Quaternary Ostracods Research Articles

Quaternary Ostracoda and Foraminifera from the Pelotas Basin, southernmost Brazil: Assemblage variation in gas-hydrate bearing sediments

Late Quaternary ostracod and foraminifera assemblages from five piston cores in Pelotas Basin, southern Brazilian margin, were analyzed in this paper. The study revealed a diverse bathyal fauna of ostracods, with abundance of the genera Apatihowella, Cytheropteron and Cytherella, interspersed with peaks of allochthonous neritic faunas. Benthic foraminifera are represented mainly by the genera Bolivina, Bulimina, Cassidulina, Epistominella, Globobulimina, Globocassidulina, Nonion, Oridorsalis and Uvigerina. Biostratigraphic analysis of planktic foraminifera positioned the samples in Pleistocene-Holocene interval. The ostracod genera Paracytherois, Cytheropteron, Cytherella, Macropyxis and the species Krithe hunti, Krithe reversa, Henryhowella asperrima, Eucytherura fossapunctata, Rimacytheropteron longipunctatum, Apatihowella besnardi and Apatihowella convexa, and also the benthic foraminifera Bolivina, Bulimina, Nonion, Nonionellina, Oridorsalis, Uvigerina, Epistominella and Cassidulina are related to environments of gas hydrates and associated with a chemosynthetic community in eutrophic-mesotrophic environments.

Oxygen and carbon isotopes and trace-element/Ca ratios in Late Quaternary ostracods Loxoconcha lepida and Palmoconcha agilis from the Black Sea: Paleoclimatic and paleoceanographic implications

Oxygen and carbon isotopes and trace-element/Ca ratios are presented for the valves of benthic ostracods Palmoconcha agilis and Loxoconcha lepida extracted from two composite sediment cores from the Black Sea shelf. The two cores together provide a complete latest Pleistocene–Holocene sedimentary record, with 16 radiocarbon-dated shells in core M02-45 and 9 in core M05-50. Results reveal environmental changes and evolution of water chemistry associated with the last reconnection of the Black Sea to the global ocean. The δ18O values in composite cores M02-45 and M05-50 exhibit ranges of ~8.0‰ and ~3.0‰, respectively; δ13C values show ranges of ~2.5‰ and ~2.0‰. There are three isotopic substages: (a) substage 1c (12.1–9.4 cal ka) represents conditions in the Neoeuxine Lake with relatively high δ13C and low δ18O, (b) substage 1b (9.4–6.3 cal ka) represents the transition from lacustrine to marine conditions with an increase in δ18O values as small amounts of Mediterranean water flowed into the Black Sea, and (c) substage 1a (6.3 cal ka to Present) represents the establishment of marine conditions like today with near-constant δ18O values and a trend of slowly increasing δ13C. Trace-element/Ca ratios show downcore trends consistent with the three isotopic substages. At ~6.3 cal ka, isotopic data and trace-element/Ca ratios exhibit a major shift, with changes in the Mg/Ca ratio suggesting an increase in water temperature from 12–14 °C to 17–19 °C. These mid-Holocene changes in ostracod-valve composition and environmental conditions coincide with the weakening of Black Sea outflow and the proliferation of marine organisms.

Taxonomic harmonization of Neogene and Quaternary candonid genera (Crustacea, Ostracoda) of the Paratethys

