Mixing Events Research Articles

Reanalysis of vertical mixing in mesocosm experiments: PeECE III and KOSMOS 2013

Abstract. Controlled manipulation of environmental conditions within large enclosures in the ocean, so-called pelagic mesocosms, has become a standard method to explore potential responses of marine plankton communities to anthropogenic change. Among the challenges of interpreting mesocosm data is the often uncertain role of vertical mixing, which usually is not observed directly. To account for mixing nonetheless, two pragmatic assumptions are common: either that the water column is homogeneously mixed or that it is divided into two water bodies with a horizontal barrier inhibiting turbulent exchange. In this study, we present a model-based reanalysis of vertical turbulent diffusion in the mesocosm experiments PeECE III and KOSMOS 2013. Our diffusivity estimates indicate intermittent mixing events along with stagnating periods and yield simulated temperature and salinity profiles that are consistent with the observations. Here, we provide the respective diffusivities as a comprehensive data product in the Network Common Data Format (NetCDF). This data product will help to guide forthcoming model studies that aim at deepening our understanding of biogeochemical processes in the PeECE III and KOSMOS 2013 mesocosms, such as the CO2-related changes in marine carbon export. In addition, we make our model code available, providing an adjustable tool to simulate vertical mixing in any other pelagic mesocosm. The data product and the model code are available at https://doi.org/10.1594/PANGAEA.905311 (Mathesius et al., 2019).

Surface cooling caused by rare but intense near-inertial wave induced mixing in the tropical Atlantic

The direct response of the tropical mixed layer to near-inertial waves (NIWs) has only rarely been observed. Here, we present upper-ocean turbulence data that provide evidence for a strongly elevated vertical diffusive heat flux across the base of the mixed layer in the presence of a NIW, thereby cooling the mixed layer at a rate of 244 W m−2 over the 20 h of continuous measurements. We investigate the seasonal cycle of strong NIW events and find that despite their local intermittent nature, they occur preferentially during boreal summer, presumably associated with the passage of atmospheric African Easterly Waves. We illustrate the impact of these rare but intense NIW induced mixing events on the mixed layer heat balance, highlight their contribution to the seasonal evolution of sea surface temperature, and discuss their potential impact on biological productivity in the tropical North Atlantic.

Sperm whale presence observed using passive acoustic monitoring from gliders of opportunity

Habitat use by the endangered Mediterranean sperm whale subpopulation remains poorly understood, especially in winter. The sustained presence of oceanographic autonomous underwater vehicles in the area presents an opportunity to improve observation effort, enabling collection of valuable sperm whale distribution data, which may be crucial to their conservation. Passive acoustic monitoring loggers were deployed on vertically profiling oceanographic gliders surveying the north-western Mediterranean Sea during winter 2012-2013 and June 2014. Sperm whale echolocation ‘usual click’ trains, characteristic of foraging activity, were detected and classified from the recordings, providing information about the presence of sperm whales along the glider tracks. Widespread presence of sperm whales in the north-western Mediterranean Sea was confirmed. Winter observations suggest different foraging strategies between the Ligurian Sea, where mobile and scattered individuals forage at all times of day, and the Gulf of Lion, where larger aggregations target intense oceanographic features in the open ocean such as fronts and mixing events, with reduced acoustic presence at dawn. This study demonstrates the ability to successfully observe sperm whale behaviour from passive acoustic monitoring gliders. We identified possible mission design changes to optimize data collected from passive acoustic monitoring glider surveys and significantly improve sperm whale population monitoring and habitat use.

