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T. M. Cronin

Publications and source records attributed to T. M. Cronin.

At least 55 records · Page 3Linked to original sources
USGS1999

Deep-sea ostracode species diversity: Response to late Quaternary climate change

Late Quaternary ostracode assemblages from the North Atlantic Ocean were studied to establish the effect of climatic changes of the past 210,000 yr (marine oxygen isotope stages 7–1) on deep-sea benthic biodiversity and faunal composition. Two-hundred and twenty five samples from the Chain 82-24 Core 4PC (41°43′N, 32°51′W, 3427 m water depth) on the western Mid-Atlantic Ridge revealed high amplitude fluctuations in ostracode abundance and diversity coincident with orbital and suborbital scale climate oscillations measured by several paleoceanographic proxy records. During the past 210,000 yr, ostracode biodiversity as measured by species number ( S ) and the Shannon–Weaver index, H ( S ), oscillated from H ( S )=0.4 during glacial periods (marine isotope stages 6, 5d, 5b, 4, and 2) to H ( S )=1.1 during interglacial and interstadial periods (stages 7, 5e, 5c, 5a, 3 and 1). A total of 23 diversity peaks could be recognized. Eleven of these signify major periods of high diversity [ H ( S )>0.8, S = 10–21] occurring every 15–20 ka. Twelve were minor peaks which may represent millennial-scale diversity oscillations. The composition of ostracode assemblages varies with Krithe -dominated assemblages characterizing glacial intervals, and Argilloecia–Cytheropteron characterizing deglacials, and trachyleberid genera ( Poseidonamicus , Echinocythereis , Henryhowella , Oxycythereis ) abundant during interglacials. Diversity and faunal composition changes can be matched to independent deep-sea paleoceanographic tracers such as benthic foraminiferal carbon isotopes, Krithe trace elements (Mg/Ca ratios), and to North Atlantic region climate records such as Greenland ice cores. When interpreted in light of ostracode species' ecology, these faunal and diversity patterns provide evidence that deep-sea benthic ecosystems experience significant reorganization in response to climate changes over orbital to millennial timescales.

Marine Micropaleontology↗
USGS1999

Neogene-quaternary Ostracoda and paleoenvironments, of the Limón basin, Costa Rica, and Bocas del Toro basin, Panama

Tropical marine ostracodes from Neogene and Quaternary sediments of the Central American Caribbean region have been the subject of biostratigraphic, ecological, taxonomic, and evolutionary studies. As part of the Panama Paleontology Project (PPP), Neogene and Quaternary ostracodes are being studied from the Central American region. The overall goal of this research is to evaluate the impact of the emergence of the Central American Isthmus as a land barrier between the Caribbean/tropical Atlantic and the Pacific oceans on marine ostracode biodiversity and the oceanic environments in which extant ostracodes evolved. Due to the ecological specificity of many living tropical ostracode species, they are ideally suited for reconstructing paleoenvironments on the basis of their occurrence in fossil assemblages, which in turn can lead to a better understanding of the tropical climatic and tectonic history of Central America. The principal aims of this chapter are: (a) to document the composition of the ostracode assemblages from the Limón Basin of Costa Rica and the Bocas del Toro Basin of Panama, two areas yielding extensive ma rine ostracode assemblages; (b) to describe the environments of deposition within these basins; and (c) to document the stratigraphic distribution of potentially agediagnostic ostracode species in the Limón and Bocas del Toro basins in order to enhance their use in Central American biostratigraphy. A secondary, but none-the-less important goal is to assemble a database on the distribution of modem ostracode species in the Caribbean and adjacent areas as a basis for comparison with fossil assemblages. Although the ecological, biostratigraphic and paleoenvironmental conclusions presented here will improve as additional material is studied, these fossil and modem ostracode databases constitute the foundation for future evolutionary and geochernical studies of tropical Caribbean and eastern Pacific Ocean ostracodes. Moreover, we present here evidence that major faunal and oceanic changes occurred in the westem Caribbean over the last 4 million years, probably related to changes in ocean circulation due to the emergence of the Isthmus as well as other climatic events.