During the Cenozoic, the constant northward movement of the African plate led to the division of the Tethys Ocean into two: the Palaeomediterranean and the Paratethyan branches. The latter was represented by a huge epicontinental sea and brackish to freshwater lakes that extended across central Europe and western Asia. Neogene and Quaternary ostracods from the Paratethys originated through major adaptive radiations, which gave rise to endemic brackish taxa. Unfortunately, much confusion surrounds their taxonomy, due to the quality of descriptions and images in the original literature and the incompleteness of the type material, making necessary a taxonomic revision. In this paper, we propose a systematic revision of several Paratethyan endemic candonid genera based on the analysis of the type material, new material collected from the type localities, and new fossil material from the Ponto-Caspian area. The study focuses on the description of the valve morphology and particularly on the geometric morphometric analysis of the valve outline. Thirty-three genera were taken into account of which four (Advenocypris, Candoniella, Graviacypris, Telekia) were considered to be junior synonyms of Typhlocypris, Pseudocandona or Candona. Moesiella is considered a nomen nudum. In the case of Caspiollina, Dacicandona, Liventalina and Turkmenella the scarcity of material and/or the poor descriptions reported in the literature prevented us from performing a full revision. The monospecific genus Thaminocypris possibly includes a teratological form. The remaining 23 genera were merged into nine valid, endemic, genera (Bakunella, Camptocypria, Caspiocypris, Hastacandona, Lineocypris, Pontoniella, Propontoniella, Typhlocyprella and Zalanyiella). Emended diagnoses and descriptions are proposed for these genera and a new species, Bakunella anae sp. nov., is described. This study considerably reduces the taxonomic uncertainty within the Paratethyan candonids, providing new data for the evaluation of the palaeobiodiversity of the Paratethyan domain. Finally, the palaeobiogeography of Paratethyan candonids during the Neogene and Quaternary is also discussed.http://zoobank.org/urn:lsid:zoobank.org:pub:EB9EC2D4-AFD2-428E-9958-C97F36ED7FF2

Quaternary ostracode and foraminiferal biostratigraphy and paleoceanography in the western Arctic Ocean

The stratigraphic distributions of ostracodes and selected calcareous benthic and planktic foraminiferal species were studied in sediment cores from ~ 700 to 2700 m water depth on the Northwind, Mendeleev, and Lomonosov Ridges in the western Arctic Ocean. Microfaunal records in most cores cover mid- to late Quaternary sediments deposited in the last ~ 600 ka, with one record covering the last ~ 1.5 Ma. Results show a progressive faunal turnover during the mid-Pleistocene transition (MPT, ~ 1.2 to 0.7 Ma) and around the mid-Brunhes event (MBE, ~ 0.4 Ma) reflecting major changes in Arctic Ocean temperature, circulation and sea-ice cover. The observed MPT shift is characterized by the extinction of species that today inhabit the sea-ice free subpolar North Atlantic and/or seasonally sea-ice free Nordic Seas (Echinocythereis sp., Rockallia cf. enigmatica, Krithe cf. aquilonia, Pterygocythereis vannieuwenhuisei). After a very warm interglacial during marine isotope stage (MIS) 11 dominated by the temperate planktic foraminifer Turborotalita egelida, the MBE experienced a shift to polar assemblages characteristic of predominantly perennial Arctic sea-ice cover during the interglacial and interstadial periods of the last 300 ka. These include the planktic foraminifera Neogloboquadrina pachyderma, the sea-ice dwelling ostracode Acetabulastoma arcticum and associated benthic taxa Pseudocythere caudata, Pedicythere neofluitans, and Polycope spp. Several species can be used as biostratigraphic markers of specific intervals such as ostracodes Rabilimis mirabilis — MIS 5 and P. vannieuwenhuisei extinction after MIS 11, and foraminiferal abundance zones Bulimina aculeata — late MIS 5 and Bolivina arctica — MIS 5-11.

An expanded ostracod-based conductivity transfer function for climate reconstruction in the Levant

We present the first modern calibration dataset linking ostracod assemblage composition to water chemistry, and other site-specific variables, in the hydrologically and geopolitically sensitive southern Levant region. A total of 42 ostracod taxa were recorded from the 178 sampled sites in Israel and Jordan. Ilyocypris spp., Heterocypris salina and Cypridopsis vidua are the most abundant taxa. Species strictly confined to freshwater conditions are Prionocypris zenkeri, Gomphocythere ortali and Prionocypris olivaceus. In contrast, H. salina, Bradleytriebella lineata and Cyprideis torosa show high frequencies in brackish waters (waters with higher conductivity). Humphcypris subterranea, G. ortali, P. olivaceus and Cypridopsis elongata apparently prefer flowing waters. Specific conductivity optima and tolerance ranges were calculated for the recorded ostracod species and may be used for the palaeoenvironmental assessment of fossil ostracod assemblages. In addition, a transfer-function for quantitative specific conductivity estimation based on 141 samples was established with weighted averaging partial least squares regression (WA-PLS). The resulting coefficient of determination r2 between observed and predicted conductivity values (0.72) and the root-mean-square error of prediction (RMSEP) in % gradient length (13.1) indicate that conductivity may be reliably estimated from ostracod assemblage data. The transfer function was first applied to last glacial ostracod assemblage data from an archaeological trench in the Sea of Galilee (northern Israel). Relatively large conductivity fluctuations between ca 1 and 7 mS cm−1 were inferred for the period 24–20 cal ka BP. In addition, four episodes of freshwater influx near the site of the trench were identified from the presence of shells of freshwater and stream-dwelling species intermingled with very abundant shells of Cyprideis torosa. The results of our study allow a better use of Quaternary ostracods from the Levant as palaeoenvironmental indicators of water-body types and past conductivity levels and will contribute to a better understanding of Quaternary environmental and climate change in the Levant.

