Variation in calcification of Reticulofenestra coccoliths over the Oligocene–Early Miocene

Coccolithophores are calcifying marine phytoplankton whose intracellularly produced calcite plates, coccoliths, have been the dominant source of calcium carbonate in open-ocean settings since the Cretaceous. An open question is whether their calcification has been affected by changing environmental conditions over geological timescales such as variations in the ocean carbon system. Previous methods using circular polarized light microscopy allowed for only the thickness of small coccoliths thinner than 1.5 µm to be quantified, but prior to the Pliocene, a significant fraction of the coccoliths exceeded this thickness and have not been quantifiable. Here, we implement a new approach for calibration of circular polarized light microscopy enabling us to quantify coccoliths which feature calcite up to 3 µm thick. We apply this technique to evaluate the evolution of calcification in the Reticulofenestra from the early Oligocene to Early Miocene in exceptionally well-preserved sediments from the Newfoundland margin. Through this time interval, coccolith thickness and the scale-invariant shape factor kse vary by about 20 % around the mean thickness of 0.37 µm and mean kse of 0.16. Lower shape factors characterize samples with a higher relative abundance of dissolution-resistant nannoliths, suggesting that dissolution may contribute to thinning of placoliths. We therefore define temporal trends in calcification only in samples in which the assemblage suggests minimal dissolution. The lowest kse characterizes the middle Oligocene, and the highest kse around 18 Ma is in the Early Miocene. High ocean dissolved inorganic carbon (DIC) concentrations have been proposed for this period of the Miocene and may be one factor contributing to high coccolith kse.</p

BENFEP, a quantitative database of BENthic Foraminifera from surface sediments of the Eastern Pacific

Foraminifera are important components of the ocean benthos and play a major role in ocean biogeochemistry and ecosystems functioning. Generating ecological baselines for ocean monitoring or biogeographical distributions requires a reference dataset of recent census data. Besides, the information from their modern biogeography can be used to interpret past environmental changes on the sea-floor. In this study, we provide the first comprehensive quantitative BENthic Foraminifera database from surface sediments of the Eastern Pacific (BENFEP). Through the collation of archival census data and its homogenization according to the most recent taxonomic standards, we are able to provide a database with 3093 sediment samples, corresponding to 2572 georeferenced stations of wide geographical coverage (60&ordm; N and 54&ordm; S) and water depths (0&ndash;7642 m). The quantitative data includes living, dead, and living and dead assemblages obtained from 47 published and unpublished documents. As well as describing the data collection and subsequent harmonization steps, we provide summarized information of metadata variables, examples of species distribution, potential applications of the database and recommendations for data archiving and publication of benthic foraminiferal data. The database is enriched with meaningful metadata for accessible data management and exploration with R and geospatial software. BENFEP will be upgraded with new records. We complement BENFEP with an additional database integrating metadata and stations geolocation of benthic foraminiferal studies dearth of quantitative data (BENFEPqual).</p

Impact of suborbital climate changes in the North Atlantic on ice sheet dynamics at the Mid-Pleistocene Transition

Early and Mid-Pleistocene climate, ocean hydrography and ice sheet dynamics have been reconstructed using a high-resolution data set (planktonic and benthic delta O-18 time series, faunal-based sea surface temperature (SST) reconstructions and ice-rafted debris (IRD)) record from a high-deposition-rate sedimentary succession recovered at the Gardar Drift formation in the subpolar North Atlantic (Integrated Ocean Drilling Program Leg 306, Site U1314). Our sedimentary record spans from late in Marine Isotope Stage (MIS) 31 to MIS 19 (1069-779 ka). Different trends of the benthic and planktonic oxygen isotopes, SST and IRD records before and after MIS 25 (similar to 940 ka) evidence the large increase in Northern Hemisphere ice-volume, linked to the cyclicity change from the 41-kyr to the 100-kyr that occurred during the Mid-Pleistocene Transition (MPT). Beside longer glacial-interglacial (G-IG) variability, millennial-scale fluctuations were a pervasive feature across our study. Negative excursions in the benthic delta O-18 time series observed at the times of IRD events may be related to glacio-eustatic changes due to ice sheets retreats and/or to changes in deep hydrography. Time series analysis on surface water proxies (IRD, SST and planktonic delta O-18) of the interval between MIS 31 to MIS 26 shows that the timing of these millennial-scale climate changes are related to half-precessional (10 kyr) components of the insolation forcing, which are interpreted as cross-equatorial heat transport toward high latitudes during both equinox insolation maxima at the equator

Life on the ice-edge: Paleoenvironmental significance of the radiolarian species Amphimelissa setosa in the northern hemisphere

