CURRENT RESEARCH
CURRENT RESEARCH: My students and I are studying the utility of gas distributions in ocean as tracers for biogeochemical and physical problems in Oceanography. Here are a few examples of recent research.
In Situ Measurements of O2 using Profiling Floats
There are more than 3000 Argo profiling floats in the ocean and ~ 300 of these floats have sensors to determine the partial pressure of oxygen. However, the oxygen measurements have not been sufficiently accurate to determine the degree of supersaturation in the surface ocean or to measure the time course of change in the oxygen minimum zones. We have developed a method for calibrating Aanderaa oxygen sensors in situ to increase their accuracy (Bushinsky et al., 2016). The figure below shows the degree of supersaturation of oxygen in the mixed layer of the Northeast Subarctic Ocean. This data has been used to determine the flux of biologically produced oxygen to the atmosphere and from this the ocean's biological carbon pump (See Bushinsky and Emerson, 2015, Yang et al., 2019).
Click Here to see a Movie of profiling floats and gliders with oxygen sensors in the Northeast Pacific at Ocean Station Papa
We have deployed more than 40 of these floats in the subtropical oceans in the northern and southern hemisphere.
The poster below shows a few examples of the degree of oxygen supersaturation in different areas of the ocean. So far, we have found that the net biological oxygen production (the ocean’s biological carbon pump) in the Northern Hemisphere is 2.0 - 2.5 mol C m-2 yr-1 in both the Pacific and Atlantic subtropical oceans. The surprising result is that values in the Southern Hemisphere are lower: about 1 mol C m-2 yr-1 in the subtropical South Atlantic, and near zero in the South Indian and Pacific Oceans. We are in the process of interpreting these results as more data from the floats roles in. The other major aspect of this research is to determine the biological pump in the Equatorial Pacific by interpreting the upper ocean oxygen measurements in this region using a 3-D ocean GCM.
N2/Ar Ratio in the World's Oceans
We have compiled N2/Ar ratios measurements in profiles from the surface to deepest depths in very different areas of the ocean. (See the figure below.) The ratio below 1000 m increases by about 0.4% from the North Atlantic to the North Pacific. Is this an indication of denitrification in sediments below 1000 meters in the ocean?? This is the subject of a recent paper by Hamme and Emerson (2013, Geophys. Res. Lett., 2013)
Argon Supersaturation as a tracer of Diapycnal Mixing in the Thermocline
The figures below illustrate: (a) the degree of Argon supersaturation determined in the thermocline (depths 150 – 800 m, density range 26.0 - 26.5 ) of the North Pacific on three transect cruises made in 2007/2008. Notice that the degree of argon supersaturation generally increases from the northern outcrop areas toward the Equator. This increase is due to the cross-isopycnal mixing of waters of different temperature and argon concentration and is proportional to the value of the diapycnal eddy diffusion coefficient. The lower figure is predicted argon supersaturation in the thermocline of a three-dimensional GCM for different diapycnal eddy diffusion coefficients. The data and results indicate that the diapycnal diffusion coefficient is low (~10-5 m2 s-1) even for a tracer which averages the signal over decadal time scales. (From Emerson et al., 2012, Geophys. Res. Lett.)
