Analysis of mangrove forest succession, using sediment cores: A case study in the cananéia -iguape coastal system, São Paulo-Brazil

Sediment cores are an essential tool for the analysis of the dynamics of mangrove succession. Coring was used to correlate changes in depositional environments and lateral sedimentary facies with discrete stages of forest succession at the Cananeia-Iguape Coastal System in southeastern Brazil. A local level successional pattern was examined based on four core series T1) a sediment bank; T2) a smooth cordgrass Spartina alterniflora bank; T3) an active mangrove progradation fringe dominated by Laguncularia racemosa, and; T4) a mature mangrove forest dominated by Avicennia schaueriana. Cores were macroscopically described in terms of color, texture, sedimentary structure and organic components. The base of all cores exhibited a similar pattern suggesting common vertical progressive changes in depositional conditions and subsequent successional colonization pattern throughout the forest. The progradation zone is an exposed bank, colonized by S. alterniflora. L. racemosa, replaces S. alterniflora as progradation takes place. As the substrate consolidates A. schaueriana replaces L. racemosa and attains the greatest structural development in the mature forest. Cores collected within the A. schaueriana dominated stand contained S. alterniflora fragments near the base, confirming that a smooth cordgrass habitat characterized the establishment and early seral stages. Cores provide a reliable approach to describe local-level successional sequences in dynamic settings subject to drivers operating on multiple temporal and spatial scales where spatial heterogeneity can lead to multiple equilibria and where similar successional end-points may be reached through convergent paths

A combined approach of benthic mapping of Caraguatatuba Bay, Brazil, with recommendations for management practices

Benthic habitat mapping is an important first step towards ecosystem-based management. In a top-down approach, benthic mapping of a semi-enclosed bay in south-eastern Brazil was performed using a combined approach of acoustic RoxAnn survey and benthic samples. An inventory of the benthic macrofauna as well as unsupervised classifications of the acoustic data provided information about sediment patterns and potential areas of ecological importance, and a new zoning scheme is suggested based on the macrofauna analysis. The RoxAnn survey proved suitable to determine sediment characteristics, however, species–environment relationships cannot be revealed by acoustic techniques only. Based on the data presented here, acoustic surveys could become an important tool in future monitoring programmes following the bottom-up approach of seabed classification protocols for an ecosystem-based management to improve existing coastal ecosystem management strategies in Brazil. A combined approach of benthic mapping of Caraguatatuba Bay, Brazil, with recommendations for management practices (PDF Download Available). Available from: https://www.researchgate.net/publication/257423766_A_combined_approach_of_benthic_mapping_of_Caraguatatuba_Bay_Brazil_with_recommendations_for_management_practices [accessed Jun 6, 2017]

The influence of deep marine circulation on gas-related seafloor morphologies over a salt tectonic domain: Case studies on the continental slope of Santos Basin, southern Brazilian margin

4th Deep Water Circulation Research Conference. Edimburgh 24-26 may 2023The Santos Basin slope is a physiographic feature whose seafloor morphology is influenced by both geological and oceanographic processes. Regarding geological processes, halokinesis has been one of the main forces driving the geological evolution of this margin and influencing the present-day seafloor morphology. Salt dynamics is considered to be responsible for the development of faults and fractures, which behave as fluid conduits toward the seafloor surface. The supply of fluids added to the nature of the sediments provide favourable conditions for the formation of gas-escape seafloor morphologies, such as pockmarks, carbonate mounds and ridges. Additionally, the observation of exhumed salt diapirs in the south-western part of the Santos Basin seafloor is suggestive of active halokinesis. Besides, oceanographic processes leave a conspicuous fingerprint in the formation of an extensive array of morphological and sedimentary seafloor features. The interaction of bottom currents with pockmarks, carbonate structures and exhumed salt diapirs erodes the seafloor relief and contributes to the formation of moats, comet marks and scours. Associated with the prevailing erosive features, bottom currents-related deposits are formed along the slope structures constituting contourite systems

Deep pockmarks as natural sediment traps: a case study from southern Santos Basin (SW Atlantic upper slope)

This study examines the role of deep pockmarks in acting as natural sediment traps. Multibeam bathymetry, single-channel seismic and sediment samples data were used for describing the morphology of pockmarks as well as the nature of sediments inside and outside these depressed features, in an area of Santos Basin (SW Atlantic upper slope), dominated by the strong flow of Brazil Current. Results show that the grain size and chemical composition of sediments inside pockmarks are distinct from the outside. Also, radiocarbon dating shows that Holocene ages are found only in samples located inside the pockmarks. Combination of sedimentological, geochemical and geochronological data allowed to recognise that deep pockmarks might present distinct sediment deposition processes when compared with those of shallow pockmarks, in which turbulence impedes sediment deposition, as reported in the literature.The authors acknowledge the crew and researchers of the two surveys held in 2016 and 2017, onboard R.V. Alpha Crucis. The São Paulo Science Foundation (FAPESP, grants 2014/08266-2, 2016/22194-7 and 2015/17763-2) funded this work. Partnerships between MM.de M., U.S. and F.L-S., are funded by FAPESP (grant 2017/50191-8) and the Brazilian National Research Council (CNPq, grant 401041/2014-0), respectively. M.M.de M. acknowledges CNPq for the research grants 303132/2014-0 and 300962/2018-5. This study was financedin partby the Coordenação deAperfeiçoamento dePessoal de Nível Superior – Brasil (CAPES) – Finance Code 001 (R.B.R. MSc. Scholarship)

