Subzero Temperatures Research Articles

Facile Synthesis and Fabrication of NIPAM-Based Cryogels for Environmental Remediation.

Herein, polymeric cryogels containing poly(N-isopropylacrylamide) were synthesized by cryo-polymerization at subzero temperature. The synthesized cryogels were loaded with silver and palladium nanoparticles by the chemical reduction method at room temperature using the reducing agent NaBH4. Moreover, for comparison with cryogels, pure poly(N-isopropylacrylamide) hydrogel and its silver hybrid were also prepared by the conventional method at room temperature. The chemical structure and functional group analysis of the pure cryogels was confirmed by Fourier transform infrared spectroscopy. The synthesis of hybrid cryogels was confirmed by the X-ray diffraction technique and energy dispersive X-ray. The pore size and surface morphology of the pure cryogels, their respective hybrid cryogels and of conventional hydrogels were studied by using the scanning electron microscopy technique. The hybrid cryogels were successfully used as a catalyst for the degradation of methyl orange dye. The degradation performance of the hybrid cryogels was much better than its counterpart hybrid hydrogel for methyl orange dye. The effect of temperature and amount of catalyst on catalytic performance was studied by UV-visible spectroscopy. The reduction follows pseudo-first-order reaction kinetics. In addition, the antibacterial activities of these cryogels were evaluated against Gram-positive bacteria (Staphylococcus aureus, ATCC: 2593) and Gram-negative bacteria (Escherichia coli, ATCC: 25922). Both hybrid cryogels have shown much better antibacterial activity for these two strains of bacteria compared to pure cryogels. The results indicate that these cryogels are potential candidates for water purification systems as well as biomedical applications.

Single-Frequency Impedance Studies on an Ionic Liquid-Based Miniaturized Electrochemical Sensor toward Continuous Low-Temperature CO2 Monitoring

Continuous greenhouse gas monitoring at sub-zero temperatures is needed for monitoring greenhouse gas emission in cold environments such as the Arctic tundra. This work reports a single-frequency electrochemical impedance sensing (SF-EIS) method for real-time continuous monitoring of carbon dioxide (CO2) at a wide range of temperatures (-15 to 40 °C) by using robust ionic liquid (IL) sensing materials and noninvasive, low-power, and low-cost impedance readout mechanisms since they cause minimal changes in the sensing interface, avoiding the baseline change for long-term continuous sensing. In addition, a miniaturized planar electrochemical sensor was fabricated that incorporates a hydrophobic 1-butyl-1-methylpyrrolidinium bis(trifluromethylsulfonyl)imide ([Bmpy][NTf2]) IL electrolyte and Pt black electrode materials. The high viscosity of the ILs facilitates the formation of thin, ordered, and concentrated layers of ionic charges, and the inverse relationship of IL viscosity with temperature makes them especially suited for impedance sensing at low temperatures. The unique low-temperature properties of ILs together with EIS transduction mechanisms are shown to be sensitive and selective for continuously monitoring CO2 at a -15 to 40 °C temperature range via impedance changes at a specifically selected frequency at the open circuit potential (OCP). Molecular dynamics simulations revealed insights into the structure and dynamics of the IL at varying temperatures in the presence of methane and CO2 and provided potential explanations for the observed sensing results. The miniaturized and flexible planar electrochemical sensor with the [Bmpy][NTf2] electrolyte was tested repeatedly at subzero temperatures over a 58-day period, during which good stability and repeatability were obtained. The CO2 impedance sensor was further tested for sensing CO2 from soil samples and shows promising results for their use in real-time monitoring of greenhouse gas emissions in cold temperatures such as permafrost soils.

Super-anti-freezing, tough and adhesive titanium carbide and L-ornithine-enhanced hydrogels

Hydrogels are highly porous three-dimensional crosslinked polymer networks consisting of hydrophilic polymers, employed most practically in medicine and industry, often as biosensors. Simple hydrogels suffer limitations in their mechanical properties, such as tensile and compression, and freeze at sub-zero temperatures, which compromise their ability as useful biosensors. In this study, the incorporation of L-ornithine-based zwitterionic monomer (OZM), titanium carbide (MXene), and glycerol within polyacrylamide hydrogels was used to prepare a novel polyacrylamide/polyL-ornithine-based zwitterion/MXene (PAM/Porn/MXene) hydrogel to improve the mechanical, adhesion, and anti-freezing properties of pure polyacrylamide hydrogels. This study also analyzed the mechanical strength (tensile and compression), adhesion, and anti-freezing properties of a novel PAM/Porn/MXene hydrogel at 1%, 4%, and 10% MXene concentrations to establish to what extent the conductive MXene material enhanced these properties and concluded that the tensile and compressive properties improved linearly with the increase in the concentrations of MXene, adhesion decreased with the increased MXene concentrations, and synergistic interaction between MXene and OZM significantly improved the anti-freezing properties up to –80 °C.

