scholarly journals Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Waters observed in the Indian sector of the Southern Ocean, 1978–2018

2020 ◽  
Author(s):  
Léo Mahieu ◽  
Claire Lo Monaco ◽  
Nicolas Metzl ◽  
Jonathan Fin ◽  
Claude Mignon
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Weddell Sea ◽  
Surprising Result ◽  
Anthropogenic Co2 ◽  
Original Dataset ◽  
Term Change ◽  
Bottom Waters ◽  
Indian Sector

Abstract. Antarctic bottom waters (AABWs) are known as a long term sink for anthropogenic CO2 (Cant) but is hardly quantified because of the scarcity of the observations, specifically at an interannual scale. We present in this manuscript an original dataset combining 40 years of carbonate system observations in the Indian sector of the Southern Ocean (Enderby Basin) to evaluate and interpret the interannual variability of Cant in the AABW. This investigation is based on regular observations collected at the same location (63° E/56.5° S) in the frame of the French observatory OISO from 1998 to 2018 extended by GEOSECS and INDIGO observations (1978, 1985 and 1987). At this location the main sources of AABW sampled is the fresh and younger Cape Darnley bottom water (CDBW) and the Weddell Sea deep water (WSDW). Our calculations reveal that Cant concentrations increased significantly in AABW, from about + 7 µmol kg-1 in 1978–1987 to + 13 µmol kg-1 in 2010–2018. This is comparable to previous estimates in other SO basins, with the exception of bottom waters close to their formation sites where Cant concentrations are about twice as large. Our analysis shows that the CT and Cant increasing rates in AABW are about the same over the period 1978–2018, and we conclude that the long-term change in CT is mainly due to the uptake of anthropogenic CO2 in the different formation regions. This is however modulated by significant interannual to pluriannual variability associated with variations in hydrological (ϴ, S) and biogeochemical (CT, AT, O2) properties. A surprising result is the apparent stability of Cant concentrations in recent years despite the increase in CT and the gradual acceleration of atmospheric CO2. The Cant sequestration by AABWs is more variable than expected and depends on a complex combination of physical, chemical and biological processes at the formation sites and during the transit of the different AABWs. The interannual variability at play in AABW needs to be carefully considered on the extrapolated estimation of Cant sequestration based on sparse observations over several years.

scholarly journals Variability and stability of anthropogenic CO<sub>2</sub> in Antarctic Bottom Water observed in the Indian sector of the Southern Ocean, 1978–2018

Ocean Science ◽  
2020 ◽  
Vol 16 (6) ◽  
pp. 1559-1576
Author(s):  
Léo Mahieu ◽  
Claire Lo Monaco ◽  
Nicolas Metzl ◽  
Jonathan Fin ◽  
Claude Mignon
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Bottom Water ◽  
Average Concentration ◽  
Weddell Sea ◽  
Total Carbon ◽  
Total Alkalinity ◽  
Antarctic Bottom Water ◽  
Indian Sector

Abstract. Antarctic Bottom Water (AABW) is known as a long-term sink for anthropogenic CO2 (Cant), but the sink is hardly quantified because of the scarcity of observations, specifically at an interannual scale. We present in this paper an original dataset combining 40 years of carbonate system observations in the Indian sector of the Southern Ocean (Enderby Basin) to evaluate and interpret the interannual variability of Cant in the AABW. This investigation is based on regular observations collected at the same location (63∘ E–56.5∘ S) in the framework of the French observatory OISO from 1998 to 2018 extended by GEOSECS and INDIGO observations (1978, 1985 and 1987). At this location the main sources of AABW sampled is the low-salinity Cape Darnley Bottom Water (CDBW) and the Weddell Sea Deep Water (WSDW). Our calculations reveal that Cant concentrations increased significantly in the AABW, from an average concentration of 7 µmol kg−1 calculated for the period 1978–1987 to an average concentration of 13 µmol kg−1 for the period 2010–2018. This is comparable to previous estimates in other Southern Ocean (SO) basins, with the exception of bottom water close to formation sites where Cant concentrations are about twice as large. Our analysis shows that total carbon (CT) and Cant increasing rates in the AABW are about the same over the period 1978–2018, and we conclude that the long-term change in CT is mainly due to the uptake of Cant in the different formation regions. This is, however, modulated by significant interannual to multi-annual variability associated with variations in hydrographic (potential temperature, Θ; salinity, S) and biogeochemical (CT; total alkalinity, AT; dissolved oxygen, O2) properties. A surprising result is the apparent stability of Cant concentrations in recent years despite the increase in CT and the gradual acceleration of atmospheric CO2. The interannual variability at play in AABW needs to be carefully considered in the extrapolated estimation of Cant sequestration based on sparse observations over several years.

