Remineralization Of Phosphorus Research Articles

Preferential remineralization of phosphorus from organic matter in river-dominated coastal sediments

In coastal sediments characterized by substantial terrestrial input, the Redfield ratio may not be adequate to determine whether phosphorus (P) is preferentially remineralized relative to carbon (C). Employing a two end-member δ13C mixing model, we observed a gradual decrease in the fraction of terrestrial organic matter as the distance from the river mouth increased. Consequently, the C/P ratio of sedimentary organic matter before early diagenetic alteration (Cu/Pu) decreased from 213 ± 26 to 126 ± 4. In contrast, the C/P ratio of sedimentary organic matter after early diagenetic alteration (Corg/Porg) increased from 208 ± 32 to 265 ± 23. The deviation of Corg/Porg ratios from Cu/Pu ratios suggests that P was preferentially remineralized from organic matter relative to C. Moreover, the degree of preferential remineralization (DPR) of P, represented by (Corg/Porg)/(Cu/Pu), increased with the distance from the river mouth, suggesting a connection to cross-shelf transport. Besides preferential P remineralization, the control mechanisms for P regeneration from sediments strongly depend on the dissolved oxygen (DO) levels of bottom water. Under oxygenated bottom water (DO >120 μM), the precipitation of Fe oxides reduced benthic DIP flux, resulting in a C/P ratio in flux well above the Cu/Pu ratio (1813 ± 725 vs. 213 ± 26). Conversely, when bottom water DO was low (DO<100 μM), the dissolution of Fe oxides and preferential P remineralization increased DIP fluxes, but the precipitation of authigenic apatite suppressed DIP fluxes, leading to C/P ratios in flux approximating Cu/Pu ratios (129 ± 35 vs. 158 ± 10 and 200 ± 82 vs. 141 ± 7). In a moderate redox state (100 < DO <120 μM), preferential P remineralization and the dissolution of Fe oxides increased DIP fluxes, resulting in C/P ratios in flux below Cu/Pu ratios (29 ± 8 vs. 131 ± 5 and 15 ± 6 vs. 126 ± 4).

Genome-resolved metagenomic analysis of Great Amazon Reef System sponge-associated Latescibacterota bacteria and their potential contributions to the host sponge and reef

The Great Amazon Reef System (GARS) is an extensive biogenic reef influenced by a plume layer of sediments. This creates an extreme environment where light is reduced, thus affecting physicochemical properties as well as living organisms such as sponges and their microbiomes. The sponge’s microbiome has numerous ecological roles, like participation in biogeochemical cycles and host nutrition, helping the sponge thrive and contributing to the ecosystem. Also, sponges and sponge-associated microorganisms are rich sources of bioactive compounds, and their products are applied in different areas, including textile, pharmaceutical, and food industries. In this context, metagenome-assembled genomes (MAG), obtained from GARS sponges microbiota, were analyzed to predict their ecological function and were prospected for biotechnological features. Thus, in this work, tissues of GARS sponges were collected, their metagenomes were sequenced and assembled, and 1,054 MAGs were recovered. Ten of those MAGs were selected based on their taxonomic classification in the candidate phylum Latescibacterota and this group’s abundance in GARS sponges. The workflow consisted of MAG’s quality definition, taxonomic classification, metabolic reconstruction, and search for bioactive compounds. Metabolic reconstruction from medium to high-quality MAGs revealed genes related to degradation and synthesis pathways, indicating functions that may be performed by GARS sponge-associated Latescibacterota. Heterotrophy, a recurring attribute in Latescibacterota that might be crucial for GARS sponge holobiont nutrition, was verified by the presence of genes related to respiration and fermentation. Also, the analyzed bacteria may contribute to the host’s survival in multiple ways, including host protection via defense systems; aid in nutrient consumption by breaking complex substrates and producing essential nutrients like vitamins and certain amino acids; and detoxification of mercury, arsenic, ammonia, and hydrogen sulfide. Additionally, genes linked to persistent organic pollutant degradation, including glyphosate, and biogeochemical cycles reactions, such as ammonification, sulfate reduction, thiosulfate disproportionation, phosphorus remineralization, and complex organic matter degradation, were identified, suggesting the participation of these Latescibacterota in bioremediation and nutrient cycling. Finally, the investigated MAGs contain genes for numerous bioactive compounds, including industrial enzymes, secondary metabolites, and biologically active peptides, which may have biotechnological value.

