Julio Rodríguez-Lázaro

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 theChain 82-24 Core 4PC (41o43 0 N, 32o51 0 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/D 0:4 during glacial periods (marine isotope stages 6, 5d, 5b, 4, and 2) to H.S/D 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, SD 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‐Cytheropteroncharacterizing 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. Published by Elsevier Science B.V.

Ostracoda and Paleoceanography

Ostracodes are mainly benthic Crustacea. They are commonly preserved in marine and marginal marine sediments and are used increasingly in Quaternary paleoceanography. The ecological sensitivity of ostracode species to temperature, salinity and dissolved oxygen have allowed paleoceanographic reconstruction of important climate-related variables over timescales ranging from 10 7 to 10 2 years. This chapter reviews recent advances in the application of ostracodes to the study of large-scale ocean and climate events caused by Cenozoic tectonic and climate changes with particular reference to Quaternary orbital forcing, thermohaline circulation, decadal and interannual (El Nino-Southern Oscillation) climate variability, and 20 th century anthropogenic factors.

Late Holocene pollution in the Gernika estuary (southern Bay of Biscay) evidenced by the study of Foraminifera and Ostracoda

The Arketas pier in the Gernika estuary (southern Bay of Biscay) has during summer periods waters with strong hypoxia (≤1 ml l−1) but curiously bears the richest assemblages of foraminifers and ostracods in the whole estuary. The most abundant species in Arketas are: Ammonia beccarii, Cribroephidium williamsoni, Haynesina germanica and Lobatula lobatula (foraminifers) Loxoconcha elliptica and Leptocythere castanea (ostracods). The benthic foraminifer sub-species A. beccarii tepida exhibits in this estuary three different morphotypes, whose distributions are controlled by changes in the salinity, dissolved oxygen and nutrient content of the waters, and thus could be used as a good indicator of environmental alteration caused by those parameters. To determine whether this environmental alteration is due to natural causes or is anthropogenic, micropalaeontologic and sedimentologic contents of a sediment core 140 cm thick have been analysed. The study of Foraminifera and Ostracoda assemblages, species diversity, and A. beccarii tepida morphotypes allows us to reconstruct the evolution of this part of the estuary over the last 3800 years. To examine anthropogenic effects at this site, we compared the occurrence of heavy metals Pb, As, with the record of A. beccarii tepida morph C in Arketas. The maximum concentration of heavy metals coincides with the maximum occurrence of A. b. tepida morph C, in the 1970s (date calculated according to the estimated rate of sedimentation in this area). This indicates that distribution of A. b. tepida morph C is, at least partially, caused by heavy metal pollution. Nevertheless, the fact that we have found no deformed tests of this taxa in Arketas induces us to think that another factor, such as dysaerobia caused by eutrophization of nutrient inputs in several areas of this estuary, might have been responsible for at least of part of the anomalous shift of A. b. tepida morph C at that time. In recent times, an increase in this anthropogenic activity was evident, reaching its maximum in the 1970s and decreasing from the 1980s. During the late Holocene period (up to 3500 years BP), this site was a middle-outer estuarine settlement, euryhaline with low to moderate salinity. This episode ends with a marine transgressive pulsation. After depositional hiatus of unknown duration, recent sediments suggest a modern palaeogeographic position of Arketas located in a lower estuary environment. The study of A. beccarii through the Holocene sediments of Arketas indicates that dysaerobic/pollution conditions were not a singular event. At the same time, the increase of A. b. tepida morph C were particularly strong over several years of the 20th Century, at precisely the time that a noticeable decrease of richness and diversity of calcareous microfauna is detected in the estuary.

