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| Titel |
Spatial variability in iron nutritional status of large diatoms in the Sea of Okhotsk with special reference to the Amur River discharge |
| VerfasserIn |
K. Suzuki, A. Hattori-Saito, Y. Sekiguchi, J. Nishioka, M. Shigemitsu, T. Isada, H. Liu, R. M. L. McKay |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1726-4170
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| Digitales Dokument |
URL |
| Erschienen |
In: Biogeosciences ; 11, no. 9 ; Nr. 11, no. 9 (2014-05-07), S.2503-2517 |
| Datensatznummer |
250117396
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| Publikation (Nr.) |
 copernicus.org/bg-11-2503-2014.pdf |
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| Zusammenfassung |
| The Sea of Okhotsk is known as one of the most biologically productive
regions among the world's oceans, and its productivity is supported in part
by the discharge of iron (Fe)-rich water from the Amur River. However, little
is known about the effect of riverine-derived Fe input on the physiology of
the large diatoms which often flourish in surface waters of the productive
continental shelf region. We conducted diatom-specific immunochemical
ferredoxin (Fd) and flavodoxin (Fld) assays in order to investigate the
spatial variability of Fe nutritional status in the microplankton-sized
(20–200 μm; hereafter micro-sized) diatoms. The Fd index, defined
as the proportion of Fd to the sum of Fd plus Fld accumulations in the cells,
was used to assess their Fe nutritional status. Additionally, active
chlorophyll fluorescence measurements using pulse–amplitude-modulated (PAM)
fluorometry were carried out to obtain the maximum photochemical quantum
efficiency (Fv/Fm) of photosystem II for the
total micro-sized phytoplankton assemblages including diatoms. During our
observations in the summer of 2006, the micro-sized diatoms were relatively
abundant (> 10 μg C L−1) in the neritic region, and
formed a massive bloom in Sakhalin Bay near the mouth of the Amur River.
Values of the Fd index and Fv/Fm were high
(>0.9 and >0.65, respectively) near the river mouth, indicating that
Fe was sufficient for growth of the diatoms. However, in oceanic waters of
the Sea of Okhotsk, the diatom Fd index declined as cellular Fld accumulation
increased. These results suggest that there was a distinct gradient in Fe
nutritional status in the micro-sized diatoms from near the Amur River mouth
to open waters in the Sea of Okhotsk. A significant correlation between
dissolved Fe (D-Fe) concentration and the Fd index was found in waters off
Sakhalin Island, indicating that D-Fe was a key factor for the
photophysiology of this diatom size class. In the vicinity of the Kuril
Islands between the Sea of Okhotsk and the Pacific Ocean, micro-sized diatoms
only accumulated Fld (i.e., Fd index = 0), despite strong vertical mixing
consistent with elevated surface D-Fe levels (>0.4 nM). Since higher Fe
quotas are generally required for diatoms growing under low-light conditions,
the micro-sized diatoms off the Kuril Islands possibly encountered Fe and
light co-limitations. The differential expressions of Fd and Fld in
micro-sized diatoms helped us to understand how these organisms respond to Fe
availability in the Sea of Okhotsk in connection with the Amur River
discharge. |
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