Research progress of CPP-ACP promoting enamel remineralization

With the improvement of people's living standards and the strengthening of awareness of caries prevention and control, enamel remineralization has received extensive attention. Fluoride is a commonly used remineralization agent in clinic and life, but its remineralization process depends on calcium and phosphorus ions in saliva. Therefore, several new remineralizers have been introduced to supplement and improve the repair ability of fluoride to dental minerals, such as bioactive glass, nano hydroxyapatite, casein phosphopeptide amorphous calcium phosphate (CPP-ACP), which can promote enamel remineralization to a certain extent. Casein phosphopeptide amorphous calcium phosphate (CPP-ACP), derived from milk, is a stable calcium phosphorus remineralization system, which can be used in the minimally invasive treatment of early enamel caries, and has attracted much attention in recent years. In this paper, the structure of CPP-ACP, the mechanism of remineralization and related research progress are systematically reviewed and summarized, so as to provide reference for basic research and clinical application.

Impact of River Damming on Downstream Hydrology and Hydrochemistry: The Case of Lower Nestos River Catchment (NE. Greece)

In this paper, a series of field surveys were carried out along the Nestos River watershed (NE Greece) to assess the influence of two hydropower dams (Thissavros and Platanovrisi) upon the hydrology, hydrochemistry and nutrients stoichiometry of the river. Results showed that Nestos hydrology, downstream of the reservoirs, is entirely governed by the man-induced hydropower-driven dam retention/release policy. Dams’ operation increased the retention of dissolved inorganic nitrogen (DIN) and total suspended solids (TSS) significantly, affecting their downstream fluxes, even under water release regime. On the contrary, dams’ construction and operation did not seem to influence the downstream fluxes of dissolved inorganic phosphorus (DIP) and silica (DSi), although these elements also depended on the releasing policy. DIN retention, combined with the dependence of DIP to the water level of Thissavros, resulted in alteration of the N:P ratio at the downstream part. Almost all nutrients were stored at the bottom layer of Thissavros reservoir, especially under the summer stratification regime. Platanovrisi reservoir acts as a buffer zone between Thissavros and the Nestos downstream part. Anoxic conditions in the reservoirs favour the transformation of nitrates into ammonia and the remineralization of phosphorus from sediments, creating a degraded environment for freshwater fauna.

Phosphogenesis, aragonite fan formation and seafloor environments following the Marinoan glaciation

Carbonates in the Sete Lagoas Formation (São Francisco craton, Brazil) preserve a record of chemical, biological, and oceanographic changes that occurred during the Ediacaran Period. The base of this formation constitutes a post-glacial cap carbonate, which contains seafloor precipitates (carbonate and barite crystal fans) as well as various authigenic and diagenetic minerals (apatite, pyrite, and barite). Here, we present petrographic and geochemical data on this unit, and discuss the significance of its mineral association for marine environments following the Marinoan (‘Snowball Earth’) glaciation. For the first time, we report well-developed apatitic cements in a Neoproterozoic cap carbonate. Isopachous and intergranular void-filling cements encrust and surround seafloor-precipitated fan crystals that precipitated as aragonite. We propose a model for the origin of this mineral association, which relates phosphogenesis and aragonite fan formation to a single set of environmental conditions. According to this model, the boundary between oxic and anoxic conditions was located at or just below the sediment-water interface. Burial of iron (oxyhydr)oxides below this boundary liberated phosphate to pore water and provided fuel for iron reduction. Iron reduction released Fe2+, which inhibited nucleation of carbonate and allowed for aragonite growth on the seafloor. Concurrently, ‘iron-pumping’ shuttled phosphate from the water column to the sediment, and perhaps in conjunction with organic phosphorus remineralization via anaerobic microbial pathways, created conditions conducive to phosphate mineralization. This model corroborates the hypotheses that aragonite crystal fan formation requires the presence of an inhibitor to carbonate nucleation, in addition to high alkalinity, and that Fe2+ serves as this inhibitor. Overall, our work documents a close association between aragonite crystal fan formation and phosphogenesis at the beginning of the Ediacaran, illuminates the paleoenvironments of cap carbonates with seafloor precipitates, and contributes to understanding of phosphogenesis following low latitude glaciations.

