Box Model Approach Research Articles

Box Model Approach for Indoor Air Quality (IAQ) Management in a Subway Station Environment

Air quality in a subway tunnel has been crucial in most of the subway environments where IAQ could be affected by many factors such as the number of passengers, the amount and types of ventilation, train operation factors and other facilities. A modeling approach has been introduced to manage the general IAQ in a subway station. Field surveys and CO₂ measurements were initially conducted to analyze and understand the relationship between indoor and outdoor air quality while considering internal pollution sources, such as passengers and subway trains, etc. The measurement data were then employed for the model development with other statistical information. For the model development, the algorithm of simple continuity was set up and applied to model the subway IAQ concerned, while considering the major air transport through staircases and tunnels. Monitored CO₂ concentration on the concourse and platform were correlated with modeling results where the correlation values for the concourse and platform were R²=0.96 and R²=0.75, respectively. It implies that the box modeling approach introduced in this study would be beneficial to predict and control the indoor air quality in subway environments.

Nutrient fluxes in the Changjiang River estuary and adjacent waters — a modified box model approach

To solve nutrient flux and budget among waters with distinct salinity difference for water-salt-nutrient budget, a traditional method is to build a stoichiometrically linked steady state model. However, the traditional way cannot cope appropriately with those without distinct salinity difference that parallel to coastline or in a complex current system, as the results would be highly affected by box division in time and space, such as the Changjiang (Yangtze) River estuary (CRE) and adjacent waters (30.75 degrees-31.75 degrees N, 122 degrees 10'-123 degrees 20'E). Therefore, we developed a hydrodynamic box model based on the traditional way and the regional oceanic modeling system model (ROMS). Using data from four cruises in 2005, horizontal, vertical and boundary nutrient fluxes were calculated in the hydrodynamic box model, in which flux fields and the major controlling factors were studied. Results show that the nutrient flux varied greatly in season and space. Water flux outweighs the nutrient concentration in horizontal flux, and upwelling flux outweighs upward diffusion flux in vertical direction (upwelling flux and upward diffusion flux regions overlap largely all the year). Vertical flux in spring and summer are much greater than that in autumn and winter. The maximum vertical flux for DIP (dissolved inorganic phosphate) occurs in summer. Additional to the fluxes of the Changjiang River discharge, coastal currents, the Taiwan Warm Current, and the upwelling, nutrient flux inflow from the southern Yellow Sea and outflow southward are found crucial to nutrient budgets of the study area. Horizontal nutrient flux is controlled by physical dilution and confined to coastal waters with a little into the open seas. The study area acts as a conveyer transferring nutrients from the Yellow Sea to the East China Sea in the whole year. In addition, vertical nutrient flux in spring and summer is a main source of DIP. Therefore, the hydrodynamic ROMS-based box model is superior to the traditional one in estimating nutrient fluxes in a complicated hydrodynamic current system and provides a modified box model approach to material flux research.

Structure of the turbidity field in the Guadalquivir estuary: Analysis of observations and a box model approach

AbstractA study is presented on the transport of suspended particulate matter (SPM) in the Guadalquivir estuary during low river flow conditions. Observations show that tidally induced SPM exceeds that associated with catchment‐derived inputs. The main mechanisms that contribute to longitudinal transport are identified and quantified by analyzing the tidally averaged and depth‐integrated SPM flux decomposition over time and space. The net transport is generally directed upstream, although differences in the direction between spring and neap tides are identified. The transport is largely controlled by the mean advection, the tidal pumping associated with the covariance between SPM concentration and current, and the tidal Stokes transport. The convergence of the transport associated to these mechanisms alone explains the presence of primary and secondary estuarine turbidity maxima. The tidal reflection at the upstream dam appears to play a significant role in their generation, as evidenced by the convergence zones of the M4 and M2 induced tidal pumping transports. The spatial structure of the transport motivates the development of a box model that describes the concentration of SPM and its exchange between different stretches along the estuary at subtidal time scales. The model is fed by the net SPM transport obtained from observations. Analysis of the morphodynamical state of the estuary using the box model indicates that erosion is dominant in the stretches close to the estuary mouth and that this sediment is transported upstream and deposited in the middle part of the estuary. This process is more influential during spring tides than during neap tides.

