scholarly journals The Southern Annular Mode (SAM) influences phytoplankton communities in the seasonal ice zone of the Southern Ocean

2019 ◽  
Author(s):  
Bruce L. Greaves ◽  
Andrew T. Davidson ◽  
Alexander D. Fraser ◽  
John P. McKinlay ◽  
Andrew Martin ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Relative Abundance ◽  
Phytoplankton Community ◽  
Southern Annular Mode ◽  
Taxonomic Composition ◽  
Austral Spring ◽  
Annular Mode ◽  
Phytoplankton Communities ◽  
Phytoplankton Community Succession ◽  
Seasonal Ice Zone

Abstract. Ozone depletion and climate change are causing the Southern Annular Mode (SAM) to become increasingly positive, driving stronger winds southward in the Southern Ocean (SO), with likely effects on phytoplankton habitat due to changes in ocean mixing, nutrient upwelling, and sea ice. This study examined the effect of the SAM and other environmental variables on the abundance of siliceous and calcareous phytoplankton in the seasonal ice zone (SIZ) of the SO. Samples were collected during repeat transects between Hobart, Australia, and Dumont d'Urville, Antarctica, centred around longitude 142° E, over 11 consecutive austral spring-summers (2002–2012). Twenty-two taxa, comprised of species, genera or higher taxonomic groups, were analysed using CAP analysis, cluster analysis and correlation. The SAM significantly affected phytoplankton community composition, with the greatest influence exerted by a SAM index averaged across 57 days centred on 11th March in the preceding autumn, explaining 13.3 % of the variance of taxa composition during the following spring–summer, and showing correlation with the relative abundance of 12 of the 22 taxa resolved. The day through the spring-summer that a sample was collected exerted the greatest influence on phytoplankton community structure (15.4 % of variance explained), reflecting the extreme seasonal variation in the physical environment in the SIZ that drives phytoplankton community succession. The response of different species of Fragilariopsis spp. and Chaetoceros spp. differed over the spring–summer and with the SAM, indicating the importance of species-level observation in detecting subtle changes in pelagic ecosystems. This study indicated that higher SAM favoured increases in the relative-abundance of large Chaetoceros spp. that predominated later in the spring–summer and reductions in small diatom taxa and siliceous and calcareous flagellates that predominated earlier in the spring–summer. Such changes in the taxonomic composition of phytoplankton, the pasture of the SO and principal energy source for Antarctic life, may alter both carbon sequestration and composition of higher tropic levels of the SIZ region of the SO.

scholarly journals The Southern Annular Mode (SAM) influences phytoplankton communities in the seasonal ice zone of the Southern Ocean

2020 ◽  
Vol 17 (14) ◽  
pp. 3815-3835
Author(s):  
Bruce L. Greaves ◽  
Andrew T. Davidson ◽  
Alexander D. Fraser ◽  
John P. McKinlay ◽  
Andrew Martin ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Community Composition ◽  
Relative Abundance ◽  
Southern Annular Mode ◽  
Trophic Levels ◽  
Individual Species ◽  
Annular Mode ◽  
Principal Coordinates ◽  
Phytoplankton Communities ◽  
Seasonal Ice Zone

Abstract. Ozone depletion and climate change are causing the Southern Annular Mode (SAM) to become increasingly positive, driving stronger winds southward in the Southern Ocean (SO), with likely effects on phytoplankton habitat due to possible changes in ocean mixing, nutrient upwelling, and sea ice characteristics. This study examined the effect of the SAM and 12 other environmental variables on the abundance of siliceous and calcareous phytoplankton in the seasonal ice zone (SIZ) of the SO. A total of 52 surface-water samples were collected during repeat resupply voyages between Hobart, Australia, and Dumont d'Urville, Antarctica, centred around longitude 142∘ E, over 11 consecutive austral spring–summer seasons (2002–2012), and spanning 131 d in the spring–summer from 20 October to 28 February. A total of 22 taxa groups, comprised of individual species, groups of species, genera, or higher taxonomic groups, were analysed using CAP analysis (constrained analysis of principal coordinates), cluster analysis, and correlation. Overall, satellite-derived estimates of total chlorophyll and measured depletion of macronutrients both indicated a more positive SAM was associated with greater productivity in the SIZ. The greatest effect of the SAM on phytoplankton communities was the average value of the SAM across 57 d in the previous austral autumn centred around 11 March, which explained 13.3 % of the variance in community composition in the following spring–summer. This autumn SAM index was significantly correlated pair-wise (p<0.05) with the relative abundance of 12 of the 22 taxa groups resolved. A more positive SAM favoured increases in the relative abundance of large Chaetoceros spp. that predominated later in the spring–summer and reductions in small diatom taxa and siliceous and calcareous flagellates that predominated earlier in the spring–summer. Individual species belonging to the abundant Fragilariopsis genera responded differently to the SAM, indicating the importance of species-level observation in detecting SAM-induced changes in phytoplankton communities. The day through the spring–summer on which a sample was collected explained a significant and larger proportion (15.4 %) of the variance in the phytoplankton community composition than the SAM, yet this covariate was a proxy for such environmental factors as ice cover and sea surface temperature, factors that are regarded as drivers of the extreme seasonal variability in phytoplankton communities in Antarctic waters. The impacts of SAM on phytoplankton, which are the pasture of the SO and principal energy source for Antarctic life, would have ramifications for both carbon export and food availability for higher trophic levels in the SIZ of the SO.

