In this volume John Murray investigates the ecological processes that control the distribution, abundance, and species diversity of benthic foraminifera in environments ranging from marsh to the deepest ocean. To interpret the fossil record it is necessary to have an understanding of the ecology of modern foraminifera and the processes operating after death leading to burial and fossilisation. This book presents the ecological background required to explain how fossil forms are used in dating rocks and reconstructing past environmental features including changes of sea level. It demonstrates how living foraminifera can be used to monitor modern-day environmental change. Ecology and Applications of Benthic Foraminifera presents a comprehensive and global coverage of the subject using all the available literature. It is supported by a website hosting a large database of additional ecological information (www.cambridge.org/0521828392) and will form an important reference for academic researchers and graduate students in Earth and Environmental Sciences.

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Ecology and Applications of Benthic Foraminifera

Mid-water oxygen minima (� 0.5 ml l � 1 dissolved O2) intercept the continental margins along much of the eastern Pacific Ocean, off west Africa and in the Arabian Sea and Bay of Bengal, creating extensive stretches of sea floor exposed to permanent, severe oxygen depletion. These seafloor oxygen minimum zones (OMZs) typically occur at bathyal depths between 200 m and 1000 m, and are major sites of carbon burial along the continental margins. Despite extreme oxygen depletion, protozoan and metazoan assemblages thrive in these envi- ronments. Metazoan adaptations include small, thin bodies, enhanced respiratory surface area, blood pigments such as haemoglobin, biogenic structure formation for stability in soupy sedi- ments, an increased number of pyruvate oxidoreductases, and the presence of sulphide-oxidising symbionts. The organic-rich sediments of these regions often support mats of large sulphide- oxidising bacteria (Thioploca, Beggiatoa, Thiomargarita ), and high-density, low-diversity meta- zoan assemblages. Densities of protistan and metazoan meiofauna are typically elevated in OMZs, probably due to high tolerance of hypoxia, an abundant food supply, and release from predation. Macrofauna and megafauna often exhibit dense aggregations at OMZ edges, but depressed densities and low diversity in the OMZ core, where oxygen concentration is lowest. Taxa most tolerant of severe oxygen depletion ( � 0.2 ml l � 1 ) in seafloor OMZs include calcare- ous foraminiferans, nematodes, and annelids. Agglutinated protozoans, harpacticoid copepods, and calcified invertebrates are typically less tolerant. High dominance and relatively low species richness are exhibited by foraminiferans, metazoan meiofauna, and macrofauna within OMZs. At dissolved oxygen concentrations below 0.15 ml l � 1 , bioturbation is reduced, the mixed layer is shallow, and chemosynthesis-based nutrition (via heterotrophy and symbiosis) becomes important. OMZs represent a major oceanographic boundary for many species. As they expand and con- tract over geological time, OMZs may influence genetic diversity and play a key role in the evo- lution of species at bathyal depths. These ecosystems may preview the types of adaptations, species, and processes that will prevail with increasing hypoxia over ecological and evolution- ary time. However, many questions remain unanswered concerning controls on faunal standing stocks in OMZs, and the physiological, enzymatic, metabolic, reproductive and molecular adap- tations that permit benthic animals to live in OMZs. As global warming and eutrophication reduce oxygenation of the world ocean, there is a pressing need to understand the functional consequences of oxygen depletion in marine ecosystems.

http://levin.ucsd.edu/publications/2003,%20OMBAR,%20Levin.pdf

Oxygen minimum zone Benthos: Adaptation and community response to hypoxia

Benthic foraminifers: proxies or problems?: A review of paleocological concepts

In the meso-oligotrophic Bay of Biscay, a diminishing downward organic matter flux with depth is accompanied by an important decrease of the live foraminiferal density. Although bottom water oxygenation is not directly influenced by organic matter input, the oxygenation of interstitial waters and the primary redox fronts do change in response to variations of the organic matter flux. The occurrence of deep and intermediate infaunal taxa can be linked to fundamental redox fronts and putative associated bacterial consortia. Our data are in agreement with the TROX-model, which explains the benthic foraminiferal microhabitat as a function of organic flux and benthic ecosystem oxygenation. Both the depth of the principle redox fronts and the microhabitat of deep infaunal species show important increases with depth. At the deepest oligotrophic stations, deep infaunal faunas become relatively poor. Therefore, the exported flux of organic matter appears to be the main parameter controlling the composition and the vertical distribution of benthic foraminiferal faunas below the sediment-water interface. The oxygenation of pore waters plays only a minor role. A species-level adaptation of the TROX-model is presented for the Bay of Biscay.