Evidence for Coupling of the Carbon and Phosphorus Biogeochemical Cycles in Freshwater Microbial Communities

Considerable attention has been given to the roles of the carbon and phosphate cycles in aquatic environments, but less attention has been given to an experimental analysis of the coupling of the C and P cycles in freshwater and marine ecosystems. Using laboratory microcosm experiments, prepared with natural pond-water microbial communities, evidence is presented for the coupling of dissolved organic C with microbial production of alkaline phosphatase driving the phosphorus cycle in freshwater microbial communities. The effects of glucose C-supplementation in microcosm microbial communities (including bacteria and heterotrophic nanoflagellates) on gains in microbial C-content and alkaline phosphatase activity (APA) were estimated in relation to control microcosms without C-supplementation. The C-supplementation increased total microbial APA (pmol min-1 µg-1 bacterial C) in the C-supplemented treatment (6.5 ± 0.6) compared to the non-supplemented cultures (5.1 ± 1.7). Microbial-bound APA in the C-supplemented treatment was particularly enhanced (4.4 ± 0.9) compared to control cultures (1.3 ± 0.8), but the amount of free (soluble) APA in the aquatic phase was less compared to the controls (n = 5, p < 0.001). Alkaline phosphatase activity was highly correlated (r = 0.97) with bacterial densities in the C-supplemented cultures, further supporting the hypothesis that C-supplementation can increase phosphorus remineralization through elevated production of microbial alkaline phosphatase. This laboratory-based, experimental study suggests that additional research on the coupling of the C and P cycles in freshwater and marine environments may yield productive insights into the finer details of the roles of these two biogeochemical cycles in aquatic microbial community dynamics.

Macro-nutrient concentrations in Antarctic pack ice: Overall patterns and overlooked processes

Antarctic pack ice is inhabited by a diverse and active microbial community reliant on nutrients for growth. Seeking patterns and overlooked processes, we performed a large-scale compilation of macro-nutrient data (hereafter termed nutrients) in Antarctic pack ice (306 ice-cores collected from 19 research cruises). Dissolved inorganic nitrogen and silicic acid concentrations change with time, as expected from a seasonally productive ecosystem. In winter, salinity-normalized nitrate and silicic acid concentrations (C*) in sea ice are close to seawater concentrations (Cw), indicating little or no biological activity. In spring, nitrate and silicic acid concentrations become partially depleted with respect to seawater (C* &amp;lt; Cw), commensurate with the seasonal build-up of ice microalgae promoted by increased insolation. Stronger and earlier nitrate than silicic acid consumption suggests that a significant fraction of the primary productivity in sea ice is sustained by flagellates. By both consuming and producing ammonium and nitrite, the microbial community maintains these nutrients at relatively low concentrations in spring. With the decrease in insolation beginning in late summer, dissolved inorganic nitrogen and silicic acid concentrations increase, indicating imbalance between their production (increasing or unchanged) and consumption (decreasing) in sea ice. Unlike the depleted concentrations of both nitrate and silicic acid from spring to summer, phosphate accumulates in sea ice (C* &amp;gt; Cw). The phosphate excess could be explained by a greater allocation to phosphorus-rich biomolecules during ice algal blooms coupled with convective loss of excess dissolved nitrogen, preferential remineralization of phosphorus, and/or phosphate adsorption onto metal-organic complexes. Ammonium also appears to be efficiently adsorbed onto organic matter, with likely consequences to nitrogen mobility and availability. This dataset supports the view that the sea ice microbial community is highly efficient at processing nutrients but with a dynamic quite different from that in oceanic surface waters calling for focused future investigations.

