Exploring the Link between Micronutrients and Phytoplankton in the Southern Ocean during the 2007 Austral Summer

Abstract. For three austral summer seasons (2013–2016, each from December to February) aerosol particles arriving at the Belgian Antarctic research station Princess Elisabeth (PE), in Dronning Maud Land in East Antarctica were characterized in terms of number concentrations of total aerosol particles (NCN) and cloud condensation nuclei (NCCN), the particle number size distribution (PNSD), the aerosol particle hygroscopicity and the influence of the air mass origin on NCN and NCCN. In general NCN was found to range from 40 to 6700 cm−3 with a median of 333 cm−3, while NCCN was found to cover a range between less than 10 and 1300 cm−3 for supersaturations (SS) between 0.1 and 0.7 %. It is shown that the aerosol is Aitken mode dominated and is characterized by a significant amount of freshly, secondarily formed aerosol particles, with 94 % and 36 % of the aerosol particles are smaller than 90 nm and &approx; 35 nm, respectively. Measurements of the basic meteorological parameters as well as the history of the air masses arriving at the measurement station indicate that the station is influenced by both, continental air masses originating from the Antarctic inland ice sheet (continental events – CE) and marine air masses originating from the Southern Ocean (marine events – ME). CEs came along with rather constant NCN and NCCN values, which we denote to be Antarctic continental background concentrations. MEs however cause large fluctuations in NCN and NCCN caused by scavenging due to precipitation or new particle formation based on marine precursors. The application of Hysplit back trajectories in form of the potential source contribution function (PSCF) analysis indicate, that the region of the Southern Ocean is a potential source of Aitken mode particles. For particles larger than &approx; 110 nm (CCN measured at SS of 0.1 %) the Antarctic ice shelf regions were found to be a potential source region, most likely due to the emission of sea salt aerosol particles, released from snow particles from surface snow layers by sublimation, e.g., during periods of high wind speed, leading to drifting or blowing snow. On the basis of the PNSDs and NCCN, the critical diameter for cloud droplet activation and the aerosol particle hygroscopicity parameter κ were determined to be 110 nm and 1, respectively, for a SS of 0.1 %. The region of the Antarctic inland plateau however was not found to feature a significant source region for CN and CCN measured at the PE station in austral summer.

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Phytoplankton dynamics at the ice-edge zone of the Lazarev Sea (Southern Ocean) during the austral summer 1994/1995 drogue study

Polar Biology ◽

10.1007/s003000100236 ◽

2001 ◽

Vol 24 (6) ◽

pp. 422-431 ◽

Cited By ~ 7

Author(s):

Pakhomov E. ◽

Ratkova T. ◽

Froneman P. ◽

Wassmann P.

Keyword(s):

Southern Ocean ◽

Austral Summer ◽

Phytoplankton Dynamics ◽

Edge Zone ◽

Ice Edge

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Meridional variations in N* and Si* along 57°30′E and 47°E transects in the indian sector of the Southern Ocean during austral summer 2011

Deep Sea Research Part II Topical Studies in Oceanography ◽

10.1016/j.dsr2.2020.104846 ◽

2020 ◽

Vol 178 ◽

pp. 104846 ◽

Cited By ~ 1

Author(s):

Bhaskar V. Parli ◽

Deepti R.G. Dessai ◽

N. Anilkumar ◽

Racheal Chacko ◽

Sini Pavithran

Keyword(s):

Southern Ocean ◽

Austral Summer ◽

Indian Sector

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Coccolithophore biodiversity controls carbonate export in the Southern Ocean

Biogeosciences ◽

10.5194/bg-17-245-2020 ◽

2020 ◽

Vol 17 (1) ◽

pp. 245-263 ◽

Cited By ~ 6

Author(s):

Andrés S. Rigual Hernández ◽

Thomas W. Trull ◽

Scott D. Nodder ◽

José A. Flores ◽

Helen Bostock ◽

...

Keyword(s):

Southern Ocean ◽

Deep Sea ◽

Global Climate ◽

Chemical Properties ◽

Austral Summer ◽

Major Fraction ◽

Oceanic Fronts ◽

Phytoplankton Communities ◽

Physical And Chemical ◽

Particulate Inorganic Carbon

Abstract. Southern Ocean waters are projected to undergo profound changes in their physical and chemical properties in the coming decades. Coccolithophore blooms in the Southern Ocean are thought to account for a major fraction of the global marine calcium carbonate (CaCO3) production and export to the deep sea. Therefore, changes in the composition and abundance of Southern Ocean coccolithophore populations are likely to alter the marine carbon cycle, with feedbacks to the rate of global climate change. However, the contribution of coccolithophores to CaCO3 export in the Southern Ocean is uncertain, particularly in the circumpolar subantarctic zone that represents about half of the areal extent of the Southern Ocean and where coccolithophores are most abundant. Here, we present measurements of annual CaCO3 flux and quantitatively partition them amongst coccolithophore species and heterotrophic calcifiers at two sites representative of a large portion of the subantarctic zone. We find that coccolithophores account for a major fraction of the annual CaCO3 export, with the highest contributions in waters with low algal biomass accumulations. Notably, our analysis reveals that although Emiliania huxleyi is an important vector for CaCO3 export to the deep sea, less abundant but larger species account for most of the annual coccolithophore CaCO3 flux. This observation contrasts with the generally accepted notion that high particulate inorganic carbon accumulations during the austral summer in the subantarctic Southern Ocean are mainly caused by E. huxleyi blooms. It appears likely that the climate-induced migration of oceanic fronts will initially result in the poleward expansion of large coccolithophore species increasing CaCO3 production. However, subantarctic coccolithophore populations will eventually diminish as acidification overwhelms those changes. Overall, our analysis emphasizes the need for species-centred studies to improve our ability to project future changes in phytoplankton communities and their influence on marine biogeochemical cycles.