Study on soil freezing characteristic curve during a freezing-thawing process

Soil freezing characteristic curve (SFCC) defines the relationship between unfrozen water content and subzero temperature. The SFCC is widely applied to estimate the soil properties. The current study explored the effects of initial water content, dry density, soil type and desalination on the SFCC during a freezing-thawing process. It showed that the initial water content, soil type and desalination had great impacts on SFCC, while the dry density had an insignificant effect on SFCC. Hysteresis behavior was observed for all the soil samples. The hysteresis behavior was obvious in the temperature range of -5°C < T < 0, but not obvious in the temperature range of T ≤ -10 °C. A new equation containing freezing/thawing point was proposed to model the SFCC. The new model and four SFCC models were evaluated with measured data in this study. It showed that the new model performed best among these models. The new model accurately mimics the SFCC and is continuous near the freezing/thawing point and 0 °C. It can be easily incorporated into numerical algorithms for coupled heat and mass transfer in cold regions.

Maternal effects and the legacy of extreme environmental events for wild mammals.

Maternal effects and the legacy of extreme environmental events for wild mammals.

Simultaneous internal heating for balanced temperature and state-of-charge distribution in lithium-ion battery packs

Lithium-ion battery cells are widely known to work reliably in a certain range of temperatures. While operating in a high-temperature condition might lead to thermal runaway, they also suffer significant performance degradation and power/energy capacity loss in sub-zero temperatures. Consequently, heating the cells before usage plays a critical role in battery-powered applications. Among different heating methods, one promising approach is internal mutual pulse heating which offers many advantages as it utilizes the internal resistance of the battery cell to create heat and increase the cell temperature. However, in the context of a large battery pack, the nonuniform distribution of temperature and State-of-Charge (SOC) between the cells heavily affect the performance of the battery pack and remain to be unsolved. In this study, we present a internal heating technique for simultaneously balancing temperature and SOC of the battery cells considering the geometrical and thermal characteristics of the battery pack without requiring the characterization of the cell impedance. The proposed technique schedules the order and timing of mutual pulse heating for different groups of cells in a battery pack to reduce the variance in temperature and SOC during and after pre-heating. The simulation results showed that the SOC and temperatures among the cells can be kept balanced while the average pack temperature is maintained around a target temperature during a long period in a wide range of temperatures below zero degrees Celsius.

Tailored Solvation and Interface Structures by Tetrahydrofuran-Derived Electrolyte Facilitates Ultralow Temperature Lithium Metal Battery Operations.

Ineffectiveness of Li-ion batteries (LIBs) in cold climates hinders electronics to work in various conditions including frigid environments, despite high demands. Given that intrinsic properties of LIB materials cause this problem, optimized cell chemistries ultimately are required for low-temperature usage. In this study, Li-metal batteries (LMBs) composed of a Li-metal anode (LMA) stabilized by a localized high-concentration electrolyte (LHCE) are found to significantly enhance low-temperature performance. The LHCE allows the LMA to have compact and regular deposition and excellent plating/stripping efficiency at sub-zero temperatures. The LHCE produces an inorganic-rich solid-electrolyte interphase with larger amounts of Li2 O/LiF interfaces, dominance of ion aggregates in Li+ solvation, and enhanced Li+ transport, which can greatly improve the LMA stability. LMB full cells based on LiNi0.8 Co0.1 Mn0.1 O2 cathodes with the tailored electrolyte show high retentions of 75 and 64 % at -20 and -40 °C, respectively. Furthermore, the LMB configuration retains its charge-discharge capability even at -60 °C.

