Table of Contents

• Dataset Description
  • Methods & Sampling
  • Data Processing Description
• Data Files
• Parameters
• Instruments
• Deployments
• Project Information
• Program Information
• Funding

The sampling details and identities are provided for each of the sample along with the FTICR MS (Fourier transform ion cyclotron resonance mass spectrometry) data for each sample. This includes: the starting and ending locations (latitudes and longitudes) and times (Greenwich mean time) as well as the sampling rates (m³ min^-1) and calculated sample volumes (m³) for each of the aerosol samples. The run times (measured in hours) and sample volumes account for periods when the sampler was stopped due to potential contamination from the ship’s stack. The FTICR MS data include: molecular formulas assigned to peaks at various m/z in Fourier Transform ion cyclotron resonance mass spectra. The formulas consist of carbon, hydrogen, oxygen, nitrogen, sulfur, and phosphorus. The ‘m/z’ and ‘intensity’ columns are generated by the Bruker software, and the molecular formula and exact mass data are generated by the investigators' molecular formula assignment protocol described in the next section.

Wozniak et al. (2014) and Gurganus et al. (2015) detail the sampling and analytical methodology for these data. The full citations are listed below. Details for the aerosol sampling can also be found in Wozniak et al. (2013).

The analytical details from Wozniak et al. (2014) are as follows:
Aerosol WSOM (10 mL) was solid-phase extracted using a styrene divinyl benzene polymer (PPL, Varian) cartridges following published procedures (e.g., Dittmar et al., 2008; Mitra et al., 2013). The PPL cartridge was rinsed with two cartridge volumes of LC–MS grade methanol and acidified Milli-Q water before the pre-filtered and acidified aerosol WSOM was loaded onto the cartridge. The relatively hydrophobic dissolved OM (DOM) is retained on the PPL cartridge while highly hydrophilic WSOM and salts (which would otherwise compete with the aerosol WSOM for charge during ESI) pass through the cartridge. The cartridge was then rinsed with 0.01 M HCl to ensure complete removal of salts, dried under a stream of ultrapure nitrogen, and eluted with one cartridge volume (~3 mL) of methanol. Though previous studies have added ammonium hydroxide prior to ESI in order to increase ionization, tests showed that higher quality spectra (more organic matter peaks) were obtained without the addition of base, and samples were infused to the ESI in methanol alone. Samples were continuously infused into an Apollo II ESI ion source of a Bruker Daltonics 12 T Apex Qe FTICR, housed at ODU’s COSMIC facility. Samples were introduced by a syringe pump at 120 uL h-1. All samples were analyzed in negative ion mode; ions were accumulated in a hexapole for 0.5 s before being transferred to the ICR cell, where 300 transients were co-added. The summed free induction decay signal was zero-filled once and sinebell apodized prior to fast Fourier transformation and magnitude calculation using the Bruker Daltonics Data Analysis software.

The data were processed as described in Wozniak et al. (2014):
All mass spectra were externally calibrated with a polyethylene glycol standard and internally calibrated with naturally occurring fatty acids and other homologous series present within the sample (Sleighter and Hatcher, 2008). A molecular formula calculator (Molecular Formula Calc v. 1.0 ©NHMFL, 1998) generated molecular formulas using carbon (12C8–50), hydrogen (1H8–100), oxygen (16O1–30), nitrogen (14N0–5), sulfur (32S0–2), and phosphorous (31P0–2). Peaks identified in process blanks (PPL extract of QMA filter blank WSOM) were subtracted from the sample peak list prior to formula assignment. Only m/z values in the range of 200-800 with a signal to noise ratio above 3 were used for molecular formula assignments. The mean mass resolution for all samples over that mass range was 560,000.

