaining largely independent of ϕp. Further, we show that whereas η increases as FXUV increases for planets above ϕpthr, the opposite is true for low-gravity planets (i.e., for sub-Neptunes). This behavior can be understood by examining the relative fractional contributions of advective and radiative losses as a function of atmospheric temperature. This novel framework enables a reliable, physically motivated prediction of the expected evaporation efficiency for a given planetary system; an analytical approximation of the best-fitting η is given in the appendix.

Effect of Quartz Aperture Covers on the Fluid Dynamics and Thermal Efficiency of Falling Particle Receivers

Abstract Falling particle receivers are an emerging technology for use in concentrating solar power systems. In this study, quartz half-shells are investigated for use as full or partial aperture covers to reduce receiver thermal losses. Quartz half-shell aperture covers offer the ability to minimally interfere with incoming solar radiation from the heliostat field while obstructing thermal radiation and advection from leaving the receiver cavity. The fluid dynamics and heat transfer of a receiver subdomain and surrounding air are modeled using ansys®fluent. We compare the percentage of total incident solar power lost due to conduction through the receiver walls, advective losses through the aperture, and radiation exiting the aperture. Contrary to expected outcomes, results show that quartz aperture covers can increase radiative losses and result in modest to nonexistent reductions in advective losses. The increased radiative losses are driven by elevated quartz half-shell temperatures and have the potential to be mitigated by active cooling and/or material selection. Quartz half-shell total transmissivity was measured experimentally using a radiometer and the National Solar Thermal Test Facility heliostat field with values up to 0.97 ± 0.01. Quartz half-shell aperture covers did not yield expected efficiency gains in numerical results due to increased radiative losses, but efficiency improvement in some numerical results and the performance of quartz half-shells subject to concentrated solar radiation suggest that quartz half-shell aperture covers should be investigated further.

Design Evaluation of a Next-Generation High-Temperature Particle Receiver for Concentrating Solar Thermal Applications

High-temperature particle receivers are being developed to achieve temperatures in excess of 700 °C for advanced power cycles and solar thermochemical processes. This paper describes designs and features of a falling particle receiver system that has been evaluated and tested at the National Solar Thermal Test Facility at Sandia National Laboratories. These advanced designs are intended to reduce heat losses and increase the thermal efficiency. Novel features include aperture covers, active air flow, particle flow obstructions, and optimized receiver shapes that minimize advective heat losses, increase particle curtain opacity and uniformity, and reduce cavity wall temperatures. Control systems are implemented in recent on-sun tests to maintain a desired particle outlet temperature using an automated closed-loop proportional–integral–derivative controller. These tests demonstrate the ability to achieve and maintain particle outlet temperatures approaching 800 °C with efficiencies between 60 and 90%, depending on incident power, mass flow, and environmental conditions. Lessons learned regarding the testing of design features and overall receiver operation are also presented.

A Comparison of Factors That Led to the Extreme Sea Ice Minima in the Twenty-First Century in the Arctic Ocean

Abstract The extreme Arctic sea ice minima in the twenty-first century have been attributed to multiple factors, such as anomalous atmospheric circulation, excess solar radiation absorbed by open ocean, and thinning sea ice in a warming world. Most likely it is the combination of these factors that drives the extreme sea ice minima, but how the factors rank in setting the conditions for these events has not been quantified. To address this question, the sea ice budget of an Arctic regional sea ice–ocean model forced by atmospheric reanalysis data is analyzed to assess the development of the observed sea ice minima. Results show that the ice area difference in the years 2012, 2019, and 2007 is driven to over 60% by the difference in summertime sea ice area loss due to air–ocean heat flux over open water. Other contributions are small. For the years 2012 and 2020 the situation is different and more complex. The air–ice heat flux causes more sea ice area loss in summer 2020 than in 2012 due to warmer air temperatures, but this difference in sea ice area loss is compensated by reduced advective sea ice loss out of the Arctic Ocean mainly caused by the relaxation of the Arctic dipole. The difference in open water area in early August leads to different air–ocean heat fluxes, which distinguishes the sea ice minima in 2012 and 2020. Further, sensitivity experiments indicate that both the atmospheric circulation associated with the Arctic dipole and extreme storms are essential conditions for a new low record of sea ice extent.

