scholarly journals Recent climate variability around the Kerguelen Islands (Southern Ocean) seen through weather regimes

2021 ◽  
Author(s):  
Benjamin Pohl ◽  
Thomas Saucède ◽  
Vincent Favier ◽  
Julien Pergaud ◽  
Deborah Verfaillie ◽  
...  
Keyword(s):  
Climate Variability ◽  
Southern Ocean ◽  
Sea Water ◽  
Southern Oscillation ◽  
Surface Wind ◽  
Southern Annular Mode ◽  
Weather Regimes ◽  
Kerguelen Islands ◽  
Recent Climate

AbstractDaily weather regimes are defined around the Kerguelen Islands (Southern Ocean) based on daily 500 hPa geopotential height anomalies derived from the ERA5 ensemble reanalysis over the period 1979-2018. Ten regimes are retained as significant. Their occurrences are highly consistent across reanalysis ensemble members. Regimes show weak seasonality and non-significant long-term trends in their occurrences. Their sequences are usually short (1-3 days), with extreme persistence values above 10 days. Seasonal regime frequency is mostly driven by the phase of the Southern Annular Mode over Antarctica, mid-latitude dynamics over the Southern Ocean like the Pacific South American mode, and to a lesser extent, tropical variability, with significant but weaker relationships with El Niño Southern Oscillation. At the local scale over the Kerguelen Islands, regimes have a strong influence on measured atmospheric and oceanic variables, including minimum and maximum air temperature, mostly driven by horizontal advections, sea water temperature recorded 5 m below the surface, wind speed and sea level pressure. Relationships are weaker for precipitation amounts. Regimes also modify regional contrasts between observational sites in Kerguelen, highlighting strong exposure contrasts. The regimes allow improving our understanding of weather and climate variability and interactions in this region; they will be used in future work to assess past and projected long-term circulation changes in the southern mid-latitudes.

scholarly journals Long-term changes in habitat and trophic level of Southern Ocean squid in relation to environmental conditions

2020 ◽  
Vol 10 (1) ◽  
Author(s):  
José Abreu ◽  
Richard A. Phillips ◽  
Filipe R. Ceia ◽  
Louise Ireland ◽  
Vítor H. Paiva ◽  
...  
Keyword(s):  
Southern Ocean ◽  
Trophic Level ◽  
Environmental Conditions ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Trophic Levels ◽  
Important Prey ◽  
Diomedea Exulans ◽  
Top Predators

Abstract Long-term studies of pelagic nekton in the Southern Ocean and their responses to ongoing environmental change are rare. Using stable isotope ratios measured in squid beaks recovered from diet samples of wandering albatrosses Diomedea exulans, we assessed decadal variation (from 1976 to 2016) in the habitat (δ13C) and trophic level (δ15N) of five important Southern Ocean squid species in relation to indices of environmental conditions—Southern Oscillation Index (SOI) and Southern Annular Mode (SAM). Based on δ13C values, corrected for the Suess effect, habitat had changed over the last 50 years for Taonius sp. B (Voss), Gonatus antarcticus, Galiteuthis glacialis and Histioteuthis atlantica but not Moroteuthopsis longimana. By comparison, mean δ15N values were similar across decades for all five species, suggesting minimal changes in trophic levels. Both SAM and SOI have increased in strength and frequency over the study period but, of the five species, only in Taonius sp. B (Voss) did these indices correlate with, δ13C and δ15N values, indicating direct relationships between environmental conditions, habitat and trophic level. The five cephalopod species therefore changed their habitats with changing environmental conditions over the last 50 years but maintained similar trophic levels. Hence, cephalopods are likely to remain important prey for top predators in Southern Ocean food webs, despite ongoing climate change.

scholarly journals Long-Term Relationships between the Marine Environment, Krill and Salps in the Southern Ocean

2010 ◽  
Vol 2010 ◽  
pp. 1-18 ◽  
Author(s):  
Chung Il Lee ◽  
Evgeny Pakhomov ◽  
Angus Atkinson ◽  
Volker Siegel
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Water Temperature ◽  
Sea Water ◽  
Southern Oscillation ◽  
Abiotic Factors ◽  
Opposite Pattern ◽  
Sea Ice Extent ◽  
Atlantic Sector

Long-term variations (1975–2002) in climatology of marine environmental parameters, Antarctic krill,Euphausia superba, and the pelagic tunicate,Salpa thompsoni, were compared within the Atlantic Sector of the Southern Ocean. Sea water temperature in the top 400 m increased at a rate of 0.020–0.030°C ⋅ yr−1, which was accompanied by the dissolved oxygen decline. Top 100 m water layer became fresher with lower concentrations of phosphates and nitrates, while at subsurface layers (200–400 m) both salinity and nutrients showed small increasing trend. Unlike phosphates and nitrates, silicate concentrations decreased in the entire water column. Shorter-term water temperature dynamics closely correlated with the El Nino events expressed as the Southern Oscillation Index which in turn was linked to the propagation of the Antarctic Circumpolar Wave (ACW). The variations of sea-ice extent matched well the changes in both air and water temperatures. In general, abundance of krill and salps showed opposite to each other trends. Due to large area considered in this study, no significant relationships between abiotic factors and both krill and salps were found. However, our analysis demonstrated that krill abundance was greater in years with lower sea water temperature, greater sea-ice extent and higher nutrient concentration, while salps showed the opposite pattern.

