The Columbia River brings buoyant fresh water to
the Pacific Ocean, along with dissolved silicate and iron, crucial to
phytoplankton growth. The plume strongly-influences Oregon
and Washington's dynamic coastal environments.
The Ocean Mixing Group seeks to understand the
role of turbulence in mixing water of riverine and oceanic origin to
produce the biochemical environment needed to fuel high biological
productivity. The 1-5 m thick plume issued from the Columbia
mouth at ~2 m/s produces high velocity shear, a sharp, bore-like front,
and generates large amplitude internal waves throughout the
region. Each of these play impoprtant roles in entraining
nutrients into the plume. Bottom boundary mixing may also bring
Fe from plume-deposited sediments into the upwelling system.
Turbulence
and Mixing in the Columbia
River Plume
Using Chameleon
(our vertical microstructure profiler) and advanced shipboard acoustics
(near-surface ADCP and 120 kHz echosounder), the Ocean
Mixing Group
obtains highly-resolved observations of velocity, density, turbulence,
optics and
acoustical backscatter within the plume and the coastal waters that
receive it. These observations reveal extremely sharp gradients
in velocity and water properties that produce intense mixing and
large-amplitude internal waves.
Shear-Driven Turbulence
- As the plume leaves the river mouth, strong vertical gradients in velocity generate turbulence at the plume's base.
Plume
Fronts
- Plume fronts are extremely sharp (>0.5 m/s changes in 10 m)
- highly nonhydrostatic
- displace fluid downwards
- may release large amplitude internal waves.
Large
Amplitude Internal Waves
- large amplitude internal waves are ubiquitous.
- displace fluid >30-m downward
- may be unstable and generate turbulence
- have associated biological response?
If you don't have electronic access to Nature, a reprint can be found here (download 500 kB pdf)
2004
Observations
Preliminary observations from the July 2004 experiment are available here.
Link to graduate student Levi Kilcher's RISE website
Participants
RISE (River Influences on Shelf Ecosystems) is a 5-year
interdisciplinary study of the Columbia River plume, funded by the
Coastal Ocean Program of the National Science Foundation.
RISE consists of participants from the Universities
of Washington, California (Santa Cruz), OHSU and Oregon State University.
RISE participants from the Ocean Mixing Group include
- Jonathan Nash (PI)
- Jim Moum (co-PI)
- Levi Kilcher (PhD student)
- Sasha Perlin (data analysis)
- Ray Kreth (engineering support)
- Mike Neely-Brown (engineering support)
