Papers by Michel M Mahiques
Frontiers in Marine Science
Mg/Ca composition (mmol/mol) derived from the chemical analysis of the planktonic foraminifera Gl... more Mg/Ca composition (mmol/mol) derived from the chemical analysis of the planktonic foraminifera Globigerinoides ruber (pink) tests (250 - 300 μm size fraction) from a marine sediment core 7610 retrieved from the SW Atlantic shelf (lat. -25.50000, long. -46.60000, 89.0 m water depth) in December 2004 during Oceanographic cruise Paleoprod, onboard the R/V Prof Wladimir Besnard.
UK'37, TEX86 and LDI indices, and temperature estimates for sediment core NAP 63-1 (South Brazil Bight), supplement to: Dauner, Ana Lúcia Lindroth; Mollenhauer, Gesine; Bícego, Márcia Caruso; de Souza, Mihael Machado; Nagai, Renata Hanae; Figueira, Rubens César Lopes; Mahiques, Michel Michaelovit... Millennial-scale oscillations are known to be important in the climatic evolution of the Atlantic... more Millennial-scale oscillations are known to be important in the climatic evolution of the Atlantic basin, but which internal processes originates these oscillations are still uncertain. In this study, we investigated how the Greenland and Antarctic climates affect the SW Atlantic through basin-wide oceanographic features (such as the NADW formation and the Agulhas leakage). We reconstructed sea surface and subsurface temperatures (SST and subT) using three lipid-based biomarker proxies (UK'37, TEX86 and LDI indexes) from a sediment core (NAP 63-1) retrieved from the SW Atlantic slope (24.8°S, 44.3°W). This location permitted to evaluate the temperature oscillations of the Brazil Current without any terrigenous or upwelling-derived biases. Both TEX86-based and LDI-based estimates represent the mean annual SST, while the UK'37-based estimates represent the subT (around 30 m water depth). The periods with the most well-mixed water column were observed during intervals of cooling...
Marine Geology, 2021
Abstract A new mixed turbidite-contourite system is described in the northern Campos Basin, south... more Abstract A new mixed turbidite-contourite system is described in the northern Campos Basin, southeastern Brazilian margin. This system is developed in a middle slope setting, and was formed through non-synchronous interaction between the turbidity current and a contour current in the same stratigraphic interval (Miocene). Depositional cycles were differentiated based on diagnostic seismic features. Seismic attributes, seismic facies, and isochron maps were used to identify alternating cycles of downslope and alongslope processes in the study area, along with the intermediate stage with features from both processes (mixed system). Seismic units were then associated with the dominant type of current. Alongslope current activity can be distinguished from the downslope current based on its acoustic characteristics (mainly low root-mean-square (RMS) amplitude values), internal architecture (clinoforms), and external geometry pattern (alongslope trend). On the other hand, downslope gravity currents develop deposits with high-amplitude or chaotic seismic facies, usually higher values of RMS amplitude, channel or channel-lobe features, erosive surfaces, and a basinward depositional trend. The first and oldest seismic unit (S1) was interpreted as a dominantly alongslope system, with vertical aggrading sigmoidal clinoforms and high-frequency, low-amplitude reflections commonly associated with fine-grained sedimentary deposits, typical of a plastered drift, along with a basinward mass transport deposit (MTD) from previous drift instability. Seismic unit S2 represents the intermediate stage where both gravity-driven and along-slope currents act asynchronously. Its is refered to as a mixed turbidite-contourite sequence that shows high-amplitude sediment waves migrating upslope and a moat feature that is carved in its upslope front. The interfingering between high- and low-amplitude reflectors, distal chaotic facies, together with sediment waves and a channel moat, points to a sand-rich deposit reworked by northward-flowing contour currents. Seismic units S3 and S4 show downslope features with chaotic facies (S3) and paleochannels with coarse basal lag deposits (high RMS amplitude values) (S4). In S4, a series of long-lived submarine channels formed. Last, seismic unit S5, referred to as the second plastered drift sequence, is marked by low-amplitude clinoforms that thin basinward. At the seafloor, submarine channel banks (formed at S4) covered by fine sediment deposits (from S5) show asymmetrical features with a slight northward depositional trend, indicating a northward-flowing bottom current, as the deposits are known to pile up in a downcurrent trend. Important information on the paleocurrents' direction was also made based on the final deposits display (e.g. terraces, sediment waves, paleochannels). Research on alternating dominant processes and transitional stages or mixed depositional systems, with both turbidites and contour currents, may provide a better understanding of deep-water depositional processes. Because these processes do not always fit previous depositional models that are mainly described for synchronous systems, new insights on cyclic non-synchronous mixed systems can improve our understanding of how mixed systems are organized through time and space. Being able to determine which were the dominant processes that controlled the sedimentation by indicating periods where the margin was mostly submitted to sediment transfer from continent to the basin and periods where the oceanic currents prevailed by redistributing sediments along the isobaths and replacing the axis of downslope transfer conduits. Setting new models on cyclic deposits and intermediate stages can have a future economic impact on potential hydrocarbon reservoir architecture.
