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Geochemical assessment of the palaeoecology, ontogeny, morphotypic variability and palaeoceanographic utility of “Dentoglobigerina” venezuelana

Geochemical assessment of the palaeoecology, ontogeny, morphotypic variability and palaeoceanographic utility of “Dentoglobigerina” venezuelana
Geochemical assessment of the palaeoecology, ontogeny, morphotypic variability and palaeoceanographic utility of “Dentoglobigerina” venezuelana
To better understand the links between the carbon cycle and changes in past climate over tectonic timescales we need new geochemical proxy records of secular change in silicate weathering rates. A number of proxies are under development, but some of the most promising (e.g. palaeoseawater records of Li and Nd isotope change) can only be employed on such large samples of mono-specific foraminifera that application to the deep sea sediment core archive becomes highly problematic. “Dentoglobigerina” venezuelana presents a potentially attractive target for circumventing this problem because it is a typically large (> 355 ?m diameter), abundant and cosmopolitan planktic foraminifer that ranges from the early Oligocene to early Pliocene. Yet considerable taxonomic and ecological uncertainties associated with this taxon must first be addressed. Here, we assess the taxonomy, palaeoecology, and ontogeny of “D.” venezuelana using stable isotope (oxygen and carbon) and Mg/Ca data measured in tests of late Oligocene to early Miocene age from Ocean Drilling Program (ODP) Site 925, on Ceara Rise, in the western equatorial Atlantic. To help constrain the depth habitat of “D.” venezuelana relative to other species we report the stable isotope composition of selected planktic foraminifera species within Globigerina, Globigerinoides, Paragloborotalia and Catapsydrax. We define three morphotypes of “D.” venezuelana based on the morphology of the final chamber and aperture architecture. We determine the trace element and stable isotope composition of each morphotype for different size fractions, to test the validity of pooling these morphotypes for the purposes of generating geochemical proxy datasets and to assess any ontogenetic variations in depth habitat. Our data indicate that “D.” venezuelana maintains a lower thermocline depth habitat at Ceara Rise between 24 and 21 Ma. Comparing our results to published datasets we conclude that this lower thermocline depth ecology for the Oligo-Miocene is part of an Eocene-to-Pliocene evolution of depth habitat from surface to sub-thermocline for “D.” venezuelana. Our size fraction data advocate the absence of photosymbionts in “D.” venezuelana and suggest that juveniles calcify higher in the water column, descending into slightly deeper water during the later stages of its life cycle. Our morphotype data show that ?18O and ?13C variation between morphotypes is no greater than within-morphotype variability. This finding will permit future pooling of morphotypes in the generation of the “sample hungry” palaeoceanographic records.
Planktic foraminifera, Dentoglobigerina venezuelana, Morphotype, Palaeoecology, Ontogeny, Mg/Ca
0377-8398
74-86
Stewart, Joseph A.
69894bea-c03d-44a9-8f12-ff55580c6009
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Edgar, Kirsty M.
c180d215-e9ee-4a79-8274-a1e8a300c07c
Anand, Pallavi
c9c35583-fcdd-440b-ab99-575c5839178d
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4
Stewart, Joseph A.
69894bea-c03d-44a9-8f12-ff55580c6009
Wilson, Paul A.
f940a9f0-fa5a-4a64-9061-f0794bfbf7c6
Edgar, Kirsty M.
c180d215-e9ee-4a79-8274-a1e8a300c07c
Anand, Pallavi
c9c35583-fcdd-440b-ab99-575c5839178d
James, Rachael H.
79aa1d5c-675d-4ba3-85be-fb20798c02f4

Stewart, Joseph A., Wilson, Paul A., Edgar, Kirsty M., Anand, Pallavi and James, Rachael H. (2012) Geochemical assessment of the palaeoecology, ontogeny, morphotypic variability and palaeoceanographic utility of “Dentoglobigerina” venezuelana. Marine Micropaleontology, 84-85, 74-86. (doi:10.1016/j.marmicro.2011.11.003).

Record type: Article

Abstract

To better understand the links between the carbon cycle and changes in past climate over tectonic timescales we need new geochemical proxy records of secular change in silicate weathering rates. A number of proxies are under development, but some of the most promising (e.g. palaeoseawater records of Li and Nd isotope change) can only be employed on such large samples of mono-specific foraminifera that application to the deep sea sediment core archive becomes highly problematic. “Dentoglobigerina” venezuelana presents a potentially attractive target for circumventing this problem because it is a typically large (> 355 ?m diameter), abundant and cosmopolitan planktic foraminifer that ranges from the early Oligocene to early Pliocene. Yet considerable taxonomic and ecological uncertainties associated with this taxon must first be addressed. Here, we assess the taxonomy, palaeoecology, and ontogeny of “D.” venezuelana using stable isotope (oxygen and carbon) and Mg/Ca data measured in tests of late Oligocene to early Miocene age from Ocean Drilling Program (ODP) Site 925, on Ceara Rise, in the western equatorial Atlantic. To help constrain the depth habitat of “D.” venezuelana relative to other species we report the stable isotope composition of selected planktic foraminifera species within Globigerina, Globigerinoides, Paragloborotalia and Catapsydrax. We define three morphotypes of “D.” venezuelana based on the morphology of the final chamber and aperture architecture. We determine the trace element and stable isotope composition of each morphotype for different size fractions, to test the validity of pooling these morphotypes for the purposes of generating geochemical proxy datasets and to assess any ontogenetic variations in depth habitat. Our data indicate that “D.” venezuelana maintains a lower thermocline depth habitat at Ceara Rise between 24 and 21 Ma. Comparing our results to published datasets we conclude that this lower thermocline depth ecology for the Oligo-Miocene is part of an Eocene-to-Pliocene evolution of depth habitat from surface to sub-thermocline for “D.” venezuelana. Our size fraction data advocate the absence of photosymbionts in “D.” venezuelana and suggest that juveniles calcify higher in the water column, descending into slightly deeper water during the later stages of its life cycle. Our morphotype data show that ?18O and ?13C variation between morphotypes is no greater than within-morphotype variability. This finding will permit future pooling of morphotypes in the generation of the “sample hungry” palaeoceanographic records.

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More information

Published date: 1 March 2012
Keywords: Planktic foraminifera, Dentoglobigerina venezuelana, Morphotype, Palaeoecology, Ontogeny, Mg/Ca
Organisations: Marine Geoscience, Paleooceanography & Palaeoclimate

Identifiers

Local EPrints ID: 336388
URI: http://eprints.soton.ac.uk/id/eprint/336388
ISSN: 0377-8398
PURE UUID: 01129522-5867-4ccb-b47d-d21c061ca20e
ORCID for Paul A. Wilson: ORCID iD orcid.org/0000-0001-6425-8906
ORCID for Rachael H. James: ORCID iD orcid.org/0000-0001-7402-2315

Catalogue record

Date deposited: 23 Mar 2012 11:35
Last modified: 15 Mar 2024 03:30

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Contributors

Author: Joseph A. Stewart
Author: Paul A. Wilson ORCID iD
Author: Kirsty M. Edgar
Author: Pallavi Anand

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