An early Eocene carbon cycle perturbation at in the Southern Alps

At least two transient events of extreme global warming occurred superimposed on the long-term latest Paleocene and early Eocene warming trend in the Paleocene-Eocene thermal maximum (PETM) (or ETM1 ~55.5 Ma) and the Elmo (or ETM2 ?53.6 Ma). Other than warmth, the best known PETM is characterized by (1) significant injection of 13C-depleted carbon into the ocean-atmosphere system, (2) deep-sea carbonate dissolution, (3) strong biotic responses, and (4) perturbations of the hydrological cycle. Documentation of the other documented and suspected "hyperthermals" is, as yet, insufficient to assess whether they are similar in nature to the PETM. Here we present and discuss biomagnetostratigraphic data and geochemical records across two lower Eocene successions deposited on a continental margin of the western Tethys: the Farra and Possagno sections in the Venetian pre-Alps. We recognize four negative carbon isotope excursions within chron C24. Three of these shifts correlate to known or suspected hyperthermals: the PETM, the Eocene thermal maximum 2 (~53.6 Ma), and the informally named "X event" (~52.5 Ma). The fourth excursion lies within a reverse subchron and occurred between the latter two. In the Farra section, the X event is marked by a ~0.6 per mil negative carbon isotope excursion and carbonate dissolution. Furthermore, the event exhibits responses among calcareous nannofossils, planktic foraminifera, and dinoflagellates that are similar to, though less intense than, those observed across the PETM. Sedimentological and quantitative micropaleontological data from the Farra section also suggest increased weathering and runoff as well as sea surface eutrophication during this event.

Carbonate system of surface sediments from the South Pacific

B/Ca ratios in Cibicides mundulus and Cibicides wuellerstorfi have been shown to correlate with the degree of calcite saturation in seawater (D[CO32-]). In the South Pacific, a region of high importance in the global carbon cycle, these species are not continuously present in down-core records. Small numbers of epibenthic foraminifera in samples present an additional challenge, which can be overcome by using laser ablation-inductively coupled-mass spectrometry (LA-ICP-MS). We present a laser ablation based core-top calibration for Cibicides cf. wuellerstorfi, a C. wuellerstorfi morphotype that is abundant in the South Pacific and extend the existing global core top calibration for C. mundulus and C. wuellerstorfi to this region. B/Ca in C. cf. wuellerstorfi are linearly correlated with D[CO32-] and possibly display a higher sensitivity to calcite saturation changes than C. wuellerstorfi. Trace element profiles through C. wuellerstorfi and C. mundulus reveal an intra-shell B/Ca variation of ±36% around the mean shell value. Mg/Ca and B/Ca display opposite trends along the shell. Both phenomena likely result from ontogenetic effects. Intra-shell variability equals intra-sample variability, mean sample B/Ca values can thus be reliably calculated from averaged spot results of single specimen. In the global B/Ca-D[CO32-] range, we observe an inverse relationship between water mass age and D[CO32-].

Gametogenic cycle of Mesodesma donacium

Large-scale environmental patterns in the Humboldt Current System (HCS) show major changes during strong El Niño episodes, leading to the mass mortality of dominant species in coastal ecosystems. Here we explore how these changes affect the life-history traits of the surf clam Mesodesma donacium. Growth and mortality rates under normal temperature and salinity were compared to those under anomalous (El Niño) higher temperature and reduced salinity. Moreover, the reproductive spatial-temporal patterns along the distribution range were studied, and their relationship to large-scale environmental variability was assessed. M. donacium is highly sensitive to temperature changes, supporting the hypothesis of temperature as the key factor leading to mass mortality events of this clam in northern populations. In contrast, this species, particularly juveniles, was remarkably tolerant to low salinity, which may be related to submarine groundwater discharge in Hornitos, northern Chile. The enhanced osmotic tolerance by juveniles may represent an adaptation of early life stages allowing settlement in vacant areas at outlets of estuarine areas. The strong seasonality in freshwater input and in upwelling strength seems to be linked to the spatial and temporal patterns in the reproductive cycle. Owing to its origin and thermal sensitivity, the expansion and dominance of M. donacium from the Pliocene/Pleistocene transition until the present seem closely linked to the establishment and development of the cold HCS. Therefore, the recurrence of warming events (particularly El Niño since at least the Holocene) has submitted this cold-water species to a continuous local extinction-recolonization process.