Bulletins of American Paleontology↗
USGS1997

Orbital forcing of deep-sea benthic species diversity

Explanations for the temporal and spatial patterns of species biodiversity focus on stability-time, disturbance-mosaic (biogenic microhabitat heterogeneity) and competition-predation (biotic interactions) hypotheses. The stability-time hypothesis holds that high species diversity in the deep sea and in the tropics reflects long-term climatic stability. But the influence of climate change on deep-sea diversity has not been studied and recent evidence suggests that deep-sea environments undergo changes in climatically driven temperature and flux of nutrients and organic-carbon during glacial-interglacial cycles. Here we show that Pliocene (2.85-2.40 Myr) deep-sea North Atlantic benthic ostracod (Crustacea) species diversity is related to solar insolation changes caused by 41,000-yr cycles of Earth's obliquity (tilt). Temporal changes in diversity, as measured by the Shannon- Weiner index, H(S), correlate with independent climate indicators of benthic foraminiferal oxygen-isotope ratios (mainly ice volume) and ostracod Mg:Ca ratios (bottomwater temperature). During glacial periods, H(S) = 0.2-0.6, whereas during interglacials, H(S) = 1.2-1.6, which is three to four times as high. The control of deep-sea benthic diversity by cyclic climate change at timescales of 103-104 yr does not support the stability-time hypothesis because it shows that the deep sea is a temporally dynamic environment. Diversity oscillations reflect large-scale response of the benthic community to climatically driven changes in either thermohaline circulation, bottom temperature (or temperature-related factors) and food, and a coupling of benthic diversity to surface productivity.

Nature↗
USGS1996

Deep-sea ostracode shell chemistry (Mg:Ca ratios) and late Quaternary Arctic Ocean history

The magnesium:calcium (Mg:Ca) and strontium:calcium (Sr:Ca) ratios were investigated in shells of the benthic ostracode genus Krithe obtained from 64 core-tops from water depths of 73 to 4411 m in the Arctic Ocean and Nordic seas to determine the potential of ostracode shell chemistry for palaeoceanographic study. Shells from the Polar Surface Water (−1 to −1.5°C) had Mg:Ca molar ratios of about 0.006–0.008; shells from Arctic Intermediate Water (+0.3 to +2.0°C) ranged from 0.09 to 0.013. Shells from the abyssal plain and ridges of the Nansen, Amundsen and Makarov basins and the Norwegian and Greenland seas had a wide scatter of Mg:Ca ratios ranging from 0.007 to 0.012 that may signify post-mortem chemical alteration of the shells from Arctic deep-sea environments below about 1000 m water depth. There is a positive correlation ( r 2 = 0.59) between Mg:Ca ratios and bottom-water temperature in Krithe shells from Arctic and Nordic seas from water depths <900 m. Late Quaternary Krithe Mg:Ca ratios were analysed downcore using material from the Gakkel Ridge (water depths 3047 and 3899 m), the Lomonosov Ridge (water depth 1051 m) and the Amundsen Basin (water depth 4226 m) to test the core-top Mg:Ca temperature calibration. Cores from the Gakkel and Lomonosov ridges display a decrease in Mg:Ca ratios during the interval spanning the last glacial/deglacial transition and the Holocene, perhaps related to a decrease in bottom water temperatures or other changes in benthic environments.