Chemocline collapse in Lake Kivu as an analogue for nitrogen cycling during Oceanic Anoxic Events

One of the outstanding issues in the study of nutrient dynamics during Oceanic Anoxic Events (OAEs) is the preservation of 15N-depleted nitrogen isotope signals, which are not observed in analogous modern environments. The favored mechanism for δ15N values below 0‰ is utilization of excess ammonium derived from underlying anoxic waters by primary producers. However, there are few modern examples available for testing this hypothesis, due to the overall well-oxygenated state of modern oceans. Here, we present sedimentary δ13Corg and δ15Nbulk data, as well as pigment biomarker ratios, from the sediments of Lake Kivu, a meromictic lake in East Africa. This system serves as a potential analogue for the development of strongly depleted δ15Nbulk in OAE black shales. We focus on intervals of organic carbon enrichment (sapropels) that are interpreted to have been the result of lake water column mixing events. Sediment δ13Corg and δ15Nbulk decrease by up to 6 and 4‰ respectively near the base of sapropel layers. These negative excursions provide evidence for the mixing of 13C-depleted dissolved inorganic carbon and ammonium in excess of photosynthetic need, derived from the deeper anoxic basin of the lake. Support of this model is also provided by photosynthetic pigment biomarkers which show significant fluctuations in phototrophic ecology consistent with water column mixing and changes in nutrient status. Further evidence for the shallowing of the chemocline during sapropel deposition is found in the presence of bacteriochlorophyll derivatives produced by phototrophic sulfide oxidizers.

Characterization of the unconventional Tuscaloosa marine shale reservoir in southwestern Mississippi, USA: Insights from optical and SEM petrography

This study presents new optical petrography and electron microscopy data, interpreted in the context of previously published petrophysical, geochemical, and mineralogical data, to further characterize the Tuscaloosa marine shale (TMS) as an unconventional reservoir in southwestern Mississippi. The basal high resistivity zone has a higher proportion of Type II sedimentary organic matter than the overlying TMS, indicating it is more prone to oil generation. Optical petrography and electron microscopy reveal a heterogeneous clay matrix with ubiquitous pyrite grains, quartz, feldspar, glaucony, foraminifera, shell fragments, and rarer occurrences of apatite and crinoid fragments as well as liptinite, alginite, inertinite, and vitrinite. Our petrographic observations suggest that higher abundances of detrital quartz grains coupled with minimal authigenic cements result in higher porosity and permeability. However, the TMS is also more clay-rich than other unconventional shale oil and gas plays, which can impair the effectiveness of hydraulic fracture stimulation. Thin section observations reveal alternating clay and calcium carbonate laminae that are interpreted to reflect changes in sediment flux. Planktonic foraminifera indicate an overlying oxygenated water column while benthic inoceramid fragments and pervasive authigenic pyrite suggest anoxic or dysoxic bottom water conditions. Apatite fragments in thin section suggest mixing events and an influx of nutrient-rich sediments. Overall, these observations suggest that a variety of paleodepositional environments occurred in the TMS and the lithofacies diversity resulting from these small-scale depositional cycles makes it difficult to determinatively identify areas conducive to enhanced economic hydrocarbon recovery.

Rapid assembly of high-Mg andesites and dacites by magma mixing at a continental arc stratovolcano

Abstract Studies of pre-eruptive processes at active volcanoes require precise petrochronological constraints if they are to contribute to hazard assessment during future eruption events. We present petrological and geochemical data and orthopyroxene diffusion time scales for samples from Late Pleistocene high-Mg andesite-dacite lavas (Mg# 53–69) at Ruapehu volcano, New Zealand, as a case study of rapid magma genesis and eruption at a continental arc stratovolcano. Assembly of Ruapehu high-Mg magmas involved the mixing of primitive magmas plus entrained mantle-equilibrated olivines with mid-crustal felsic mush bodies, yielding hybridized magmas with ubiquitous pyroxene reverse-zoning patterns. Orthopyroxene Fe-Mg interdiffusion time scales linked to quantitative crystal orientation data show that most lavas erupted <10 days after resumption of crystal growth following magma mixing events. The eruption of lavas within days of mixing events implies that pre-eruptive warnings may be correspondingly short.

