The North American Carbon Program Plan (NACP)
A Report of the Committee of the
U.S. Carbon Cycle Science Steering Group

Appendix 3

 Ocean Carbon Initiatives and Ocean Observations
 

Ocean Carbon Initiatives

Recent workshops sponsored by NSF, NOAA, and NASA identified research objectives to improve understanding of carbon dynamics in the ocean. Several themes were common among these federal agencies:

  • What are the critical components of the ocean carbon cycle regulating the partitioning of CO2 between the atmosphere and the ocean on seasonal to interannual time scales, and how can we improve prediction of the response of these processes to changes in environmental conditions (e.g., due to global warming)?

  • How do we adequately characterize the non-steady-state behavior of oceanic systems?

  • How do components of the ocean system-physical and ecological-move between semi-stable states?

  • What are the stabilizing (negative) and destabilizing (positive) feedbacks inherent in the system?

  • How can biological, physical, and chemical processes be more realistically represented in ocean carbon cycle models?

  • What are the potential responses of marine ecosystems and ocean biogeochemical cycles to climate?

Implementation of any research effort that addresses ocean carbon cycling in a global context will require an integrated Earth systems approach that incorporates many disciplines and interagency partners. Below are brief descriptions of the interagency planning efforts for an ocean carbon program that directly address the scientific questions of the NACP.

NOAA GCC

The NOAA Global Carbon Cycle (GCC) Program currently focuses its efforts on the large-scale distributions and fluxes of CO2 in the open ocean regions of the North Atlantic and North Pacific Oceans. Given adequate enhanced resources, the NOAA GCC program envisions a major expansion of sea surface CO2 measurements and related properties in the North Atlantic and the North Pacific (including the equatorial Pacific), and potentially the coastal regions. The measurements will be made primarily using 8 to 12 volunteer observing ships (VOS), supplemented by time-series measurements. The North Atlantic and North Pacific studies will provide constraints for improved inverse model estimates of the North American carbon sink, yield robust values of air-sea CO2 fluxes in the coastal and open ocean regions on both sides of North America, and give important and extensive new information about biogeochemical processes.

NSF CoOP

The NSF CoOP (Coastal Ocean Processes) Program is currently sponsoring research on the transport and controlling biogeochemical processes at a variety of U.S. margin environments. The CoOP research plan is to conduct process and modeling studies on shelves that differ in the dominant physical processes that influence cross-margin transport and control biogeochemical characteristics. CoOP studies thus attempt to isolate key processes that have some global generality and to study these in detail on margins where effects can be isolated with a maximum degree of confidence. Modeling studies are integrated with the process studies and used to synthesize and generalize study results. CoOP presently supports research programs along margins characterized by wind-induced transport on the coasts of California and Oregon.

NSF RiOMar

As a component of NSF’s global carbon cycle research efforts, the RiOMar (River-dominated Ocean Margins) initiative focuses on process studies of carbon transformations and transport in continental margins impacted by major river inputs (such as the Mississippi River system in North America). The decadal-scale storage of terrestrial carbon within the terrestrial portions of some river systems may be much more important than previously recognized. Recent findings suggest that the age of DOC and POC being discharged from rivers is generally older and more variable (i.e., across different river systems) than previously believed. RiOMar systems are important global sites for burial of organic carbon and other biogeochemically important materials. Globally, about 90% of modern organic carbon burial occurs in RiOMar systems (deltas and associated shelf environments). Despite the prominence of sediment burial, large quantities of organic carbon are remineralized in RiOMar environments, as a result of diagenetic transformations and subsequent transport in dissolved or colloidal forms. Annually, the total organic carbon burial in marine sediments is equivalent to less than one-third of the riverine organic carbon discharge---indicating that riverine organic matter is rapidly mineralized or preferentially transported off the margin.

NASA Planning

NASA has conducted several workshops to plan an extensive program of observations of carbon cycling and air-sea fluxes in selected coastal and open ocean regions surrounding the continental United States and Alaska. The plans focus on quantification of air-sea CO2 fluxes, carbon transport (including downward export out of the mixed layer), and biogeochemical transformations of carbon (e.g., photochemistry of DOC). The existing suite of satellite-observed ocean parameters includes surface winds (scatterometry and passive microwave radiometry), ocean circulation (altimetry), sea surface temperature (SST; infrared radiometry), and chlorophyll-a concentrations (ocean color) and primary production (ocean color with additional ancillary information on SST, mixed layer depth, surface irradiance, etc.). Future algorithm development efforts will focus on additional carbon products such as dissolved organic carbon, particulate organic carbon, new production, export production, phytoplankton functional groups (e.g., coccolithophores, trichodesium) and air-sea CO2 fluxes using remote-sensing inputs. NASA currently has an airborne combination pulse-probe LIDAR/hyperspectral radiometer for phytoplankton and ocean carbon studies and an airborne microwave radiometer for ocean salinity measurements, both of which would be extremely useful for the coastal studies envisioned under the NACP. A satellite salinity mission has been proposed to the most recent Earth System Sciences Pathfinder program, but the evaluations have not been released as yet. NASA is also developing a lidar system for profiling particle concentrations from a ship or aircraft. Appendix 1 provides a summary of the relevant satellite and aircraft observations that are available, under development, approved, or under discussion for the next decade.

To better utilize remote-sensing data for understanding the underlying physical, biological, and chemical processes, investments have been discussed to develop refined ocean carbon cycle process and ecosystem models capable of integrating remote-sensing and in situ measurements. Related modeling activities are already underway as part of the NASA Seasonal-to-Inter-annual Prediction Program (NSIPP), which is developing methodologies for assimilating physical oceanographic data into global-scale coupled ocean-atmosphere numerical models. Development will integrate biological/chemical/physical modeling on several scales, including detailed process models, local and regional site-specific models, diagnostic, inverse and data assimilation models, and global ocean biogeochemical models.

