scholarly journals Biogeography of the Southern Ocean: environmental factors driving mesoplankton distribution South of Africa

PeerJ ◽  
2021 ◽  
Vol 9 ◽  
pp. e11411
Author(s):  
Alexander Vereshchaka ◽  
Eteri Musaeva ◽  
Anastasiia Lunina
Keyword(s):  
Southern Ocean ◽  
Current Knowledge ◽  
Chlorophyll Concentration ◽  
Diel Cycle ◽  
Quantitative Structure ◽  
Southern Boundary ◽  
Qualitative Structure ◽  
Circumpolar Current ◽  
Zooplankton Communities ◽  
The Impact

Spatial distribution of zooplankton communities depends on numerous factors, especially temperature and salinity conditions (hydrological factor), sampled depth, chlorophyll concentration, and diel cycle. We analyzed and compared the impact of these factors on mesoplankton abundance, biodiversity, quantitative structure based on proportion of taxa and qualitative structure based on presence/absence of taxa in the Southern Ocean. Samples (43 stations, three vertical strata sampled at each station, 163 taxa identified) were collected with a Juday net along the SR02 transect in December 2009. Mesoplankton abundance in discrete vertical layers ranged from 0.2 to 13,743.6 ind. m−3, i.e., five orders of magnitude, maximal and minimal values were recorded in the upper mixed and in the deepest layer, respectively. Within the combined 300-m layer, abundances ranged from 16.0 to 1,455.0 ind. m−3, i.e., two orders of magnitude suggesting that integral samples provide little information about actual variations of mesoplankton abundances. A set of analyses showed that depth was the major driver of mesoplankton distribution (abundance, biodiversity, quantitative structure), hydrological factors influenced two of them (quantitative and qualitative structure), chlorophyll concentration strongly affected only quantitative structure, and diel cycle had an insignificant effect on mesoplankton distribution. Using our current knowledge of the fine structure of the Antarctic Circumpolar Current, we compared effects of four hydrological fronts, i.e., boundaries between different water-masses with distinct environmental characteristics, and eight dynamic jets (narrow yet very intense currents) on mesoplankton distribution. Subtropical, Polar, and Subantarctic Fronts drove quantitative and qualitative structure of mesoplankton assemblages (decreasing in order of influence), while the Southern Boundary affected only qualitative structure. Effects of dynamic jets were insignificant. We suggest that mesoplankton composition is driven by hydrological parameters and further maintained through compartmentalization by fronts. Impact of local eddies and meanders on biodiversity, abundance, qualitative and quantitative structure of mesoplankton is comparable to that of hydrological fronts. Qualitative structure of mesoplankton assemblages mirrors hydrological structure of the Southern Ocean better than quantitative structure and may be recommended for biogeographic analyses of the Southern Ocean. Comparisons with previous reports from the same area retrieved no significant changes in mesoplankton distribution during the period 1992–2009.

scholarly journals Archaeal intact polar lipids in polar waters: a comparison between the Amundsen and Scotia seas

2021 ◽  
Vol 18 (11) ◽  
pp. 3485-3504
Author(s):  
Charlotte L. Spencer-Jones ◽  
Erin L. McClymont ◽  
Nicole J. Bale ◽  
Ellen C. Hopmans ◽  
Stefan Schouten ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Water Column ◽  
Ice Sheet ◽  
Amundsen Sea ◽  
Antarctic Ice Sheet ◽  
Southern Boundary ◽  
West Antarctic Ice Sheet ◽  
Scotia Sea ◽  
West Antarctic ◽  
Circumpolar Current

