30 September 2018, Volume 29 Issue 3

    

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  Contents of Vol. 29 No. 3

  Editorial Office

  Advances in Polar Science. 2018, 29(3): 0-0.

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  Special Issue: Polar Climate Change: Driving Processes, Extreme Events, and Global Linkages
  
  Foreword
  
  Trend
  
  Workshop on Polar Climate Changes and Extreme Events .. 151
  Zhaomin WANG, Xiangdong ZHANG, John TURNER & Annette RINKE
  
  Articles
  
  Atmospheric feedbacks on Arctic summer sea-ice anomalies in ensemble simulations of a coupled regional climate model..156
  Annette RINKE, Dörthe HANDORF, Wolfgang DORN, Klaus DETHLOFF, John C. MOORE & Xiangdong ZHANG
  
  A glacial control on the eruption rate of Mt Erebus, Antarctica ..165
  Maximillian VAN WYK de VRIES
  
  Determination of Arctic melt pond fraction and sea ice roughness from Unmanned Aerial Vehicle (UAV) imagery..181
  WANG Mingfeng, SU Jie, LI Tao, WANG Xiaoyu, JI Qing, CAO Yong, LIN Long & LIU Yilin
  
  Extreme events as ecosystems drivers: Ecological consequences of anomalous Southern Hemisphere weather patterns during the 2001/2002 austral spring-summer..190
  Dana M. BERGSTROM, Eric J. WOEHLER, Andrew R. KLEKOCIUK, Michael J. POOK & Robert A. MASSOM
  
  Trends of summertime extreme temperatures in the Arctic..205
  SUI Cuijuan & YU Lejiang
  
  Simulated impact of Southern Hemisphere westerlies on Antarctic Shelf Bottom Water temperature..215
  LIN Xia & WANG Zhaomin
  
  The study of ice shelf-ocean interaction—techniques and recent results..222
  Keith W. NICHOLLS
  
Foreword
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  Foreword

  Zhaomin Wang Kent Moore, Annette Rinke, John Turner

  Advances in Polar Science. 2018, 29(3): 1-1.

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  The climates of the polar regions are important components of the global Earth system and have experienced dramatic changes in recent decades. These changes and their possible influences on and feedback with processes across the rest of the globe have raised great research challenges regarding the processes involved. In addition, the polar regions have been the least observed and understood regions. To improve our understanding and prediction of polar climate changes, and associated extreme events and global impacts, a number of international initiatives for polar climate research, such as Year of Polar Prediction (YOPP) and the Multidisciplinary drifting Observatory for the Study of Arctic Climate (MOSAiC), have been planned and implemented.
  
  To promote collaborations between Chinese polar scientists and scientists from other nations, a workshop on “Polar Climate Change: Driving Processes, Extreme Events, and Global Linkages” was held over 23–24 October 2017, at Hohai University, Nanjing, China. During this workshop the participants presented new research results, identified knowledge gaps and research priorities, and discussed future international collaborations related to the following three themes: (i) polar climate changes and their global linkages; (ii) polar climate and weather extremes and disastrous ice conditions; (iii) polar ocean circulation and ocean-ice-atmosphere interactions.
  
  The workshop led to the publication of this special issue, which is seen as a lasting outcome of the meeting. This special issue brings together a selection of papers based on the presentations given during the workshop, along with several other papers that are closely related to the workshop themes. In addition to the workshop report that summarizes the recent research results presented during the workshop, another seven articles cover polar climate changes, polar extreme events, and ocean-ice-atmosphere interactions. Three articles examine processes related to polar climate changes: Atmospheric feedbacks on Arctic summer sea-ice anomalies in ensemble simulations of a coupled regional climate model; A glacial control on the eruption rate of Mt Erebus, Antarctica; Determination of Arctic melt pond fraction and sea ice roughness from Unmanned Aerial Vehicle (UAV) imagery. Two articles are related to polar extreme events: Extreme events as ecosystems drivers: Ecological consequences of anomalous Southern Hemisphere weather patterns during the 2001/2002 austral spring-summer; Trends of summer extreme temperatures in the Arctic. Two articles address issues related to ice shelf-ocean interactions: Simulated impact of Southern Hemisphere westerlies on Antarctic Continental Shelf Bottom Water temperature; The study of ice shelf-ocean interaction—techniques and recent results.
  
