Table of Contents

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

Niskin seawater samples were collected in 250 ml bottles and poisoned with 100 µl of mercuric chloride. In the lab, approximately 100 ml was transferred from the bottle to a bubbler attached to a high vacuum line. Samples were acidified with 1 ml of 50% phosphoric acid before stripping with He gas at 200 ml min⁻¹. CO₂ gas was collected cryogenically in a liquid nitrogen cold trap after removal of water vapor. CO₂ yield was calculated manometrically (1σ = 5 µmol kg⁻¹) before transfer to a vacuum flask for isotopic analysis.

Data Quality Flags:
2 = good;
3 = questionable;
 4 = bad. 

BCO-DMO Processing:
- renamed fields to comply with BCO-DMO naming conventions;
- converted Start_Time_UTC field to 4 digits;
- created Start_ISO_DateTime_UTC field.

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:
The ocean has absorbed about a third of the fossil fuel carbon dioxide (CO2) that humans have emitted, slowing the accumulation of CO2 and its associated trapping of thermal energy in the atmosphere. The research aims to improve our understanding of how this ocean uptake of CO2 will change when ocean circulation responds to continuing changes in climate. Researchers will use observations of the isotopic ratio of carbon (13C/12C) of seawater and atmospheric samples, as a high signal/noise method to determine air-sea transfer rates and storage in the ocean interior of fossil-fuel CO2. Also, a state-of the art ocean C-cycling model will be used to validate the model's air-sea exchange rates and upper ocean storage of fossil-fuel CO2. The additional information provided by 13CO2 will establish important benchmarks on ocean-atmosphere and biosphere-atmosphere C exchanges in models used for forecasting future changes in climate. Results would be incorporated into an outreach program through the University of Washington's Program on Climate Change to educate the public on the impact of human activity and climate on the ocean, atmosphere, and earth. One postdoc would be supported and trained as part of this project.

To better understand the processes that control the evolution of the anthropogenic carbon dioxide (CO2) signal in the ocean, we will utilize two characteristics of dissolved inorganic 13Carbon (DIC13) that distinguish it from DIC. First, the 10x longer air-sea equilibration time for DIC13 yields a well-constrained air-sea 13CO2 flux in all basins that is resolvable on decadal time scales. Second, the anthropogenic DIC13 accumulation in the ocean is quantifiable to better signal to noise than anthropogenic DIC itself. The availability of ocean del13C and DIC data from WOCE, CLIVAR and GO-SHIP provide the opportunity to quantify, based on observations alone, the evolution and transports of the anthropogenic DIC and DIC13 signal on regional and global scales in the ocean. Implementation of the anthropogenic DIC and DIC13 perturbations into an ocean model, driven by interannually varying winds, will yield simulations of the DIC and DIC13 evolution that we will compare to observations, helping to identify likely processes causing interdecadal shifts in the rate of this evolution. The combination of observations and model analysis tracking the decadal DIC13 and DIC perturbations are designed to improve our insight into the ocean's important role in modulating climate by taking up and storing anthropogenic CO2.

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.

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.