Abstract. The West Antarctic Ice Sheet (WAIS) is one of the largest potential sources of future sea-level rise, with glaciers draining the WAIS thinning at an accelerating rate over the past 40 years. Due to complexities in calibrating palaeoceanographic proxies for the Southern Ocean, it remains difficult to assess whether similar changes have occurred earlier during the Holocene or whether there is underlying centennial- to millennial-scale forcing in oceanic variability. Archaeal lipid-based proxies, specifically glycerol dialkyl glycerol tetraether (GDGT; e.g. TEX86 and TEX86L), are powerful tools for reconstructing ocean temperature, but these proxies have been shown previously to be difficult to apply to the Southern Ocean. A greater understanding of the parameters that control Southern Ocean GDGT distributions would improve the application of these biomarker proxies and thus help provide a longer-term perspective on ocean forcing of Antarctic ice sheet changes. In this study, we characterised intact polar lipid (IPL)-GDGTs, representing (recently) living archaeal populations in suspended particulate matter (SPM) from the Amundsen Sea and the Scotia Sea. SPM samples from the Amundsen Sea were collected from up to four water column depths representing the surface waters through to Circumpolar Deep Water (CDW), whereas the Scotia Sea samples were collected along a transect encompassing the sub-Antarctic front through to the southern boundary of the Antarctic Circumpolar Current. IPL-GDGTs with low cyclic diversity were detected throughout the water column with high relative abundances of hydroxylated IPL-GDGTs identified in both the Amundsen and Scotia seas. Results from the Scotia Sea show shifts in IPL-GDGT signatures across well-defined fronts of the Southern Ocean. Indicating that the physicochemical parameters of these water masses determine changes in IPL-GDGT distributions. The Amundsen Sea results identified GDGTs with hexose-phosphohexose head groups in the CDW, suggesting active GDGT synthesis at these depths. These results suggest that GDGTs synthesised at CDW depths may be a significant source of GDGTs exported to the sedimentary record and that temperature reconstructions based on TEX86 or TEX86L proxies may be significantly influenced by the warmer waters of the CDW.

scholarly journals On the Relationship between Southern Ocean Overturning and ACC Transport

2013 ◽  
Vol 43 (1) ◽  
pp. 140-148 ◽  
Author(s):  
Adele K. Morrison ◽  
Andrew McC. Hogg
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Large Scale ◽  
Meridional Overturning Circulation ◽  
Meridional Transport ◽  
Stress Changes ◽  
Transport Response ◽  
Meridional Overturning ◽  
Circumpolar Current ◽  
The Impact

Abstract The eddy field in the Southern Ocean offsets the impact of strengthening winds on the meridional overturning circulation and Antarctic Circumpolar Current (ACC) transport. There is widespread belief that the sensitivities of the overturning and ACC transport are dynamically linked, with limitation of the ACC transport response implying limitation of the overturning response. Here, an idealized numerical model is employed to investigate the response of the large-scale circulation in the Southern Ocean to wind stress perturbations at eddy-permitting to eddy-resolving scales. Significant differences are observed between the sensitivities and the resolution dependence of the overturning and ACC transport, indicating that they are controlled by distinct dynamical mechanisms. The modeled overturning is significantly more sensitive to change than the ACC transport, with the possible implication that the Southern Ocean overturning may increase in response to future wind stress changes without measurable changes in the ACC transport. It is hypothesized that the dynamical distinction between the zonal and meridional transport sensitivities is derived from the depth dependence of the extent of cancellation between the Ekman and eddy-induced transports.

Multi-scale factors influencing seabird assemblages in the African sector of the Southern Ocean

2013 ◽  
Vol 26 (1) ◽  
pp. 38-48 ◽  
Author(s):  
Morgan L. Commins ◽  
Isabelle Ansorge ◽  
Peter G. Ryan
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Antarctic Circumpolar Current ◽  
Polar Front ◽  
Latitudinal Gradients ◽  
Antarctic Polar Front ◽  
Sea Ice Extent ◽  
Southern Boundary ◽  
Circumpolar Current ◽  
The Antarctic

AbstractOceanic fronts are important foraging areas for many top predators, but they also define biogeographical boundaries to animals in the Southern Ocean and play a role in structuring seabird assemblages. Understanding the factors driving patterns in the spatial and temporal distribution of seabirds is important to infer the likely impact of a changing climate. Latitudinal transects south of Africa in two summers indicate that fronts and sea ice extent play key roles in determining seabird assemblages. We observed 37 seabird taxa and found five seabird assemblages. The Subtropical Convergence and pack ice-edge form the strongest biogeographical boundaries, whereas the Sub-Antarctic Front and Antarctic Polar Front are less well defined. As summer progresses, the Southern Antarctic Circumpolar Current Front (the Antarctic Divergence or southern boundary of the Antarctic Circumpolar Current) becomes important, when a distinct seabird assemblage forms north of the retreating sea ice following an influx of great shearwatersPuffinus gravis(O'Reilly), blue petrelsHalobaena caerulea(Gmelin), Kerguelen petrelsLugensa brevirostris(Lesson) and southern fulmarsFulmarus glacialoides(Smith). Seabird assemblages show strong seasonality and are predictable between years. They are structured primarily by latitudinal gradients and secondarily by seasonal variation in sea-surface temperature and ice cover within their latitudinal habitat zones.