Controls on carbon export in the subtropical North Atlantic

We present a lower trophic level pelagic ecosystem model that allows the investigation of the role of hydrography, bacterial remineralization and detritus consumption on the strength of carbon export and its attenuation. We apply the model to investigate the controls on the carbon export at the Bermuda Atlantic Time-Series Study site (BATS) and the European Station for Time series in the Ocean, Canary Islands (ESTOC) in the subtropical North Atlantic. In previous field studies, export ratios at 200 m (the ratio between particulate carbon export below the euphotic zone and primary production) were found to be 300–400% smaller at ESTOC compared to BATS. Our model results show that the magnitude and temporal variability of primary productivity and modeled carbon export are modulated by the intensity and duration of vertical mixing events. BATS, with a more dynamic physical environment, has winter mixed-layer depths on average 80 m deeper than ESTOC and is characterized by pulses of enhanced productivity and export. Our model demonstrates the influence of hydrography on export attenuation through (i) more stable water column dynamics at ESTOC that increase particle remineralization time scales and weaken export strength at ESTOC compared to BATS; and (ii) higher water temperatures at BATS in the mesopelagic between 200 and 500 m that increase remineralization rates compared to ESTOC. This results in reduced differences in export ratios within the mesopelagic between both stations that is confirmed by observations. Strengthening remineralization through (i) adding zooplankton feeding on detritus and (ii) increasing bacterial remineralization rates decrease export at all depths at both stations, and increase the modeled difference in 200 m export ratios between BATS and ESTOC from 7% to 17%, a difference that is still much smaller than observed. While we could demonstrate the skill of our model in testing the mechanisms that could lead to differences in regional carbon export, our results indicate that hydrography-driven residence times, zooplankton feeding on detritus and enhanced bacterial remineralization rates alone are insufficient in driving export ratio differences between BATS and ESTOC. On the other hand, modeled export proved to be highly sensitive to prescribed particle sinking speeds. Thus, community and site dependent processes that lead to variations in particle sinking speed and remineralization, together with potential differences in vertical migration by zooplankton and horizontal transport, may be additional processes explaining the observed differences in export ratios at BATS and ESTOC.

Phosphorus Coupling Obfuscates Lithium Geospeedometry in Olivine

Lithium zoning in zircon and olivine provides a powerful record of crystal histories and magmatic processes in volcanic systems. Characterizing Li behavior in olivine is important because it is one of the few elements in basaltic systems that tracks short duration magmatic processes (e.g., < a few days). However, the potential for trace element coupling and the competing effects of crystal growth and subsequent diffusion obfuscate interpretations of Li zoning patterns and their use for geospeedometry. Here, we use diverse analytical techniques (EPMA, LA-ICPMS, nanoSIMS) to untangle records of growth and diffusion in carefully oriented olivine crystals from Kīlauea (Hawai‘i). Li, P, and Al are targeted because they show correlations despite contrasting behaviors during growth and diffusion. Lithium zoning exhibits two styles: 1) non-coupled, wherein Li (1-3 ppm) shows diffuse zoning over 10s-100s of μm between the crystal core and rim with low (10s of ppm) and homogeneous P, and 2) coupled, wherein sub-ppm Li enrichments <40 μm wide are correlated with P-rich zones (100s of ppm) that preserve a blueprint of crystal growth. Non-coupled Li zoning modeled for diffusive re-equilibration yields hours-days timescales, reflecting magma mixing events that primed the system for eruption. Coupled Li peaks consistently occur where analyses traverse the dendritic framework of P zoning that reflects rapid crystal growth. This correlation results from Li+ ions partially satisfying charge balancing requirements of P5+ ions in the olivine lattice. Aluminum balances most of the P budget in olivine but has uncommon correlations with Li peaks. Transects can exhibit both non-coupled and coupled Li behavior, preserving histories of both crystal growth and diffusive re-equilibration. Modeling a Li enrichment peak with the Li diffusion coefficient yields a timescale of <3 minutes, too short to represent the time elapsed following crystallization. If the Li and P peaks are modeled using the diffusion coefficient for P, congruent timescales of 5-11 days suggest they have the potential to record magmatic processes. Several caveats such as poorly constrained initial conditions and analytical challenges limit the practicality of enrichment peak geospeedometry. Only broad zoning of non-coupled Li should be modeled for timescales of magmatic processes.

