Carbon Export Rates Research Articles

Plankton community changes during the last 124 000years in the subarctic Bering Sea derived from sedimentary ancient DNA.

Current global warming results in rising sea-water temperatures, and the loss of sea ice in Arctic and subarctic oceans impacts the community composition of primary producers with cascading effects on the food web and potentially on carbon export rates. This study analyzes metagenomic shotgun and diatom rbcL amplicon sequencing data from sedimentary ancient DNA of the subarctic western Bering Sea that records phyto- and zooplankton community changes over the last glacial-interglacial cycles, including the last interglacial period (Eemian). Our data show that interglacial and glacial plankton communities differ, with distinct Eemian and Holocene plankton communities. The generally warm Holocene period is dominated by picosized cyanobacteria and bacteria-feeding heterotrophic protists, while the Eemian period is dominated by eukaryotic picosized chlorophytes and Triparmaceae. By contrast, the glacial period is characterized by microsized phototrophic protists, including sea ice-associated diatoms in the family Bacillariaceae and co-occurring diatom-feeding crustaceous zooplankton. Our deep-time record of plankton community changes reveals a long-term decrease in phytoplankton cell size coeval with increasing temperatures, resembling community changes in the currently warming Bering Sea. The phytoplankton community in the warmer-than-present Eemian period is distinct from modern communities and limits the use of the Eemian as an analog for future climate scenarios. However, under enhanced future warming, the expected shift toward the dominance of small-sized phytoplankton and heterotrophic protists might result in an increased productivity, whereas the community's potential of carbon export will be decreased, thereby weakening the subarctic Bering Sea's function as an effective carbon sink.

Iron and manganese availability drives primary production and carbon export in the Weddell Sea

Next to iron (Fe), recent phytoplankton-enrichment experiments identified manganese (Mn) to (co-)limit Southern Ocean phytoplankton biomass and species composition. Since taxonomic diversity affects aggregation time and sinking rate, the efficiency of the biological carbon pump is directly affected by community structure. However, the impact of FeMn co-limitation on Antarctic primary production, community composition, and the subsequent export of carbon to depth requires more investigation. In situ samplings of 6 stations in the understudied southern Weddell Sea revealed that surface Fe and Mn concentrations, primary production, and carbon export rates were all low, suggesting a FeMn co-limited phytoplankton community. An Fe and Mn addition experiment examined how changes in the species composition drive the aggregation capability of a natural phytoplankton community. Primary production rates were highest when Fe and Mn were added together, due to an increased abundance of the colonial prymnesiophyte Phaeocystis antarctica. Although the community remained diatom dominated, the increase in Phaeocystis abundance led to highly carbon-enriched aggregates and a 4-fold increase in the carbon export potential compared to the control, whereas it only doubled in the Fe treatment. Based on the outcome of the FeMn-enrichment experiment, this region may suffer from FeMn co-limitation. As the Weddell Sea represents one of the most productive Antarctic marginal ice zones, our findings highlight that in response to greater Fe and Mn supply, changes in plankton community composition and primary production can have a disproportionally larger effect on the carbon export potential.

Mechanistic constraints on the trade-off between photosynthesis and respiration in response to warming.

Phytoplankton are responsible for half of all oxygen production and drive the ocean carbon cycle. Metabolic theory predicts that increasing global temperatures will cause phytoplankton to become more heterotrophic and smaller. Here, we uncover the metabolic trade-offs between cellular space, energy, and stress management driving phytoplankton thermal acclimation and how these might be overcome through evolutionary adaptation. We show that the observed relationships between traits such as chlorophyll, lipid content, C:N, and size can be predicted on the basis of the metabolic demands of the cell, the thermal dependency of transporters, and changes in membrane lipids. We suggest that many of the observed relationships are not fixed physiological constraints but rather can be altered through adaptation. For example, the evolution of lipid metabolism can favor larger cells with higher lipid content to mitigate oxidative stress. These results have implications for rates of carbon sequestration and export in a warmer ocean.

