The fate of a southwest Pacific bloom: gauging the impact of submesoscale vs. mesoscale circulation on biological gradients in the subtropics
The temporal evolution of a surface chlorophyll <i>a</i> bloom sampled in the western tropical South Pacific during the 2015 Oligotrophy to UlTra-oligotrophy PACific Experiment (OUTPACE) cruise is examined. This region is usually characterized by largely oligotrophic conditions, i.e....
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2017-07-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/14/3471/2017/bg-14-3471-2017.pdf |
| Summary: | The temporal evolution of a surface chlorophyll <i>a</i> bloom sampled in
the western tropical South Pacific during the 2015 Oligotrophy to
UlTra-oligotrophy PACific Experiment (OUTPACE) cruise is examined. This region is
usually characterized by largely oligotrophic conditions, i.e. low
concentrations of inorganic nutrients at the surface and deep
chlorophyll <i>a</i> maxima. Therefore, the presence of a surface bloom
represents a significant perturbation from the mean ecological state.
Combining in situ and remote sensing datasets, we characterize both the
bloom's biogeochemical properties and the physical circulation
responsible for structuring it. Biogeochemical observations of the bloom
document the bloom itself, a subsequent decrease of surface
chlorophyll <i>a</i>, significantly reduced surface phosphate
concentrations relative to subtropical gyre water farther east, and a
physical decoupling of chlorophyll <i>a</i> from a deep nitracline. All
these characteristics are consistent with nitrogen fixation occurring within
the bloom. The physical data suggest surface mesoscale circulation is the
primary mechanism driving the bloom's advection, whereas balanced motions
expected at submesoscales provide little contribution to observed flow.
Together, the data provide a narrative where subtropical gyre water can
produce significant chlorophyll <i>a</i> concentrations at the surface that
is stirred, deformed, and transported great distances by the mesoscale
circulation. In this case, for the time period considered, the transport is in
an easterly direction, contrary to both the large-scale and mean mesoscale
flow. As a result, future studies concerning surface production in the region
need to take into account the role complex mesoscale structures play in
redistributing subtropical gyre water. |
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| ISSN: | 1726-4170 1726-4189 |