Downward cloud venting of the central African biomass burning plume during the West Africa summer monsoon

Abstract. Between June and September large amounts of biomass burning aerosol are released into the atmosphere from agricultural fires in central and southern Africa. Recent studies have suggested that this plume is carried westward over the Atlantic Ocean at altitudes between 2 and 4 km and then northward with the monsoon flow at low levels to increase the atmospheric aerosol load over coastal cities in southern West Africa (SWA), thereby exacerbating air pollution problems. However, the processes by which these fire emissions are transported into the planetary boundary layer (PBL) are still unclear. One potential factor is the large-scale subsidence related to the southern branch of the monsoon Hadley cell over the tropical Atlantic. Here we use convection-permitting model simulations with COSMO-ART to investigate for the first time the contribution of downward mixing induced by clouds, a process we refer to as downward cloud venting in contrast to the more common process of upward transport from a polluted PBL. Based on a monthly climatology, model simulations compare satisfactory with wind fields from reanalysis data, cloud observations, and satellite-retrieved carbon monoxide (CO) mixing ratio. For a case study on 2 July 2016, modelled clouds and rainfall show overall good agreement with Spinning Enhanced Visible and InfraRed Imager (SEVIRI) cloud products and Global Precipitation Measurement Integrated Multi-satellitE Retrievals (GPM-IMERG) rainfall estimates. However, there is a tendency for the model to produce too much clouds and rainfall over the Gulf of Guinea. Using the CO dispersion as an indicator for the biomass burning plume, we identify individual mixing events south of the coast of Côte d'Ivoire due to midlevel convective clouds injecting parts of the biomass burning plume into the PBL. Idealized tracer experiments suggest that around 15 % of the CO mass from the 2–4 km layer is mixed below 1 km within 2 d over the Gulf of Guinea and that the magnitude of the cloud venting is modulated by the underlying sea surface temperatures. There is even stronger vertical mixing when the biomass burning plume reaches land due to daytime heating and a deeper PBL. In that case, the long-range-transported biomass burning plume is mixed with local anthropogenic emissions. Future work should provide more robust statistics on the downward cloud venting effect over the Gulf of Guinea and include aspects of aerosol deposition.

Multi-banded pumice in the Campo de la Piedra Pómez rhyolitic ignimbrite (Southern Puna plateau): Pre-eruptive physical and chemical interactions between mafic and rhyolitic melts

The rhyolitic Campo de la Piedra Pómez ignimbrite crops out in the Southern Puna of NW Argentina and it is related to the youngest caldera-complex (Cerro Blanco caldera complex) of the Central Andes (73 - 4 kyr). The presence of rhyolitic pumice and mafic enclaves with different compositional and textural features, which variability can be observed within a single juvenile clast (multiple-banded pumice), characterized these deposits. The enclaves are associated with hybrid (trachydacitic) pumice and sporadic remnants of rhyolitic material included in the trachydacite. To unravel the possible role of the mafic recharge as eruption trigger, the occurrence of mixing events and the mechanisms of enclave formation, we studied the enclaves and silicic pumice material (petrography, whole rock analyses, mineral and glass chemistry) to decipher the magmatic interaction between the host rhyolitic melt and the enclave-forming magmas. Results allowed recognizing two main mafic recharge events. During the first episode, the mixing of the rhyolite with the injecting magma generated sporadic dacitic products. Mixing was favored by the relatively high temperature of both the injecting magma and the rhyolitic melt, as revealed by clinopyroxene-liquid, plagioclase-liquid and two-pyroxene geothermometers (≥875 °C). The second mafic recharge event involved magma that remained confined at the bottom of the reservoir and crystallized with differential cooling rates. At the interface with the silicic host, the magma generated sub-millimetric mineral assemblage in which amphibole has normally zoned rims. Differently, within the body of the mafic intrusion, crystallization proceeded with a lower undercooling degree, generating a coarser crystalline assemblage in which amphibole crystals do not display zoning. The convergence of different thermobarometric models (applied to the rhyolite, trachydacite, and enclaves) suggests that these magmas interacted at a crustal depth of ca. 2.7 Kbar, here interpreted as the base of the Campo de la Piedra Pómez rhyolitic reservoir (~10 Km b.s.l.). A time lapse occurred between the last mafic recharge and the eruptive events, where the felsic magma cooled down to ~800 °C and the amphibole re-equilibration took place.

