Table of Contents

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

On-ship aerosol sampling was conducted on the R/V Dong Fang Hong-3 during a cruise to the western NP from October 31 to December 1, 2019. We used two portable aerosol particle samplers (model 2030, Qingdao Laoying Environmental Technology Co.) with a filter size of 9 cm O.D. The GF/F filters were precombusted (550 °C, 4 h) before used, and the sampling period was 18 to 72 h for each filter with an air flow rate of 100 L/min based on the cruise track. A total of 16 samples were collected during the cruise.

For the aerosol samples, we measured the concentrations of aerosol particulate OC (POC), total nitrogen (TN), and carbon isotope (13C and 14C) compositions of aerosol OC. All measurements were conducted at the Center for Isotope Geochemistry and Geochronology (CIGG) at the Qingdao National Laboratory for Marine Science and
Technology (QNLM) in Qingdao, China. For atmospheric POC measurements, a cut piece of filter containing particles was acidified first with 10% high-purity HCl to remove inorganic carbon and then dried at 50 °C. Concentrations of POC and TN were measured using an elemental analyzer (Elementar vario Isotope select) with analytical standard deviations of ±0.03% for OC, and ±0.04% for TN (n = 6). The δ13C values of POC were measured using a Thermo Delta V advantage isotope ratio mass spectrometer coupled with an Elemental Analyzer-IsoLink CN. Values of δ13C were reported in ‰ relative to 13C standards (IAEA-CH-3, cellulose, and IAEA-600 caffeine), and the analytic precision was ≤0.2‰ (n = 10). For POC 14C measurements, the pretreated flters were placed separately in double quartz tubes (precombusted at 850 °C for 2 h) with CuO and Ag wires added. The tubes were then evacuated on a vacuum line, flame sealed, and combusted at 850 °C for 2 h (Druffel et al., 1992). CO2 resulting from POC oxidation was collected cryogenically and quantifed monometrically on a vacuum line. The purified CO2 was converted to graphite using the closed tube iron reduction method (Xu et al., 2007; Walker et al., 2019) and 14C was measured by accelerator mass spectrometry (AMS, NEC 0.5MV XCAMS). Δ14C results were reported, and conventional radiocarbon ages [years before present (BP)] were calculated based on the study by Stuiver and Polach (1977).

Nitrogen (15N /14N) and oxygen (18O /16O) isotope analyses of nitrate were conducted at the Department of Earth, Environmental, and Planetary Sciences at Brown University in Providence, RI (USA). After the frozen samples were received at Brown University, a 5 × 5 cm square was cut from the center of the filter at room temperature and extracted in a pre-cleaned bottle with ~100 mL of MQ water (exact amounts were recorded via weight) and then sonicated for 1 h. After sonication, the filters were removed, and the samples were frozen at -20 ◦C until further analyses.

The denitrifier method (Casciotti et al., 2002; Sigman et al., 2001) was used to complete nitrate (15N /14N) and oxygen (18O /16O) isotope analyses via nitrous oxide on a continuous flow isotope ratio mass spectrometer. Values were reported in ‰ relative to standards.

Instruments:

Portable aerosol particle samplers: aerosol samples were collected with portable aerosol particle samplers (model 2030, Qingdao Laoying Environmental Technology Co.) with a filter size of 9 cm O.D.

Elemental analyzer: the concentrations of POC and TN were measured using an elemental analyzer (Elementar vario Isotope select).

Thermo Delta V mass spectrometer: the δ13C values of POC were measured using a Therm Delta V advantage isotope ratio mass spectrometer coupled with an Elemental Analyzer-IsoLink CN.

Thermo Delta V Plus Isotope Ratio Mass Spectrometer: used in continuous flow mode for ammonium, nitrate, and oxygen isotope analyses.

Accelerator mass spectrometry: the Δ14C values of POC were measured by accelerator mass spectrometry (AMS, NEC 0.5MV XCAMS).

* Adjusted parameter names to comply with database requirements
* Converted sampling latitude and longitude notation from decimal, minute, seconds to decimal degrees. Rounded these fields to 5 decimals
* Converted date to ISO notation (Y-m-d)
* Merged sampling date and time columns and created DateTime variable in ISO format

NSF Award Abstract:
Nitrogen is an essential element for life, and its availability can limit the growth of phytoplankton in the surface waters of the oceans. One source of nitrogen to surface waters is deposition from the atmosphere, which is the result of reactive nitrogen emissions from both human (anthropogenic) activities and natural processes. Anthropogenic nitrogen emissions to the atmosphere and nitrogen deposition to the oceans have increased exponentially since preindustrial times. In fact, global modeling studies have suggested that as much as 80% of total nitrogen deposition to the oceans is anthropogenic in origin, and that the magnitude of input to the global oceans rivals estimates of biological nitrogen fixation. The impacts associated with this increased nitrogen deposition are clear in both terrestrial and coastal systems, but the implications for open ocean biogeochemistry are less well studied. Recent work in the North Pacific Ocean (NPO) has suggested that increased nitrogen due to anthropogenic atmospheric deposition is detectable even in the open ocean, while other work can explain nutrient dynamics based upon natural biological and physical processes. The investigators propose to study the influence of both anthropogenic and natural sources on the deposition of nitrogen (as nitrate, ammonium, and organic nitrogen) in the NPO. This will be based on collection of aerosol and rainwater samples year-round at two sites: (1) Chang-Dao Island, China where they expect high anthropogenic nitrogen inputs; and (2) Oahu, Hawaii where they expect marine sources to dominate. They will also collect ship-based samples in the marine boundary layer via already planned short-term research cruises in each season. In addition to the scientific outcomes, this project will provide for human resources and professional development of the team members (faculty members, a graduate student, undergraduate student, and technicians), advance international collaborations, and contribute to education and public outreach. Identifying the sources of nitrogen deposition to the open ocean is crucial for understanding anthropogenic impacts on biogeochemical cycles. A primary question is, is nitrogen deposition the result of external, anthropogenic processes or does it represent recycled nitrogen from the ocean's point of view? The specific objectives of this project are to: characterize the atmospheric composition and sources of inorganic (ammonium and nitrate) and organic nitrogen with an emphasis on seasonality; diagnose the influence of air-sea exchange versus anthropogenic sources of nitrogen on atmospheric deposition; and determine the isotopic composition of gaseous and particulate inorganic nitrogen in the marine boundary layer via ship-based sample collections in the NPO. Using concentration and isotopic measurements of reactive nitrogen species, in addition to transport and chemical box modeling, the study aims to characterize nitrogen deposition in two locations with very different source influences. This study will provide the first comprehensive, seasonal analysis of the isotopic values of reactive nitrogen species in the NPO atmosphere where nitrogen deposition is considered intense. Ultimately this project will lead to a better understanding of how anthropogenic changes in the atmospheric nitrogen cycle may influence the biogeochemistry of the surface ocean as well as the composition of the marine atmosphere.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.