The free amino acid composition of seawater obtained without desalting and preconcentration

A conventional amino acid analyzer was modified to allow detection of dissolved free amino acids in a direct injection of 0.5 to 2.0 ml of seawater. The amino acids were monitored fluorimetrically by reaction with o-phthaldialdehyde after column chromatography. The accuracies of two commonly employed desalting methods, cation exchange resin and copper Chelex, were determined by comparison with the direct injection method. After correcting the results of the desalting methods for the procedural blank and recovery rate for each individual amino acid, the amino acid compositions on a mole percent basis as determined by these methods resembled approximately the true composition determined by direct injection. However, on an absolute basis the cation resin method overestimates and the copper Chelex method underestimates the total amount of dissolved free amino acids. The reasons for these discrepancies are discussed. Using the direct injection method, the spectra of dissolved free amino acids in surface seawater samples from different locations were determined. As opposed to the relatively uniform patterns reported in most past investigations, the amino acid spectra found were highly variable. In a number of samples, the acidic amino acids dominated the spectra. Valine was also high in many samples. In a depth profile the deep samples were dominated by arginine. Application of the method to real-time shipboard analyses of dissolved free amino acids is discussed.     

Determination of dissolved nucleic acids in seawater by the fluorescence dye, ethidium bromide

A new method for the determination of dissolved double-stranded deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) in seawater was developed, evaluated and used to study the fates of these nucleic acids in marine ecosystems. These nucleic acids, which were pre-concentrated on a hydroxyapatite column, were determined fluorometrically by the use of ethidium bromide dye, which binds specifically to the double-stranded polynucleotide. No dissolved organic matter coexisting in the pre-concentrated sample solution interfered in the analysis of DNA and RNA. Column recoveries of DNA and RNA in a sample volume of up to 11 were 93% and 97%, respectively, and 90% of both at 51. The detection limits of DNA and RNA concentrated from a 51 sample by this fluorometric method were 0.6 and 1.1 μg l⁻¹, respectively. The concentration of dissolved nucleic acids in the waters from Tokyo Bay and Sagami Bay showed great variation in space and time. DNA ranged from 1 to 32 μg l⁻¹, and RNA from below the detection limit to 34 μg l⁻¹. The total amount of phosphorus in nucleic acids was an important fraction (12.9 ± 8.2%) of the dissolved organic phosphorus (DOP) and showed a good correlation with DOP.     

The amino acid composition of estuarine colloidal material

Amino acids were determined in estuarine colloidal and particulate material from near surface waters ranging from fresh to brackish water (12 g kg^?1 salinity). The hydrolizable amino acids and associated ammonia account for an average of 80% of the nitrogen present in colloidal samples, and approximately 75% of the nitrogen from particulate fractions of the same samples. The relative proportions of these amino acids are similar to those of a cultured estuarine diatom. There are no significant amounts of D amino acids, or non-protein amino acids characteristic of bacteria in sediments and soil. A single deep-water sample (25 m) shows some evidence of bottom mud resuspension by the presence of a possible aspartic acid-hydroxyproline dimer.     

Composition and bacterial utilization of free amino acids in tropical mangrove sediments

The composition and bacterial utilization of dissolved free amino acids (DFAA) in tropical mangrove sediments was examined. Amino acid concentrations (300–900 ng total DFAA ml⁻¹) and composition were similar to that of other organic-rich, anaerobic sediments with lowest and highest concentrations in the low and mid intertidal zones, respectively. The non-protein amino acid, β-glutamic acid, rarely reported in previous studies, was found as a major component of the interstitial DFAA pool. Intracellular amino acids from some cultured strains of sulphate-reducing bacteria (e.g. Desulfobacter app) showed the presence of β-glutamic acid as a major cellular constituent suggesting that these bacteria may be a source of this amino acid in mangrove pore waters. In high intertidal sediments, bacterial growth rates (μ) correlated significantly with total DFAA concentrations with depth.Amino acid concentrations and composition differed significantly between sediments and overlying tidal waters. Flux chamber experiments showed negligible amino acid flux out of the sediments in untreated chambers, but rates of amino acid flux ranged from 27 to 69 mgN m⁻² day⁻¹ (= 81–207 mg C.m⁻² day⁻¹) in chambers where poisons were applied to the sediment surface. Such fluxes could account for between 9–38% and 5–19% of the nitrogen and carbon required to support the levels of bacterial productivity measured in surface (0–1 cm) sediments. These experiments suggest that bacterial populations in surface sediments are capable of utilizing all of the amino acid flux to the sediment-water interface in tropical mangroves.     

