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.

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.

Reshuffling of Nutrients in the Southern Ocean

2020 ◽  
Author(s):  
Ivy Frenger ◽  
Ivana Cerovecki ◽  
Matthew Mazloff
Keyword(s):  
Southern Ocean ◽  
Water Mass ◽  
Driving Forces ◽  
Water Masses ◽  
Global Ocean ◽  
Upper Ocean ◽  
Physical Processes ◽  
Near Surface ◽  
Deep Waters ◽  
Ocean Productivity

&lt;p&gt;Deep waters upwell in the Southern Ocean, replete with nutrients. Some of these nutrients enter lighter mode and intermediate waters (MIW), fueling upper ocean productivity in the otherwise nutrient depleted (sub)tropical waters. However some of the upwelled nutrients are retained in the Southern Ocean or leak into denser bottom waters (AABW), making them unavailable for upper ocean productivity. Despite its fundamental importance for the global ocean productivity, this &amp;#8220;reshuffling&amp;#8221; of nutrients between Southern Ocean water masses, and its driving forces and temporal variability, have not been quantified to date.&lt;/p&gt;&lt;p&gt;We analyze the globally major limiting macronutrient, nitrate (NO&lt;sub&gt;3&lt;/sub&gt;), using the results of a data-assimilating coupled ocean-sea-ice and biogeochemistry model, the Biogeochemical Southern Ocean State Estimate (B-SOSE), for the years 2008 &amp;#8211; 2017. Using a water mass framework, applied to five day averaged SOSE output south of 30&lt;sup&gt;o&lt;/sup&gt;S, we quantify the processes controlling NO&lt;sub&gt;3&lt;/sub&gt; inventories and fluxes. The water mass framework enables us to assess the relative importance of physical processes (such as surface buoyancy fluxes and diapycnal mixing) and biogeochemical processes (such as productivity and remineralization) in driving the transfer of NO&lt;sub&gt;3&lt;/sub&gt; from upwelling deep waters (CDW) to MIW and AABW, and its interannual variability.&lt;/p&gt;&lt;p&gt;Our results show that two thirds of the NO&lt;sub&gt;3&lt;/sub&gt; supplied to MIW occurs through lightening, or transforming, of CDW waters during the course of the overturning circulation. The other third of the NO&lt;sub&gt;3&lt;/sub&gt; supplied to MIW occurs through upward mixing of NO&lt;sub&gt;3&lt;/sub&gt; from NO&lt;sub&gt;3&lt;/sub&gt;-enriched CDW. This means that physical processes determine the mean MIW NO&lt;sub&gt;3&lt;/sub&gt; content. Biology does not have a net effect on MIW NO&lt;sub&gt;3&lt;/sub&gt;: while biological uptake draws down the MIW concentration of&amp;#160; NO&lt;sub&gt;3&lt;/sub&gt; near the surface, remineralization of organic matter compensates for this MIW loss below the surface. Also, we find that the productivity in the subtropical waters south of 30&lt;sup&gt;o&lt;/sup&gt;S is fed through both, the canonical upward mixing of NO&lt;sub&gt;3&lt;/sub&gt; through the thermocline, and through the near surface supply from MIW. Thus, again, water mass transformation is playing a large role in nutrient distributions.&amp;#160;&lt;/p&gt;&lt;p&gt;In ongoing work, we assess the drivers of variability of the reshuffling of NO&lt;sub&gt;3&lt;/sub&gt; between water masses and their potential sensitivity to climate change.&lt;/p&gt;

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.

scholarly journals Stochastic Subgrid-Scale Ocean Mixing: Impacts on Low-Frequency Variability

2017 ◽  
Vol 30 (13) ◽  
pp. 4997-5019 ◽  
Author(s):  
Stephan Juricke ◽  
Tim N. Palmer ◽  
Laure Zanna
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
Time Scales ◽  
High Frequency ◽  
Low Frequency ◽  
Global Ocean ◽  
Small Scale ◽  
Subgrid Scale ◽  
Low Frequency Variability ◽  
Ocean Models

