Coccolithophore populations and their contribution to carbonate export during an annual cycle in the Australian sector of the Antarctic zone
The Southern Ocean is experiencing rapid and relentless change in its physical and biogeochemical properties. The rate of warming of the Antarctic Circumpolar Current exceeds that of the global ocean, and the enhanced uptake of carbon dioxide is causing basin-wide ocean acidification. Observatio...
| Main Authors: | , , , , , |
|---|---|
| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2018-03-01
|
| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/15/1843/2018/bg-15-1843-2018.pdf |
| Summary: | The Southern Ocean is experiencing rapid and relentless change in its
physical and biogeochemical properties. The rate of warming of the Antarctic
Circumpolar Current exceeds that of the global ocean, and the enhanced
uptake of carbon dioxide is causing basin-wide ocean acidification.
Observational data suggest that these changes are influencing the
distribution and composition of pelagic plankton communities. Long-term and
annual field observations on key environmental variables and organisms are a
critical basis for predicting changes in Southern Ocean ecosystems. These
observations are particularly needed, since high-latitude systems have been
projected to experience the most severe impacts of ocean acidification and
invasions of allochthonous species.<br><br>
Coccolithophores are the most prolific calcium-carbonate-producing
phytoplankton group playing an important role in Southern Ocean
biogeochemical cycles. Satellite imagery has revealed elevated particulate
inorganic carbon concentrations near the major circumpolar fronts of the
Southern Ocean that can be attributed to the coccolithophore <i>Emiliania huxleyi</i>. Recent
studies have suggested changes during the last decades in the distribution
and abundance of Southern Ocean coccolithophores. However, due to limited
field observations, the distribution, diversity and state of coccolithophore
populations in the Southern Ocean remain poorly characterised.<br><br>
We report here on seasonal variations in the abundance and composition of
coccolithophore assemblages collected by two moored sediment traps deployed
at the Antarctic zone south of Australia (2000 and 3700 m of depth) for 1 year in 2001–2002. Additionally, seasonal changes in coccolith weights of
<i>E. huxleyi</i> populations were estimated using circularly polarised
micrographs analysed with C-Calcita software. Our findings indicate
that (1) coccolithophore sinking assemblages were nearly monospecific for
<i>E. huxleyi</i> morphotype B/C in the Antarctic zone waters in
2001–2002; (2) coccoliths captured by the traps experienced weight and
length reduction during summer (December–February); (3) the estimated annual
coccolith weight of <i>E. huxleyi</i> at both sediment traps
(2.11 ± 0.96 and 2.13 ± 0.91 pg at 2000 and 3700 m) was
consistent with previous studies for morphotype B/C in other Southern Ocean
settings (Scotia Sea and Patagonian shelf); and (4) coccolithophores accounted
for approximately 2–5 % of the annual deep-ocean CaCO<sub>3</sub> flux. Our
results are the first annual record of coccolithophore abundance, composition
and degree of calcification in the Antarctic zone. They provide a baseline
against which to monitor coccolithophore responses to changes in
the environmental conditions expected for this region in coming decades. |
|---|---|
| ISSN: | 1726-4170 1726-4189 |