Variations of particulate proteins and dissolved amino acids in coastal seawater

The relationships existing between the protein-containing fraction of particulate matter and amino acids dissolved in seawater were studied in the Gulf of Marseille at different periods of the year. The concentration of particulate proteins was almost zero in February and attained maximum values during April and May, the average concentrations of dissolved amino acids (total) varied between 900 and 1200 nmole l^?1 but larger variations were encountered at the surface and in the vicinity of the sediment. The influence of meteorological conditions and the effect of the sediment on the distribution of nitrogenous substances were taken into account. Combined dissolved amino acids were more abundant than free dissolved amino acids in 90% of the cases. The concentrations of dissolved amino acids observed in a zone bordering the North Mediterranean are comparable to those found in other regions of the world.     

Tracing dissolved organic matter cycling in the eastern boundary of the temperate North Atlantic using absorption and fluorescence spectroscopy

Apparent oxygen utilization (AOU), dissolved organic carbon (DOC), coloured dissolved organic matter (CDOM) absorption spectra, and CDOM fluorescence characteristic of aromatic amino acids (excitation/emission 280 nm/320 nm; F(280/320)) and marine-humic like substances (320 nm/410 nm; F(320/410)) were measured in full depth during a cruise in the temperate Eastern North Atlantic (ENA). An optimum multi-parameter (OMP) inverse method was run to calculate water mass proportion-weighted average (archetypal) concentrations of these chemical parameters for all water masses and samples. Archetypal concentrations retain the variability due to water mass mixing and basin scale mineralization from the water mass formation sites to the study area. Conversely, the difference between measured and archetypal concentrations, retain the variability due to dissimilarities in mineralization processes within the study area. Our analysis indicates that DOC supported 26±3% of the AOU in the dark temperate ENA and that basin scale processes occurring at and from the formation area of the water masses explained 63% of the total DOC variability. Our data also suggests that DOC remineralized at the basin scale was of lower molecular weight, and with a lower proportion of fluorescent aromatic amino acids than found within the study area. The relationship between the absorption coefficient at 254 nm (a_CDOM(254)) and AOU indicates that a_CDOM(254) was consumed during organic matter remineralization in the dark ocean, with 55% of the variability being explained by basin scale processes. The relationships of F(320/410) with AOU and DOC confirmed that marine humic-like substances are produced by microbial degradation processes, at a rate of 6.1±0.9×10⁻³ mg equivalents of QS mol AOU⁻¹. Our results also indicate that basin-scale remineralization processes account for 85% of the total variability of F(320/410), emphasizing that large scale processes control the formation of humic-like substance in the dark ENA.     

Measurement of krypton-85 in the ocean

To measure ⁸⁵Kr in the ocean, methods have been developed to extract gases from large volumes of water, to isolate trace quantities of krypton from these extracted gases, and to measure low levels of ⁸⁵Kr radioactivity. Gases are extracted with an efficiency of 91% by a continuous flow, vacuum extraction technique which operates at a water flow rate of 7 l min⁻¹. Typically, 4 l of gas are extracted from a 250-l seawater sample. Using a combination of chemical reactions and gas chromatography, approximately 20 μl of krypton and 100 ml of argon are isolated from a 4-l gas sample, with recoveries in excess of 95 and 99%. ⁸⁵Kr radioactivity is measured with miniature gas proportional counters (1 ml volume). The counting efficiency ranges from 63 to 70% and the counter background ranges from 0.03 to 0.06 cpm. The minimum detectable amount of ⁸⁵Kr is 0.4 dpm/ml Kr and the precision for surface water samples is ± 4%. The dynamic range of the measurement is approximately 100.     

Anaerobic metabolism in lagoon sediments from Davies Reef,Great Barrier Reef

Sulphate reduction rates were measured in the lagoon sediments at Davies Reef, on the Great Barrier Reef, Australia. Sulphate reduction rates averaged 0·622 mmol sulphate m⁻² day⁻¹, over the 0–12 cm depth of sediment, compared to an average heterotrophic oxygen uptake rate by the sediment of 27 mmol oxygen m⁻² day⁻¹. Thus sulphate reduction to acid-volatile sulphide appeared to account for only about 5% of the total organic matter degradation, although the proportion may be greater if sulphate reduction to tin-reducible sulphide was taken into account. Although dissolved sulphate concentration in the sediment pore water was that of sea water, a large excess (equivalent to about 0·8% of the sediment dry weight) of precipitated sulphate was present in the sediment. This excess could not be attributed to precipitated strontium sulphate, and there was no exchange between the dissolved and precipitated sulphate. Methane formation in these superficial sediments was not detectable.     

