Seasonal succession of phytoplankton community structure from autonomous sampling at the Australian Southern Ocean Time Series (SOTS) observatory

Eriksen, Ruth; Trull, TW; Davies, Diana M.; Jansen, Peter; Davidson, AT; Westwood, Karen J.; Enden, Rick van den

doi:10.3354/meps12420

Cited by 46 publications

(64 citation statements)

References 93 publications

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“…The upper ocean at the SOTS site is representative of conditions for a large proportion of the Indian and Australian sectors of the sub-Antarctic Southern Ocean (Trull et al 2001b). The SOTS site is within the sub-Antarctic HNLC region, so chl a concentrations are low throughout the year (Bowie et al 2011, Ebersbach et al 2011, Eriksen et al 2018), as we observed during our study. In addition, silicate concentrations are seasonally low (< 2 µmol kg −1 in summer), compared to the more southern polar frontal zone and other HNLC areas (Rintoul & Trull 2001, Trull et al 2001c.…”

Section: Discussionsupporting

confidence: 78%

Effect of anthropogenic warming on microbial respiration and particulate organic carbon export rates in the sub-Antarctic Southern Ocean

Cavan¹,

Boyd²

2018

Aquat. Microb. Ecol.

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Microbial respiration of particulate organic carbon (POC) is one of the key processes controlling the magnitude of POC export from the surface ocean and its storage on long timescales in the deep. Metabolic processes are a function of temperature, such that warming sea temperatures should increase microbial respiration, potentially reducing POC export. To investigate this in the Southern Ocean, we measured microbial oxygen consumption of large particles over a 10°C temperature range (summer maximum + 8°C) to then estimate the decrease in export by 2100. Our results showed that POC-normalised respiration increased with warming. We estimate that POC export (scaled to primary production) could decrease by 17 ± 7% (SE) by 2100, using projected regional warming (+1.9°C) from the IPCC RCP 8.5 ('business-as-usual' scenario) for our sub-Antarctic site. Increased microbial respiration is one of many processes that will be altered by future climate change, which could all modify carbon storage in the future. Our estimate of the potential decline in carbon sequestration is within previous estimates from lab and field experiments, but higher than simple mechanistic models. To explore our results further, we used the metabolic theory of ecology (MTE) to determine the activation energy of microbial respiration, which was 0.9 eV. This is higher than classical MTE (0.6−0.7 eV), suggesting that sub-Antarctic microbes are particularly sensitive to temperature change. Such regional characteristics in the response of organisms to increased temperatures should be accounted for in large-scale or global model analyses to ensure that the results do not underestimate microbial responses to warming.

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Section: Discussionsupporting

confidence: 78%

Effect of anthropogenic warming on microbial respiration and particulate organic carbon export rates in the sub-Antarctic Southern Ocean

Cavan¹,

Boyd²

2018

Aquat. Microb. Ecol.

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“…along with moderate phytoplankton biomass39 . The low dust flux to this area originates primarily from Australia, with the highest fluxes between October and March40 .…”

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confidence: 99%

Resupply of mesopelagic dissolved iron controlled by particulate iron composition

et al. 2019

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Dissolved iron supply controls half of ocean primary productivity. Resupply by remineralization of sinking particles, and subsequent vertical mixing, largely sustains 2 this productivity. However, our understanding of the drivers of dissolved iron resupply, and their influence on its vertical distribution across the oceans, is still limited due to sparse observations. There is a lack of empirical evidence for what controls subsurface iron remineralization due to difficulties in studying mesopelagic biogeochemistry. Here, we present estimates of particulate transformations to dissolved iron, concurrent oxygen consumption and iron-binding ligand replenishment based on in situ mesopelagic experiments. Dissolved iron regeneration efficiencies (i.e., replenishment/oxygen consumption) were ten-to one hundred-fold higher in low-dust Subantarctic waters relative to higher-dust Mediterranean sites. Regeneration efficiencies are heavily influenced by particle composition. Their make-up dictates ligand release, controls scavenging, modulates ballasting, and may lead to differential remineralization of biogenic versus lithogenic iron. At high-dust sites these processes together increase the iron remineralization length-scale. Modelling reveals that in oceanic regions near deserts, enhanced lithogenic fluxes deepen the ferricline, which alter vertical patterns of dissolved iron replenishment, and set its redistribution at the global scale. Such wideranging regeneration efficiencies drive different vertical patterns in dissolved iron replenishment across oceanic provinces. Globally, the productivity of major phytoplankton groups, including diatoms and diazotrophs, is set by dissolved iron (DFe) supply 1. Twenty years of research has revealed diverse modes of DFe supply, from dust to hydrothermal vents, and their regional influences 2,3. Iron biogeochemistry is a rapidly evolving field, driving the development of global modelling initiatives 4. However, iron cycling in the oceans' interior, a fundamental component of iron biogeochemistry 5,6 , represents a major unknown, and critically is hindering model development 7 .

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“…Precise comparison of temporal changes in microplankton composition with the evolution of environmental drivers requires high-resolution sensor data coupled with sampling of the water column at discrete depths (e.g. 41 ). Since such information is only available for the surface layer at the SOTS observatory (see Supplement 1 for details), the exploration of the relationship between environmental change and succession of E. huxleyi morphotypes was only conducted on this time series.…”

Section: Statisticsmentioning

confidence: 99%

Full annual monitoring of Subantarctic Emiliania huxleyi populations reveals highly calcified morphotypes in high-CO2 winter conditions

Rigual-Hernández

Trull

Flores

et al. 2020

Sci Rep

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Ocean acidification is expected to have detrimental consequences for the most abundant calcifying phytoplankton species Emiliania huxleyi. However, this assumption is mainly based on laboratory manipulations that are unable to reproduce the complexity of natural ecosystems. Here, E. huxleyi coccolith assemblages collected over a year by an autonomous water sampler and sediment traps in the Subantarctic Zone were analysed. The combination of taxonomic and morphometric analyses together with in situ measurements of surface-water properties allowed us to monitor, with unprecedented detail, the seasonal cycle of E. huxleyi at two Subantarctic stations. E. huxleyi subantarctic assemblages were composed of a mixture of, at least, four different morphotypes. Heavier morphotypes exhibited their maximum relative abundances during winter, coinciding with peak annual TCO 2 and nutrient concentrations, while lighter morphotypes dominated during summer, coinciding with lowest TCO 2 and nutrients levels. The similar seasonality observed in both time-series suggests that it may be a circumpolar feature of the Subantarctic zone. Our results challenge the view that ocean acidification will necessarily lead to a replacement of heavily-calcified coccolithophores by lightly-calcified ones in subpolar ecosystems, and emphasize the need to consider the cumulative effect of multiple stressors on the probable succession of morphotypes.

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Seasonal succession of phytoplankton community structure from autonomous sampling at the Australian Southern Ocean Time Series (SOTS) observatory

Cited by 46 publications

References 93 publications

Effect of anthropogenic warming on microbial respiration and particulate organic carbon export rates in the sub-Antarctic Southern Ocean

Effect of anthropogenic warming on microbial respiration and particulate organic carbon export rates in the sub-Antarctic Southern Ocean

Resupply of mesopelagic dissolved iron controlled by particulate iron composition

Full annual monitoring of Subantarctic Emiliania huxleyi populations reveals highly calcified morphotypes in high-CO2 winter conditions

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