Respiration and ingestion rates of calanoid copepod in the northern Benguela Current System measured ex situ during the RSS Discovery D356 cruise in 2010

Respiration rates of 16 calanoid copepod species from the northern Benguela upwelling system were measured on board RRS Discovery in September/October 2010 to determine their energy requirements and assess their significance in the carbon cycle. Copepod species were sampled by different net types. Immediately after the hauls, samples were sorted to species and stages (16 species; females, males and C5 copepodids) according to Bradford-Grieve et al. (1999). Specimens were kept in temperature-controlled refrigerators for at least 12 h before they were used in experiments. Respiration rates of different copepod species were measured onboard by optode respirometry (for details see Köster et al., 2008) with a 10-channel optode respirometer (PreSens Precision Sensing Oxy-10 Mini, Regensburg, Germany) under simulated in situ conditions in temperature-controlled refrigerators. Experiments were run in gas-tight glass bottles (12-13 ml). For each set of experiments, two controls without animals were measured under exactly the same conditions to compensate for potential bias. The number of animals per bottle depended on the copepods size, stage and metabolic activity. Animals were not fed during the experiments but they showed natural species-specific movements. Immediately after the experiments, all specimens were deep-frozen at - 80 °C for later dry mass determination (after lyophilisation for 48 h) in the home lab. The carbon content (% of dry mass) of each species was measured by mass-spectrometry in association with stable isotope analysis and body dry mass was converted to units of carbon. For species without available carbon data, the mean value of all copepod species (44% dry mass) was applied. For the estimation of carbon requirements of copepod species, individual oxygen consumption rates were converted to carbon units, assuming that the expiration of 1 ml oxygen mobilises 0.44 mg of organic carbon by using a respiratory quotient (RQ) of 0.82 for a mixed diet consisting of proteins (RQ = 0.8-1.0), lipids (RQ = 0.7) and carbohydrates (RQ = 1.0) (Auel and Werner, 2003). The carbon ingestion rates were calculated using the energy budget and the potential maximum ingestion rate approach. To allow for physiological comparisons of respiration rates of deep- and shallow-living copepod species without the effects of ambient temperature and different individual body mass, individual respiration rates were temperature- (15°C, Q10=2) and size-adjusted. The scaling coefficient of 0.76 (R2=0.556) is used for the standardisation of body dry mass to 0.3 mg (mean dry mass of all analysed copepods), applying the allometric equation R= (R15°C/M0.76)×0.30.76, where R is respiration and M is individual dry mass in mg.

Coral-algae metabolism and diurnal changes in the CO2-carbonate system of bulk sea water

Precise measurements were conducted in continuous flow seawater mesocosms located in full sunlight that compared metabolic response of coral, coral-macroalgae and macroalgae systems over a diurnal cycle. Irradiance controlled net photosynthesis (Pnet), which in turn drove net calcification (Gnet), and altered pH. Pnet exerted the dominant control on [CO3]2- and aragonite saturation state (Omega arag) over the diel cycle. Dark calcification rate decreased after sunset, reaching zero near midnight followed by an increasing rate that peaked at 03:00 h. Changes in Omega arag and pH lagged behind Gnet throughout the daily cycle by two or more hours. The flux rate Pnet was the primary driver of calcification. Daytime coral metabolism rapidly removes dissolved inorganic carbon (DIC) from the bulk seawater and photosynthesis provides the energy that drives Gnet while increasing the bulk water pH. These relationships result in a correlation between Gnet and Omega arag, with Omega arag as the dependent variable. High rates of H+ efflux continued for several hours following mid-day peak Gnet suggesting that corals have difficulty in shedding waste protons as described by the Proton Flux Hypothesis. DIC flux (uptake) followed Pnet and Gnet and dropped off rapidly following peak Pnet and peak Gnet indicating that corals can cope more effectively with the problem of limited DIC supply compared to the problem of eliminating H+. Over a 24 h period the plot of total alkalinity (AT) versus DIC as well as the plot of Gnet versus Omega arag revealed a circular hysteresis pattern over the diel cycle in the coral and coral-algae mesocosms, but not the macroalgae mesocosm. Presence of macroalgae did not change Gnet of the corals, but altered the relationship between Omega arag and Gnet. Predictive models of how future global changes will effect coral growth that are based on oceanic Omega arag must include the influence of future localized Pnet on Gnet and changes in rate of reef carbonate dissolution. The correlation between Omega arag and Gnet over the diel cycle is simply the response of the CO2-carbonate system to increased pH as photosynthesis shifts the equilibria and increases the [CO3]2- relative to the other DIC components of [HCO3]- and [CO2]. Therefore Omega arag closely tracked pH as an effect of changes in Pnet, which also drove changes in Gnet. Measurements of DIC flux and H+ flux are far more useful than concentrations in describing coral metabolism dynamics. Coral reefs are systems that exist in constant disequilibrium with the water column.