Lagrangian evaluation of marine aerosols sources in an Earth System Model.

2020 ◽  
Author(s):  
Emanuele Tovazzi ◽  
Daniel Partridge ◽  
Jim Haywood ◽  
Alistair Sellar ◽  
Dalvi Mohit ◽  
...  
Keyword(s):  
Wind Speed ◽  
Southern Ocean ◽  
Aerosol Particles ◽  
Chlorophyll Concentration ◽  
Winter Season ◽  
Organic Aerosols ◽  
Sea Surface ◽  
Shortwave Radiation ◽  
Earth System ◽  
The Impact

<p><span>Increasing the current understanding of how the Earth will respond to a warming climate requires a more accurate representation of aerosols by Earth system models (ESMs). Reducing current uncertainties </span><span>associated with model estimates of climate change sensitivity to greenhouse gas emissions is hampered by our understanding of the impact aerosol particles have on the radiative budget via their interactions with clouds. </span><span>The complexity of such interactions leads to their imperfect representation in models. </span></p><p>Emissions of marine organic aerosols play a relevant role on cloud formation in regions where there is a high concentration of phytoplankton, for example in the Southern Ocean (SO). Comparisons between GCMs and satellite observations over the SO show that the models simulate too little reflection of shortwave radiation and this is strongly linked with modelled cloud properties. A potential cause of this issue is a source of missing aerosols in the ESM.</p><p><span>In this study we evaluate the ability of a state-of-the-art ESM, UKESM1, in reproducing aerosol particles originating from organic marine sources that reach a measurement station in pristine air through long-range transport. UKESM1 is developed by the Met. Office and our simulation is nudged by reanalysis datasets for a fair comparison with observations. </span><span>This ESM is unique in using its ocean biogeochemistry module to interactively simulate the emission of marine organic aerosols.</span><span> To this end, a novel Lagrangian trajectory framework for evaluating GCMs has been developed. This method makes use of satellite measurements of chlorophyll concentration (a proxy of phytoplankton abundance in the sea surface) at the sea surface, together with </span><span>the cloud condensation nuclei (CCN) concentration at 0.5% of supersaturation measured at Cape Grim (Southern Ocean, Tasmania) station.</span><span> Chlorophyll and wind speed data are collocated along air mass trajectories, which are calculated through the HYSPLIT model. </span><span>A source-receptor analysis is then performed to look for potential spatial correlation between the </span><span>collocated </span><span>chlorophyll concentration experienced by air parcel paths coming from a defined clean air sector of the boundary layer (to avoid anthropogenic influences) and CCN measurements. Additionally, a temporal correlation analysis is performed in this framework. This method is applied to both UKESM1 output data and observations to evaluate aerosol processes in climate models. </span></p><p><span>Preliminary results show a positive correlation in model data between marine organic activity and CCN production that is found also in the observations. Despite the model well representing the seasonal variability of CCN at the station, the model struggles to reproduce the positive relationship obtained from the observations between wind speed and CCN concentration during the winter season. This can be attributed to a potential missing source in the model.</span></p>

The impact of biometric parameters of a hydromacrophyte habitat on the structure of zooplankton communities in various types of small water bodies

2009 ◽  
Vol 38 (2) ◽  
Author(s):  
Natalia Kuczyńska-Kippen ◽  
Barbara Nagengast ◽  
Tomasz Joniak
Keyword(s):  
Water Bodies ◽  
Small Water ◽  
Biometric Parameters ◽  
Zooplankton Communities ◽  
The Impact ◽  
Small Water Bodies

The impact of biometric parameters of a hydromacrophyte habitat on the structure of zooplankton communities in various types of small water bodies

