Moacyr Araujo

Cross-Wavelet Bias Corrected by Normalizing Scales

AbstractThe cross-wavelet transform (XWT) is a powerful tool for testing the proposed connections between two time series. Because of XWT’s skeletal structure, which is based on the wavelet transform, it is suitable for the analysis of nonstationary periodic signals. Recent work has shown that the power spectrum based on the wavelet transform can produce a deviation, which can be corrected by choosing a proper rectification scale. In this study, it is shown that the standard application of the XWT can also lead to a biased result. A corrected version of the standard XWT was constructed using the scale of each series as normalizing factors. This correction was first tested with an artificial example involving two series built from combinations of two harmonic series with different amplitudes and frequencies. The standard XWT applied to this example produces a biased result, whereas the correct result is obtained with the use of the proposed normalization. This analysis was then applied to a real geophysica...

Eutrophication effects on phytoplankton size-fractioned biomass and production at a tropical estuary.

Size-fractioned phytoplankton (pico, nano and microplankton) biomass and production were estimated throughout a year at Recife harbor (NE Brazil), a shallow well mixed tropical hypereutrophic estuary with short residence times but restricted water renewal. Intense loads of P-PO4 (maximum 14 μM) resulted in low N:P ratios (around 2:1), high phytoplankton biomass (B=7.1-72 μg chl-a L(-1)), production (PP=10-2657 μg C L(-1) h(-1)) and photosynthetic efficiency (P(B)=0.5-45 μg C μg chl-a(-1)), but no oxygen depletion (average O2 saturation: 109.6%). Nanoplankton dominated phytoplankton biomass (66%) but micro- and nanoplankton performed equivalent primary production rates (47% each). Production-biomass models indicate an export of the exceeding microplankton biomass during most of the year, possibly through grazing. The intense and constant nutrient and organic matter loading at Recife harbor is thus supporting the high microplankton productivity that is not accumulating on the system nor contributing to oxygen depletion, but supporting the whole systems trophic web.

Interannual to decadal changes in the western boundary circulation in the Atlantic at 11°S

The western boundary current system off Brazil is a key region for diagnosing variations of the Atlantic meridional overturning circulation (AMOC) and the southern subtropical cell. In July 2013 a mooring array was installed off the coast at 11°S similar to an array installed between 2000 and 2004 at the same location. Here we present results from two research cruises and the first 10.5 months of moored observations in comparison to the observations a decade ago. Average transports of the North Brazil Undercurrent and the Deep Western Boundary Current (DWBC) have not changed between the observational periods. DWBC eddies that are predicted to disappear with a weakening AMOC are still present. Upper layer changes in salinity and oxygen within the last decade are consistent with an increased Agulhas leakage, while at depths water mass changes are likely related to changes in the North Atlantic as well as tropical circulation changes.

Carbon dioxide emissions from estuaries of northern and northeastern Brazil

The carbon dioxide flux through the air–water interface of coastal estuarine systems must be quantified to understand the regional balance of carbon and its transport through adjacent coastal regions. We estimated and calculated the emissions of carbon dioxide (FCO2) and the partial pressure of CO2 (pCO2) values in 28 estuarine environments at a variety of spatial scales in the northern and northeastern regions of Brazil. The results showed a mean FCO2 (water to air) of 55 ± 45 mmol·m−2·d−1. Additionally, a negative correlation between dissolved oxygen saturation and pCO2 was observed, indicating a control by biological processes and especially by organic matter degradation. This leads to increased dissolved CO2 concentration in estuarine waters which results in a pCO2 that reached 8,638 μatm. Our study suggests that northern and northeastern Brazilian estuaries act as sources of atmospheric CO2. The range of pCO2 observed were similar to those found in inner estuaries in other places around the world, with the exception of a few semi-arid estuaries (Köppen climate classification – BSh) in which record low levels of pCO2 have been detected.

