Distribution, vertical position and ecological implications of shallow gas in Bahía Blanca estuary (Argentina)

Abstract

The aim of this thesis is to characterize the shallow gas deposits of the inner area of the Bahía Blanca estuary and to evaluate the effect of the gas-bearing sediments on the associated subtidal benthic communities. For this purpose, the distribution of shallow gas in the estuary was mapped through the analysis of highresolution seismic records. Based on this map, two study sites were selected (with gas and control) that only differed in the presence of gas in contact with the surface of the seabed. Acoustic methods were used to determine the stratigraphy and morphology of the site with gas and the adjacent area. In addition, the gas sediments were evaluated by means of the following analyses: grain size, organic matter content, X-rays and HPLC head space measurement. The benthic organisms of both sites were compared in terms of abundance, biomass, diversity, evenness, species richness, taxonomic and functional structure. The gas was found widely distributed in the estuary, both near and in contact with the surface of the seabed of the inner area of the Bahía Blanca estuary. It was evidenced in the form of acoustic turbidity and acoustic blanking. The seismo-stratigraphic column presented five seismic sequences of the late Pleistocene-Holocene. It was established that the gas origin is biogenic, being associated with a Middle Holocene deposit, from which it migrated until it was in contact with the surface of the seabed due to the permeability of the overlying strata. The gas in the surface of the seabed was evidenced in sonograms by means of the attenuation of the acoustic signal, which evidences a low cohesion Índice Dedicatoria…………………………………………………………………………………………………….I

Fauna associated with shallow-water methane seeps in the Laptev Sea

“…However, recent results obtained from the southwestern Barents Sea showed increased taxonomic richness within the seepage sites (Sen et al, 2019b). Outside the Arctic similar species richness patterns were reported from the Gulf of Mexico (Cordes et al, 2010) and Argentina (Bravo et al, 2018).…”

“…The reasons for this are unknown so far, since no environmental parameters measured directly at benthic stations are available. The peculiarly higher values of macrofaunal diversity (Shannon-Wiener index) within the cold seeps are known only for a few seep areas, e.g., for the Vestnesa Ridge (Åström et al, 2018), for the South-Western Barents Sea (Sen et al, 2019b) and for the Bahía Blanca estuary in Argentina (Bravo et al, 2018).…”

Peer Review #1 of "Fauna associated with shallow-water methane seeps in the Laptev Sea (v0.1)"

“…However, recent results obtained from the southwestern Barents Sea showed increased taxonomic richness within the seepage sites (Sen et al, 2019b). Outside the Arctic similar species richness patterns were reported from the Gulf of Mexico (Cordes et al, 2010) and Argentina (Bravo et al, 2018). Manuscript to be reviewed found in this area in the depth range 50-2000 m (Sirenko et al, 2004), which is more species than anywhere else in the high Arctic (Buzhinskaja, 2010).…”

“…peculiarly higher values of macrofaunal diversity (Shannon-Wiener index) within the cold seeps are known only for a few seep areas, e.g. for the Vestnesa Ridge(Åström et al, 2018), for the South-Western Barents Sea(Sen et al, 2019b) and for the Bahía Blanca estuary in Argentina(Bravo et al, 2018).…”

Los poliquetos como indicadores biológicos en Latinoamérica y el Caribe

“…Recientemente, altas densidades del poliqueto Aricidea sp. se hallaron indicando depósitos de gas (Bravo et al 2018).…”