Model evaluation of methods for estimating surface emissions and chemical lifetimes from satellite data

Column densities from satellite retrievals can provide valuable information for estimating emissions and chemical lifetimes objectively across the globe. To better understand the uncertainties associated with these estimates, we test four methods using simulated column densities from a point source: a box model approach, a 2D Gaussian fit, an Inverse Radius fit and an Exponentially-Modified Gaussian fit. The model results were simulated using the WRF and CAMx models for the year 2005, for a single point source outside Atlanta in Georgia, USA with specified emissions and three chemical scenarios: no chemical reactions, 12 h chemical lifetime and 1 h chemical lifetime. No other sources were included in the simulations. We find that the box model provides reliable estimates irrespective of plume speed and plume direction, if the plume speed and the chemical lifetime are known accurately. The 2D Gaussian fit was found to be sensitive to plume speed and direction, and requires omnidirectional dispersion in order to have a decent fit. However, the 2D Gaussian fit is only an approximate fit to the data, and the discrepancies mean that the results are dependent on the geographical domain used for the optimization. An Inverse Radius fit is introduced to correct this issue, which is found to provide improved emissions and lifetime estimates. The Exponentially-Modified Gaussian fit also gave improved estimates. It is however dependent on accurate plume rotation such that reported chemical lifetimes with this method could be significantly underestimated.

Degradation in urban air quality from construction activity and increased traffic arising from a road widening scheme

Road widening schemes in urban areas are often proposed as a solution to traffic congestion and as a means of stimulating economic growth. There is however clear evidence that new or expanded roads rapidly fill with either displaced or induced traffic, offsetting any short-term gains in eased traffic flows. What has not been addressed in any great detail is the impact of such schemes on air quality, with modelled impact predictions seldom validated by measurements after the expansion of road capacity. In this study we made use of a road widening project in London to investigate the impact on ambient air quality (particulate matter, NOX, NO2) during and after the completion of the road works.PM10 increased during the construction period up to 15μgm−3 during working hours compared to concentrations before the road works. A box modelling approach was used to determine a median emission factor of 0.0022kgPM10m−2month−1, three times larger than that used in the UK emission inventory (0.0007kgPM10m−2month−1). Peaks of activity released 0.0130kgPM10m−2month−1, three and eight times smaller than the peak values used in the European and US inventories. After the completion of the widening there was an increase in all pollutants from the road during rush hour: 2–4μgm−3 for PM10; 1μgm−3 for PM2.5; 40 and 8μgm−3 for NOX and NO2, respectively. NO2 EU Limit Value was breached after the road development illustrating a notable deterioration in residential air quality. Additionally, PM10, but not PM2.5, glutathione dependent oxidative potential increased after the road was widened consistent with an increase in pro-oxidant components in the coarse particle mode, related to vehicle abrasion processes. These increased air pollution indices were associated with an increase in the number of cars, taxis and LGVs.

The carbon budget in the northern Adriatic Sea, a winter case study

AbstractThis paper presents a winter carbon budget for the northern Adriatic Sea, obtained through direct measurements during two multidisciplinary cruises and literature data. A box model approach was adopted to integrate estimates of stocks and fluxes of carbon species over the total area. The oligotrophy at the basin scale and the start of primary productivity well before the onset of spring stratification were observed. In winter, the system underwent a complete reset, as the mixing of water masses erased any signal of previous hypoxia or anoxia episodes. The northern Adriatic Sea was phosphorus depleted with respect to C and N availability. This fact confirms the importance of mixing with deep‐sea water for P supply to biological processes on the whole. Despite the abundant prokaryotic biomass, the microbial food web was less efficient in organic C production than phytoplankton. In the upper layer, the carbon produced by primary production exceeded the fraction respired by planktonic community smaller than 200 µm. On the contrary, respiration processes prevailed in the water column below the pycnocline. The carbon budget also proved that the northern Adriatic Sea can be an effective sink for atmospheric CO2 throughout the entire winter season.