 
 Initial Concepts for Ocean Observations
 

The ocean observation component of the NACP is focused on addressing two basic issues: (1) How much carbon is sequestered by the oceans (coastal and open), in particular in the Northern Hemisphere? (2) How do energetic coastal processes influence atmospheric carbon dioxide in the marine boundary layer? The division between the open and coastal oceans is operationally defined as the boundary between the highly variable surface waters near the coast and the relatively stable offshore waters. The location of this boundary depends on the region and environmental conditions, generally from 50 to 500 km from shore (Figure A3.1). The open ocean and coastal observation networks outlined below are expected to develop in coordination with the ring of coastal atmospheric stations and will provide information for extended periods on interannual variability. The intensive work proposed in the Coastal Network section is planned for 2004-2006 to complement NASA and NSF field programs.

Open Ocean Network

The North Atlantic and North Pacific studies will provide information on the boundary conditions for the NACP and help place NACP data in a larger scale context, providing critical constraints for improved inverse model estimates of the North American carbon sink. The NACP will benefit greatly from implementation of existing and enhanced open ocean plans that focus on large-scale distributions and fluxes of CO2 (see Bender et al., 2001). The primary component of these programs will be measurements of surface seawater and atmospheric CO2 using automated shipboard instruments on 8 to 12 VOS that transit the North Pacific and North Atlantic. Ship tracks will repeat at monthly to seasonal intervals, with likely lines between Seattle and Tokyo, Los Angeles and Hong Kong, Southampton and Panama, and Lisbon and New York, designed to cover the range of oceanographic regions. Time-series stations located at key spots in the North Atlantic and North Pacific will provide data on higher frequency variability. Process studies in the

Figure A3.1

Figure A3.1. pCO2 variability in surface waters across the continental margin of the west coast of the United States, showing the high degree of variability in coastal upwelling regions out to a distance of approximately 200 km from the coast (data provided by Francisco Chavez of MBARI).

North Atlantic and North Pacific will also contribute to the effort. These data will yield robust values of air-sea CO2 fluxes in open ocean regions on both sides of North America, and will provide ocean-atmosphere fluxes to help constrain improved inverse model estimates of the North American carbon sink.

Long-term studies by programs like RiOMar will provide valuable information on land-ocean interactions and transformations. NACP will provide a forum for the coastal oceanography and terrestrial scientists to coordinate efforts and better ensure that no major source or sink regions in the wetland and coastal environments are missed. Both nearshore terrestrial and ocean scientists will work with atmospheric scientists to interpret signals observed in coastal towers and aircraft profiles.

NACP Coastal Ocean Network

The coastal ocean program for the NACP is envisioned as a set of meridional and zonal VOS ship transects and time-series stations, focusing on high-resolution observations of the air-sea fluxes of CO2 in the continental margins of North America (Figure A3.2). The time-series moorings will make high-resolution measurements in the surface water and atmosphere, included calibrated data for atmospheric CO2 comparable to CMDL island stations.

Monthly or seasonal transects perpendicular to the coast, intersecting the time-series moorings, will characterize the onshore-offshore gradients, placing the data from the moorings in a spatial context. Measurements will include basic meteorological and hydrographic data, atmospheric and oceanic pCO2, organic carbon, nutrients, and primary production, allowing calculation of net oceanic CO2 fluxes. The observations will be coordinated with aircraft surveys to obtain large-scale vertical and horizontal distributions of atmospheric CO2. A limited number of sites in representative ecosystems will be intensively studied, including the Mid-Atlantic Bight, the South Atlantic Bight, the West Coast region, the Gulf of Maine, the Mississippi Delta region and the Bering Sea. These sites will be centered at the time-series moorings.

Coordination with Satellite Observations

Figure A3.2

Figure A3.2. Proposed sampling domains for open-ocean and coastal regions within the scope of the NACP. Surface water pCO2 measurements and ancillary measurements will be made on VOS ships and moorings. The red dots show the locations of coastal time series and the black lines indicate time-series surveys.

Field observations required for algorithm development (bio-optical and atmospheric correction), satellite calibration and product validation, and model process parameterization and formulation to the greatest degree possible will be acquired to ensure complete data sets. The field measurements will include inherent and apparent ocean optical properties, biological properties (species, pigments, photosynthetic rates, etc.), and chemical and hydrographic properties (salinity, nutrients, dissolved and particulate carbon concentrations, etc.). In most cases, these field experiments will be joint cruises with NOAA and NSF. The NASA strategy will be to augment open ocean sampling on NOAA and NSF cruises in the North Atlantic and North Pacific and at the Bermuda and Hawaii time-series sites. For the more complex coastal studies, a detailed interagency strategy will be developed to account for the use of smaller vessels (fewer investigators, hydrographic winches, wet lab space, etc.) and differing data collection strategies (time series, surveys, process studies, algorithm development, etc.). Algorithm development and process parameterization studies will require at least seasonal cruises in a variety of sites to capture the variability needed for these formulations. Suggested coastal sites for bio-optical algorithm development are the same regions suggested for the intensive studies.

The acquisition of observations will be coordinated for each cruise so to minimize redundancy, maintain data consistency and quality, and maximize data use. Finally, an interagency strategy for data submission, quality assurance, and management is being developed. One example of an existing data management arrangement is collaboration between the NASA Sensor Inter-comparison and Merger for Interdisciplinary Oceanic Studies (SIMBIOS) project and NOAA’s National Oceanographic Data Center (NODC), where bio-optical data collected by NASA-supported investigators for ocean color algorithm development and product validation is provided to NODC for general distribution.

 
 
 
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