A late quaternary ostracod record from the Tso Kar basin (North India) with a note on the distribution of recent species

The fossil ostracod associations from a radiocarbon dated sediment core (15.3–0 cal kyr) of the high altitude (4,527 m a.s.l.) hyperhaline Tso Kar lake in North India reveal changes in ostracod species abundances and composition. These document the process of lake formation and ongoing desiccation during the latest quaternary and broadly confirm the results of previous geochemical, geomorphological and pollen analysis. The most striking feature of the core record is a period of freshwater conditions between 9.0 and 6.5 cal kyr BP, as calculated by means of an ostracod-based conductivity transfer function. This early- to mid-Holocene interval of the core correlates with similar ostracod assemblages (Cytherissa lacustris—Candona candida—Eucypris afghanistanensis) of an outcrop section at the basin margin, about 98 m above the modern lake level and marks the highest lake level under the influence of an intensified Indian Summer Monsoon. After 6.5 cal kyr BP, Limnocythere inopinata is the sole representative of the ostracod fauna in the sediment core, which suggests rising salinity conditions most probably due to lake shallowing. From 3.2 cal kyr BP to present, the near absence of ostracods in the core Tk106 is most likely a consequence of salinisation of the lake towards the hyperhaline conditions that are realised at present. Although the modern morphology and physico-chemical properties of Tso Kar lake are in contrast to the past lake conditions, most of the ostracod species, except for Limnocythere mirabilis found in the sediment core, are also identified from surface sediment and outcrop samples. In contrast, Heterocypris salina and Eucypris dulcifons are widespread in the shallow surface waters with a total dissolved solids content ranging from 0.6 to 15.0 g L−1, but are excluded from the core record and outcrop strata. At a basinal scale, the lake shrinkage and segregation into the Tso Kar and hydrologically open freshwater lake Startsapuk Tso have forced diversification of ostracod taxa, probably as an effect of the emergence of new ecological niches under enhanced “environmental pressure”.

Primeras citas de ostrácodos (Crustacea) del Pleistoceno tardío de la provincia de Formosa, Argentina

First records of ostracods (Crustacea) from the late Pleistocene of the Formosa province, Argentina. We report the presence of Quaternary ostracods in the Province of Formosa, Argentina, found on the banks of the Bermejo Rriver, in the town of Villa Escolar. Tthe fossil site is placed 100 km from the city of Formosa, in the region of Laishi. Tthese outcrops were deposited at different moments of the Quaternary period during arid climate, causing the development of dunes and loess mantles. Is likely that the analyzed outcrops correspond to the Bermejo Formation (late Pleistocene). ostracods come from clay-silt levels and belong to the genera: Cytheridella, Cyprideis, Cypridopsis and Candona. Tthis ostracod association would indicate environments of continental influence, freshwater, shallow, silt-clay background with low energy streams.

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.

Depredación de ostrácodos del Cuaternario del sur de la provincia de Buenos Aires, Argentina

Depredation of Quaternary ostracods from southern Buenos Aires province, Argentina. The presence of fossil traces in ostracods valves from different quaternary palaeoenvironments in southern Buenos Aires province, Argentina, are studied in this paper. A number of 12500 specimens were analyzed and a total of 33 bored valves were separated. Two types of depredation fossil traces were determined: Oichnus simplex Bromley and Oichnus paraboloides Bromley, which comprised more than 60% of the total boreholes. The highest percentage of valves with evidence of predation (3.33%) was registered in sediments of a continental permanent lagoon with favourable trophic conditions and high density of ostracods. There was not relationship between the borehole diameter and the size of the predated valves. Evidences of depredation were registered in species with smooth valves as well as in species with adorned valves.