Biogeochemical cycle of nitrogen in a tropical mangrove ecosystem, east coast of India

Like many coastal systems, nitrogen is the critical limiting factor for mangrove net production. This study used a box model approach to assess the nitrogen budget in the Sundarban mangrove ecosystem, which acts as a sink for atmospheric nitrogen in terms of NOx, NH3, N2, and water column dissolved inorganic nitrogen. The coupling of biosphere and atmosphere in terms of atmospheric NOx and NH3 uptake showed that uptake of ammonia (130×106molyr−1) was about six fold as large as that of NOx, (22×106molyr−1). The nitrogen stored by the processes such as plant uptake of NOx, NH3 from the atmosphere, nitrogen fixation (5×109molyr−1), and sediment water exchange (8×106molyr−1) was about two times as large as that of recycled nitrogen from litter (3×109molyr−1), and could account 74% of the nitrogen required for mangrove net production. Most of the nitrogen was conserved in the living biomass (living biomass: 118×103molha−1 versus soil: 3×103molha−1). The loss of nitrogen was 23% of the total amount that was conserved from the external sources in the Sundarban mangrove system. Thus, the coastal ecosystem like Sundarban mangroves could retain only 0.2% (8×106mol) of the annual river flux of nitrogen to the coastal waters and nitrogen is generally conserved within the system.

Area fluxes of carbon dioxide, methane, and carbon monoxide derived from airborne measurements around Greater London: A case study during summer 2012

AbstractAirborne measurements of thermodynamic properties and carbon dioxide (CO2), methane (CH4), and carbon monoxide (CO) mole fractions were recorded on board the FAAM BAe‐146 UK research aircraft and used to characterize the inflow and outflow from Greater London on 30 July 2012. All three trace gases were observed to be significantly enhanced downwind of Greater London with spatially resolved plumes of comparable extent and position. A mass budget calculation using a box model approach (and uncertainty propagation) was used to determine net regional fluxes of 21 ± 3 µmol CO2 m−2 s−1, 0.13 ± 0.02 µmol CH4 m−2 s−1, and 0.12 ± 0.02 µmol CO m−2 s−1 for Greater London. These fluxes are comparable with simultaneous surface observations and previous studies in urban environments. A comparison was made with the 2010 UK National Atmospheric Emissions Inventory (NAEI), and fluxes from this study are found to be factors 2.3 for CO2 and 2.2 for CO larger than those estimated by the spatially disaggregated NAEI (2011) for Greater London. Fluxes of CH4 were found to be a factor 3.4 larger than the UK NAEI (2009). The efficacy of this mass balance approach, in general, is also discussed in terms of key assumptions and uncertainties, and we offer advice for future studies on how uncertainties could be reduced.

Atlantic meridional ocean heat transport at 26° N: impact on subtropical ocean heat content variability

Abstract. Local climate is significantly affected by changes in the oceanic heat content on a range of timescales. This variability is driven by heat fluxes from both the atmosphere and the ocean. In the Atlantic the meridional overturning circulation is the main contributor to the oceanic meridional heat transport for latitudes south of about 50° N. The RAPID project has been successfully monitoring the Atlantic meridional overturning at 26° N since 2004. This study demonstrates how these data can be used to estimate the variability of the basin-wide ocean heat content in the upper 800 m between 26° and 36° N. Traditionally the atmosphere is seen to dominate the ocean heat content variability. However, previous studies have looked at smaller areas in the Gulf Stream region, finding that the ocean dominates deseasoned fluctuations of ocean heat content, while studies of the whole North Atlantic region suggest that the atmosphere may be dominant. In our study we use a box model to investigate fluctuations of the ocean heat content in the subtropical North Atlantic between 26° and 36° N. The box model approach is validated using 19 yr of high-resolution general circulation model (GCM) data. We find that in both the GCM- and RAPID-based data the ocean heat transport dominates the deseasoned heat content variability, while the atmosphere's impact on the ocean heat content evolution stabilizes after 6 months. We demonstrate that the utility of the RAPID data goes beyond monitoring the overturning circulation at 26° N, and that it can be used to better understand the causes of ocean heat content variability in the North Atlantic. We illustrate this for a recent decrease in ocean heat content which was observed in the North Atlantic in 2009 and 2010. Our results suggest that most of this ocean heat content reduction can be explained by a reduction of the meridional ocean heat transport during this period.