The Impact of ENSO on Wave Breaking and Southern Annular Mode Events

2010 ◽  
Vol 67 (9) ◽  
pp. 2854-2870 ◽  
Author(s):  
Tingting Gong ◽  
Steven B. Feldstein ◽  
Dehai Luo
Keyword(s):  
El Niño ◽  
Wave Breaking ◽  
El Nino ◽  
Southern Annular Mode ◽  
La Niña ◽  
Background Flow ◽  
Austral Spring ◽  
Annular Mode ◽  
La Nina ◽  
The Impact

Abstract This study examines the relationship between intraseasonal southern annular mode (SAM) events and the El Niño–Southern Oscillation (ENSO) using daily 40-yr ECMWF Re-Analysis (ERA-40) data. The data coverage spans the years 1979–2002, for the austral spring and summer seasons. The focus of this study is on the question of why positive SAM events dominate during La Niña and negative SAM events during El Niño. A composite analysis is performed on the zonal-mean zonal wind, Eliassen–Palm fluxes, and two diagnostic variables: the meridional potential vorticity gradient, a zonal-mean quantity that is used to estimate the likelihood of wave breaking, and the wave breaking index (WBI), which is used to evaluate the strength of the wave breaking. The results of this investigation suggest that the background zonal-mean flow associated with La Niña (El Niño) is preconditioned for strong (weak) anticyclonic wave breaking on the equatorward side of the eddy-driven jet, the type of wave breaking that is found to drive positive (negative) SAM events. A probability density function analysis of the WBI, for both La Niña and El Niño, indicates that strong anticyclonic wave breaking takes place much more frequently during La Niña and weak anticyclonic wave breaking during El Niño. It is suggested that these wave breaking characteristics, and their dependency on the background flow, can explain the strong preference for SAM events of one phase during ENSO. The analysis also shows that austral spring SAM events that coincide with ENSO are preceded by strong stratospheric SAM anomalies and then are followed by a prolonged period of wave breaking that lasts for approximately 30 days. These findings suggest that the ENSO background flow also plays a role in the excitation of stratospheric SAM anomalies and that the presence of these stratospheric SAM anomalies in turn excites and then maintains the tropospheric SAM anomalies via a positive eddy feedback.

Response of the Southern Ocean to the Southern Annular Mode: Interannual Variability and Multidecadal Trend

2010 ◽  
Vol 40 (7) ◽  
pp. 1659-1668 ◽  
Author(s):  
A. M. Treguier ◽  
J. Le Sommer ◽  
J. M. Molines ◽  
B. de Cuevas
Keyword(s):  
Kinetic Energy ◽  
Southern Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
Meridional Circulation ◽  
Southern Annular Mode ◽  
Eddy Kinetic Energy ◽  
Overturning Circulation ◽  
Annular Mode ◽  
Meridional Overturning

Abstract The authors evaluate the response of the Southern Ocean to the variability and multidecadal trend of the southern annular mode (SAM) from 1972 to 2001 in a global eddy-permitting model of the DRAKKAR project. The transport of the Antarctic Circumpolar Current (ACC) is correlated with the SAM at interannual time scales but exhibits a drift because of the thermodynamic adjustment of the model (the ACC transport decreases because of a low renewal rate of dense waters around Antarctica). The interannual variability of the eddy kinetic energy (EKE) and the ACC transport are uncorrelated, but the EKE decreases like the ACC transport over the three decades, even though meridional eddy fluxes of heat and buoyancy remain stable. The contribution of oceanic eddies to meridional transports is an important issue because a growth of the poleward eddy transport could, in theory, oppose the increase of the mean overturning circulation forced by the SAM. In the authors’ model, the total meridional circulation at 50°S is well correlated with the SAM index (and the Ekman transport) at interannual time scales, and both increase over three decades between 1972 and 2001. However, given the long-term drift, no SAM-linked trend in the eddy contribution to the meridional overturning circulation is detectable. The increase of the meridional overturning is due to the time-mean component and is compensated by an increased buoyancy gain at the surface. The authors emphasize that the meridional circulation does not vary in a simple relationship with the zonal circulation. The model solution points out that the zonal circulation and the eddy kinetic energy are governed by different mechanisms according to the time scale considered (interannual or decadal).

