Concentrations and elemental stoichiometry of suspended particulate organic carbon, nitrogen, phosphorus, and oxygen demand for respiration (C:N:P:−O2) play a vital role in characterizing and quantifying marine elemental cycles. Here, we present Version 2 of the Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN) dataset. Version 1 is a previously published dataset of particulate organic matter from 70 different studies between 1971 and 2010, while Version 2 is comprised of data collected from recent cruises between 2011 and 2020. The combined GO-POPCORN dataset contains 2673 paired surface POC/N/P measurements from 70°S to 73°N across all major ocean basins at high spatial resolution. Version 2 also includes 965 measurements of oxygen demand for organic carbon respiration. This new dataset can help validate and calibrate the next generation of global ocean biogeochemical models with flexible elemental stoichiometry. We expect that incorporating variable C:N:P:-O2 into models will help improve our estimates of key ocean biogeochemical fluxes such as carbon export, nitrogen fixation, and organic matter remineralization.
|Measurement(s)||particulate matter • particulate carbon oxygen demand • particulate phosphorus|
|Technology Type(s)||elemental analyzer • potassium dichromate • ash-hydrolysis|
|Factor Type(s)||location • period|
|Sample Characteristic - Environment||ocean|
|Sample Characteristic - Location||global|
Background & Summary
The elemental ratio between carbon (C), nitrogen (N), phosphorus (P), and oxygen (O2) demand for respiration is a fundamental quantity that couples nutrient uptake by primary producers, organic carbon export, and remineralization1,2,3. Most ocean biogeochemical models from the pre-CMIP6 era have exclusively used the fixed canonical Redfield C:N:P and respiration quotient -O2:C of 106:16:1 and 1, respectively, to link nutrient uptake and convert to and from organic carbon. However, it is now widely accepted in the oceanographic community that C:N:P:-O2 in the surface ocean are variable through space and time. Previous global compilation studies4,5 have shown that C:P and N:P are systematically higher than the Redfield ratios of 106:1 and 16:1 in the nutrient-deplete subtropical gyres, lower in the nutrient-rich subpolar and polar regions, and approximately equal to the Redfield values in the tropical and upwelling regions. The respiration quotient of particulate organic matter (POM) in terms of -O2:C and -O2:P has also been shown to be spatially variable through direct observations and inverse modeling6,7,8. In light of these recent observations, our understanding of the oceanic ecosystem elemental stoichiometry has evolved rapidly over the last ten years.
Here we present Version 2 (“v2”) of the Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN) dataset (Fig. 1). We refer to Version 1 (“v1”) as a previously published data compilation9, in which POC/N/P was collated from 70 cruises and time-series between 1971 and 2010. Version 1 has served multiple purposes, such as calibration and validation of ocean biogeochemical models, including those used in the latest coupled model intercomparison project (CMIP6)10,11,12, and identifying drivers of global-scale spatiotemporal variability in C:N:P13,14. However, several limitations of GO-POPCORN v1 were identified. First, there was a significant bias towards regions of frequent oceanographic research, leading to samples being concentrated in the North Atlantic, Eastern North Pacific Ocean, Mediterranean Ocean, and near the Palmer Station in the Southern Ocean (Fig. 1). Second, aggregated data samples were collected using different techniques, such as differing blank measurements and detection limits. Third, a large proportion of measurements came from time-series studies at a fixed geographical location: Hawaiian Ocean Time-series (HOT), Bermuda Atlantic Time-series Study (BATS), and CARIACO Ocean Time-series program.
GO-POPCORN v2 is a new compendium of global POC/N/P collected between 2011 and 2020 as part of Bio-GO-SHIP (the Biological initiative for the Global Ocean Ship-based Hydrographic Investigations Program)15,16 and the Arctic Integrated Ecosystem Research Program (IERP)17. The v2 dataset contains 2581 paired measurements (of which 2093 measurements are from the surface ocean) of POC/N/P and 965 measurements of particulate chemical oxygen demand (PCOD), which is the oxygen needed for full respiration of organic carbon7. The new version has a comprehensive geographic range, and the samples were collected across all major oceanic regions from 70°S to 73°N (Fig. 2) across 2188 stations using a consistent methodology and quality control (Table 1).