An Introduction to Marine Sediments with an Emphasis on Sediment Organic Matter Remineralization

SummaryThe processes occurring in the upper several meters of marine sediments have a profound effect on the local and global cycling of many elements. For example, the balance between organic carbon preservation and remineralization in sediments represents the key link between carbon cycling in active, surface reservoirs in the oceans, atmosphere, and on land, and carbon that cycles on much longer, geological time scales, i.e., in sedimentary rock, and in coal and petroleum deposits. Understanding processes occurring in surficial marine sediment is also important in the accurate interpretation of paleoceanographic sediment records, since sediment processes can sometimes significantly alter the primary “depositional” signal recorded in the sediments. In coastal and estuarine sediments nitrogen and phosphorus remineralization in the sediments can provide a significant fraction of the nutrients required by primary producers in the water column. Similarly, in coastal and estuarine sediments subjected to elevated anthropogenic inputs of certain toxic metals, sediment processes affect the extent to which these sediments represent “permanent” versus “temporary” sinks for these metals.The geochemistry of marine sediments is controlled by both the composition of the material initially deposited in the sediments and the chemical, biological or physical processes that affect this material after its deposition. These processes fall within the general category of what is commonly referred to as early diagenesis. One very crucial aspect of the study of early diagenesis in marine sediments is that the oxidation, or remineralization, of organic matter deposited in the sediments is either the direct or indirect causative agent for many of these early diagenetic changes. Given this pivotal role that organic matter remineralization plays in many early diagenetic processes, significant efforts have gone into understanding and quantifying these processes.This lecture provides a brief introduction to marine sediment geochemistry focusing on the basic controls on organic matter remineralization in sediments. It is based on a lecture I recently gave to an undergraduate geology class in stratigraphy. I believe that it could also be useful in an undergraduate class in general oceanography, low temperature geochemistry or environmental geochemistry.Lecture summaryThe geochemistry of marine sediments is controlled by both the composition of the material initially deposited in the sediments and the chemical, biological or physical processes that affect this material after its deposition. These processes fall within the general category of what is commonly referred to as early diagenesis. One key aspect of the study of early diagenesis in marine sediments is that the oxidation, or remineralization, of sediment organic matter is either the direct or indirect causative agent for many early diagenetic changes.Given the pivotal role that organic matter remineralization plays in early diagenetic processes, significant efforts have gone into understanding and quantifying these processes. This lecture provides a brief introduction to marine sediment geochemistry, focusing on the basic controls of organic matter remineralization in sediments. I believe that the lecture could be useful in an undergraduate class in general oceanography, low temperature geochemistry or environmental geochemistry. It could also be useful in introductory graduate classes in these latter two areas.

TAPHONOMY OF CAMBRIAN PHOSPHATIC SMALL SHELLY FOSSILS

Small shelly fossils are preserved as apatite steinkerns in the Cambrian Series 2–3 Thorntonia Limestone, Australia. Petrological observations indicate that phosphorus delivered to Thorntonia sediment was remobilized before precipitating in microenvironments defined by the matrix-filled interiors of small, mostly conical skeletons. A previous geochemical study concluded that both organic matter and iron oxides sourced phosphorus to Thorntonia sediments, and that anoxia governed phosphorus remobilization within the sediment column. This contribution asks: What factors allowed for the selective preservation of skeleton interiors, and what biases result from this preservation? We find that small shells physically trapped phosphorus-laden pore waters, creating local conditions where kinetic barriers to apatite precipitation could be overcome. Only a subset of Thorntonia Limestone skeletons is preserved by apatite, showing evidence of selectivity with respect to shell size, shape, and orientation. Both the biological and physical factors that govern phosphorus remineralization and precipitation have changed through time, accounting for the opening and closing of the Ediacaran-Cambrian phosphatization taphonomic window. The opening of this window may have required a global increase in phosphate delivery to the oceans.

