Modern Ostracod Research Articles

Comparative optical and radiocarbon dating of laminated Holocene sediments in two maar lakes: Lake Keilambete and Lake Gnotuk, south-western Victoria, Australia

Sediment core chronologies of optical dates on single-grains/very small aliquots of sand-sized quartz are compared with Accelerator Mass Spectrometry (AMS) radiocarbon (14C) chronologies from ostracod carbonate, mixed carbonates, sedimentary organic matter and charcoal in order to establish the age of laminated Holocene sediments in maar crater lakes Keilambete and Gnotuk, Victoria, Australia. Samples for optical and AMS 14C dating were taken from the same Mackereth cores, allowing a direct comparison of the two techniques from two laminated sedimentary sequences. Additional AMS 14C samples were taken from water in Lake Keilambete and from groundwater discharging into Lake Keilambete from the crater wall, with equivalent reservoir ages of 150 ± 30 and 1940 ± 30 years respectively.AMS 14C dating of modern ostracod carbonate in Lake Keilambete demonstrates a reservoir age of 670 ± 175 years. Optical dating of ‘single-grain/very small aliquots’ of sand-sized-quartz indicate the presence of a radiocarbon reservoir in Lake Keilambete that is consistent with that measured on modern ostracods, and also demonstrate that there is no 14C reservoir in Lake Gnotuk during the Holocene. The chronology presented here supports the premise that previously published bulk conventional 14C dates from Lake Keilambete were affected by old carbon, meaning that past chronologies require revision.Limitations on the use of optical dating of single-grain/very small aliquots include the relative paucity of sand-sized quartz, which decreases the precision of the sample equivalent dose (De), and is further confounded by low environmental dose rates and resultant large uncertainties on the final age assessment. Nevertheless, evidence for partial bleaching confirms that single-grain quartz dating is the most appropriate luminescence technique, and may prove a useful alternative in situations where 14C dating is unsuitable or an alternative chronometer is required.

Amino acids in lacustrine ostracodes, part III: Effects of pH and taxonomy on racemization and leaching

Amino acids in ostracode valves are abundant and well preserved in Quaternary sediments. Ostracode valves are increasingly useful targets for amino acid geochronologic investigations yet little is known about the influence of taxonomy or environmental variables on ostracode protein diagenesis. This paper documents the effects of taxonomy and elevated environmental pH on the amino acid composition of ostracode valves. In one experiment, modern ostracode valves from the genus Candona (Cypridoidea) and Limnocythere (Cytheroidea) were submerged in pH 7 and pH 10 buffers and heated at 120 °C for up to 32 d. The buffer solutions and a subset of the ostracode valves were analyzed for their total hydrolysable amino acid (THAA) d/ l values and concentrations. The remaining valves were analyzed for their free amino acid (FAA) d/ l values and concentrations. In a second experiment, modern valves from four species of ostracodes within the Cypridoidea were heated at 110 °C for up to 160 d. THAA aspartic acid (Asp) and glutamic acid (Glu) d/ l values were monitored. Finally, the amino acid compositions in a suite of fossil Candona valves from outcrops in the western United States, including the problematic Ana River section, are compared across a broader spectrum of amino acid data. A total of 586 samples were analyzed. The results show that both THAA and FAA d/ l values and concentrations were higher in ostracode valves heated in pH 10 buffer than in valves heated in pH 7 buffer. THAA d/ l values in the buffers were consistently higher than in the associated ostracode valves. Amino acids were readily leached from modern Limnocythere valves but minimal leaching was observed from young fossil Candona valves. The extent of leaching was not pH dependent. The rates and extent of racemization for Asp and Glu were similar in Candona spp. and Limnocythere valves heated in either pH 7 or 10 buffers. The rates and extent of amino acid racemization for alanine, valine, and epimerization of isoleucine were consistently lower in Limnocythere valves, regardless of pH environment. Asp racemized significantly faster in Heterocypris valves than in Candona or Ilyocypris valves. There were no substantial differences in the rate of Glu racemization in Heterocypris, Candona, or Ilyocypris valves, nor in the rate of racemization of Asp or Glu in valves from three species of Candona. The heating experiments demonstrate that environmental pH can have significant impact on the amino acid composition of ostracode valves. Differences in the rates of amino acid racemization were detected at both the family and superfamily level. The Ana River Candona valves are strongly enriched in Asp, Glu, and glycine when compared with other fossil Candona valves. These results are not explained by taxonomic differences or by diagenesis under basic (alkaline) environmental conditions. Instead, they suggest that other environmental variables during valve calcification may be responsible for the unique amino acid signature of the Ana River material.