Krill body size drives particulate organic carbon export in West Antarctica.

The export of carbon from the ocean surface and storage in the ocean interior is important in the modulation of global climate1-4. The West Antarctic Peninsula experiences some of the largest summer particulate organic carbon (POC) export rates, and one of the fastest warming rates, in the world5,6. To understand how warming may alter carbon storage, it is necessary to first determine the patterns and ecological drivers of POC export7,8. Here we show that Antarctic krill (Euphausia superba) body size and life-history cycle, as opposed to their overall biomass or regional environmental factors, exert the dominant control on the POC flux. We measured POC fluxes over 21 years, the longest record in the Southern Ocean, and found a significant 5-year periodicity in the annual POC flux, which oscillated in synchrony with krill body size, peaking when the krill population was composed predominately of large individuals. Krill body size alters the POC flux through the production and export of size-varying faecal pellets9, which dominate the total flux. Decreases in winter sea ice10, an essential habitat for krill, are causing shifts in the krill population11, which may alter these export patterns of faecal pellets, leading to changes in ocean carbon storage.

Diurnal Regulation of Leaf Photosynthesis Is Related to Leaf-Age-Dependent Changes in Assimilate Accumulation in Camellia oleifera.

In order to clarify the mechanism of diurnal changes in photosynthesis of leaves of different leaf ages in Camellia oleifera, current-year leaves (CLs) and annual leaves (ALs) were used as the test materials to analyze the diurnal changes in photosynthetic parameters, assimilate contents and enzyme activities, as well as structural differences and expression levels of sugar transport regulating genes. The rate of net photosynthesis in CLs and ALs was highest in the morning. During the day, there was a decrease in the CO2 assimilation rate, and this decrease was greater in ALs than in CLs at midday. The maximal efficiency of photosystem II (PSII) photochemistry (Fv/Fm) showed a decreasing trend as the sunlight intensity increased, but no significant difference between CLs and ALs was found. Compared with CLs, ALs showed a greater decrease in the carbon export rate at midday and the levels of sugars and starch increased significantly in ALs, accompanied by higher enzyme activity of sucrose synthetase and ADP-glucose pyrophosphorylase. In addition, compared with CLs, ALs had a larger leaf vein area and higher leaf vein density, as well as higher expression levels of sugar transport regulating genes during the day. It is concluded that the excessive accumulation of assimilate is an important factor contributing to the midday depression of photosynthesis in Camellia oleifera annual leaves on a sunny day. Sugar transporters may play an important regulatory role in excessive accumulation of assimilate in leaves.

Response of dissolved organic carbon dynamics to salinity in a Constructed Fen Peatland in the Athabasca Oil Sands region

AbstractIn northern Alberta, oil sands mining disturbs the boreal landscape, and reclamation to an ‘equivalent land capability’ is required. Industry is testing peatland construction as part of landscape reclamation. To determine if constructed peatlands can be self‐sustaining, an understanding of the cycling of solutes in pore water and their interactions with dissolved organic carbon (DOC) is needed since DOC can represent an important carbon loss from peatlands. DOC is of interest due to its biotic origin and use by the microbial community and impact on carbon budgets. Additionally, salinity as a control on DOC quantity and quality may be important in oil sands reclaimed systems due to the likelihood of elevated sodium (Na+) from saline groundwater input derived from tailings used to construct catchments, and natural sources. For this research, DOC concentration and quality, and Na+ concentration were measured in the rooting zone (10 and 30 cm depth) of Nikanotee Fen to evaluate the role of Na+ in DOC dynamics. DOC concentration and quality suggested that DOC in the fen was largely sourced from vegetation inputs, with quality also suggesting increases in vegetation inputs between years. Elevated Na+ at 30 cm below ground surface corresponded with high concentrations of labile DOC. At 10 cm below ground surface, sampling location and temperature were the best predictors of DOC concentration and quality. With expected increases in Na+, increased production of mobile and microbially active DOC may lead to higher rates of carbon export.

