Southern Ocean Iron Experiment (SOFeX) Cruise
January 5 - February 26, 2002
January 15, 2002: Day 11
Drifter: -56 3.9594-171 59.2332
Ship: -56 1.9782-171 57.408
Lagrangian track is path relative to the drifting buoy. The grid that we formed initially is shown above in red.Those tracks are all relative to the position of the drifting buoy, which was moving north.
The actual track is the path over the earth's surface, this is much different - look at the grid shown in blue. Which do you believe?Were now steaming over a coarser grid to measure SF6, iron and a suite of other parameters.Were about half-way done and the red grid is looking more correct.
Ken Johnson writes: Well, its happening in the North Patch.We finished adding iron at 0330 this morning and traversed outside the patch to the western corner, where we had begun adding iron two days earlier.Immediately on entering the patch, there was a sharp increase in the ratio of variable fluorescence to maximum fluorescence.Fv/Fm is a measure of the photosynthetic 'health' of the microscopic phytoplankton.No iron, and the phytoplankton that are present at the time of iron fertilization can use only a few of the photons of light that their chlorophyll captures for photosynthesis.So most of that light is re-radiated (fluoresces) back into the water.The variable fluorescence Fv is small.An instrument called the Fast Repetition Rate (FRR) Fluorometer measures the value of Fv/Fm.It was extremely low before we added iron, indicating the phytoplankton could not use light and were re-radiating it.The area with iron is now nearing maximum values of Fv/Fm.Adding iron has restored the physiological health of the plankton.
That is the first sign that adding iron has affected this community.The really interesting question now, is whether there will be a change in phytoplankton biomass as a result of this change in physiology.There is almost no dissolved silicon in the North Patch waters.That means that diatoms, which form a siliceous shell (creating diatomaceous earth when they sink into the sediments), cannot grow.In all other iron fertilization experiments, it was an increase in diatoms that produced the large biomass changes that followed iron addition.
What will happen here?It will probably take more than a week to see the large scale changes in the phytoplankton community.We will be gone by then, off to form a patch near 66S.We will leave the North Patch for the MELVILLE to sample.They are in Lyttelton now, loading ship at the same dock that we sailed from 9 days ago.It will be an act of faith for us to leave our patch and head south without being there to 'hand it off'.Hopefully, we will know enough about its trajectory to guide MELVILLE to their first destination.And we will leave several drifting buoys to mark the North Patch location.But the buoys are an unfaithful marker of the patch location, as youll see.
We are now conducting a survey to define the dimensions of the patch.As we laid out the patch, the waters were marked with SF6 - sulfur hexafluoride.Kevin Sullivan and Craig Neill from the NOAA AOML lab in Miami are making these measurements.The grid that we formed initially is shown above in red.Those tracks are all relative to the position of the drifting buoy, which was moving north.The actual track of the ship over the earths surface is much different - look at the grid shown in blue. Which do you believe?Were now steaming over a coarser grid to measure SF6, iron and a suite of other parameters.Were about half-way done and the red grid is looking more correct.But it is also apparent that the drifting buoy has slipped almost to the northernmost edge of the patch.Bad luck if were going to use these drifters to help MELVILLE find the patch.
Well, thats it for now - almost time for e-mail to be transmitted to shore.