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Southern Annular Mode Causes Antarctic Peninsula Ice to Melt

Posted on: October 25, 2019

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RELATED POSTS ON ANTARCTICA [LINK1] [LINK2] [LINK3] 

 

THIS POST IS A REVIEW OF DICKENS ET AL 2019 PUBLISHED IN NATURE-RESEARCH SCIENTIFIC REPORTS [LINK] {CITATION AND ABSTRACT BELOW}. 

  1. W. A. Dickens, G. Kuhn, M. J. Leng, A. G. C. Graham, J. A. Dowdeswell, M. P. Meredith, C.-D. Hillenbrand, D. A. Hodgson, S. J. Roberts, H. Sloane & J. A. Smith, “Enhanced glacial discharge from the eastern Antarctic Peninsula since the 1700s associated with a positive Southern Annular Mode”, Scientific Reports volume 9, Article number: 14606 (2019)  [LINK TO FULL TEXT] 
  2. ABSTRACT: The Antarctic Peninsula Ice Sheet is currently experiencing (2019) sustained and accelerating loss of ice. Determining when these changes were initiated and identifying the main drivers is hampered by the short instrumental record (1992 to present). Here we present a 6,250 year record of glacial discharge based on the oxygen isotope composition of diatoms (δ18Odiatom) from a marine core located at the north-eastern tip of the Antarctic Peninsula. We find that glacial discharge – sourced primarily from ice shelf and iceberg melting along the eastern Antarctic Peninsula – remained largely stable between ~6,250 to 1,620 cal. yr BP, with a slight increase in variability until ~720 cal. yr. BP. An increasing trend in glacial discharge occurs after 550 cal. yr BP (A.D. 1400), reaching levels unprecedented during the past 6,250 years after 244 cal. yr BP (A.D. 1706). A marked acceleration in the rate of glacial discharge is also observed in the early part of twentieth century (after A.D. 1912). Enhanced glacial discharge, particularly after the 1700s is linked to a positive Southern Annular Mode (SAM). We argue that a positive SAM drove stronger westerly winds, atmospheric warming and surface ablation on the eastern Antarctic Peninsula whilst simultaneously entraining more warm water into the Weddell Gyre, potentially increasing melting on the undersides of ice shelves. A possible implication of our data is that ice shelves in this region have been thinning for at least ~300 years, potentially predisposing them to collapse under intensified anthropogenic warming. 
  3. GRIST REPORT ON DICKENS ET AL 2019:  The publication of Dickens 2019 was quickly followed by an article on the climate alarmism publication GRIST with the breathless claim that “New study: Antarctica’s tipping point is closer than we thought: By Nathanael Johnson on Oct 24, 2019. Antarctic ice sheets have been melting rapidly for hundreds of years, much longer than scientists previously thought, according to a study out Thursday. The findings suggest that estimates for global sea-level rise need to be reworked and that we’re even closer to the day that fish start chasing each other through New York City’s subway tunnels. So natural climate change had cued up the massive Antarctic ice shelves to collapse before human-caused climate change turned up the heat. A random shift in wind patterns has been melting the ice caps for the last 300 years, the scientists wrote, “potentially predisposing them to collapse under intensified anthropogenic warming.” [FULL TEXT]

 

 

