Publication Date:
2022-05-25
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): 1999-2019, doi:10.1016/j.dsr2.2007.06.019.
Description:
The annual phytoplankton bloom occurring north of the Crozet Plateau provides a rare
opportunity to examine the hypothesis that natural iron fertilisation can alleviate
HNLC conditions normally associated with the Southern Ocean. Therefore, during
CROZEX, a large multidisciplinary study performed between November 2004 and
January 2005, measurements of total dissolved iron (DFe, ≤ 0.2 μm) were made on
seawater from around the islands and atmospheric iron deposition estimated from rain
and aerosol samples.
DFe concentrations were determined by flow injection analysis with N,N-dimethyl- pphenylenediamine
dihydrochloride (DPD) catalytic spectrophotometric detection. DFe
concentrations varied between 0.086 nM and 2.48 nM, with low values in surface
waters. Enrichment of dissolved iron (〉1 nM) at close proximity to the islands
suggests that the plateau and the associated sediments are a source of iron. Waters
further north also appear to be affected by this input of coastal and shelf origin,
although dissolved iron concentrations decrease as a function of distance to the north
of the plateau with a gradient of ~0.07 nM.km-1 at the time of sampling. Using lateral
and vertical diffusion coefficients derived from Ra isotope profiles and also estimates
of atmospheric inputs, it was then possible to estimate a DFe concentration of ~0.55
nM to the north of the islands prior to the bloom event, which is sufficient to initiate
the bloom, the lateral island source being the largest component. A similar situation is
observed for other Sub-Antarctic Islands such as Kerguelen, South Georgia, that
supply dissolved iron to their surrounding waters, thus, enhancing chlorophyll
concentrations.
Description:
These cruises
were the two first of the Crozex project, which was a contribution to a British BICEP
(Biophysical Interactions and Control of Export Production)-NERC program. This
work was also supported by NERC Grant NE/B502844/1 and a NERC PhD
studentship for M.F.
Keywords:
Dissolved iron
;
Crozet Islands
;
Crozet Islands
;
HNLC
Repository Name:
Woods Hole Open Access Server
Type:
Preprint
Format:
application/pdf
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