ForamEcoGEnIE 2.0: incorporating symbiosis and spine traits into a trait-based global planktic foraminiferal model

Abstract. Planktic foraminifera are major marine calcifiers in the modern ocean, regulating the marine inorganic carbon pump, and generating marine fossil archives of past climate change. The foraminifera contain ecogroups with and without spines and algal symbionts, creating functional trait diversity which expands their ecological niches. Here, we incorporate symbiosis and spine traits into the symbiont-barren non-spinose foraminifer functional type in EcoGEnIE to represent all the extant foraminifera species. We calibrated the modelled new traits using Latin hypercube sampling (LHS) and identified the optimal model parameters from an ensemble of 1200 runs compared with global observations from core-top sediment samples, sediment traps, and plankton nets. The model successfully describes the global distribution and seasonal abundance variation of the four major foraminiferal functional groups. The model reproduces the dominance of the symbiont-obligate group in subtropical gyres and of the symbiont-barren types in the productive subpolar oceans. Global annual mean biomass and foraminifer-derived carbon export rate are correctly predicted compared to data, with biomass ranging from 0.001 to 0.010 mmol C m−3 and organic carbon export 0.002–0.031 mmol C m−2 d−1. The model captures the seasonal peak time of biomass and organic carbon export but struggles to reproduce the amplitude of both in productive areas. The sparseness and uneven distribution of observations and the model's limitation in upwelling regions likely contribute to this discrepancy. Our model overcomes the lack of major groups in the previous ForamEcoGEnIE 1.0 version and offers the potential to explore foraminiferal ecology dynamics and its impact on biogeochemistry in modern, future, and paleogeographic environments.

The role of earthquakes and storms in the fluvial export of terrestrial organic carbon along the eastern margin of the Tibetan plateau: A biomarker perspective

Driven by earthquakes and intense rainfall, steep tectonically active mountains are hotspots of terrestrial organic carbon mobilization from soils, rocks, and vegetation by landslides into rivers. Subsequent delivery and fluvial mobilization of organic carbon from different sources can impact atmospheric CO2 concentrations across a range of timescales. Extreme landslide triggering events can provide insight on processes and rates of carbon export. Here we used suspended sediment collected from 2005 to 2012 at the upper Min Jiang, a main tributary of the Yangtze River on the eastern margin of the Tibetan Plateau, to compare the erosion of terrestrial organic carbon before and after the 2008 Wenchuan earthquake and a storm-derived debris flow event in 2005. To constrain the source of riverine particulate organic carbon (POC), we quantified lignin phenols and n-alkanoic acids in the suspended sediments, catchment soils and landslide deposits. We found that riverine POC had higher inputs of less-degraded, discrete organic matter at high suspended sediment loads, while the source of POC seemed stochastic at low suspended sediment concentrations. The debris flow in 2005 mobilized a large amount of POC, resulting in an export of lignin within a single day equivalent to a normal year. In comparison, the 2008 Wenchuan earthquake increased the flux of POC and particulate lignin, albeit with limited impact on POC sources in comparison to seasonal variations. Our results highlight the important role of episodic events in the fluvial export of terrestrial carbon.

A trait‐based carbon export model for mesopelagic fishes in the Gulf of Mexico with consideration of asynchronous vertical migration, flux boundaries, and feeding guilds