Late quaternary environmental changes in Patagonia as inferred from lacustrine fossil and extant ostracods

In the present study, we compare modern and Quaternary ostracods from two lacustrine basins: Laguna Cari-Laufquen (41°S) and Lago Cardiel (49°S) in Patagonia. Taxonomic and quantitative analyses along with isotopic and chemical studies of the extant ostracod fauna indicate that distinct ostracod associations can be identified as a function of conductivity. Three ostracod associations can be distinguished: (1) springs, ponds and small creeks, characterized by low conductivity (e.g. 1015 µs cm−1); (2) lakes and permanent ponds, characterized by medium conductivity (e.g. 1625 µs cm−1) and (3) ephemeral lacustrine environments, generally characterized by higher conductivity (e.g. 16 480 µs cm−1) These modern ostracod associations were also identified in older sequences from sediments outcropping in the Laguna Cari-Laufquen current shoreline, as well as in sediment cores from Lago Cardiel. The predominance of Limnocythere rionegroensis Cusminsky & Whatley in the Cari-Laufquen sections suggests the development of a saline and turbid lake during the Late Pleistocene and Early Holocene, and thus higher precipitation at these latitudes. Changes in ostracod abundance and associations have been observed in Lago Cardiel during the last approximately 16 000 calibrated years BP. Conductivity is known to change as a function of the ratio of precipitation to evaporation and a decrease in conductivity from the Late Pleistocene to the Middle Holocene suggests substantial hydrological variations (i.e. increase of the precipitation/evaporation ratio suggests minor conductivity). These two examples show that ostracods provide an excellent proxy for interpreting palaeoclimatic and palaeoenvironmental changes in Patagonia.

Amino acid racemization in lacustrine ostracodes, part I: effect of oxidizing pre-treatments on amino acid composition

Bleaching biominerals reduces the concentration of amino acids to a residual fraction which is thought to be preserved within intra-crystalline proteins. Intra-crystalline amino acids represent a relatively closed-system and may be superior for amino acid geochronological and paleothermometry investigations. Here we quantify the effects of extended bleaching (to 144 h) on amino acid concentrations and d/ l values in the valves of seven modern ostracode species. Then we compare the effects of increasingly aggressive pre-treatments (sonication, exposure to 3% hydrogen peroxide for 2 h, and exposure to 10% bleach for 48 h) on amino acid concentrations and d/ l values in fossil ostracode ( Candona) valves from numerous locations throughout the western United States and northern Mexico. Bleaching modern ostracode valves results in a rapid order-of-magnitude reduction in amino acid concentrations and a slight increase in d/ l values. Amino acid concentrations in five of the seven modern species increased slightly after prolonged exposure to bleach, suggesting that bleaching weakens a resistant protein source within the ostracode valves. Increasingly aggressive pre-treatments had virtually no effect on amino acid concentrations, d/ l values, or inter-sample variability in fossil Candona valves older than about 1 ka. Candona valves younger than about 1 ka showed a progressive decrease in amino acid concentrations with more aggressive oxidizing pre-treatments. Valves older than 1 ka generally had amino acid concentrations < 10 nM mg −1. A delayed increase in amino acid concentrations (15–30 nM mg −1), followed by a gradual decrease to residual concentrations consistently < 10 nM mg −1, was observed in both outcrop and core samples. We propose that a large amount of weakly bound proteins is leached geologically instantaneously from Candona valves. Long-term (10’s of ka) diagenesis gradually weakens and then destroys a secondary pool of tightly bound proteins contained within the valves. Residual amino acid concentrations are likely derived from intra-crystalline proteins and resistant inter-crystalline proteins that are essentially immune to leaching. Candona valves deposited in pluvial Lake Chewaucan and exposed in sediments that crop out along the Ana River, Oregon, have unexpectedly well-preserved proteins and lower d/ l values compared to fossil Candona valves of similar age from other locations. The Ana River results argue for developing site-specific calibrations for amino acid geochronology or paleothermometry studies that utilize ostracodes.