REVIEW COMMENTS ON DICKENS ET-AL 2019  

  1. The paper says that (1) the Antarctic Peninsula is experiencing sustained and accelerating loss of ice in 2019 and (2) this loss of ice is explained by unusually strong westerly winds caused by unusually strong Positive Southern Annular Mode (PSAM) cycles.
  2. That “unusually strong” PSAM causes “unusual ice loss on the Antarctic Peninsula implies that  normal PSAM causes normal ice loss on the Antarctic Peninsula. Therefore an ice melt cycle must exist on the Antarctic Peninsula synchornized with the Southern Annular Mode (SAM). Yet, no evidence for such a cyclical ice melt cycle on the Antarctic Peninsula exists much less one that is synchronized with the SAM.  (Bibliography below).
  3. The continued effort by climate scientists to explain Antarctic ice melt events in terms of atmospheric phenomena is the product of the atmosphere bias of atmospheric scientists such that known geological features of the Antarctic Peninsula that provide a more rational explanation of ice melt events are overlooked as described in a related post [LINK] .
  4. The assumption that Antarctic Peninsula ice melt events are cyclical  and synchronized with cyclical atmospheric phenomena of convenience is inconsistent with the highly localized and random nature of such ice melt events; but consistent with the randomness of geothermal activity.
  5. The graphic below is a map of Antarctica overlaid with markings that identify locations of known geologically active areas. The black hash-marked area is the West Antarctic Rift. It is a region of intense geological activity  with more than 150 known active land and sub-marine volcanoes A rift is a linear section of the lithosphere where it is being pulled apart by magmatic forces with release of heat. This geologically active area includes all of the Antarctic Peninsula and most of West Antarctica. The associated fault lines extend into the ocean as well as to the islands off the coast of the Antarctic Peninsula shown in the map below the chart for the West Antarctic Rift.
  6. Of particular note are the South Georgia Island where three volcanoes erupted simultaneously in 2016, and and the South Shetland Island where the Deception Island Collapse Caldera is located. A specific feature of volcanic activity along the West Antarctic Rift are sub glacial eruptions that create dramatic glacial melt and ice shelf melt events often interpreted in the media in terms of anthropogenic global warming and sea level rise as described in a related post [LINK] .
  7. In this response to explanation of ice melt events in the Antarctic Peninsula in terms of the Southern Annular Mode we argue that in geological active area of this nature with localized and random ice melt events, atmospheric explanations of ice melt can only be considered when geological explanations fail. In other words, for a SAM explanation of ice melt on the Antarctic Peninsula, it must first be shown that no geological explanation exists and that therefore an external cause of the ice melt event must be found. A further complication is that the highly localized and random nature of these events would be difficult to explain in terms of atmospheric phenomena.