Hydrothermal Models Constrained by Fine‐Scale Seismic Velocities Confirm Hydrothermal Cooling of 7–63 Ma South Atlantic Crust

AbstractAlthough 70% of the Earth's heat loss occurs in the oceans, the nature of hydrothermal heat flow in oceanic crust is controversial. Lithospheric cooling models, heat flow measurements, and seismic experiments provide conflicting accounts on the longevity of hydrothermal systems and their efficiency at removing heat from the crust. Here we present five hydrothermal models along a crustal flowline in the western South Atlantic at ∼31°S to quantify how conductive and advective heat loss change as a function of crustal age and structure. The model sites cover crustal ages of 7–63 Ma and are collocated with planned drill sites of International Ocean Discovery Program Expeditions 390 and 393. We constrained our hydrothermal models with detailed physical property distributions that we estimated from new high‐resolution seismic velocity models. The hydrothermal models yield conductive and advective heat fluxes that closely match lithospheric cooling models and conductive heat flow measurements on the seafloor, supporting a hydrothermal sealing age of ∼65 Ma. Our results also agree with global estimates of fluid volume flux into the oceans and are consistent with a previously published analysis of upper crustal seismic velocities in the study area, indicating ongoing hydrothermal activity at relatively old crustal ages. This study broadly confirms and unifies existing concepts of oceanic heat flow and its modes of transport. Moreover, it provides a regional framework of seismic velocities and modeled hydrothermal fluxes, in which future in‐situ measurements can be integrated.

Insights into the environmental conditions contributing to variability in the larval recruitment of the tropical sardine Sardinella lemuru

• Biophysical model used to determine conditions experienced by sardine larvae • Larvae from peak spawning period experienced more optimal conditions for survival • Lower temperature and higher chlorophyll-a offset higher advective loss • Temporal variability in these conditions can affect sardine stocks • Current management plans need to account for environmental variability apart from fishing pressure The small pelagic fishery in the southern Philippines is one of the largest contributors to fisheries production in the country, and is dominated by the Bali sardine Sardinella lemuru . This species is a year-round spawner that has its peak spawning period during the northeast monsoon (NEM) months of November to February. However, there is still limited information on the conditions that affect this species’ survival during its early life history stages. Here, we attempt to discern the importance of temperature, prey density and advection on sardine larvae. The larvae were represented as passive particles that were released in known spawning grounds to simulate dispersal. The conditions the larvae experienced, namely, temperature and estimated prey density based on satellite chlorophyll-a values were recorded at each time step until the estimated recruitment age of 60 days. The temporal and spatial averaged conditions of recruited sardines showed that sardines spawned during the NEM months experienced higher chlorophyll-a, lower (more optimal) sea surface temperature, albeit higher advective loss, than sardines spawned during other months. Comparisons between years showed that during higher reported catch years, sardine larvae experienced lower temperatures and higher retention nearshore. Our results emphasize that sardine stock management efforts need to recognize the contribution of the temporally variable sardine environment to patterns in sardine recruitment and consequently in catches.

Morphology of radio relics – I. What causes the substructure of synchrotron emission?

ABSTRACT High-resolution radio observations of cluster radio relics often show complex spatial and spectral features. However, it is not clear what these features reveal about the underlying magnetic field properties. We performed three-dimensional magnetohydrodynamical simulations of merger shock waves propagating through a magnetized, turbulent intracluster medium. Our model includes the diffusive shock acceleration (DSA) of cosmic ray electrons, their spatial advection and energy losses at run-time. With this set-up we can investigate the relation between radio substructure and pre-shock plasma conditions in the host cluster. We find that upstream turbulence plays a major role in shaping the properties of radio relics produced downstream. Within the assumption of DSA, we can reproduce the observed discrepancy between the X-ray derived Mach number of shocks, and the Mach number inferred from radio spectra. Our simulated spectral index maps and profiles across the radio relic also suggest that the standard deviation of the upstream magnetic field must be relatively small ($\sigma _B\le 1 \, \mu$G) in order to reproduce observations and therefore radio relics can potentially constrain the distribution of magnetic fields in galaxy clusters outskirts.

The overriding role of hydrological factors on zooplankton community: evidence from a shallow tropical reservoir (Koka, Ethiopia).

