Hi fellow SOFeXer’s

 I wanted to update the group on the evolving 234Th derived particle flux
story and “final” POC flux values for the S-patch for SOFeX.  Last week,
we added final calibration factors in to our 234Th data set and I was
somewhat surprised initially, that the regular decrease in 234Th in patch
in the upper 50m now seems lower- i.e. less of an enhancement to particle
export within the top 50m in the patch.  The bottom line is that my
fluxes for Th & POC (& bSi), IN vs. OUT at 50m are not as high or
different as currently posted on the web site.  The  50m POC flux
averages 6 +/- 1.5 IN and 3 +/- 1.5 OUT, in units of mM C /m2/d.

 I had made these calculations assuming that the largest change in export
would be seen within the upper 50m.  However, when I look at the 234Th
profiles, the largest difference IN vs OUT is in the subsurface
response.  In the data around 80-120m, I have an “excess” of 234Th that
is derived from remineralization of 234Th off of sinking particles.  This
is something we’ve seen before, but never as well resolved because of
generally much more limited 234Th data sets.  Given our high vertical
resolution and extensive time-series 234Th data set, I can resolve and
quantify changes in sub-mixed layer export.  While outside of the patch,
particle fluxes continue to drop off below 60-80m, IN stations show a
progressively larger flux at depth (driven by the lack of
remineralization, i.e. a progressive decrease in 234Th excess).  This
implies a biological response at depth to the patch above.  The net
result is not necessarily a higher shallow export in response to Fe, but
a more efficient transport of material below 100m!  The 100m POC flux
averages are on the order of 12 +/-3 IN and 4.5 +/- 2 OUT.

 Attached are two sets of data slides I’ll be showing along with others
at SF AGU to support this story.  I provide them to you in advance so
that you are alerted to the changes since our August PI meeting in the
particle flux data, and to point out for those of you with samples below
the patch, that there could be other indicators of particle
remineralization effects in the “shadow” of the patch.

 There is obviously much more to the story than I can put in one email
and it is still evolving here, so feel free to contact me if this impacts
your SF AGU talk directly and you want more details, or please let me
know if you have other insights on this evolving subsurface export
story.  No, we did not see the final demise/export response to Fe in
SOFeX, but we did see an interesting and provocative subsurface response
that enhanced export efficiency of sinking particles.  I’ll try to
suggest some possible mechanisms and (in 12 minutes in SF!) make further
comparisons of these data to other Fe fertilization studies and the
natural conditions we say during AESOPS.

 Hope to see you in SF.  Ken