Table of Contents

• Coverage
• Dataset Description
  • Methods & Sampling
  • Data Processing Description
  • BCO-DMO Processing Description
• Data Files
• Supplemental Files
• Related Publications
• Parameters
• Instruments
• Deployments
• Project Information
• Funding

DOP (Dissolved Organic Phosphorus) concentration observations in the global ocean between 1990 and 2021.

Sampling and analytical procedures: 

For samples in this study, Whatman glass-fiber filters (GF/F) with a nominal 0.7 µm pore size were used to filter samples collected on the P18-2016 and GOA2013 cruises. Polycarbonate filters with a nominal 0.4 µm pore size were used to filter samples collected on the CoFeMUG and WebbPacific2007 cruises. Polyesthersulfone (PES) filters with a nominal 0.2 µm pore size were used to filter samples collected from SCALE, SWINGS, P06-2017, ETSP2010, ETSP2011 and GOM2019 cruises. All samples were stored in high density polyethylene bottles at -20 ˚C until measuring total dissolved phosphorus (TDP) concentration.

DOP (Dissolved Organic Phosphorus) concentrations in this study were calculated as the difference between TDP concentrations ([TDP]) and SRP concentrations ([SRP]) of samples ([DOP] = [TDP] - [SRP]). For DOP concentrations reported here, TDP concentrations were measured by the ash/hydrolysis method based on Monaghan and Ruttenberg, 1999. Briefly, for samples collected >1 year prior to analysis, the sample pH was reduced to 1 by adding ~150 µL 6 M ACS-grade HCl to the sample bottle and placing the bottle in a reciprocal shaker overnight. Then, 6 ml of the acidified sample was added to an acid washed, 500 ˚C combusted glass vial, and 0.6 ml of 4.3 M NaCl/0.3 M MgSO4 solution was added to the acidified sample. Subsequently, vials were put into a drying oven at 70 ˚C until appearing dry (often 4-5 days). Then, each vial was covered with aluminum foil and transferred to a muffle oven to bake at 130 ˚C for 3 hours and then at 500 ˚C for 4.5 hours. Afterwards, 1.8 mL 0.75 M ACS-grade HCl was added to each vial and capped tightly with Teflon-lined caps, then heated at 80 ˚C for 20 min to hydrolyze the polyphosphate left after ashing. After heating, 4.2 mL ultra-pure water (18.2 MΩ_ cm) was added to each vial and heated at 80 ˚C for 10 min to dissolved all remaining solids. I assume quantitative conversion of DOP to SRP and the resulting SRP concentration was measured by using the colorimetric phosphomolybdate-blue method (Hansen and Koroleff, 1999). The final DOP concentration was calculated by the difference between SRP concentration and TDP concentration ([DOP] = [TDP] - [SRP]). 

TDP concentrations collected from the published literature were measured by three methods: ash/hydrolysis, UV oxidation, and wet oxidation. The ash/hydrolysis method was also used on samples from the Pulse-26, STN F, KT00A, B, KT01Eq, EN391 and SJ0609 cruises. Wet oxidation is a chemical oxidation where a persulfate reagent is added to seawater and then heated to 120 ˚C for 30 minutes to convert DOP to SRP (Hansen and Koroleff, 1999). Wet oxidation methods were employed to determine TDP concentrations on cruises including BIOSOPE, OUTPACE, KH-11-10, KH-12-3, KH-13-7, KH-14-3, KH-17-4, SATL2004, KM0415, Line P and Latitude II cruises, and at the BATS site. UV oxidation is a photochemical oxidation method using UV radiation to covert DOP to SRP (Armstrong et al., 1966). UV oxidation methods were used to measure the TDP concentrations on cruises including AMT 10, AMT 12, AMT 14, AMT 15, AMT 16, D279,  36N, Line P, GB 93, MAB 94, MAB 96, Cavender-Barres cruises, and at Station ALOHA

Processing notes from researchers:

Any reported negative DOP concentration (DOP concentrations <0 µM) is marked as “BDL”( below detection limits) in this dataset. A quality flag is added to the DOP concentration by using WOCE Water Sample Quality Codes. In this dataset, DOP concentrations with “BDL” are flagged with code 3 (“questionable measurements”) and other DOP concentrations are flagged with code 2 (“acceptable measurement”). 