Global solar irradiation prediction using a multi-gene genetic programming approach

In this paper, a nonlinear symbolic regression technique using an evolutionary algorithm known as multi-gene genetic programming (MGGP) is applied for a data-driven modelling between the dependent and the independent variables. The technique is applied for modelling the measured global solar irradiation and validated through numerical simulations. The proposed modelling technique shows improved results over the fuzzy logic and artificial neural network (ANN) based approaches as attempted by contemporary researchers. The method proposed here results in nonlinear analytical expressions, unlike those with neural networks which is essentially a black box modelling approach. This additional flexibility is an advantage from the modelling perspective and helps to discern the important variables which affect the prediction. Due to the evolutionary nature of the algorithm, it is able to get out of local minima and converge to a global optimum unlike the back-propagation (BP) algorithm used for training neural networks. This results in a better percentage fit than the ones obtained using neural networks by contemporary researchers. Also a hold-out cross validation is done on the obtained genetic programming (GP) results which show that the results generalize well to new data and do not over-fit the training samples. The multi-gene GP results are compared with those obtained using its single-gene version and also the same with four classical regression models in order to show the effectiveness of the adopted approach.

A novel model approach to bridge the gap between box models and classic 3D models in estuarine systems

The multiple hydrodynamic and ecological processes characterizing estuarine systems make ecological modelling an essential tool for ecosystem-based management by increasing the understanding of the complex interactions and by quantifying the effects of various natural and anthropogenic pressures. The modelling technique used is dominated by computational simple box model approaches with a low spatial resolution and coupled 3D hydrodynamic-ecological models with high computational requirements. In this paper we present a novel concept (Flexsem) which combines the computational simplicity and condensed hydrodynamics from box models with a high spatial resolution characterizing coupled 3D models. The modelling framework Flexsem is a fast, flexible and user-friendly tool specifically targeted towards scientific and management challenges of the complex biogeochemical processes in coastal zone ecosystems. We use Flexsem to simulate the physical conditions in a typical Danish estuary, Horsens Fjord utilizing unstructured computational meshes to vary the complexity of grid geometry and resolution. The results showed that the model was able to reproduce the physical conditions in the estuary and provide reliable estimates for the tracer residence time.

Dynamics and exchange fluxes of methane in the estuarine mangrove environment of the Sundarbans, NE coast of India

The distribution and exchange fluxes of methane (CH4) were measured in a mangrove vegetated island and its bordering estuarine system of the Sundarbans mangrove biosphere from June 2010 to December 2011 on monthly basis. The onset of methane production is evident in the forest sediment at about 25 cm deep sediment layer under strong redox condition having an average Eh value of −175.7 mV and showing a 2.8 folds increase in the pore water dissolved methane concentration at that depth in comparison to the surface layer. The average diffusive flux of methane from this methane producing layer to surface was calculated to be 591 ± 106 nmol m−2 d−1. The depth profiles of NO2−–N, SO4−2–S, acid volatile sulphide, organic carbon and dissolved methane in the sediment cores from inter-tidal zones showed distinct trends representing signatures of denitrification, sulfate reduction and methanogenesis in the sediment layers. The methane emission from the sediment–atmosphere interface was observed to be maximum during monsoon and higher emission rates was recorded from upper littoral zone. The annual average atmospheric methane mixing ratio was 2.038 ± 0.07 ppmv. This mangrove biosphere was found to act as source for methane during monsoon while as sink during pre and postmonsoon seasons. Estuarine surface water showed a very high degree of super saturation about 2748 ± 730% for dissolved methane at an annual basis and act as a significant source of methane having an annual average exchange flux of 408 ± 110 nmol m−2 h−1. A box model approach has been adopted at annual basis to understand the distribution and dynamics of methane in this mangrove environment.