scholarly journals Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Matthis Auger ◽  
Rosemary Morrow ◽  
Elodie Kestenare ◽  
Jean-Baptiste Sallée ◽  
Rebecca Cowley
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Global Ocean ◽  
Maximum Temperature ◽  
Near Surface ◽  
Temperature Changes ◽  
Temperature Trends ◽  
Deep Waters ◽  
Term Change

AbstractDespite playing a major role in global ocean heat storage, the Southern Ocean remains the most sparsely measured region of the global ocean. Here, a unique 25-year temperature time-series of the upper 800 m, repeated several times a year across the Southern Ocean, allows us to document the long-term change within water-masses and how it compares to the interannual variability. Three regions stand out as having strong trends that dominate over interannual variability: warming of the subantarctic waters (0.29 ± 0.09 °C per decade); cooling of the near-surface subpolar waters (−0.07 ± 0.04 °C per decade); and warming of the subsurface subpolar deep waters (0.04 ± 0.01 °C per decade). Although this subsurface warming of subpolar deep waters is small, it is the most robust long-term trend of our section, being in a region with weak interannual variability. This robust warming is associated with a large shoaling of the maximum temperature core in the subpolar deep water (39 ± 09 m per decade), which has been significantly underestimated by a factor of 3 to 10 in past studies. We find temperature changes of comparable magnitude to those reported in Amundsen–Bellingshausen Seas, which calls for a reconsideration of current ocean changes with important consequences for our understanding of future Antarctic ice-sheet mass loss.

scholarly journals Southern Ocean in-situ temperature trends over 25 years emerge from interannual variability

2020 ◽  
Author(s):  
Matthis Auger ◽  
Rosemary Morrow ◽  
Elodie Kestenare ◽  
Jean-Baptiste Sallée
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Global Ocean ◽  
West Antarctica ◽  
Near Surface ◽  
Temperature Changes ◽  
Temperature Trends ◽  
Deep Waters ◽  
Term Change

Abstract Despite playing a major role for the global ocean heat storage, the Southern Ocean remains the most sparsely measured region of the global ocean. Here, a unique 25-year temperature time-series of the upper 800 m, repeated several times a year across the Southern Ocean, allows us to document the long-term change within water-masses and how it compares to the interannual variability. Three regions stand out as having strong change that is radically different from the interannual variability: warming of the subantarctic waters (0.29±0.09°C per decade); cooling of the near-surface subpolar waters (-0.07±0.04°C per decade); and warming of the subsurface subpolar deep waters (0.04±0.01°C per decade). Our results highlight that this subsurface warming of subpolar deep waters is, counter-intuitively, the largest change of the section regarding interannual variability. This robust warming is associated with a large shallowing (39±11 m per decade), which has been significantly underestimated by a factor of 3 to 10 in past studies. We find temperature changes of comparable magnitude to those reported in West Antarctica, which calls for a reconsideration of current ocean changes with important consequences for our understanding of future Antarctic ice-sheet mass loss.

The Southern Ocean benthic fauna and climate change: a historical perspective

1992 ◽  
Vol 338 (1285) ◽  
pp. 299-309 ◽  
Keyword(s):  
Global Warming ◽  
Southern Ocean ◽  
Environmental Change ◽  
Benthic Communities ◽  
Benthic Fauna ◽  
Marine Fauna ◽  
Short Term Change ◽  
Term Change ◽  
Continental Ice Sheets