Arctic quaternary ostracods and their use in paleoreconstructions

The paper deals with original and published data on fossil ostracodal assemblages from the Eurasian Arctic Kara, Laptev and Chuckchi seas. As a whole, six ecologically different assemblages were distinguished (freshwater, brackish water, marine of the inner, middle and outer shelves and upper continental slope), they replace each other upcore reflecting a gradual increase in water depth and distance from the coast. These assemblages are stable in the entire Arctic region and can be used for interpretation of environments in different Arctic areas.

Deep-sea ostracods from the South Atlantic sector of the Southern Ocean during the last 370,000 years

We report changes of deep-sea ostracod fauna during the last 370,000 yr from the Ocean Drilling Program (ODP) Hole 704A in the South Atlantic sector of the Southern Ocean. The results show that faunal changes are coincident with glacial/interglacial-scale deep-water circulation changes, even though our dataset is relatively small and the waters are barren of ostracods until mid-MIS (Marine Isotope Stage) 5.KritheandPoseidonamicuswere dominant during the Holocene interglacial period and the latter part of MIS 5, when this site was under the influence of North Atlantic Deep Water (NADW). Conversely,HenryhowellaandLegitimocytherewere dominant during glacial periods, when this site was in the path of Circumpolar Deep Water (CPDW). Three new species (Aversovalva brandaoae, Poseidonamicus hisayoae, andKrithe mazziniae) are described herein. This is the first report of Quaternary glacial/interglacial scale deep-sea ostracod faunal changes in the Southern and South Atlantic Oceans, a key region for understanding Quaternary climate and deep-water circulation, although the paucity of Quaternary ostracods in this region necessitates further research.

Quantitative reconstruction of lake conductivity in the Quaternary of the Near East (Israel) using ostracods

Surface sediments, water samples and environmental data from 37 lakes, ponds and streams in Israel were analysed to determine the main variables controlling ostracod species distributions. Multivariate statistical analysis revealed that the greatest amounts of variation in the distribution of the ostracod taxa among the 37 water bodies were explained by the host water δD value (12.9%), water temperature (11.0%), mean January air temperature (10.5%), electrical conductivity (9.5%), and the Mg and NO3 concentrations (7.8 and 7.1%, ion concentrations as % of the anions or cations). A supplementary data set comprising ostracod species composition and electrical conductivity readings for 24 water bodies was available from previous research and was merged with the 37 samples data set to develop an ostracod-based transfer function for the reconstruction of electrical conductivities. A weighted averaging partial least squares regression (WA-PLS) provided the best results with a relatively high coefficient of determination (r2) between measured and inferred electrical conductivity values of 0.73, a root mean square error of prediction of 0.13 (13.4% of gradient length) and a maximum bias of 0.24 (23.9% of gradient length), as assessed by leave-one-out cross-validation based on 56 water bodies. The application of the EC transfer function onto (sub)fossil ostracod assemblages from Holocene and early to mid Pleistocene lake sediments provided EC values consistent with other proxies and demonstrated that Quaternary ostracod assemblages from subaqueous sediments can now be used to trace the hydrological history of water bodies in the Near East. A better understanding of past hydrological conditions in response to the natural climate variability is crucial in regions that face restricted water resources and rising demands in times of rapid climate and environmental change.

The effects of diagenesis on the trace element and stable isotope geochemistry of non-marine ostracod valves

The trace-element and stable-isotope geochemistry of non-marine ostracod valves is a valuable tool in palaeolimnology. However, the potential effects of early diagenesis on geochemical composition are poorly documented. In this study, the effect of partial dissolution on the trace-element (Sr and Mg) and isotopic (18O/16O and 13C/12C) composition of late Quaternary non-marine ostracod valves was investigated. Both unaltered and extremely degraded valves of the species Cypretta brevisaepta recovered from the same core level had trace-element and stable-isotope ratios that were drawn from the same statistical population, suggesting that the geochemical effects of early diagenesis are minimal. However, since the possibility remains that diagenesis could under certain circumstances alter valve chemistry, only valves in pristine condition should be used in palaeoenvironmental studies whenever feasible.