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Upper-ocean hydrodynamics along meridional sections in the southwest Indian sector of the Southern Ocean during austral summer 2007

Polar Science ◽

10.1016/j.polar.2009.03.001 ◽

2009 ◽

Vol 3 (1) ◽

pp. 13-30 ◽

Cited By ~ 8

Author(s):

Alvarinho J. Luis ◽

M. Sudhakar

Keyword(s):

Southern Ocean ◽

Austral Summer ◽

Upper Ocean ◽

Ocean Hydrodynamics ◽

Indian Sector

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Distribution and recurrence of phytoplankton blooms around South Georgia, Southern Ocean

Biogeosciences ◽

10.5194/bg-10-217-2013 ◽

2013 ◽

Vol 10 (1) ◽

pp. 217-231 ◽

Cited By ~ 33

Author(s):

I. Borrione ◽

R. Schlitzer

Keyword(s):

Southern Ocean ◽

Austral Summer ◽

Wide Field ◽

Phytoplankton Blooms ◽

Chl A ◽

South Georgia ◽

The North ◽

Wide Field Of View ◽

Georgia Basin ◽

Second Peak

Abstract. South Georgia phytoplankton blooms are amongst the largest of the Southern Ocean and are associated with a rich ecosystem and strong atmospheric carbon drawdown. Both aspects depend on the intensity of blooms, but also on their regularity. Here we use data from 12 yr of SeaWiFS (Sea-viewing Wide Field-of-view Sensor) ocean colour imagery and calculate the frequency of bloom occurrence (FBO) to re-examine spatial and temporal bloom distributions. We find that upstream of the island and outside the borders of the Georgia Basin, blooms occurred in less than 4 out of the 12 yr (FBO < 4). In contrast, FBO was mostly greater than 8 downstream of the island, i.e., to the north and northwest, and in places equal to 12, indicating that blooms occurred every year. The typical bloom area, defined as the region where blooms occurred in at least 8 out of the 12 yr, covers the entire Georgia Basin and the northern shelf of the island. The time series of surface chlorophyll a (Chl a) concentrations averaged over the typical bloom area shows that phytoplankton blooms occurred in every year between September 1997 and September 2010, and that Chl a values followed a clear seasonal cycle, with concentration peaks around December followed in many years by a second peak during late austral summer or early autumn, suggesting a bi-modal bloom pattern. The bloom regularity we describe here is in contrast with results of Park et al. (2010) who used a significantly different study area including regions that almost never exhibit bloom conditions.

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Evaluation of Southern Ocean cloud in the HadGEM3 general circulation model and MERRA-2 reanalysis using ship-based observations

Atmospheric Chemistry and Physics ◽

10.5194/acp-20-6607-2020 ◽

2020 ◽

Vol 20 (11) ◽

pp. 6607-6630 ◽

Cited By ~ 2

Author(s):

Peter Kuma ◽

Adrian J. McDonald ◽

Olaf Morgenstern ◽

Simon P. Alexander ◽

John J. Cassano ◽

...

Keyword(s):

Boundary Layer ◽

Southern Ocean ◽

General Circulation ◽

Cloud Cover ◽

Atmospheric Stability ◽

Austral Summer ◽

Circulation Model ◽

Radiation Budget ◽

Cloud Albedo ◽

Low Cloud

Abstract. Southern Ocean (SO) shortwave (SW) radiation biases are a common problem in contemporary general circulation models (GCMs), with most models exhibiting a tendency to absorb too much incoming SW radiation. These biases have been attributed to deficiencies in the representation of clouds during the austral summer months, either due to cloud cover or cloud albedo being too low. The problem has been the focus of many studies, most of which utilised satellite datasets for model evaluation. We use multi-year ship-based observations and the CERES spaceborne radiation budget measurements to contrast cloud representation and SW radiation in the atmospheric component Global Atmosphere (GA) version 7.1 of the HadGEM3 GCM and the MERRA-2 reanalysis. We find that the prevailing bias is negative in GA7.1 and positive in MERRA-2. GA7.1 performs better than MERRA-2 in terms of absolute SW bias. Significant errors of up to 21 W m−2 (GA7.1) and 39 W m−2 (MERRA-2) are present in both models in the austral summer. Using ship-based ceilometer observations, we find low cloud below 2 km to be predominant in the Ross Sea and the Indian Ocean sectors of the SO. Utilising a novel surface lidar simulator developed for this study, derived from an existing Cloud Feedback Model Intercomparison Project (CFMIP) Observation Simulator Package (COSP) – active remote sensing simulator (ACTSIM) spaceborne lidar simulator, we find that GA7.1 and MERRA-2 both underestimate low cloud and fog occurrence relative to the ship observations on average by 4 %–9 % (GA7.1) and 18 % (MERRA-2). Based on radiosonde observations, we also find the low cloud to be strongly linked to boundary layer atmospheric stability and the sea surface temperature. GA7.1 and MERRA-2 do not represent the observed relationship between boundary layer stability and clouds well. We find that MERRA-2 has a much greater proportion of cloud liquid water in the SO in austral summer than GA7.1, a likely key contributor to the difference in the SW radiation bias. Our results suggest that subgrid-scale processes (cloud and boundary layer parameterisations) are responsible for the bias and that in GA7.1 a major part of the SW radiation bias can be explained by cloud cover underestimation, relative to underestimation of cloud albedo.

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