Table of Contents

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

Geospatial Synthesis of Chromophoric (color-absorbing) Dissolved Organic Matter (CDOM) Distribution in the Gulf of Mexico

PI: Christopher Osburn, Dept. Marine, Earth, and Atmospheric Sciences, NC State University

Co-PIs: Thomas Bianchi, Texas A&M University, Bob Chen, University of Massachusetts-Boston; Paula Coble, University of South Florida; Eurico D'Sa, Louisiana State University

This dataset is affiliated with the North American Carbon Program (NACP). For additional information, please see the entry at the NACP site.

This data set will be a synthesis of bio-optical data on chromophoric or color-absorbing dissolved organic matter (CDOM) in the coastal regions the Gulf of Mexico - an immediate goal of the NACP and OCB programs. Absorption spectra and DOC concentrations from the Organic Matter Cycli project will be reported. In addition to in situ absorption spectra and DOC concentrations some study locations may also report fluorescence (estimate of chlorophyll a concentration), plus CTD and dissolved oxygen measurements

CDOM affects on water quality and water clarity are part of a high priority issue identified by the Gulf of Mexico Alliance (GOMA). Each of the PI's listed has historical CDOM data from coastal regions of the Gulf of Mexico, ranging from the Texas coast to West Florida Shelf.

The historic CDOM synthesis data set will provide a resource for validating remote sensing algorithms that predict water clarity properties in the coastal areas of the Gulf of Mexico. Each dataset to be shared by a PI is linked to specific research cruises. Thus the database has temporal and spatial coverage and associated metadata. In Years 1-2 of the project, data will be collated from each PI and transformed into a format amenable to data rescue by BCO-DMO. The structure of the resulting database will provide a mechanism by which future data sets may be integrated by members of the scientific community, through the project. In Year 2, as data comes online, it will be used to validate a coastal CDOM remote sensing algorithm for the Gulf of Mexico. Co-PI D'Sa has a decision support science website (http://gulf-coast.lsu.edu/index.html) that will provide water clarity data products based on CDOM algorithms.

The goal of the project is to have a functional database of CDOM information for two objectives. One objective is to provide coastal oceanographers with a clearinghouse for CDOM data that can be accessed and to which future cruise-related data acquisitions can be added. The second objective is to provide a resource for decision makers who require water clarity data on spatial and time scales for which satellite imagery may be used. For the second goal to be met, we have as an objective the validation of CDOM algorithms using the proposed database. Once the algorithm is validated, water clarity data products can be generated by users using the GCIS website, which will link to the CDOM database hosted by BCO-DMO.

The CDOM database will also provide pilot data for research proposals to NSF from our team. Part of our evolving project is to produce geospatial models of CDOM distributions in the Gulf of Mexico from the inflows of multiple rivers as well as the Loop Current. Functional models of CDOM distributions will further aid in remote sensing algorithm development and validation and in the general understanding of terrestrial C flux to the Gulf of Mexico.

Modification History:
September 2010: added processed Atchafalaya data from Chris Osburn
December 2010: raw/unprocessed Mississippi Plume absorption coefficients were added but then quickly removed
June 2011: added processed Mississippi Plume data from Bob Chen; a_lambda units corrected to "per meter" (had been incorrectly specified as "per nanometer" in earlier version)

Samples were collected at the surface either in bucket grabs or from the Pelican's flow-through system, or by CTD. Samples were filtered through 0.2 micrometer polyethersulfone filters into baked (550 degrees Celsius; 5 hr. minimum) collection vials and stored at 4 degrees Celsius in the dark until return to the lab (about 3 days time). Absorbance was measured on a Shimadzu 1601UV spectrophotometer from 200 to 800 nm at 1 nm intervals versus air. All a(λ) values are blank corrected for Milli-Q water.

Parameters reported will include:
a_lambda = absorption coefficient at each wavelength (250-750 nm), in m-1
DOC = dissolved organic carbon concentration (micromolar).  For DOC, different techniques were used and are identified for each deployment.

Absorption coefficients (a) are calculated from absorbance (A) according to Equation 1:

where L is the pathlength in meters (0.1 m). The absorption coefficients were then modeled from 250 to 750 nm using Equation 2:

Excitation-emission matrix (EEM) fluorescence spectra and 13C-DOC values were measured on most of these samples.

NACP-OCB Coastal Synthesis: Gulf of Mexico region

The objective of the NACP coastal synthesis activities is to stimulate the synthesis and publication of recent observational and modeling results on carbon cycle fluxes and processes along the North American continental margin, a critical unknown in the North American carbon budget. NACP/OCB researchers have identified the Gulf of Mexico as being one of the regions of special interest for this coastal synthesis activity.

Phase 1. Regional Carbon Budgets

The first phase of the coastal synthesis will be to develop a carbon budget for each region based on a compilation of existing data, which will require literature searches, web searches of databases, etc. Although full community participation is welcome and encouraged, Paula Coble volunteered to lead the Gulf of Mexico Phase 1 synthesis efforts.

Some key elements of the database synthesis are:

• Climatology
• pCO2
• riverine delivery, inc losses and inputs on the way
• rates of processes
• ocean color data and products
• export out of coastal regions
• DIC, PIC, DOC, POC
• Nutrients
• Other fluxes
• model output

plus uncertainty analysis and quality control related to those observations

Phase 2. Community Modeling and Database Development

The second phase of the coastal synthesis will involve community modeling activity to refine the regional carbon budgets.