Sub-Recent Ostracoda from Bosten Lake, NW China

Abstract. In spite of early work by Daday (1903) and by Sars (1903a, b), the Recent and sub-Recent non-marine ostracod faunas of NW China remain poorly known. There is only little information included in later works, which have tended to focus on fossil Tertiary and Quaternary ostracods (e.g. Sun et al., 1999), rather than on Recent or sub-Recent taxa, although Yu & Martens (1997) have presented a very preliminary checklist for China as a whole.In an attempt to improve this situation, this note reports on ostracods collected from the largest ‘freshwater’ lake of NW China. Bosten Hu (Lake) (c. lat. 42°N, long. 87°E) covers an area of about 1020 km2 at an altitude of 1048 m above sea-level in an intermontane basin of the Chinese Tianshan Mountains. The lake has an outlet to the Tarim Basin in the south and had a salinity of about 1.0 g l−1 in 1950 which increased to 1.5 g l−1 in 1978 due to withdrawal of water from the main tributary (Kaidu He) for irrigation purposes. The lake is rather shallow with a maximum depth of 15.7 m, its volume being about 9.9 km3 (Berkner, 1993).Sampling of surface mud from the uppermost centimetres of the lake bottom and of plankton samples was carried out along several transects in nearly all parts of the lake. Altogether, 33 samples were collected by a mud grabber or a handnet, and by a diver. Surprisingly, no living specimens were found, although ostracod valves were very abundant in . . .

Palaeoceanographical changes recorded by Cenozoic deep‐sea ostracod assemblages from the South Atlantic and the Southern Ocean (ODP Sites 1087 and 1088)

Cenozoic palaeoceanography of the SE Atlantic and Southern Oceans has been investigated using Late Eocene/Early Oligocene to Quaternary ostracod assemblages from 49 samples of ODP Sites 1087 and 1088. Although the overall abundance of ostracods is relatively low (means of 17 and 49 specimens per sample at Sites 1087 and 1088, respectively) and there is an apparently high level of endemism (ranging from 50% to 80% at Sites 1087 and 1088), three major changes in the faunal assemblages are identified at Site 1087 (denoted A, B and C) and two at Site 1088 (denoted B′ and C′). The assemblage boundaries, detected on the basis of stepwise changes in the abundance, diversity, dominance, endemism, faunal turnover and relative abundance of common taxa, coincide broadly with previously identified, ostracod-based palaeoceanographical ‘events’ discussed by Benson and co-workers over the last two decades. The data do not extend sufficiently far back to record the initiation of Assemblage A, but the faunal change between Assemblages A and B, marked by a decline in abundance, species diversity and faunal turnover, occurs within the Middle Miocene (NN5-6). It coincides with a previously documented palaeoceanographical ‘event’ at 16–14 Ma which, we suggest, may be related to the initiation of North Atlantic Deep Water (NADW) production and/or an expansion of the East Antarctic ice sheet. Assemblage B′ is subdivided into the two Sub-assemblages B′1 and B′2 mainly on the basis of an increase in diversity, a peak in faunal turnover and a drop in the relative abundance of the genus Krithe in early Late Miocene time (NN9, c. 10.5 Ma). The B′1/B′2 Sub-assemblage boundary cannot be related to any previously documented faunal change in deep-sea ostracods. Changes associated with the boundaries between Assemblages B and C, and B′ and C′, which we believe to be synchronous, both include a decrease in diversity and abundance. In addition, two strong turnover peaks occur near the B′/C′ boundary at Site 1088. The B/C and B′/C′ boundaries coincide with a previously documented midPliocene ‘event’ (3.5 Ma) (NN15-16) which may be linked to putative closure of the Straits of Panama and increased production of NADW, the latter in turn leading to increased production of Antarctic Intermediate Water (AAIW) and Antarctic Bottom Water (AABW). Alternatively, fiuctuations in size of the Antarctic ice sheet during possible Pliocene warm periods could indirectly be responsible for the observed midPliocene faunal changes.