Internal cycling of dissolved barium in water column of the Bay of Bengal

Dissolved barium concentrations in water column of the Bay of Bengal along the 87°E transect (~6°N to ~21°N) have been measured to track the dispersion of its large influx from the Ganga–Brahmaputra river system and the outflow to the equatorial Indian Ocean. A typical barium concentration–depth profile shows relatively higher Ba concentrations in surface waters (depth ≤5m) followed by a minimum in the depth interval ~50–150m and an increase at greater depth. The barium concentrations in surface waters (depth≤5m) of the Bay of Bengal vary from ~35nmol/kg at the southernmost station 0806 to ~113nmol/kg close to mouth of the Hooghly estuary (station 0816). The Ba data in upper layers (depth ≤100m), excluding the very high Ba at station 0816, generally show a strong and significant inverse correlation with salinity (R2=0.75; P<0.0001). This indicates the southward flow of dissolved Ba from the Ganga–Brahmaputra river system that also includes its contributions by particle release and submarine groundwater discharge. The subsurface Ba minimum found in this study are ubiquitous and most probably a result of Ba uptake on settling particulates. On the other hand, the Ba concentrations in deep waters (depth >500m) is controlled dominantly by water mixing as suggested by a very strong and significant inverse correlation with salinity (R2>0.95; P<0.0001). Exceptions to this conservative behavior are the “hot-spots” of dissolved Ba in bottom waters, which are probably resulted by the dissolution of sediments at and/or below the sediment–water interface.Attempts were made to budget the Ba abundance in the Bay of Bengal using a two box model approach; surface (top ~100m) and deep waters (below ~100m). Under the steady state the annual Ba influx from the Ganga–Brahmaputra river system seems to be balanced through its removal via sinking particulates as a result there is no lateral outflow of dissolved Ba from the Ganga–Brahmaputra to the equatorial Indian Ocean through top ~100m of the Bay of Bengal. Most of this sinking particulate Ba (~95%) is regenerated again in the lower box, preferentially in the intermediate waters ~100–500m. Therefore, frequently ventilated intermediate waters of the Bay of Bengal, receiving a large input of dissolved Ba through particle remineralization can be a significant source of dissolved Ba to the Indian Ocean.

Viscous propagation of two-dimensional non-Newtonian gravity currents

This paper presents the results of a detailed experimental and theoretical investigation on the viscous propagation of non-Newtonian gravity currents. Laboratory gravity currents are generated in a horizontal rectangular tank by releasing a constant flux of high-concentration fluid mud suspensions that exhibit profound non-Newtonian (shear thinning) behavior. Experimental observations on the propagation of fluid mud gravity currents revealed that viscous propagation of these currents was typically preceded by two phases as expected: an initial momentum-driven horizontal buoyant wall jet and a buoyancy-driven inertial phase. The experimental transition times, t**, and positions, x**, at which fluid mud gravity currents transition into viscous propagation phase were determined. The experimental data that correspond to the viscous propagation of fluid mud gravity currents (i.e. experimental time, t ⩾ t**, and front position, xN ⩾ x**) were used to evaluate the predictive capabilities of two well-known mathematical modeling approaches: the lubrication theory approximation and the box-model approaches. Regarding the lubrication theory approximation, a recently developed self-similarity solution for viscous propagation of power-law gravity currents that has not been experimentally evaluated was used. Regarding the box-model approach, a viscous box-model solution for two-dimensional (2D) non-Newtonian gravity currents was developed. The evaluation of these models using experimental data revealed that both models were in good agreement with the experimental observations, despite several simplifying assumptions embedded in each. Given its more advanced mathematical development, the lubrication theory approximation model provides a more complete description of a gravity current (i.e. shape and velocity variation along the gravity current) than the box model at the expense of a relatively simple computational effort.