Tropical Atlantic Contributions to Strong Rainfall Variability Along the Northeast Brazilian Coast

Tropical Atlantic (TA) Ocean-atmosphere interactions and their contributions to strong variability of rainfall along the Northeast Brazilian (NEB) coast were investigated for the years 1974–2008. The core rainy seasons of March-April and June-July were identified for Fortaleza (northern NEB; NNEB) and Recife (eastern NEB; ENEB), respectively. Lagged linear regressions between sea surface temperature (SST) and pseudo wind stress (PWS) anomalies over the entire TA and strong rainfall anomalies at Fortaleza and Recife show that the rainfall variability of these regions is differentially influenced by the dynamics of the TA. When the Intertropical Convergence Zone is abnormally displaced southward a few months prior to the NNEB rainy season, the associated meridional mode increases humidity and precipitation during the rainy season. Additionally, this study shows predictive effect of SST, meridional PWS, and barrier layer thickness, in the Northwestern equatorial Atlantic, on the NNEB rainfall. The dynamical influence of the TA on the June-July ENEB rainfall variability shows a northwestward-propagating area of strong, positively correlated SST from the southeastern TA to the southwestern Atlantic warm pool (SAWP) offshore of Brazil. Our results also show predictive effect of SST, zonal PWS, and mixed layer depth, in the SAWP, on the ENEB rainfall.

Quantitative Ecological Risk Assessment of Industrial Accidents: The Case of Oil Ship Transportation in the Coastal Tropical Area of Northeastern Brazil

ABSTRACT Accidents such as toxic spills can cause massive damage to local ecosystems and hamper the sustainable development of hazardous industries. Models that only consider regularly occurring pollution are unable to truly quantify ecological risks (ecorisks) from these industries. This work presents a methodology capable of quantifying ecorisks related to rare and extreme events such as industrial accidents. We developed a procedure that integrates information from different studies that contributes to characterize ecorisks from industrial accidents: (1) reliability analysis, (2) fate and transport modeling, (3) individual-level toxicological assessment, and (4) population modeling. The methodology is exemplified by an application to oil ship transportation to supply Brazils Suape industrial complex. A fish population was strategically chosen to represent the ecosystems health of Suape beach. For the critical accidental scenarios, their frequencies of occurrence were estimated and the space–time evolution of oil simulated. The ecorisks were quantified in terms of time and population probability of fish extinction, categorized and compared against a no-accident scenario. The total ecorisks from all scenarios were presented as a FN curve, where N is the average number of deaths in the population and F the cumulative frequency of accidents with potential to cause N or more deaths.

Variação sazonal da estrutura de massas de água na plataforma continental do Amazonas e área oceânica adjacente

This work analyzes hydrographic properties (temperature and salinity) obtained from three oceanographic cruises performed along the Amazon continental shelf and adjacent oceanic areas of the western equatorial Atlantic. Field data covered three distinct periods and river discharge situation: the maximum river outflow during boreal spring (May 1999); the transition flow period (maximum to minimum discharges) during summer (August 2001), and minimum river flow during autumn (November 1997). The analysis of CTD hydrographic profiles identified four water masses: Coastal Water (CW), Tropical Surface Water (TSW), South Atlantic Central Water (SACW) and Antarctic Intermediary Water (AIW). Results suggest that wind shear variability acts over the horizontal distribution of surface water masses (CW and TSW), while the subsurface waters (SACW and AIW) are influenced by seasonal variability of the NBC transport and the presence of anticyclonic rings at the NBC retroflection area. Vertical transects analysis show that SACW is strongly expanded during the transition river flow regime (about 70 m at 49oW and 220 m at 50oW), which corresponds to the period when NBC and North Equatorial Countercurrent (NECC) reach their maximum strengths.

Seasonal changes in the mixed and barrier layers in the western Equatorial Atlantic

Climate is closely related to the dynamics of the surface layer of the tropical Atlantic and the exchange between this latter and the atmosphere, and wearther forecasting will improve with increasing understanding of the processes that govern the relative distribution of thermodynamic properties of the water column. This paper focuses on the isolation of warm surface waters from the cold ones of the deep ocean by a salinity induced barrier layer (BL) in the western equatorial Atlantic (3oS-7oN; 40o-52oW), based on 487 CTD profiles (REVIZEE - 1995-2001). The main process contributing to the seasonal BL formation is the discharge of low salinity waters from the Amazon river. During boreal late winter/spring (Mar-May; high river discharge), deeper isothermal (ZT) and mixed layers (ZM) prevail and the formation of a 16m-thick BL was clearly determined the formation of a salt-induced marked pycnocline within a deeper isothermal layer. However, during the boreal autumn (Oct-Dec; low river discharge), density stratification was mainly determined by temperature distribution (ZM m ZT; BLT = ZM - ZT m 0). There was no clear register of a BL on the Amazon shelf, but a maximum BL (40 m) formed near the shelf break at 45°W.