On the impact of sea ice in a global ocean circulation model

1997 ◽  
Vol 25 ◽  
pp. 111-115 ◽  
Author(s):  
Achim Stössel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Ocean Circulation ◽  
General Circulation ◽  
Thermohaline Circulation ◽  
Circulation Model ◽  
Deep Ocean ◽  
Global Ocean ◽  
Convective Activity ◽  
The Impact

This paper investigates the long-term impact of sea ice on global climate using a global sea-ice–ocean general circulation model (OGCM). The sea-ice component involves state-of-the-art dynamics; the ocean component consists of a 3.5° × 3.5° × 11 layer primitive-equation model. Depending on the physical description of sea ice, significant changes are detected in the convective activity, in the hydrographic properties and in the thermohaline circulation of the ocean model. Most of these changes originate in the Southern Ocean, emphasizing the crucial role of sea ice in this marginally stably stratified region of the world's oceans. Specifically, if the effect of brine release is neglected, the deep layers of the Southern Ocean warm up considerably; this is associated with a weakening of the Southern Hemisphere overturning cell. The removal of the commonly used “salinity enhancement” leads to a similar effect. The deep-ocean salinity is almost unaffected in both experiments. Introducing explicit new-ice thickness growth in partially ice-covered gridcells leads to a substantial increase in convective activity, especially in the Southern Ocean, with a concomitant significant cooling and salinification of the deep ocean. Possible mechanisms for the resulting interactions between sea-ice processes and deep-ocean characteristics are suggested.

scholarly journals Urban Fire Severity and Vegetation Dynamics in Southern California

2020 ◽  
Vol 13 (1) ◽  
pp. 19
Author(s):  
Lauren E. H. Mathews ◽  
Alicia M. Kinoshita
Keyword(s):  
Vegetation Cover ◽  
Vegetation Index ◽  
Normalized Difference Vegetation Index ◽  
Current Knowledge ◽  
Fire Severity ◽  
Satellite Image ◽  
Burn Severity ◽  
Native Vegetation ◽  
Riparian Areas ◽  
The Impact

A combination of satellite image indices and in-field observations was used to investigate the impact of fuel conditions, fire behavior, and vegetation regrowth patterns, altered by invasive riparian vegetation. Satellite image metrics, differenced normalized burn severity (dNBR) and differenced normalized difference vegetation index (dNDVI), were approximated for non-native, riparian, or upland vegetation for traditional timeframes (0-, 1-, and 3-years) after eleven urban fires across a spectrum of invasive vegetation cover. Larger burn severity and loss of green canopy (NDVI) was detected for riparian areas compared to the uplands. The presence of invasive vegetation affected the distribution of burn severity and canopy loss detected within each fire. Fires with native vegetation cover had a higher severity and resulted in larger immediate loss of canopy than fires with substantial amounts of non-native vegetation. The lower burn severity observed 1–3 years after the fires with non-native vegetation suggests a rapid regrowth of non-native grasses, resulting in a smaller measured canopy loss relative to native vegetation immediately after fire. This observed fire pattern favors the life cycle and perpetuation of many opportunistic grasses within urban riparian areas. This research builds upon our current knowledge of wildfire recovery processes and highlights the unique challenges of remotely assessing vegetation biophysical status within urban Mediterranean riverine systems.

scholarly journals Effects of the Marine Biotoxins Okadaic Acid and Dinophysistoxins on Fish

2021 ◽  
Vol 9 (3) ◽  
pp. 293
Author(s):  
Mauro Corriere ◽  
Lucía Soliño ◽  
Pedro Reis Costa
Keyword(s):  
Okadaic Acid ◽  
Harmful Algal Blooms ◽  
Algal Blooms ◽  
Current Knowledge ◽  
Global Climate ◽  
Scientific Evidence ◽  
Shellfish Poisoning ◽  
Morphological Alterations ◽  
The Impact ◽  
Dsp Toxins

Natural high proliferations of toxin-producing microorganisms in marine and freshwater environments result in dreadful consequences at the socioeconomically and environmental level due to water and seafood contamination. Monitoring programs and scientific evidence point to harmful algal blooms (HABs) increasing in frequency and intensity as a result of global climate alterations. Among marine toxins, the okadaic acid (OA) and the related dinophysistoxins (DTX) are the most frequently reported in EU waters, mainly in shellfish species. These toxins are responsible for human syndrome diarrhetic shellfish poisoning (DSP). Fish, like other marine species, are also exposed to HABs and their toxins. However, reduced attention has been given to exposure, accumulation, and effects on fish of DSP toxins, such as OA. The present review intends to summarize the current knowledge of the impact of DSP toxins and to identify the main issues needing further research. From data reviewed in this work, it is clear that exposure of fish to DSP toxins causes a range of negative effects, from behavioral and morphological alterations to death. However, there is still much to be investigated about the ecological and food safety risks related to contamination of fish with DSP toxins.