Geomorphological features along the shelf of the southern Brazilian margin: Implications for shallow-water sediment transport induced by ocean currents

Chirp profiles collected on the southern Brazilian shelf were combined with sedimentological and hydrodynamic data to characterize shelf geomorphology, focusing on the development of outer shelf bedforms and their genetic links with major oceanic currents. Outer shelf sediment accumulations are interpreted as two scales of bedforms, such as dunes and sand ridges. In the São Paulo Bight, cuspate bedforms are bounded landward by a geomorphological scarp. The sector between Florianopolis and Mostardas also exhibits frequent asymmetric bedforms, whereas the inner- middle shelf is covered by semitransparent sheets. The southern Rio Grande Cone is characterized by stratified deposits covering vast outer shelf areas. Surficial sediment samples reveal a dominantly muddy composition and relatively high carbonate contents. Hydrodynamic data indicate a major influence of the Brazil Current over the São Paulo Bight. The prolific bedform outer-shelf environment is assumed to be mostly relict formed in a transgressive shallow-water setting. The sand ridges are believed to have evolved from a moribund stage characterized by morphological degradation to a relict stage, with preservation enhanced by fine-grained winnowing, coarse sediment armoring, and early cementation. Bedform migration seems to be occurring on the São Paulo Bight due to the presence of a nearly permanent meander of the Brazil Current. Over most of the inner shelf, the northward advection of sediments mainly led by the Brazilian Coastal Current has formed extensive fine-grained deposits. The occurrence of a relict shelf scarp may have conditioned the formation of the outer-shelf bedform environment. The vast spatial distribution of bedforms over most of the outer shelf seems comparable with other shelf areas, such as the south African shelf, dominated by the influence of unidirectional oceanic currents. Dune dimensions are lower on the Brazilian shelf, due to their relict character, the geomorphological configuration of the margin, and the scarcity of sand sources.The authors acknowledge the crew and researchers of R/V Alpha Crucis (University of São Paulo), who participated in Mudbelts I and II cruises. Funding was provided by the São Paulo Science Foundation (FAPESP), grants 2010/06147-5 and 2015/17763-2. F.J. Lobo acknowledges FAPESP for the concession of grant n° 2019/27436-0 as a Visiting Researcher at Instituto Oceanografico, University of São Paulo, from 29 January to 11 March 2023. A. López-Quirós thanks funding provided by FJC2021-047046-I (MCIN/AEI/10.13039/501100011033 and NextGenerationEU/PRTR). M.M. de Mahiques acknowledges the Brazilian Council for Scientific and Technological Development (CNPq) for Research Grant No. 300962/2018-5.Peer reviewe

The Alpha Crucis Carbonate Ridge (ACCR): Discovery of a giant ring-shaped carbonate complex on the SW Atlantic margin

Recently acquired bathymetric and high-resolution seismic data from the upper slope of Santos Basin, southern Brazilian margin, reveal a major geomorphological feature in the SW Atlantic that is interpreted as a carbonate ridge - the Alpha Crucis Carbonate Ridge (ACCR). The ACCR is the first megastructure of this type described on the SW Atlantic margin. The ~17 × 11-km-wide ring-shaped ACCR features tens of >100-m-high steep-sided carbonate mounds protruding from the surrounding seabed and flanked by elongated depressions. Comet-like marks downstream of the mound structures indicate that the area is presently influenced by the northward flow of the Intermediate Western Boundary Current (IWBC), a branch of the Subtropical Gyre that transports Antarctic Intermediate Water. Abundant carbonate sands and gravels cover the mounds and are overlain by a biologically significant community of living and dead ramified corals and associated invertebrates. The IWBC acts as a hydrodynamic factor that is responsible for both shaping the bottom and transporting coral larvae. We contend that the ACCR was formed by upward fluid flow along active sub-surface faults and fractures that formed by lateral extension generated by the ascending movement of salt diapirs at depth. The ACCR provides an important modern and accessible analogue for a seabed carbonate build-up related to sub-surface hydrocarbon systems.The authors are indebted to the crew and researchers who participated in the Jan-Feb 2019 survey aboard the R.V. Alpha Crucis for their constant support. Acknowledgements are also due to the São Paulo Science Foundation (FAPESP grants 2014/08266-2, 2015/17763-2, and 2016/22194-0). MMdeM acknowledges the Brazilian National Research Council (CNPq, grant 300962/2018-5). The partnership between MMdeM and the US was supported by FAPESP (grant 2017/50191-8 – SPRINT Program). The partnership between MMdeM and F.J.L. was supported by CNPq (grant 401041/2014-0). The authors gratefully acknowledge support from Shell Brasil through the BIOIL project at the Oceanographic Institute of the University of São Paulo and the strategic importance of the support given by ANP through R&D levy regulation. We thank Petrel-Schlumberger for providing academic licenses that enabled the seismic interpretation