The high-latitude Northern Hemisphere is a key region in the global climate balance. Variations in sea-ice extent affect biological productivity, CO2 exchange and carbon drawdown. Marine proxies indicative of proximity of the ice-marginal zone are therefore essential to understand these processes. Amphimelissa setosa is nowadays a dominant radiolarian species in the Arctic basin and very abundant in the high-latitude North Atlantic. This species, now absent from the North Pacific, has been widely used as a qualitative proxy of modern and past environmental conditions in the high-latitude Northern Hemisphere. Using our new and published data on the distribution of A. setosa in plankton, sediment trap, surface sediment and downcore samples, we provide a quantitative ecological context for the occurrence of this species. We find that the optimal depth and season of A. setosa in the modern North Atlantic and the Chukchi Sea are 160 m and the late boreal summer/early fall (August–October), respectively. A regression model combining environmental variables (temperature, salinity, silicate and chlorophyll-a concentrations, apparent oxygen utilization, sea-ice) at that season and depth, are able to explain 43% of the distribution of this species in surface sediments. Based on these new findings, we conclude that the presence of A. setosa in surface sediments is closely related to high primary production in the proximity of the sea-ice and areas of ice rafting. The onset of this species started at ca. 1.5 Ma in the North Pacific, linked to a gradual cooling, increased silica availability and southward advance of the ice-margins since the Early Pleistocene. Amphimelissa setosa’s decline in this region was likely caused by the development of a quasi-permanent halocline, perennial sea-ice and depletion of silica during marine isotope stage 4. In the high-latitude North Atlantic, the relative abundance of A. setosa appears to be related to cooling and supply of dissolved silica from the continent during ice-rafting events. The comprehensive approach taken in this study suggest that A. setosa is a useful proxy to explore past variations in the ice-cover in the high-latitude Northern Hemisphere.Shirshov Institute of Oceanology | Ref. 0149-2019-000

Upregulation of phytoplankton carbon concentrating mechanisms during low CO2 glacial periods and implications for the phytoplankton pCO2 proxy

Unidad de excelencia María de Maeztu MdM-2015-0552Published alkenone εp records spanning known glacial pCO2 cycles show considerably less variability than predicted by the diffusive model for cellular carbon acquisition and isotope fractionation. We suggest this pattern is consistent with a systematic cellular enhancement of the carbon supply to photosynthesis via carbon concentrating mechanisms under the case of carbon limitation during low pCO2 glacial time periods, an effect also manifest under carbon limitation in experimental cultures of coccolithophores as well as diatoms. While the low-amplitude εp signal over glacial pCO2 cycles has led some to question the reliability of εp for reconstructing long-term pCO2, the [CO2]aq in the tropical oceans during glacial pCO2 minima represents the most extreme low CO2 conditions likely experienced by phytoplankton in the Cenozoic, and the strongest upregulation of carbon concentrating mechanisms. Using a statistical multilinear regression model, we quantitatively parse out the factors (namely light, growth rate, and [CO2]aq), that contribute to variation in εp in alkenone-producing algae, which confirms a much smaller dependence of εp on [CO2]aq in the low [CO2]aq range, than inferred from the hyperbolic form of the diffusive model. Application of the new statistical model to two published tropical εp records spanning the late Neogene produces much more dynamic pCO2 estimates than the conventional diffusive model and reveals a significant pCO2 decline over the last 15 Ma, which is broadly consistent with recent results from boron isotopes of foraminifera. The stable isotopic fractionation between coccolith calcite and seawater dissolved inorganic carbon (here Δcoccolith-DIC) also shows systematic variations over glacial-interglacial cycles which may, following future experimental constraints, help estimate the degree of upregulation of parts of the algal carbon concentrating mechanism over glacial cycles

Ocean and atmosphere teleconnections modulate east tropical Pacific productivity at late to middle Pleistocene terminations

The modern Eastern Equatorial Pacific (EEP) is a key oceanographic region for regulating the Earth's climate system, accounting for between 5–10% of global marine production whilst also representing a major source of carbon dioxide efflux to the atmosphere. Changes in ocean dynamics linked to the nutrient supply from the Southern Ocean have been suggested to have played a dominant role in regulating EEP productivity over glacial–interglacial timescales of the past 500 ka. Yet, the full extent of the climate and oceanic teleconnections and the mechanisms promoting the observed increase of productivity occurring at glacial terminations remain poorly understood. Here we present multi-proxy, micropaleontological, geochemical and sedimentological records from the easternmost EEP to infer changes in atmospheric patterns and oceanic processes potentially influencing regional primary productivity over glacial–interglacial cycles of the mid-late Pleistocene (∼0–650 ka). These proxy data support a leading role for the north–south migration of the Intertropical Convergence Zone (ITCZ) in shaping past productivity variability in the EEP. Productivity increases during glacial periods and notably peaks at major and “extra” glacial terminations (those occurring 1–2 precession cycles after some major terminations) coincident with the inferred southernmost position of the ITCZ. The comparison of our reconstructions with proxy records of climate variability suggests the intensification of related extratropical atmospheric and oceanic teleconnections during deglaciation events. These processes may have re-activated the supply of southern sourced nutrients to the EEP, potentially contributing to enhanced productivity in the EEP and thus counterbalancing the oceanic carbon dioxide outgassing at glacial terminations

