Robin Whatley

Micropaleontological evidence for increased meridional heat transport in the north atlantic ocean during the pliocene.

The Middle Pliocene (∼3 million years ago) has been identified as the last time the Earth was significantly warmer than it was during the Last Interglacial and Holocene. A quantitative micropaleontological paleotemperature transect from equator to high latitudes in the North Atlantic indicates that Middle Pliocene warmth involved increased meridional oceanic heat transport.

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.

Late Quaternary marginal marine deposits and palaeoenvironments from northeastern Buenos Aires Province, Argentina: A review

The late Quaternary marginal marine deposits along eastern Argentina (Southwestern Atlantic) are reviewed according to our present knowledge. In the northeastern coastal area of Buenos Aires Province they have been assigned to a series of transgressions and regressions ranging from the late Pliocene to the late Quaternary. The most widely accepted model is Frenguellis (1957) classical chronostratigraphical scheme of: ‘Belgranense’, late Pleistocene marine sediments at 3–6 m above m.s.l. and ca. 26,000−>35,000 14C years BP, the ‘Querandinense’, Pleistocene-Holocene estuarine sediments below or at present m.s.l., and the most extensive ‘Platense’, mid-Holocene marine deposits at 4.5−2 m above m.s.l. dated at ca. 8000-1340 14C years BP. The restricted ‘Belgranense’ deposits, recorded in Samborombon Bay, in Magdalena at ca. 32,000 BP, near Mar Chiquita at ca. 24,900 and 30,500 BP and southwards in Bahia Blanca at ca. 26,000–35,500 BP, may belong to an interstadial (Gonzalez et al., 1986). The molluscan composition suggests a marine invasion of the area but not a typical interglacial cycle characterized by euhaline and warm water elements. However, the oxygen isotope record argues against an interstadial during the interval 34−27 ka and the chronological control for these deposits is very poor, suggesting that they most probably have been elevated neotectonically. The Pleistocene-Holocene ‘Querandinense’ deposits, extensively distributed along the Bonaerensian coastal plain and continental shelf (ca. 11,000 14C years BP), with very low faunal diversity, abundance of freshwater ostracods and absence of the warm water molluscs characteristic of the Holocene ridges, indicate low salinity and cool water conditions. Further dating and isotope analysis of these deposits are required for a better understanding of the chronology of climatic events by the end of the Pleistocene in this area and to establish whether or not they could correspond to the Younger Dryas event of the northern hemisphere. ‘Platense’ littoral ridges formed between ca. 7600 and 2500 BP extend in several subparallel rows from ca. 34° S to ca. 39° S. They formed either as beaches or possibly as sublittoral bars in Samborombon Bay, where they reach 120 km long, 10–30 m wide and up to 5 m thick at 4.5–5 m above m.s.l., or in the supratidal and intertidal zones in Mar Chiquita at 2–4 m above m.s.l. Molluscs and ostracods suggest a brackish marine to marine brackish environment of lower salinity than the modern Atlantic littoral. During the mid-Holocene, the oceanic waters were mixing with large amounts of Antarctic ice melting in the South Atlantic (Isla, 1990) probably reducing salinity along the Bonaerensian littoral. The oldest littoral ridges accumulated during the Hypsithermal and in the Punta Indio area, their different geometry and alignment, greatest age, highest diversity and warmer affinity of the molluscan fauna suggest a short interval of reversal of the atmospheric circulation pattern. Further research is necessary for a better understanding of the chronology of the marine late Quaternary deposits, coastal evolution and climatic changes in this area.

The platycopid signal: a means of detecting kenoxic events using Ostracoda

It has been shown that during Jurassic and Cretaceous kenoxic events, while other groups of benthonic Ostracoda severely decline and eventually disappear, the Platycopina tend to survive. The survival of the platycopids is attributed to their being filter feeders who, in dysaerobic conditions manage to obtain sufficient oxygen by virtue of the greater volume of water which they circulate across their respiratory surface in the course of their normal feeding behaviour. The podocopid ostracods, which are predators, scavengers and deposit feeders, are unable to survive the diminished oxygen concentrations which characterise these events. The platycopid genus Cytherella is shown to dominate the oxygen mininmum zone in two different parts of the Atlantic at the present day.

