Understanding the spatial and temporal complexity of the coastal ocean is a long-standing challenge. Quantifying the interactions between atmospheric and terrestrial forcing, and coupled physical, chemical, and biological processes, is critical to elucidating the role of coastal margins in the global carbon cycle, and developing strategies for managing coastal resources in a changing climate.

Learn more about the various themes within Coastal Ocean Dynamics and Ecosystems:

Shelf/Slope Exchange

Shelf/slope exchange processes are important mechanisms that transfer significant amounts of heat, salt, and organic matter between continental shelves and the deep sea. These mechanisms, however, are highly variable in space and time. Many may span the area of kilometers in the horizontal dimension, but may only span a few meters vertically into the water column. Exchange may last only a few days. Extreme events such as storms appear to play a large role in sustaining exchange and dissipating heat, salt, and organic matter.

Traditional shipboard sampling cannot provide sufficient resolution in time or space to fully examine and quantify these shelf/slope processes. As a result, it is not possible to derive robust budgets for carbon, heat, salt, and other properties on continental shelves.

Without a complete understanding of shelf/slope processes, scientists have been unable to quantify the flux of carbon between continental shelves and the deep sea. Additionally, shelf/slope exchanges are critical in structuring continental shelf food webs. For example, megafauna, such as whales, are often known to congregate at locations of intense exchange, driven there likely by the availability of food.

High-frequency spatial and temporal data collected by the OOI Network on the U.S. east and west coasts will enable scientists to quantify these exchange mechanisms and identify their impact on shelf/slope biogeochemistry.

Because exchange can vary in location along the shelf/slope due to the passage of offshore features (e.g., warm/cold core rings) it is very important to collect real-time, in situ data. Additionally, the OOI will have mobile assets, AUVs, deployed in these areas who can be program to navigate towards these temporary features.

Profilers will collect high-frequency data to characterize the water column, from the seafloor to the sea surface. In doing so they will be able to capture properties of water masses that pass through the array. Meteorological measurements will be taken to study the impact of wind forcing on exchange.

Given that the many of the shelf/slope waters are optically complex, the OOI sampling strategy will include optical characterization of dissolved and particulate material (e.g., sediment, phytoplankton, and detritus) in the water column.

To enable future studies of other shelves and processes, the Pioneer array itself will be re-deployable at the completion of the initial study.

Related Science Questions

  • How do shelf/slope exchange processes structure the physics, chemistry, and biology of continental shelves?
  • What processes lead to heat, salt, nutrient, and carbon fluxes across the mid-Atlantic Bight shelf-break front?
  • What is the relationship between the variability in shelf-break frontal jets and along-front structure in phytoplankton distributions?
  • What aspects of interannual variability (in stratification, offshore circulation patterns, jet velocities, and wind forcing) are most important for modulating shelf/slope exchange of dissolved and particulate materials?

Hypoxia on Continental Shelves

Dissolved oxygen concentrations in continental shelf waters are influenced by a variety of physical, chemical, and biological processes. These processes occur over spatial scales of meters to thousands of kilometers, and from hours to decades.  Dissolved oxygen in seawater is crucial to the survival of marine animals. The coastal ocean is vulnerable to low oxygen (hypoxic) zones and events that may involve significant marine die-offs.

Unlike hypoxic events fueled by anthropogenic nutrients and limited circulation of semi-enclosed estuaries or embayments, hypoxia on the continental shelf, such as off the coast of Oregon, is driven by atmospheric forcing, upwelling/downwelling, and variability in ocean circulation.

The formation and duration of hypoxic areas are subject to climate variability and variations in upwelling/downwelling and oceanic flow on seasonal, interannual, El Niño Southern Oscillation, and inter-decadal scales. Understanding hypoxic events and impacts to marine ecosystems requires the ability to observe physical, chemical, and biological conditions across the continental shelf to slope waters, for periods spanning years (seasonal to interannual change) to decades (El Niño Southern Oscillation and Pacific Decadal Oscillation shifts).

OOI’s distributed network of fixed and mobile platforms will permit studies of the frequency, intensity, and mechanisms driving the invasion of low dissolved oxygen water on continental shelves. Large, three-dimensional data volumes collected by gliders will provide detailed information for making maps of the low dissolved oxygen waters. Gliders will also adaptively map the spatial extent and morphology of the low dissolved oxygen intrusion.

For studies of coastal ocean processes, from event-scale changes, to interannual variability, to interdecadal trends, data will be collected by permanent and movable instrumented arrays that have sufficient power and bandwidth to support multidisciplinary sensors. These nodes will also collect time series of the gradients in physical and biogeochemical properties across the continental shelf and slope.

By combining these data with simultaneous observations of the meteorological forcing and oceanic flows measured at high vertical resolution, scientists will be able to study the corresponding chemical and biological response to the low dissolved oxygen water.

Related Science Questions

  • What are the dynamics of hypoxia on continental shelves?
  • What are the relative contributions of low-oxygen, nutrient-rich source water, phytoplankton production from local upwelling events and along-shore advection, and local respiration in driving shelf water hypoxia in the Northern California Current?
  • What are the impacts of shelf hypoxic conditions on living marine resources?
  • How are wind-driven upwelling, circulation, and biological responses in the coastal zone affected by the El Niño Southern Oscillation, water mass intrusions, and inter-decadal variability?