Invasive fishes generate biogeochemical hotspots in a nutrient-limited system.

Fishes can play important functional roles in the nutrient dynamics of freshwater systems. Aggregating fishes have the potential to generate areas of increased biogeochemical activity, or hotspots, in streams and rivers. Many of the studies documenting the functional role of fishes in nutrient dynamics have focused on native fish species; however, introduced fishes may restructure nutrient storage and cycling freshwater systems as they can attain high population densities in novel environments. The purpose of this study was to examine the impact of a non-native catfish (Loricariidae: Pterygoplichthys) on nitrogen and phosphorus remineralization and estimate whether large aggregations of these fish generate measurable biogeochemical hotspots within nutrient-limited ecosystems. Loricariids formed large aggregations during daylight hours and dispersed throughout the stream during evening hours to graze benthic habitats. Excretion rates of phosphorus were twice as great during nighttime hours when fishes were actively feeding; however, there was no diel pattern in nitrogen excretion rates. Our results indicate that spatially heterogeneous aggregations of loricariids can significantly elevate dissolved nutrient concentrations via excretion relative to ambient nitrogen and phosphorus concentrations during daylight hours, creating biogeochemical hotspots and potentially altering nutrient dynamics in invaded systems.

The marine phosphorus cycle

The marine phosphorus cycle

The role of shelf nutrients on glacial‐interglacial CO2: A negative feedback

In the past 800 thousand years and before industrialization, the largest variations in atmospheric CO2 concentration (pCO2) occurred in connection with the glacial cycles that characterized Earth's climate over this period. One curious feature of at least the last four glacial‐interglacial cycles is that atmospheric pCO2 reached about the same upper limit of 280 ppm during peak interglacial periods and about the same lower limit of 180 ppm during peak glacial periods. Here, we show using a numerical model of earth system that enhanced shelf sediment weathering during glacial sea level lowstands tends to raise pCO2 even after carbonate compensation and thus stabilize pCO2 from further reduction. This is because not all nutrients from weathering will be utilized by biology but more importantly because the spatial distributions of carbon and phosphorus from weathering become decoupled in such a way that carbon is preferentially stored in the upper ocean and phosphorus in the deep ocean. In addition, the C:P ratios in continental margin sediments are generally much higher than the Redfield ratio due to preferential remineralization of phosphorus in shelf sediment diagenesis. When these factors are accounted for in our model, the input of organic matter, which corresponds to the observed negative shift in ocean δ13C during glacial periods, raises pCO2 by approximately 14 ppm. The same mechanisms operating in the opposite directions during interglacial highstand tend to lower pCO2 and stabilize it from further increase. The impact of sea level‐driven continental shelf exposure and submersion of CO2 is therefore a negative feedback that may have contributed to limiting the variation of Pleistocene pCO2 to the observed 100 ppm range.

On nitrogen fixation and preferential remineralization of phosphorus

Regional and global nitrogen fixation rates are often estimated from geochemical tracers related to N* (= NO3− − 16PO43−). However the patterns of this tracer reflect the influence of numerous processes including nitrogen fixation, denitrification, remineralization of organic matter, variable stoichiometry, atmospheric deposition and physical transport. Here we have used idealized models to illustrate how preferential remineralization of organic phosphorous may explain observed features of N* distribution in the North Atlantic Ocean, including a subsurface maximum and an increased temporal variability in the mid‐thermocline. If preferential remineralization of phosphorus is key in shaping the oceanic distribution of N*, published estimates of nitrogen fixation may be underestimating the marine nitrogen fixation rate by as much as a factor of three.