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.

A late Quaternary ostracod record from Wallywash Great Pond, a Jamaican marl lake

Two assemblages typify the ostracod fauna of a 9.23 meter core taken from Wallywash Great Pond, a small perennial freshwater marl lake in Jamaica. The first, dominated by Cypretta brevisaepta, lived in deep water, similar to present-day conditions. The second, dominated by Candonopsis sp., reflects the existence of a shallower lake. The core has a basal date of c. 125 kaBP. Four inferred deep-water phases occurred in the period 125–93.5 kaBP with periods of inferred shallower water in between. The lake was dry between 93.5 kaBP and c. 10 kaBP as suggested by the absence of ostracods or fossils of other aquatic organisms. Ostracod faunal evidence indicates that there have been three highstands and two lowstands of the lake during the Holocene, although ostracods are not preserved in the organic mud and lignite that formed under swampy conditions as the basin filled at the start of the Holocene and during part of the two subsequent lowstands of the lake. A major hydrological perturbation, associated with the flooding of the nearby Black River catchment around 1.2 kaBP, caused an increase in the ostracod species diversity of the Great Pond, although this was relatively short lived and the lake attained a faunal composition similar to present around 1 kaBP. Major variations in ostracod assemblages in the core thus represent lake-level changes and accord well with previously-published interpretations of water depth based on lithofacies variation and stable oxygen isotope ratios in authigenic carbonates.

Quaternary ostracods as palaeoceanographic indicators: a case study off southern Australia

Abstract There is increasing use of ostracods in palaeoceanographic interpretation, yet few comparisons have been made with existing foraminiferal indicators. This paper examines ostracod records from two cores taken off southern Australia and compares them with foraminiferal records of abundance and dissolution. Core E55-6 from the continental margin of Victoria is located in 2346 m water depth. Core E27-30, located south of Tasmania in a water depth of 3552 m, lies to the north of the present position of the Subtropical Convergence. While benthic foraminiferal abundances parallel ostracod abundances in core E55-6, this is not the case in core E27-30. In the latter core, peaks in ostracod abundance are offset from peaks in foraminiferal abundance. This is attributed to high phytodetrital input associated with the Subtropical Convergence. An ostracod-based dissolution index is compared with foraminiferal dissolution data from both cores. The ostracod dissolution index shows greater sensitivity than foraminiferal fragmentation in water depths well above the lysocline and suggests that carbonate dissolution at these depths may be underestimated using foraminiferal indices. The impact of dissolution on ostracods can also be seen as a reduction in abundance. This is evident in both cores, although the impact is greater in the shallower core, suggesting that carbonate saturation may be a factor in the distribution of ostracods in the deep sea. Further investigation of the effects of carbonate saturation on individual ostracod taxa will enhance their utility as palaeoceanographic tools.

Late Quaternary ostracod and planktonic foraminiferal dissolution signals from the eastern Tasman Sea — palaeoenvironmental implications

Abstract A recently developed ostracod corrosion index is compared (and contrasted) with planktonic foraminiferal fragmentation in latest Quaternary carbonate sediments from the Challenger Plateau, eastern Tasman Sea. Although assemblage data for ostracodal corrosion and planktonic foraminiferal fragmentation are similar (accepting a foraminiferal peak which anticipates the ostracod signal by about 8 kyr in isotopic stage 3, and a second peak which lags that for Ostracoda in isotopic stage 1 by an equivalent amount), plots of carapace corrosion of some ostracod genera show no such relationship. The planktonic foraminiferal fragmentation in core GR 5 4 during the last three isotopic stages duplicates the δ18O signal, suggesting regional surface-water temperature changes had a significant influence on that signal. In contrast, the corrosion index for representatives of the ostracod genus Krithe accurately tracks the δ13C for those 3 isotopic stages. We conclude that the intensity of degradation of those ostracod valves is an accurate reflection of productivity fluctuations in surface-water through time.

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)

Lagoonal to Reefal Ostracod Assemblages from Holocene and Recent Deposits, Chesterfield Islands and Northern New Caledonia (Southwestern Pacific)