Nutrients play a critical role in oceanic primary productivity and the biological pump. However, compared to hydrographic parameters such as temperature and salinity, nutrient observations are limited due to their labor-intensive and costly measurements. Thus, nutrient observations are several orders of magnitude sparser than hydrographic observations. In this study, we first established a rigorous data quality control procedure to clean the hydrographic and nutrient (including NO3-, NO2-, DIP, and Si(OH)4) observations collected from World Ocean Database (WOD) and CLIVAR and Carbon Hydrographic Data Office (CCHDO) in the North Pacific. Subsequently, the cleaned and high-quality CCHDO dataset was used to train three machine learning models - Random Forest, Light Gradient Boosting Machine (LightGBM), and Gaussian Process Regression - to establish relationships between nutrient concentrations and key variables, including space coordinates (longitude, latitude, and depth), time variables (year and month), and water mass properties (indexed by potential temperature and salinity). Validation shows that the reconstruction closely matches the observations, with Root Mean Squared Errors (RMSEs) of <1.41, <0.071, <0.089 and <3.07 & micro;mol kg(-1) for NO3-, NO2-, DIP, and Si(OH)4, respectively. The validated models were then applied to reconstruct nutrient concentrations from the hydrographic observations in WOD, most of which lacked direct nutrient measurements. This resulted in similar to 473 million reconstructed nutrient data points across 1.92 million stations for each nutrient, spanning from 1895 to 2024, representing a 2127- to 2393-fold increase compared to the original nutrient observations in the North Pacific (197 539 to 222 234). This new dataset will be valuable for studying nutrient transport and budgets, spinning up and validating ocean biogeochemical models, assessing long-term nutrients and their stoichiometric changes driven by anthropogenic forcing and climate change. The dataset generated in this study is openly available via Zenodo (10.5281/zenodo.17451417) (Du et al., 2025).

The deep ocean is widely viewed as a stable reservoir of dissolved organic carbon (DOC) that is highly resistant to microbial degradation. However, this paradigm may be oversimplified. In a cross-latitude survey conducted in the northwestern Pacific Ocean (155 degrees E, 28.5 degrees N-41.5 degrees N), bulk DOC concentrations were found to be relatively constant below 1,000 m with little variation across latitude. Despite this stability, compound-specific analyses revealed unexpectedly high abundance of hydrolyzable amino acids, up to 1.1% of DOC, at depths of 1,000-4,000 m between 30 degrees N and 36 degrees N. This amino acid enrichment, doubling the typical levels observed in other deep-sea basins and comparable to upper ocean values, reflected episodic inputs of semi-labile DOC likely derived from actively settling fresh particles. These findings reveal hidden reservoirs of bioavailable DOC in the deep ocean, a feature not captured by bulk analysis, challenging the conventional view of deep-sea DOC as predominantly refractory and stable.

Dissolved organic matter (DOM) pool acts as both nutrient source and sink in the oligotrophic surface ocean. However, the drivers of seasonal variations in DOM stoichiometry and their relationship to nutrient cycling remain poorly understood. Here, we present a seasonal synthesis of dissolved organic nitrogen (DON) and phosphorus (DOP) distributions across the surface North Pacific Subtropical Gyre (NPSG) with associate biogeochemical measurements. In the central NPSG, summer exhibited elevated DON and depleted DOP, coinciding with a fourfold increase in N2-fixation rates compared with winter. This seasonal shift reflects preferential DOP utilization and accumulation of DON via N2-fixation. Mass and isotopic balance models confirm that DOP can supply about 40%-100% of summer phosphorus demand while about 50% of fixed nitrogen partitions into DON. These findings demonstrate that seasonal DOM stoichiometric flexibility encode dynamic nutrient cycling, highlighting the fundamental role of DOM transformation in regulating ocean biogeochemical processes.

