Rationale for Repeat Hydrography Surveys in Support of Clivar and Carbon Cycle Objectives

The U.S. Global Ocean Carbon and Repeat Hydrography Program is part of the international GO-SHIP program, which carries out a systematic and global re-occupation of select hydrographic sections to quantify changes in storage and transport of heat, fresh water, carbon dioxide (CO2), and related parameters. By integrating the scientific needs of the carbon and hydrography/tracer communities, major synergies and cost savings are achieved. In addition to efficiency, the coordinated approach produces scientific advances that exceed those of individual programs. These advances contribute to the following overlapping scientific objectives:

  • Data for Model Calibration and Validation
  • Carbon System Studies
  • Heat and Freshwater Storage and Flux Studies
  • Deep and Shallow Water Mass and Ventilation Studies
  • Calibration of Autonomous Sensors

The scientific objectives are important both for research programs, such as CLIVAR (Climate Variability and Prediction) and the carbon programs, and for operational activities such as GOOS and GCOS (Global Ocean/Carbon Observing Systems). The program addresses community needs that one component of a global observing system for the physical climate/CO2 system should include periodic observations of hydrographic variables, CO2 system parameters, and tracers throughout the water column.

The Global Ocean Ship-Based Hydrographic Investigations Program (GO-SHIP) brings together scientists with interests in physical oceanography, the carbon cycle, marine biogeochemistry and ecosystems, and other users and collectors of hydrographic data to develop a globally coordinated network of sustained hydrographic sections as part of the global ocean/climate observing system. GO-SHIP’s development of a globally coordinated network of sustained ship-based hydrographic sections has become an integral component of the ocean observing system.

The objective of the repeat hydrography program is to maintain decadal time-scale sampling of ocean transports and inventories of climatically significant parameters, such as carbon system components, nutrients, freshwater and heat over the entire water column. Earlier programs [e.g., WOCE and JGOFS during the 1990s] provided a full depth baseline data set that can be used, along with other data, for detection of future changes, and showed where atmospheric constituents are entering the oceans. The repeat hydrographic measurements reveal much about the stability of internal pathways and changing patterns in ocean properties. They continue to serve as a baseline to assess changes in the ocean’s biogeochemical cycle in response to natural and/or anthropogenic activity. Long-term measurements are used to follow global warming-induced changes in the ocean’s transport of heat and freshwater, which could affect the circulation by altering thermohaline overturning. While autonomous sampling programs such as Argo and the basin-scale volunteer observing ship programs can sample a portion of the climate-relevant fields, that is, parameters important for heat and freshwater in the upper part of the water column, they cannot at this time sample the entire water column nor can they sample important chemical tracer constituents. These semi-autonomous programs also cannot provide calibrated data; sensors presently in use are subject to drift and require occasional verification by in situ measurements. Broader societal impacts of the program include: broad and near immediate dissemination of data to enhance scientific and technological understanding; societal benefits of collection of a high quality data set, use of the data to assess climate change, and a resource for model calibration of the climate system; promotion of training and learning for graduate students, postdoctoral scientists, and new scientists.

This web site is supported by grant funds from the National Science Foundation. Any opinions, findings, and conclusions or recommendations expressed in this web site are those of the PIs, James Swift and Lynne Talley, and do not necessarily reflect the views of the supporting Federal agency.

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