Elisabeth M. Brouwers

Microfaunal Evidence for Elevated Pliocene Temperatures in the Arctic Ocean

The migration of thermophilic marine Ostracoda into the Arctic Ocean during the Pliocene indicates that winter and summer ocean temperatures around Arctic margins were ≥ 0 °C and > 3 °C, respectively, and that ice-free conditions existed for most or all of the Arctic. By at least 3.5–3.0 Ma, probably earlier, the opening of the Bering Strait allowed marine organisms to migrate through the Arctic Ocean, mostly from the Pacific Ocean. Migrant taxa such as Cythere, Hemicythere, and Neomonoceratina are known from Pliocene deposits of Alaska and Canada as well as Neogene deposits of the North Pacific and Atlantic oceans. On the basis of ecological and Zoogeographic information on ostracode species from more than 800 modern “core top” samples for the North Atlantic, North Pacific, and Arctic Oceans, we determined winter and summer temperature tolerances for migrant taxa to be at or above about 0 °C and 3 °C. This suggests ice-free summers, and probably, a perennially ice-free Arctic Ocean in some regions. Elevated water temperatures in the Arctic Ocean between 3.5 and 2.0 Ma is supported by evidence for late Pliocene increased meridional heat transport in the North Atlantic Ocean.

Early Tertiary marine fossils from northern Alaska: Implications for Arctic Ocean paleogeography and faunal evolution

Marine mollusks and ostracodes indicate a post-Danian Paleocene to early Eocene (Thanetian to Ypresian) age for a fauna from the Prince Creek Formation at Ocean Point, northern Alaska, that also contains genera characteristic of the Cretaceous and Neogene-Quaternary. The life-association of heterochronous taxa at Ocean Point resulted from an unusual paleogeographic setting, the nearly complete isolation of the Arctic Ocean from about the end of the Cretaceous until sometime in the Eocene, in which relict Cretaceous taxa survived into Tertiary time while endemic taxa evolved in situ; these later migrated to the northern mid-latitudes. Paleobiogeographic affinities of the Ocean Point association with mild temperate faunas of the London Basin (England), Denmark, and northern Germany indicate that a shallow, intermittent Paleocene seaway extended through the Norwegian-Greenland Sea to the North Sea Basin. Early Tertiary Arctic Ocean paleogeography deduced from faunal evidence agrees with that inferred from plate-tectonic reconstructions.

Late Maastrichtian and Danian ostracode faunas from northern Alaska: reconstructions of environment and paleogeography

A 300-m sequence of well-exposed fossiliferous outcrops in bluffs along the Colville River, northern Alaska, has yielded diverse, well-preserved Maastrichtian and Danian ostracode assemblages. High-latitude faunas of this age are uncommon, so that this locality provides a unique opportunity to reconstruct an ancient arctic environment. The Maastrichtian strata are nonmarine flood-plain deposits and contain diverse terrestrial and aquatic fossils. The paleoenvironment was a broad, flat, water-saturated delta plain with a diverse herbaceous ground cover, emergent and subaquatic vegetation, and a dry ground upland microthermal forest of deciduous coniferous and broad-leaved plants

An Arctic and Subarctic ostracode database: biogeographic and paleoceanographic applications

A new Arctic Ostracode Database-2015 (AOD-2015) provides census data for 96 species of benthic marine Ostracoda from 1340 modern surface sediments from the Arctic Ocean and subarctic seas. Ostracoda is a meiofaunal, Crustacea group that secretes a bivalved calcareous (CaCO3) shell commonly preserved in sediments. Arctic and subarctic ostracode species have ecological limits controlled by temperature, salinity, oxygen, sea ice, food, and other habitat-related factors. Unique species ecology, shell chemistry (Mg/Ca ratios, stable isotopes), and limited stratigraphic ranges make them a useful tool for paleoceanographic reconstructions and biostratigraphy. The database, described here, will facilitate the investigation of modern ostracode biogeography, regional community structure, and ecology. These data, when compared to downcore faunal data from sediment cores, will provide a better understanding of how the Arctic has been affected by climatic and oceanographic change during the Quaternary. Images of all species and biogeographic distribution maps for selected species are presented, with brief discussion of representative species’ biogeographic and ecological significance. Publication of AOD-2015 is open-sourced and will be available online at several public websites with latitude, longitude, water depth, and bottom water temperature for most samples. It includes material from Arctic abyssal plains and submarine ridges, continental slopes, and shelves of the Kara, Laptev, East Siberian, Chukchi, Beaufort Seas, and several subarctic regions.