kamis03

SOUTHERN ANNULAR MODE BIBLIOGRAPHY
The Southern Annular Mode (or SAM) is a ring of climate variability that encircles the South Pole and extends out to 45 South Latitude. The SAM creates alternating windiness and storm activity in the middle latitudes and higher latitudes, over the southern oceans and Antarctic sea ice zone (50–70˚S). In its positive phase, the SAM is associated with relatively light winds and more settled weather over the mid latitudes, together with enhanced westerly winds over the southern oceans. In the negative phase, the westerlies increase in the mid latitudes, with more unsettled weather, while windiness and storm activity ease over the southern oceans” (David Thompson)
  1. Baldwin, Mark “Annular modes in global daily surface pressure” Geophysical Research Letters 28.21 (2001): 4115-4118Annular modes are patterns characterized by synchronous fluctuations in surface pressure of one sign over the polar caps and the opposite sign at lower latitudes. The Southern Annular Mode (SAM) and Northern Annular Mode (NAM, also called the Arctic Oscillation) patterns are the leading empirical orthogonal functions (EOFs) of slowly‐varying, hemispheric, cold‐season, sea‐level pressure anomalies (deviations from climatology). Daily indices of the SAM and NAM are a measure of the similarity between surface pressure anomaly patterns and the annular modes. Here it is shown that the first two EOF time series of daily, global, year‐round, zonally‐averaged surface pressure are nearly identical to the SAM and NAM indices. Together they account for more than 57% of the daily variance of zonally‐averaged surface pressure. The SAM and NAM patterns extend through the tropics, well into the opposite hemispheres. Fluctuations of the SAM and NAM indices are accompanied by inter-hemispheric transfer of mass.
  2. Kwok, Ron, and Josefino C. Comiso. “Spatial patterns of variability in Antarctic surface temperature: Connections to the Southern Hemisphere Annular Mode and the Southern Oscillation.” Geophysical Research Letters 29.14 (2002): 50-1.  The 17‐year (1982–1998) trend in surface temperature shows a general cooling over the Antarctic continent, warming of the sea ice zone, with moderate changes over the oceans. Warming of the peripheral seas is associated with negative trends in the regional sea ice extent. Effects of the Southern Hemisphere Annular Mode (SAM) and the extrapolar Southern Oscillation (SO) on surface temperature are quantified through regression analysis. Positive polarities of the SAM are associated with cold anomalies over most of Antarctica, with the most notable exception of the Antarctic Peninsula. Positive temperature anomalies and ice edge retreat in the Pacific sector are associated with El‐Niño episodes. Over the past two decades, the drift towards high polarity in the SAM and negative polarity in the SO indices couple to produce a spatial pattern with warmer temperatures in the Antarctic Peninsula and peripheral seas, and cooler temperatures over much of East Antarctica. [FULL-TEXT]
  3. Marshall, Gareth J. “Trends in the Southern Annular Mode from observations and reanalyses.” Journal of Climate 16.24 (2003): 4134-4143. Several papers have described a significant trend toward the positive phase of the Southern Hemisphere annular mode (SAM) in recent decades. The SAM is the dominant mode of atmospheric variability in the Southern Hemisphere (SH) so such a change implies a major shift in the broadscale climate of this hemisphere. However, the majority of these studies have used NCEP–NCAR reanalysis (NNR) data  (2003), which are known to have spurious negative trends in SH high-latitude pressure. Thus, given that the SAM describes the relative atmospheric anomalies at mid- and high southern latitudes, these errors in the NNR data have the potential to invalidate the published findings on changes in the SAM. Therefore, it is important that a “true” benchmark of trends in the SAM is available against which future climate scenarios as revealed through climate models can be examined. In this paper this issue is addressed by employing an empirical definition of the SAM so that station data can be utilized to evaluate true temporal changes: six stations are used to calculate a proxy zonal mean sea level pressure (MSLP) at both 40° and 65°S during 1958–2000. The observed increase in the difference in zonal MSLP between 40°S (increasing) and 65°S (decreasing) is shown to be statistically significant, with the trend being most pronounced since the mid-1970s. However, it is demonstrated that calculated trends in the MSLP difference between 40° and 65°S and the SAM itself are exaggerated by a factor of 3 and 2, respectively, in the NNR. The SH high-latitude errors in the early part of this reanalysis are greatest in winter as are subsequent improvements. As a result, the NNR shows the greatest seasonal trend in the SAM to be in the austral winter, in marked contrast to observational data, which reveal the largest real increase to be in summer. Equivalent data from two ECMWF reanalyses, including part of the new ERA-40 reanalysis, are also examined. It is demonstrated that ERA-40 provides an improved representation of SH high-latitude atmospheric circulation variability that can be used with high confidence at least as far back as 1973—and is therefore ideal for examining the recent trend in the SAM—and with more confidence than the NNR right back to 1958.
