Phytoplankton growth response to Asian dust addition in the northwest Pacific Ocean versus the Yellow Sea
In this study, five on-board microcosm experiments were performed in the subtropical gyre, the Kuroshio Extension region of the northwest Pacific Ocean (NWPO), and the Yellow Sea (YS) in order to investigate phytoplankton growth following the addition of artificially modified mineral dust (AM dus...
| Main Authors: | , , , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-02-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/749/2018/bg-15-749-2018.pdf |
| Summary: | In this study, five on-board microcosm experiments were performed in the
subtropical gyre, the Kuroshio Extension region of the northwest Pacific
Ocean (NWPO), and the Yellow Sea (YS) in order to investigate phytoplankton
growth following the addition of artificially modified mineral dust (AM dust)
and various nutrients (nitrogen (N), phosphorus (P), iron (Fe), N + P, and
N + P + Fe). The two experiments carried out with AM-dust addition in
the subtropical gyre showed a maximum chlorophyll <i>a</i> (Chl <i>a</i>) concentration
increase of 1.7- and 2.8-fold, while the cell abundance of large-sized
phytoplankton ( > 5 µm) showed a 1.8- and 3.9-fold increase,
respectively, relative to the controls. However, in the Kuroshio
Extension region and the YS, the increases in maximum Chl <i>a</i> and cell
abundance of large-sized phytoplankton following AM-dust addition were at
most 1.3-fold and 1.7-fold larger than those in the controls, respectively. A
net conversion efficiency index (NCEI) newly proposed in this study,
size-fractionated Chl <i>a</i>, and the abundance of large-sized phytoplankton
were analysed to determine which nutrients contribute to supporting
phytoplankton growth. Our results demonstrate that a combination of
nutrients, N–P or N + P + Fe, is responsible for phytoplankton growth in the
subtropical gyre following AM-dust addition. Single nutrient addition, i.e.,
N in the Kuroshio Extension region and P or N in the YS, controls the
phytoplankton growth following AM-dust addition. In the AM-dust-addition
experiments, in which the increased N–P or P was identified to determine
phytoplankton growth, the dissolved inorganic P from AM dust
(8.6 nmol L<sup>−1</sup>) was much lower than the theoretically estimated minimum
P demand (∼ 20 nmol L<sup>−1</sup>) for phytoplankton growth. These
observations suggest that additional supply augments the bioavailable P stock
in incubated seawater with AM-dust addition, most likely due to an enhanced
solubility of P from AM dust or the remineralization of the dissolved organic P. |
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| ISSN: | 1726-4170 1726-4189 |