Photosynthesis Zone Research Articles

Characteristics of aquatic biospheres on temperate planets around Sun-like stars and M dwarfs

ABSTRACTAquatic biospheres reliant on oxygenic photosynthesis are expected to play an important role on Earth-like planets endowed with large-scale oceans insofar as carbon fixation (i.e. biosynthesis of organic compounds) is concerned. We investigate the properties of aquatic biospheres comprising Earth-like biota for habitable rocky planets orbiting Sun-like stars and late-type M dwarfs such as TRAPPIST-1. In particular, we estimate how these characteristics evolve with the available flux of photosynthetically active radiation (PAR) and the ambient ocean temperature (TW), the latter of which constitutes a key environmental variable. We show that many salient properties, such as the depth of the photosynthesis zone and the net primary productivity (i.e. the effective rate of carbon fixation), are sensitive to PAR flux and TW and decline substantially when the former is decreased or the latter is increased. We conclude by exploring the implications of our analysis for exoplanets around Sun-like stars and M dwarfs.

Zavisimost' kvantovogo vykhoda fotosinteza ot pogloshcheniya sveta fitoplanktonom: polucheniye kolichestvennykh svyazey dlya otsenki pervichnoy produktsii v Chernom more

Purpose. Based on the results of the investigations that were performed during the scientific cruise and included the water hydrophysical characteristics, the chlorophyll a concentration, the photosynthesis-light dependences, the spectral light absorption coefficients by phytoplankton, and the spectral quantum downwelling irradiance, the dependence of the photosynthesis quantum yield upon the environmental factors was studied with the purpose of adaptation of the developed for the Baltic Sea approach for assessing the photosynthesis quantum yield, to the Black Sea. Methods and Results. Complex hydrophysical and biological studies were carried out at several depths within the photosynthesis zone. Spectral bio-optical parameters were measured in accordance with the modern NASA protocol (2018). The experiments on studying the photosynthesis-light relationship were performed under the temperature and light conditions close to the in situ ones. The quantum yield of photosynthesis was calculated based on the parameters of photosynthesis-light dependences (photosynthesis efficiency, light saturation parameter) and the spectral light absorption coefficients by phytoplankton pigments. It was found out that the main photosynthetic characteristics of phytoplankton including the photosynthesis maximum quantum yield and the portion of photoprotective accessory pigments in the total light absorption by phytoplankton varied with depth within the euphotic zone due to phytoplankton adaptation to the environment factors during the period of water seasonal stratification. The relationship between the photosynthesis quantum yield and the number of solar energy quanta absorbed by the photosynthetically active phytoplankton pigments was revealed. The results of the performed research allowed for modifying the equation for calculating the quantum yield for the Black Sea environment conditions according to the approach developed for the other water areas. Conclusions. For the first time, comprehensive studies carried out in the Black Sea and including the measurements of the photosynthesis-light dependences, the spectral light absorption coefficients by phytoplankton and spectral downwelling irradiance at particular optical depths within the euphotic zone enabled to reveal the equation for calculating the photosynthesis quantum yield, which could be applied for calculating primary production of the Black Sea using the spectral approach based both on the results of in situ measurements and the remote sensing data.

Residual Sediments of the Vema Fracture Zone, Central Atlantic

The Vema Fracture Zone orthogonally intersecting the Mid-Atlantic Ridge along 11° N is a complex tectono-sedimentary system, through which bottom water is transferred from the western to the eastern Atlantic. The southern surrounding of the fault valley is an extended (about 320 km) transverse ridge. At the early stages of the Vema System evolution, the ridge was located at shallow depths in the photosynthesis zone, which led to the formation of extensive biogenic carbonate buildups on its surface. Spreading, general sinking of the system, and associated movements along faults caused disintegration of ultramafic basement and bioherms with subsequent fractionation of colluvial–pelagic sediments and their eastward transport by bottom currents. The formation of coarse-grained residual sands completely devoid of pelitic material is associated with the high flow rates of Antarctic bottom waters. The presence of rounded pebbles of organogenic limestones and ultramafic rocks with traces of bioproductivity indicates that clastic material was transferred over a few hundred kilometers.