Sargasso Sea phosphorus biogeochemistry: an important role for dissolved organic phosphorus (DOP)

Abstract. Inorganic phosphorus (SRP) concentrations in the subtropical North Atlantic are some of the lowest in the global ocean and have been hypothesized to constrain primary production. Based upon data from several transect cruises in this region, it has been hypothesized that dissolved organic phosphorus (DOP) supports a significant fraction of primary production in the subtropical North Atlantic. In this study, a time-series of phosphorus biogeochemistry is presented for the Bermuda Atlantic Time-series Study site, including rates of phosphorus export. Most parameters have a seasonal pattern, although year-over-year variability in the seasonal pattern is substantial, likely due to differences in external forcing. Suspended particulate phosphorus exhibits a seasonal maximum during the spring bloom, despite the absence of a seasonal peak in SRP. However, DOP concentrations are at an annual maximum prior to the winter/spring bloom and decline over the course of the spring bloom while whole community alkaline phosphatase activities are highest. As a result of DOP bioavailability, the growth of particles during the spring bloom occurs in Redfield proportions, though particles exported from the euphotic zone show rapid and significant remineralization of phosphorus within the first 50 m below the euphotic zone. Based upon DOP data from transect cruises in this region, the southward cross gyral flux of DOP is estimated to support ~25% of annual primary production and ~100% of phosphorus export. These estimates are consistent with other research in the subtropical North Atlantic and reinforce the hypothesis that while the subtropics may be phosphorus stressed (a physiological response to low inorganic phosphorus), utilization of the DOP pool allows production and accumulation of microbial biomass at Redfield proportions.

Modeling the impact of iron and phosphorus limitations on nitrogen fixation in the Atlantic Ocean

Abstract. The overarching goal of this study is to simulate subsurface N* (sensu, Gruber and Sarmiento, 1997; GS97) anomaly patterns in the North Atlantic Ocean and determine the basin wide rates of N2-fixation that are required to do so. We present results from a new Atlantic implementation of a coupled physical-biogeochemical model that includes an explicit, dynamic representation of N2-fixation with light, nitrogen, phosphorus and iron limitations, and variable stoichiometric ratios. The model is able to reproduce nitrogen, phosphorus and iron concentration variability to first order. The latter is achieved by incorporating iron deposition directly into the model's detrital iron compartment which allows the model to reproduce sharp near surface gradients in dissolved iron concentration off the west coast of Africa and deep dissolved iron concentrations that have been observed in recent observational studies. The model can reproduce the large scale N* anomaly patterns but requires relatively high rates of surface nitrogen fixation to do so (1.8×1012 moles N yr−1 from 10° N–30° N, 3.4×1012 moles N yr−1 from 25° S–65° N). In the model the surface nitrogen fixation rate patterns are not co-located with subsurface gradients in N*. Rather, the fixed nitrogen is advected away from its source prior to generating a subsurface N* anomaly. Changes in the phosphorus remineralization rate (relative to nitrogen) linearly determine the surface nitrogen fixation rate because they change the degree of phosphorus limitation, which is the dominant limitation in the Atlantic in the model. Phosphorus remineralization rate must be increased by about a factor of 2 (relative to nitrogen) in order to generate subsurface N* anomalies that are comparable to the observations. We conclude that N2-fixation rate estimates for the Atlantic (and globally) may need to be revised upward, which will help resolve imbalances in the global nitrogen budget suggested by Codispoti et al. (2001) and Codispoti (2007).