A multi-level memristor, implemented with inexpensive precursors and well-defined mechanisms, will be significant for the development of high-density memory in the coming big data era. Sulfur, a cheap element extracted from petroleum and natural gas, holds fascinating potential for use in information memory. In this work, a three-component hybrid, [Cu(Phen)2I]2Cu2I4S8 (Phen = 1,10-phenanthroline), was synthesized. In this structure, strong pi-pi stacking interactions among Phen ligands, cuprophilic interactions in (Cu2I4)2- anions, and C-H & ctdot;I/S hydrogen bonds contributed to the formation of a quasi-3D network. A FTO/hybrid/Ag memristor was fabricated, exhibiting ternary memory performance with a high ON2/ON1/OFF current ratio (104.50/101.47/1) and a ternary yield of 68%. The memristor could operate at a high temperature of 185 degrees C. Based on the structural characteristics of the hybrid, FIB-SEM measurements on the Ag/hybrid/Ag model device, double logarithm analysis of the I-V curve, memory performance of the three individual precursors, and external voltage-dependent PXRD, its ternary resistive switching performance could be explained as follows: upon continuous external voltages, the transition OFF -> ON1 was driven by enhanced pi-pi stacking interactions among the Phen ligands, and the current jump ON1 -> ON2 resulted from the formation of a conductive S8/(Cu2I4)2- layer bearing cuprophilic interactions via S8 relaxation. This works extends the strategy of sulfur relaxation in multi-level memories from coordinated polysulfides to uncoordinated ones. The use of inexpensive precursors, combined with the distinct structure-property correlation, provides a promising avenue for implementing novel high-density memristors.

Riverine inputs of ammonium (NH4+) and suspended particulate matter (SPM) from human activities have increased significantly over the past few decades, greatly affecting coastal nitrogen cycling and water quality. However, it remains poorly understood how NH4+ consumption in eutrophic estuaries responds to increasing SPM levels. Using 15N-labeling techniques, we quantified ammonia oxidation (AO) and ammonium uptake (AU) during SPM addition experiments across the salinity gradient of the Jiulong River Estuary, a typically human-impacted, eutrophic, and turbid estuary in China. The results showed that adding in situ SPM stimulated AO at the freshwater end (salinity 1.1), but had minimal impact on AO or AU in regions with intermediate salinity. At the seawater end (salinity 28.0), in situ SPM increased both AO and AU, especially enhancing AU. Furthermore, adding riverine SPM collected from freshwater, mainly of terrestrial origin, to seawater caused weaker stimulation of NH4+ consumption, particularly in AU. These varied responses suggest that NH4+ consumption pathways are controlled by substrate availability, particle source, and the composition of ammonia-utilizing microbial communities in the estuary. This study provides new mechanistic insights into how particles influence NH4+ dynamics in eutrophic estuaries, with important implications for nitrogen cycling and water quality under increasing human impacts.

Haptophytes (Eukaryota, Hacrobia) play a crucial role in the energy budget and element cycling of diverse aquatic ecosystems due to their ability to engage in both phototrophic and mixotrophic nutritional modes. Nevertheless, there is a significant lack of knowledge regarding the short-term variations, such as diel dynamics, of their ecological features. During a short time frame in the summer of 2018, samples were collected from three distinct water layers in the South China Sea, including surface water, the deep chlorophyll maximum (DCM) layer, and 200 m depth. Fluorescence in situ hybridization coupled with tyramide signal amplification was used to quantify haptophyte cell abundance. Most haptophyte communities in all three water layers were composed of cells 2–5 µm in size, while the proportion of cells < 2 µm increased with water depth. High-throughput sequencing of the V4 hypervariable regions of the SSU rRNA revealed that Chrysochromulina and Phaeocystis predominated the community, and the former was more abundant in the surface water and 200 m depth and the latter was more abundant in the DCM layer. Higher abundance of small cells (< 2 µm and 2–5 µm) during the night was found compared to the day time, whereas large cells (5–10 µm and 10–20 µm) were more prevalent during the day time. The results of correlation analyses showed that haptophyte abundance was possibly impacted by both environmental biotic (heterotrophic nanoflagellates, heterotrophic bacteria, and viruses) and abiotic (temperature, salinity, and nutrients) factors.