In global ocean models, the representation of small-scale, high-frequency processes considerably influences the large-scale oceanic circulation and its low-frequency variability. This study investigates the impact of stochastic perturbation schemes based on three different subgrid-scale parameterizations in multidecadal ocean-only simulations with the ocean model NEMO at 1° resolution. The three parameterizations are an enhanced vertical diffusion scheme for unstable stratification, the Gent–McWilliams (GM) scheme, and a turbulent kinetic energy mixing scheme, all commonly used in state-of-the-art ocean models. The focus here is on changes in interannual variability caused by the comparatively high-frequency stochastic perturbations with subseasonal decorrelation time scales. These perturbations lead to significant improvements in the representation of low-frequency variability in the ocean, with the stochastic GM scheme showing the strongest impact. Interannual variability of the Southern Ocean eddy and Eulerian streamfunctions is increased by an order of magnitude and by 20%, respectively. Interannual sea surface height variability is increased by about 20%–25% as well, especially in the Southern Ocean and in the Kuroshio region, consistent with a strong underestimation of interannual variability in the model when compared to reanalysis and altimetry observations. These results suggest that enhancing subgrid-scale variability in ocean models can improve model variability and potentially its response to forcing on much longer time scales, while also providing an estimate of model uncertainty.

scholarly journals A Comparison of the Variability and Changes in Global Ocean Heat Content from Multiple Objective Analysis Products During the Argo Period

2021 ◽  
pp. 1-47
Author(s):  
Xinfeng Liang ◽  
Chao Liu ◽  
Rui M. Ponte ◽  
Don P. Chambers
Keyword(s):  
Southern Ocean ◽  
Interannual Variability ◽  
North Atlantic ◽  
Southern Oscillation ◽  
Heat Content ◽  
Global Scale ◽  
Ocean Heat Content ◽  
Objective Analysis ◽  
Global Ocean ◽  
Ocean Measurements

AbstractOcean heat content (OHC) is key to estimating the energy imbalance of the earth system. Over the past two decades, an increasing number of OHC studies were conducted using oceanic objective analysis (OA) products. Here we perform an intercomparison of OHC from eight OA products with a focus on their robust features and significant differences over the Argo period (2005-2019), when the most reliable global scale oceanic measurements are available. For the global ocean, robust warming in the upper 2000 m is confirmed. The 0-300 m layer shows the highest warming rate but is heavily modulated by interannual variability, particularly the El Niño–Southern Oscillation. The 300-700 m and 700-2000 m layers, on the other hand, show unabated warming. Regionally, the Southern Ocean and mid-latitude North Atlantic show a substantial OHC increase, and the subpolar North Atlantic displays an OHC decrease. A few apparent differences in OHC among the examined OA products were identified. In particular, temporal means of a few OA products that incorporated other ocean measurements besides Argo show a global-scale cooling difference, which is likely related to the baseline climatology fields used to generate those products. Large differences also appear in the interannual variability in the Southern Ocean and in the long-term trends in the subpolar North Atlantic. These differences remind us of the possibility of product-dependent conclusions on OHC variations. Caution is therefore warranted when using merely one OA product to conduct OHC studies, particularly in regions and on timescales that display significant differences.

Mechanisms behind the precipitation increase in Norway

2021 ◽  
Author(s):  
Kjersti Konstali ◽  
Asgeir Sorteberg
Keyword(s):  
Relative Humidity ◽  
Interannual Variability ◽  
Vertical Velocity ◽  
Absolute Magnitude ◽  
Diagnostic Model ◽  
Positive Trend ◽  
Water Vapour Content ◽  
Near Surface ◽  
Precipitation Increase

&lt;p&gt;We use a dataset with observations of daily precipitation from 55 homogeneity tested stations in Norway over the period 1900-2019 available from MET-Norway. These observations show that precipitation in Norway has increased monotonically by 19% since 1900. Notably, over half of the overall increase was recorded within the decade of 1980-1990. To examine possible mechanisms behind the precipitation increase, we use a diagnostic model to separate the effects of changes in vertical velocity, temperature and relative humidity. We use vertical velocity, near-surface temperature and relative humidity from two reanalysis products, ECMWF&amp;#8217;s ERA-20C and NOAA&amp;#8217;s 20th Century Reanalysis. The model-based precipitation estimates capture the interannual variability as well as the long-term trend, but the absolute magnitude of precipitation is underestimated. Within our model, we find that the variability in vertical velocity chiefly determines the interannual variability and long-term trends. In fact, the trend in vertical velocities contributes with more than 75% of the total modelled trend in precipitation between 1900-2019, and more than 60% of the anomalies between 1980-1990. However, over the last decades (1979 to 2019), changes in temperature and relative humidity are the main contributors to the trend. Thus, different physical processes shape the trend at different times. We hypothesize that the strong precipitation increase in the 1980&amp;#8217;s is linked to an unusual high number of low pressure systems reaching Norway from the North-Atlantic. In recent decades, direct effects of global warming (rising temperatures and hence increased water vapour content) are thought to be the main cause of the positive trend in precipitation over Norway.&amp;#160;&lt;/p&gt;

