Species diversity variations in Neogene deep-sea benthic foraminifera at ODP Hole 730A, western Arabian Sea

Abstract. This study describes and illustrates the evolution of deep-sea benthic foraminifera from the Blake Ridge during the late Neogene. In total, 305 species of benthic foraminifera belonging to 107 genera were identified. The Blake Ridge receives fine-grained nannofossil-bearing hemipelagic sediments, transported from the Canadian continental margin by the Deep Western Boundary Undercurrent (DWBUC). We thus presume that changes in benthic foraminifera at Ocean Drilling Program (ODP) sites 991A, 994C, 995A and B and 997A reflect mainly changes in the intensity of the DWBUC, which is closely related to North Atlantic Deep Water (NADW) production. However, the dominance of Uvigerina peregrina, U. proboscidea and Cassidulina carinata during the late Miocene in all the holes suggests an increased influence of Southern Component Waters in the Blake Ridge region. During the early Pliocene (4.8–2.8 Ma) in all the sites benthic faunal assemblages suggest that there was an increased transport of organic-rich sediments by the DWBUC from the Canadian margin to the Blake Ridge, driven by increased production of NADW. During this time the species diversity (Sanders' rarefied values) was low. In the younger interval (since 2.8 Ma), the faunal data suggest less transport of organic-rich sediments to the Blake Ridge, which appears to be related to weakening of the DWBUC during cold intervals. An increase in species diversity at 3 Ma probably resulted from decreased population of bacteria due to low organic matter and/or less competition. In the late Pleistocene (c. 0.6 Ma), Stilostomella lepidula became extinct in all the studied holes, suggesting that this species may have possessed a mode of feeding which no longer existed in the cold, well-oxygenated oceans of the present.

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Species diversity of Miocene deep-sea benthic Foraminifera and watermass stratification in the northeastern Indian Ocean

Micropaleontology ◽

10.2113/47.2.111 ◽

2001 ◽

Vol 47 (2) ◽

pp. 111-124 ◽

Cited By ~ 8

Author(s):

A. K. Gupta

Keyword(s):

Species Diversity ◽

Indian Ocean ◽

Benthic Foraminifera ◽

Deep Sea

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Deep-sea benthic foraminiferal species diversity in the NE Atlantic and NW Arabian sea: a synthesis

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/s0967-0645(97)00041-6 ◽

1998 ◽

Vol 45 (1-3) ◽

pp. 165-201 ◽

Cited By ~ 67

Author(s):

Andrew J Gooday ◽

Brian J Bett ◽

Rizpah Shires ◽

P.John D Lambshead

Keyword(s):

Species Diversity ◽

Deep Sea ◽

Arabian Sea ◽

Ne Atlantic ◽

Foraminiferal Species

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Effect of early Oligocene cooling on the deep-sea benthic foraminifera at IODP hole 1138A, Kerguelen Plateau (Southern Ocean)

10.5194/egusphere-egu21-6414 ◽

2021 ◽

Author(s):

Rakesh Kumar ◽

Abhayanand Singh Maurya ◽

Dharmendra Pratap Singh

Keyword(s):

Species Diversity ◽

Southern Ocean ◽

Southern Hemisphere ◽

Benthic Foraminifera ◽

Deep Sea ◽

Bottom Water ◽

Diversity Indices ◽

Marine Ecology ◽

Kerguelen Plateau ◽

Early Oligocene

Benthic foraminifera are typical unicellular marine fauna forming calcareous tests that are commonly used as a proxy to infer the past climatic variabilities. To study the benthic foraminiferal response, we collected 146 samples from IODP hole 1138A, the Southern Ocean (Indian Sector, water depth of 1140 m). We computed various diversity parameters of benthic foraminifera, i.e., Shannon-weaver index (H(S)), Equitability (E'), Hurlbert's diversity index (Sm), Fisher's alpha index (&#945;), and Species richness (S). The calculated diversity indices with the abundance of dominant early Oligocene (33.5 to 31.2 million years ago) benthic foraminifera taxa reveal significant palaeoceanographic changes viz. cooling and warming events in the Southern Ocean. The early Oligocene interval exhibits an unusual condition at hole 1138A dominated by high oxygen species, intermediate food supply, well-ventilated, cold, and corrosive bottom water condition. The calculated values of all diversity parameters increase from 33.7 Ma to 32.8 Ma while attaining the maximum from 32.8 Ma to 32.2 Ma, followed by a decreasing trend. The highest value of diversity parameters coincides with the Oi-1 events. The relative increase in the species diversity between Oi-1 (33.5 Ma) and Oi-1b (31.7 Ma) events correspond to the brief interruption of Warm Saline Deep Water (WSDW). The enhanced values of low species diversity by high seasonality and relatively cold, strong bottom-water currents after Eocene-Oligocene Transition (EOT; 33.9 Ma) and after Oi-1b (31.7 Ma) event relates to the intensification of Antarctic Circumpolar Current (ACC) and Antarctic Bottom Water (AABW) along with the substantial buildup of the southern hemisphere glaciation. The abrupt decrease of abundance of species such as Nuttallides umbonifera, Astrononion echolsi, and Uvigerina peregerina at the end of the studied interval (31.3 Ma) further corroborates the major southern hemisphere glaciation. The present study of the benthic foraminiferal abundance and diversity indices therefore reveals the cooling of the Southern Ocean at early and late stages of the studied interval interrupted by a short-lived warming event. The study further enhances the understanding of paleo-marine ecology by evaluating the response of deep-sea benthic foraminifera to global climate change.Keywords: Kerguelen Plateau, Benthic Foraminifera, Southern Ocean, early Oligocene

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