Live (Rose Bengal stained) foraminiferal faunas from the northern Arabian Sea: faunal succession within and below the OMZ

[摘要] Live (Rose Bengal stained) benthic foraminifera fromthe Murray Ridge, within and below the northern Arabian Sea oxygen minimumzone (OMZ), were studied in order to determine the relationship betweenfaunal composition, bottom water oxygenation (BWO), pore water chemistry andorganic matter (organic carbon and phytopigment) distribution. A series ofmulticores were recovered from a ten-station oxygen (BWO: 2–78 μM)and bathymetric (885–3010 m depth) transect during the winter monsoon inJanuary 2009. Foraminifera were investigated from three different sizefractions (63–125 μm, 125–150 μm and>150 μm). The larger foraminifera (>125 μm)were strongly dominated by agglutinated species (e.g. Reophaxspp.). In contrast, in the 63–125 μm fraction, calcareous taxawere more abundant, especially in the core of the OMZ. On the basis of aprincipal components analysis, three foraminiferal groups were identified andcorrelated to the environmental parameters by canonical correspondenceanalysis. The faunas from the shallowest stations, in the core of the OMZ(BWO: 2 μM), were composed of "low oxygen" species, typical ofthe Arabian Sea OMZ (e.g. Rotaliatinopsis semiinvoluta,Praeglobobulimina sp., Bulimina exilis, Uvigerinaperegrina type parva). These taxa are adapted to the very low BWOconditions and to high phytodetritus supplies. The transitional group,typical for the lower part of the OMZ (BWO: 5–16 μM), is composedof species that are tolerant as well to low-oxygen concentrations, but maybe less critical with respect to organic supplies (e.g.Globocassidulina subglobosa, Ehrenbergina trigona). Belowthe OMZ (BWO: 26–78 μM), where food availability is more limitedand becomes increasingly restricted to surficial sediments, cosmopolitancalcareous taxa were present, such as Bulimina aculeata,Melonis barleeanus, Uvigerina peregrina andEpistominella exigua. Miliolids were uniquely observed in this lastzone, reflecting the higher BWO and/or lower organic input. At these deepersites, the faunas exhibit a clear succession of superficial, intermediate anddeep infaunal microhabitats, which can be linked to the deeper oxygen andnitrate penetration into the sediment.

[学科分类] 地球化学与岩石