  4. Gillett, N. Pꎬ, T. Dꎬ Kell, and P. D. Jones. “Regional climate impacts of the Southern Annular Mode.” Geophysical Research Letters 33.23 (2006).  Previous work on the influence of the Southern Annular Mode (SAM) on surface climate has focused mainly on individual countries. In this study we use station observations of temperature and rainfall to identify the influence of the SAM on land regions over the whole of the Southern Hemisphere. We demonstrate that the positive phase of the SAM is associated with a significant cooling over Antarctica and much of Australia, and a significant warming over the Antarctic Peninsula, Argentina, Tasmania and the south of New Zealand. The positive phase of the SAM is also associated with anomalously dry conditions over southern South America, New Zealand and Tasmania, due to the southward shift of the stormtrack; and to anomalously wet conditions over much of Australia and South Africa. These influences on populated regions of the Southern Hemisphere may have implications for weather and seasonal forecasting, and for future climate change. [[FULL TEXT] .
  5. Thompson, David. “The southern annular mode and New Zealand climate.” Water & Atmosphere 14.2 (2006): 24-25.  The Southern Annular Mode (or SAM) is a ring of climate variability that encircles the South Pole and extends out to the latitudes of New Zealand. (Its counterpart, the NAM, centres on the North Pole and affects climate in the northern hemisphere.) The SAM involves alternating changes in windiness and storm activity between the middle latitudes, where New Zealand lies (40–50˚S), and higher latitudes, over the southern oceans and Antarctic sea ice zone (50–70˚S). In its positive phase, the SAM is associated with relatively light winds and more settled weather over New Zealand latitudes, together with enhanced westerly winds over the southern oceans. In the opposite (negative) phase, the westerlies increase over New Zealand, with more unsettled weather,while windiness and storm activity ease over the southern oceans. [FULL TEXT PDF]
  6. Arblaster, Julie M., and Gerald A. Meehl. “Contributions of external forcings to southern annular mode trends.” Journal of climate 19.12 (2006): 2896-2905.  An observed trend in the Southern Hemisphere annular mode (SAM) during recent decades has involved an intensification of the polar vortex. The source of this trend is a matter of scientific debate with stratospheric ozone losses, greenhouse gas increases, and natural variability all being possible contenders. Because it is difficult to separate the contribution of various external forcings to the observed trend, a state-of-the-art global coupled model is utilized here. Ensembles of twentieth-century simulations forced with the observed time series of greenhouse gases, tropospheric and stratospheric ozone, sulfate aerosols, volcanic aerosols, solar variability, and various combinations of these are used to examine the annular mode trends in comparison to observations, in an attempt to isolate the response of the climate system to each individual forcing. It is found that ozone changes are the biggest contributor to the observed summertime intensification of the southern polar vortex in the second half of the twentieth century, with increases of greenhouse gases also being a necessary factor in the reproduction of the observed trends at the surface. Although stratospheric ozone losses are expected to stabilize and eventually recover to pre-industrial levels over the course of the twenty-first century, these results show that increasing greenhouse gases will continue to intensify the polar vortex throughout the twenty-first century, but that radiative forcing will cause widespread temperature increases over the entire Southern Hemisphere[FULL TEXT] .
  7. Marshall, Gareth J. “Half‐century seasonal relationships between the Southern Annular Mode and Antarctic temperatures.” International Journal of Climatology: A Journal of the Royal Meteorological Society 27.3 (2007): 373-383. In this short communication, we examine the relationship between the Southern Hemisphere Annular Mode (SAM) and Antarctic near‐surface temperatures using data from Antarctic stations for 1957–2004. This near half‐century period is significantly longer than those analysed in previous studies. Furthermore, the four seasons are considered independently while the longer datasets allow the temporal stability of the relationship to be investigated. A general pattern of positive (negative) correlations between the strength of the SAM and temperatures in the northern Antarctic Peninsula (East Antarctica) is shown to be valid for the last half‐century but detailed differences are established between the seasons. These include a seasonal change in the sign of the relationship at one station, while at others there are single seasons when temperatures there are, or, in some cases, are not, significantly related to the SAM. Generally, SAM–temperature correlations are stronger across Antarctica in austral autumn and summer. Estimates of the contribution