Welcome to John Marra's Homepage
Lamont-Doherty Earth Observatory of Columbia University
61 RT 9W, Palisades, NY 10964-8000, USA
phone: (845) 365-8891
fax: (845) 365-8150
I am a Doherty Senior Scholar, and part of the Marine Biology group in the Division of Biology and Paleoenvironment at LDEO.
My research covers several areas in Biological Oceanography, but particularly concerns the problem of the productivity of the ocean. I want to understand how physical forcing affects the variability of phytoplankton production in ocean ecosystems. As such
, I have done research on the effects of monsoons in the Arabian Sea and in Indonesia, the effects of frontal systems, and the springtime restratification in
the North Atlantic. I have been involved in the Joint Global Ocean Flux Study in the North Atlantic (1989), the Arabi
an Sea (1994-1995) and more recently, in the Southern Ocean (1997-1998).
An important driver of primary production is, of course, solar radiation, and thus, the optical properties of the ocean, and their variability, are a strong interest of mine. Solar radiation entering the sea not only drives photosynthesis, but also heats
the ocean, leading to stratification and stability, and therefore a changed environment.
I have two recent manuscripts (submitted) that deal with the issue of productivity in the ocean. The first is an observation of the compensation irradiance (where photosynthesis is ba
lanced by respiration). During the Marine Light - Mixed Layers program, we deployed a mooring in the North Atlantic Ocean south of Iceland in early 1989, and observed the inception of the spring bloom. I used the changes in the chlorophyll-a concentration
s at particular depths to calculate what the compensation irradiance should be based on the critical depth criterion. My values, at about 0.1-0.3 mol photons per meter squared per day, are at about 1% of surface irradiance.
In the second manuscript, written with Dick Barber (Duke University), we hypothesize a means of calculating phytoplankton and heterotrophic respiration separate from each other. Observa
tions of phytoplankton respiration in natural populations are almost non-existent, despite their obvious importance. And, needless to say, it has never been observed with respect to heterotrophic respiration. The method is based on the loss of carbon over
night, that is the difference between carbon uptake (based on 14C) from dawn-to-dusk and over 24 hours. We think this is a significant advance.
Other Projects in Progress
- Thomas Moore, my student/associate, is working on a project in the Leeuwin Current. (His web-site also lists publications and data from our recent NASA-supported project in the Indonesian Seas
- I am a member of the Primary Productivity Algorithm Round-Robin, PPARR. We are now working on Part 3, and results will be presented at an upcoming Ocean Science meeting. My algo
rithm has been published as an LDEO Technical Report
- There will be a special session at the Portland Ocean Sciences Meeting (26-30 January 2004) describing our observations at the Shelfbreak Front south of New England.
- I'm still interested in fisheries problems.
I've got lots of data. You can access the data through our browser, BioInfo. Bioinfo contains data from Biowatt (the Western North Atlantic; 1985 and 1987), Marine Light-Mixed Layers (the No
rth Atlantic, south of Iceland, 60N/20W; 1989 and 1991), and the Forced Upper Ocean Dynamics Experiment (Arabian Sea) and Arabian Sea Expedition (1994-1995) (A password is required to access data from these last two programs.) The data browser is currentl
y maintained by my associate Cheng Ho. It is best to contact us if you wish to use the data, since some explanation may be required. Some of the optical data has found its way to the World-Wide Ocean Optics
Database, listed below under Oceanographic Links.