Award: OCE-1660012

The central focus of this project was an intercomparison of different methods for measuring the rate of sinking carbon due to biological processes in the upper kilometer of the ocean.  There are many methods in use, but no agreed-upon best way of making these measurements.  In this study we carried out simultaneous trials of different types of sediment traps (devices that collect sinking “marine snow”), cameras and light scattering sensors that detect marine snow, and one chemical tracer method that can detect how much marine snow sank in the several weeks prior to measurements.  This intercomparison had 3 main priorities:

1) a direct comparison of the amount and composition of marine snow collected by two types of robotic, depth-seeking sediment traps and one more traditional type of trap that is moored to a floating buoy.

2) a comparison of the sediment trap measurements, above, to the amount of marine snow that sank just prior to measurements using the chemical tracer method.

3) a comparison of trap and chemical tracers to optical (cameras and light sensors) methods that assess the amount of sinking marine snow, and the sizes of these particles.

Our main findings include

 

1. Cone-shaped sediment traps appeared to collect lower amounts of sinking marine snow than cylindrical traps but particles collected by all trap types had a similar composition. These chemical measurements were consistent with images of the collected particles in different trap types.
2. Particles filtered directly from the ocean with underwater pumps had similar chemical compositions to the marine snow collected in sediment traps, except that particles collected in cone-shaped traps were depleted in a chemical tracer that indicates perhaps the smallest particles were not as efficiently collected.
3. Chemical tracers of past sinking marine snow flux agreed relatively well with sediment trap measurements, although there was some variability over distances of around 10 kilometers.
4. Different participating labs chemically analyzed portions of the same samples, and found that their techniques were in agreement.

 

Understanding the ocean’s role in the carbon cycle is important for broader societal issues, including estimates of the rate of expected climate change due to increases in CO2 in the atmosphere, some of which is transferred via sinking particles and stored in the deep ocean. Sinking particles also serve as an important mechanism for removal of man-made pollutants from the surface to the deep ocean. They are also a source of energy to the ocean mid and deep waters, impacting ecosystems and hence fisheries. Despite the importance of sinking marine particles in the cycling of carbon and other important ocean nutrients and chemicals, marine snow remains difficult to collect in a consistent, reproducible manner. We have tested various particle collection devices that are used in ocean sciences, and by making this intercomparison we have provided a community service in that their characteristcs have been quantified for future users who might use these instruments on ocean going research vessels.  In addition, we have migrated the one of the trap designs to a commercial float platform and are in the process of disseminating the design details to other users through the scientific literature.

 

 

 

 

Last Modified: 10/28/2019
Modified by: Margaret Estapa