that trends in the SAM have made to Antarctic near‐surface temperature change between 1957 and 2004 are greatest in autumn: in this season they exceed 1°C at half the 14 stations examined with a maximum change of − 1.4 °C. There does not appear to have been any significant long‐term change in the strength of SAM‐temperature relationships over the period examined, even with the onset of ozone depletion. However, on an annual basis, the long‐term relationship between the SAM and near‐surface temperatures can be disrupted and even reversed at some stations although coastal East Antarctica appears stable in this respect. These findings give support to the exploitation of appropriate ice core data to determine long‐term changes in the SAM based upon transfer functions derived from recent data. Copyright © 2006 Royal Meteorological Society.
  8. Lenton, Andrew, and Richard J. Matear. “Role of the southern annular mode (SAM) in Southern Ocean CO2 uptake.” Global Biogeochemical Cycles 21.2 (2007).  A biogeochemical ocean general circulation model, driven with NCEP‐R1 and observed atmospheric CO2 history, is used to investigate and quantify the role that the Southern Annular Mode (SAM), identified as the leading mode of climate variability, has in driving interannual variability in Southern Ocean air‐sea CO2 fluxes between 1980 and 2000. Our simulations show the Southern Ocean to be a region of decreased CO2 uptake during the positive SAM phase. The SAM induces changes in Southern Ocean CO2 uptake with a 2‐month time lag explaining 42% of the variance in the total interannual variability in air‐sea CO2 fluxes. Our analysis shows that the response of the Southern Ocean to the SAM is primarily governed by changes in ΔpCO2 (67%), and that this response is driven by changes in ocean physics that control the supply of nutrients to the upper ocean, primarily Dissolved Inorganic Carbon (DIC). The SAM is predicted to become stronger and more positive in response to climate change and our results suggest this will decrease the Southern Ocean CO2 uptake by 0.1PgC/yr per unit change in the SAM.
  9. Meneghini, Belinda, Ian Simmonds, and Ian N. Smith. “Association between Australian rainfall and the southern annular mode.” International Journal of Climatology: A Journal of the Royal Meteorological Society 27.1 (2007): 109-121. In this study, we explore the relationships between seasonal Australian rainfall and the Southern Annular Mode (SAM). We produce two seasonal indices of the SAM: the Antarctic Oscillation Index (AOI), and an Australian regional version (AOIR) using ERA‐40 mean sea‐level pressure (MSLP) reanalysis data. The seasonal rainfall data are based on gridded monthly rainfall provided by the Australian Bureau of Meteorology. For the period 1958–2002 a significant inverse relationship is found between the SAM and rainfall in southern Australia, while a significant in‐phase relationship is found between the SAM and rainfall in northern Australia. Furthermore, widespread significant inverse relationships in southern Australia are only observed in winter, and only with the AOIR. The AOIR accounts for more of the winter rainfall variability in southwest Western Australia, southern South Australia, western and southern Victoria, and western Tasmania than the Southern Oscillation Index. Overall, our results suggest that changes in the SAM may be partly responsible for the current decline in winter rainfall in southern South Australia, Victoria, and Tasmania, but not the long‐term decline in southwest Western Australian winter rainfall. Copyright © 2006 Royal Meteorological Society.
  10. Lovenduski, Nicole S., et al. “Enhanced CO2 outgassing in the Southern Ocean from a positive phase of the Southern Annular Mode.” Global Biogeochemical Cycles 21.2 (2007). We investigate the interannual variability in the flux of CO2 between the atmosphere and the Southern Ocean on the basis of hindcast simulations with a coupled physical‐biogeochemical‐ecological model with particular emphasis on the role of the Southern Annular Mode (SAM). The simulations are run under either pre‐industrial or historical CO2 concentrations, permitting us to separately investigate natural, anthropogenic, and contemporary CO2 flux variability. We find large interannual variability (±0.19 PgC yr−1) in the contemporary air‐sea CO2 flux from the Southern Ocean (<35°S). Forty‐three percent of the contemporary air‐sea CO2 flux variance is coherent with SAM, mostly driven by variations in the flux of natural CO2, for which SAM explains 48%. Positive phases of the SAM are associated with anomalous outgassing of natural CO2 at a rate of 0.1 PgC yr−1 per standard deviation of the SAM. In contrast, we find an anomalous uptake of anthropogenic CO2 at a rate of 0.01 PgC yr−1 during positive phases of the SAM. This uptake of anthropogenic CO2 only slightly mitigates the outgassing of natural CO2, so that a positive SAM is associated with anomalous outgassing in contemporaneous times. The primary cause of the natural CO2 outgassing is anomalously high oceanic partial pressures of CO2 caused by elevated dissolved inorganic carbon (DIC) concentrations. These anomalies in DIC are primarily a result of the circulation changes associated with the southward shift and strengthening of the zonal winds during positive phases of the SAM. The secular, positive trend in the SAM has led to a reduction in the rate of increase of the uptake of CO2 by the Southern Ocean over the past 50 years.