The Seasonal Cycle of Upper-Ocean Mixing at 8°N in the Bay of Bengal

AbstractWe describe the seasonal cycle of mixing in the top 30–100 m of the Bay of Bengal as observed by moored mixing meters (χpods) deployed along 8°N between 85.5° and 88.5°E in 2014 and 2015. All χpod observations were combined to form seasonal-mean vertical profiles of turbulence diffusivity KT in the top 100 m. The strongest turbulence is observed during the southwest and postmonsoon seasons, that is, between July and November. The northeast monsoon (December–February) is a period of similarly high mean KT but an order of magnitude lower median KT, a sign of energetic episodic mixing events forced by near-inertial shear events. The months of March and April, a period of weak wind forcing and low near-inertial shear amplitude, are characterized by near-molecular values of KT in the thermocline for weeks at a time. Strong mixing events coincide with the passage of surface-forced downward-propagating near-inertial waves and with the presence of enhanced low-frequency shear associated with the Summer Monsoon Current and other mesoscale features between July and October. This seasonal cycle of mixing is consequential. We find that monthly averaged turbulent transport of salt out of the salty Arabian Sea water between August and January is significant relative to local E − P. The magnitude of this salt flux is approximately that required to close model-based salt budgets for the upper Bay of Bengal.

CAMPUR KODE PEMAKAIAN BAHASA INDONESIA PADA WACANA IKLAN

This study is entitled "Mixing Indonesian Language Codes in Advertising Discourse". The use of Indonesian in discourse advertisements has taken place in another language, namely local languages and foreign languages. This study examines the factors that cause code mixing, the types and forms / forms of code mixing, and the social meaning that is caused by the code mixing. The study uses the method of observation (observation) and data collection techniques, descriptive qualitative methods used in analyzing data, and informal methods used to collect the results of the analysis. In this study found two kinds of mixed codes, namely mixed codes into local languages (Balinese and Javanese) and mixed codes out of English. The shape and form of the code that is found is a mixture of code in the form of words, namely nouns, verbs, adjectives and adverbs. In addition to the form of words also found a mixture of code in the form of phrases, namely nominal phrases, verbal phrases, and prepositional phrases. There are two causes of code mixing in discourse, namely intralinguistic factors and extralinguistic factors. The code mixing events in the discourse are related to the language and social background, so that social meaning arises due to the code mixing behavior. Social meaning that emerges, shows more educated, shows social class, shows creativity, and shows the practical and regionalism.

Social network analysis in pigs: impacts of significant dyads on general network and centrality parameters

In general, one animal is considered dominant over another animal if it has won more fights than its opponent. Whether this difference in won and lost fights is significant is neglected in most studies. Thus, the present study evaluates the impact of two different calculation methods for dyadic interactions with a significant asymmetric outcome on the results of social network analysis regarding agonistic interactions of pigs in three different mixing events (weaned piglets, fattening pigs and gilts). Directly after mixing, all animals were video recorded for 17 (fattening pigs, gilts) and 28 h (weaned piglets), documenting agonistic interactions. Two calculation methods for significant dyads, that is, dyadic interactions with a clear dominant subordinate relationship in which one animal has won significantly more fights than its encounter, were proposed: pen individual limits were calculated by a sign test considering the differences of won and lost fights of all dyadic interactions in each pen; dyad individual limits were determined by a one-sided sign test for each individual dyad. For all data sets (ALL, including all dyadic interactions; PEN or DYAD, including only significant dyads according to pen or dyad individual limits), networks were built based on the information of initiator and receiver with the pigs as nodes and the edges between them illustrating attacks. General network parameters describing the whole network structure and centrality parameters describing the position of each animal in the network were calculated. Both pen and dyad individual limits revealed only a small percentage of significant dyads for weaned piglets (12.4% or 8.8%), fattening pigs (4.2% or 0.6%) and gilts (3.6% or 0.4%). The comparison between the data sets revealed only high Spearman’s rank correlation coefficients (rS) for the density, that is, percentage of possible edges that were actually present in the network, whereas the centrality parameters showed only moderate rS values (0.37 to 0.75). Thus, the rank order of the animals changed due to the exclusion of insignificant dyads, which shows that the results obtained from social network analysis are clearly influenced if insignificant dyads are excluded from the analyses. Due to the fact that the pen individual limits consider the overall level of agonistic interactions within each pen, this calculation method should be preferred over the dyad individual limits. Otherwise, too many animals in the group became isolated nodes with zero centrality for which no statement about their position within the network can be made.