Environmental change is the norm and it is likely that, particularly on the geological timescale, the temperature regime experienced by marine organisms has never been stable. These temperature changes vary in timescale from daily, through seasonal variations, to long-term environmental change over tens of millions of years. Whereas physiological work can give information on how individual organisms may react phenotypically to short-term change, the way benthic communities react to long-term change can only be studied from the fossil record. The present benthic marine fauna of the Southern Ocean is rich and diverse, consisting of a mixture of taxa with differing evolutionary histories and biogeographical affinities, suggesting that at no time in the Cenozoic did continental ice sheets extend sufficiently to eradicate all shallow-water faunas around Antarctica at the same time. Nevertheless, certain features do suggest the operation of vicariant processes, and climatic cycles affecting distributional ranges and ice-sheet extension may both have enhanced speciation processes. The overall cooling of southern high-latitude seas since the mid-Eocene has been neither smooth nor steady. Intermittent periods of global warming and the influence of Milankovitch cyclicity is likely to have led to regular pulses of migration in and out of Antarctica. The resultant diversity pump may explain in part the high species richness of some marine taxa in the Southern Ocean. It is difficult to suggest how the existing fauna will react to present global warming. Although it is certain the fauna will change, as all faunas have done throughout evolutionary time, we cannot predict with confidence how it will do so.

Impact of Winds and Southern Ocean SSTs on Antarctic Sea Ice Trends and Variability

2021 ◽  
Vol 34 (3) ◽  
pp. 949-965
Author(s):  
Edward Blanchard-Wrigglesworth ◽  
Lettie A. Roach ◽  
Aaron Donohoe ◽  
Qinghua Ding
Keyword(s):  
Southern Ocean ◽  
Sea Ice ◽  
Interannual Variability ◽  
Initial Conditions ◽  
Regional Scale ◽  
Earth System ◽  
Anthropogenic Forcing ◽  
Antarctic Sea Ice ◽  
Long Term Trends

AbstractAntarctic sea ice extent (SIE) has slightly increased over the satellite observational period (1979 to the present) despite global warming. Several mechanisms have been invoked to explain this trend, such as changes in winds, precipitation, or ocean stratification, yet there is no widespread consensus. Additionally, fully coupled Earth system models run under historic and anthropogenic forcing generally fail to simulate positive SIE trends over this time period. In this work, we quantify the role of winds and Southern Ocean SSTs on sea ice trends and variability with an Earth system model run under historic and anthropogenic forcing that nudges winds over the polar regions and Southern Ocean SSTs north of the sea ice to observations from 1979 to 2018. Simulations with nudged winds alone capture the observed interannual variability in SIE and the observed long-term trends from the early 1990s onward, yet for the longer 1979–2018 period they simulate a negative SIE trend, in part due to faster-than-observed warming at the global and hemispheric scale in the model. Simulations with both nudged winds and SSTs show no significant SIE trends over 1979–2018, in agreement with observations. At the regional scale, simulated sea ice shows higher skill compared to the pan-Antarctic scale both in capturing trends and interannual variability in all nudged simulations. We additionally find negligible impact of the initial conditions in 1979 on long-term trends.

Demography and life cycle of Antarctic krill, Euphausia superba, in the Indian sector of the Southern Ocean: long-term comparison between coastal and open-ocean regions

2000 ◽  
Vol 57 (S3) ◽  
pp. 68-90 ◽  
Author(s):  
E A Pakhomov
Keyword(s):  
Southern Ocean ◽  
Life Span ◽  
Antarctic Krill ◽  
Age Groups ◽  
Substantial Reduction ◽  
Euphausia Superba ◽  
Age Composition ◽  
Indian Sector ◽  
Antarctic Krill Euphausia Superba

Size/age composition and reproductive status of Antarctic krill, Euphausia superba, in the central part of the Indian sector of the Southern Ocean, e.g., the Cooperation Sea (Prydz Bay region) and the Cosmonaut Sea, during austral summers 1977-1990 were summarized to estimate growth rates, longevity, reproduction, recruitment, life span, and mortality rates. The life span of Antarctic krill exceeds 5 years in both the Cosmonaut and Cooperation seas. The age composition of the southern and northern groupings differs markedly, with substantial reduction in numbers of early age groups in the northern grouping. Long-term observations of spawning success, recruitment, and age composition suggest that a self-sustained grouping of krill persists in the Cooperation Sea south of the Antarctic Divergence. However, periodic gene flow via recruits from surrounding regions most probably accounts for the lack of spatial genetic differences between the Cooperation Sea and adjacent areas, thus preventing the establishment of an isolated subpopulation in the region investigated. The major factor responsible for the substantial interannual variability in krill dynamics appears to be macroscale oceanographic and atmospheric circulations, which determine a level of environmental isolation of the Cooperation Sea from adjacent waters.