Respiration rates and abundances of dominant copepods of the northern Benguela Current System

Respiration rates of 16 calanoid copepod species from the northern Benguela upwelling system were measured on board RRS Discovery in September/October 2010 to determine their energy requirements and assess their significance in the carbon cycle. Individual respiration rates were standardised to a mean copepod body mass and a temperature regime typical of the northern Benguela Current. These adjusted respiration rates revealed two different activity levels (active and resting) in copepodids C5 of Calanoides carinatus and females of Rhincalanus nasutus, which reduced their metabolism during dormancy by 82% and 62%, respectively. An allometric function (Imax) and an energy budget approach were performed to calculate ingestion rates. Imax generally overestimated the ingestion rates derived from the energy budget approach by >75%. We suggest that the energy budget approach is the more reliable approximation with a total calanoid copepod (mainly females) consumption of 78 mg C m-2 d-1 in neritic regions and 21 mg C m-2 d-1 in oceanic regions. The two primarily herbivorous copepods C. carinatus (neritic) and Nannocalanus minor (oceanic) contributed 83% and 5%, respectively, to total consumption by calanoid copepods. Locally, C. carinatus can remove up to 90% of the diatom biomass daily. In contrast, the maximum daily removal of dinoflagellate biomass by N. minor was 9%. These estimates imply that C. carinatus is an important primary consumers in the neritic province of the northern Benguela system, while N. minor has little grazing impact on phytoplankton populations further offshore. Data on energy requirements and total consumption rates of dominant calanoid copepods of this study are essential for the development of realistic carbon budgets and food-web models for the northern Benguela upwelling system.

Properties of seawater (partial pressure of carbon dioxide (pCO2)) from a ProOceanus CO2-Pro sensor mounted on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) sampled the world oceans on board a 36 m long schooner, collecting environmental data and organisms from viruses to planktonic metazoans for later analyses using modern sequencing and state-of-the-art imaging technologies. Tara Oceans Data are particularly suited to study the genetic, morphological and functional diversity of plankton. The present data set provides continuous measurements of partial pressure of carbon dioxide (pCO2), using a ProOceanus CO2-Pro instrument mounted on the flowthrough system. This automatic sensor is fitted with an equilibrator made of gas permeable silicone membrane and an internal detection loop with a non-dispersive infrared detector of PPSystems SBA-4 CO2 analyzer. A zero-CO2 baseline is provided for the subsequent measurements circulating the internal gas through a CO2 absorption chamber containing soda lime or Ascarite. The frequency of this automatic zero point calibration was set to be 24 hours. All data recorded during zeroing processes were discarded with the 15-minute data after each calibration. The output of CO2-Pro is the mole fraction of CO2 in the measured water and the pCO2 is obtained using the measured total pressure of the internal wet gas. The fugacity of CO2 (fCO2) in the surface seawater, whose difference with the atmospheric CO2 fugacity is proportional to the air-sea CO2 fluxes, is obtained by correcting the pCO2 for non-ideal CO2 gas concentration according to Weiss (1974). The fCO2 computed using CO2-Pro measurements was corrected to the sea surface condition by considering the temperature effect on fCO2 (Takahashi et al., 1993). The surface seawater observations that were initially estimated with a 15 seconds frequency were averaged every 5-min cycle. The performance of CO2-Pro was adjusted by comparing the sensor outputs against the thermodynamic carbonate calculation of pCO2 using the carbonic system constants of Millero et al. (2006) from the determinations of total inorganic carbon (CT ) and total alkalinity (AT ) in discrete samples collected at sea surface. AT was determined using an automated open cell potentiometric titration (Haraldsson et al. 1997). CT was determined with an automated coulometric titration (Johnson et al. 1985; 1987), using the MIDSOMMA system (Mintrop, 2005). fCO2 data are flagged according to the WOCE guidelines following Pierrot et al. (2009) identifying recommended values and questionable measurements giving additional information about the reasons of the questionability.