scholarly journals Climate variability in West Antarctica derived from annual accumulation-rate records from ITASE firn/ice cores

2004 ◽  
Vol 39 ◽  
pp. 585-594 ◽  
Author(s):  
Susan Kaspari ◽  
Paul A. Mayewski ◽  
Daniel A. Dixon ◽  
Vandy Blue Spikes ◽  
Sharon B. Sneed ◽  
...  
Keyword(s):  
Climate Variability ◽  
Moisture Transport ◽  
Southern Oscillation ◽  
Accumulation Rate ◽  
Drainage System ◽  
Ice Cores ◽  
Cyclonic Activity ◽  
West Antarctica ◽  
Sea Level Pressure

AbstractThirteen annually resolved accumulation-rate records covering the last ~200 years from the Pine Island–Thwaites and Ross drainage systems and the South Pole are used to examine climate variability over West Antarctica. Accumulation is controlled spatially by the topography of the ice sheet, and temporally by changes in moisture transport and cyclonic activity. A comparison of mean accumulation since 1970 at each site to the long-term mean indicates an increase in accumulation for sites located in the western sector of the Pine Island–Thwaites drainage system. Accumulation is negatively associated with the Southern Oscillation Index (SOI) for sites near the ice divide, and periods of sustained negative SOI (1940–42, 1991–95) correspond to above-mean accumulation at most sites. Correlations of the accumulation-rate records with sea-level pressure (SLP) and the SOI suggest that accumulation near the ice divide and in the Ross drainage system may be associated with the mid-latitudes. The post-1970 increase in accumulation coupled with strong SLP–accumulation-rate correlations near the coast suggests recent intensification of cyclonic activity in the Pine Island– Thwaites drainage system.

Variations in Precipitation across the Southern Ocean

2020 ◽  
Vol 33 (24) ◽  
pp. 10653-10670
Author(s):  
M. J. Manton ◽  
Y. Huang ◽  
S. T. Siems
Keyword(s):  
Southern Ocean ◽  
Climate Model ◽  
Southern Oscillation ◽  
Zonal Flow ◽  
Southern Annular Mode ◽  
Accurate Estimate ◽  
Precipitation Anomaly ◽  
Unique Region ◽  
Pressure Anomaly ◽  
Climate Model Simulations

AbstractThe Southern Ocean lies beneath a unique region of the global atmosphere with minimal effects of landmasses on the zonal flow. The absence of landmasses also means that in situ observations of precipitation are limited to a few ocean islands. Two reanalyses and two satellite-based gridded datasets are analyzed to estimate the character of the distribution of precipitation across the region. The latitudinal variation is computed across three longitudinal sectors, representing the Pacific, Atlantic, and Indian Oceans. The most recent ECMWF reanalysis (ERA5) is found to produce the most accurate estimate of the mean profile and seasonal cycle of precipitation. However, there is little consistency in the estimates of trends in monthly anomalies of precipitation. A more consistent description of precipitation trends is found by using linear regression of the precipitation anomaly with the local mean sea level pressure anomaly, the southern annular mode, and the Southern Oscillation index. In broad terms, precipitation is found to be decreasing at lower latitudes and increasing at higher latitudes, which is consistent with earlier climate model simulations on the impacts of anthropogenic climate change.

scholarly journals Atmospheric Meridional Moisture Flux over the Southern Ocean: A Story of the Amundsen Sea

2013 ◽  
Vol 26 (20) ◽  
pp. 8055-8064 ◽  
Author(s):  
Maria Tsukernik ◽  
Amanda H. Lynch
Keyword(s):  
Southern Ocean ◽  
Moisture Transport ◽  
Southern Oscillation ◽  
Moisture Flux ◽  
Southern Annular Mode ◽  
Complex Nature ◽  
Regional Variability ◽  
Amundsen Sea ◽  
The Pacific ◽  
Meridional Moisture Transport

Abstract The Antarctic ice sheet constitutes the largest reservoir of freshwater on earth, representing tens of meters of sea level rise if it were to melt completely. However, because of the remote location of the continent and the concomitant sparse data coverage, much remains unknown regarding the climate variability in Antarctica and the surrounding Southern Ocean. This study uses the high-resolution ECMWF Interim Re-Analysis (ERA-Interim) data during 1979–2010 to calculate the meridional moisture transport associated with the mean circulation, planetary waves, and synoptic-scale systems. The resulting moisture flux, which is dominated by the synoptic scales, is largely consistent with results from theoretical assumptions and previous studies. Here, high interannual and regional variability in the total meridional moisture flux is found, with no significant trend over the last 30 years. Further, the variability of the meridional moisture flux cannot be explained by the southern annular mode or El Niño–Southern Oscillation, even in the Pacific sector. In addition, the Amundsen Sea sector experiences the highest variability in meridional moisture transport and reveals a statistically significant decrease in the moisture flux at synoptic scales along the coastal zone. These results suggest that the Amundsen Sea provides a window on the complex nature of atmospheric moisture transport in the high southern latitudes.