Supplementary material 1. Summary of the grain size and geochemical results Supplementary materia... more Supplementary material 1. Summary of the grain size and geochemical results Supplementary material 2. Stereomicroscopic images of the distinct sand fraction composition. 1) Siliciclastic with less than 20% of phosphorite, 2) Siliciclastic with 20% to 50% of oxidized phosphorite, 3) 50%-80% of oxidized phosphorite and, 4) Oxidized phosphoritic sand.
Oceanography: Open Access, 2014
Earth Surface Processes and Landforms, 2017
This study describes the formation of two successive baymouth spits systems on the southeastern B... more This study describes the formation of two successive baymouth spits systems on the southeastern Brazilian coast and the degradation of the first system. The study area includes the Jureia Beach spit, the deflected Ribeira de Iguape River mouth, the central Iguape sandy headland, the Icapara Inlet of the Mar Pequeno Lagoon and the northern end of the Comprida Island barrier spit. The wave and river flow patterns were combined with the coastline evolution and the alongshore migration rates deduced from satellite images. Initially, both spits showed convergent alongshore migration rates equal to or less than 83 m/yr. However, the extreme river flow due to high rainfall during a very strong El Niño event in 1983 eroded the inland side of the Jureia Beach spit, which finally retreated due to wave erosion. In 1989, a sand bank emerged in the river mouth, which attached to the central headland forming a recurved northeastward spit. In 1994, the high fluvial discharge associated with another very strong El Niño event caused the landward migration of the new spit and emersion of a second sand bank. This second sand bank merged with the Jureia Beach spit in 1997 at an alongshore migration rate of 1795.6 m/yr. Wave erosion of the central headland continued and the attached spit disappeared in 2000. In 2009, the headland erosion merged the river mouth and the Icapara Inlet, which resulted in flanking baymouth spits in a configuration that remains today. Therefore, two models for the formation of baymouth spits have been documented for wave-dominated microtidal coasts in humid tropical regions with intense fluvial discharge. The convergent longshore migration of the spits is controlled by both the bidirectional longshore drift and the fluvial discharge, the latter eroding the fronting spit, supplying sediments and acting as a hydraulic blockage for longshore drift.
Science Advances, 2016
A novel Amazonian reef biome was discovered, encompassing large rhodolith and sponge beds under l... more A novel Amazonian reef biome was discovered, encompassing large rhodolith and sponge beds under low light, low oxygen, and high POC.