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Live benthic foraminiferal faunas from the Bay of Biscay: faunal density, composition, and microhabitats

Publisher Summary This chapter focuses on the paleoceanographical proxies based on deep-sea benthic foraminiferal assemblage characteristics, and presents the following three proxy relationships that are promising: those between benthic foraminiferal faunas and benthic ecosystem oxygenation, export productivity, and deep-sea water mass characteristics. Under most circumstances the composition of deep-sea benthic foraminiferal assemblages is controlled by a rather limited number of environmental factors. The available proxies based on benthic foraminiferal assemblage composition show that they have major potential, but further research is needed to add or improve the quantitative aspects. In many cases, such as bottom water oxygenation, and Corg flux to the ocean floor, it can be done by significantly increasing the size of existing databases. In other cases such as periodicity of the organic flux, time series observations are necessary. A major obstacle is insufficient knowledge of the differences between recent and fossil faunas due to taphonomical alterations. This phenomenon, of importance for all paleoceanographic proxies, can to some extent be solved relatively easily in the case of foraminiferal assemblages by detailed studies of their vertical succession in sediments deposited in the last 5,000 years, when environmental conditions were probably rather invariable in many areas. Proxies based on foraminiferal assemblage composition are fundamentally different from all geochemical proxies, and thus may provide independent reconstructions of essential oceanographic parameters.

Chapter Seven Paleoceanographical Proxies Based on Deep-Sea Benthic Foraminiferal Assemblage Characteristics

A conceptual model explaining benthic foraminiferal microhabitats

Benthic foraminiferal ecomarker species of the terminal Cretaceous (late Maastrichtian) deep-sea Tethys

We quantified the horizontal distribution of Late Cretaceous (late Maastrichtian) benthic foraminifera for 10 upper bathyal to abyssal localities, that cover a wide range of environmental settings throughout the Tethyan realm. For the first time, a quantitative faunal study is performed in order to identify and explain the differences between Late Cretaceous benthic foraminiferal faunas from the deep open ocean and from the shallower marginal seas of the Tethys. The results from correspondence analysis indicate that the main arrangement of the various sites coincides with a paleobathymetric ranking, which we consider to be primarily a reflection of gradients in trophic resources and oxygen levels. Five benthic foraminiferal assemblages were found to characterize bathymetrically and latitudinally different environmental settings within the Tethyan realm: (1) a Marginal Tethyan Assemblage (e.g., large Cibicidoides spp. and Sliteria varsoviensis) characteristic of the relatively highly fertile environment of the southern Central Tethyan margin, (2) an Abyssal Tethyan Assemblage (e.g., Aragonia spp. and Nuttallides truempyi) that signifies the more oligotrophic deep open-ocean conditions in the Western Tethys, (3) a Northwestern Tethyan Assemblage containing some high latitude ("boreal") faunal elements (e.g., Gavelinella pertusa and Stensioeina pommerana) characteristic of the northernmost part of the Western Tethys, (4) a Shallow Bathyal Assemblage (e.g., Bolivinoides draco and Eouvigerina subsculptura), which is composed of more or less ubiquitous taxa, and finally, (5) a Deep Bathyal Assemblage (e.g., Bulimina trinitatensis and Gavelinella beccariiformis), which also has a mostly ubiquitous distribution except for the shallow sites of the southern margin of the Central Tethys, where it is virtually absent. Morphotype analysis of the total fauna reveals distinct differences in proportions of endobenthic and epibenthic morphologies between the various sites, but a clear trend between the deep open ocean and the marginal seas cannot readily be discerned. However, a comparison of the proportions of morphotypes within the five assemblages resulting from correspondence analysis signifies clear trends between the various environmental settings. This enables us to distinguish various trophic regimes within the Tethyan realm; yet, we found no faunal indications of either true oligotrophic or eutrophic settings. We conclude that large areas of the latest Cretaceous bathyal environment of the Tethys were more or less mesotrophic in character, but nevertheless, abundance-patterns of morphogroups within each of the five assemblages were found to reflect depth-related gradients, which in turn are influenced by variations in food availability and oxygen concentration at the seafloor.

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Joen G.V. Widmark

Papers

A conceptual model explaining benthic foraminiferal microhabitats

Benthic foraminiferal ecomarker species of the terminal Cretaceous (late Maastrichtian) deep-sea Tethys

Benthic foraminiferal faunas and trophic regimes at the terminal Cretaceous Tethyan seafloor

A conceptual model explaining benthic foraminiferal microhabits

Biogeography of terminal Cretaceous benthic foraminifera: deep-water circulation and trophic gradients in the deep South Atlantic