scholarly journals Phony peach disease: past and present impact on the peach industry in the southeastern U.S.A

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Kendall A. Johnson ◽  
Clive H. Bock ◽  
Phillip M. Brannen
Keyword(s):  
New Technologies ◽  
Current Knowledge ◽  
Future Research ◽  
Management Options ◽  
Disease Epidemiology ◽  
Pathogen Diversity ◽  
Foundational Research ◽  
Global Threat ◽  
And Control ◽  
The Impact

Abstract Background Phony peach disease (PPD) is caused by the plant pathogenic bacterium Xylella fastidiosa subsp. multiplex (Xfm). Historically, the disease has caused severe yield loss in Georgia and elsewhere in the southeastern United States, with millions of PPD trees being removed from peach orchards over the last century. The disease remains a production constraint, and management options are few. Limited research has been conducted on PPD since the 1980s, but the advent of new technologies offers the opportunity for new, foundational research to form a basis for informed management of PPD in the U.S. Furthermore, considering the global threat of Xylella to many plant species, preventing import of Xfm to other regions, particularly where peach is grown, should be considered an important phytosanitary endeavor. Main topics We review PPD, its history and impact on peach production, and the eradication efforts that were conducted for 42 years. Additionally, we review the current knowledge of the pathogen, Xfm, and how that knowledge relates to our understanding of the peach—Xylella pathosystem, including the epidemiology of the disease and consideration of the vectors. Methods used to detect the pathogen in peach are discussed, and ramifications of detection in relation to management and control of PPD are considered. Control options for PPD are limited. Our current knowledge of the pathogen diversity and disease epidemiology are described, and based on this, some potential areas for future research are also considered. Conclusion There is a lack of recent foundational research on PPD and the associated strain of Xfm. More research is needed to reduce the impact of this pathogen on peach production in the southeastern U.S., and, should it spread internationally, wherever peaches are grown.

scholarly journals Going “Green” in the Prevention and Management of Atherothrombotic Diseases: The Role of Dietary Polyphenols

2021 ◽  
Vol 10 (7) ◽  
pp. 1490
Author(s):  
Ana Reis ◽  
Sara Rocha ◽  
Victor de Freitas
Keyword(s):  
Risk Factors ◽  
Fruits And Vegetables ◽  
Current Knowledge ◽  
Cholesterol Biosynthesis ◽  
Dietary Polyphenols ◽  
Nutritional Strategy ◽  
Flavonoid Intake ◽  
Health Promoting ◽  
Socio Economic Impact ◽  
The Impact

During the 20th century processed and ready-to-eat foods became routinely consumed resulting in a sharp rise of fat, salt, and sugar intake in people’s diets. Currently, the global incidence of obesity, raised blood lipids, hypertension, and diabetes in an increasingly aged population contributes to the rise of atherothrombotic events and cardiovascular diseases (CVD) mortality. Drug-based therapies are valuable strategies to tackle and help manage the socio-economic impact of atherothrombotic disorders though not without adverse side effects. The inclusion of fresh fruits and vegetables rich in flavonoids to human diets, as recommended by WHO offers a valuable nutritional strategy, alternative to drug-based therapies, to be explored in the prevention and management of atherothrombotic diseases at early stages. Though polyphenols are mostly associated to color and taste in foods, food flavonoids are emerging as modulators of cholesterol biosynthesis, appetite and food intake, blood pressure, platelet function, clot formation, and anti-inflammatory signaling, supporting the health-promoting effects of polyphenol-rich diets in mitigating the impact of risk factors in atherothrombotic disorders and CVD events. Here we overview the current knowledge on the effect of polyphenols particularly of flavonoid intake on the atherothrombotic risk factors and discuss the caveats and challenges involved with current experimental cell-based designs.

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