Presence and regulation of alkaline phosphatase activity in eukaryotic phytoplankton from the coastal ocean: Implications for dissolved organic phosphorus remineralization

The biologically important constituents of the dissolved organic phosphorus (DOP) pool, their bioavailability, and their cycling in coastal systems are still poorly understood. Here we use the enzyme alkaline phosphatase as a metric of DOP bioavailability and track the activity of this enzyme in a coastal system. We observed alkaline phosphatase activity (APA) in the >0.2-μm size fraction of all surface samples tested during an Oregon coast cruise in August 2001. Although there was not a significant trend between APA and phosphate concentration in the data set as a whole, chlorophyll a-normalized APA was elevated at the station with the lowest dissolved inorganic phosphate (DIP) concentration. Activity was also elevated in nutrient-addition experiments in which nitrate amendments were Used to force community drawdown of DIP. These data are consistent with phosphate regulation of APA. A cell-specific APA assay revealed that the percentage of diatoms with APA mimicked the trend in the hydrolytic rate, but such a trend was not observed for the dinoflagellates. Further, the percentage of dinoflagellate cells with APA was routinely higher than the percentage of diatom cells with activity. In nutrient-addition experiments designed to evaluate the regulation of APA, diatom taxa expressed APA less frequently than dinoflagellates, but they displayed a tighter regulation of the activity by DIP than dinoflagellates. The variability observed in the presence and regulation of APA in these eukaryotic phytoplankton indicates that DOP bioavailability is a potential driver of phytoplankton nutrition and species composition in the coastal ocean.

Net community production in terms of C, N, P and Si in the Antarctic Circumpolar Current and its influence on regional water mass characteristics

The net impact of biological production and regeneration (Net Community Production) on surface water dissolved inorganic carbon, nitrogen, phosphorus, and silica (NCP DIC, NCP DIN, NCP PO 4 , and NCP Si ( OH ) 4 , respectively) were evaluated from nutrient data collected in the Antarctic Circumpolar Current (ACC) along 170°W between October 1997 and March 1998. Budgets were constructed in zonal bands that subdivided the ACC into a southern, seasonally ice-covered region, and three northern, and increasingly less stratified regions. Frontal positions, air–sea gas exchange, divergent Ekman flow, and meridional nutrient gradients were tracked through time to isolate biological change. The budget resolved the southerly progression of peak productivity with time in conjunction with the retreating ice-edge and the change from a production-dominated to a respiration-dominated system. Seasonal values of NCP DIC, NCP DIN, NCP PO 4 , NCP Si ( OH ) 4 from north of the Antarctic Polar Front (APF) to the South Antarctic Circumpolar Front (SACCF) along 170°W averaged 2.6, 0.27, 0.02, and 1.9 mol m −2, respectively. The influx of atmospheric CO 2 was a significant component (20–38%) of NCP DIC and varied from 6.8 to 12.8 g C m −2 season −1 across the region because of high winds in the north, and large surface pCO 2 deficits in the south. Although seasonal NCP DIC was fairly uniform across the region, NCP DIN was about 1.5 x greater, and NCP Si ( OH ) 4 was 2 x greater south of the APF compared to north of it. The present zonal pattern of NCP Si ( OH ) 4 differs from that suggested previously, in that we estimate greater production north of the APF and near the SACCF and relatively less just south of the APF, mainly because of the inclusion of a seasonally variable horizontal flux in the present analysis. In each sub-region, peak rates of NCP DIN and NCP PO 4 preceded those of NCP DIC and NCP Si ( OH ) 4 . Peak diatom growth periods exhibited NCP DIN / NCP PO 4 ratios (11–14) well below Redfield values. In addition, more rapid remineralization of phosphorus, and to a lesser extend nitrogen, as compared to carbon and silica were apparent late in the season. Increases in the NCP Si ( OH ) 4 / NCP DIN ratio through time were consistent with intensifying iron limitation south of the APF. The inter-nutrient comparisons highlight the functional differences among nutrient fluxes, in that, nutrients with relatively low surface remineralization like silicic acid are dependent on meridional transport to replenish surface pools, while surface pools of rapidly recycled nutrients, such as phosphate, can be replenished mainly by vertical mixing in winter. We suggest that biological processes in the Pacific ACC region play an important role in lowering the N/P ratio of the Antarctic Intermediate Water (AAIW).