scholarly journals Orange is the new white: taxonomic revision of Tritonia species (Gastropoda: Nudibranchia) from the Weddell Sea and Bouvet Island

Polar Biology ◽  
2021 ◽  
Author(s):  
Maria Eleonora Rossi ◽  
Conxita Avila ◽  
Juan Moles
Keyword(s):  
Southern Ocean ◽  
Phylogenetic Analyses ◽  
Taxonomic Revision ◽  
Molecular Data ◽  
Molecular Techniques ◽  
Weddell Sea ◽  
Valid Species ◽  
Phylogenetic Position ◽  
Antarctic Waters

AbstractAmong nudibranch molluscs, the family Tritoniidae gathers taxa with an uncertain phylogenetic position, such as some species of the genus Tritonia Cuvier, 1798. Currently, 37 valid species belong to this genus and only three of them are found in the Southern Ocean, namely T. challengeriana Bergh, 1884, T. dantarti Ballesteros & Avila, 2006, and T. vorax (Odhner, 1926). In this study, we shed light on the long-term discussed systematics and taxonomy of Antarctic Tritonia species using morpho-anatomical and molecular techniques. Samples from the Weddell Sea and Bouvet Island were dissected and prepared for scanning electron microscopy. The three molecular markers COI, 16S, and H3 were sequenced and analysed through maximum-likelihood and Bayesian methods. The phylogenetic analyses and species delimitation tests clearly distinguished two species, T. challengeriana widely spread in the Southern Ocean and T. dantarti endemic to Bouvet Island. Colouration seems to be an unreliable character to differentiate among species since molecular data revealed both species can either have orange or white colour morphotypes. This variability could be explained by pigment sequestration from the soft coral species they feed on. Morphological analyses reveal differences between Antarctic and Magellanic specimens of T. challengeriana. However, the relationship between T. challengeriana specimens from these two regions remains still unclear due to the lack of molecular data. Therefore, the validity of the T. antarctica Martens & Pfeffer, 1886, exclusively found in Antarctic waters requires further systematic work.

scholarly journals Snow conditions in northern Europe: the dynamics of interannual variability versus projected long-term change

2021 ◽  
Vol 15 (4) ◽  
pp. 1677-1696
Author(s):  
Jouni Räisänen
Keyword(s):  
Interannual Variability ◽  
Climate Models ◽  
Snow Water Equivalent ◽  
Regional Climate ◽  
Northern Europe ◽  
Total Precipitation ◽  
Winter Climate ◽  
Mild Winter ◽  
Term Change

Abstract. Simulations by the EURO-CORDEX (European branch of the Coordinated Regional Climate Downscaling Experiment) regional climate models indicate a widespread future decrease in snow water equivalent (SWE) in northern Europe. This concurs with the negative interannual correlation between SWE and winter temperature in the southern parts of the domain but not with the positive correlation observed further north and over the Scandinavian mountains. To better understand these similarities and differences, interannual variations and projected future changes in SWE are attributed to anomalies or changes in three factors: total precipitation, the snowfall fraction of precipitation and the fraction of accumulated snowfall that remains on the ground (the snow-on-ground fraction). In areas with relatively mild winter climate, the latter two terms govern both the long-term change and interannual variability, resulting in less snow with higher temperatures. In colder areas, however, interannual SWE variability is dominated by variations in total precipitation. Since total precipitation is positively correlated with temperature, more snow tends to accumulate in milder winters. Still, even in these areas, SWE is projected to decrease in the future due to the reduced snowfall and snow-on-ground fractions in response to higher temperatures. Although winter total precipitation is projected to increase, its increase is smaller than would be expected from the interannual covariation of temperature and precipitation and is therefore insufficient to compensate the lower snowfall and snow-on-ground fractions. Furthermore, interannual SWE variability in northern Europe in the simulated warmer future climate is increasingly governed by variations in the snowfall and snow-on-ground fractions and less by variations in total precipitation.

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