AbstractFish‐mediated carbon export provides a significant proportion of the biological carbon pump in oligotrophic regions. Bioenergetic models estimate this carbon transport, but many lack species‐specific traits and no carbon export model has been developed in the mesopelagic Gulf of Mexico. Intensive mesopelagic sampling efforts in the northern and eastern Gulf of Mexico have provided high‐resolution information regarding community composition, species' vertical migratory characteristics, diel depth occupancies, and diets. A stochastic, individual‐based model was developed for deep‐pelagic fishes in the northern Gulf of Mexico to estimate bioenergetic rates and carbon export fluxes. Fishes that ate gelatinous zooplankton consumed more mass per body weight per day than predators of cephalopods and fishes, ostensibly to increase the throughput of prey with less carbon (gelata) or more refractory materials (Crustacea). A dynamic energy budget submodel indicated that during 81% of occurrences, asynchronous vertically migrating fishes rested for 1 d before migrating again, but migrations on successive days were possible. In terms of carbon export, myctophids and stomiids contributed greater than 53% and 12% of the active carbon flux for the entire assemblage in all scenarios. The assemblage‐wide carbon export rate driven by vertically migrating fishes was 0.14–0.72 mg C m−2 d−1, 61% of the ingested carbon by the assemblage. Incorporating species‐specific traits and individual variability in bioenergetic models allows for more complex research questions (e.g., the effect of feeding guilds and asynchronous migration on carbon export) compared to the carbon export models that otherwise assume all fishes within a functional group are equivalent.

Dynamics of carbon export from leaves as translocation affected by the coordination of carbohydrate availability in field strawberry

Carbon export from leaves as translocation is a result of plant coordination of leaf carbohydrate availability. Carbohydrate availability coordination is actively studied in model plants (Arabidopsis) under regulated conditions and can be optimized to increase productivity. However, in horticultural crops grown under field conditions, carbon export dynamics and coordination are poorly understood. The objective of this study was to analyze the dynamics of carbon export from leaves and the effects of carbohydrate availability coordination on these dynamics in strawberry grown under field conditions. Through three different day/night cycles, we measured leaf carbohydrate concentrations and photosynthetic rates and evaluated the dynamics of carbon export based on the leaf carbon balance. During the daytime, when carbon resources are almost entirely supplied by photosynthesis, strawberry leaves stored sucrose and starch. Starch synthesis was remarkable when sucrose concentration exceeded 150 mmol m−2, and the carbon export rate tended to increase. In the nighttime, when carbon resources are supplied by leaf sucrose and starch stored during the daytime, the starch concentrations decreased linearly and the carbon export rate was lower than the daytime level. These results indicate that in the daytime, the coordination of leaf carbohydrate availability for starch storage and carbon export was affected by leaf sucrose concentration, whereas, at night, it was regulated by leaf carbon storage levels at dusk rather than sucrose concentration. Thus, this study elucidates the basis of carbon export dynamics in strawberry leaves under field conditions, advancing our understanding of the role of leaf carbohydrates in translocation.

Cyclonic eddies modulate temporal and spatial decoupling of particulate carbon, nitrogen, and biogenic silica export in the North Pacific Subtropical Gyre

AbstractMesoscale eddies may enhance nutrient injection into the photic zone and ultimately the magnitude and composition of particle export to depth. Using satellite altimetry, we identified 38 cyclonic eddies that passed in close proximity to the Hawaii Ocean Time‐series (HOT) Station ALOHA, located in the North Pacific Subtropical Gyre, from 1993 to 2018. Particulate carbon (C), nitrogen (N), and biogenic silica (Si) export rates, measured using free floating sediment traps deployed at 150 m as part of HOT, were then associated with either the eddy core or edge based on distance to the eddy center and time of eddy evolution. Elemental fluxes varied significantly within and among individual eddies depending on season and eddy age. Spatially, biogenic Si fluxes were enhanced relative to particulate C and N fluxes at both the cores and edges, with temporally highest particulate C, N and biogenic Si fluxes occurring during the mature stage (3–8 weeks). On average, biogenic Si fluxes were 200 ± 80% (30–270% increase) higher relative to non‐eddy and during non‐bloom periods, with modest enhanced particulate C (10–30% increase) and N (10–20% increase) fluxes. In contrast, during the bloom season (July and August), elemental fluxes were all reduced by 20% relative to non‐eddy references, suggesting that cyclonic eddies depress export during the bloom period. Our results indicate that cyclonic eddies not only increase, but differentially impact the sinking export of critical biological elements, thereby contributing to long term ecological changes in foodwebs that rely on silica as well as carbon for growth.

