Spatial sediment variability in a tropical tide dominated estuary: Sources and drivers Silvia H.M. Sousa a, * , Paulo A.L. Ferreira a , Maria V.A. Martins b, c , Eduardo Siegle a , Paula G.C. Amaral a , Rubens C.L. Figueira a , Cintia Yamashita a , Andr  e R. Rodrigues a , Michel M. Mahiques a a Instituto Oceanogr afico, Universidade de S~ ao Paulo, Praça do Oceanogr afico, 191, Cidade Universit aria, 05508-120, S~ ao Paulo, SP, Brazil b Universidade do Estado do Rio de Janeiro, Faculdade de Geologia, Av. S~ ao Francisco Xavier, 542, Maracan~ a, 20550-013, Rio de Janeiro, RJ, Brazil c Departamento de Geoci^ encias, GeoBioTec, Universidade de Aveiro, Campus de Santiago, 3810-193, Aveiro, Portugal article info Article history: Received 1 April 2016 Received in revised form 26 July 2016 Accepted 8 August 2016 Available online 9 August 2016 Keywords: Sedimentary dynamics Caravelas estuary Total organic carbon Stable isotopes Metals Rare earth elements abstract Surficial sediment composition and spatial variability reflect the dynamics and level of natural and anthropogenic impact in estuarine systems. The aim of this study is to evaluate some key environmental and sedimentary variables, as well as to evaluate the current environmental quality in the tide- dominated Caravelas estuarine system (Brazil). Sixty-five surficial sediment samples were studied for grain size as well as calcium carbonate, total organic carbon, total nitrogen, metals, semi-metals and rare earth elements and for organic matter d 13 C. Based on the spatial distribution of these data and sum- marizing our findings, three sectors can be individualized in the Caravelas estuarine system: i. Barra Velha inlet; ii. the main channel of the Caravelas estuary, and iii. the channel interconnecting Caravelas and Nova Viçosa estuaries. In the inlet the sedimentary organic matter is provided essentially by marine sources, which corroborates the small continental input. Freshwater dissolved organic carbon and par- ticulate organic carbon occur in the interconnecting channel, proving the occurrence of the residual transport towards the Caravelas estuary, with continental contribution towards Caravelas River. The geochemical fingerprint indicates that the Barreiras Group, composed by Neogene terrigenous deposits, located west of the study area, as an important source of terrigenous material to the entire Caravelas estuary system. The higher values of heavy rare earth elements (between 20 and 30 mg kg 1 ) in the northern sector of the study area may be related to the high degree of chemical weathering in magmatic or metamorphic rocks, which occur to the north of the study area. © 2016 Elsevier Ltd. All rights reserved. 1. Introduction Estuaries are natural places that provide goods and services that are of economic and ecological importance. They act as filters for river and streams’ sediments and pollutants before its waters flow into the ocean and play an important role in the cycling of many biogeochemically important elements. According to Dürr et al. (2011), tidal systems account for 22% of the global coastline, showing its relevance while serving as active filters of both dis- solved and suspended material being exchanged through the coastline. Being sensitive environments where rapid changes occur, it is of central importance to scientists, managers and policy makers to understand the response of these natural systems to ongoing changes (Mitchell et al., 2015). In the last decades, the coastal marine zones have been commonly submitted to high anthropo- genic pressure and have been highly modified by urban, industrial and port developments and/or by natural processes (e.g., erosion, river discharge), leading to changes in the water quality and health of the ecosystem (e.g., Nichols et al., 1986; Alve and Olsgard, 1999; Cearreta et al., 2002; Azevedo et al., 2008). Therefore, ecosystem management has been increasingly common as well as decision making processes, which in turn are strongly dependent of the knowledge of ecosystem functioning (Azevedo et al., 2008). In this study we focus into the tropical tide dominated Caravelas - Nova Viçosa estuarine system, located in the northeastern coast of Brazil (State of Bahia). Added to its importance is that it reaches the ocean nearby the Abrolhos reef complex, considered the largest * Corresponding author. E-mail address: smsousa@usp.br (S.H.M. Sousa). Contents lists available at ScienceDirect Journal of South American Earth Sciences journal homepage: www.elsevier.com/locate/jsames http://dx.doi.org/10.1016/j.jsames.2016.08.004 0895-9811/© 2016 Elsevier Ltd. All rights reserved. Journal of South American Earth Sciences 72 (2016) 115e125