Climate-driven body-size trends in the ostracod fauna of the deep Indian Ocean

Abstract: Body size is a common focus of macroevolutionary, macroecological and palaeontological investigations. Here, we document body-size evolution in 19 species-level ostracod lineages from the deep Indian Ocean (Deep Sea Drilling Program Site 253) over the past 40 myr. Body-size trajectories vary across taxa and time intervals, but most lineages (16/19) show net gains in body size. Because many modern ostracod taxa are larger in colder parts of their geographical range, we compared the timing and magnitude of these size changes to established Cenozoic deep-water cooling patterns confirmed through δ18O measurements of benthic foraminifera in the samples studied. These data show a significant negative correlation between size changes and temperature changes (ostracods get larger as temperatures get colder), and that systematic size increases only occur during intervals of sustained cooling. In addition, statistical support for an explicit temperature-tracking model exceeds that of purely directional evolution. We argue that this Cope’s Rule pattern is driven by secular changes in the environment, rather than any universal or intrinsic advantages to larger body sizes, and we note some difficulties in the attempts to link Cope’s Rule to observations made within a single generation.

Distribution, diversity and ecology of modern freshwater ostracodes (Crustacea), and hydrochemical characteristics of Lago Petén Itzá, Guatemala

We analyzed modern ostracode species assemblages and water column physico-chemical characteristics in Lago Péten Itzá, Guatemala. Lake waters are dominated by sulfate, bicarbonate, calcium and magnesium and display a total ion concentration of ~11 meq L-1. Eleven extant ostracode species were identified. We found higher abundances of living ostracodes, as well as relatively higher species richness (eight species) and biodiversity (H of 1.6) between the littoral zone and a water depth of 20 m. At water depths &gt;40 m, these variables all decreased. The thermocline is located at a water depth of ~20-40 m. Cluster analysis revealed three water depth ranges in the lake of importance to ostracode distribution: 1) littoral zone (0.1-3 m), 2) water depths from the base of the littoral zone to the base of the thermocline (3-40 m), and 3) water depths below the thermocline (40-160 m). The assemblage "Darwinula-Heterocypris-Pseudocandona-Strandesia" is characteristic of waters &lt;15 m. The "Cypridopsis-Cytheridella-Limnocythere" assemblage characterizes waters &lt;40 m and "Physocypria" indicates waters &gt;40 m. Ostracode taxa from Lago Petén Itzá show specific ecological preferences related to water depth and associated physico-chemical characteristics, thus illustrating the potential of ostracodes as indicators of lake level changes and hydrodynamics.

The Platycopid Signal of oxygen depletion in the ocean: A critical evaluation of the evidence from modern ostracod biology, ecology and depth distribution

The use of relative abundances of filter-feeding platycopid ostracods in estimating past levels of dissolved oxygen in the ocean (the “Platycopid Signal Hypothesis”) is examined, paying particular attention to evidence from faunistic, biological and ecological studies. The degree of support for the hypothesis has been overstated; available data on ostracod depth distribution show that previous claims for platycopid dominance in the Oxygen Minimum Zone in different oceanic regions are misleading and based on only a few studies. Observations and experimental studies on living platycopids are limited in scope and should be treated with caution. We conclude that previously published and widely applied calibrations of platycopid abundance against dissolved oxygen levels are inadequately justified by the available data. Any further application of the Platycopid Signal technique should necessarily address these criticisms.