Influence of 1997-98’ El Niño event on the planktonic communities from The Alboran Sea (Western Mediterranean)

The Alboran Sea is the westernmost basin of the Mediterranean Sea. Its particular location, as entrance of the Atlantic Surface Water (ASW) into the Mediterranean, has led to an intense paleoceanographic and paleoclimatic research. Nevertheless, only a limited number of studies provide information related to the dynamics and ecological characteristics of the downward particle flux. In order to determine the influence of seasonal oceanographic changes on the export of particles in the Alboran Sea, one mooring line, ALB-5-F, was deployed from July 1997 to May 1998 at 35º55.47’N/01º30.77’W. The mooring location was under the influence of the Almeria-Oran Front (AOF), which is formed by the interaction between the Atlantic jet and the denser and more saline Mediterranean waters. Information based on SeaWIFS images of chlorophyll-a concentration, current-meter, and meteorological data on wind direction and intensity were used. The annual oceanographic pattern of the AOF during the studied period was directly related to the evolution of the Western Anticyclonic Gyre (WAG) and to the 1997-98’ El Niño Event. Detailed analyses of the planktonic foraminifera, diatom and phytolith fluxes reflect seasonal changes in the main hydrographic and meteorological features in the eastern Alboran Sea. El Niño Event caused a sea surface temperature (SST) increase during fall that forced the proliferation of Globigerinoides ruber and the reduction of the diatoms. Benthic tests were also collected in the sediment trap; highest fluxes of the group were probably related to high bottom water activity. Wind-driven particles were collected along the year, but their fluxes follow the local wind regim

De los métodos y las maneras, número 8

Por octava ocasión el Posgrado en Diseño de la división de Ciencias y Artes para el Diseño, en colaboración con el comité organizador de “De los métodos y las maneras”, logró reunir investigaciones de especialistas en el ámbito del diseño y la investigación, así como de alumnos de tres de las cinco líneas de investigación del posgrado de diseño. Este libro es muestra de una constante al presentar temas en torno a las metodologías para hacer investigación en Diseño, además de ser una herramienta teórico - práctica, para apoyar tanto a docentes como estudiantes de los posgrados en diseño.Coordinación del Posgrado de Ciencias y Artes para el DiseñoGustavo Iván Garmendia Ramírez, coordinador; Sandra Rodríguez Mondragón, compilación y diseño editorial; Martín Lucas Flores Carapia, Diseño de la portad

Miocene to present oceanographic variability in the Scotia Sea and Antarctic Ice Sheet dynamics: Insight from revised seismic-stratigraphy following IODP Expedition 382

Scotia Sea and the Drake Passage is key towards understanding the development of modern oceanic circulation patterns and their implications for ice sheet growth and decay. The sedimentary record of the southern Scotia Sea basins documents the regional tectonic, oceanographic and climatic evolution since the Eocene. However, a lack of accurate age estimations has prevented the calibration of the reconstructed history. The upper sedimentary record of the Scotia Sea was scientifically drilled for the first time in 2019 during International Ocean Discovery Program (IODP) Expedition 382, recovering sediments down to ∼643 and 676 m below sea floor in the Dove and Pirie basins respectively. Here, we report newly acquired high resolution physical properties data and the first accurate age constraints for the seismic sequences of the upper sedimentary record of the Scotia Sea to the late Miocene. The drilled record contains four basin-wide reflectors – Reflector-c, -b, -a and -a' previously estimated to be ∼12.6 Ma, ∼6.4 Ma, ∼3.8 Ma and ∼2.6 Ma, respectively. By extrapolating our new Scotia Sea age model to previous morpho-structural and seismic-stratigraphic analyses of the wider region we found, however, that the four discontinuities drilled are much younger than previously thought. Reflector-c actually formed before 8.4 Ma, Reflector-b at ∼4.5/3.7 Ma, Reflector-a at ∼1.7 Ma, and Reflector-a' at ∼0.4 Ma. Our updated age model of these discontinuities has major implications for their correlation with regional tectonic, oceanographic and cryospheric events. According to our results, the outflow of Antarctic Bottom Water to northern latitudes controlled the Antarctic Circumpolar Current flow from late Miocene. Subsequent variability of the Antarctic ice sheets has influenced the oceanic circulation pattern linked to major global climatic changes during early Pliocene, Mid-Pleistocene and the Marine Isotope Stage 11