scholarly journals Southern Annular Mode Influence on Wintertime Ventilation of the Southern Ocean Detected in Atmospheric O 2 and CO 2 Measurements

2020 ◽  
Vol 47 (4) ◽  
Author(s):  
Cynthia D. Nevison ◽  
David R. Munro ◽  
Nicole S. Lovenduski ◽  
Ralph F. Keeling ◽  
Manfredi Manizza ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Southern Annular Mode ◽  
Annular Mode

Response of the Southern Ocean overturning circulation to extreme Southern Annular Mode conditions

2020 ◽  
Author(s):  
Kial Douglas Stewart ◽  
Andrew McC. Hogg ◽  
Matthew H. England ◽  
Darryn W. Waugh
Keyword(s):  
Southern Ocean ◽  
Southern Annular Mode ◽  
Overturning Circulation ◽  
Annular Mode

scholarly journals Decadal Variability of the ENSO Teleconnection to the High-Latitude South Pacific Governed by Coupling with the Southern Annular Mode*

2006 ◽  
Vol 19 (6) ◽  
pp. 979-997 ◽  
Author(s):  
Ryan L. Fogt ◽  
David H. Bromwich
Keyword(s):  
High Latitude ◽  
Decadal Variability ◽  
Southern Oscillation ◽  
Phase Relationship ◽  
South Pacific ◽  
Southern Annular Mode ◽  
Height Anomaly ◽  
Austral Spring ◽  
Annular Mode ◽  
The Pacific

Abstract Decadal variability of the El Niño–Southern Oscillation (ENSO) teleconnection to the high-latitude South Pacific is examined by correlating the European Centre for Medium-Range Weather Forecasts (ECMWF) 40-yr Re-Analysis (ERA-40) and observations with the Southern Oscillation index (SOI) over the last two decades. There is a distinct annual contrast between the 1980s and the 1990s, with the strong teleconnection in the 1990s being explained by an enhanced response during austral spring. Geopotential height anomaly composites constructed during the peak ENSO seasons also demonstrate the decadal variability. Empirical orthogonal function (EOF) analysis reveals that the 1980s September–November (SON) teleconnection is weak due to the interference between the Pacific–South American (PSA) pattern associated with ENSO and the Southern Annular Mode (SAM). An in-phase relationship between these two modes during SON in the 1990s amplifies the height and pressure anomalies in the South Pacific, producing the strong teleconnections seen in the correlation and composite analyses. The in-phase relationship between the tropical and high-latitude forcing also exists in December–February (DJF) during the 1980s and 1990s. These results suggest that natural climate variability plays an important role in the variability of SAM, in agreement with a growing body of literature. Additionally, the significantly positive correlation between ENSO and SAM only during times of strong teleconnection suggests that both the Tropics and the high latitudes need to work together in order for ENSO to strongly influence Antarctic climate.

scholarly journals No Clear Response in the Stormwater Phytoplankton Community to Biocide Contamination

Water ◽  
2020 ◽  
Vol 12 (11) ◽  
pp. 3120
Author(s):  
Greta Minelgaite ◽  
Diana A. Stephansen ◽  
Márta Simon ◽  
Morten L. Fejerskov ◽  
Jes Vollertsen
Keyword(s):  
Statistical Analysis ◽  
Phytoplankton Community ◽  
Taxonomic Composition ◽  
Community Response ◽  
The Other ◽  
Phytoplankton Communities ◽  
Mesocosm Experiments ◽  
Laboratory Microcosm ◽  
Stormwater Pond ◽  
Natural Phytoplankton

This study investigated the responses of natural phytoplankton communities of an urban stormwater pond to biocide contamination. The biocides carbendazim, terbutryn, diuron, and irgarol 1051, and their mixture, were used in two laboratory microcosm and one outdoor mesocosm studies at concentrations of 10, 100, and 1000 ng L−1. The water samples were collected in a pond receiving significant biocide contamination. The mesocosm study was carried out in the same pond. The phytoplankton community response was evaluated after 10–15 days of exposure, with respect to its taxonomic composition, abundance and biovolume. No significant changes were observed in any of the experiments. Only at the highest applied terbutryn concentration were lower numbers of taxa identified in both microcosm and mesocosm experiments. Additionally, increases in Chlorophyta abundance and biovolume, along with an increase in irgarol concentration, were observed throughout the three experiments. Nevertheless, the statistical analysis did not confirm any significant differences among the biocide treatments. These results suggest that the biocide concentrations probably were below the harmful or toxic threshold to the stormwater pond phytoplankton. On the other hand, as the investigated pond phytoplankton taxa face biocide inputs throughout the year, they could have already adapted to the tested biocide contamination.

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