Ocean Acidification Affects Redox-Balance and Ion-Homeostasis in the Life-Cycle Stages of Emiliania huxleyi

Ocean Acidification (OA) has been shown to affect photosynthesis and calcification in the coccolithophore Emiliania huxleyi, a cosmopolitan calcifier that significantly contributes to the regulation of the biological carbon pumps. Its non-calcifying, haploid life-cycle stage was found to be relatively unaffected by OA with respect to biomass production. Deeper insights into physiological key processes and their dependence on environmental factors are lacking, but are required to understand and possibly estimate the dynamics of carbon cycling in present and future oceans. Therefore, calcifying diploid and non-calcifying haploid cells were acclimated to present and future CO2 partial pressures (pCO2; 38.5 Pa vs. 101.3 Pa CO2) under low and high light (50 vs. 300 µmol photons/m**2 /s). Comparative microarray-based transcriptome profiling was used to screen for the underlying cellular processes and allowed to follow up interpretations derived from physiological data. In the diplont, the observed increases in biomass production under OA are likely caused by stimulated production of glycoconjugates and lipids. The observed lowered calcification under OA can be attributed to impaired signal-transduction and ion-transport. The haplont utilizes distinct genes and metabolic pathways, reflecting the stage-specific usage of certain portions of the genome. With respect to functionality and energy-dependence, however, the transcriptomic OA-responses resemble those of the diplont. In both life-cycle stages, OA affects the cellular redox-state as a master regulator and thereby causes a metabolic shift from oxidative towards reductive pathways, which involves a reconstellation of carbon flux networks within and across compartments. Whereas signal transduction and ion-homeostasis appear equally OA-sensitive under both light intensities, the effects on carbon metabolism and light physiology are clearly modulated by light availability. These interactive effects can be attributed to the influence of OA and light on the redox equilibria of NAD and NADP, which function as major sensors for energization and stress. This generic mode of action of OA may therefore provoke similar cell-physiological responses in other protists.

Rates of organic matter transformation within the production-destruction cycle of the White Sea

Rates of organic matter (OM) transformation within the production-destruction cycle of the White Sea were estimated on the basis of measured activity values of redox enzymes of the electron transport system and of hydrolytic enzymes (phosphatase and protease). It was found that OM oxidation processes were the most intensive in the Kandalaksha Bay, while minimum oxidation rates were characteristic of central parts of the Dvina and Onega bays. It was revealed that the highest rates of phosphate mineralization were characteristic of the central part of the sea and near-mouth areas of the Onega and Kandalaksha bays, with the lowest rates in the Dvina Bay. During the period of intense primary production when resources of inorganic phosphorus were practically depleted, high rates of phosphate regeneration were observed. It was shown that populations of micro- and zooplankton in the White Sea were characterized by low activation energies of the principal metabolism reactions (3-6 kcal/mol), which allowed these populations to provide exchange intensity comparable to that of inhabitants of warm waters during all the seasons.

Seawater carbonate chemistry and effects of CO2 and their modulation by light in the life-cycle stages of the coccolithophore Emiliania huxleyi strains RCC 1216 and 1217 during experiments, 2012

The effects of ocean acidification on the life-cycle stages of the coccolithophore Emiliania huxleyi and their by light were examined. Calcifying diploid and noncalcifying haploid cells (Roscoff culture collection 1216 and 1217) were acclimated to present-day and elevated CO2 partial pressures (PCO2; 38.5 vs. 101.3 Pa, ., 380 vs. 1000 matm) under low and high light (50 vs. 300 mmol photons m-2 s-1). Growth rates as well as quotas and production rates of C and N were measured. Sources of inorganic C for biomass buildup were using a 14C disequilibrium assay. Photosynthetic O2 evolution was measured as a function of dissolved inorganic C and light by means of membrane-inlet mass spectrometry. The diploid stage responded to elevated PCO2 by shunting resources from the production of particulate inorganic C toward organic C yet keeping the production of total particulate C constant. As the effect of ocean acidification was stronger under low light, the diploid stage might be less affected by increased acidity when energy availability is high. The haploid stage maintained elemental composition and production rates under elevated PCO2. Although both life-cycle stages involve different ways of dealing with elevated PCO2, the responses were generally modulated by energy availability, being typically most pronounced under low light. Additionally, PCO2 responses resembled those induced by high irradiances, indicating that ocean acidification affects the interplay between energy-generating processes (photosynthetic light reactions) and processes competing for energy (biomass buildup and calcification). A conceptual model is put forward explaining why the magnitude of single responses is determined by energy availability.