Appraisal of sedimentary alkenones for the quantitative reconstruction of phytoplankton biomass

Marine primary productivity (PP) is the driving factor in the global marine carbon cycle. Its reconstruction in past climates relies on biogeochemical proxies that are not considered to provide an unequivocal signal. These are often based on the water column flux of biogenic components to sediments (organic carbon, biogenic opal, biomarkers), although other factors than productivity are posited to control the sedimentary contents of the components, and their flux is related to the fraction of export production buried in sediments. Moreover, most flux proxies have not been globally appraised. Here, we assess a proxy to quantify past phytoplankton biomass by correlating the concentration of C37 alkenones in a global suite of core-top sediments with sea surface chlorophyll-a (SSchla) estimates over the last 20 y. SSchla is the central metric to calculate phytoplankton biomass and is directly related to PP. We show that the global spatial distribution of sedimentary alkenones is primarily correlated to SSchla rather than diagenetic factors such as the oxygen concentration in bottom waters, which challenges previous assumptions on the role of preservation on driving concentrations of sedimentary organic compounds. Moreover, our results suggest that the rate of global carbon export to sediments is not regionally constrained, and that alkenones producers play a dominant role in the global export of carbon buried in the seafloor. This study shows the potential of using sedimentary alkenones to estimate past phytoplankton biomass, which in turn can be used to infer past PP in the global ocean.

Organic Carbon Export and Loss Rates in the Red Sea

AbstractThe export and fate of organic carbon in the mesopelagic zone are still poorly understood and quantified due to lack of observations. We exploited data from a biogeochemical‐Argo float that was deployed in the Red Sea to study how a warm and hypoxic environment can affect the fate of the organic carbon in the ocean's interior. We observed that only 10% of the particulate organic carbon (POC) exported survived at depth due to remineralization processes in the upper mesopelagic zone. We also found that POC exported was rapidly degraded in a first stage and slowly in a second one, which may be dependent on the palatability of the organic matter. We observed that apparent oxygen utilization (AOU)‐based loss rates (a proxy of the remineralization of total organic matter) were significantly higher than the POC‐based loss rates, likely because changes in AOU are mainly attributed to changes in dissolved organic carbon. Finally, we showed that POC‐ and AOU‐based loss rates could be expressed as a function of temperature and oxygen concentration. These findings advance our understanding of the biological carbon pump and mesopelagic ecosystem.

Cold acclimation has a differential effect on leaf vascular bundle structure and carbon export rates in natural Arabidopsis accessions originating from southern and northern Europe.

Acclimation to low but non‐freezing temperature represents an ecologically important process for Arabidopsis thaliana but also for many other plant species from temperate regions. Cold acclimation comprises and affects numerous molecular and physiological processes and the maintenance of sugar supply of sink tissue by photosynthetically active source tissue is essential for plant survival. Here, changes in vascular bundle (VB) structure at the leaf petiole were analysed together with sucrose exudation rates before and after cold acclimation. Six natural Arabidopsis accessions originating from southern and northern Europe were compared. Photosynthetic efficiency, that is, maximum and effective quantum yield of photosystem II, revealed a significant effect of environmental condition. Only for northern accessions was a highly significant negative correlation observed between leaf sucrose exudation rates, xylem, and petiole cross‐sectional areas. Furthermore, only for northern accessions was a significant increase of VB and leaf petiole cross‐sectional area observed during cold acclimation. In contrast, variance of cross‐sectional areas of cold acclimated southern accessions was strongly reduced compared to control plants, while mean areas remained similar under both conditions. In summary, these findings suggest that natural Arabidopsis accessions from northern Europe significantly adjust sink strength and leaf VB structure to maintain plant growth and photosynthesis under low temperature.