Highly conductive and tough double‐network hydrogels for smart electronics

AbstractDevelopment and understanding of highly mechanically robust and electronically conducting hydrogels are extremely important for ever‐increasing energy‐based applications. Conventional mixing/blending of conductive additives with hydrophilic polymer network prevents both high mechanical strength and electronic conductivity to be presented in polymer hydrogels. Here, we proposed a double‐network (DN) engineering strategy to fabricate PVA/PPy DN hydrogels, consisting of a conductive PPy‐PA network via in‐situ ultrafast gelation and a tough PVA network via a subsequent freezing/thawing process. The resultant PVA/PPy hydrogels exhibited superior mechanical and electrochemical properties, including electrical conductivity of ~6.8 S/m, mechanical strength of ~0.39 MPa, and elastic moduli of ~0.1 MPa. Upon further transformation of PVA/PPy hydrogels into supercapacitors, they demonstrated a high capacitance of ~280.7 F/g and a cycle life of 2000 galvanostatic charge/discharge cycles with over 94.3% capacity retention at the current density of 2 mA/cm2 and even subzero temperatures of −20 °C. Such enhanced mechanical performance and electronic conductivity of hydrogels are mainly stemmed from a synergistic combination of continuous electrically conductive PPy‐PA network and the two interpenetrating DN structure. This in‐situ gelation strategy is applicable to the integration of ionic‐/electrical‐conductive materials into DN hydrogels for smart‐soft electronics, beyond the most commonly used PEDOT:PSS‐based hydrogels.

Experimental study on the competition between carbon dioxide hydrate and ice below the freezing point

As climate change and industrial requirements intensify, the potential of CO2 hydrates for carbon storage has attracted increasing attention. However, despite continuous progress, the subzero phase behavior of the CO2-H2O system is not well understood and merits further research. To investigate the competing and coexisting growth mechanisms of CO2 gas hydrate and ice below the quadruple point, we conducted experiments at both the micrometer-scale and mesoscale scales. The growth morphology of hydrate and ice at large and small subcooling temperatures was observed in situ in a high-pressure optical cell, and the thermodynamic behavior of the competitive process after hydrate formation was investigated in a high-pressure reactor with sands. When hydrates and ice are formed together at small subcooling temperatures, preferential hydrate formation leads to ice dissolution or even disappearance. At large subcooling temperatures, ice forms first, and the hydrate mainly forms a fibrous envelope. A small decrease in the subzero temperature after hydrate formation partially decomposes the hydrates owing to ice formation, followed by more rapid hydrate production. This study provides a thorough and expanded understanding of the competition between ice and hydrates by connecting the evolution of crystal frameworks with the thermodynamic features of the process.

Proteostasis in ice: the role of heat shock proteins and ubiquitin in the freeze tolerance of the intertidal mussel, Mytilus trossulus.

The bay mussel, Mytilus trossulus, is an animal that can survive extracellular ice formation. Depending on air and ocean temperatures, freeze tolerant intertidal organisms, like M. trossulus, may freeze and thaw many times during the winter. Freezing can cause protein denaturation, leading to an induction of the heat shock response with expression of chaperone proteins like the 70kDa heat shock protein (HSP70), and an increase in ubiquitin-conjugated proteins. There has been little work on the mechanisms of freeze tolerance in intertidal species, limiting our understanding of this survival strategy. Additionally, this limited research has focused solely on the effects of single freezing events, but the act of repeatedly crossing the freezing threshold may present novel physiological or biochemical stressors that have yet to be discovered. Mytilus are important ecosystem engineers and provide habitat for other intertidal species, thus understanding their physiology under thermal extremes is important for preserving shoreline health. We predicted that repeated freeze exposures would increase mortality, upregulate HSP70 expression, and increase ubiquitin conjugates in mussels, relative to single, prolonged freeze exposures. Mytilus trossulus from Vancouver, Canada were repeatedly frozen for a combination of 1 × 8h, 2 × 4h, or 4 × 2h. We then compared mortality, HSP70 expression, and the quantity of ubiquitin-conjugated proteins across experimental groups. We found a single 8-h freeze caused significantly more mortality than repeated freeze-thaw cycles. We also found that HSP70 and ubiquitinated protein was upregulated exclusively after freeze-thaw cycles, suggesting that freeze-thaw cycles offer a period of damage repair between freezes. This indicates that freeze-thaw cycles, which happen naturally in the intertidal, are crucial for M. trossulus survival in sub-zero temperatures.

