An official website of the United States government
Abstract Photolysis of dissolved organic matter using high‐intensity, ultraviolet (UV) light has been utilized since the 1960s as a method for the oxidation and subsequent quantification of dissolved organic nitrogen and phosphorus (DON and DOP) in both freshwater and marine water. However, conventional UV systems yielded variable and sometimes unreliable results; consequently, the method fell out of favor throughout much of the oceanographic community. Researchers turned to other oxidation methods such as persulfate oxidation or high‐temperature combustion, even though they have difficulty when DON and DOP are <10% of the total dissolved N and P (for example, in the deep sea and in surface waters at high latitudes). Here, we revive the UV oxidation method using modernized light‐generating equipment and high‐precision colorimetric analysis of the oxidation products, resulting in the most well‐constrained full ocean depth profiles of DON and DOP that are available to date. At Station ALOHA, in the North Pacific Subtropical Gyre, in the depth range of 900–4800 m, we find that DON is 2.2 ± 0.2μmol L−1(n = 49), DOP is 0.049 ± 0.004μmol L−1(n = 19), and the DOC : DON : DOP molar stochiometric relationship is 759 : 45 : 1. Preliminary estimates for the global ocean inventories of refractory DON and DOP are placed at 43.6 Pg N and 2.14 Pg P.
more »
« less
Regionally Variable Contribution of Dissolved Organic Phosphorus to Marine Annual Net Community Production
Abstract Marine dissolved organic phosphorus (DOP) serves as an organic nutrient to marine autotrophs, sustaining a portion of annual net community production (ANCP). Numerical models of ocean circulation and biogeochemistry have diagnosed the magnitude of this process at regional to global scales but have thus far been validated against DOP observations concentrated within the Atlantic basin. Here we assimilate a new marine DOP data set with global coverage to optimize an inverse model of the ocean phosphorus cycle to investigate the regionally variable role of marine DOP utilization by autotrophs contributing to ANCP. We find ∼25% of ANCP accumulates as DOP with a regionally variable pattern ranging from 8% to 50% across nine biomes investigated. Estimated mean surface ocean DOP lifetimes of ∼0.5–2 years allow for transport of DOP from regions of net production to net consumption in subtropical gyres. Globally, DOP utilization by autotrophs sustains ∼14% (0.9 Pg C yr−1) of ANCP with regional contributions as large as ∼75% within the oligotrophic North Atlantic and North Pacific. Shallow export and remineralization of DOP within the ocean subtropics contributes ∼30%–80% of phosphate regeneration within the upper thermocline (<300 m). These shallow isopycnals beneath the subtropical gyres harboring the preponderance of remineralized DOP outcrop near the poleward edge of each gyre, which when combined with subsequent lateral transport equatorward by Ekman convergence, provide a shallow overturning loop retaining phosphorus within the subtropical biome, likely helping to sustain gyre ANCP over multiannual to decadal timescales.
more »
« less
- PAR ID:
- 10384514
- Publisher / Repository:
- DOI PREFIX: 10.1029
- Date Published:
- Journal Name:
- Global Biogeochemical Cycles
- Volume:
- 36
- Issue:
- 12
- ISSN:
- 0886-6236
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
More Like this
-
-
Significant rates of export production and nitrogen fixation occur in oligotrophic gyres in spite of low inorganic nutrient concentrations in surface waters. Prior work suggests that dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) are important nutrient sources when inorganic nutrients are scarce. In particular, DOP has been shown to be an important P source for diazotrophs, which may be better suited to using low concentrations of organic vs. inorganic P. Prior modeling work has also suggested that DOP is important for supporting export production in oligotrophic gyres. However, validation of such models is limited by the number of upper ocean DOP concentration measurements, especially in the South Pacific and Indian Oceans. Here, we present measurements of DOP concentration from the 2016 GO-SHIP I08S and I09N meridional transect in Eastern Indian Ocean, and DON and DOP concentration measurements from the 2017 GO-SHIP P06 zonal transect in the subtropical South Pacific Ocean. Together with DOC and DON concentration measurements from prior occupations of the same GO-SHIP lines we evaluated changes in euphotic zone DOC:DON:DOP stoichiometry. Stoichiometry changes across these two transects are used to infer regions of preferential DON and/or DOP production and consumption. Specifically, north of 36 S in the Indian Ocean an increase in DOC:DON and DOC:DOP concentration ratios, from 11:1 to 14:1 and 118:1 to 190:1, respectively, are observed. Similarly, west of 136 W in the South Pacific Ocean significant increases in DOC:DOP and DON:DOP concentration ratios are observed, from 224:1 to 398:1 and 21:1 to 39:1, respectively. These stoichiometric shifts in upper ocean DOC:DON:DOP concentration ratios are considered in the context of ocean circulation, especially upwelling patterns in the Indian and eastern Pacific Oceans, as well as prior observations of the distribution of nitrogen fixation, especially in the western tropical South Pacific.more » « less
