Foraminifer and Ostracod Occurrence in a Cool-Water Carbonate Factory of the Cape Adare (Ross Sea, Antarctica): A Key Lecture for the Climatic and Oceanographic Variations in the Last 30,000 Years

Romana Melis,Gianguido Salvi

doi:10.3390/geosciences10100413

Abstract

Foraminifers and ostracods were studied in a gravity-core recovered near Cape Adare (Ross Sea, Antarctica) with the aim of identifying the climatic and oceanographic variations during the last 30 ka. The sedimentary sequence represents conditions of a cool-water carbonate factory, which evidences that during the Marine Isotope Stage 2 (MIS2) the area was ice-free and very productive. The overall preservation of delicate skeletal remains such as bryozoans and molluscs indicated moderate bottom currents. This carbonate factory was interrupted by some terrigenous levels, representing conditions of instability/retreat of the ice shelves southward. The younger levels were referred to the meltwater pulse (MWP)-1A and 1B events. The Holocene sequence comprised more terrigenous sediments, reflecting high bottom-currents similar to the present-day conditions. Very abundant and well preserved foraminifers and ostracods, representative of shelf-upper slope paleoenvironments, were recovered. Epistominella exigua, among the foraminifers, suggested the influence of the Circumpolar Deep Water during some periods of the late Quaternary. Heavy-test taxa, such as Cibicides refulgens, indicated strengthening bottom hydrodynamics. As for the ostracods, peaks in the presence of Australicythere devexa, Bairdoppilata simplex and Pseudocythere aff. caudata together with significant values of Polycope spp. allowed us to identify environments rich in nutrients with the influence of cold and deep water upwelling phenomena.

Highlights

Scientific interest in polar biogenic carbonates has increased over time as they are very important paleoecological proxies in the study of high latitude settings where abiogenic glacial sediments often prevail
We present the study of these microorganisms in core ANTA91-9, located near Cape Adare, on the outer continental Ross Sea shelf
The analysis of the foraminifer and ostracod assemblages in core ANTA91-9, collected in the area where the carbonate factories operated, offered us a possible interpretation of some paleoenvironmental/climatic events that have affected this area of the Ross Sea over the last 30 ka, while considering with caution the results obtained by a single sedimentary series

Summary

Introduction

Scientific interest in polar biogenic carbonates has increased over time as they are very important paleoecological proxies in the study of high latitude settings where abiogenic glacial sediments often prevail. Large amounts of siliciclastic sediments related to glacier activities limit the biogenic carbonate production and accumulation Due to these conditions, biogenic carbonate deposits on the Antarctic shelves are very localised in space and in time [2,4,5,6,7,8,9,10,11]. Studies in the Ross Sea area show that several metres of thick carbonate-rich sequences occur on the north-western banks (Mawson and Pennell), outer continental shelf (northern Drygalski Trough), and upper slope [5,8,9,10,12] These gravel- to sand-sized biogenic sediments mainly consist of bryozoan, stylasterine hydrocoral, mollusc, barnacle, foraminifer, ostracod and echinoid tests, skeletal parts or Geosciences 2020, 10, 413; doi:10.3390/geosciences10100413 www.mdpi.com/journal/geosciences

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