Iron-limited biology

[m.hadfield]

I am applying ROMS for simulations of flow and plankton growth in the vicinity of New Zealand's Chatham Rise. South of the rise there are HNLC conditions: surface nitrate in summer drops no lower than 10 mmol N m^-3 and ocean-colour data show a modest late-summer phytoplankton bloom. This is due to lack of iron (and possibly silicate).

I did a test run with BIO_FASHAM and got the (unrealistic) behaviour one would expect: an excessively large spring bloom every year, reducing surface nitrate well below observed values. In subtropical waters north of the rise, the behaviour is much more reasonable.

Does anyone know of ROMS and/or the Fasham-type biology model being used in iron-limited areas?

I have various ideas about what to do next but would like to know of anyone else's experiences.

[kate]

Talk to Liz Dobbins and Sarah Hinkley at PMEL. They are running an NPZ type model with an iron category in it.

[dobbins]

Did someone mention my name?

Sarah and I are modeling the Gulf of Alaska, which has higher than expected productivity on the shelf. The theory is that there is more iron there. Sarah had a 10 compartment bio model of the GOA, and Craig Lewis configured it as a ROMS subroutine. Then we added the iron box.

Since iron dynamics are poorly understood, we have a simple iron field which is nudged back to a climatology field on a 30 day timescale. The phytoplankton experience iron limitation, just as they experience light and nutrient limitation. We basically followed Katja Fennel's approach ("Impact of iron control on phytoplankton production in the modern and glacial Southern Ocean", DSR II 50 (2003) 833-851) Katja's model was 1D, and I don't think she used ROMS, but I think she's using ROMS in 3D now.

It's pretty easy to write new biology code if Fasham isn't working for you. If you need more details on iron itself, Sarah is writing a paper describing our approach.