Median C:N:P for paired surface POM samples from GO-POPCORN v1 and v2 are 140:19:1 and 136:21:1, respectively (Fig. 3). The data spread is noticeably smaller in v2 compared to v1. Specifically, the interquartile range (IQR) in v2 is reduced by a factor of 2–3 compared to that of v1 (IQR of C:P, N:P, C:N in versions 1 and 2 are [103, 13, 2] and [43, 6, 1], respectively). About 90% of observed C:P and N:P from v2 are above the Redfield ratios of 106 and 16, respectively (Fig. 3a,b). This contrasts with v1, where only 75% of samples collected have C:P and N:P above the Redfield ratios. In both versions, the observed mode for C:N is around the Redfield C:N of 6.7, but values are more tightly clustered around 5–8 in v2 (Fig. 3c). The median -O2:C from v2 is 1.14, with an IQR of 0.17 (Fig. 3d). Thus, surface organic matter is generally more reduced than pure carbohydrate, with a respiration quotient of 1 (i.e., Redfield -O2:C)18,19. In summary, both the quantity and the quality of the data have significantly improved in v2 over v1.
GO-POPCORN v1 is an exhaustive compilation of POM collected by 70 independent studies and cruises from 1971 to 2010. Refer to the original description paper9 for more details on how the v1 dataset was compiled.
GO-POPCORN v2 comprises samples from 12 recent cruises between 2011 and 2020 (Table 1). These sampling efforts have been supported by GO-SHIP (C13.520, I07N21, I09N22, and P1823), SOCCOM and Plymouth Marine Laboratory Atlantic Meridional Transect (AMT-2824), National Science Foundation Dimensions of Biodiversity (AE131925, BVAL4626, NH141827), and North Pacific Research Board Arctic Integrated Ecosystem Research Program (OS170128, OS190128, SKQ201709S29, SKQ201813S29).
The POM samples were collected and analyzed using the consistent sampling method described previously30,31,32,33. Briefly, 3–8 L seawater was collected from the flow-through underway system or CTD. Samples from underway systems were filtered using 30 µm nylon mesh to remove large particles from the sample. Samples were then collected on GF/F filters (Whatman, nominal pore size 0.7 µm) that were precombusted at 500 °C for 5 h to remove any traces of inorganic carbon as well as organic contaminants. Whenever possible, POC, PON, and POP were sampled in triplicate, and PCOD was sampled in sextuplicate. Triplicate sampling occurred hourly in cruises AMT-28 and I07N; every 4 hours for C13.5, I09N, and P18; and once a day for AE1319, BVAL46, NH1418, OS1701, OS1901, SKQ201709S, and SKQ201813S. Differences in the sample collection are based on differences in the hypotheses being tested. For example, hourly sampling in AMT-28 and I07N is aimed toward capturing the diurnal changes in elemental stoichiometry34.
POC and PON samples were measured using a CN Flash 1112 EA or 240-XA/440-XA elemental analyzer and were calibrated using a known quantity of atropine (C17H23NO3). Inorganic carbonates were removed using concentrated hydrochloric acid fumes before analysis by storing filters in a desiccator for 24 hours. The mean detection limits for POC and PON, defined as ~3x standard deviation of the low standards, are ~2.4 μg and ~3.0 μg, respectively. POP was analyzed using the modified ash-hydrolysis method described previously with spectrophotometric detection at 885 nm35,36. The detection limit for POP is ~0.3 μg. It is important to note that measured particulate N and P are not devoid of inorganic N (e.g., aerosol-derived particulate nitrogen species) and P (e.g., polyphosphate granules), respectively. Furthermore, POM analyzed using this protocol includes contributions of dead materials in addition to live plankton cells, including a wide diversity of heterotrophs.
PCOD was quantified using the new, modified assay7 based on the determination of residual potassium dichromate following organic matter oxidation with silver sulfate as the catalyst under the strongly acidic condition at 150 °C for 2h37,38,39. As dichromate does not oxidize ammonium, the assay aims explicitly to quantify the oxygen demand from organic carbon (but not organic nitrogen). To remove the interference of chloride ions from the precipitation of silver chloride, mercuric sulfate was added40. Dichromate was quantified by absorbance at 600 nm using HACH-certified phthalate-based COD standards. We could not directly quantify the detection limit for PCOD as the PCOD chemistry method is highly sensitive (see Technical Validation).