Fate modeling of nonylphenol ethoxylates and their metabolites in the Dutch Scheldt and Rhine estuaries: validation with new field data

The environmental behavior of nonylphenol ethoxylates (A₉PEO) in the Rhine and Scheldt estuaries (The Netherlands) was investigated using a hydrodynamic advection-dispersion fate model (ECoS 3). The model was validated with the results of field studies, in which A₉PEO as well as the metabolites nonylphenoxy ethoxy acetic acids (A₉PEC) and nonylphenol (NP) were analyzed in sediment, water and suspended particulate material (SPM) samples using LC–MS methods. Maximum actual concentrations observed in surface sediments were 620, 560 and 1100 ng g⁻¹ d.w. for A₉PEO, A₉PEC and NP, respectively. In the dissolved phase, maximum observed concentrations amounted to 1100 ng L⁻¹ (A₉PEO), 6500 ng L⁻¹ (A₉PEC) and 960 ng L⁻¹ (NP). Clear spatial trends were observed for dissolved A₉PEO and metabolites in the Scheldt estuary, with decreasing concentrations going downstream. This concentration decrease was steeper than for conservatively behaving compounds. This trend was not visible in the Rhine estuary. The fate model was applied to A₉PEO and metabolites in both estuaries. Transport of chemicals in the water column was considered as a longitudinal one-dimensional process through a number of estuary segments. For the Rhine estuary, to cope with the stratification observed, a model structure was chosen consisting of two water layers above each other, between which exchange was possible. Sedimentation/erosion processes were included in the model. A biodegradation scheme was incorporated, and rates were adjusted to fit the calculated concentration profiles with the actual profiles of both A₉PEO and its metabolites. In this way, field biodegradation rates for A₉PEO, A₉PEC and NP could be derived, which were in agreement with values from literature. The measured dissolved concentration profiles as well as salinity and concentrations of SPM could be described successfully by the model. The concentrations calculated in SPM and sediment were of the same order of magnitude as the actual concentrations. In the Rhine estuary, additional sources of A₉PEO had to be included to account for the relatively high concentrations in the middle of the estuary. The fate model for the Scheldt estuary could be slightly improved by using salinity-dependent biodegradation rates. A sensitivity analysis of the model showed that in the Scheldt estuary, the environmental process with the strongest influence on the dissolved concentration profiles of A₉PEO and metabolites is biodegradation. In the Rhine estuary, the water residence time is too short for significant biodegradation to occur, and in this estuary the dissolved concentration profiles were mainly influenced by the additional A₉PEO sources.     

239,240Pu in estuarine and shelf waters of the north-eastern United States

The distribution of ^239,240Pu between dissolved and particulate forms has been measured in four estuaries on the north-east coast of the United States (Connecticut River, Delaware Bay, Chesapeake Bay, and Mullica River). The data cover the whole salinity range from freshwater input to shelf waters at 35‰ and includes one profile from a nearly anoxic basin in the Chesapeake Bay.In the organic-rich Mullica River estuary, large-scale removal of riverine dissolved ^239,240Pu occurs at low salinities due to salt-induced coagulation, a mechanism analogous to that for iron and humic acids. Within the 0 to 25–30‰ zone in the other three estuaries, the activity of dissolved ^239,240Pu increases almost conservatively. The activities of particulate ^239,240Pu are highest in the more turbid waters of low salinity regime (0–15‰), but become increasingly insignificant with respect to dissolved ^239,240Pu as salinities increase. At higher salinities corresponding to shelf water, there is a sharp increase in dissolved ^239,240Pu activity. The dissolved ^239,240Pu activity within each estuary appears to be inversely related to the flushing time of water. For example, Chesapeake Bay has a 6–12 month flushing time and has much lower dissolved ^239,240Pu activities than does the Connecticut River Estuary which has a flushing time of a few days. This and other data from the shelf waters are interpreted as indicating that the sharp decrease in dissolved ^239,240Pu activities between shelf and estuarine waters is driven by removal within the estuaries themselves rather than on the shelf.Dissolved ^239,240Pu activities are lower in the nearly-anoxic bottom waters of Chesapeake Bay indicating enhanced removal by redox transformation of Pu [i.e., Pu(V) to Pu(IV)].     