Due to changes in global climate and local hydrological variability, land-water interactions are considered the prevailing processes underpinning aquatic ecology. Periodic meteorological conditions could have significant effect upon freshwater plankton communities by modifying the relative influences of biotic and abiotic structuring factors. However, the influence of unusual meteorological events, such as the El-Niño Southern Oscillation cycles, and advection on zooplankton communities of tropical shallow lakes and reservoirs are not fully understood. The present study, therefore, aimed to explore the relationship between hydrological factors and zooplankton community structure in Koka Reservoir, Ethiopia. Field measurements and collection of water samples and zooplankton were performed at monthly intervals from January to August 2016 at three sampling sites along a stretch of the reservoir from the river mouth to the center and the outlet (dam). The results showed post-El-Niño hydrological events (i.e., elevated riverine runoff and higher levels of turbidity) and associated advective losses can disrupt zooplankton community structure at the river mouth site, particularly during the rainy period. The results suggest that integrated watershed management activities are important aquatic resource management options in small- and medium-sized lakes and reservoirs.

An invasive macroalga alters ecosystem metabolism and hydrodynamics on a tidal flat

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 628:1-16 (2019) - DOI: https://doi.org/10.3354/meps13143 FEATURE ARTICLE An invasive macroalga alters ecosystem metabolism and hydrodynamics on a tidal flat Martin P. Volaric*, Peter Berg, Matthew A. Reidenbach Department of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22904, USA *Corresponding author: mpv3a@virginia.edu ABSTRACT: Invasive macroalgae represent a growing global concern, yet there has been little research detailing their effects on native ecosystem metabolism and flow hydrodynamics. In this in situ study, we made aquatic eddy covariance oxygen flux and profiling acoustic Doppler velocimetry measurements over high and low density sites within an invasive Gracilaria vermiculophylla (also referred to as Agarophyton vermiculophyllum) macroalgal mat located on a tidal flat along the Virginia (USA) coast. Mean ± SE (n) submerged dark and light oxygen flux over the high density site were -178 ± 9 (144) and 139 ± 26 (104) mmol m-2 d-1, respectively, vs. -71 ± 7 (45) and 32 ± 15 (48) mmol m-2 d-1 over the low density site. The high density site was highly productive, with gross primary production of 169 ± 12 mmol m-2 d-1 (mean ± SE), yet maintained overall metabolic balance, as net ecosystem metabolism was -22 ± 39 mmol m-2 d-1. Close agreement with literature values for air-exposed flux measurements suggests that our results are good first-order approximations of true daily values, demonstrating that this invasion has significantly enhanced tidal flat productivity. Flow and turbulence were significantly attenuated by Gracilaria, resulting in decreased bed shear stress within the algal canopy, likely stabilizing tidal flat sediments and inhibiting mass transport at the sediment-water interface. Turbulence above the canopy was enhanced, but there was no increase in downward momentum transfer. These changes to the hydrodynamic environment decrease the risk of detachment and subsequent advective loss of algae, suggesting a positive feedback that facilitates algal invasion. KEY WORDS: Invasive seaweeds · Macroalgae · Gracilaria vermiculophylla · Oxygen flux · Aquatic eddy covariance · Agarophyton vermiculophyllum · Productivity Full text in pdf format Information about this Feature Article NextCite this article as: Volaric MP, Berg P, Reidenbach MA (2019) An invasive macroalga alters ecosystem metabolism and hydrodynamics on a tidal flat. Mar Ecol Prog Ser 628:1-16. https://doi.org/10.3354/meps13143 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 628. Online publication date: October 10, 2019 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2019 Inter-Research.

Scalings pertaining to current sheet disruption mediated by the plasmoid instability

Analytic scaling relations are derived for a phenomenological model of the plasmoid instability in an evolving current sheet, including the effects of reconnection outflow. Two scenarios are considered, where the plasmoid instability can be triggered either by an injected initial perturbation or by the natural noise of the system (here referred to as the system noise). The two scenarios lead to different scaling relations because the initial noise decays when the linear growth of the plasmoid instability is not sufficiently fast to overcome the advection loss caused by the reconnection outflow, whereas the system noise represents the lowest level of fluctuations in the system. The leading order approximation for the current sheet width at disruption takes the form of a power law multiplied by a logarithmic factor, and from that, the scaling relations for the wavenumber and the linear growth rate of the dominant mode are obtained. When the effects of the outflow are neglected, the scaling relations agree, up to the leading order approximation, with previously derived scaling relations based on a principle of least time. The analytical scaling relations are validated with numerical solutions of the model.