A liquid metal-fluoropolymer artificial protective film enables robust lithium metal batteries at sub-zero temperatures.

Batteries that are both high-energy-density and durable at sub-zero temperatures are highly desirable for deep space and subsea exploration and military defense applications. Our design incorporates a casting membrane technology to prepare a gallium indium liquid metal (LM)/fluoropolymer hybrid protective film on a lithium metal anode. The LM not only spontaneously forms a passivation alloy layer with lithium but also reduces the nucleation potential barrier and homogenizes the Li+ flux on the surface of the lithium anode. The fluoropolymer's polar functional groups (-C-F-) effectively induce targeted dispersion of gallium indium seeds, and the unique pit structure on the surface provides oriented sites for lithium plating. By implementing these strategies optimally, the protected lithium metal anode remains in operation at a current density of 20 mA cm-2 with an over-potential of about 50.4 mV after 500 h, and the full cells have a high capacity retention rate of up to 98.5% at a current density of 0.5 C after 100 cycles. Furthermore, the battery shows improved low temperature performance at -30 °C, validating the potential of the protective film to enable battery operation at sub-zero temperatures.

Recent progress in aqueous akali-metal-ion batteries at low temperatures

Aqueous alkali-metal-ion batteries are a popular frontier research area, expected to apply for large-scale energy storage due to their high safety, low cost, and environmental friendliness. Depending on diversified social development, batteries ought to function in various ambient, including polar regions and high-altitude locales. Delivering excellent electrochemical performance at low temperatures is crucial to develop aqueous alkali-metal-ion batteries. This review summarizes the representative research progress in the field of aqueous low-temperature alkali-metal-ion batteries in recent years, based on the subjects of electrolyte, electrode, and interface. Firstly, we discussed the challenges of aqueous alkali-metal-ion batteries operated at low temperatures and the corresponding failure mechanisms. At subzero temperatures, aqueous alkali-metal-ion batteries couldn't work or exhibit little capacity, arising from the frozen electrolytes, electrode materials with slow kinetics, and huge interface impedances, which seriously limits their wide application in low-temperature conditions. Then, combined with the latest research work, various strategies have been investigated to improve the electrochemical performance of batteries at low temperatures. To date, the strategies for reducing the freezing point of electrolytes have primarily focused on breaking H-bonds between free water molecules by increasing salt concentration, adding organic/inorganic additives, and using hydrogel as electrolytes. In terms of electrodes, the related studies have concentrated on regulating the structure and morphology of electrodes, introducing the dual ion battery mechanism, and using organic materials and Zn electrodes to alleviate the slow ion dynamics of electrodes. In addition, adding appropriate organic solvents that can generate protective layers with low interface impedance on the electrode surface in the electrolyte can also improve the low-temperature performance of aqueous alkali-metal-ion batteries. Finally, we evaluated multi-dimensionally all strategies, expected to provide a comprehensive reference and point out the direction for the further improvement and practical application of the aqueous alkali-metal-ion batteries at low temperatures.

Sub-zero microRNA expression in the liver of the frozen hatchling painted turtle, Chrysemys picta marginata.

The Midland painted turtle (Chrysemys picta marginata) are the highest known vertebrate species to experience and survive freezing and sub-zero temperatures. Painted turtles typically hatch from their eggs in the fall and remain underground in their nests until the following spring. While in these nests over the winter, hatchling turtles withstand over 50 % of their total extracellular body water freezing. Herein, the expression of microRNAs (miRNAs) was investigated in response to freezing stress in the hatchling painted turtle liver. A total of 204 known miRNAs were identified to be expressed in turtles, with 17 being upregulated and 13 being downregulated during freezing. KEGG and GO analyses suggested that upregulated miRNAs inhibit genes of cell cycle and Focal adhesion and Adherens junction, suggesting their role in downregulation of central metabolic processes necessary for metabolic rate depression (MRD) and maintaining the tissue homeostasis. Only 9 of the 36 enriched KEGG pathways were less targeted by miRNAs during freezing, including linoleic acid metabolism and multiple signaling pathways. These predicted upregulated pathways likely promote homeoviscous adaptation and expression of pro-survival/protective proteins for metabolic adaptations necessary for defence of liver during MRD. Overall, miRNA-seq analysis of liver revealed a strong role of miRNA in the adaptive strategy that not only enables hatchlings to substantially suppress their nonessential energy needs but also makes them flexible enough to restore and protect their basal organ functions by activating pro-survival processes.