Carbonyls are ubiquitous in the troposphere and play a crucial role in atmospheric oxidation capacity (AOC), particularly in photochemistry-active regions such as the Tibetan Plateau (TP). However, the composition and evolution of carbonyls over the TP is still poorly understood due to a lack of comprehensive observations and modelling. Here, we conducted an intensive field measurement of 37 carbonyls and their precursors at a sub-urban site in Lhasa during summer 2022. Markedly higher levels of carbonyls (7.24 +/- 3.83 ppbv) were found during ozone pollution episodes, with 36 % higher than those during non-episodes. Formaldehyde was the most abundant carbonyl (38 %), which primarily originating from photochemical secondary formations. Simulations using the Rapid adaptive Optimization Model for Atmospheric Chemistry (ROMAC) indicated strong AOC in Lhasa, with the daytime maximum of center dot OH and center dot HO2 of 9.8 x 10(6) and 4.2 x 10(8) molecules cm(-3), respectively, which were even higher than that in most of the megacities in China. Notably, AOC significantly enhanced with the increasing carbonyls during the episodes, with the concentrations of center dot OH and center dot HO2 were boosted 21 % and 67 % than those during non-episodes, respectively. Budget analysis revealed that the center dot HO2 + NO (88 %) and center dot OH + VOC (74 %) pathways dominated the generation and loss of center dot OH, respectively. And for center dot HO2, they were center dot RO2 + NO (67 %) and center dot HO2 + NO (83 %). This study provides valuable insights into the strong AOC in the ecologically-fragile and climate-sensitive TP region, and highlighted the crucial role of anthropogenic-biogenic interactions in the active photochemistry of TP.

The cyclonic eddy uplifts nutrient-rich seawater into the euphotic zone, typically directly enhancing phytoplankton abundance and primary production. However, its impact on heterotrophic prokaryotic production (HPP) remains unclear due to the complex interplay of multiple indirect factors governing this process. Here, we conducted a comprehensive investigation of the distribution of picophytoplankton and heterotrophic prokaryotes, prokaryotic community structure, and HPP within a cyclonic eddy in the western North Pacific subtropical gyre. The results indicated that despite the higher abundance of picophytoplankton accompanied by nutrient upwelling at the eddy core compared to the edge, higher levels of HPP were observed at the eddy edge between 100 and 200 m, consistent with the distribution of the low nucleic acid content (LNA) prokaryotes. The significant positive correlation between HPP and the proportion of LNA group in total heterotrophic prokaryotes suggested a primary contribution from the LNA group over the high nucleic acid content (HNA) group. SAR11, a typical member of the LNA group, may primarily contribute to the elevated HPP observed at the eddy edge. The changes in temperature, nutrients, and light intensity induced by the cyclonic eddy may significantly influence the distribution and activity of HNA and LNA groups, potentially exerting a greater impact on HPP compared to phytoplankton-related factors. These findings contribute to understanding the underlying mechanisms of HPP responses to cyclonic eddies in the oligotrophic open ocean.

Sulfadoxine (SDX) is a broad-spectrum veterinary antibiotic, which was used alone for the treatment of various infections in the past, and detected ubiquitously in the aqueous environment. However, understanding SDX's photo- and microbial degradation within the environment, especially in marine matrixes, remains limited. This research hones in on SDX's degradation dynamics in seawater. Photodegradation emerges as the dominant process, surpassing microbial degradation in speed and efficiency. Notably, 90% of SDX is photo-degraded within 12 h, while only 52% is removed via microbial degradation over two weeks. Time-of-flight mass spectrometry provides high-resolution molecular mass information on degradation products. The molecular structures of hydrolysis, photo-, and microbial degradation products are deduced from accurate precursor and fragment ion masses, alongside an integrated data processing workflow. Six hydrolysis products arise from the treatment, and photodegradation and microbial degradation yield nine and eighteen products, respectively. Molecular insights from these products inform plausible degradation pathways involving hydrolysis, photodegradation, and microbial degradation. Processes like bond cleavage, methylation, hydroxylation, oxidation, reduction, and methoxylation are identified and associated with degradation. This study presents a comprehensive workflow for acquiring and processing degradation product data linked to emerging organic pollutants. Moreover, it contributes to our comprehension of the environmental fate of veterinary drugs in marine ecosystems.