Seasonal and interannual variability of sea‐air CO2 fluxes in the tropical Atlantic affected by the Amazon River plume

CO2 fugacities obtained from a merchant ship sailing from France to French Guyana were used to explore the seasonal and interannual variability of the sea-air CO2 exchange in the western tropical North Atlantic (TNA; 5–14°N, 41–52°W). Two distinct oceanic water masses were identified in the area associated to the main surface currents, i.e., the North Brazil Current (NBC) and the North Equatorial Current (NEC). The NBC was characterized by permanent CO2 oversaturation throughout the studied period, contrasting with the seasonal pattern identified in the NEC. The NBC retroflection was the main contributor to the North Equatorial Counter Current (NECC), thus spreading into the central TNA, the Amazon River plume, and the CO2-rich waters probably originated from the equatorial upwelling. Strong CO2 undersaturation was associated to the Amazon River plume. Total inorganic carbon drawdown due to biological activity was estimated to be 154 µmol kg−1 within the river plume. As a consequence, the studied area acted as a net sink of atmospheric CO2 (from −72.2 ± 10.2 mmol m−2 month−1 in February to 14.3 ± 4.5 mmol m−2 month−1 in May). This contrasted with the net CO2 efflux estimated by the main global sea-air CO2 flux climatologies. Interannual sea surface temperature changes in the TNA caused by large-scale climatic events could determine the direction and intensity of the sea-air CO2 fluxes in the NEC. Positive temperature anomalies observed in the TNA led to an almost permanent CO2 outgassing in the NEC in 2010.

Mathematical modelling as a management tool for water quality control of the tropical Beberibe estuary, NE Brazil

Sewage disposal in natural waters is a common problem in most countries. Large inputs of organic matter and nutrients from raw sewage to a weak hydrodynamic environment may lead to deterioration of the water quality. Widely available riverine and estuarine models such as QUAL-2E and MUDLARK can be used to adequately model these situations. Beberibe is a low hydrodynamic estuary that runs through a densely populated region in the Recife Metropolitan Area (RMA), Northeast Brazil, and receives untreated domestic sewage from aproximately 200 000 inhabitants. The mouth of the estuary is shallow and tortuous, causing a large reduction in tidal propagation. The low river flow is strongly influenced by rain seasonality at the upstream boundary, with mean values varying from 4.9 m3 s−1 in the wet winter to 1.4 m3 s−1 during the dry summer. A major program to build sewage plants was planned to increase the water quality of the RMA rivers. This study focuses on water quality modelling of the Beberibe estuary basin, formed by the Beberibe River and two small tributaries. Numerical simulations of temperature, dissolved oxygen, biochemical oxygen demand, nitrate, ammonia, phosphate and faecal coliforms were carried out, targeting the expected population growth in the following 20 years. The QUAL-2E and the MUDLARK models were coupled at the tidal intrusion limit, with the estuarine sector modelled by the MUDLARK while QUAL-2E was used in the upper river. A longitudinal dispersion coefficient related to tidal excursion was introduced into the MUDLARK algorithm to better determine the tidal effect on the distribution of water quality variables. Both models were calibrated successfully and verified with a 4 year water quality data series from the Pernambuco State Environmental Agency (Companhia Pernambucana do Meio Ambiente — CPRH). Results showed that the river flow is a major factor controlling the water quality. Even the most efficient treatment applied was not able to bring water quality up to all desirable levels during dry summer months, mainly considering dissolved oxygen and biochemical oxygen demand. Results also confirm that the spring-neap cycle does not significantly affect water quality, probably due to the strong tidal attenuation at the estuary mouth.