Urbanization alters coastal plain stream carbon export and dissolved oxygen dynamics

Coastal plain streams in the southeastern United States supply carbon that supports important coastal ecosystems, but the effects of urbanization on carbon export from these streams have not been extensively studied. This study aimed to determine how urbanization changes coastal plain stream organic matter quality, rates of carbon export, and dissolved oxygen dynamics that have implications for stream ecosystem function. Organic matter quality, organic carbon export, and dissolved oxygen concentrations were measured for multiple years (2009 & 2013–2015) in North Carolina coastal plain streams that spanned a gradient of urbanization. Based on spectral characteristics, dissolved organic matter (DOM) quality appeared to shift from characteristic blackwater in minimally impacted streams to clear streamwater in urban streams due to large reductions in chromophoric DOM concentrations, aromaticity, and molecular weight. Differences in spectral indices and characteristics of dissolved organic carbon export suggest that urbanization reduced natural sources of DOM and provided various urban sources of DOM that were likely more bioavailable. Particulate organic matter in the urban streams was indicative of more labile autochthonous sources than that of the less impacted streams, and rates of particulate carbon export increased and shifted to higher flows with watershed impervious surface cover. Diel variation of dissolved oxygen increased with watershed impervious surface cover, indicating that urbanization and associated changes in carbon and nutrient cycling altered stream function. While the effects of urbanization on carbon export were similar to previous studies in other regions, the unique blackwater state of natural streams and receiving waters in the study area make them especially susceptible to negative ecological impacts from altered carbon and nutrient export. Management actions that conserve or restore natural carbon sources to the stream may help mitigate multiple negative effects of urbanization in southeastern US coastal plain streams.

High Net Primary Production of Mediterranean Seagrass (Posidonia oceanica) Meadows Determined With Aquatic Eddy Covariance

We report primary production and respiration of Posidonia oceanica meadows determined with the non-invasive aquatic eddy covariance technique. Oxygen fluxes were measured in late spring at an open-water meadow (300 m from shore), at a nearshore meadow (60 m from shore), and at an adjacent sand bed. Despite the oligotrophic environment, the meadows were highly productive and highly autotrophic. Net ecosystem production (54 to 119 mmol m-2 d-1) was about one-half of gross primary production. In adjacent sands, net primary production was a tenth- to a twentieth smaller (4.6 mmol m-2 d-1). Thus, P. oceanica meadows are an oasis of productivity in unproductive surroundings. During the night, dissolved oxygen was depleted in the open-water meadow. This caused a hysteresis where oxygen production in the late afternoon was greater than in the morning at the same irradiance. Therefore, for accurate measurements of diel primary production and respiration in this system, oxygen must be measured within the canopy. Generally, these measurements demonstrate that P. oceanica meadows fix substantially more carbon than they respire. This supports the high rate of organic carbon accumulation and export for which the ecosystem is known.

Carbon export from leaves is controlled via ubiquitination and phosphorylation of sucrose transporter SUC2

All multicellular organisms keep a balance between sink and source activities by controlling nutrient transport at strategic positions. In most plants, photosynthetically produced sucrose is the predominant carbon and energy source, whose transport from leaves to carbon sink organs depends on sucrose transporters. In the model plant Arabidopsis thaliana, transport of sucrose into the phloem vascular tissue by SUCROSE TRANSPORTER 2 (SUC2) sets the rate of carbon export from source leaves, just like the SUC2 homologs of most crop plants. Despite their importance, little is known about the proteins that regulate these sucrose transporters. Here, identification and characterization of SUC2-interaction partners revealed that SUC2 activity is regulated via its protein turnover rate and phosphorylation state. UBIQUITIN-CONJUGATING ENZYME 34 (UBC34) was found to trigger turnover of SUC2 in a light-dependent manner. The E2 enzyme UBC34 could ubiquitinate SUC2 in vitro, a function generally associated with E3 ubiquitin ligases. ubc34 mutants showed increased phloem loading, as well as increased biomass and yield. In contrast, mutants of another SUC2-interaction partner, WALL-ASSOCIATED KINASE LIKE 8 (WAKL8), showed decreased phloem loading and growth. An in vivo assay based on a fluorescent sucrose analog confirmed that SUC2 phosphorylation by WAKL8 can increase transport activity. Both proteins are required for the up-regulation of phloem loading in response to increased light intensity. The molecular mechanism of SUC2 regulation elucidated here provides promising targets for the biotechnological enhancement of source strength.

