Table of Contents

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

Sampling:

Size-fractionated particles were collected using dual-flow McLane Research in-situ pumps (WTS-LV) and 142-millimeter (mm) "mini-MULVFS" filter holders (Bishop et al., 2012; Lam et al., 2018; Lam et al., 2015a; Xiang and Lam, 2020). At most of the stations, two casts of 8 pumps each and two filter holders per pump were deployed to collect samples at 16 depths throughout the water column. At super stations, a 24-depth profile was obtained with three casts. The targeted depths of the wire-out were corrected using pressure readings from a self-recording Seabird 19plus CTD at the end of the line. One filter holder/flowpath was loaded with a Sefar polyester mesh prefilter (51 micrometers (μm) pore size, called the "Qp" filter) and paired Whatman QMA quartz fiber filters (1 μm pore size) in series ("QMA-side"). The other filter holder/flowpath was also loaded with a 51 μm prefilter (called the "Sp" filter), but it was followed by paired 0.8 μm Pall Supor800 polyethersulfone filters ("Supor-side"). A 150 μm Sefar polyester mesh was placed underneath all 51 μm prefilters and QMA filters as a support to facilitate filter handling but not analyzed. All filters and filter holders were acid-leached before use based on the recommended methods in the GEOTRACES sample and sample-handling protocols Cutter et al., 2010). QMA filters were pre-combusted at 450 degrees Celsius (°C) for 4 hours after acid leaching.

A special plate was manufactured for one of the pumps that could hold two additional mini-MULVFS filter holders that were loaded with full filter sets but not connected to plumbing. These 'dipped blank' filters included the full filter sets (51 µm prefilter on top of paired QMA or paired Supor filters) with a 0.2um Supor polyethersulfone filter on top of the 51 µm polyester prefilters to exclude all particles from the main filter set. These were processed identically to the regular filters and functioned as full process blanks A total of 49 dipped blank filters were used for blank subtraction, calculations of uncertainties, and determination of detection limits (Table 2).

In this dataset, data reported from the 51 μm prefilter are referred to with an "LPT" suffix to indicate large particulate total concentrations (>51 μm). Samples could come from the QMA side ("Qp" filter) or the Supor side ("Sp" filter) and are treated equivalently. Data reported from the main filters (QMA—1-51 μm —or Supor—0.8-51 μm) are from the top filter of the pair only, and are referred to with an "SPT" suffix to indicate the small particulate total concentrations.

Analytical Procedures:

Particulate organic carbon (POC) and particulate nitrogen (PN):
For SPT particles, a 25 mm punch of QMA filter was dried at 55°C at sea. LPT (>51 µm) particles were rinsed at sea from the Sp filter using 0.2 µm-filtered seawater onto a 25mm 0.8µm Ag filter (Sterlitech) and dried at 55°C at sea. These samples were beta counted for ²³⁴Th at sea by the CafeTh lab at WHOI, then sent to the Lam lab at UCSC for POC and PN analyses. POC and PN sample processing was similar to what was described in Xiang and Lam (2020). Filter samples were dismounted from the beta mounts. Typically, a 22 mm QMA subpunch or the entire 25 mm 0.8 µm Ag filter were fumed in a desiccator with concentrated HCl and dried in the oven at 60 °C overnight, and then pelletized with 30mm tin discs from EA Consumables. Tin disc encapsulated samples were measured using a CE Instruments NC 2500 model Carbon/Nitrogen Analyzer interfaced to a ThermoFinnigan Delta Plus XP isotope ratio mass spectrometer (IRMS) at the Stable Isotope Laboratory at University of California, Santa Cruz. Isotopic results obtained from the IRMS were calibrated using reference materials Acetanilide (C8H9NO). The effect of dissolved organic carbon sorption is corrected with isotopic values of dipped blanks. The isotopic data are expressed in the standard delta notation as per mil deviations (‰) with respect to international standards of Pee Dee Belemnite (PDB) and atmospheric nitrogen. The precision of the internal standard (Pugel) analyzed along with the samples in the run is 0.07‰ for d13C and 0.14‰ for d15N.