Facies Structure and Quantitative Parameters of Pleistocene Sedimentation on the Deep-Sea Floor of the Southern Pacific Ocean and in the Scotia Sea

Based on the data from long sediment cores retrieved by R/V Eltanin (United States) during the 1950s–1960s, Neo- and Eopleistocene lithofacies maps of the southern Pacific Ocean (scale 1 : 20 000 000) and Scotia Sea (scale 1 : 10 000 000) were compiled for the first time. For the Scotia Sea, schemes of isopachites are shown on the respective lithofacies maps. All maps are processed with the volumetric method proposed by A.B. Ronov. The results revealed that accumulation rates of the terrigenous and siliceous sediments increased during the Pleistocene in both sedimentation basins due to neotectonic activity in the Antarctic Peninsula, which enhanced fluxes of not only terrigenous matter but also nutrients delivered by melted waters to the photosynthesis zone via vertical circulation.

Phytoplankton Bloom and Photosynthetically Active Radiation in Coastal Waters

The effect of a phytoplankton bloom on the change with depth of photosynthetically available radiation (PAR), the spectral downwelling irradiance in coastal waters, and the phytoplankton ability to absorb PAR in the sea is estimated. The 10-fold increase in the chlorophyll a concentration (from 0.4 to 4.0 mg/m3) during a diatom/ dinoflagellate bloom leads to a decrease in water transparency and a narrowing of the photosynthesis zone. As a consequence, the average PAR within the phytoplankton habitat layer is almost halved. A diatom/dinoflagellate bloom is accompanied by changes in the downwelling irradiance spectrum at the same PAR level (optical depths). The penetrating irradiance maximum near the bottom of the euphotic zone shifts to longer wavelengths (~550–600 nm) as compared to background conditions (~500–550 nm). The increase in diatom/dinoflagellate biomass and the concomitant change in the downwelling irradiance spectrum are accompanied by a decrease in the specific absorption coefficient of phytoplankton pigments up to about three times that under background conditions at the same optical depths. The downwelling irradiance spectrum at fixed optical depths and the ability of cells to absorb light change slightly as compared to background conditions when coccolithophores bloom.

Variability of Particulate Organic Phosphorus in the Northwestern Part of the Black Sea

Based on long-term (1985–1995) monitoring data, the paper considers the peculiarities of seasonal variability in the spatial and vertical distribution of particulate organic phosphorus (РPOM) in the surface layer and in the photosynthetic zone in the northwestern Black Sea. Regression equations, experimental data, and satellite observations for the chlorophyll a concentration allowed us to evaluate the seasonal longterm (1979–1995) variability in РPOM in the surface layer and photosynthesis zone. The ratios of the concentrations of particulate organic carbon, nitrogen, phosphorus, and chlorophyll a are calculated and statistical estimates of seasonal changes in the РPOM in the areas with different degrees of influence of river runoff and water of open seas are obtained. The consistency of intra-annual changes in the concentrations of РPOM, chlorophyll a, and phytoplankton biomass is shown, which indicates the role of phytoplankton in the formation of РPOM and in its intra- and interannual variability in the northwestern part of the sea. It is shown that long-term seasonal variations in РPOM and related changes in the concentration of chlorophyll a depend on the variability of bulk river runoff, the extent of its abundance in the northwestern shelf, and regional hydrometeorological conditions.

Abundance and richness of key Antarctic seafloor fauna correlates with modelled food availability.

Most seafloor communities at depths below the photosynthesis zone rely on food that sinks through the water column. However, the nature and strength of this pelagic-benthic coupling and its influence on the structure and diversity of seafloor communities is unclear, especially around Antarctica where ecological data are sparse. Here we show that the strength of pelagic-benthic coupling along the East Antarctic shelf depends on both physical processes and the types of benthic organisms considered. In an approach based on modelling food availability, we combine remotely sensed sea-surface chlorophyll-a, a regional ocean model and diatom abundances from sediment grabs with particle tracking and show that fluctuating seabed currents are crucial in the redistribution of surface productivity at the seafloor. The estimated availability of suspended food near the seafloor correlates strongly with the abundance of benthic suspension feeders, while the deposition of food particles correlates with decreasing suspension feeder richness and more abundant deposit feeders. The modelling framework, which can be modified for other regions, has broad applications in conservation and management, as it enables spatial predictions of key components of seafloor biodiversity over vast regions around Antarctica.