Observations of Restratification after a Wind Mixing Event in a Shallow Highly Stratified Estuary

In stratified estuaries susceptible to wind mixing events, the changes in stratification have important implications for estuarine dynamics. Understanding the timescale associated with these mixing events and indirect wind impacts is dependent on estimating the restratification timescale. Bay-wide stratification observations, turbulence time series, and long-term data were examined to quantify the response mechanisms and restratification times in Mobile Bay. Observations showed moderate increases in stratification occurred over 2–3 days after the mixing event and were spatially variable. Turbulence data and model results that further highlight the period of returning stratification had changes in the relative contribution of tidal straining and gravitational exchange for the residual circulation in the estuary. Estimates of dissipation for the two ADVs averaged 2.6–3.1 × 10−5 m2 s−3 prior to the mixing event and increased to 1.4–8.5 × 10−4 m2 s−3 after the mixing event. These changes showed with increasing stratification; the turbulent dissipation decreased. These results highlight initial high returns in stratification are slowed over time as the exchange and mixing in the bay develop, and stratification returns to its premixed state.

Crustal anatexis and mantle-derived magmas forming Neoarchean A-type granitoids in Carajás Province, northern Brazil: Petrological evidence and tectonic control

Neoarchean hybrid granitoids from the Vila União suite are located in the central portion of the Canaã dos Carajás domain, Carajás Province (Amazonian craton, Brazil), and suggest that magma mixing events played an important role in their origin. According to complete evidence, including field observations, petrography, geochemical modeling, zircon SHRIMP and LA-MC-ICP-MS U-Pb ages, and Nd-Hf isotope data, we propose a geodynamic model based on initial mafic underplating promoted by lower crustal delamination, which generated mantle-derived mafic melts that were injected into the lower/middle crust (composed of Mesoarchean felsic granulite) and caused partial melting, producing leucogranitic melts. The interaction between these contrasting felsic and mafic magmas occurred by both mixing and mingling processes. The hybrid magma ascent and emplacement occurred in a N–S pure shear-dominated transpressional tectonic regime, with an E–W sinistral sense of tectonic movement, in which the hybrid melt was channeled into pre-existing shear zones trending E–W (Itacaiúnas shear zone). This tectonic regime (transpressional) proceeded coevally with the hybrid magma cooling, producing 2.75–2.73 Ga Neoarchean deformed A-type granitoids with a syntectonic nature in the Vila União suite, in addition to the Pium diopside-norite, which represents the mafic endmember generated by underplating.

Integrated major and trace element study of clinopyroxene in basic, intermediate and acidic volcanic rocks from the middle Okinawa Trough: Insights into petrogenesis and the influence of subduction component