The Ocean Carbon and Biogeochemistry (OCB) program focuses on the ocean's role as a component of the global Earth system, bringing together research in geochemistry, ocean physics, and ecology that inform on and advance our understanding of ocean biogeochemistry. The overall program goals are to promote, plan, and coordinate collaborative, multidisciplinary research opportunities within the U.S. research community and with international partners. Important OCB-related activities currently include: the Ocean Carbon and Climate Change (OCCC) and the North American Carbon Program (NACP); U.S. contributions to IMBER, SOLAS, CARBOOCEAN; and numerous U.S. single-investigator and medium-size research projects funded by U.S. federal agencies including NASA, NOAA, and NSF.

The scientific mission of OCB is to study the evolving role of the ocean in the global carbon cycle, in the face of environmental variability and change through studies of marine biogeochemical cycles and associated ecosystems.

The overarching OCB science themes include improved understanding and prediction of: 1) oceanic uptake and release of atmospheric CO2 and other greenhouse gases and 2) environmental sensitivities of biogeochemical cycles, marine ecosystems, and interactions between the two.

The OCB Research Priorities (updated January 2012) include: ocean acidification; terrestrial/coastal carbon fluxes and exchanges; climate sensitivities of and change in ecosystem structure and associated impacts on biogeochemical cycles; mesopelagic ecological and biogeochemical interactions; benthic-pelagic feedbacks on biogeochemical cycles; ocean carbon uptake and storage; and expanding low-oxygen conditions in the coastal and open oceans.

The North American Carbon Program (NACP) is a multidisciplinary research program to obtain scientific understanding of North America's carbon sources and sinks and of changes in carbon stocks needed to meet societal concerns and to provide tools for decision makers. Successful execution of the NACP will require an unprecedented level of coordination among observational, experimental, and modeling efforts regarding terrestrial, oceanic, atmospheric, and human components. The NACP is supported by a number of different federal agencies through a variety of intramural and extramural funding mechanisms and award instruments. NACP will rely upon a rich and diverse array of existing observational networks, monitoring sites, and experimental field studies in North America and its adjacent oceans. Integrating these different program activities and maximizing synergy amongst them, will require expert guidance beyond the norm for large field programs in Earth system science and global climate change.

Central Objective

The central objective of the North American Carbon Program is to measure and understand the sources and sinks of Carbon Dioxide (CO₂), Methane (CH₄), and Carbon Monoxide (CO) in North America and in adjacent ocean regions.

Goals

• Develop quantitative scientific knowledge, robust observations, and models to determine the emissions and uptake of CO₂, CH₄, and CO, changes in carbon stocks, and the factors regulating these processes for North America and adjacent ocean basins.
• Develop the scientific basis to implement full carbon accounting on regional and continental scales. This is the knowledge base needed to design monitoring programs for natural and managed CO₂ sinks and emissions of CH₄.
• Support long-term quantitative measurements of fluxes, sources, and sinks of atmospheric CO₂ and CH₄, and develop forecasts for future trends.

Science Questions

• What is the carbon balance of North America and adjacent oceans? What are the geographic patterns of fluxes of CO₂, CH₄, and CO? How is the balance changing over time?
• What processes control the sources and sinks of CO₂, CH₄, and CO, and how do the controls change with time?
• Are there potential surprises where sources increase or sinks disappear?
• How can we enhance and manage long-lived carbon sinks, and provide resources to support decision makers?

The NACP Science Steering Group (SSG) provides scientific leadership for the NACP. (NACP SSG)

Program Data: The data from most projects associated with the NACP program are not managed by BCO-DMO.  Information about most projects and their results are available from the Program and Data site URLs shown above.  However, some exceptions are the NACP/OCB coastal synthesis projects listed below when the project section is expanded.

In late June 2008, the OCB Project Office sent out a call for participation in the Coastal Synthesis Activity as part of the North American Carbon Program (NACP) Interim Synthesis Activities. The objective of this activity is to stimulate the synthesis and publication of recent observational and modeling results on carbon cycle fluxes and processes along the North American continental margin. The current state of knowledge of the magnitude, spatial distribution, and inter-annual variability of carbon sources and sinks in coastal waters is incomplete. Thus, the goal of this activity is to synthesize individual, small-scale studies across broader spatial and temporal scales to improve quantitative assessments of the North American coastal carbon cycle. Because the coastal oceans have important and complex linkages with terrestrial, atmospheric, and open ocean biogeochemical cycles, we encourage the participation of researchers focused on both organic and inorganic carbon, as well as nitrogen and phosphorous cycle topics related to carbon balance and related issues such as hypoxia impacts on continental margins.

Planning for the coastal synthesis activity was initiated during a breakout session at the 2008 OCB Summer Science Workshop. The proposed coastal synthesis activity is initially broken into five U.S. geographical sub-regions (Atlantic Coast, Pacific Coast, Gulf Coast, Arctic Coast, and Laurentian Great Lakes), with leads identified for each region. Researchers were encouraged to consider ongoing projects and think about how those projects might relate to one or more of the regional syntheses. Additional information available at the NACP Web site (http://www.nacarbon.org/cgi-bin/working_groups/wg.pl) includes a list of active NACP Interim Synthesis activities and working groups.

The majority of data sets uploaded for this project will be synthesis data sets, representing an integration of previously compiled data from the various sub-regions.

Related Links:

NACP Coastal Synthesis Web Site (includes regional links)