Новый фитоинкубатор с регулированием температуры и освещенности для мониторинга экологических параметров водных экосистем

During sea ecological expeditions at determination of organic substance formation speed in the course of photosynthesis (sizes of primary production) researchers face need related to creation of special conditions for an exposition of containing the phytoplankton water samples which have been selected at different stations and depths, widely spaced and with different temperature and illumination values. Now for primary production measurement in all marine ecosystems’ photosynthesis zone which has an extent equal to several tens of meters, the standard methods for incubation of containing the phytoplankton water samples in the conditions of constant temperatures and illumination, considerably different from those horizons, where the studied samples were taken, are used. Such a technique based on the water samples incubation at artificial lighting in controlled temperature conditions has been accepted as the main one in the international ecological and monitoring programs (HELCOM, SCOR, etc.). Discrepancy of light and temperature conditions in a sample selection point and in the experiment can lead to distortions at a primary production assessment and light dependences determination. Primary production sizes’ correct determination at photosynthesis zone’s different depths with different temperature and illumination values demands creation of the most approached to the natural conditions for the exposition of containing the phytoplankton water samples. A new phyto-incubator for the water sample incubation at the primary production measurement is described in this paper. The phyto-incubator consists of light and thermo isolated cells with a system of temperature and illumination individual adjustment in each of the cells. The incubation of different samples containing the phytoplankton is carried out in various stabilized conditions on temperature and illumination by a constant light stream, established for each cell separately. Illumination and temperature values can be choose as any of the set range of sizes. Such installation allows to set a "grid" of parameters on temperature and illumination, on exhibiting duration, and to receive predictive estimates for primary production at the change of external conditions. Invention patent No. 2547685 "Incubator and Approach for Water Samples Incubation" has been obtained on the developed incubator. This phyto-incubator type can be also used for various ecological experiments with natural populations of plankton organisms in laboratory conditions.

Assessment of Flux of Particulate Organic Phosphorus from the Photosynthesis Zone of the Deep-Water Section of the Black Sea

Simultaneously measured concentrations of particulate organic phosphorus (PPIM), particulate organic carbon (CPIM) and chlorophyll in the 0−100 m water layer, obtained over the years 1985−1994 in the western and central parts of the Black Sea were generalized. According to these indicators and regression equations, calculated on the basis of them, a series of weighted averages of the PPIM concentration in the deep-water part of the sea throughout the year was restored. On the basis of the calculated weighted average PPOM concentrations and rate of its sedimentation, within-year variability of sediment PPOM flux from the photosynthesis zone was estimated. Its maximal values corresponded to the cold, minimal − to the warm period of the year. Average annual values of PPOM flux, obtained on the basis of average monthly weighted mean of its concentrations, and calculated on the basis of the long-term average monthly values of the «new» primary production were practically identical and amounted to 46 and 44.9 mg-at P·m−2·year−1 respectively.

Basic regularities of the formation of “new” and regeneration production in the Black Sea

Based on the experimental data obtained in 1990–1993 by the method of isotopic tracers with the help of a stable isotope of nitrogen (15N), we establish basic regularities of the formation of “new” and regeneration production in the Black Sea and reveal the factors specifying their combination. It is shown that the rates of nitrate and ammonium uptake by microplankton vary from the minimum values in winter to the maximum values in summer. In the surface layer, the uptake of nitrates corresponding to the amount of “new” production in deep-water layers is equal to ∼ 50% (in winter) and ∼ 30% (in summer) of the total uptake of inorganic nitrogen compounds by microplankton. In the zone of photosynthesis, the average fractions of nitrates are equal to 31 ± 10% in winter and 41 ± 10% in summer. The minimum values of this parameter are attained in the middle of spring and in autumn. The fraction of “new” production (f-ratio) and the integral content of nitrates in the zone of photosynthesis are connected by a hyperbolic dependence. The period of cyclic transformations of nitrates in this zone decreases from several dozens of days at the beginning of winter to 12 h in the mid-spring. In summer, this period is equal, on the average, to one day. The average period of cyclic transformations of ammonium is equal to 15 ± 4 h in winter and 5 ± 3 h in summer.

