About the Lab

Broadly, we're interested in how physical and biological processes interact in the upper ocean. Mostly this takes the form of physics influencing phytoplankton productivity by modulating thermocline depth, upwelling rates and vertical turbulent mixing. But biology can also influence physics via the influence of phytoplankton on the heat budget of the upper ocean. Here's a list of the kinds of biological-physical interactions we've investigated, with related publications (reprints available).

 

Kelvin Waves ~ El Niño / La Niña ~ Tropical Instability Waves ~ Phytoplankton and the upper ocean heat budget

 

Kelvin Waves:

Kelvin Waves influence surface productivity by modulating the depth of the thermocline. This is important because the thermocline, particularly in the equatorial Pacific, represents the 'cap' on top of a nutrient source. The closer it is to the surface, the greater the supply of nutrients to the euphotic zone. The figure below, from Chavez et al. [1998], shows a time series of winds, thermocline depth and chlorophyll from 0°, 155°W (central equatorial Pacific) during the onset of the 1997-98 El Niño. Note that winds are to the west (upwelling-favorable) for the period shown, and that chlorophyll changes as the thermocline deepens and shoals.

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El Niño / La Niña:

The 1997-98 El Niño has been described as the strongest ever observed. At the peak of the event, sea surface temperatures in excess of 29°C spanned the entire equatorial Pacific, and chlorophyll concentrations were among the lowest recorded. The SeaWiFS ocean color satellite, launched in 1997, documented the ~20-fold change in surface ocean chlorophyll from January to July 1998 (see figure).

See also: Strutton, P.G. and Chavez, F.P. (2000) Primary productivity in the equatorial Pacific during the 1997-98 El Niño. Journal of Geophyiscal Research, 105(C11), 26,089-26,101. and Ryan, J.P., Polito, P.S., Strutton, P.G. and Chavez, F.P. (2002) Anomalous phytoplankton blooms in the equatorial Pacific. Progress in Oceanography, 55, 263-285.

 

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Tropical Instability Waves:

Tropical Instability Waves (TIWs) are amazing, 1000km wavelength features that dominate the physical circulation of the equatorial Pacific (and Atlantic) for the latter part of the calendar year. The TIW-induced distortion of the chlorophyll field is somewhat visible in the figure above, but even more so in the image below.

 

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Phytoplankton and the upper ocean heat budget:

Phytoplankton absorb solar radiation in order to perform photosynthesis, but this process is not 100% efficient, so many of the photons absorbed by a phytoplankton cell are re-emitted as fluorescence or heat. Therefore, the presence of phytoplankton in the upper ocean impacts the vertical distribution of absorbed solar radiation. High mixed layer chlorophyll (phytoplankton) concentrations lead to enhanced heating of the mixed layer (and less penetration of that heat into the deeper ocean) and perhaps greater potential for exchange of that heat with the atmosphere. Conversely, low mixed layer chlorophyll concentrations enable greater penetration of heat into the deeper ocean where it may be prevented from exchange with the atmosphere for time scales anywahere from days to years.

The figure to the right demonstrates the changes in chlorophyll, solar radiation, mixed layer depth and heating rate that occured in the equatorial Pacific between the peak of the 1997-98 El Niño and the subsequent La Niña.

 

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