Constraints corresponding to the standard range of atomic composition for natural organic matter were applied during formula assignment following previous work (Stubbins et al., 2010; Wozniak et al., 2008): (1) O/C ≤ 1.2; (2) 0.3 ≤ H/C ≤ 2.25; (3) N/C ≤ 0.5; (4) S/C ≤ 0.2; (5) P/C ≤ 0.2; (6) DBE ≥ 0 and an integer value. The term DBE is the number of double bond equivalents, which is the number of double bonds and rings in a formula (e.g., Hockaday et al., 2006). The measured m/z values and assigned formula calculated exact masses all agreed within the maximum allowed error of 1.0 ppm, and >90% of formulas were within 0.5 ppm. An unequivocal formula is found for m/z values below 450, but above this, multiple formulas may match the measured m/z value. In order to ensure a unique formula per peak, additional constraints are placed on the proportion of heteroatoms using the following criteria (Kujawinski et al., 2009): 1) each formula should have numbers of N and S atoms that are each fewer than the number of oxygen atoms, and 2) the sum of the N and S atoms should be the lowest possible.

The spectral magnitude for a given peak results from a combination of the concentrations of the isomeric compounds representing a given molecular formula in the actual WSOM, how ionizable those compounds are using ESI, and the FTICR MS analytical window. ESI FTICR MS is thus not a purely quantitative technique.

References:
Gurganus, S. C., A. S. Wozniak, and P. G. Hatcher. 2015. Molecular characteristics of the water soluble organic matter in size resolved aerosols collected over the North Atlantic Ocean. Marine Chemistry, 170, 37-48, doi:10.1016/j.marchem.2015.01.007

Hockaday, W., Grannas, A., Kim, S., and Hatcher, P. 2006. Direct molecular evidence for the degradation and mobility of black carbon in soils from ultrahigh-resolution mass spectral analysis of dissolved organic matter from a fire-impacted forest soil. Org. Geochem., 37, 501-510. doi:10.1016/j.orggeochem.2005.11.003

Kujawinski, E. B., Longnecker, K., Blough, N. V., Vecchio, R. D., Finlay, L., Kitner, J. B., and Giovannoni, S. J. 2009. Identification of possible source markers in marine dissolved organic matter using ultrahigh resolution mass spectrometry. Geochim. Cosmochim. Acta, 73, 4384-4399. doi:10.1016/j.gca.2009.04.033

Mitra, S., Wozniak, A. S., Miller, R., Hatcher, P. G., Buonassissi, C., and Brown, M. 2013. Multiproxy probing of rainwater dissolved organic matter (DOM) composition in coastal storms as a function of trajectory. Mar. Chem., 154, 67-76. doi:10.1016/j.marchem.2013.05.013

Sleighter, R. L. and Hatcher, P. G. 2008. Molecular characterization of dissolved organic matter (DOM) along a river to ocean transect of the lower Chesapeake Bay by ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Mar. Chem., 110, 140-152. doi:10.1016/j.marchem.2008.04.008

Stubbins, A., Spencer, R. G., Chen, H., Hatcher, P. G., Mopper, K., Hernes, P. J., Mwamba, V. L., Mangangu, A. M., Wabakanghanzi, J. N., and Six, J. 2010. Illuminated darkness: Molecular signatures of Congo River dissolved organic matter and its photochemical alteration as revealed by ultrahigh precision mass spectrometry. Limnol. Oceanogr., 55, 1467-1477. doi:10.4319/lo.2010.55.4.1467

Wozniak, A.S., Bauer, J.E., Sleighter, R.L., Dickhut, R.M., Hatcher, P.G. 2008. Technical Note: Molecular characterization of aerosol-derived water soluble organic carbon using ultrahigh resolution electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry. Atmos. Chem. Phys., 8, 5099-5111. doi:10.5194/acp-8-5099-2008

Wozniak, A. S., R. L. Sleighter, H. Abdulla, A. S. Priest, P. L. Morton, R. U. Shelley, W. M. Landing, and P. G. Hatcher. 2013. Relationships among aerosol water soluble organic matter, iron and aluminum in European, North African, and Marine air masses from the 2010 US GEOTRACES cruise. Marine Chemistry, 154, 24-33. doi:10.1016/j.marchem.2013.04.011

Wozniak, A.S., A. S. Willoughby, S. C. Gurganus, P. G. Hatcher. 2014. Distinguishing molecular characteristics of aerosol water soluble organic matter from the 2011 trans-North Atlantic US GEOTRACES cruise. Atmospheric Chemistry and Physics, 14, 8419-8434, doi:10.5194/acp-14-8419-2014

BCO-DMO Processing:
- Modified parameter names to conform with BCO-DMO naming conventions;
- merged FTICR data with sample information;
- added cruise id, event numbers, and station numbers from BCO-DMO GEOTRACES NAT master event file;
- replaced missing data with 'nd';
- converted date-time fields to ISO format;
- changed longitude values to negative.