As a new type of biological treatment process, membrane aerated biofilm reactors (MABRs), which have received extensive attention and research in recent years, could reduce energy consumption by 70% compared to the traditional activated sludge process. The MABR system uses bubble-free aeration membrane material as the carrier, the counter-diffusion mechanism of oxygen and pollutants enables ammonium oxidizing bacteria (AOB) and nitrate oxidizing bacteria (NOB) to adhere to the membrane surface so that simultaneous nitrification and denitrification (SND) can occur to achieve simultaneous nitrogen and carbon removal. Currently, MABR technology has been successfully applied to the treatment of municipal sewage, various industrial wastewater, pharmaceutical, high salinity, high ammonia, aquaculture wastewater, landfill leachate and black and odorous water bodies in rivers. Many laboratory experiments and pilot-scale MABR reactors have been used to study the performance of membrane materials, the mechanism of pollutant removal and the effects of different factors on the system. However, the performance of MABR is affected by factors such as dissolved oxygen (DO), pH, C/N, biofilm thickness, hydraulic retention time (HRT), temperature, etc., which limits large-scale promotion. Therefore, membrane materials, membrane modules, biofilm, application of MABR technology, influencing factors of MABR system performance, and limitations and perspectives of MABR are reviewed in this paper, and we expect to provide valuable information.

Nitrite, an intermediate product of the oxidation of ammonia to nitrate (nitrification), accumulates in upper oceans, forming the primary nitrite maximum (PNM). Nitrite concentrations in the PNM are relatively low in the western North Pacific subtropical gyre (wNPSG), where eddies are frequent and intense. To explain these low nitrite concentrations, we investigated nitrification in cyclonic eddies in the wNPSG. We detected relatively low half-saturation constants (i.e., high substrate affinities) for ammonia and nitrite oxidation at 150 to 200 meter water depth. Eddy-induced displacement of high-affinity nitrifiers and increased substrate supply enhanced ammonia and nitrite oxidation, depleting ambient substrate concentrations in the euphotic zone. Nitrite oxidation is more strongly enhanced by the cyclonic eddies than ammonia oxidation, reducing concentrations and accelerating the turnover of nitrite in the PNM. These findings demonstrate a spatial decoupling of the two steps of nitrification in response to mesoscale processes and provide insights into physical-ecological controls on the PNM.

This data set contains: 1)the sampling information and DOC concentrations of the samples; 2) statistics of DOC concentrations, SPE-DOC concentrations, SPE-DOC Δ14C values, SPE-DOC δ13C values, and carbon extraction efficiencies determined for samples from stations F2 and DC6; 3)Molecular characteristics of DOM throughout two water columns at stations F2 and DC6, including the relative abundance of different compound groups and intensity-weighted indices.