Geological Society Special Publication↗
USGS1995

North Atlantic deepwater temperature change during late pliocene and late quaternary climatic cycles

Variations in the ratio of magnesium to calcium (Mg/Ca) in fossil ostracodes from Deep Sea Drilling Project Site 607 in the deep North Atlantic show that the change in bottom water temperature during late Pliocene 41,000-year obliquity cycles averaged 1.5°C between 3.2 and 2.8 million years ago (Ma) and increased to 2.3°C between 2.8 and 2.3 Ma, coincidentally with the intensification of Northern Hemisphere glaciation. During the last two 100,000-year glacial-to-interglacial climatic cycles of the Quaternary, bottom water temperatures changed by 4.5°C. These results show that glacial deepwater cooling has intensified since 3.2 Ma, most likely as the result of progressively diminished deep-water production in the North Atlantic and of the greater influence of Antarctic bottom water in the North Atlantic during glacial periods. The ostracode Mg/Ca data also allow the direct determination of the temperature component of the benthic foraminiferal oxygen isotope record from Site 607, as well as derivation of a hypothetical sea-level curve for the late Pliocene and late Quaternary. The effects of dissolution on the Mg/Ca ratios of ostracode shells appear to have been minimal.

Science↗
USGS1994

Late Pliocene climate change 3.4-2.3 Ma: paleoceanographic record from the Yabuta Formation, Sea of Japan

Late Pliocene paleoceanographic changes in the Sea of Japan between 3.4 and2.3 Ma were investigated through study of molluscs, diatoms, and ostracodes from the Yabuta Formation in Toyama Prefecture. The period 3.4-2.7 Ma was characterized by relatively high sea level and cool water benthic faunas. A progressive paleoceanographic shift towards colder oceanic conditions and lower sea level occurred beginning near 2.7 Ma, intensifying about 2.5 Ma, when important changes in ostracode and molluscan faunas occurred. Between 2.7 and 2.3 Ma, eight glacial events can be inferred based on drops in sea level of 50-60 m and increasing proportions of cold, shallow water ostracode species whose modern ecology and zoogeography indicate colder winter water temperatures (3-4??C). The glacial events between 2.5 and 2.3 Ma were the most intense. Preliminary interpretation of the faunal and oceanographic events of the Yabuta Formation suggests that they correspond to Northern Hemispheric cooling also known from North Atlantic deep-sea oxygen isotope, IRD, and planktic foraminiferal records, North Pacific diatom and radiolarian record, and the Chinese loess sequences. The eight glacial events may record a 41,000-yr obliquity cycle which characterized other late Pliocene climate proxy records. Inferred sea level drops near 2.5-2.3 Ma of about 50-60 m provide direct evidence from an ocean margin setting that supports deep sea oxygen isotopic evidence indicating major changes in global ice volume changes.

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS1994

Cenozoic climate and paleogeographic changes in the Pacific region

This special issue represents the proceedings of the symposium, held as part of the 29th International Geological Congress, 1992. Other relevant papers on Cainozoic climate change in Japan are also included. Data is assembled from the Pacific Ocean itself, its marginal seas, in particular the Sea of Japan, and the surrounding coastal states. The palaeoenvironment of the region is reconstructed from the analysis of micropalaeontological, isotopic and stratigraphic data from deep-sea and terrestrial cores. -S.J.Stone

Palaeogeography, Palaeoclimatology, Palaeoecology↗
USGS1993

Pliocene palaeotemperature reconstruction for the southern North Sea Based on Ostracoda