13th International Congress of the Brazilian Geophysical Society & EXPOGEF, Rio de Janeiro, Brazil, 26–29 August 2013, 2013
The Holocene sedimentation on Flamengo Bay and Boqueirao Strait is investigated through compariso... more The Holocene sedimentation on Flamengo Bay and Boqueirao Strait is investigated through comparison of sedimentological and geophysical data, both surficial and subsurficial. Since these two compartments are hydrodinamically related, their understanding can lead to increase the knowledge of oceanographic changes that occurred along the Holocene. The methodology included high-resolution seismic, sidescan sonar and bathymetry.
e Sousa, SHdM, Figueira, RCL, Tassinari, CCG, Furtado, VV, Passos, RF, 2004. Hydrodynamically driven patterns of recent sedimentation in the shelf and upper slope off Southeast Brazil
Anais da Academia Brasileira de Ciencias, 2014
The role played by human activity in coastline changes indicates a general tendency of retreating... more The role played by human activity in coastline changes indicates a general tendency of retreating coasts, especially deltaic environments, as a result of the recent trend of sea level rise as well as the blockage of the transfer of sediments towards the coast, especially due to the construction of dams. This is particularly important in deltaic environments which have been suffering a dramatic loss of area in the last decades. In contrast, in this paper, we report the origin and evolution of an anthropogenic delta, the Valo Grande delta, on the south-eastern Brazilian coast, whose origin is related to the opening of an artificial channel and the diversion of the main flow of the Ribeira de Iguape River. The methodology included the analysis of coastline changes, bathymetry and coring, which were used to determine the sedimentation rates and grain-size changes over time. The results allowed us to recognize the different facies of the anthropogenic delta and establish its lateral and ...
From Pole to Pole, 2012
Monitoring has been developed by Antarctic Programmes such as Antarctic New Zealand (www.antarcti... more Monitoring has been developed by Antarctic Programmes such as Antarctic New Zealand (www.antarcticanz.govt.nz) and the US Antarctic Programme (USAP) (http://www.usap.gov) considering expansion of human activities and inevitable environmental.
Polar Biology, 2014
The Antarctic continent is one of the most protected areas on the planet, but is dynamically resp... more The Antarctic continent is one of the most protected areas on the planet, but is dynamically responding to environmental change on a global scale. Change in the air temperature may affect the organic matter production in the area. Biomarkers such as sterols, n-alkanols and phytol in three sediment cores from Admiralty Bay, Antarctica, were determined to identify the type of organic matter, variation in input and possible relationship with general temperature changes over the past decades. The concentrations ranged from 0.91 to 13.99 lg g-1 (dry weight) of total sterols, 0.20-2.14 lg g-1 of total n-alkanols and 0.13-2.38 lg g-1 of phytol. Cholest-5-en-3b-ol was the most abundant sterol. The fecal sterols, 5b-cholestan-3b-ol and 5b-cholestan-3a-ol, occurred at low concentration (\0.01-0.15 lg g-1), below the baseline values for this region. The lower carbon chain n-alkanols were more abundant, which suggested that algae, bacteria and zooplankton were the primary sources of the sedimentary organic matter. Phytol exhibited little variation across all of the cores, which appears to be the result of degradation. Variation in the concentration of compounds in one core was compared with the variation in mean air temperature (MAT) over time; this preliminary association showed a tendency toward increased concentration during the period in which the MAT was more elevated.