The use of Ostracoda to reconstruct the oxygen levels of Late Palaeozoic oceans

Abstract It has been recently demonstrated that, in post-Palaeozoic and modern oceans, filter-feeding ostracods totally dominate over deposit feeders during times of dysaerobia. In modern oceans, the filter-feeding Platycopida, the sole extant group with this feeding strategy, in terms of abundance completely dominate the oxygen minimum zone, despite occurring there in low specific diversity. The percentage of filter feeders has been used previously to locate kenoxic events and to determine palaeoxygen levels in Liassic, Cenomanian and Palaeogene oceans. (The term kenoxic is used to denote an event when oxygen levels were reduced. Most so-called anoxic events, which for the name implies total deprivation of oxygen were, in fact, kenoxic. A kenoxic event produces dysaerobic rather than anaerobic conditions.) In the present paper, Upper Palaeozoic Ostracoda are analysed and it is concluded that the Palaeocopida, Metacopina, Platycopina, Kloedenellacea and the Paraparchitacea were filter-feeders. Filter-feeders were, therefore, much more diverse in the Palaeozoic than subsequently. In the palaeopsychrosphere, all ostracods, even podocopids, acquired peculiar adaptations to allow them to live in the oxygen minimum zone. Using the percentage of filter-feeding ostracod species of shelf seas as a guide, relative oxygen levels for the seas which deposited the carbonate platforms of northwest Europe during the Emsian to Visean interval are calculated. Changes in oceanic oxygen are related to global climatic changes, especially in temperature and are, therefore, important in any considerations of palaeoclimatology. Our reconstructions for both dissolved oxygen and sea water temperatures from the late Early Devonian to the Early Carboniferous, based upon the percentage of filter-feeding species, clearly depict the Late Devonian Events, as a time of low oxygen, high temperatures and high filter-feeders (into the Frasnian). There was a subsequent cooling and improved oxygenation (into the Famennian) and a glacial maximum marked by a low percentage of filter-feeders in the Lower Tournaisian. This was followed by a slight increase in the percentage of filter-feeders into the Visean; a signal of lower levels of oxygen but continuing in a contrasted climate. A model which yields reference points giving absolute values of oxygen is proposed for Late Palaeozoic benthic marine environments.

The Krithe problem: A case history of the distribution of Krithe and Parakrithe (Crustacea, Ostracoda) in the South China Sea

Abstract The distribution of 12 species of Krithe and 4 species of Parakrithe through the depth range of 150–4000 m and 5 depth stratified water masses in the South China Sea reveals that there is no correlation between size and shape of the anterior vestibulum and levels of dissolved oxygen, nor between the length of specimens and water depth. Given this evidence from elsewhere, it is recommended that the Peypouquet hypothesis, which argues for these relationships, should be re-evaluated and not used as a palaeoceanographical tool. It is suggested that the relative abundance of Krithe, as a percentage of the total ostracod fauna, may be an important factor in reconstructing palaeodepth. In the South China Sea, despite its somewhat restricted nature and endemically low oxygen levels, the Krithidae are shown to be the dominant deep-sea Ostracoda.

The depth distribution of Ostracoda from the Greenland Sea

Sixteen box core samples of Recent sediment collected in three transects across the East Greenland shelf and slope were analysed for Ostracoda. The samples which range in depth from 274 m to 3355 m, yielded a total of 52 species belonging to 25 genera. No less than 26 of the species also occur in the adjacent Scoresby Sund fjord complex. The fauna represents an interesting mixture of high latitude shallow water Arctic species and others known from bathyal and abyssal depths in the North Atlantic, including some pandemic deep sea species. Many species occur in shallower water here than in the North Atlantic due to the colder water. The fauna comprised of three associations (Shelf/Upper Slope; Slope: Lower Slope/Abyss). A marked faunal turnover occurs at the Upper Slope. The study raises questions concerning the constancy and universality of the relationship between certain ostracod species and water masses.