Stable isotope and ostracode species assemblage evidence for lake level changes of Nam Co, southern Tibet, during the past 600 years

Ostracode species assemblages and stable oxygen and carbon isotopes of shells from two 210Pb-dated short cores of 78 cm and 47 cm length taken from Lake Nam Co, southern Tibet, provide information about lake level history of the past approximately 600 years at decadal resolution. A transfer function is applied to reconstruct paleo-water depths from modern ostracodes. Ostracode assemblages and isotope data from five species allow a subdivision into phases of lake level evolution. Before ∼1600 AD relatively low oxygen isotope values and high abundances of deep water (>30 m) ostracodes (i.e. ? Leucocythere dorsotuberosa, ? Leucocythere dorsotuberosa f. postilirata) suggest a lake level ∼10 m higher than today. Between ∼1600 AD and 1800 AD, more positive oxygen isotope values and higher abundances of shallow water ostracodes (i.e. Ilyocypris cf. mongolica, Candona xizangensis) suggest a lake level approximately 40 m below modern level. Between 1800 AD and ∼1920 AD oxygen isotopes are characterized by a trend to more negative values followed by a trend to more positive ones. These trends are interrupted by several short-term fluctuations but overall, oxygen isotope values suggest a drop in lake level. A clearer lake level picture is provided by species assemblages that suggest a continuously increasing lake level since 1900 AD. Precipitation data from meteorological stations nearby show an increase in precipitation in the last 30 years. The low lake level between 1600 AD and 1800 AD is contemporary to the Little Ice Age. During that cold period, meltwater input into the lake decreased. This underlines the sensitivity of the level of Lake Nam Co to temperature changes on the Tibetan Plateau.

Modern benthic ostracodes from Lutzow-Holm Bay, East Antarctica: paleoceanographic, paleobiogeographic, and evolutionary significance

Research Article| November 01, 2007 Modern benthic ostracodes from Lützow-Holm Bay, East Antarctica: paleoceanographic, paleobiogeographic, and evolutionary significance Moriaki Yasuhara; Moriaki Yasuhara 1U.S. Geological Survey, 926A National Center, Reston, Virginia 20192, USA *Present address: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA. Search for other works by this author on: GSW Google Scholar Masako Kato; Masako Kato 2Institute of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan Search for other works by this author on: GSW Google Scholar Noriyuki Ikeya; Noriyuki Ikeya 2Institute of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan Search for other works by this author on: GSW Google Scholar Koji Seto Koji Seto 3Research Center for Coastal Lagoon Environments, Shimane University, Matsue 690-8504, Japan email: moriakiyasuhara@gmail.com or yasuharam@si.edu Search for other works by this author on: GSW Google Scholar Author and Article Information Moriaki Yasuhara *Present address: Department of Paleobiology, National Museum of Natural History, Smithsonian Institution, Washington, DC 20013-7012, USA. 1U.S. Geological Survey, 926A National Center, Reston, Virginia 20192, USA Masako Kato 2Institute of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan Noriyuki Ikeya 2Institute of Geosciences, Faculty of Science, Shizuoka University, Shizuoka 422-8529, Japan Koji Seto 3Research Center for Coastal Lagoon Environments, Shimane University, Matsue 690-8504, Japan email: moriakiyasuhara@gmail.com or yasuharam@si.edu Publisher: Micropaleontology Press Received: 01 Aug 2007 Accepted: 21 Jan 2008 First Online: 03 Mar 2017 Online ISSN: 0026-2803 Print ISSN: 1937-2795 © 2007 The Micropaleontology Project, Inc. Micropaleontology (2007) 53 (6): 469–496. https://doi.org/10.2113/gsmicropal.53.6.469 Article history Received: 01 Aug 2007 Accepted: 21 Jan 2008 First Online: 03 Mar 2017 Cite View This Citation Add to Citation Manager Share Icon Share Facebook Twitter LinkedIn MailTo Tools Icon Tools Get Permissions Search Site Citation Moriaki Yasuhara, Masako Kato, Noriyuki Ikeya, Koji Seto; Modern benthic ostracodes from Lützow-Holm Bay, East Antarctica: paleoceanographic, paleobiogeographic, and evolutionary significance. Micropaleontology 2007;; 53 (6): 469–496. doi: https://doi.org/10.2113/gsmicropal.53.6.469 Download citation file: Ris (Zotero) Refmanager EasyBib Bookends Mendeley Papers EndNote RefWorks BibTex toolbar search Search Dropdown Menu toolbar search search input Search input auto suggest filter your search All ContentBy SocietyMicropaleontology Search Advanced Search Abstract Seventy-three ostracode species from 38 genera were recovered from the 55 surface sediment samples in Lützow-Holm Bay, northeastern Antarctica. We investigated bathymetric and geographic distributions of modern benthic ostracode species in the bay and compared this fauna with published modern and fossil ostracode data of Antarctic and southern South American regions. The results show: (1) Four biotopes and three sub-biotopes are recognized based on Q-mode cluster analysis, which suggest distributions of modern ostracodes are mainly controlled by water-mass structure, ice scouring, and light availability. (2) Comparison between the Lützow-Holm Bay fauna and other ostracode faunas from Antarctica and southern South America shows high endemism and homogeneity of Antarctic ostracode fauna, suggesting in situ evolution of most extant Antarctic species. (3) Most species are endemic to the Antarctica, a few species also inhabit South American waters. You do not have access to this content, please speak to your institutional administrator if you feel you should have access.