Streamlined Methods for Processing and Cryopreservation of Cell Therapy Products Using Automated Systems.

Streamlined procedures for processing and cryopreservation of cell therapies using good laboratory practices are integral to biomanufacturing process development and clinical applications. The protocol herein begins with the preparation of human cell types cultured as adherent (i.e., mesenchymal stromal cells, MSCs) or suspension cells (i.e., peripheral blood mononuclear cells, PBMCs) to comprehensively demonstrate procedures that are applicable to commonly used primary cell cultures. Cell processing steps consist of preparing high yields of cells for cryopreservation using instruments routinely used in cell manufacturing, including the Finia® Fill and Finish System and a controlled-rate freezer. The final steps comprise the storage of cells at subzero temperatures in liquid nitrogen vapor phase followed by the analysis of cell phenotypes before and after processing and cryopreservation, along with cell quality metrics for validation. Additionally, the protocol includes important considerations for the implementation of quality control measures for equipment operation and cell handling, as well as Good Laboratory Practices for cell manufacturing, which are essential for the translational use of cell therapies. Key features • The protocol applies to small- or large-scale manufacturing of cell therapy products. • It includes streamlined procedures for processing and cryopreservation of cells cultured as adherent cells (MSCs) and suspension cells (PBMCs). • Provides temperature control and rapid partitioning of sample in cryopreservation solution to maintain high viability of a range of cell types throughout the procedures. • This protocol employs the Finia® Fill and Finish System and a controlled-rate freezer. Graphical overview.

Boosting PEDOT energy storage with a redox anthraquinone dopant for a flexible hydrogel supercapacitor at sub-zero temperatures

A high energy density flexible supercapacitor is fabricated using AQS–PEDOT/PAA hydrogel electrodes, which achieves efficient solar-thermal conversion for the prevention of capacitance decay under subzero conditions.

Competitive proton-trapping strategy enhanced anti-freezing organohydrogel fibers for high-strain-sensitivity wearable sensors.

Stretchable organohydrogel fibers are attracting considerable interest for next-generation flexible and wearable soft strain sensors due to their excellent stability in harsh environments. However, due to the uniformly distributed ions and reduced number of carriers in the whole material, the sensitivity of organohydrogel fibers under subzero temperature is not desirable, which significantly hinders their practical application. Herein, a newly competitive proton-trapping strategy was designed to obtain anti-freezing organohydrogel fibers for high-performance wearable strain sensors via a simple freezing-thawing process, in which tetraaniline (TANI), serving as the proton trapper, and representing the shortest repeated structural unit of polyaniline (PANI), was physically crosslinked with polyvinyl alcohol (PVA) (PTOH). The as-prepared PTOH fiber exhibited an outstanding sensing performance at -40 °C due to the unevenly distributed ion carriers and the highly breakable proton-migration pathways, with a high gauge factor of 24.6 at a strain of 200-300%. Moreover, the existence of hydrogen bonds between the TANI and PVA chains endowed PTOH with a high tensile strength (1.96 MPa) and toughness (8.0 MJ m-3). Accordingly, strain sensors made from PTOH fibers and knitted textiles could monitor human motions rapidly and sensitively, demonstrating their potential as wearable anti-freezing anisotropic strain sensors.

THE EXPERIMENTAL STUDIES OF A BIOTHERMAL INSTALLATION FOR CALF HOUSE FLOOR’S HEATING RESULTS

Farm animal manure is one of renewable energy resources types that the selfheating at humus process’s property has had. It allocates bioheat suitable for use (heating water for animals watering and cows' udders washing, livestock premises floor heating, etc.). The authors have developed and tested a biothermal installation to increase the efficiency at bioheat released during manure selfheating’s using. The biothermal installation with temperature sensors at the inlet is equipped, as well as at the installation outlet and in the manure mass, at characteristic’s points directly. The active selfheating period is 40-42 days from the start date. Studies have established the average selfheating temperature of the manure mass (3000-3100 kg - a mixture of horse and sheep manure in a ratio of 1:1, humidity 70-75%) for this period, which is 57.9 ± 5.67 °C at a variation’s coefficient of 9,8% with an air temperature fluctuation of 17°C...-2°C. Fluctuation of air temperature does not significantly affect the process of manure mass selfheating. At subzero ambient temperature, the manure selfheating with a slight slowdown continuing . In the steadystate operation mode, the average water temperature at the biothermal installation’s entrance and at the exit from it, is respectively, 44.9 °C and 54.9 °C. This biothermal installation’s average heating capacity and thermal power are 50-53 kJ/kg and 320-325 watts.