On-Line Monitoring of Charge Unit by Using Fiber Bragg Grating Temperature Sensors

2012 ◽  
Vol 503-504 ◽  
pp. 1672-1678
Author(s):  
Zhao Yang ◽  
Xiao Ping Xu ◽  
Chuan Li ◽  
Yan Chen ◽  
Jiang Chun Xu ◽  
...  
Keyword(s):  
Ambient Temperature ◽  
Fiber Bragg Grating ◽  
Minimum Temperature ◽  
Maximum Temperature ◽  
Daily Minimum Temperature ◽  
Bragg Grating ◽  
Temperature Changes ◽  
Temperature Range ◽  
On Line

The charge unit supply power when the power is cut off. It has been the necessary components in every type of substations to ensure the continuous operations of electric relays, automatic devices and circuit breakers. By using contacting electrical insulating Fiber Bragg Grating temperature sensor, the monitored equipment can be measured and controlled under the safe temperature. The temperatures of three fans and environment have been surveyed since June 6, 2010, in the charge unit of Yanjin substation’s main control room. The real-time monitoring of 24-hours indicates that the temperature changes in the range of 1°C. At the long-term of 479 days, the average daily minimum temperature range of three fans is 12.48°C, and the maximum range is 23.07°C. The maximum temperature is 39.14°C on April 30, 2011, and the minimum temperature is 23.98°C on January 10, 2011. The daily average of ambient temperature range is 12.04 °C, the maximum temperature is 38.38 °C on July 16, 2010, and the minimum temperature is 26.34 °C on January 9, 2011. The maximum difference between the temperature of fan and the ambient temperature is 7.60 °C on October 23, 2010. According to the relevant standards and monitoring results, the maximum threshold of fan temperature is defined to 85°C, and the threshold of temperature rise is 20°C.

scholarly journals Observational evidence of temperature trends at two levels in the surface layer

2016 ◽  
Vol 16 (2) ◽  
pp. 827-841 ◽  
Author(s):  
X. Lin ◽  
R. A. Pielke Sr. ◽  
R. Mahmood ◽  
C. A. Fiebrich ◽  
R. Aiken
Keyword(s):  
Surface Layer ◽  
Surface Temperature ◽  
Current Knowledge ◽  
Observational Evidence ◽  
Lapse Rate ◽  
High Quality ◽  
Near Surface ◽  
Temperature Trends ◽  
Screen Level

Abstract. Long-term surface air temperatures at 1.5 m screen level over land are used in calculating a global average surface temperature trend. This global trend is used by the IPCC and others to monitor, assess, and describe global warming or warming hiatus. Current knowledge of near-surface temperature trends with respect to height, however, is limited and inadequately understood because surface temperature observations at different heights in the surface layer of the world are rare especially from a high-quality and long-term climate monitoring network. Here we use high-quality two-height Oklahoma Mesonet observations, synchronized in time, fixed in height, and situated in relatively flat terrain, to assess temperature trends and differentiating temperature trends with respect to heights (i.e., near-surface lapse rate trend) over the period 1997 to 2013. We show that the near-surface lapse rate has significantly decreased with a trend of −0.18 ± 0.03 °C (10 m)−1 per decade indicating that the 9 m height temperatures increased faster than temperatures at the 1.5 m screen level and/or conditions at the 1.5 m height cooled faster than at the 9 m height. However, neither of the two individual height temperature trends by themselves were statistically significant. The magnitude of lapse rate trend is greatest under lighter winds at night. Nighttime lapse rate trends were significantly more negative than daytime lapse rate trends and the average lapse rate trend was three times more negative under calm conditions than under windy conditions. Our results provide the first observational evidence of near-surface temperature changes with respect to height that could enhance the assessment of climate model predictions.

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