Magmatism is very common in the Okinawa Trough. However, the influence of magmatic processes, including fractional crystallization and magma mixing, on the petrogenesis of volcanic rocks is poorly understood. The in situ major and trace element compositions of clinopyroxene in co-genetic basalts, andesites, trachyandesites and rhyolites from the Iheya Ridge in the middle Okinawa Trough are examined to determine their petrogenesis and the influence of slab subduction. Regarding the types of mineral zoning, in basalt and andesite, clinopyroxene phenocrysts are unzoned. In trachyandesite, the clinopyroxene phenocrysts can be classified into three groups: normal zoned, oscillatory zoned and unzoned. Similarly, unzoned and reverse zoned clinopyroxene phenocrysts are the two main structures in rhyolites. According to the major element contents and distinct distribution patterns of rare earth elements (REEs), we identify various clinopyroxene domains in their host volcanic rocks. Type 1 clinopyroxene domains in basalts and trachyandesites are dark, have high Mg# values and are strongly depleted in light REEs (LREEs) with no significant Eu anomalies. The Type 2 clinopyroxene domains in basalts and trachyandesites and all clinopyroxene phenocrysts in andesites are bright, have low Mg# values and are strongly depleted in LREEs and have significant negative Eu anomalies. Clinopyroxene domains in rhyolites have significant negative Eu anomalies and can be divided into two types: Type 1 clinopyroxene domains are characterized by strong depletion in LREEs, Sr, P and high field strength elements (HFSEs), while Type 2 clinopyroxene domains are slightly depleted in LREEs and have small negative P anomalies. The continuously changing major element composition and parallel distribution of trace element spider diagrams suggest that all these clinopyroxene phenocrysts in the studied volcanic rocks were derived from co-genetic magmas and the compositional transition of clinopyroxene from basalts to rhyolites attributed to different extents of fractional crystallization of various minerals (e.g., clinopyroxene, orthopyroxene, plagioclase and apatite). The oscillatory zoned and reversed zoned clinopyroxene phenocrysts show that magma mixing and recharge events with co-genetic magmas are common in the middle Okinawa Trough magma system. The origin of clinopyroxene phenocrysts involves contributions from subducted sedimentary components of 2.5% sediment melts and 1.5% sediment fluids and is deduced based on the equilibrium melts of clinopyroxene phenocrysts in basalts. The geochemical study of clinopyroxene provides evidence for the contributions of magmatic processes and slab subduction to the petrogenesis of Okinawa Trough volcanic rocks.

Agonistic Interactions in Pigs-Comparison of Dominance Indices with Parameters Derived from Social Network Analysis in Three Age Groups.

Simple SummaryThe importance of animals within a social group can be ranked with the aid of centrality parameters, e.g., measures derived from social network analysis. In the present study, it was investigated whether these centrality parameters capture a similar rank order compared to dominance indices which are calculated based on the number of won and lost fights. Social networks for animals in three repeated mixing events were built (weaned piglets, fattening pigs, gilts) based on different types of interactions (in the present study, initiating and receiving agonistic interactions, and winning or losing a fight). Centrality parameters based on active behavior, especially winning an agonistic interaction, showed a similar rank order compared to the dominance indices. Also, the results of partial least squares structural equation modelling showed that the networks built on information about winning or losing a fight could best illustrate the dominance structure with an explained variance of about 60% for all three age groups. Thus, network analysis can provide information about the dominance structure within the group and also has the advantage of including indirect relationships between the animals which cannot be supported by the dyadic approach.Dominance indices are often calculated using the number of won and lost fights of each animal focusing on dyadic interactions. Social network analysis provides new insights into the establishment of stable group structures going beyond the dyadic approach. Thus, it was investigated whether centrality parameters describing the importance of each animal for the network are able to capture the rank order calculated by dominance indices. Therefore, two dominance indices and five centrality parameters based on two network types (initiator-receiver and winner-loser networks) were calculated regarding agonistic interactions observed in three mixing events (weaned piglets, fattening pigs, gilts). Comparing the two network types, the winner-loser networks demonstrated highly positive correlation coefficients between out-degree and outgoing closeness and the dominance indices. These results were confirmed by partial least squares structural equation modelling (PLS-SEM), i.e., about 60% of the variance of the dominance could be explained by the centrality parameters, whereby the winner-loser networks could better illustrate the dominance hierarchy with path coefficients of about 1.1 for all age groups. Thus, centrality parameters can portray the dominance hierarchy providing more detailed insights into group structure which goes beyond the dyadic approach.