Chapter 3 - Ostracod Taxa as Palaeoclimate Indicators in the Quaternary

Abstract We review the utility of ostracods for palaeoclimatic reconstruction at different taxonomic levels. Ostracods can provide palaeoenvironmental information based on several approaches. The chemical and isotopic composition of their mineral shells as well as the relatively minor organic component trapped within the carbonate lattice may give direct quantitative evidence of conditions in their natural habitat. Morphological observations and detailed morphometric records of valve size, shape and outline within a species may provide subtle clues to environmental changes between different habitats or adjacent stratigraphic intervals. Uniformitarian approaches can be applied to species, genera and supra-generic classifications but with decreasing resolution and increasing uncertainty in palaeoenvironmental significance (1) the higher the taxonomic unit and (2) the older the material geologically. The classical methodology of combining the habitat and environmental preferences of individual species to infer palaeoclimatic conditions remains as valid today as when such observations were first made in the nineteenth century.

Neogene biostratigraphy and paleoenvironments of Enewetak Atoll, equatorial Pacific Ocean

Abstract Micropaleontologic analyses of Neogene sediments from Enewetak Atoll, Marshall Islands, provide data on the age of lagoonal deposits, stratigraphic disconformities and the paleoenvironmental and subsidence history of the atoll. Benthic foraminifers, planktic foraminifers, calcareous nannofossils and ostracodes were studied from six boreholes, the deepest penetrating 1605 feet below the lagoon floor into upper Oligocene strata. The Oligocene-Miocene boundary occurs at about 1200 ft below the lagoon floor. The early and middle Miocene is characterized by brief periods of deposition and numerous hiatuses. Ostracodes and benthic foraminifers indicate a shallow-marine reefal environment with occasional brackish water conditions. Upper Miocene and lower Pliocene deposits placed in calcareous nannofossil Zones NN9–15 and in planktic foraminifer Zones N16–19 contain species-rich benthic microfaunas which indicate alternating reefal and brackish water mangrove environments. The upper Pliocene contains at least two major depositional hiatuses that coincide with a major faunal turnover in benthic foraminiferal and ostracode assemblages. The Quaternary is characterized by benthic microfaunas similar to those of modern atoll lagoons and is punctuated by at least 11 disconformities which signify periods of low sea level. Atoll subsidence rates during the last 10 Ma averaged 30 to 40 m/m.y.

Synonymies of Leptocythere klutinensis Forester and Brouwers, 1985, and Cytheromorpha knikensis Forester and Brouwers, 1985

Dr. E. I. Schornikov (Institute of Marine Biology, Far East Branch, Academy of Sciences of Russia, Vladivostok) has kindly sent comparative specimens informing us that two of our species described from the Gulf of Alaska are junior synonyms of species that Schornikov described in 1974. Leptocythere klutinensis Forester and Brouwers, 1985, p. 364–366, figures 4.1–4.8, 7.6 is a junior synonym of Leptocythere polymorpha Schornikov, 1974, p. 155–157, text-figure 10, Plate 2, figure 3. Cytheromorpha knikensis Forester and Brouwers, 1985, 357–362, figures 5.1–5.8, 6.3–6.6, 7.1–7.2, is a junior synonym of Cytheromorpha lagunae Schornikov, 1974, 153–155, text-figure 9.