Comparison study of the modern ostracod associations in the Kara and Laptev seas: Ecological aspects

Recent ostracod assemblages were investigated from coretop sediment samples collected in the eastern Kara Sea from water depths down to 300 m. A total of 45 species were identified, 27 of them were reported for the Kara Sea for the first time. The Kara Sea data were compared with our results on the distribution of ostracods in the eastern Laptev Sea. The spatial distribution of recent taxa and the ecological groupings demonstrate a clear relation to dominant environmental factors which range from estuarine to full-marine conditions. Four assemblages related to average summer bottom water salinities were established: (1) a freshwater assemblage from the inner estuaries of the Ob' and Yenisei rivers with salinities less than 2 and from thermokarst lagoons of the southern Laptev Sea coast with strong salinization in winter; (2) a brackishwater assemblage of the outer estuaries of the Ob' and Yenisei rivers with salinities up to 26; (3) a mixed euryhaline–marine assemblage dominated by euryhaline species Paracyprideis pseudopunctillata and Heterocyprideis sorbyana from the inner shelf river-affected zone of the Kara and Laptev seas, where salinities range between 26 and 32; (4) a taxonomically diverse marine assemblage dominated by shallow-water marine taxa from the northern parts of the Kara and Laptev shelves and upper continental slope with stable bottom environments and a salinity higher than 32. Abundant euryhaline species found at greater water depths are identified as part of an ice-rafted assemblage. They are possibly entrained into the newly formed fast ice during autumn storms and freeze-up period and then transported to the distal open-sea areas during summer.

Quantitative analysis of freshwater ostracode assemblages in southwestern Yukon Territory, Canada

Relations between modern ostracode assemblages and environmental variables from lakes in the southwest Yukon and northern British Columbia were explored. A total of 29 freshwater species representing 8 genera were identified from the sediments of 36 lakes, with the number of species ranging between 3 and 8 per lake. Species widespread throughout the study area include Cyclocypris ampla, Candona candida, Cypria turneri, Cypria ophtalmica, and Candona protzi. The Mg/Ca ratio is an important factor determining the ostracode species composition of a lake. Species richness is at a maximum when the lake water has intermediate values of conductivity. Lakes in which one species clearly dominates the assemblage (‰>‰70% relative abundance) have water saturated with respect to CaCO3. Mg/Ca ratio, depth and Sr are the environmental factors that are most highly correlated with species distributions in this region.