  11. Stammerjohn, Sharon E., et al. “Trends in Antarctic annual sea ice retreat and advance and their relation to El Niño–Southern Oscillation and Southern Annular Mode variability.” Journal of Geophysical Research: Oceans 113.C3 (2008).  Previous studies have shown strong contrasting trends in annual sea ice duration and in monthly sea ice concentration in two regions of the Southern Ocean: decreases in the western Antarctic Peninsula/southern Bellingshausen Sea (wAP/sBS) region and increases in the western Ross Sea (wRS) region. To better understand the evolution of these regional sea ice trends, we utilize the full temporal (quasi‐daily) resolution of satellite‐derived sea ice data to track spatially the annual ice edge advance and retreat from 1979 to 2004. These newly analyzed data reveal that sea ice is retreating 31 ± 10 days earlier and advancing 54 ± 9 days later in the wAP/sBS region (i.e., total change over 1979–2004), whereas in the wRS region, sea ice is retreating 29 ± 6 days later and advancing 31 ± 6 days earlier. Changes in the wAP/sBS and wRS regions, particularly as observed during sea ice advance, occurred in association with decadal changes in the mean state of the Southern Annular Mode (SAM; negative in the 1980s and positive in the 1990s) and the high‐latitude response to El Niño–Southern Oscillation (ENSO). In general, the high‐latitude ice‐atmosphere response to ENSO was strongest when ‐SAM was coincident with El Niño and when +SAM was coincident with La Niña, particularly in the wAP/sBS region. In total, there were 7 of 11 ‐SAMs between 1980 and 1990 and the 7 of 10 +SAMs between 1991 and 2000 that were associated with consistent decadal sea ice changes in the wAP/sBS and wRS regions, respectively. Elsewhere, ENSO/SAM‐related sea ice changes were not as consistent over time (e.g., western Weddell, Amundsen, and eastern Ross Sea region), or variability in general was high (e.g., central/eastern Weddell and along East Antarctica).
  12. Reboita, Michelle Simões, Tércio Ambrizzi, and Rosmeri Porfírio da Rocha. “Relationship between the southern annular mode and southern hemisphere atmospheric systems.” Revista Brasileira de Meteorologia 24.1 (2009): 48-55.  Seasonal relationship between the Southern Annular Mode (SAM) and the spatial distribution of the cyclone systems over Southern Hemisphere is investigated for the period 1980 to 1999. In addition, seasonal frontogenesis and rainfall distribution over South America and South Atlantic Ocean during different SAM phases were also analyzed. It is observed that during negative SAM phases the cyclone trajectories move northward when compared to the positive one, and in the South America and South Atlantic sector there is intense frontogenetic activity and positive anomaly precipitation over the Southeast of the South America. In general, SAM positive phase shows opposite signals.
  13. Visbeck, Martin. “A station-based southern annular mode index from 1884 to 2005.” Journal of Climate 22.4 (2009): 940-950Atmospheric pressure observations from the Southern Hemisphere are used to estimate monthly and annually averaged indexes of the southern annular mode (SAM) back to 1884. This analysis groups all relevant observations in the following four regions: one for Antarctica and three in the subtropical zone. Continuous surface pressure observations are available at a number of locations in the subtropical regions since the end of the nineteenth century. However, year-round observations in the subpolar region near the Antarctic continent began only during the 1940–60 period. The shorter Antarctic records seriously compromise the length of a traditionally estimated SAM index. To improve the situation “proxy” estimates of Antarctic sea level pressure anomalies are provided based on the concept of atmospheric mass conservation poleward of 20°S. This allows deriving a longer SAM index back to 1884. Several aspects of the new record, its statistical properties, seasonal trends, and the regional pressure anomaly correlations, are presented. [FULL TEXT]
  14. Abram, Nerilie J., et al. “Evolution of the Southern Annular Mode during the past millennium.” Nature Climate Change 4.7 (2014): 564.  The Southern Annular Mode (SAM) is the primary pattern of climate variability in the Southern Hemisphere1,2, influencing latitudinal rainfall distribution and temperatures from the subtropics to Antarctica. The positive summer trend in the SAM over recent decades is widely attributed to stratospheric ozone depletion2; however, the brevity of observational records from Antarctica1—one of the core zones that defines SAM variability—limits our understanding of long-term SAM behaviour. Here we reconstruct annual mean changes in the SAM since AD 1000 using, for the first time, proxy records that encompass the full mid-latitude to polar domain across the Drake Passage sector. We find that the SAM has undergone a progressive shift towards its positive phase since the fifteenth century, causing cooling of the main Antarctic continent at the same time that the Antarctic Peninsula has warmed. The positive trend in the SAM since AD 1940 is reproduced by multimodel climate simulations forced with rising greenhouse gas levels and later ozone depletion, and the long-term average SAM index is now at its highest level for at least the past 1,000 years. Reconstructed SAM trends before the twentieth century are more prominent than those in radiative-forcing climate experiments and may be associated with a teleconnected response to tropical Pacific climate. Our findings imply that predictions of further greenhouse-driven increases in the SAM over the coming century3 also need to account for the possibility of opposing effects from tropical Pacific climate changes.  