Much of this text appeared in an article published in OCB News, October 2008, by the OCB Project Office.

The first U.S. GEOTRACES Atlantic Section will be specifically centered around a sampling cruise to be carried out in the North Atlantic in 2010. Ed Boyle (MIT) and Bill Jenkins (WHOI) organized a three-day planning workshop that was held September 22-24, 2008 at the Woods Hole Oceanographic Institution. The main goal of the workshop, sponsored by the National Science Foundation and the U.S. GEOTRACES Scientific Steering Committee, was to design the implementation plan for the first U.S. GEOTRACES Atlantic Section. The primary cruise design motivation was to improve knowledge of the sources, sinks and internal cycling of Trace Elements and their Isotopes (TEIs) by studying their distributions along a section in the North Atlantic (Figure 1). The North Atlantic has the full suite of processes that affect TEIs, including strong meridional advection, boundary scavenging and source effects, aeolian deposition, and the salty Mediterranean Outflow. The North Atlantic is particularly important as it lies at the "origin" of the global Meridional Overturning Circulation.

It is well understood that many trace metals play important roles in biogeochemical processes and the carbon cycle, yet very little is known about their large-scale distributions and the regional scale processes that affect them. Recent advances in sampling and analytical techniques, along with advances in our understanding of their roles in enzymatic and catalytic processes in the open ocean provide a natural opportunity to make substantial advances in our understanding of these important elements. Moreover, we are motivated by the prospect of global change and the need to understand the present and future workings of the ocean's biogeochemistry. The GEOTRACES strategy is to measure a broad suite of TEIs to constrain the critical biogeochemical processes that influence their distributions. In addition to these "exotic" substances, more traditional properties, including macronutrients (at micromolar and nanomolar levels), CTD, bio-optical parameters, and carbon system characteristics will be measured. The cruise starts at Line W, a repeat hydrographic section southeast of Cape Cod, extends to Bermuda and subsequently through the North Atlantic oligotrophic subtropical gyre, then transects into the African coast in the northern limb of the coastal upwelling region. From there, the cruise goes northward into the Mediterranean outflow. The station locations shown on the map are for the "fulldepth TEI" stations, and constitute approximately half of the stations to be ultimately occupied.

Figure 1. The proposed 2010 Atlantic GEOTRACES cruise track plotted on dissolved oxygen at 400 m depth. Data from the World Ocean Atlas (Levitus et al., 2005) were plotted using Ocean Data View (courtesy Reiner Schlitzer). [click on the image to view a larger version]

Hydrography, CTD and nutrient measurements will be supported by the Ocean Data Facility (J. Swift) at Scripps Institution of Oceanography and funded through NSF Facilities. They will be providing an additional CTD rosette system along with nephelometer and LADCP. A trace metal clean Go-Flo Rosette and winch will be provided by the group at Old Dominion University (G. Cutter) along with a towed underway pumping system.

The North Atlantic Transect cruise began in 2010 with KN199 leg 4 (station sampling) and leg 5 (underway sampling only) (Figure 2).

KN199-04 Cruise Report (PDF)

Figure 2. The red line shows the cruise track for the first leg of the US Geotraces North Atlantic Transect on the R/V Knorr in October 2010.  The rest of the stations (beginning with 13) will be completed in October-December 2011 on the R/V Knorr (courtesy of Bill Jenkins, Chief Scientist, GNAT first leg). [click on the image to view a larger version]

The section completion effort resumed again in November 2011 with KN204-01A,B (Figure 3).