Quaternary glacial and deglacial Ostracoda in the thermocline of the Little Bahama Bank (NW Atlantic): palaeoceanographic implications

Abstract We determined faunal and oceanographic changes during the last glacial and deglacial in the Providence Channel, Little Bahama Bank (LBB), using modern ocean (from LBB, Florida–Hatteras Slope and Blake Plateau, western North Atlantic) and late Quaternary (LBB) distributions of the benthic ostracode genus Krithe from the mid-depth (300–1600 m) subtropical North Atlantic Ocean. Nine species of Krithe are limited in their bathymetric distribution by warm bottom water temperatures (or a temperature-related parameter) in the thermocline of the modern Atlantic. During the last glacial interval in the northwest Providence Channel of the Little Bahama Bank, five species of Krithe ( K. aequabilis , K. dolichodeira , K . gr. minima , K. reversa and K. trinidadensis ) migrated upslope; conversely, during the deglaciation, most Krithe species migrated downslope, re-occupying their deeper niches. These vertical species migrations are attributed to decreased glacial bottom water temperatures and perhaps increased dissolved oxygen during the last glacial and warmer water temperatures during the deglacial. Based upon thermal values of recent depth ranges of selected species of Krithe , we estimate that glacial waters cooled about 4°C (shallower than 900 m) and about 2°C (deeper than 900 m) and deglacial waters warmed about the same values in shallow and mid-depth water masses, comparing to modern temperatures. The discovery of common Halocypris , a mesopelagic ostracode, in Little Bahama Bank glacial and deglacial sediments also suggests greater oxygenation relative to the late Holocene.

A General Introduction to Ostracods: Morphology, Distribution, Fossil Record and Applications

Abstract A general introduction to the Ostracoda is presented. Following an outline of ostracodological activity, the characteristic features of the Quaternary ostracods are reviewed, including morphology, distribution, fossil history and applications. Palaeobiological highlights of the group are particularly noted; ostracods possess the most complete fossil record among the arthropods and play an important role in the understanding of the evolution of sex in metazoans. Morphology is described and illustrated, including the soft parts (limbs) as well as the calcitic bivalved carapace, and the systematic value of these features at superfamily level is discussed. The high ecological plasticity of the ostracods is discussed in relation to the particular capacities that have allowed them to occupy practically all types of aquatic water bodies since Early Palaeozoic times, resulting in a long and successful evolutionary history. Finally, important applications of the ostracods in fields such as palaeobiology, palaeoceanography, palaeolimnology, palaeoclimatology and palaeoenvironmental analysis are outlined.

Paleoenvironmental evolution of the Pliocene Villarroya Lake, northern Spain. A multidisciplinary approach

Abstract The Pliocene Villarroya basin fill consists of lacustrine and alluvial deposits over 100 m thick. The lacustrine deposits, up to 30 m thick, comprise three sequences. The two lower sequences consist of profundal, laminated deposits formed by mostly terrigenous facies that are overlain by charophytic carbonates and varves. The uppermost, third sequence made up of massive bioturbated mudstones corresponds to a very shallow lacustrine–palustrine environment. Bulk mineralogy comprises carbonates, clay minerals, quartz and feldspars. The carbonates are: exogenic, biogenic calcite and biogenic aragonite. Biogenic calcite constitutes ostracod shells and charophyte stem encrustations, whereas aragonite forms gastropod shells and, in some varve intervals, charophyte encrustations. The clay minerals are illite, kaolinite, palygorskite, chlorite and paragonite, which are inherited from source rocks, and smectite and interstratified clays, which are probably formed in the soils of the source area. Variations in clay mineralogy reflect the interplay between the climate, tectonic rejuvenation and the paleogeography of the basin. The pollen assemblages indicate significant variations in climate: a first phase of varying climate was followed by cool-temperate and sub-humid phases that culminated in a temperate and dry episode, which is recorded in the lower part of the second lacustrine sequence. This was succeeded by a marked warm and humid episode, which may be correlated with the Mid-Pliocene warmth about 3.0 Ma and the subsequent cooling phase, which is recorded in the upper, third sequence. In the two lower sequences (profundal lacustrine deposits), ostracods indicate oligosaline to mesosaline waters with salinity variations and some warm and Na–Cl episodes. Molluscs are characterized by hydrobiids, suggesting a salinity stress. In the upper, palustrine deposits, the ostracods and aquatic mollusc assemblages indicate fresh, cold waters. Faunal records indicate that changes in salinity do not correlate with climate, suggesting phases of significant saline inputs to the lake which were recorded in the lower first sequence and in the upper part of the second sequence. The lacustrine sequence of Villarroya record pronounced variations in climate and in the lacustrine environment. However, there are no consistent relationships between the climate conditions inferred from the pollen data and the sedimentary record of the environmental changes, showing that other factors, especially tectonics, have exerted an influence on the paleoenvironmental evolution, and on the sedimentary record of the Pliocene Villarroya lake.