  15. Amy E Hessl, Kathryn Jane Allen, Tessa R. VanceReconstructions of the southern annular mode (SAM) during the last millennium: November 2017 Progress in Physical Geography 41(3):030913331774316.  The leading mode of atmospheric variability in the Southern Hemisphere is the Southern Annular Mode (SAM), which affects the atmosphere and ocean from the mid-latitudes to the Antarctic. However, the short instrumental record of the SAM does not adequately represent its multi-decadal to centennial-scale variability. Long palaeoclimatic reconstructions of the SAM would improve our understanding of its low frequency behavior and its effects on regional temperature, rainfall, sea ice, and ecosystem processes. In this progress report, we review three published palaeoclimatic reconstructions available for understanding multi-decadal to centennial-scale variability of the SAM. Reconstructions reviewed here show similar patterns of decadal SAM variability during the last two centuries, but earlier centuries are less coherent. Reconstructions clearly maintain similar trends towards more positive SAM states since the onset of significant anthropogenic climate forcing from rising greenhouse gas (GHG) concentrations and ozone depletion and these excursions appear unprecedented over at least the last 500 years. We describe how new multi-proxy reconstructions of the SAM could further improve our understanding of its long-term variability and effects across all geographic sectors of the Southern Hemisphere. Here, we recommend careful selection and development of proxies in SAM-sensitive regions and seasons. In particular, proxies related to cool-season conditions and from the poorly-sampled Indian Ocean sector would allow for a true circumpolar and year-round reconstruction of past SAM variability. [FULL TEXT]
  16. Dätwyler, Christoph, et al. “Teleconnection stationarity, variability and trends of the Southern Annular Mode (SAM) during the last millennium.” Climate dynamics 51.5-6 (2018): 2321-2339.  The Southern Annular Mode (SAM) is the leading mode of atmospheric interannual variability in the Southern Hemisphere (SH) extra-tropics. Here, we assess the stationarity of SAM spatial correlations with instrumental and paleoclimate proxy data for the past millennium. The instrumental period shows that temporal non-stationarities in SAM teleconnections are not consistent across the SH land areas. This suggests that the influence of the SAM index is modulated by regional effects. However, within key-regions with good proxy data coverage (South America, Tasmania, New Zealand), teleconnections are mostly stationary over the instrumental period. Using different stationarity criteria for proxy record selection, we provide new austral summer and annual mean SAM index reconstructions over the last millennium. Our summer SAM reconstructions are very robust to changes in proxy record selection and the selection of the calibration period, particularly on the multi-decadal timescale. In contrast, the weaker performance and lower agreement in the annual mean SAM reconstructions point towards changing teleconnection patterns that may be particularly important outside the summer months. Our results clearly portend that the temporal stationarity of the proxy-climate relationships should be taken into account in the design of comprehensive regional and hemispherical climate reconstructions. The summer SAM reconstructions show no significant relationship to solar, greenhouse gas and volcanic forcing, with the exception of an extremely strong negative anomaly following the AD 1257 Samalas eruption. Furthermore, reconstructed pre-industrial summer SAM trends are very similar to trends obtained by model control simulations. We find that recent trends in the summer SAM lie outside the 5–95% range of pre-industrial natural variability. Our proxy data and reconstruction results are available at the NOAA paleoclimatology database (https://www.ncdc.noaa.gov/paleo/study/23130). The input proxy databases are available at https://www.ncdc.noaa.gov/paleo-search/study/16196 (data labelled N14 in SM Table S4 and S5),  https://doi.org/10.6084/m9.figshare.c.3285353 (P17), https://www.ncdc.noaa.gov/paleo-search/study/13673 (V12), and https://www.ncdc.noaa.gov/paleo/study/22589 (S17).

    382_2017_4015_MOESM1_ESM.pdf (3.7 mb)

    Supplementary material 1 (PDF 3806 KB)

2 Responses to "Southern Annular Mode Causes Antarctic Peninsula Ice to Melt"

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