In GO-POPCORN v1, most studies used similar techniques and sample volumes, but there are many slight deviations in the technical approach, including the measurement sensitivity, detection limits, the number of replicates, and the overall cleanliness (i.e., contamination) of procedures9. It is also worth noting that the POP measurements were grossly undersampled compared to POC and PON measurements in GO-POPCORN v1.
In GO-POPCORN v2, the POM samples were collected and quantified using consistent protocols. Before POM sampling, all the carboys used were rinsed at least twice with the pre-filtered underway seawater. The filtered volume of seawater was consistent between all POM (POC/N and POP) samples at each station and varied on a per-station basis to ensure that the amount of collected material was minimally impacted by the difference in filtration time. Initial rinsing and the large sampling volume were aimed at reducing the effect of a time delay caused by the underway system. The methods used for quantifying POC/N43 and POP36 are based on previously described and validated standard techniques.
POM described in this dataset are “small size-class” samples, where a 30 µm nylon mesh pre-filter was attached to the underway outlet to remove large plankton and particulates. In the Southern Ocean Section of the P18 cruise, we have separately collected “large-class” of POM >30 µm and showed that the larger particles constitute, on average, 17% of the total POC and PON concentrations and 31% of the total POP concentration32. The same study showed that a large size fraction of POM in P18 had statistically lower C:P, C:N, and N:P compared to a small size fraction of POM. However, the general effect of particle size on the C:N:P stoichiometry of POM is not yet clear.
For the technical validation of the novel PCOD assay, we tested for (1) interference using standard additions of a HACH-certified phthalate-based COD standard, (2) a linear correspondence between input amounts and absorbance, (3) the degree of variance with respect to POC measurement technique, and (4) biases for different substrates. In summary, we found that (1) the sample interference is limited, (2) there is indeed a linear relationship between filtered sample volume and PCOD, (3) variance for PCOD is higher compared to POC; hence it is vital to prepare and oxidize the high volume of POC to minimize relative error and ensure accurate determination of -O2:C, and (4) a high correspondence between theoretical and observed values for different substrates. A full detailed description of PCOD assay validation is described elsewhere7.
This dataset is the most comprehensive global compilation of surface POM and PCOD. By combining this dataset with datasets of temperature, nutrients, and plankton community composition, regional and global drivers of C:N:P:-O2 can be identified. The dataset is also useful for evaluating outputs from ocean biogeochemical models with flexible C:N:P:-O2 stoichiometry, with important implications for future ocean carbon, nitrogen, and oxygen dynamics.
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We want to acknowledge the captains and crew of the R/V Atlantic Explorer, R/V New Horizon, R/V Ronald H. Brown, R/V Roger Revelle, R/V Sikuliaq, R/V Ocean Star and the R.R.S. James Clark Ross, as well as all the members of Bio-GO-SHIP and IERP. We also thank Andy Rees from Plymouth Marine Laboratory. This work was supported by National Science Foundation (GRFP to ARM, OCE-1046297, 1559002, 1848576, and 1948842 to ACM, OCE-1045966 and 1258836 to MWL), NASA (NESSF16R to CAG, 80NSSC21K1654 to ACM), NOAA (101813-Z7554214 to ACM and NOAA Cooperative Institutes, Award #NA19NES4320002, at the Cooperative Institute for Satellite Earth System Studies), National Institutes of Health (T32AI141346 to MLB), UCI Graduate Division (Chancellor’s Club Fellowship to ARM), Simons Foundation (Postdoctoral Fellowship in Marine Microbial Ecology #724483 to TT) and North Pacific Research Board (Arctic IERP Project A92 & A96 to MWL). The Atlantic Meridional Transect is funded by the UK Natural Environment Research Council through its National Capability Long-term Single Centre Science Programme, Climate Linked Atlantic Sector Science (grant number NE/R015953/1). This study contributes to the international IMBeR project and is contribution number 383 of the AMT programme.
The authors declare no competing interests.
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Tanioka, T., Larkin, A.A., Moreno, A.R. et al. Global Ocean Particulate Organic Phosphorus, Carbon, Oxygen for Respiration, and Nitrogen (GO-POPCORN). Sci Data 9, 688 (2022). https://doi.org/10.1038/s41597-022-01809-1