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

Abstract 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 (r2 = 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.

Enhanced Arctic Amplification Began at the Mid-Brunhes Event ~400,000 years ago

Arctic Ocean temperatures influence ecosystems, sea ice, species diversity, biogeochemical cycling, seafloor methane stability, deep-sea circulation, and CO2 cycling. Today’s Arctic Ocean and surrounding regions are undergoing climatic changes often attributed to “Arctic amplification” – that is, amplified warming in Arctic regions due to sea-ice loss and other processes, relative to global mean temperature. However, the long-term evolution of Arctic amplification is poorly constrained due to lack of continuous sediment proxy records of Arctic Ocean temperature, sea ice cover and circulation. Here we present reconstructions of Arctic Ocean intermediate depth water (AIW) temperatures and sea-ice cover spanning the last ~ 1.5 million years (Ma) of orbitally-paced glacial/interglacial cycles (GIC). Using Mg/Ca paleothermometry of the ostracode Krithe and sea-ice planktic and benthic indicator species, we suggest that the Mid-Brunhes Event (MBE), a major climate transition ~ 400–350 ka, involved fundamental changes in AIW temperature and sea-ice variability. Enhanced Arctic amplification at the MBE suggests a major climate threshold was reached at ~ 400 ka involving Atlantic Meridional Overturning Circulation (AMOC), inflowing warm Atlantic Layer water, ice sheet, sea-ice and ice-shelf feedbacks, and sensitivity to higher post-MBE interglacial CO2 concentrations.

Ostracoda as Proxies for Quaternary Climate Change: Overview and Future Prospects

Abstract Ostracod crustaceans are excellent Quaternary palaeoclimate proxies. As microfossils they supply evidence of past climatic conditions via indicator species, transfer function and mutual climatic range methods as well as the trace-element and stable-isotope geochemistry of their shells. We provide an overview of 17 contributions to the book Ostracoda as proxies for Quaternary climate change , highlight some of the emerging innovations and concerns, and assess the future prospects for ostracod applications in the field of Quaternary palaeoclimatology. The science of using ostracods as Quaternary palaeoclimate proxies has matured, well beyond the pioneering stage, and their application now needs to be tempered with critical awareness of their limitations. Key areas for future attention include palaeogenetics, improving knowledge of the ecology of living ostracods and the factors influencing their shell geochemistry, the establishment of global distributional databases and, as a necessary corollary to the last-mentioned, a programme of taxonomic harmonisation on a global scale. Finally, we emphasise the need for multi-proxy testing of methods, comparing ostracod-inferred climatic parameters with those derived from other proxies such as beetles, chironomids and foraminifera.

The Neogene Mediterranean origin of Cyprideis torosa (Jones, 1850)

Although Cyprideis torosa is one of the most studied ostracods, its ecophenotypic variability has always impeded a clear definition of its carapace morphology. As a consequence, it is often difficult to identify this species in fossil material and very little is known about its phylogenetic origin. In this paper, we attempt to answer two main questions: when and from what species did C. torosa originate? To reach this goal we first analysed living and Recent populations of C. torosa collected from different salinity environments to define its variability. We found that the valve outline, the size of rounded normal sieve pores and the percentage width of the anterior inner lamella seem to vary independently of salinity. Secondly, to look for possible ancestors we analysed several Neogene species and found that Cyprideis sp. from the mid-Serravallian of Spain could possibly be the common ancestor of the Late Miocene Mediterranean and Lake Pannon lineages and that C. torosa is strictly linked to the Mediterranean stock, particularly to the phyletic lineage C. ruggierii–C. crotonensis. In this framework Cyprideis gr. torosa originated in the late Tortonian and C. torosa s.s. is thought to have been differentiated from C. crotonensis at the beginning of the Calabrian. Supplementary material: biometric tables and the list of the examined material is available at https://dx.doi.org/10.6084/m9.figshare.c.3636170.v1