Publication Date:
2022-05-26
Description:
Author Posting. © Elsevier B.V., 2007. This is the author's version of the work. It is posted here by permission of Elsevier B.V. for personal use, not for redistribution. The definitive version was published in Deep Sea Research Part II: Topical Studies in Oceanography 54 (2007): 1989-1998, doi:10.1016/j.dsr2.2007.06.003.
Description:
Elevated levels of productivity in the wake of Southern Ocean island systems are
common despite the fact that they are encircled by high nutrient low chlorophyll (HNLC) waters.
In the Crozet Plateau region, it has been hypothesized that iron from island runoff or sediments
of the plateau could be fueling the austral summer phytoplankton bloom. Here, we use radium
isotopes to quantify the rates of surface ocean iron supply fueling the bloom in the Crozet
Plateau region. A 1-D eddy-diffusion-mixing model applied to a 228Ra profile (t1/2 = 5.75 yr) at a
station north of the islands suggested fast vertical mixing in the upper 300 m (Kz = 11-100 cm2 s-
1) with slower mixing between 300 and 1000 m (Kz = 1.5 cm2 s-1). This estimate is discussed in
the context of Kz derived from the CTD/LADCP data. In combination with the dissolved Fe
profile at this location, we estimated a vertical flux of between 5.6 and 31 nmol Fe m-2 d-1. The
cross-plateau gradients in the short-lived radium isotopes, 224Ra (t1/2 = 3.66 d) and 223Ra (t1/2 =
11.4 d), yielded horizontal eddy diffusivities (Kh) of 39 m2 s-1 and 6.6 m2 s-1, respectively. If we
assume that the islands (surface runoff) alone were supplying dissolved Fe to the bloom region,
then the flux estimates range from 2.3 to 14 nmol Fe m-2 d-1. If the plateau sediments are
considered a source of Fe, and conveyed to the bloom region through deep winter mixing
combined with horizontal transport, then this flux may be as high as 64 to 390 nmol Fe m-2 d-1.
Combined, these Fe sources are sufficient to initiate and maintain the annual phytoplankton
bloom.
Description:
This work was
funded by grants from the Natural Environment Research Council [NE/B502844/1] and the
National Science Foundation (ANT-0443869 to M.A.C).
Keywords:
Radium isotopes
;
Iron
;
Productivity
;
Ocean mixing
;
Southern Ocean
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
Permalink