In situ measurements of photosynthetic activity and respiration of intertidal benthic microalgal communities undergoing vertical migration

Abstract This paper presents the results of a field study on the short-term variability in photosynthetic activity of inter-tidal microphytobenthos using non-destructive techniques in situ. Photosynthetic rate (measured using oxygen microelectrodes), productive biomass and photosynthetic efficiency (dark-fluorescence and effective quantum efficiency of PSII, respectively, measured by PAM fluorometry) were measured in situ during a low-tide exposure period on an intertidal mudflat in the Tagus Estuary, Portugal. Community photosynthesis displayed large temporal variation. Maximum activity (24.3 mmol O2 m-2 h-1) was found at noon while minimum activity (8.7 mmol O2 m-2 h-1) was found at the end of the exposure period. Productive biomass followed a similar pattern. During the course of the exposure period, productive biomass peaked halfway through, and decreased by 80% towards the end of the exposure period. These changes in productive biomass were followed by significant changes in the species composition/cell size as well as changes in photosynthetic efficiency of the microphytobenthic community in the surface sediment. The obtained results therefore suggest that microphytobenthic community-level photosynthesis is controlled by migratory movements of microalgae and by variations in photosynthetic efficiency. The latter could be induced by changes in the species composition/cell size in the photic zone due to microalgal migrations. It is suggested that the migration pattern and, hence, photosynthesis is linked to changes in salinity, temperature and light, changes that are difficult to simulate accurately in the laboratory. Respiration rates obtained during the day were much higher than those obtained at night, and also displayed a marked hour-to-hour variation. Depth integrated respiration within the photosynthesis zone (0.33 mm) represented 80 to 90% of the respiration in the entire oxic zone, suggesting a tight coupling between photosynthesis and respiration.

Periphyton responses to a hydraulic gradient in a regulated river in New Zealand

SUMMARY1. Periphyton species composition, chlorophyll a concentration, organic matter biomass, and metabolic activity were analysed at a site in a regulated river with low nutrient concentrations to investigate population and community level responses to a spatial gradient in hydraulic conditions. The communities were dominated by diatoms over the full hydraulic range [0.1–0.5m depth, 0.1–1.5ms−1 velocity, and 0.01–1.5 Froude number (Fr)] with Cymbella kappii, Synedra ulna, and Gomphoneis herculeana having the highest relative biovolumes.2. Unexpectedly, Cymbella kappii and Synedra ulna were abundant or co‐dominant at all levels of velocity and Fr. Gomphoneis herculeana was most abundant within the mid‐velocity range (velocity = 0.8–1.2ms−1).3. The physiognomy of the communities changed with a change in hydraulic conditions. There was progressively more diatom mucilage as velocity and Fr increased which resulted in a macroscopic change from relatively thin films (1–2mm) at low velocities and Fr (in pool habitats), to thick (approximately 10mm) mats at higher velocities and Fr (in riffle habitats). Associated with this, ash‐free dry mass (APDM) increased strongly, but chlorophyll a concentration did not, resulting in a decrease in % chlorophyll a over the gradient.4. The results of experiments conducted in an in situ benthic chamber showed no significant differences in gross primary production between two communities of different biomass, but indicated a slightly decreasing trend with increasing velocity (0.14 to 0.38 ms−1). In contrast, community respiration increased greatly with mat biomass and also as a function of increased water velocity. The combined AFDM, chlorophyll a and metabolic results indicated that the zone of photosynthesis was maintained at the surface of the mats, with variable amounts of mucilage being secreted below, depending on hydraulic conditions.5. The diatom community had considerable physiognomic plasticity through the accumulation of mucilage. It is suggested that this high mucilage secretion may be an active feedback mechanism to help ameliorate environmental stress. If so, present theory on velocity control of periphytic algal development in streams, which is essentially based on passive responses, needs expanding. It is concluded that the response of periphyton to spatial differences in habitat hydraulics in streams is highly complex and it may be difficult to define clear hydraulic habitat preference curves for periphyton communities in nutrient‐poor streams.

