The impact of rapid human development on coastal regions and shallow water systems is not fully understood and remains a research priority. Results of the proposed planning meeting will be expanded U.S. – China research collaborations on interrelated research themes of coastal and ocean environments that are heavily impacted by human activity and climate variability and change, and that, in turn, have the potential to create widespread societal and environmental changes. Human development activities will both affect and be affected by these changes. Resolving (through research) uncertainties about how such changes occur would provide knowledge needed to support national and international policy decisions about sustainable human development and environmental protection.

Numerous research parallels exist between, for example, the impacts of outflow from the Changjiang and Mississippi Rivers on the East China Sea and Gulf of Mexico, respectively. Both basins are heavily populated and the natural processes have been disrupted by dam construction, land use and land cover change, and other factors. The outflow of the rivers carries large amounts of sediment and nutrients, which profoundly affect the biogeochemical conditions on the continental shelf. This can lead to a variety of processes that can cause environmental and economic damage such as hypoxia (low oxygen concentrations in sea water which adversely affect marine life) or shifts in coastal productivity. Large rivers are also a primary source of carbon to the ocean and therefore directly contribute to the global carbon cycle and climate change. Inversely, climate variability and change affect river discharge through changes in precipitation patterns. Comprehensive and long-term observations of riverine fluxes to the ocean are virtually non-existent; therefore, many of the processes and their variability are poorly understood. The Changjiang and Mississippi Rivers rank fifth and seventh in water discharge and fourth and seventh in sediment discharge. While these systems are being studied independently, both would benefit from combined and comparative research. Joint observations and modeling of both systems will allow for intercomparisons and knowledge sharing that will lead to improved protection and management of riverine, estuarine, coastal, and ocean resources.

Similarly, mounting evidence suggests that sea-surface temperature (SST) variability in the tropical oceans has a dramatic influence on regional and global weather patterns. Over the North American continent, fluctuations in seasonal rainfall are known to be linked to the El Niño-Southern Oscillation, while decadal or longer time scale fluctuations are linked to SST anomalies in both the tropical Pacific and tropical Atlantic. Over the Asian continent, the prime climatic phenomena controlling the rainfall fluctuations are the Asian Monsoons and El Niño-Southern Oscillation, which tie closely to SST variability in the Indo-Pacific. Positive trends in heavy precipitation have been observed over the U.S. and the southern part of China over the past decades, while significant negative trends are observed in northern China. Are these changes in the precipitation patterns caused by changes in ocean circulation in the Indo-Pacific and tropical Atlantic, respectively? If so, the coastal and continental shelf ecosystem processes in the Changjiang and Mississippi river basins must be remotely connected to these ocean circulation changes, because variation in river discharge is affected by precipitation and snow melt, which in turn are affected by climate variability and change. However, how climate information flows from global through regional to local scales is not clear, nor is it clear what aspects of the ocean circulation changes are most critical for driving the regional climate and local ecosystems. Given the many commonalities between the two systems and the unique features that each system possesses, a comparative study of the Indo-Pacific and Atlantic climate systems and their respective impacts on the coastal and continental shelf ecosystem processes in the Changjiang and Mississippi River basins is an ideal area for bilateral collaborations.

This joint research proposals that will result from this planning meeting will be relevant to societal issues shared by the U.S. and China and beyond, ranging from local and regional fisheries economies to permanent changes in global climate. They will also form the basis for important research advances, and for the training of coastal, ocean, and climate scientists capable of addressing critical environmental concerns related to our coastal and ocean environments at all scales in space and time. Collaborators and students from both countries will benefit from this program through increased access to multiple, parallel study regions, including both observational and modeling activities and results. Shared results can inform the development and refinement of comprehensive models of both the Changjiang and Mississippi basins and respective coastal environments and receiving waters. Three specific proposal ideas that were identified during the Washington, D.C. meetings are presented below.

1. Coastal Hypoxia: The standard paradigm for the formation of hypoxia in the coastal ocean requires the input of freshwater and nutrients and organic material. The nutrient and organic loading provide the hypoxic potential, represented by the amount of organic material that is available to be respired, to the fuel the formation of hypoxia. The stratification envelope represents the area of the shelf that is sufficiently stratified to prevent the ventilation of the lower layer – the region over which water mass and circulation patterns allow persistent and widespread hypoxia to develop. In both coastal ocean regions influenced by the Changjiang and Mississippi River systems, hypoxia formation is driven by the combined and competing effects of the physical processes that control stratification and the biochemical processes that effect dissolved oxygen concentration. We plan to investigate how the relatve contributions of these different processes change with proximity to the river source and control the duration, extent and severity of hypoxia in the coastal ocean and to examine the potential affects of climate change on these processes.


2. Biogeochemical Processes: RiOMars are dynamic regions that receive terrestrial and marine organic carbon. (OCterr and OCM). Rivers such as the Changjiang Mississippi (and associated deltaic environments) provide major pathways for the delivery of OCterr to margin regions and the deep sea. The orientation and proximity of river mouth-canyon systems determines the potential role these regions play as: 1) distinct depocenters for OC burial and 2) an OC export pathway to the deep sea. Once introduced by rivers or fixed on the shelf, OCterr and deposited on shelf regions, where it mixes with OCM and is either decomposed or transported to deeper regions. Knowing the fate, transport, and burial of this OC is critical to understanding carbon sequestration and eutrophication processees on continental margins. By analyzing the chemical composition and spatial/temporal dynamics of water column dissolved and particulate materials, along with surface sediments and down-core changes (e.g., paleo-reconstruction) we plan to examine the dominant past and recent changes biogeochemical processes in these RiOMars.


3. Dynamics of Loop Current and Luzon Current Systems: The Loop Current that connects the Caribbean Sea to the Gulf of Mexico and the Luzon Current that connects the Philippine Sea to the South China Sea share many dynamical similarities, including their eddy-shedding processes and interconnectivities to the basin-scale ocean circulations. Each of these circulation systems affects significantly the off-shore transport processes of the river discharge from the respective river system, and both are affected by the basin-scale ocean circulation changes in response to global climate change.