Phytoplankton contribute almost half of the world's total primary production. The exudates and viral lysates of phytoplankton are two important forms of dissolved organic matter (DOM) in aquatic environments and fuel heterotrophic prokaryotic metabolism. However, the effect of viral infection on the composition and biological availability of phytoplankton-released DOM is poorly understood. Here, we investigated the optical characteristics and microbial utilization of the exudates and viral lysates of the ecologically important unicellular picophytoplankton Prochlorococcus Our results showed that Prochlorococcus DOM produced by viral lysis (Pro-vDOM) with phages of three different morphotypes (myovirus P-HM2, siphovirus P-HS2, and podovirus P-SSP7) had higher humic-like fluorescence intensities, lower absorption coefficients, and higher spectral slopes than DOM exuded by Prochlorococcus (Pro-exudate). The results indicate that viral infection altered the composition of Prochlorococcus-derived DOM and might contribute to the pool of oceanic humic-like DOM. Incubation with Pro-vDOM resulted in a greater dissolved organic carbon (DOC) degradation rate and lower absorption spectral slope and heterotrophic bacterial growth rate than incubation with Pro-exudate, suggesting that Pro-vDOM was more bioavailable than Pro-exudate. In addition, the stimulated microbial community succession trajectories were significantly different between the Pro-exudate and Pro-vDOM treatments, indicating that viral lysates play an important role in shaping the heterotrophic bacterial community. Our study demonstrated that viral lysis altered the chemical composition and biological availability of DOM derived from Prochlorococcus, which is the numerically dominant phytoplankton in the oligotrophic ocean.IMPORTANCE The unicellular picocyanobacterium Prochlorococcus is the numerically dominant phytoplankton in the oligotrophic ocean, contributing to the vast majority of marine primary production. Prochlorococcus releases a significant fraction of fixed organic matter into the surrounding environment and supports a vital portion of heterotrophic bacterial activity. Viral lysis is an important biomass loss process of Prochlorococcus However, little is known about whether and how viral lysis affects Prochlorococcus-released dissolved organic matter (DOM). Our paper shows that viral infection alters the optical properties (such as the absorption coefficients, spectral slopes, and fluorescence intensities) of released DOM and might contribute to a humic-like DOM pool and carbon sequestration in the ocean. Meanwhile, viral lysis also releases various intracellular labile DOM, including amino acids, protein-like DOM, and lower-molecular-weight DOM, increases the bioavailability of DOM, and shapes the successive trajectory of the heterotrophic bacterial community. Our study highlights the importance of viruses in impacting the DOM quality in the ocean.

As a key intermediate in the nitrogen cycle, nitrite is involved in multiple biological pathways that regulate the distribution and availability of nitrogen in the ocean. In the oligotrophic gyres, nitrite accumulates near the base of the euphotic zone, demonstrating a subsurface maximum, termed the primary nitrite maximum; while in subpolar regions, nitrite concentrations are elevated in the near‐surface ocean. As yet, the mechanisms controlling this meridional pattern remain unclear. Here, we present vertically resolved profiles of rates of nitrite production and consumption extending from the Subtropical Gyre to the Subarctic Front in the North Pacific Ocean. Our results indicate that the latitudinal distributions of nitrite across this basin are influenced by variations in phytoplankton‐nitrifier interactions. In the well‐lit oligotrophic surface, phytoplankton dominates rapid nitrite cycling via coupled release and re‐assimilation; below the euphotic zone, diminished light stress on nitrite oxidizers results in rapid turnover and limits nitrite. By contrast, in subpolar regions where nitrate concentrations are elevated in the euphotic zone, nitrite is released during assimilative nitrate reduction and competition between phytoplankton and nitrifiers for ammonium is relaxed, facilitating ammonia oxidation. These processes, together with differential light sensitivities of ammonia and nitrite oxidizers, allow net accumulation of nitrite. Furthermore, we demonstrate a substantial contribution of urea oxidation in forming the primary nitrite maximum and balancing the two steps of marine nitrification. Our findings reveal physical‐biological interactive controls on nitrite cycling and distributions in the ocean and help disentangle the complex effect of phytoplankton‐microbe interactions on marine nitrogen biogeochemistry.