Modern and Holocene sublittoral ostracod assemblages (Crustacea) from the Caspian Sea: A unique brackish, deep-water environment

We present a reconnaissance study of sublittoral ostracods from a number of Caspian Sea core-tops collected during a joint French–Russian scientific cruise in 1994 (cores from between 13 and 875 m water depth). The modern ostracods show little depth restriction and this reflects the hydrography of the Caspian Sea which maintains relatively constant conditions (> 5 °C, 13‰ salinity) below 50 m throughout the year. We also present the ostracod faunal record from a 10 m core of laminated sediments, recovered from the Central Caspian Basin (at a water depth of 475 m), which we believe shows repetitive, quasi-cyclic changes in bottom-water conditions over approximately the last 14–15,000 years with a major change at about the late Glacial to Holocene transition. The faunal record from this core illustrates the potential of these sediments for reconstructing environmental changes in the Caspian region during the late Quaternary to Holocene. The continuous occurrence of in situ benthic meiofauna throughout the core also indicates that the bottom-water must have remained ventilated throughout this period although variability in the faunal assemblages may reflect long and short-term changes in the strength of ventilation.

Functional morphology of Palaeozoic ostracods: phylogenetic implications

Recent discussions of ostracod systematics have focused on soft anatomy, both as seen in extant groups and as recorded by rare examples of special fossil preservation. The position of the fossil Palaeocopina and Leperditicopida, for which no substantial soft part evidence has yet been found, remains in the view of post-Palaeozoic workers uncertain, with some doubt as to whether they should be retained within the Ostracoda. The evolution of carapace bauplans (e.g. the development of brood pouches and lobal structures in palaeocopids as well as the development of adductor muscle scar patterns, calcified inner lamellae and carapace incisures in podocopines) is discussed in relation to presumed soft anatomy. It seems possible to distinguish between plesiomorphic (ancestral, simple) and apomorphic (derived, advanced) characters and consider their significance in ostracod systematics. Although the presumed ‘protostracod’ is not known, the combination of soft anatomy, carapace architecture and behaviour (feeding techniques, brood care) provide evidence of a general body plan which appeared (at the latest) during the Ordovician and continuously evolved towards the anatomy of modern ostracods. In parallel lineages, plesiomorphic forms have died out (leperditicopids and most palaeocopines as well as metacopines), while apomorphic lineages (‘drepanellid archetype’ of palaeocopines; resistant platycopines, podocopines and myodocopines) have survived all extinction events. The evidence supports the retention of the Palaeocopina (and probably the Leperditicopida) in the Ostracoda.

HORNE, D. J. &amp; MARTENS, K. (eds) 2000. Evolutionary Biology and Ecology of Ostracoda. Developments in Hydrobiology Series no. 148. Reprinted from Hydrobiologia419 (2000). Papers presented at the 13th International Symposium on Ostracoda (ISO97), Chatham, 27–31 July 1997. xi + 197 pp. Dordrecht, Boston, London: Kluwer Academic Publishers. Price Euros 131.50, US $148.00, £90.00 (hard covers). ISBN 0 7923 6396

‘Evolutionary Biology and Ecology of Ostracoda’ was one of the themes from the International Ostracod Symposium held at the University of Greenwich in 1997. Fifteen papers read at that meeting are included in this volume, with a preface by the editors that provides a good overview of its contents. Ostracods are small bivalved crustaceans that have invaded most aquatic environments and which have a fossil record extending back to the Ordovician and probably earlier. Subjects covered include cloning, parasitism, reproduction, ontogeny, enigmatic light-reflecting organs, the origins of modern non-marine ostracods, and Catastrophe Theory applied to carapace morphology. …

Ostracode-based reconstruction from 23,300 to about 20,250 cal yr BP of climate, and paleohydrology of a groundwater-fed pond near St. Louis, Missouri