Rapid, high-precision potentiometric titration of alkalinity in ocean and sediment pore waters

A system for rapid, high precision potentiometric determination of alkalinity in sea water and sediment pore water is presented. Two titration units were used: a 40 ml unit for seawater and a small volume unit for sediment pore water. Titration time was normally less than 10 minutes per sample, including sample exchange. With a 40 ml sample volume, the relative standard deviation of the alkalinity obtained in the laboratory was 0.05% and at sea 0.1 %. The small-volume system (0.5–1.5 ml) gave a precision of 0.07%. Five titration points, in two groups after the second equivalence point, were used to evaluate the equivalence volume. Results from equilibrium calculations and computer simulated alkalinity titrations show that it was possible to use a non-modified Gran function [(V₀ +v)^*10^(E/Z)] and still achieve good accuracy and precision.     

Composition and flux of particulate amino acids and chloropigments in equatorial Pacific seawater and sediments

Compositions and fluxes of amino acids and major chloropigments were measured in the central equatorial Pacific Ocean as part of the US JGOFS EqPac program. Fluxes decreased by several orders of magnitude, from 400 to 0.03 mg amino acid m⁻² d⁻¹ and from 9 mg to 0.0004 μg chloropigment m⁻² d⁻¹, between production in the surface waters and accumulation at the sea floor. Most rapid losses were in surface waters and at the sediment interface. Losses from the mid-water column were as great as those in surface waters or at the sediment interface, but occurred over a much greater depth range. Export flux estimates based on floating sediment traps were higher near the equator and decreased poleward, similar to primary production.Little meridional difference was apparent in composition of either amino acids or pigments in exported material over the 24° of latitude sampled in spite of the large (factor of 5–6) difference in fluxes. However, pigment composition changed dramatically with depth in the water column, and considerable diagenesis occurred before particles reached the sediment. Pigment compositions suggest that suspended particles were more degraded in the northern than in the southern hemisphere, possibly due to differences in food chain structure. Compositional changes in amino acids occurred in the water column, but were most noticeable at the sediment–seawater interface. Increases in the relative proportions of aspartic acid and glycine with depth were more consistent with preferential preservation within the particulate matrix than with any inherent stability of these compounds to heterotrophic consumption. The contribution of amino acids and pigments to total organic carbon clearly shows that selective degradation of organic matter occurs with depth; this is not evident from total organic carbon data alone. Amino acids contributed about a quarter of the total organic carbon (OC) in surface waters and 16% of the OC in sediment; pigments decreased from 1% of total OC in surface waters to <0.001% in sediments. Decreases in the contribution of amino acids to total organic carbon may be due to transformation into uncharacterizeable material as well as to respiration.     

Variations of dissolved organic matter during a plankton bloom: qualitative aspects,based on sugar and amino acid analyses

Water samples collected during a spring plankton bloom in the northern North Sea were investigated for dissolved organic carbon (DOC), total dissolved sugars (TDS) and dissolved amino acids (TDAA). Their concentrations varied in the range of 0.6 to >4 mg 1^?1 for DOC, 40—400 γg 1^?1 for TDS and 100—850γg 1^?1 for TDAA. TDS and TDAA contributed to less than 20% of the DOC, but showed variations independent of each other. Changes in the efficiency of heterotrophic utilization and its selectivity seem to have caused these variations. These, together with differences in the sources of dissolved organic matter — phytoplankton and detrital materials — were also reflected in the qualitative composition of TDS and TDAA in the water column. In the TDS fraction glucose and mannose showed maxima during the phytoplankton bloom and galactose, rhamnose, xylose, arabinose and fucose after it. Glutamic acid registered maximum in the early stages of the phytoplankton bloom, histidine towards its end and aspartic acid, glycine, alanine and lysine after it. Serine was present in large amounts throughout the investigated time interval. The results of the present study are discussed in the light of previously published data on the formation and utilization of dissolved organic matter in the sea.     