The advective supply of allochthonous dissolved organic carbon (DOC) from open ocean to marginal seas through western boundary current intrusion influences the regional carbon inventory and microbial activities. However, there is limited observation about this process and its biogeochemical impacts on marginal seas. In this study, we investigated the biodegradation of allochthonous DOC carried by the intrusion of the Kuroshio Current into South China Sea (SCS). Using an isopycnal mixing model, the exchange and biodegradation processes of Kuroshio-intruded DOC were quantified. We estimated that approximately 10% of the surface DOC was remineralized due to the enhanced biodegradation in the SCS. This result was supported by the on-deck bioassay experiments that were conducted under different environmental contexts. The results of modeling and on-deck incubations indicate that DOC biodegradation was enhanced by the sharp gradient of environment factors, including nutrients supply, microbial species, and bio-lability of DOC in the frontal zone during the surface water mass mixing. The amount of carbon released from the enhanced DOC degradation by Kuroshio intrusion was estimated to be approximately equal to 8.6 Tg C yr(-1). Concomitantly, the amount of nitrogen released could contribute 0.19-0.70 mmol N m(-2) d(-1) to the surface of SCS which is comparable to the total supply from deeper water and nitrogen fixation in surface waters. This study suggests that the enhanced biodegradation of DOC during the western boundary currents intrusion could serve as an important sink of oceanic DOC, and thus provide an additional nutrient source to marginal seas.

Elucidating the chemical structure of dissolved organic matter (DOM) is key to understanding this large yet enigmatic carbon pool. Over the last two decades much progress has been made in assigning exceptionally accurate molecular formulas of DOM owing to the application of ultrahigh resolution mass spectrometry, but little is known about the number of isomers in each molecular formula, a question essentially related to the total number of organic molecules in DOM. Such information is critical for a further understanding of the formation and long-term stability of refractory DOM in the ocean. In this work, we used ion mobility quadrupole time of flight liquid chromatography tandem mass spectrometry (IM Q-TOF LC/MS/MS) to analyze DOM samples collected in different aquatic environments including south Texas rivers, Gulf of Mexico, and South China Sea. Our data showed that generally less than 23% of all detected DOM formulas, which shared a small fraction of common molecules (ca. 12%) detected by direct-infusion Fourier transform ion cyclotron resonance MS, contained structurally distinct isomers (represented by "isomer clusters"). In addition, isomer diversity, in terms of how different the structures are, decreased with degradation in both natural and incubation samples. Specifically, the number of structurally distinct isomers was lower at river mouth and open ocean than coastal waters, where organic matter tends to be fresher due to high primary production; and with depth in water column, isomer diversity of DOM also decreased. Results from a set of incubation experiments also showed that the percentages of riverine DOM molecules that have multiple isomer clusters decreased with time, suggesting that biodegradation decreases the diversity of molecules from an isomer perspective. Overall, these results suggested that isomers, at least in a certain fraction of DOM, are highly constrained, and that degradation decreases its isomeric diversity. (C) 2021 Elsevier Ltd. All rights reserved.

Nitrogen (N), as a critical element for microbial metabolisms, recycles rapidly in the euphotic ocean. Oxidation by nitrifiers is a competing pathway for phytoplankton assimilation of regenerated N (NH4+ and urea). Sharing the overlapping substrates may result in competitive exclusion, thus, niche separation for the two assemblages. Both pathways are sensitive to light, but whether light intensity will intensify or alleviate such resource competition in the euphotic zone remains poorly explored in the field at the community level. By using N-15 labeling techniques, paired kinetic responses of uptake and oxidation were conducted in single bottles under manipulated light intensities for both NH4+ and urea. We found light stimulated the maximum rate (R-m) and specific affinities (alpha(U)) of both NH4+ and urea uptake. In contrast, light effects were opposite for oxidation kinetics (R-m and alpha(O)). As irradiance increased, the rapid increase in alpha(U) and concomitant decrease in alpha(O) imply a distinctive competition advantage of photosynthetic organisms over oxidizers under substrate-limited environments. The ratio of alpha(U)/alpha(O) for NH4+ ranged from 0.8 to 3089 (5.8-46,788 for urea) showing a distinct increasing pattern as ambient light increases, demonstrating that phytoplankton overwhelms nitrifiers throughout the oligotrophic euphotic zone, driving down concentrations and maintaining short turnover times of the two regenerated N substrates. Moreover, phytoplankton relied equally on NH4+ and urea; yet, nitrifiers preferred NH4+ to urea. In the nitrate-depleted euphotic ocean, light acts as a crucial driver for utilization pathways of regenerated N and vertical niche separation.