Evolution of heat flow, hydrothermal circulation and permeability on the young southern flank of the Costa Rica Rift

SUMMARYWe analyse 67 new conductive heat-flow measurements on the southern flank of the Costa Rica Rift (CRR). Heat-flow measurements cover five sites ranging in oceanic crustal age between approximately 1.6 and 5.7 Ma, and are co-located with a high-resolution multichannel seismic line that extends from slightly north of the first heat-flow site (1.6 Ma) to beyond ODP Hole 504B in 6.9 Ma crust. For the five heat-flow sites, the mean observed conductive heat flow is ≈85 mW m−2. This value is approximately 30 per cent of the mean lithospheric heat flux expected from a half-space conductive cooling model, indicating that hydrothermal processes account for about 70 per cent of the heat loss. The advective heat loss fraction varies from site to site and is explained by a combination of outcrop to outcrop circulation through exposed basement outcrops and discharge through faults. Supercritical convection in Layer 2A extrusives occurs between 1.6 and 3.5 Ma, and flow through a thinly sedimented basement high occurs at 4.6 Ma. Advective heat loss diminishes rapidly between ≈4.5 and ≈5.7 Ma, which contrasts with plate cooling reference models that predict a significant deficit in conductive heat flow up to ages ≈65 ± 10 Ma. At ≈5.7 Ma the CRR topography is buried under sediment with an average thickness of ≈150 m, and hydrothermal circulation in the basement becomes subcritical or perhaps marginally critical. The absence of significant advective heat loss at ≈5.7 Ma at the CRR is thus a function of both burial of basement exposure under the sediment load and a reduction in basement permeability that possibly occurs as a result of mineral precipitation and original permeability at the time of formation. Permeability is a non-monotonic function of age along the southern flank of the CRR, in general agreement with seismic velocity tomography interpretations that reflect variations in the degree of ridge-axis magma supply and tectonic extension. Hydrothermal circulation in the young oceanic crust at the southern flank of CRR is affected by the interplay and complex interconnectedness of variations in permeability, sediment thickness, topographical structure, and tectonic and magmatic activities with age.

Surface and advective heat fluxes in the western margin of the Gulf of Tehuantepec.

We present the annual cycles of the monthly surface and advective heat fluxes from La Boquilla and Tangolunda, two points in the western margin of the Gulf of Tehuantepec. Computations are function of averaged (2011–2013) daily seawater temperature at 5 m depth, interpolated daily SST satellite and daily meteorological data except cloud cover, estimated from ICOADS. The advective heat flux is a result of the imbalance between the net surface heat flux and the heat content rate of change in a 25 m depth water column. Most of the meteorological variables and heat fluxes, show intra-seasonal variability related to the cloud cover that accompanies the Intertropical Convergence Zone position relative to the study area. The latent heat flux, calculated using two distinct exchange coefficients, according to Bunker and to Liu, and the long wave heat flux, are about the same magnitude in each site. In all the computations, the net surface heat flux is positive throughout the year (into the ocean) and correspondingly there is an exportation of advective heat flux along the year from the water column. Large advective heat losses, in February and October, occur when measured southeastward currents are strong. Small losses occur, in May and January, when currents are weak and towards different directions. Currents arriving to the area from the west, seem correspond to mixed water from the tropical Pacific off central México in February. In October, however, similar currents seem to be part of the Costa Rica Coastal Current after leaving the Tehuantepec Bowl. The largest net surface heat flux difference between the two sites (<10 Wm-2), arises from the differences in the meteorological time series recorded at each site rather than from distinct SST and seawater temperature values, or from the two distinct exchange coefficients. In comparison to these results, the magnitude of the net surface heat flux from NCEP is smaller and negative in November, due to a smaller short wave gain but larger latent and sensible heat losses. These heat fluxes estimations are the first of their kind at the western margin of the Gulf of Tehuantepec and the southern coast of the Mexican Pacific.