scholarly journals Effect of climate variability on event frequency of sorghum ergot in Australia

2003 ◽  
Vol 54 (6) ◽  
pp. 599 ◽  
Author(s):  
Enli Wang ◽  
Malcolm Ryley ◽  
Holger Meinke
Keyword(s):  
Climate Variability ◽  
Southern Oscillation ◽  
Climatic Conditions ◽  
Considerable Research ◽  
Significant Difference ◽  
Negative Effect ◽  
Claviceps Africana ◽  
Relative Risk Assessment ◽  
Resistant Genotypes

The significant effect of ergot, caused by Claviceps africana, on the Australian sorghum industry, has led to considerable research on the identification of resistant genotypes and on the climatic conditions that are conducive to ergot outbreaks. Here we show that the potential number of monthly ergot events differs strongly from year to year in accordance with ENSO (El Niño–Southern Oscillation)-related climate variability. The analysis is based on long-term weather records from 50 locations throughout the sorghum-growing areas of Australia and predicts the potential number of monthly ergot events based on phases of the Southern Oscillation Index (SOI). For a given location, we found a significant difference in the number of potential ergot events based on SOI phases in the preceding month, with a consistently positive SOI phase providing the greatest risk for the occurrence of ergot for most months and locations. This analysis provides a relative risk assessment for ergot outbreaks based on location and prevailing climatic conditions, thereby assisting in responsive decision-making to reduce the negative effect of sorghum ergot.

scholarly journals Decadal Changes of Wind Stress over the Southern Ocean Associated with Antarctic Ozone Depletion

2007 ◽  
Vol 20 (14) ◽  
pp. 3395-3410 ◽  
Author(s):  
Xiao-Yi Yang ◽  
Rui Xin Huang ◽  
Dong Xiao Wang
Keyword(s):  
Southern Ocean ◽  
Wind Stress ◽  
Zonal Wind ◽  
Ozone Depletion ◽  
Surface Wind ◽  
Southern Annular Mode ◽  
Mean Flow ◽  
Annular Mode ◽  
Surface Wind Stress ◽  
Antarctic Ozone

Abstract Using 40-yr ECMWF Re-Analysis (ERA-40) data and in situ observations, the positive trend of Southern Ocean surface wind stress during two recent decades is detected, and its close linkage with spring Antarctic ozone depletion is established. The spring Antarctic ozone depletion affects the Southern Hemisphere lower-stratospheric circulation in late spring/early summer. The positive feedback involves the strengthening and cooling of the polar vortex, the enhancement of meridional temperature gradients and the meridional and vertical potential vorticity gradients, the acceleration of the circumpolar westerlies, and the reduction of the upward wave flux. This feedback loop, together with the ozone-related photochemical interaction, leads to the upward tendency of lower-stratospheric zonal wind in austral summer. In addition, the stratosphere–troposphere coupling, facilitated by ozone-related dynamics and the Southern Annular Mode, cooperates to relay the zonal wind anomalies to the upper troposphere. The wave–mean flow interaction and the meridional circulation work together in the form of the Southern Annular Mode, which transfers anomalous wind signals downward to the surface, triggering a striking strengthening of surface wind stress over the Southern Ocean.

Climate variability and breeding parameters of a transhemispheric migratory seabird over seven decades

2020 ◽  
Vol 642 ◽  
pp. 191-205 ◽  
Author(s):  
CA Price ◽  
K Hartmann ◽  
TJ Emery ◽  
EJ Woehler ◽  
CR McMahon ◽  
...  
Keyword(s):  
Climate Variability ◽  
Environmental Conditions ◽  
Large Scale ◽  
Southern Oscillation ◽  
Southern Annular Mode ◽  
Trophic Levels ◽  
Climate Indices ◽  
Ecological Processes ◽  
Spatial And Temporal Scales ◽  
Breeding Parameters

Climate variability affects physical oceanographic systems and environmental conditions at multiple spatial and temporal scales. These changes can influence biological and ecological processes, from primary productivity to higher trophic levels. Short-tailed shearwaters Ardenna tenuirostris are transhemispheric migratory procellariiform seabirds that forage on secondary consumers such as fish (myctophids) and zooplankton (euphausiids). In this study, we investigated the breeding parameters of the short-tailed shearwater from a colony of 100 to 200 breeding pairs at Fisher Island, Tasmania, Australia, for the period 1950 to 2012, with the aim to quantify the relationship between breeding parameters with large-scale climate indices in the Northern (i.e. Northern Pacific Index and Pacific Decadal Oscillation) and Southern Hemispheres (i.e. El Niño-Southern Oscillation and Southern Annular Mode). Through the use of generalised linear models, we found that breeding participation among short-tailed shearwaters was affected by climate variability with a 12-mo temporal lag. Furthermore, breeding success decreased in years of increased rainfall at the colony. These findings demonstrate that both large-scale climate indices and local environmental conditions could explain some of the variability among breeding parameters of the short-tailed shearwater.

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