The water chemistry of a groundwater-fed sinkhole-pond near St. Louis, Missouri, and its associated climate during the last glaciation are reconstructed by comparison with autecological data of modern ostracodes from about 5,500 sites in Canada. A 4.8-m succession of fossiliferous sediment yielded ostracode assemblages that collectively are generally found today in ponds in North America including the species Cyclocypris ampla, C. laevis, Cypridopsis vidua, Candona crogmaniana, C. distincta, and C. ohioensis. Fossils of Picea needles and the ostracode Cyclocypris sharpei imply that best analog sites for the succession are in central to south-central Canada. The pond formed 23,300 ± 400 cal yr BP when a sinkhole became plugged by a clay bed about 1 m thick. By about 20,250 cal yr BP, the pond had desiccated and was buried by loess. The sediment accumulation rate was about 0.18 cm/yr, and each sample interval (6 cm) represents a time slice of ≈33 years. Data from this record provides the first fairly high resolution proxy record of the glacial paleoclimate of the mid-latitude of North America. The analog data indicate the water in the hydrologically-open spring-fed pond was less than 1 m deep. The paleoclimatic reconstructions imply gradually drier conditions and uniform, cool temperatures. The shallow water depth indicates that the temperature reconstruction is robust with mean annual temperatures (MATs) that ranged between 0.8 and 3.9°C, and mean July temperatures that ranged from 16.8 and 18.1°C. Other estimated climatic parameters include mean annual precipitation (MAP; 430 to 840 mm/yr), and moisture balance (P-E; −111 to 298 mm/yr). Compared to values measured today at St. Louis, the MAP was about 400 mm less, MAT about 10°C cooler, and P-E, about the same. These values are consistent with other published reconstructions based on modern analog analysis of fossil beetles and pollen, and paleothermometry based on amino acid racemization. The total dissolved solids (TDS) progressively increased from about 87 to 431 mg/L. Changes in TDS reflect either the balance between the relative inputs of karst groundwater and overland flow, or changes in the duration of water-rock interaction associated with the groundwater. The postulated long-term 900 ± 200 year cyclicity of growing-season moisture and temperature, attributed to El Nino-Southern Oscillation cycles, is not expressed in the reconstructed hydrologic or climatic data. This is attributed, in part, to the mediating effect on temperature by monothermic groundwater input to this flow-through system.

Assemblage diversity and isotopic signals of modern ostracodes and host waters from Patagonia, Argentina

Ostracode species assemblages and stable oxygen and carbon isotope ratios of living and recent ostracodes, together with δ 18O and δ 13C DIC (DIC: dissolved inorganic carbon) values of host water samples, provide a first data set that characterizes a wide range of modern aquatic environments in the Laguna Cari-Laufquen (41°S, 68–69°W) and the Lago Cardiel area (48–49°S, 70–71°W) in Patagonia, Argentina. This data set will ultimately be used to interpret and calibrate data acquired from lake sediment cores with the goal of reconstructing past climate. Species assemblages and isotope values can be assigned to three groups: (1) springs, seeps and streams, (2) permanent ponds and lakes, and (3) ephemeral ponds and lakes. Springs, seeps and streams are characterized by Darwinula sp., Heterocypris incongruens, Eucypris fontana, Amphicypris nobilis and Ilyocypris ramirezi. Ostracode and water isotope values range between −13 and −5‰ for oxygen, and between −15 and −3‰ for carbon. They are the most negative of the entire sample set, reflecting ground water input with little or no evaporative enrichment. Limnocythere patagonica, Eucypris labyrinthica, Limnocythere sp. and Eucypris aff. fontana are typical species of permanent ponds and lakes. Isotope values indicate high degree of evaporation of lake waters relative to feeder springs and streams and range between −7 and +5‰ for oxygen, and −5 and +4‰ for carbon. Limnocythere rionegroensis is the dominant species in ephemeral ponds and lakes. These systems display the most enriched isotope values in both ostracodes and host waters, extending from −5 to +7‰ for oxygen, and from −5 to +6‰ for carbon. Living ostracodes show a positive offset from equilibrium values of up to 2‰ for oxygen. Carbon isotope values are up to 6‰ more negative than equilibrium values in highly productive pools. Comparison of ostracode and host water isotope signals permits assessment of the life span of the aquatic environments. Valves from dead ostracodes collected from ephemeral ponds and lakes show a wide scatter with each sample providing a snapshot of the seasonal history of the host water. The presence of the stream species I. ramirezi and a wide range of ostracode isotope values suggest that ephemeral ponds and lakes are fed by streams during spring run-off and seasonally dry. A temporary character of waters is also indicated by H. incongruens, a drought-resistant species that occupies most springs and seeps. In addition, L. rionegroensis has adjusted its reproduction strategies to its environment. Whereas only females were collected in fresh host waters, males were found in ephemeral ponds and lakes with higher solute content. Sexual reproduction seems to be the more successful reproduction strategy in waters with high and variable salinities and affected by seasonal droughts. The temporary character of the aquatic environments shows that the availability of meteoric water controls the life span of host waters and underlines the sensitivity of the area to changes in precipitation.