-
Abstract Surface ocean marine dissolved organic matter (DOM) serves as an important reservoir of carbon (C), nitrogen (N), and phosphorus (P) in the global ocean, and is produced and consumed by both autotrophic and heterotrophic communities. While prior work has described distributions of dissolved organic carbon (DOC) and nitrogen (DON) concentrations, our understanding of DOC:DON:DOP stoichiometry in the global surface ocean has been limited by the availability of DOP concentration measurements. Here, we estimate mean surface ocean bulk and semi‐labile DOC:DON:DOP stoichiometry in biogeochemically and geographically defined regions using newly available marine DOM concentration databases. Global mean surface ocean bulk (C:N:P = 387:26:1) and semi‐labile (C:N:P = 179:20:1) DOM stoichiometries are higher than Redfield stoichiometry, with semi‐labile DOM stoichiometry similar to that of global mean surface ocean particulate organic matter (C:N:P = 160:21:1) reported in a recent compilation. DOM stoichiometry varies across ocean basins, ranging from 251:17:1 to 638:43:1 for bulk and 83:15:1 to 414:49:1 for semi‐labile DOM C:N:P, respectively. Surface ocean DOP concentration exhibits larger relative changes than DOC and DON, driving surface ocean gradients in DOC:DON:DOP stoichiometry. Inferred autotrophic consumption of DOP helps explain intra‐ and inter‐basin patterns of marine DOM C:N:P stoichiometry, with regional patterns of water column denitrification and iron supply influencing the biogeochemical conditions favoring DOP use as an organic nutrient. Specifically, surface ocean marine DOM exhibits increasingly P‐depleted stoichiometries from east to west in the Pacific and from south to north in the Atlantic, consistent with patterns of increasing P stress and alleviated iron stress.more » « less
-
null (Ed.)Dissolved organic phosphorus (DOP) has a dual role in the surface ocean as both a product of primary production and as an organic nutrient fueling primary production and nitrogen Fixation, especially in oligotrophic gyres. Though poorly constrained, understanding the geographic distribution and environmental controls of surface ocean DOP concentration is critical to estimating distributions and rates of primary production and nitrogen Fixation in the global ocean. Here we pair DOP concentration measurements with a metric of phosphate (PO43-) stress (P*), satellite-based chlorophyll a concentrations, and iron stress estimates to explore their relationship with upper 50 m DOP stocks. Our results show that PO43- and iron stress work together to control surface DOP concentrations at basin scales. SpeciFcally, upper 50 m DOP stocks decrease with increasing phosphate stress, while alleviated iron stress leads to either surface DOP accumulation or loss depending on PO43- availability. Our work suggests an interdependence between DOP concentration, inorganic nutrient ratios, and iron availability, and establishes a predictive framework for DOP distributions in the global surface ocean.more » « less
-
Abstract A mechanistic understanding of dissolved organic phosphorus (DOP) utilization, and its role in the marine P cycle, requires knowledge of DOP molecular composition. In this study, a recently developed approach coupling electrodialysis and reverse osmosis with solution31P‐NMR analysis was used to examine DOP composition within a tidally dominated salt‐marsh estuary (North Inlet, South Carolina) over seasonal and tidal time frames. The isolation technique allowed for near complete recovery of the DOP pool (90% ± 13%;n= 12) with six broad compound classes quantified: phosphonates, phosphomonoesters, phosphodiesters, pyrophosphate, di‐ and tri‐phosphate nucleotides (nucleoPα), and polyphosphate. Our results indicate that phosphomonoesters (ca. 61%) and phosphodiesters (ca. 31%) comprise the majority of the DOP pool, with relatively small contributions from pyrophosphates (ca. 4%), phosphonates (ca. 2%), nucleoPα(ca. 1%), and polyphosphates (ca. 1%). The study found no significant differences in DOP composition or concentration between tidal stages, despite significant tidal changes in dissolved organic nitrogen (DON):DOP stoichiometry. Significant seasonal variation was observed, with higher concentrations of phosphonates, nucleoPα, and monophosphates and lower phosphomonoester concentrations in Fall relative to all other seasons. We hypothesize that these seasonal variations reflect the balance between specific compound class seasonal production, lability, and local P demands associated with marine vs. terrestrial sources. Our results indicate that DOP composition exists at a dynamic equilibrium that is strongly conserved across diverse marine environments.more » « less