Soil water dynamics at a midlatitude test site: Field measurements and box modeling approaches

► Simple box models can describe soil water dynamics at midlatitudes. ► The only meteorological forcing used is daily rainfall. ► Three models are validated both in “in-sample” and in forecast mode. ► Best model: leakage and evapotranspiration are nonlinear functions of soil water. We test the ability of three box models ( Milly, 1993 , Kim et al., 1996 , Laio et al., 2001b ) to describe soil moisture dynamics in a regularly monitored experimental site in northwestern Italy. The models include increasingly complex representations of leakage and evapotranspiration processes. We force the models with the local rainfall, and we determine model parameters with a least-square minimization procedure. We study separately summer and annual dynamics. When we use the models to reproduce annual dynamics, we include a simple representation of the annual cycle of evapotranspiration. We test the models both in simulation mode, estimating their parameters from the same data used to verify them, and in forecast mode, determining the model parameters from one period, and using them to forecast soil water dynamics in a different period. The results indicate that simple box models can estimate soil water dynamics at midlatitudes, using rainfall as the only meteorological driver. The models displaying the best performances include the representation of leakage and evapotranspiration as nonlinear functions of soil water content.

Time series modeling of daily abandoned calls in a call centre

Models for evaluating and predicting the short periodic time series in daily abandoned calls in a call center are developed. Abandonment of calls due to impatient is an identified problem among most call centers. The two competing models were derived using Fourier series and the Box and Jenkins modeling approaches. The selected models were shown to be both parsimonious and adequate using the P-P plots, Q-Q plots and residual analysis. In validating and comparing the models some efficiency measures were used with a view to determining the model which best represent the population under investigation. Fourier series model was found to be more efficient than Box and Jenkins model. The data for application were got from a GSM telephone provider.KEY WORDS: Call center; Tele-queue; abandoned calls; Fourier time series; Periodogram; Moving average, Autoregressive process

Geochemical monitoring of volcanic lakes. A generalized box model for active crater lakes

In the past, variations in the chemical contents (SO42−, Cl−, cations) of crater lake water have not systematically demonstrated any relationships with eruptive activity. Intensive parameters (i.e., concentrations, temperature, pH, salinity) should be converted into extensive parameters (i.e., fluxes, changes with time of mass and solutes), taking into account all the internal and external chemical–physical factors that affect the crater lake system. This study presents a generalized box model approach that can be useful for geochemical monitoring of active crater lakes, as highly dynamic natural systems. The mass budget of a lake is based on observations of physical variations over a certain period of time: lake volume (level, surface area), lake water temperature, meteorological precipitation, air humidity, wind velocity, input of spring water, and overflow of the lake. This first approach leads to quantification of the input and output fluxes that contribute to the actual crater lake volume. Estimating the input flux of the volcanic fluid (Qf- kg/s) –– an unmeasurable subsurface parameter –– and tracing its variations with time is the major focus during crater lake monitoring. Through expanding the mass budget into an isotope and chemical budget of the lake, the box model helps to qualitatively characterize the fluids involved. The (calculated) Cl− content and dD ratio of the rising volcanic fluid defines its origin. With reference to continuous monitoring of crater lakes, the present study provides tips that allow better calculation of Qf in the future. At present, this study offers the most comprehensive and up-to-date literature review on active crater lakes.

