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NORTH AMERICAN CONTINENTAL MARGINS a Synthesis and Planning Workshop NORTH AMERICAN CONTINENTAL MARGINS A Synthesis and Planning Workshop Report of the North American Continental Margins Working Group for the U.S. Carbon Cycle Scientific Steering Group and Interagency Working Group U.S. Carbon Cycle Science Program Washington D.C. Editors Burke Hales, Wei-Jun Cai, B. Greg Mitchell, Christopher L. Sabine, and Oscar Schofield The workshop was supported by the Carbon Cycle Interagency Working Gloup (CCIWG). The CCIWG includes the Department of Energy, the U. S. Geological Survey of the U. S. Department of the Interior, the National Aeronautics and Space Administration, the National Institute of Standards and Technology, the National Oceanic and Atmospheric Administration of the U. S. Department of Commerce, the National Science Foundation, and the U. S. Department of Agriculture. This report was printed by the University Corporation for Atmospheric Research (UCAR) under award number NA06OAR4310119 from the National Oceanic and Atmospheric Administration, U. S. Department of Commerce. The statements, findings, conclusions, and recomendations are those of the authors and do not necessarily reflect the views of any agency or program. Recommended citation: Burke Hales, Wei-Jun Cai, B. Greg Mitchell, Christopher L. Sabine, and Oscar Schofield [eds.], 2008: North American Continental Margins: A Synthesis and Planning Workshop. Report of the North American Continental Margins Working Group for the U.S. Carbon Cycle Scientific Steering Group and Interagency Working Group. U.S. Carbon Cycle Science Program, Washington, DC, 110 pp. ii Table of Contents Executive Summary .............................................................................................................................................. 1 Introduction .......................................................................................................................................................... 3 Workshop Motivation and Description ............................................................................................................. 15 North America’s Atlantic Coast .......................................................................................................................... 23 North America’s Pacific Coast ............................................................................................................................ 35 North America’s Gulf of Mexico Coast ............................................................................................................... 49 Continental Margins of the Arctic Ocean and Bering Sea ................................................................................. 57 The Laurentian Great Lakes ............................................................................................................................... 73 North American Rivers and Estuaries ................................................................................................................ 83 Observation and Synthesis of Carbon Cycling on the Continental Margins .................................................... 97 Workshop Conclusions and Recommendations .............................................................................................. 109 iii Executive Summary Continental margins represent a potentially large, and study of the carbon cycling in the entirety of these but largely unconstrained, flux of CO2 between the margins is complicated as a result. coastal ocean surface and atmosphere, with efforts In September of 2005, North American to predict this flux generating estimates of either a Continental Margins: A Synthesis and Planning sink or a source of approximately 1 Pg C yr-1, which Workshop was held in Boulder, Colorado to assess the is significant globally relative to, e.g., pelagic air-sea state of carbon cycle science in the margins surrounding exchange. Large variability inherent in these settings North America, and to offer recommendations guiding makes extrapolation based on sparse sampling difficult. future research. The meeting was attended by over 50 Further confounding these efforts are uncertainties scientists representing over 40 institutions and agencies, as to the boundaries of the coastal margins, both in with expertise relevant to the measurement and seaward and landward extent. There is sensitivity of interpretation of carbon cycling in the major marginal global margin air-sea CO2-flux calculations to the settings surrounding North America. The dominant inclusion or exclusion of estuaries. Other marginal processes driving carbon transport and transformation environments, such as salt-marshes, mangrove forests, in the major geographical regions (Pacific, Atlantic, and tide flats may exchange large quantities of CO2 Gulf, and Arctic coasts) of the margins, in addition to directly with the atmosphere, and it is unclear whether the Laurentian Great Lakes and river/estuary systems, these fluxes are accounted for in regional to global were discussed, as well as subregional variations in scale CO2 budgets. In addition to air-sea gas exchange, this process-dominance. State-of-the-art in-water and the modes and magnitudes of carbon transport across remote-sensing measurement approaches were reviewed other key boundaries in the coastal oceans are poorly with respect to their application in the coastal setting, understood. Net exchange between pelagic and coastal as were synthetic approaches such as biogeochemical oceans; between estuaries and coastal oceans; between modeling based on general circulation and box-models, the coastal water column and seafloor; and between and data assimilation. Further discussion involved the subaerial coastal environments and the atmosphere are needs for clear process-based definition of geographical all areas that have received limited study. subregions, integrative results of process study, and the The knowledge of carbon cycling in North relevance of historical datasets that may not have been America’s continental margins suffers similar applied to carbon cycle interpretations. deficiencies. There have been few integrative, carbon- The group made several recommendations. focused, interdisciplinary studies in these settings, and These were: only very recently has the totality of surface pCO 2 • Increase the platform-of-opportunity data in the waters surrounding North America been measurements in the coastal settings whenever comprehensively evaluated. This effort suggests that possible. Specifically, take advantage of existing the net air-sea flux in the open coastal waters (i.e., moored deployment opportunities (such as excluding estuaries and embayments) is nearly zero, navigational and NOAA NDBC buoys), and of but with uncertainty approaching ±40 Tg C yr-1. The ships that operate primarily in coastal settings small net flux estimate appears to be a sensitive balance (including coastal research and commercial/ between regions of large CO uptake at high latitudes 2 recreational vessels). This may require the and large CO offgassing at low latitudes. These regions 2 development of new technology that is better are the most undersampled of the coastal oceans, suited for these deployments. and raise the possibility of even larger uncertainties. North America’s continental margins are defined by • Encourage examination of existing data that may large variability in carbon-cycle-relevant processes and reside in the gray literature or in data reports from parameters. There is large regional variation in the non carbon-focused research programs. There importance of processes that control carbon transfer was a general consensus that there is much data between terrestrial, oceanic, and atmospheric reservoirs, that has been undersynthesized in the context of 1 Executive Summary North American Continental Margins carbon cycling. Nutrient or oxygen measurements; • Develop a plan for integrated process and synthesis biological standing stock data; and hydrographic study in representative subregions previously or circulation observations among others could all identified by the efforts listed above. Base this be interpreted from the perspective of the carbon plan on a control-volume concept, where net cycle. reactions of carbon within, and net fluxes across key boundaries of, the control volume can be • Develop models that are better suited for constrained. Encourage parallel implementation of application to coastal carbon cycling, both in terms modeling and in-water process study, as opposed to of appropriate spatial and temporal resolution, and modeling studies that follow fieldwork. also in terms of inclusion of processes not typically incorporated in oceanic models. The group did not make recommendations for • Improve remote-sensing algorithms so that strategies or timelines for agency implementation complications in nearshore waters can be of these recommendations. Some of the above overcome. These include increasing spatial and recommendations could obviously be implemented temporal resolution, improving atmospheric immediately through the existing funding structure. corrections, and accounting for complicating There is clear benefit in some of these efforts preceding factors such as increased sediment load and others—for example, the synthesis of existing datasets CDOM concentrations. and the definition of study subregions would help in planning the process and synthesis studies—while • Develop new in-water technologies for increased others—such as the development of improved models, coverage of carbon-relevant
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