The development of a large northeastern Atlantic shelf ostracod database has confirmed that an intrinsic relationship exists between watermass temperature and the spatial (latitudinal) distribution of benthonic shelf Ostracoda. A second Pliocene ostracod database, using assemblages from four boreholes in The Netherlands and a number of localities from the East Anglian Neogene succession has also been constructed. A quantitative method of modern analogues and the Squared Chord Distance dissimilarity coefficient has been employed as a means of calculating the level of similarity between Recent and Neogene assemblages and, therefore, to aid in the reconstruction of palaeotemperatures in the southern North Sea Basin during the Pliocene. The results, in the form of contoured dissimilarity values, indicate the presence of at least seven palaeoceanographical climatic phases between ca. 5.2 and 1.6 Ma BP. An early Pliocene cooling phase (ecozone A), in which the fauna is dominated by the cryophilic species; Palmenella limicola (Norman), Elofsonella concinna (Jones), Robertsonites tuberculatus (Sars), Neomonoceratina tsurugasakensis (Tabuki) and Acanthocythereis dunelmensis (Norman), supervenes a period of stable subtropical conditions in the Miocene. A ‘mid’ Pliocene warming phase (ecozone B), which has been documented throughout the North Atlantic, can be recognized in the faunal composition of the sublittoral ostracod assemblages of both The Netherlands and East Anglia. A hiatus between the Coralline and Waltonian crags is thought to be associated with a deterioration in climatic conditions. Recent analogues to The Netherlands faunas of ecozone C (first phase late Pliocene cooling, ca. 2.9 Ma BP) indicate a decrease of approximately 5–6°C in mean summer surface temperatures. A return to elevated temperatures, of a Mauritanian aspect, can be seen in the fauna of the FA2 zone and Waltonian Crag. This amelioration of climate occurred prior to the Praetiglian cold phase (second phase late Pliocene cooling, ca. 2.4 Ma BP) which again saw the reintroduction of cryophilic species including Baffinicythere howei Hazel, Fimarchinella logani (Brady, Crosskey and Robertson) and Hemicythere emarginata (Sars), into the southern North Sea during the Newbournian and Butleyan stages. The final phase of the latest Pliocene (third phase late Pliocene cooling) is only documented in the ostracod fauna of the Norwich Crag. Evidence in the covariance of Loxoconchidae and Norwegian provincial cryophilic species, indicates that the Polar Front may have been as much as 2000 km further south during the deposition of the Chillesford Sand Member (Norwich Crag Fm., ca. 2.0-1.6 Ma BP).

Quaternary Science Reviews↗
USGS1993

Terrestrial and marine records of climatic and environmental changes during the Pliocene in subtropical Florida

Pollen, ostracode, and benthic foraminifer assemblages deposited during sea-level high-stands in subtropical Florida record a climate change during the period 4.5-1.0 Ma. Before 3.5 Ma, open-shelf marine faunas and pollen assemblages with abundant Pinus , Quercus , Fagus , Carya , and nonarboreal pollen were present, indicating cooler conditions than today. From ∼3.5 to 1.0 Ma, marine and terrestrial records indicate warmer conditions, similar to those existing in south Florida today. Combined with evidence for much warmer than modern conditions at high latitudes, these data suggest that increased poleward oceanic heat transport, possibly related to the emergence of the Central American isthmus between ∼3.5 and 2.5 Ma, was a major influence on mid-Pliocene warmth.

Geology↗
USGS1992

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.

Science↗
USGS1991

Pliocene shallow water paleoceanography of the North Atlantic ocean based on marine ostracodes

Middle Pliocene marine ostracodes from coastal and shelf deposits of North and Central America and Iceland were studied to reconstruct paleotemperatures of shelf waters bordering portions of the Western Boundary Current System (including the Gulf Loop Current, Florida Current, Gulf Stream and North Atlantic Drift). Factor analytic transfer functions provided Pliocene August and February bottom-water temperatures of eight regions from the tropics to the subfrigid. The results indicate: (1) meridional temperature gradients in the western North Atlantic were less steep during the Pliocene than either today or during Late Pleistocene Isotope Stage 5e; (2) tropical and subtropical shelf waters during the Middle Pliocene were as warm as, or slightly cooler than today; (3) slightly cooler water was on the outer shelf off the southeastern and mid-Atlantic coast of the U.S., possibly due to summer upwelling of Gulf Stream water; (4) the shelf north of Cape Hatteras, North Carolina may have been influenced by warm water incursions from the western edge of the Gulf Stream, especially in summer; (5) the northeast branch of the North Atlantic Drift brought warm water to northern Iceland between 4 and 3 Ma; evidence from the Iceland record indicates that cold East Greenland Current water did not affect coastal Iceland between 4 and 3 Ma; (6) Middle Pliocene North Atlantic circulation may have been intensified, transporting more heat from the tropics to the Arctic than it does today.