Version 2 dataset updates:

Data quality flag column added

The PO4 column has been renamed to SRP (soluble reactive phosphorus) to improve accuracy 

Version 3 dataset updates:

Metadata (e.g. sampling date, Salinity, Temperature, NO3+NO2 and SRP) have been added for the cruise Gulf of Alaska 2013, AMT10, AMT12, AMT14, AMT15, AMT17, KH-11-10, KH-12-3, KH-13-7, KH-14-3, KH-17-4, OC279, OC297, OC318, and OC325.

Version 4 dataset updates:

Dr. Kaycie Lanpher shared DOP concentration observations from the GO-SHIP P06-2017 cruise based on the published article (Lanpher & Popendorf, 2021) with the Contact Zhou Liang,  and these DOP concentration observations were added into the DOPv2021 dataset with their authorization.

Fields renamed to conform with BCO-DMO standard data practices

Date format converted to yyyy-mm-dd from mm/dd/yy

Removed commas from the reference field

This study was global in nature, but included significant numbers of analyses from: GO-SHIP cruises (P06-2017, P18-2016, I08S-2016, I09N-2016); Eastern Tropical South Pacific; Atlantic, Pacific, and Indian Ocean sectors of the Southern Ocean; Gulf of Alaska; and the western Pacific.

NSF Award Abstract:
Phytoplankton play an important role in the Earth's elemental cycles of carbon and nitrogen. In addition to sunlight, phytoplankton living in the surface waters of the oceans require the elements nitrogen and phosphorus for growth. Much of these nutrients are supplied in their inorganic forms from mixing of deep waters towards the surface during the winter months when vertical stability of the water column breaks down. However much of the low latitude oceans, 45degS45degN, suffer from limited nutrient input to sunlit surface waters due to strong thermal stratification (vertical stability) of the upper water column. As a consequence, tropical and subtropical phytoplankton have devised alternative ways of acquiring nitrogen and phosphorus. Marine nitrogen fixation is a process by which specialized microbes utilize the abundant nitrogen gas from the atmosphere to convert elemental nitrogen into the bioavailable form ammonia. These nitrogen fixing phytoplankton and many others also use organic forms of phosphorus in the low latitude ocean where inorganic nutrients are often scarce. This project will significantly increase the number of dissolved organic nitrogen and dissolved organic phosphorus concentration measurements, especially from the currently under-sampled Pacific and Indian Oceans. Changes in the concentration of organic nutrients across the surface ocean will be used to infer rates of organic nutrient use by phytoplankton in numerical models. Specifically, the role for the biological uptake of dissolved organic phosphorus to stimulate the processes of marine nitrogen fixation and photosynthesis in the low latitude ocean will be quantified from the combined data and model output. The project will train one graduate student and several undergraduate students in both laboratory chemical analysis techniques and numerical simulation of ocean biological and chemical processes. New scientific knowledge will be shared with the public via a social media campaign and will inform the development of the next generation of global climate models.

The marine biogeochemical modeling community has identified the lack of dissolved organic nitrogen (DON) and especially dissolved organic phosphorus (DOP) concentration measurements from the upper 300 m of the global ocean as crucial gaps in our ability to accurately model export production and N2 fixation rates in the subtropics. The proposed work will significantly increase global data coverage of marine DON and DOP concentration measurements, in particular from under-sampled ocean regions in the Indian Ocean, western, central, and eastern tropical South Pacific, Gulf of Alaska, eastern subtropical and subpolar South Pacific, Southern Ocean, subtropical North Atlantic, and tropical South Atlantic Ocean basins. These new measurements will be assimilated in state-of-the-art biogeochemical models to constrain the relative cycling rates of DOP and DON and to quantify the role of preferential DOP consumption as a P source supporting export production and N2 fixation in the low latitude ocean. Model output will solve for the regionally-resolved fraction of new production that accumulates as DON and DOP, autotrophic DOP uptake rates, as well as the remineralization rates for DON and DOP. The model output will also include the first regionally variable rate estimates of euphotic zone DOP consumption sustaining export production and N2 fixation to be constrained by observations from the Pacific and Indian Oceans. Thus, the new concentration measurements and diagnostic modeling will allow us to evaluate the quantitative role for regional variability in DOP consumption and recycling that supports export production and N2 fixation in the low latitude ocean.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.