Benthic foraminifera from the deep-water Niger delta (Gulf of Guinea): Assessing present-day and past activity of hydrate pockmarks

Abstract

cited By 8International audienceWe present ecological and isotopic (δ18O and δ13C) data on benthic foraminifera sampled from 4 deep-sea stations in a pockmark field from the deep-water Niger delta (Gulf of Guinea, Equatorial Atlantic Ocean). In addition, a series of sedimentological and (bio)geochemical data are shown to back up foraminiferal observations. All stations are located within 1.2km of each other, so prevailing oceanographic conditions can be assumed to be similar at each site. Two of the sites (GMMC-01 and GMMC-02) are located in a pockmark (named "pockmark A") where current methane seepages were recorded by ROV observations. A third station (GMMC-03) is located in the topographic depression interpreted as a collapsed pockmark (named "pockmark B"). The fourth site (GMMC-04) is a reference station, without evidence of past or present seepages. Our observations show that degraded organic matter with low bio-availability is present at all stations with a preferential burial of organic compounds in topographic depressions (GMMC-03 station). Authigenic aragonite is abundant in surface sediments at stations GMMC-01 and -02. Its precipitation is likely related to high rates of methane oxidation during past seep events in episodically active pockmark A. In contrast, the absence of anaerobic methanotrophic Archaea (ANME) during the sampling period (November 2011) suggests that only moderate sulphide and methane oxidation take place close to the sediment-water interface. Compared to the reference site GMMC-04, living foraminifera at the collapsed and episodically active pockmarks show minor changes in terms of diversity, standing stocks and faunal composition. However, the δ13C signal of living and dead (but well-preserved) foraminiferal species (Ceratobulimina contraria, Melonis barleeanus, Uvigerina peregrina) is depleted in the episodically active pockmark A compared to the other stations. Overgrowth of authigenic carbonate on altered foraminifera generates an important shift to lower δ13C values. Dead faunas carry a complex time-averaged message, integrating taphonomic gains and losses related to the temporal variability of gas emission. They reveal major faunal differences that may be useful to detect gas hydrate seepages in different pockmark stages. © 2014 Elsevier Ltd

Benthic foraminifera as proxies of marine influence in the Orosei marine caves, Sardinia, Italy

“…In 2014, studies were conducted on the BT and BM caves, and these studies were based on the quantitative data of the total (living plus dead) assemblage, while also considering possible postmortem processes (van Hengstum & Scott, ), which allowed the reliable definition of ecozones (Bergamin et al, ; Romano, Bergamin, et al, ). Additionally, in this research, the total foraminiferal assemblage was considered a proxy for the definition of reliable ecozones, corresponding to the average conditions during the deposition of the sediment analysed (Fontanier et al, ; Frezza & Carboni, ; Jorissen et al, ; Leorri, Cearreta, Irabien, & Yusta, ).…”

Characteristics of meiofauna in extreme marine ecosystems: a review

“…This work suggests that foraminiferal species observed in cold seep areas are not endemic and may be recruited from adjacent non-seep zones (e.g. Sen Gupta and Aharon 1994;Kitazato 1996;Sen Gupta et al 1997;Rathburn et al 2000Rathburn et al , 2003Lobegeier and Sen Gupta 2008;Martin et al 2010;Fontanier et al 2014b).…”

“…Living benthic foraminifera from modern cold seeps have been investigated in a number of studies (e.g. Sen Gupta and Aharon 1994;Kitazato 1996;Sen Gupta et al 1997Rathburn et al 2000Rathburn et al , 2003Bernhard et al 2001Bernhard et al , 2010Torres et al 2003Torres et al , 2010Martin et al 2004Martin et al , 2010Heinz et al 2005;Panieri 2006;Mackensen et al 2006;Lobegeier and Sen Gupta 2008;Fontanier et al 2014b). This work suggests that foraminiferal species observed in cold seep areas are not endemic and may be recruited from adjacent non-seep zones (e.g.…”

Unique Authigenic Mineral Assemblages and Planktonic Foraminifera Reveal Dynamic Cold Seepage in the Southern South China Sea

“…The δ 13 C composition of foraminifera is a common proxy for reconstructing changes in paleoceanographic and paleo-climate conditions, because foraminifera are sensitive to these changes and ubiquitous in marine settings [38,39]. In cold-seep areas, owing to the prokaryote food source for foraminifera and cemented authigenic carbonate or the incorporation of dissolved inorganic carbon (DIC) with negative d 13 C values into the shells, the foraminifera δ 13 C values can be depleted extremely in 13 C in the stratigraphic record, with more negative δ 13 C values (−4% to −25% ) than those found in typical marine settings (0 < δ 13 C < 1.5% ) [38][39][40][41][42][43][44][45][46][47][48][49]. Hence, it can be interpreted as an indicator of methane seepages over geological time [40,41,[50][51][52][53][54][55][56][57][58][59][60][61][62].…”

“…Hence, it can be interpreted as an indicator of methane seepages over geological time [40,41,[50][51][52][53][54][55][56][57][58][59][60][61][62]. Furthermore, the abundances and diversities of the foraminiferal assemblages at cold seeps are generally lower than those of typical marine settings (non-seep areas) [42,43,[63][64][65][66]. Several studies investigated the correlation between benthic foraminiferal communities (composition, abundance, diversity and dominant species) and hydrocarbon emissions [43,59,[67][68][69][70].…”