Recent non-marine Ostracoda from Jamaica, West Indies

Abstract. Ostracods were sampled qualitatively at 22 sites from 15 waterbodies in the western part of Jamaica and determinations of the water chemistry and habitat characteristics were made at each locality. Most of the ostracods found belong to the Cypridinae, Cypridopsinae, Cyclocypridinae and Darwinulidae. There is a clear distinction between the faunas found in the larger, permanent lakes and the smaller ponds. The latter are subject to large fluctuations in volume and may desiccate either seasonally or interannually. Within the largest lake, Wallywash Great Pond, there is some degree of spatial zonation in the ostracod faunas that appears to be related to water depth and aquatic macrophyte occurrence. The distribution of modern ostracods within Wallywash Great Pond suggests that the late Quaternary faunal sequence from this lake is primarily a function of lake-level changes.

Glacial Meltwater in Lake Huron during Early Postglacial Time as Inferred from Single-Valve Analysis of Oxygen Isotopes in Ostracodes

δ 18O measurements of benthic ostracodes are used to reconstruct the δ 18O history of Lake Huron and Georgian Bay water between 10,600 and 7600 14C yr B.P. This δ 18O record was calibrated using a comparison of the δ 18O values of modern ostracodes and Lake Huron water, where a fractionation of 1.0358 was measured between the oxygen isotope ratios of the most isotopically positive ostracode Candona subtriangulata and lake water. The most positive shell δ 18O value was used because it is precipitated in the cold (0° to 2°C) water common to both deep and shallow environments. The δ 18O of Lake Huron water reflects a large glacial meltwater component for much of its history before 7600 14C yr B.P. Times of low lake level correlate with the highest ratio of glacial meltwater to local precipitation in the basin (most negative δ 18O values). Georgian Bay water was more negative in δ 18O than Lake Huron water of the same age; this reflects a higher proportion of glacial meltwater in Georgian Bay and its separation from Lake Huron during times of low lake level.

Quantitative Analysis of Ostracoda and Water Masses around Japan: Application to Pliocene and Pleistocene Paleoceanography

Quantitative Analysis of Ostracoda and Water Masses around Japan: Application to Pliocene and Pleistocene Paleoceanography

Lacustrine ostracodes as hydrochemical indicators in lakes of the north-central United States

The modern ostracode distribution in lakes of the north-central United States shows how ostracode abundances are related to concentrations of major ions such as calcium, sulfate, and bicarbonate. These relationships are quantified for species living in lakes that range from fresh water (200 μS cm-1) to saline water (17 000 μS cm-1). Lakes located in the Minnesota forests have different ostracode assemblages and different water chemistry than lakes located on the prairie of North Dakota and South Dakota. These differences are attributed to differences in precipitation and rock-water interactions. Multivariate analyses of the ostracode and water chemistry data set indicate that different ostracode species are associated with different water types. For example, Limnocythere sappaensis and Heterocypris glaucus are found in bicarbonate-enriched sulfate-dominated waters, whereas Limnocythere staplini is found in bicarbonate-depleted sulfate-dominated waters. Candona ohioensis and Limnocythere itasca are found in fresh water, and Candona rawsoni is eurytopic and found in both bicarbonate-enriched and bicarbonate-depleted sulfate-dominated waters. Ostracodes can be used to identify changes in both ionic composition (solutes) and ionic concentration.