Studies of the deep water fauna and related problems

1. 1. Investigations on the Kuril Trench, carried out in 1953 by the Soviet expedition on the Research Ship Vitjaz allowed several general principles to be laid down in the change of the bottom and the pelagic faunas with increasing depth. 2. 2. The biomass of benthos and plankton in the ultra-abyssal zone (> 6,000 m) is 1,000 times less than in the surface zone. 3. 3. With the increase of depth the variety of species of benthos decreases ; its diversity increases at first and then decreases, for the most part within the ultra-abyssal zone. 4. 4. The colouring change of bottom and pelagic animals also takes place differently according to depth. Many pelagic animals are pigmented up to depths of 6–7,000 m. Only the plankton of the ultra-abyssal zone is totally devoid of pigment (except the amphipad Andaniexis subabyssi Birst. et M. Vin.). The bottom animals become pigmentless, at depths greater than about 2,000 m. Possibly this dissimilarity is due to vertical migrations of broad range peculiar to pelagic animals. 5. 5. The relative importance of predators of plankton increases with depth. This contracts with the bottom animals, for which there is an increase in relative importance of detritus eaters and a lesser importance of predators at increasing depths. 6. 6. One of the many sources of food supply for the abyssal and ultra-abyssal fauna is provided by the transportation of organic matter from the zone of photosynthesis down to the great depths by means of vertical migration of zooplankton, performed either within each fixed vertical zone, or having a still broader range. During their vertical migrations the upper layers of deep-sea animals become the prey of the lower dwellers and thus the organic matter produced in the zone of photosynthesis is brought to the greatest depths of the ocean. 7. 7. The body-size comparison of species of the same genus inhabiting different depths shows a tendancy to greater body-size with greater depth. This is true for both bottom and pelagic animals. It cannot be explained by temperature changes. 8. 8. The deep-sea fauna comprises a great quantity of ancient and primative forms. 9. 9. The zoogeographic regions of the ocean ought to be determined from separate vertical zones. In addition, the determination of zoogeographic regions of the abyssal zone will show not only the connections and the hydrological regime of the contemporary seas and oceans but also those of the seas and oceans of the remote past. 10. 10. The ultra-abyssal faunas of each trench must comprises endemic species or even units of a higher taxonomic grade. A set of these species was discovered in the extreme depths of the Kuril Trench.

The Annual Energy Budget of an Inland Lake

The variation in the quantity of solar radiation delivered to the surface of an inland lake during the course of the year is the principal factor in determining the physical, chemical and biological cycle of changes that take place within the water. This is true especially of lakes which are situated in temperate latitudes where there are considerable differences between summer and winter temperatures of the air and of the water. In the deeper lakes which become covered with ice for a few to several weeks during the winter, the annual cycle consists of four phases which correspond roughly to the four seasons of the year. (1) There is a winter stagnation period in which the water is inversely stratified while the lake is covered with ice; that is, the warmest water is at the bottom and the coldest at the surface. (2) There is an overturning and circulation of the entire body of water following the disappearance of the ice in spring. (3) As the temperature rises above the point of maximum density (40 C.) in the spring, the free circulation of the water is hindered as a result of the difference in density between the warm upper layer and the cold lower stratum; this is due to the fact that most of the warming takes place in a comparatively thin upper stratum. From 65 to 90 per cent or more of the sun and sky radiation is cut off by the upper meter of water, depending upon the color and the transparency. This large reduction is due chiefly to reflection at the surface, to the rapid absorption of the radiation by the water itself and by the stains and suspensoids that may be present in the water. With the further rise in the temperature of the upper water as the season advances, a summer stratification is established. This is a direct stratification in which there is a warm upper stratum, a cold lower stratum and a transition zone between them in which the temperature changes rapidly from that of the warm upper water to that of the cold stratum below; naming them in order from surf ace to bottom, they are known as the epilimnion, the thermocline or mesolimnion, and the hypolimnion. In the deeper lakes these three strata persist throughout the summer. (4) The fourth stage is represented by the autumnal cooling and overturning, which is followed by a complete circulation of the water until the lake becomes covered with ice. The circulation of the water in spring and autumn distributes the dissolved substances uniformly from surface to bottom, but a more or less marked difference in the chemical character of the upper and lower strata develops during the two stratification periods, especially in summer. The seasonal changes in the physical and chemical characteristics of the water have an important effect upon aquatic life. The spring rise in temperature speeds up life processes and the increase in the amount of solar radiation at this time makes conditions more favorable for photosynthesis. Likewise the circulation of the water in spring and autumn brings dissolved substances into the upper stratum, which is the zone of photosynthesis, where they can be readily obtained by the aquatic plants. The phytoplankton responds promptly to these favorable growing conditions and, as a result, the standing crop of plankton is usually much larger during the two circulation periods 1 From the Limnological Laboratory of the Wisconsin Geological and Natural History Survey. Notes and reports No. 92.