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Volume 37, issue 1 | Copyright
J. Micropalaeontol., 37, 295-303, 2018
© Author(s) 2018. This work is distributed under
the Creative Commons Attribution 4.0 License.

Research article 08 Feb 2018

Research article | 08 Feb 2018

On a grain of sand – a microhabitat for the opportunistic agglutinated foraminifera Hemisphaerammina apta n. sp., from the early Eocene Arctic Ocean

David H. McNeil1 and Lisa A. Neville2,3 David H. McNeil and Lisa A. Neville
  • 1Geological Survey of Canada, Natural Resources Canada, Calgary, Alberta, T2L 2A7, Canada
  • 2Enviro-Verse Ltd., Calgary, Alberta, T2P 2T8, Canada
  • 3Department of Earth Sciences, Brock University, St. Catharines, Ontario, L2S 3A1, Canada

Abstract. Hemisphaerammina apta n. sp. is an attached monothalamous agglutinated foraminifera discovered in shelf sediments of the early Eocene Arctic Ocean. It is a simple yet distinctive component of the endemic agglutinated foraminiferal assemblage that colonized the Arctic Ocean after the microfaunal turnover caused by the Paleocene–Eocene Thermal Maximum. Associated foraminifera are characterized by a high percentage of monothalamous species (up to 60%) and are entirely agglutinated indicating a brackish (mesohaline) early Eocene Arctic Ocean. Hemisphaerammina apta occurs exclusively as individuals attached to fine detrital grains (0.2 to 1.8mm) of sediment. It is a small species (0.06 to 0.2mm in diameter), fine-grained, with a low hemispherical profile, no floor across the attachment area, no substantive marginal flange, no internal structures, and no aperture. Lacking an aperture, it apparently propagated and fed through minute (micrometre-sized) interstitial pores in the test wall. Attachment surfaces vary from concave to convex and rough to smooth. Grains for attachment are diverse in shape and type but are predominantly of quartz and chert. The presence of H. apta in the early Eocene was an opportunistic response to an environment with an active hydrological system (storm events). Attachment to grains of sand would provide a more stable base on a sea floor winnowed by storm-generated currents. Active transport is indicated by the relative abundance of reworked foraminifera mixed with in situ species. Contemporaneous reworking and colonization by H. apta is suggested by its attachment to a reworked specimen of Cretaceous foraminifera.

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Short summary
Approximately 50 million years ago, global CO2 levels were abnormally high and the arctic climate was comparable to today’s southern USA. Our research analysed the geological and ecological conditions of this warm Arctic with a focus on one micro-organism that survived by being attached to fine grains of sand in a storm-prone Arctic Ocean. It emerged after CO2-caused mass extinction and colonized the Arctic when CO2 levels averaged 500 ppm. Today's CO2 levels are moving toward that level.
Approximately 50 million years ago, global CO2 levels were abnormally high and the arctic...