Influence of episodic wind events on thermal stratification and bottom water hypoxia in a Great Lakes estuary

Hypoxia formation and breakdown were tracked during 2015 in Muskegon Lake estuary at multiple locations, and five years (2011–2015) of time-series buoy observatory data were evaluated for the effect of episodic wind-events on lake mixing. Bi-weekly water temperature and dissolved oxygen (DO) profiles at four locations revealed that hypoxia occurred at all sites and persisted for 2–3 months during summer 2015. On one date in late-summer, up to 24% of the lake’s volume was estimated to be mildly hypoxic (DO < 4 mg L−1) as defined by lake sturgeon requirements. Patterns of wind speed and water column stability in late spring indicated that high winds and low stability delayed the onset of hypoxia while in late summer low winds and high stability delayed degradation of hypoxia. Wind speeds appear to play a great role in the interannual variability of stratification and subsequent hypoxia. Water temperature and DO profiles taken before and after one mid-summer mixing event (wind speed >7.7 m s−1 for 10 h), indicated that while the wind was unable to completely mix the entire water column, it deepened the epilimnion by ∼1.5 m and sheared a thin layer from the upper hypolimnion. By entraining internally loaded nutrients, such episodic wind-events may initiate and sustain algal blooms in nutrient limited surface waters. Quantifying the variable role of wind and mixing events will be key to integrating limnological processes into climate models of the future.

Resilience of Natural Phytoplankton Communities to Pulse Disturbances from Micropollutant Exposure and Vertical Mixing

Freshwaters are increasingly exposed to complex mixtures of pharmaceutical and personal care products (PPCPs) from municipal wastewater, which are known to alter freshwater communities' structure and functioning. However, their interaction with other disturbances and whether their combined effects can impact ecological resilience (i.e., the ability of a system to tolerate disturbances without altering the system's original structure and processes) remain unexplored. Using in situ mesocosms in 2 lakes with different nutrient levels (mesotrophic and eutrophic), we assessed whether a pulse exposure to sublethal concentrations of 12 PPCPs affects the ecological resilience of natural phytoplankton communities that experienced an abrupt environmental change involving the destabilization of the water column through mixing. Such mixing events are predicted to increase as the effects of climate change unfold, leading to more frequent storms, which disrupt stratification in lakes and force communities to restructure. We assessed their combined effects on community metrics (biomass, species richness, and composition) and their relative resilience using 4 indicators (cross-scale, within-scale, aggregation length, and gap length), inferred from phytoplankton communities by discontinuity analysis. The mixing disturbance alone had negligible effects on the community metrics, but when combined with chemical contaminants significant changes were measured: reducing total biomass, species richness, and altered community composition of phytoplankton. Once these changes occurred, they persisted until the end of the experiment (day 20), when the communities' structures from the 2 highest exposure levels diverged from the controls. The resilience indicators were not affected by PPCPs but differed significantly between lakes, with lower resilience found in the eutrophic lake. Thus, PPCPs can significantly alter community structures and reinforce mechanisms that maintain ecosystems in a "degraded state." Environ Toxicol Chem 2019;38:2197-2208. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Antarctic phytoplankton community composition and size structure: importance of ice type and temperature as regulatory factors

Climate change at the Western Antarctic Peninsula (WAP) is predicted to cause major changes in phytoplankton community composition, however, detailed seasonal field data remain limited and it is largely unknown how (changes in) environmental factors influence cell size and ecosystem function. Physicochemical drivers of phytoplankton community abundance, taxonomic composition and size class were studied over two productive austral seasons in the coastal waters of the climatically sensitive WAP. Ice type (fast, grease, pack or brash ice) was important in structuring the pre-bloom phytoplankton community as well as cell size of the summer phytoplankton bloom. Maximum biomass accumulation was regulated by light and nutrient availability, which in turn were regulated by wind-driven mixing events. The proportion of larger-sized (> 20 µm) diatoms increased under prolonged summer stratification in combination with frequent and moderate-strength wind-induced mixing. Canonical correspondence analysis showed that relatively high temperature was correlated with nano-sized cryptophytes, whereas prymnesiophytes (Phaeocystis antarctica) increased in association with high irradiance and low salinities. During autumn of Season 1, a large bloom of 4.5-µm-sized diatoms occurred under conditions of seawater temperature > 0 °C and relatively high light and phosphate concentrations. This bloom was followed by a succession of larger nano-sized diatoms (11.4 µm) related to reductions in phosphate and light availability. Our results demonstrate that flow cytometry in combination with chemotaxonomy and size fractionation provides a powerful approach to monitor phytoplankton community dynamics in the rapidly warming Antarctic coastal waters.