The influence of thermal pressure on the catalytic properties of SHS converter blocks during pre-start preparation of a diesel engine

The study is aimed at solving the important environmental problem of reducing harmful exhaust gas emissions from diesel engines with pre-heaters when operating at subzero ambient temperatures. The issue of cleaning the exhaust gases of the pre-heater in the catalytic converter during the heating of the catalytic units during the pre-start preparation period of the 8Ch12/12 diesel engine is considered. It was found that an increase in the specific heat flow and volumetric thermal gas pressure on the porous SHS catalytic material leads to an improvement in catalytic properties in exhaust gas purification processes. An increase in heat flow from 1589 to 3807 mJ/(m3×h) led to a decrease in the estimated values of harmful emissions: nitrogen oxides – by 1.6 times; carbon monoxide – 1.9 times; hydrocarbons – 1.23 times; solid particles - 2.1 times. It was revealed that when the exhaust gas temperature changed from 650 to 810 K, the efficiency of cleaning from solid particles increased from 50 to 75%, from nitrogen oxides - from 20 to 83%, and carbon monoxide - from 53 to 75%. An increase in the quality of hydrocarbon purification is noted up to 790 K; the quality of purification changes from 32 to 47%.

Snow Surface Microbial Diversity at the Detection Limit within the Vicinity of the Concordia Station, Antarctica.

The Concordia Research Station provides a unique location for preparatory activities for future human journey to Mars, to explore microbial diversity at subzero temperatures, and monitor the dissemination of human-associated microorganisms within the pristine surrounding environment. Amplicon sequencing was leveraged to investigate the microbial diversity of surface snow samples collected monthly over a two-year period, at three distances from the Station (10, 500, and 1000 m). Even when the extracted total DNA was below the detection limit, 16S rRNA gene sequencing was successfully performed on all samples, while 18S rRNA was amplified on 19 samples out of 51. No significant relationships were observed between microbial diversity and seasonality (summer or winter) or distance from the Concordia base. This suggested that if present, the anthropogenic impact should have been below the detectable limit. While harboring low microbial diversity, the surface snow samples were characterized by heterogeneous microbiomes. Ultimately, our study corroborated the use of DNA sequencing-based techniques for revealing microbial presence in remote and hostile environments, with implications for Planetary Protection during space missions and for life-detection in astrobiology relevant targets.

Interactive effects of nutrients and temperature on herbivorous predation in a coastal plankton community

AbstractMarine microbial communities in coastal environments are subject to both seasonal fluctuations and anthropogenic alterations of environmental conditions. The separate influences of temperature and resource‐dependency on phytoplankton growth, community, and ecosystem metabolism are relatively well understood. However, winners and losers in the ocean are determined based on the interplay among often rapidly changing biological, chemical and physical drivers. The direct, indirect, and interactive effects of these conditions on planktonic food web structure and function are poorly constrained. Here, we investigated how simultaneous manipulation of temperature and nutrient availability affects trophic transfer from phytoplankton to herbivorous protists, and their resulting implications at the ecosystem level. Temperature directly affected herbivorous protist composition; ciliates dominated (66%) in colder treatment and dinoflagellates (60%) at warmer temperatures. Throughout the experiments, grazing rates were < 0.1 d−1, with higher rates at subzero temperatures. Overall, the nutrient–temperature interplay affected trophic transfer rates antagonistically when nutrients were amended, and synergistically, when nutrients were not added. This interaction resulted in higher percentages of primary production consumed under nutrient unamended compared to nutrient amended conditions. At the ecosystem level, these changes may determine the fate of primary production, with most of the production likely exported out of the pelagic zone in high‐temperature and nutrient conditions, while high‐temperature and low‐nutrient availability strengthened food web coupling and enhanced trophic transfer. These results imply that in warming oceans, management of coastal nutrient loading will be a critical determinant of the degree of primary production removal by microzooplankton and dependent ecosystem production.