Impact of Changes to the Atmospheric Soluble Iron Deposition Flux on Ocean Biogeochemical Cycles in the Anthropocene

AbstractIron can be a growth‐limiting nutrient for phytoplankton, modifying rates of net primary production, nitrogen fixation, and carbon export ‐ highlighting the importance of new iron inputs from the atmosphere. The bioavailable iron fraction depends on the emission source and the dissolution during transport. The impacts of anthropogenic combustion and land use change on emissions from industrial, domestic, shipping, desert, and wildfire sources suggest that Northern Hemisphere soluble iron deposition has likely been enhanced between 2% and 68% over the Industrial Era. If policy and climate follow the intermediate Representative Concentration Pathway 4.5 trajectory, then results suggest that Southern Ocean (>30°S) soluble iron deposition would be enhanced between 63% and 95% by 2100. Marine net primary productivity and carbon export within the open ocean are most sensitive to changes in soluble iron deposition in the Southern Hemisphere; this is predominantly driven by fire rather than dust iron sources. Changes in iron deposition cause large perturbations to the marine nitrogen cycle, up to 70% increase in denitrification and 15% increase in nitrogen fixation, but only modestly impacts the carbon cycle and atmospheric CO2concentrations (1–3 ppm). Regionally, primary productivity increases due to increased iron deposition are often compensated by offsetting decreases downstream corresponding to equivalent changes in the rate of phytoplankton macronutrient uptake, particularly in the equatorial Pacific. These effects are weaker in the Southern Ocean, suggesting that changes in iron deposition in this region dominates the global carbon cycle and climate response.

Information limitation and the dynamics of coupled ecological systems.

The dynamics of large ecological systems result from vast numbers of interactions between individual organisms. Here, we develop mathematical theory to show that the rate of such interactions is inherently limited by the ability of organisms to gain information about one another. This phenomenon, which we call 'information limitation', is likely to be widespread in real ecological systems and can dictate both the rates of ecological interactions and long-run dynamics of interacting populations. We show how information limitation leads to sigmoid interaction rate functions that can stabilize antagonistic interactions and destabilize mutualistic ones; as a species or type becomes rare, information on its whereabouts also becomes rare, weakening coupling with consumers, pathogens and mutualists. This can facilitate persistence of consumer-resource systems, alter the course of pathogen infections within a host and enhance the rates of oceanic productivity and carbon export. Our findings may shed light on phenomena in many living systems where information drives interactions.

Cyanobacteria and cyanophage contributions to carbon and nitrogen cycling in an oligotrophic oxygen-deficient zone

Up to half of marine N losses occur in oxygen-deficient zones (ODZs). Organic matter flux from productive surface waters is considered a primary control on N2 production. Here we investigate the offshore Eastern Tropical North Pacific (ETNP) where a secondary chlorophyll a maximum resides within the ODZ. Rates of primary production and carbon export from the mixed layer and productivity in the primary chlorophyll a maximum were consistent with oligotrophic waters. However, sediment trap carbon and nitrogen fluxes increased between 105 and 150 m, indicating organic matter production within the ODZ. Metagenomic and metaproteomic characterization indicated that the secondary chlorophyll a maximum was attributable to the cyanobacterium Prochlorococcus, and numerous photosynthesis and carbon fixation proteins were detected. The presence of chemoautotrophic ammonia-oxidizing archaea and the nitrite oxidizer Nitrospina and detection of nitrate oxidoreductase was consistent with cyanobacterial oxygen production within the ODZ. Cyanobacteria and cyanophage were also present on large (>30 μm) particles and in sediment trap material. Particle cyanophage-to-host ratio exceeded 50, suggesting that viruses help convert cyanobacteria into sinking organic matter. Nitrate reduction and anammox proteins were detected, congruent with previously reported N2 production. We suggest that autochthonous organic matter production within the ODZ contributes to N2 production in the offshore ETNP.