Particulate inorganic carbon (PIC):
A UIC Carbon dioxide coulometer was used for PIC measurement. Briefly, PIC on SPT QMA punches or 1/16 LPT QMA-side prefilter was converted to CO₂ by addition of 2 N sulfuric acid. CO₂ produced is carried by a gas stream into a coulometer cell where CO₂ is quantitatively absorbed by a cathode solution, reacted to form a titratable acid and measured based on the change in current.

Biogenic silica (bSi):
A 1-hour alkaline leach with 0.2 M NaOH at 85°C was used to leach bSi for both size fractions prior to the measurement on a Lachat QuikChem 8000 Flow Injection Analyzer at UCSC. A 4-hour time-series leaching approach to correct for the contribution from lithogenic Si was applied to a subset of stations and the deepest 3-4 bare bottom samples from all stations (cf., Barão et al., 2015; DeMaster, 1981; Lam et al., 2018). Lithogenic Si was only important for some near-bottom samples, so the intercept ("t0" value) was used for the near-bottom samples; the 1-hour timepoint was used for all other samples.

Particulate trace metals (pTM):
pTM total concentrations (SPT, LPT): The digestion method of pTM is based on a refluxing method (Cullen and Sherrell, 1999; Planquette and Sherrell, 2012) with light modifications similar to the "Piranha method" in Ohnemus et al. (2014). In brief, the Supor filter was adhered to the wall by surface tension in a 15-milliliter (mL) flat-bottom screw-cap Savillex vial to avoid immersion. After 4-hours of refluxing at 110 °C with an ultrapure (ARISTAR® or Optima grade) 50% HNO3/10% HF (v/v) mixture, digestion acids were transferred into secondary vials and heated to near dryness. The residue was heated in 50% HNO3/15% H2O2 (v/v) to dryness at 110 °C. The final residue was re-dissolved with 2 mL 5% HNO3 spiked with 1 ppb In. Two certified reference materials (BCR-414 and PACS-2) were digested routinely alongside the samples to assure the quality of each digestion.

pTM leachable concentrations (SPL): A 1/16ᵗʰ slice of Supor filter was leached using the "Berger Leach", a weak acid leach comprising 25% Q-grade acetic acid and 0.02M reagent grade hydroxylamine hydrochloride (Berger et al. 2008). Samples are submerged in the Berger Leach solution and heated in a 95°C water bath for 10 minutes, cooled at room temperature for about 1.3 hours, and then centrifuged for 30 minutes at 4100 rpm. Total leach time should be 2 hours. The supernatant is transferred to a 15 mL Savillex vial and dried for over an hour at 110°C. The residue is redissolved and dried in concentrated HNO3 twice and brought up in 5% HNO2 spiked with 1 ppb In. Two certified reference materials (BCR-414 and PACS-2) were leached routinely alongside the samples to assure the quality of each leach.

Analysis by ICP-MS: Sample solutions were analyzed using an Element XR high-resolution ICP-MS (Thermo Scientific) at the UCSC Plasma Analytical Facility. Elemental concentrations were standardized using multi-element, external standard curves prepared from NIST atomic absorption-standards in 5% HNO₃. Instrument drift and matrix effects were corrected using the internal 1ppb In standard and monitored using a mixed element run standard. Concentrations were determined using external standard curves of mixed trace elements standards. If a parameter was measured on the ICP-MS, the isotope and resolution (LR=Low Resolution; MR=Medium Resolution) used for the concentration measurement are indicated in Table 4.

Further details on instrumentation can be found in Table 3.

Blank subtraction:
Dipped blanks were assessed for each analyte for spatial trends, indicating potential variation in adsorption blanks, and grouped accordingly (see Table 1). Outliers for each measurement type were excluded using Chauvenet's criterion (Glover et al., 2011). The median of the appropriately grouped db filters was then used in blank subtraction to take into account the adsorption and sample handling blanks.