Quaternary Science Reviews↗
USGS1991

Stratigraphy and paleoceanography of Pliocene deposits of Karaginsky Island, eastern Kamchatka, U.S.S.R.

The lithology and paleontology of Pliocene deposits from Karaginsky Island, off eastern Kamchatka Peninsula, U.S.S.R., are described in order to provide a paleoceanographic reconstruction of this region of the eastern North Pacific Ocean. The stratigraphic sequence is divided into three suites — the Limimtevayamian, the Ust-Limimtevayamian, and the Tusatuvayamian, which correspond to three standard Pacific diatom zones — the Thalassiosira oestrupii, Neodenticula koizumi-N. kamtschatica , and N. koizumi . The entire sequence is further subdivided into six members and 18 distinct beds on the basis of molluscan assemblages and three members and seven beds on the basis of benthic foraminiferal assemblages. Marine ostracodes are described from the Limimtevayamian suite. The marine invertebrate assemblages from Karaginsky Island provide evidence that: (1) ocean water temperatures were warmer than today about 4 Ma and again about 3.5-3.0 Ma; (2) several Arctic-Atlantic species of molluscs and ostracodes migrated to the eastern North Pacific between 4.2−3.0 Ma, presumably through the proto-Bering Strait; (3) many species found in the Karaginsky Island Pliocene represent Pacific taxa which migrated through the Arctic into the North Atlantic during the late Pliocene.

eastern Kamchatka, Karaginsky Island↗
USGS1991

Neogene biostratigraphy and paleoenvironments of Enewetak Atoll, equatorial Pacific Ocean

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. ?? 1991 Elsevier Science Publishers B.V. All rights reserved.

Marine Micropaleontology↗
USGS1990

Climatic influences on species: Evidence from the fossil record

The detailed Neogene and Quaternary paleoclimatic reconstructions now available provide a means to test how species respond to environmental change. Paleontologic studies of marine organisms show that climatic change causes evolution (via cladogenesis and anagenesis), ecophenotypic variation, migration, morphologic stasis and extinction. Evolution during climatic change is a rare event relative to the number of climatic cycles that have occurred, but climate-related environmental barriers, usually temperature, may play an important role in the isolation of populations during allopatric speciation.

Trends in Ecology and Evolution↗
USGS1990

A quantitative micropaleontologic method for shallow marine peleoclimatology: Application to Pliocene deposits of the western North Atlantic Ocean

A transfer function was developed to estimate summer and winter paleotemperatures for arctic to tropical regions of the western North Atlantic Ocean using fossil ostracode assemblages. Q-mode factor analysis was run on ostracode assemblages from 100 modern bottom sediment samples from continental shelves of North America, Greenland and the Caribbean using 59 ostracode taxa. Seven factors accounting for 80% of the variance define assemblages that correspond to frigid, subfrigid, cold temperate, mild temperate, warm temperate, subtropical and tropical climatic zones. Multiple regression of the factor matrix against observed February and August bottom temperatures yielded an astracode transfer function with an accuracy of about ??2??C. The transfer function was used to reconstruct middle Pliocene (3.5-3.0 Ma) shallow marine climates of the western North Atlantic during the marine transgression that deposited the Yorktown Formation (Virginia and North Carolina), the Duplin Formation (South and North Carolina) and the Pinecrest beds (Florida). Middle Pliocene paleowater temperatures in Virginia averaged 19??C in August and 13.5??C in February, about 5??C to 8??C warmer than at comparable depths off Virginia today. August and February water temperatures in North Carolina were 23??C and 13.4??C, in South Carolina about 23??C and 13.5??C and in southern Florida about 24.6??C and 15.4??C. Marine climates north of 35??N were warmer than today; south of 35??N, they were about the same or slightly cooler. Thermal gradients along the coast were generally not as steep as they are today. The North Atlantic transfer function can be applied to other shallow marine Pliocene and Pleistocene deposits of eastern North America. ?? 1990 Elsevier Science Publishers B.V.

Marine Micropaleontology↗