A multi-variable box model approach to the soft tissue carbon pump

Abstract. The canonical question of which physical, chemical or biological mechanisms were responsible for oceanic uptake of atmospheric CO2 during the last glacial is yet unanswered. Insight from paleo-proxies has led to a multitude of hypotheses but none so far have been convincingly supported in three dimensional numerical modelling experiments. The processes that influence the CO2 uptake and export production are inter-related and too complex to solve conceptually while complex numerical models are time consuming and expensive to run which severely limits the combinations of mechanisms that can be explored. Instead, an intermediate inverse box model approach of the soft tissue pump is used here in which the whole parameter space is explored. The glacial circulation and biological production states are derived from these using proxies of glacial export production and the need to draw down CO2 into the ocean. We find that circulation patterns which explain glacial observations include reduced Antarctic Bottom Water formation and high latitude upwelling and mixing of deep water and to a lesser extent reduced equatorial upwelling. The proposed mechanism of CO2 uptake by an increase of eddies in the Southern Ocean, leading to a reduced residual circulation, is not supported. Regarding biological mechanisms, an increase in the nutrient utilization in either the equatorial regions or the northern polar latitudes can reduce atmospheric CO2 and satisfy proxies of glacial export production. Consistent with previous studies, CO2 is drawn down more easily through increased productivity in the Antarctic region than the sub-Antarctic, but that violates observations of lower export production there. The glacial states are more sensitive to changes in the circulation and less sensitive to changes in nutrient utilization rates than the interglacial states.

Estimation of Phosphorus Flux in a Stratified Estuary Using a Mass Balance Model

The study examined the summertime behavior of phosphorus (P) and estimated P fluxes in the Inohana Lake Estuary, Shizuoka, Japan through a field observation conducted in the summer of 2007 and a box model approach. The sedimentation flux of P was significantly correlated with the overlying chlorophyll-a concentration. The box model provided a good estimate of the summer-averaged water flux. The P mass balance method yielded the release flux of P, which approximated the observed value. For the P exchange between the Inohana Lake Estuary and Hamana Bay, on the net flux, particulate P flows out into Hamana Bay through the upper layer, while dissolved P (phosphate P) flows into the Inohana Lake Estuary through the lower layer. For the P exchange between the upper and lower layers, the upward transport of P from the lower layer was more than 10 (∼100) times greater than the downward transport of P. The results showed that P accumulates in the bottom sediment during the summer. This study indicates the possibility that the P input from Hamana Bay is dominant over the river P input in summer season with significant density stratification.

Estimating iron and aluminum removal rates in the eastern equatorial Pacific Ocean using a box model approach

Iron limitation plays an important role in maintaining the high-nitrate low-chlorophyll (HNLC) condition in the equatorial upwelling zone. The rate and depth of upwelling control Fe supply to the euphotic zone. This study constrains the transport fluxes and budget of two trace metals, Fe and Al, in the upper ocean. They are co-delivered to the eastern equatorial Pacific surface waters via the Equatorial Undercurrent and upwelling but show distinct biogeochemical cycling processes. We combine the results of the in situ measurements of dissolved Fe and Al (dFe and dAl) with the modeled velocity fields to calculate the physical fluxes. The model calculations are evaluated with the conservation of heat, volume transport, NO 3 and Si(OH) 4 budgets for the equatorial Pacific. The vertical flux due to upwelling provides averaged dFe and dAl supply rates of 1.45 μmol m −2 d −1 and 11.51 μmol m −2 d −1, respectively. The sum of the net physical fluxes in the eastern equatorial Pacific for dFe and dAl are 0.41 μmol m −2 d −1 and 2.77 μmol m −2 d −1, respectively. These estimates are equal to the net biological and chemical removal rates of dFe and dAl. The calculated dFe:C net removal ratio is in the range of 3-9 μmol:mol, which agrees with most other estimates. This suggests that the majority of net dFe removal is due to biological uptake in the upper water column. The results of this box model approach illustrate the usefulness of combining the modeled outputs and in situ measurements, which provide additional constraints on Fe transport and cycling in the equatorial Pacific and possibly other HNLC regions.