Ocean & Coastal Management, 2013
Marine Pollution Bulletin, 2013
Journal of Iberian Geology, 2011
This work evaluates the quality of the sediment in Ria de Aveiro, a coastal lagoon located at N o... more This work evaluates the quality of the sediment in Ria de Aveiro, a coastal lagoon located at N of Portugal that is under strong anthropic influence, and the effects of the contamination on benthic foraminifera. The initial approach for measuring pollution was done through the load pollution index (LPI), based on As, Cd, Cr, Cu, Ni, Pb and Zn concentrations, and determined by total digestion of the sediments (TDS). This information was complemented by conducting a metal fractionation technique (sequential chemical extraction-SCE) in some of the most contaminated samples in order to define the relevance of different metal bearingphases (exchangeable cations adsorbed by clay and co-precipitated with carbonates, absorbed by organic matter and retained in the mineralogical phase) and to evaluate the toxic heavy metal availability. Multivariable statistical analyses were carried out taking into consideration the geochemical results, as well as the biotic (percentage of species/groups of species; foraminifer abundance and diversity) and abiotic variables, such as sediment content in mud, total organic carbon (TOC) and Eh. SCE results show that most of the element concentration in the sediments is retained in the resistant mineralogical phase. However, the higher bioavailability of some toxic elements, such as As, Cd, Cu, Hg, Ni, Pb and Zn, found in Laranjo Bay, Aveiro City, Aveiro Harbours and Espinheiro Channel, have a generic negative impact on benthic foraminifera of the Aveiro lagoon. Differential sensitivity of benthic foraminifera to high concentrations of heavy metals may exist. Quinqueloculina seminulum, for instance, seems to be more tolerant to higher bioavailable concentrations of Pb and Cu than Ammonia tepida or Haynesina germanica. Both
Continental Shelf Research, 2014
ABSTRACT The vertical distribution (0 to 100 m) of planktonic foraminifera was investigated based... more ABSTRACT The vertical distribution (0 to 100 m) of planktonic foraminifera was investigated based on 40 tow samples that were collected in 8 stations, during the austral summer of 2002, in a geographically restricted area (23°S–25°S and 40°W–44°W) on the southeastern Brazilian continental margin. Species' abundances are low (less than 10 specimens/m3), which is typical of an oligotrophic area. The foraminifera assemblage is mainly composed of warm water species (Globigerinoides ruber white and pink forms), with a predominance of spinose and symbiont-bearing species. Temperature and inorganic nutrient enrichment of the surface are the main factors that control foraminiferal abundance and diversity; nevertheless salinity can also influence the ecological descriptors. The role of the deep chlorophyll maximum (DCM) in the distribution of foraminifera is not always clear, but the increase in the abundance of G. ruber (white and pink) seems to be related to a deeper DCM, and high salinities (S>36.5). The ecological habitat of these species is affected by the depth of the mixed layer, with a predominance of the white form in deeper layers. Increases in the foraminiferal diversity are related to the dynamics of the Brazil Current system, which displaces the area of high productivity in the euphotic zone off the coast. The abundances of Globigerina bulloides, Globigerina falconensis, Globigerinella calida and Globigerinella siphonifera follow the nutrient enrichment of the surface water mass, corroborating the usefulness of these species as paleoproductivity proxies in the study area. These data confirm the use of diversity measurements and assemblages composition for reconstructing past water column structures in subtropical oceans.
Continental Shelf Research, 2013
ABSTRACT Novel and unusual sinkhole-like features are described for the Abrolhos Bank continental... more ABSTRACT Novel and unusual sinkhole-like features are described for the Abrolhos Bank continental shelf, eastern Brazil, based on geophysical and geological assessments. These unusual structures are large cup-shaped depressions similar to sink/blueholes (10-75 m in diameter, 8-39 m in height), occurring in a consolidated carbonate substrate in the mid and outer shelf. A total of 36 such features, locally named buracas, were found between 41 and 161 km off the coast and between 24 and 65 m depth (the bottom of these features may be as deep as 93 m). The buracas' walls are mainly composed of encrusting coralline algae. Radiocarbon dating has provided ages of 5400 +/- 90 yr Cal BP, 8630 +/- 90 yr Cal BP and 39,200 +/- 400 yr BP. Besides providing a comprehensive description of these novel structures within the mesophotic zone, the potential mechanisms by which these sinkhole-like structures originated are discussed here, as well as the possible active mechanisms impeding their filling with sediments and biogenic material. We hypothesize that their origin could be related to either typical sinkhole formation during subaerial exposure or to a partially Holocene growth pattern influenced by antecedent morphology and gas/fluid escaping due to organic matter decomposition. The buracas are relevant not only because they comprise outstanding novel features, but also because they are relevant targets for marine conservation, as they enhance productivity and aggregate biomass in a region under growing fishing pressure.
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Papers by Michel M Mahiques