KN204-01A,B Cruise Report (PDF)

Figure 3. Station locations occupied on the US Geotraces North Atlantic Transect on the R/V Knorr in November 2011.  [click on the image to view a larger version]

Data from the North Atlantic Transect cruises are available under the Datasets heading below, and consensus values for the SAFe and North Atlantic GEOTRACES Reference Seawater Samples are available from the GEOTRACES Program Office: Standards and Reference Materials

ADCP data are available from the Currents ADCP group at the University of Hawaii at the links below:
KN199-04   (leg 1 of 2010 cruise; Lisbon to Cape Verde)
KN199-05   (leg 2 of 2010 cruise; Cape Verde to Charleston, NC)
KN204-01A (part 1 of 2011 cruise; Woods Hole, MA to Bermuda)
KN204-01B (part 2 of 2011 cruise; Bermuda to Cape Verde)

Description from NSF award abstract:
The atmospheric delivery of soluble Fe to the ocean is an important process contributing to oceanic primary production and the drawdown of atmospheric CO2. Combustion influenced air masses carry highly soluble Fe, but the reasons for this increased solubility remain unclear despite the importance to global carbon cycling. Acidic organic matter (OM) components (e.g., -COOH groups) can complex with trace metals, yet no study to date has investigated the comprehensive molecular characteristics of aerosol OM for their role as a determinant of Fe solubility.

In this project, researchers at Old Dominion University will study the relationship between the molecular characteristics of marine aerosol water soluble OM (WSOM) and Fe solubility. Marine particulate aerosols collected during GEOTRACES cruises will be examined to identify WSOM characteristics that may play a role in delivering soluble and bioavailable Fe to the N. Atlantic Ocean. Aerosol WSOM will be characterized using advanced molecular and chemometric techniques to test whether:
(1) continental combustion-influenced aerosol samples show molecular characteristics unique from those of continental dust influenced samples, having characteristics consistent with higher contributions from OM with acidic functional group;
(2) aerosol WSOM examined along a gradient of Fe solubility show concurrent changes in the relative magnitude of highly oxygenated compounds and contributions from acidic functional groups; and
(3) 2D HMBC NMR reveal unique components in composite continental combustion influenced samples relative to marine and dust-influenced samples, and these unique components include OM with carboxyl functional groups that can bind Fe.

This project will be the first of its kind to extensively examine WSOM molecular characteristics and Fe solubility on concurrently collected aerosol samples. The results will be useful for understanding Fe distributions and biogeochemical cycling in the ocean. A potentially transformative aspect of this proposal will be the identification of aerosol WSOM molecular components unique to combustion influenced air masses that have the potential to facilitate aerosol Fe solubility.

The findings of this project are expected to be highly relevant to oceanic and global biogeochemical cycling of OM and many trace metals that form organic complexes. Combustion-influenced OM associations may help explain patterns in the global oceanic distribution of other trace metals and provide key insights into oceanic processes (e.g., primary production, biological pump).

GEOTRACES is a SCOR sponsored program; and funding for program infrastructure development is provided by the U.S. National Science Foundation.

GEOTRACES gained momentum following a special symposium, S02: Biogeochemical cycling of trace elements and isotopes in the ocean and applications to constrain contemporary marine processes (GEOSECS II), at a 2003 Goldschmidt meeting convened in Japan. The GEOSECS II acronym referred to the Geochemical Ocean Section Studies To determine full water column distributions of selected trace elements and isotopes, including their concentration, chemical speciation, and physical form, along a sufficient number of sections in each ocean basin to establish the principal relationships between these distributions and with more traditional hydrographic parameters;

* To evaluate the sources, sinks, and internal cycling of these species and thereby characterize more completely the physical, chemical and biological processes regulating their distributions, and the sensitivity of these processes to global change; and

* To understand the processes that control the concentrations of geochemical species used for proxies of the past environment, both in the water column and in the substrates that reflect the water column.

GEOTRACES will be global in scope, consisting of ocean sections complemented by regional process studies. Sections and process studies will combine fieldwork, laboratory experiments and modelling. Beyond realizing the scientific objectives identified above, a natural outcome of this work will be to build a community of marine scientists who understand the processes regulating trace element cycles sufficiently well to exploit this knowledge reliably in future interdisciplinary studies.

Expand "Projects" below for information about and data resulting from individual US GEOTRACES research projects.