长江口海域水文环境要素分布及溶解氧垂向输运

本文基于2016年长江口海域(舟山绿华山)的连续观测数据,分析了该海域水文环境要素分布,并估算了溶解氧跨跃层垂向输运。本次观测发现,水体的温度、盐度和溶解氧剖面具有明显的分层结构,三者跃层具有相同的变化趋势且主要受潮流变化影响。通过计算,得到跃层浮性频率的平方(N2)在10–3—10–2/s2之间,剪切的平方(S2)介于10–5—10–2/s2。潮流活动会激发水体剪切不稳定促进水体中溶解氧的垂向交换。最后,采用简化的一维溶解氧垂向输运模型,得到观测周期内跨跃层输运的溶解氧的含量为4.75mmol/(m2·d),佐证层化是长江口海域出现氧亏损现象的主要原因之一。     

Characterization of the proteinaceous matter in marine aerosols

Marine aerosols play a dominant role in the transfer of oceanic material to the atmosphere. Most marine aerosol originates when air bubbles burst at the sea surface ejecting material from the sea surface microlayer and bubble surface layers into the air. Concentrations of chemical compounds in these surface layers often differ from their concentrations in bulk water. We examined the enrichment of aerosols with proteinaceous matter and attempted to characterize the physical nature and sources of this matter. We measured concentrations of dissolved free (DFAA), dissolved combined (DCAA), and particulate (PAA) amino acids, transparent stainable particles (TSP), and bacteria and virus-like particles as carriers of protein, in natural and simulated aerosols. We also evaluated D/L ratios certain amino acids in all amino acid fractions.DFAA and DCAA enriched the aerosols we sampled by 1.2–20 times compared to bulk seawater; PAA enrichment was usually higher (up to 50-fold). Aerosols contained particles typical of seawater, e.g., microorganisms, organic debris, inorganic particles with adsorbed organic matter, but also a large number of semitransparent gel-like particles, which all contained amino acids. Some of these particles were probably scavenged from bulk water, but new particles produced as bubbles burst at the surface comprised at least 10% of total proteinaceous matter in the aerosol. D/L ratios of certain amino acid suggested that the particles were most likely made from dissolved polymers secreted by phytoplankton that were concentrated on bubble surfaces and in the microlayer. Examination with Alcian Blue (a dye that targets carbohydrates) and Coomassie Blue (a dye that targets proteins) showed that most TSP in the aerosols contained both proteins and polysaccharides. Microorganisms enriched the aerosols by up to two orders of magnitude, but contributed less than 4% to the total protein pool.     

Dissolved carbohydrates in seawater. II,A spectrophotometric procedure for total carbohydrate analysis and polysaccharide estimation

A procedure is described which adds a hydrolysis step to the Johnson and Sieburth 3-methyl-2-benzothiazolinone hydrazone hydrochloride (MBTH) assay for total dissolved monosaccharides. The advantages of the monosaccharide test are retained in the total carbohydrate test, giving nearly equivalent responses for a variety of combined carbohydrates. A total sample of 50 ml is adequate for both total carbohydrate and monosaccharide assays which permit the estimation of polysaccharide by difference. Values for Narragansett Bay and adjacent waters ranged from 452 to 2023 μg l^?1 for total dissolved carbohydrate, 272 to 1353 μg l^?1 for polysaccharide, and 153 to 814 μg l^?1 for monosaccharide, which accounted for 6–18%, 4–13%, and 2–5% of the total dissolved carbon, respectively. We suggest that this is a sensitive and precise procedure which will be useful for investigating the distribution of dissolved carbohydrates in seawater and factors which affect its production, distribution and utilization.     

Determination of copper complexation with natural organic ligands in seawater by equilibration with MnO2 II. Experimental procedures and application to surface seawater

The MnO₂ adsorption method combined with voltammetry is proposed for the direct determination of metal complexation in seawater of various salinities as a more satisfactory alternative to direct voltammetric measurements and bioassay methods. A small quantity of MnO₂ is equilibrated with copper ions in filtered seawater. Natural organic ligands in the seawater compete for copper with the MnO₂. Total dissolved copper is measured by differential pulse anodic stripping voltammetry after filtration and acidification of the sample. Preconcentration of natural water samples is unnecessary and measurement is performed at the natural equilibrium pH of the aerated sample. The analytical limit of detection of the method depends on contamination from the filtration step, and for copper complexation a ligand concentration of 5 × 10^?8 M was obtained. The sensitivity can be increased by use of radioisotopes as tracers. The method is very versatile in that complexation of various metals may be determined by any analytical method that measures total dissolved metal concentrations. Neither organic ligands nor their complexes with copper adsorb on the MnO₂ at pH8, but at pH 1.8 MnO₂ is an efficient scavenger for electroactive organic material.Samples of surface water from the Irish Sea and the Atlantic Ocean were found to contain ligand concentrations of 1.7 × 10^?7 and 1.1 × 10^?7 M, with conditional stability constants (log values) of 9.84 ± 0.13 and 9.86 ± 0.23, respectively, at pH 8.0.     