No blank corrections were made to the stable isotopic composition of C (d13C) and N (d15N) for the LPT and SPT particles and are given as raw values. Note that poorly loaded filters will have great uncertainty in the isotopic compositions.

Error propagation:
For most parameters, we could not routinely run replicates, so almost all errors reported are determined from the standard deviation of dipped blank filters (Table 1), converted to concentrations using volume filtered. This assumes that the blank subtraction is the largest source of error.

Quality Flags:
The detection limit was defined as three times the standard deviation of the dipped blank filters. Values below the detection limit were flagged as QF=6 in the GTSPP convention (also adopted by SeaDataNet and recommended by the GEOTRACES programme).

Lab quality control (QC) included running standard reference materials for POC&PN (acetanilide), and for pTM (BCR414 and PACS-2; see Table 2), as well as participation in intercalibration exercises.

All data have been assigned quality flags using the GTSPP convention and interpretation:

1 = good; passed lab QC and oceanographically consistent.

2 = possibly good; oceanographically consistent, but have minor sampling/instrumental issues.

3 = possibly bad; not oceanographically consistent, or have major sampling/instrumental issues

4 = bad; failed lab QC (including all failed pumps when only small or no volume was pumped through the filter), or known issue with samples. For a measured parameter from a failed pump, if the filter sample was analyzed and a non-zero volume was recorded so that a concentration could be derived, this concentration is reported with QF=4. These values are generally not reliable because recorded volumes for failed pumps are probably not correct. If a zero volume was recorded, then a concentration could not be derived, and the value is reported as "NaN" with QF=4. For a derived parameter from a failed pump, this QF=4 applies if any of the parameters on which it is based had a QF=4 but is not "NaN".

6 = below detection limit.

9 = data missing (including all "nd"). For a measured parameter, this QF applies to lost or missing samples that were not measured. For a derived parameter, this QF=9 applies if any of the parameters on which it is based is missing (QF=9) or is "NaN".

- Imported original file "RR1815_allparams_DoOR_data_submit_Lam_v1.xlsx" into the BCO-DMO system.
- Added the start date and start time columns from the RR1815 event log, based on GEOTRACES event number; used event log (v4) obtained from BCO-DMO (dataset ID 776755) on 2024-01-30.
- Renamed fields/columns to comply with BCO-DMO naming conventions.
- Removed empty columns.
- Rounded depth column to 1 decimal place (only if values had more than 1 decimal place); rounded all other numeric columns to 5 decimal places.
- Saved the final file as "919139_v1_rr1815_size-fractionated_particles.csv".

Update/Correction to Table 4:
On 2025-03-06, the units of measurement for bSi were corrected to nmol/L in both the Parameters section of the metadata and in the Table 4 supplemental file. They were previously reported incorrectly as pmol/L.

A 60-day research cruise took place in 2018 along a transect form Alaska to Tahiti at 152° W. A description of the project titled "Collaborative Research: Management and implementation of the US GEOTRACES Pacific Meridional Transect", funded by NSF, is below. Further project information is available on the US GEOTRACES website and on the cruise blog. A detailed cruise report is also available as a PDF.

Description from NSF award abstract:
GEOTRACES is a global effort in the field of Chemical Oceanography in which the United States plays a major role. The goal of the GEOTRACES program is to understand the distributions of many elements and their isotopes in the ocean. Until quite recently, these elements could not be measured at a global scale. Understanding the distributions of these elements and isotopes will increase the understanding of processes that shape their distributions and also the processes that depend on these elements. For example, many "trace elements" (elements that are present in very low amounts) are also important for life, and their presence or absence can play a vital role in the population of marine ecosystems. This project will launch the next major U.S. GEOTRACES expedition in the Pacific Ocean between Alaska and Tahiti. The award made here would support all of the major infrastructure for this expedition, including the research vessel, the sampling equipment, and some of the core oceanographic measurements. This project will also support the personnel needed to lead the expedition and collect the samples.