The Provincial Distribution of Shallow Water Indo-Pacific Marine Ostracoda: Origins, Antiquity, Dispersal Routes and Mechanisms

The geographical distribution of Indo-Pacific and Southern Ocean shallow marine podocopid and platycopid ostracods of Tertiary to Recent age is recorded. Some 285 publications were con-sulted and the 2,599 species are shown to fall into 13 zoogeographical provinces. These range con-siderably both in areal extent and the degree of endemism of their faunas. The provinces are: East African, Arabian, Bengalian, East Indian, Kymerian, Japanese, Australian, New Zealand, Sou-thern and Southwestern Pacific, Western-North and Central American, Western South American, and Southern Ocean. A series of link diagrams and tables demonstrate both the endemism and the affinities, at the species level, of the faunas of the various provinces. The overall level of endemism is high. Less than 20% of the faunas of any province occur outside that province; the mean for all provinces is only 8%. Faunal relationships between provinces and the age of occurrences of various species are used to demonstrate that the East Indian, Southwest Pacific region was a locus from which ostracods have, since the Miocene, migrated out, particularly westwards around the Indian Ocean to the Bengalian, Arabian and East African Provinces. A northward and southward migra-tion from this locus is also demonstrated. A limited eastward migration is also shown. Sixteen species which occur as fossils in the Solomon Islands are used to document this migration, which seems to have taken place post the closure of the Tethys, from which time the 13 provinces also date. Various mechanisms by which shallow marine ostracods can migrate over the very large distances involved in the Indo-Pacific are discussed. It is concluded that probably the major factor is passive migration by ocean currents.

Ostracoda and dysaerobia in the Lower Jurassic of Wales: the reconstruction of past oxygen levels

Abstract The Ostracoda are a subclass of small Crustacea which inhabit most aquatic environments; they have been recorded from the Cambrian through to the Recent. The biology of one group of marine Ostracoda, the Platycopina (Triassic-Recent), enables them to better withstand decreased levels of dissolved oxygen, in their immediate environment, than other ostracods. Study of a number of geological sections has already shown that this suborder often dominates stratigraphical intervals which are considered to be representative of dysaerobic conditions. In the light of this work the changing faunal composition of the Lower Jurassic of the Mochras Borehole, Wales is interpreted as a series of environmental changes which include fluctuating oxygen levels. The degree of dysaerobia is assessed and its effect on the rate of faunal turnover is discussed.

Recent podocopid Ostracoda of the Sedili River and Jason Bay, southeastern Malay Peninsula

The recent podocopid Ostracoda of the Sedili River, its estuary and the open shelf of Jason Bay, off the southeast coast of the Malay Peninsula, have been studied quantitatively. The distribution of live and dead assemblages is recorded. A total of 101 species were recorded in the study. Of these, 50 were recorded live in the area. In the freshwater system of the Sedili River, only two species were recorded live, in the brackish water of the Sedili Estuary only 4 live species were recorded while 48 live species were recovered from the open shelf. The dead assemblage exhibits a much higher diversity yet lower dominance than the live assemblage and constitutes a total of 98 species from the 3 biotopes. The dead representatives of species which also occur live are more widely distributed than their live counterparts due to postmortem transportation. In this study one new genus is erected, Malaycythereis, n. gen., and the following new species and subspecies are erected: Malaycythereis trachodes, Caudites asiaticus, C. scopulicolusjasonensis, Cytherella incohatus, Hemicytheridea wangi, Keijella gonia, Loxoconcha malayensis, L. triconicula, Neocytheretta murilineata, Paracytheroma ventrosinuosa, Semicytherura contraria, Leptocythere pulchra, and Xestoleberis malaysiana.