Enrichment of organochlorine contaminants in the sea surface microlayer: An organic carbon-driven process

Over 50 seawater samples from two different sites—Barcelona (Spain) and Banyuls-sur-Mer (France)—were analyzed in order to study the extent and postulate the processes driving the enrichment of hydrophobic organic pollutants in the sea surface microlayer (SML). A number of individual polychlorinated biphenyl (PCB) congeners (41) were measured to study their partitioning between the particulate (fraction > 0.7 μm) and the dissolved + colloidal phases (fraction < 0.7 μm), with the latter being differentiated into estimated dissolved and colloidal phases. In addition, several organochlorine pesticides were also measured, namely, HCB, α-HCH, γ-HCH, 4,4′-DDE, 4,4′-DDD and 4,4′-DDT. The presence of PCB congener profiles found in the SML suggests a dynamic coupling with the atmosphere in Banyuls sampling site, whereas offshore Barcelona the presence of highly chlorinated congeners was due to persistent sediment resuspension. The average PCB concentration in the SML dissolved + colloidal phase were higher in Banyuls (7.8 ng L^{− 1}) than in Barcelona (3.6 ng L^{− 1}) samples, but in the particulate phase concentrations were higher in Barcelona (3.2 ng L^{− 1}) to that of Banyuls (1.4 ng L^{− 1}). However, PCB concentrations in the SML generally also showed large variability. Enrichment factors of PCBs and other organochlorine compounds in the SML with respect to the underlying water column ranged from 0.2 to 7.4. This may be explained for both the dissolved + colloidal and particulate phases by the enrichment in the SML of organic carbon (OC) as discerned from particle–water and colloid–water partitioning.     

A note on the Japan Sea Proper Water

The water under the main thermocline in the Japan Sea is a single water mass referred to as the Japan Sea Proper Water. It can be defined as having temperature below 2.0°C, salinity above 34.00%, and dissolved oxygen below 7.0 ml 1⁻¹. In the north most of the water above the potential temperature 0.1°C depth (about 800–1000 m) is a mode water, with σ_θ of 27.32 to 27.34 kg m⁻³. North of 40°N it has high oxygen (more than 6.00 ml 1⁻¹) with a distinct discontinuity (oxygen-cline) at the bottom of the mode water. The most probable region for the formation of the water is the area north of 41°N between 132° and 134°E. The deeper water probably is formed in the norther area of 43°N, and directly fills the main part of the Japan Basin north of 41°N and east of 134°E.     

Seasonal trends in the abundance, composition and bioavailability of particulate and dissolved organic matter in the Chukchi/Beaufort Seas and western Canada Basin

The objectives of this study were to investigate the seasonality, abundance, sources and bioreactivity of organic matter in the water column of the western Arctic Ocean. The concentrations of particulate and dissolved amino acids and amino sugars, as well as bulk properties of particulate and dissolved organic matter (DOM), were measured in shelf, slope and basin waters collected during the spring and summer of 2002. Particulate organic matter concentrations in shelf waters increased by a factor of 10 between spring and summer. Dissolved organic carbon (DOC) and nitrogen (DON) concentrations exhibited only minor seasonal variations, whereas dissolved amino acid concentrations doubled between spring and summer, and dissolved amino sugars increased by 31% in shelf waters of the Chukchi and Beaufort Seas. Concentrations of DOC did not exhibit a significant seasonal change in surface waters of the Canada Basin, but dissolved amino acid concentrations increased by 45% between spring and summer. No significant seasonal differences were detected in the concentration or composition of DOM in waters below 100 m in depth. Concentrations of particulate and dissolved amino acids and amino sugars were strongly correlated with chlorophyll-a, indicating a plankton source of freshly produced organic matter. The amino acid and amino sugar compositions of freshly produced DOM indicated that a large portion of this material is bioavailable. While freshly produced DOM was found to be relatively bioreactive, preformed DOM in the Arctic appears to be less bioreactive but similar in degradation state to average DOM in the Atlantic and Pacific. These data demonstrate substantial summer production of POM and DOM on the Chukchi and Beaufort shelves that is available for utilization in shelf waters and export to the Canada Basin.