This project would support the essential sampling operations and infrastructure for the U.S. GEOTRACES Pacific Meridional Transect along 152° W to support a large variety of individual science projects on trace element and isotope (TEI) biogeochemistry that will follow. Thus, the major objectives of this management proposal are: (1) plan and coordinate a 60 day research cruise in 2018; (2) obtain representative samples for a wide variety of TEIs using a conventional CTD/rosette, GEOTRACES Trace Element Sampling Systems, and in situ pumps; (3) acquire conventional CTD hydrographic data along with discrete samples for salinity, dissolved oxygen, algal pigments, and dissolved nutrients at micro- and nanomolar levels; (4) ensure that proper QA/QC protocols are followed and reported, as well as fulfilling all GEOTRACES intercalibration protocols; (5) prepare and deliver all hydrographic data to the GEOTRACES Data Assembly Centre (via the US BCO-DMO data center); and (6) coordinate all cruise communications between investigators, including preparation of a hydrographic report/publication. This project would also provide baseline measurements of TEIs in the Clarion-Clipperton fracture zone (~7.5°N-17°N, ~155°W-115°W) where large-scale deep sea mining is planned. Environmental impact assessments are underway in partnership with the mining industry, but the effect of mining activities on TEIs in the water column is one that could be uniquely assessed by the GEOTRACES community. In support of efforts to communicate the science to a wide audience the investigators will recruit an early career freelance science journalist with interests in marine science and oceanography to participate on the cruise and do public outreach, photography and/or videography, and social media from the ship, as well as to submit articles about the research to national media. The project would also support several graduate students.

NSF Award Abstract:
A researcher at the University of California, Santa Cruz will analyze the chemical composition of marine particles collected from the ocean. Marine particles will be collected in two size classes, 1-51um and >51um along the U.S. GEOTRACES Pacific Meridional Transect (PMT), which will sample from Alaska to Tahiti along 152°W. The smaller particles generally remain suspended in seawater, where they can interact with dissolved elements in seawater, whereas the larger particles tend to sink which means these elements can be transported to the bottom of the ocean. We will measure a suite of trace elements (e.g. iron, aluminum, zinc, manganese, cadmium, copper, cobalt, titanium, and barium), some of which are required for life, and others that act as tracers of oceanographic processes, as well as the major biologically-produced carrier phases (e.g. particulate organic carbon and the biominerals, calcium carbonate and biogenic silica) in the size-fractionated particles collected from the US PMT section. The data will be used to assess the relative importance of particle concentration, composition, and size distribution on the cycling and removal of trace elements and their isotopes (TEIs). Results will not only contribute to the overall goal of the GEOTRACES program, but also provide critical information to other science communities interested in the role of particles in sequestering carbon from the atmosphere through a process known as the biological carbon pump. A graduate student and a postdoc will be supported and trained on this project, and undergraduate students will be involved in several aspects of this work. The results from this study will be integrated into class curricula taught by the researcher. The scientist will also work with a science journalist who will sail on the expedition to translate the process and initial results of this research to the public.

Particles play essential roles in the cycling and distribution of trace elements and isotopes (TEI) in the ocean by being sources and sinks for many TEIs. The scavenging of dissolved TEIs by particles is a major removal term for many particle-associated TEIs, but is poorly understood and represents a major uncertainty in our understanding of the biogeochemical cycling of many TEIs. The scavenging of TEIs is affected by particle size, concentration, and composition, whereas the subsequent removal of particles by sinking is influenced by particle dynamics processes such as particle aggregation and disaggregation. We will measure the major (particulate organic matter, calcium carbonate, opal, lithogenic particles) and minor (particulate trace metals) phase compositions of size-fractionated particles (1-51um; >51um) collected by in-situ filtration on the the US GEOTRACES Pacific Meridional Transect (PMT). The PMT will be the first meridional section of the US GEOTRACES program and will cross many gradients in surface productivity, biological community composition, subsurface silica concentrations, and depth of the calcite saturation horizon. Therefore, the US PMT section is expected to vary dramatically in particle concentration, composition, and size distribution, allowing us to examine the factors controlling scavenging efficiency in the ocean.

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.