Sea bottom anoxia in the Archipelago Sea, northern Baltic Sea—Implications for phosphorus remineralization at the sediment surface

The effects of the hydrophysical environment on oxygen conditions and P remineralization at sediment surface were studied in the Archipelago Sea, northern Baltic Sea. At 94 sites, the water column was profiled for conductivity, temperature and oxygen, and the topmost sediment was collected for P and C fractions and (oxy)hydroxide Fe analysis. The near-bottom water and sediment parameters as well as visual observations on the vertical colour distribution in the sediment cores were used to statistically classify the sediment surfaces into oxic, anoxic and suboxic (fluctuating oxygen conditions) bottoms. The anoxic bottoms occurred in the basins with water depths less than 47 m, and the suboxic bottoms were most common in the basins with depths between 20–60 m, while the oxic bottoms dominated in the depths over 60 m. It was concluded that the preferential development of oxygen deficiency in the shallow basins results from the combined effects of complex topography and seasonal temperature stratification on both vertical and lateral bottom water exchange. In the anoxic bottoms, C / P ratios suggest enhanced release of P compared to the oxic and suboxic bottoms. In the suboxic bottoms, high inorganic P concentrations and the strong coupling between P and Fe suggest active transformation of organic P to the inorganic P phases, probably due to the fluctuating oxygen conditions. Differences in the spatial distribution of the P, C and Fe were insignificant except for detrital P, which decreased seawards.

Laboratory study of nitrogen and phosphorus remineralization during the decomposition of coastal plankton and seston

The decomposition of cultured marine phytoplankton ( Skeletonema costatum) and natural estuarine seston from Narragansett Bay, RI, was studied at two temperatures (8°C and 18°C) in bottles containing sterile bay-water (30‰) and in bay-water with micro-organisms small enough to pass through a glass fibre filter (nominally < 1μ). About 50% of the particulate organic nitrogen (PON) and particulate phosphorus (PP) was immediately released to the water in dissolved organic forms from both types of organic matter. Comparison of changes in the dissolved organic nitrogen (DON) fraction in the sterile and non-sterile systems indicated that nearly all of the DON initially released was subsequently remineralized. Ammonification proceeded only in non-sterile bay-water. 20–25% of the PP was converted to dissolved inorganic-P (DIP) fraction after only 7 h in both sterile and non-sterile bay-water. Following autolytic releases of DON, DOP and DIP the initial rates of N and P remineralization were temperature dependent: Q 10 values for PON and PP decay during first phase of microbially mediated decomposition ranged from 1·3 to 6·4. Rates of remineralization then slowed so that about equal amounts of nutrients were remineralized (45–50% of the N and 57–60% of the P in the phytoplankton and 60–63% of the N and 36–60% of the P in the natural seston) after 30 days storage at either temperature. During 30 days of decomposition in non-sterile seawater the N P ratios in the dissolved inorganic fractions converged on the ratios of total-N/total-P initially present in the bottles. Kinetic analysis of the decay of total organic-N (TON) and total organic-P (TOP) in the non-sterile systems and analysis of similar sets found in the literature showed that the initial stages of the decomposition of N and P from planktonic POM in vitro could be modelled as the sequential decay, at first-order rates, of two particulate fractions. The first, more labile, fraction comprised about 60% of the particulate N and P. First-order rate constants (− k, base e) for decomposition during the 1st and 2nd phases were 0·02 to 0·2 day −1 and 0·003 to 0·02 day −1, respectively. The decay rates are far too slow to account for the ‘rapid in situ recycling’ of nutrients needed to support phytoplankton production when other means of nutrient resupply (by advection, fixation, rainfall, etc.) are very low.

Systems and organismal aspects of phosphorus remineralization

During a six-month study at Lake George, N.Y., zooplankton contributed an average of 19.4% of the phosphate required for algal photosynthesis. Values ranged from 44.1% prior to the unimodal phytoplankton pulse to 4.6% during the phytoplankton bloom. Copepods accounted for a large percentage (21–68%) of the SRP recycled during the growing season examined, whereas, the cladocera provided only a small percentage of remineralization (6.9%).