  We anticipate that the outcomes of this workshop and the publication of this special issue will provide a foundation for further research on polar climate changes and extreme events. Finally, we would like to thank all the workshop participants, all the authors and reviewers of the papers for their contributions to this workshop and the production of this special issue.
Articles
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  Simulated impact of Southern Hemisphere westerlies on Antarctic Shelf Bottom Water temperature

  LIN Xia, WANG Zhaomin

  Advances in Polar Science. 2018, 29(3): 3-19. https://doi.org/10.13679/j.advps.2018.3.00215

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  The Southern Hemisphere (SH) westerly winds have intensified and shifted poleward since the 1970s and this trend is projected to sustain under future anthropogenic forcing. The influences of intensified SH westerlies on the Antarctic coastal waters are still not clear. The variability of Antarctic Continental Shelf Bottom Water (ASBW) temperature is crucial for ice shelf basal melting and hence ice shelf mass balance in Antarctica. In order to understand the impacts of SH westerlies on the variability of ASBW temperature, atmospheric forcing in 1992 with weak westerlies and in 1998 with strong westerlies are used to drive a high-resolution ocean-sea ice general circulation model, MITgcm-ECCO2. Our simulated results show that under the atmospheric forcing in 1998, the ASBW becomes warmer in most regions around Antarctica except the coastal region between 60°–150°W, than for the case under atmospheric forcing in 1992. The warming of ASBW around Antarctica is due to the intense shoaling and warming of CDW induced by enhanced Ekman pumping as well as strengthened subpolar gyres. The strengthened subpolar gyres favor the transportation of warm water to the coast of Antarctica. The cooling of ASBW along the coast of the western Antarctic Peninsula is caused by stronger coastal currents, which bring colder water downstream from the northwest flank of the Weddell Sea.
Trends
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  Workshop on Polar Climate Changes and Extreme Events

  Zhaomin WANG, Xiangdong ZHANG, John TURNER, Annette RINKE

  Advances in Polar Science. 2018, 29(3): 151-155. https://doi.org/10.13679/j.advps.2018.3.00151

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Articles
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  Atmospheric feedbacks on Arctic summer sea-ice anomalies in ensemble simulations of a coupled regional climate model

  Annette RINKE, Dörthe HANDORF, Wolfgang DORN, Klaus DETHLOFF, John C. MOORE, Xiangdong ZHANG

  Advances in Polar Science. 2018, 29(3): 156-164. https://doi.org/10.13679/j.advps.2018.3.00156

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  Ensemble simulations with the Arctic coupled regional climate model HIRHAM-NAOSIM have been analyzed to investigate atmospheric feedbacks to September sea-ice anomalies in the Arctic in autumn and the following winter. Different “low minus high ice” composites have been calculated using selected model runs and different periods. This approach allows us to investigate the robustness of the simulated regional atmospheric feedbacks to detected sea-ice anomalies. Since the position and strength of the September sea-ice anomaly varies between the different “low minus high ice” composites, the related simulated atmospheric patterns in autumn differ depending on the specific surface heat flux forcing through the ocean-atmosphere interface. However, irrespective of those autumn differences, the regional atmospheric feedback in the following winter is rather insensitive to the applied compositing. Neither the selection of simulations nor the considered period impacts the results. The simulated consistent large-scale atmospheric circulation pattern shows a wave-like pattern with positive pressure anomaly over the region of the Barents/Kara Seas and Scandinavia/western Russia (“Scandinavian-Ural blocking”) and negative pressure anomaly over the East Siberian/Laptev Seas.
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  A glacial control on the eruption rate of Mt Erebus, Antarctica

  Maximillian VAN WYK de VRIES vanwy@umn.edu

  Advances in Polar Science. 2018, 29(3): 165-180. https://doi.org/10.13679/j.advps.2018.3.00165

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  Mt Erebus is the most active Antarctic volcano, on the flanks of the world’s largest ice sheet. Despite this, the interactions between its eruptions and the ice cover have not been studied in detail. Focusing on the most recent deglaciation, we build a glacial retreat model and compare this to recent lava geochemistry measurements to investigate the processes involved. This analysis exposes a previously unknown link between Antarctic glaciation and eruptions, of vital importance to the understanding of volcanism in this context. We find that deglaciation led to rapid emptying of the shallow magma plumbing system and a resulting peak in eruption rates synchronous with ice retreat. We also find that the present day lavas do not represent steady state conditions, but originate from a source with up to 30% more partial melting than older >4 ka eruptions. This finding that deglaciation affects volcanism both on short and longer timescales may prompt a re-evaluation of eruptions in glaciated and previously glaciated terrains both in Antarctica and beyond.
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  Determination of Arctic melt pond fraction and sea ice roughness from Unmanned Aerial Vehicle (UAV) imagery

  WANG Mingfeng, SU Jie, LI Tao, WANG Xiaoyu, JI Qing, CAO Yong, LIN Long, LIU Yilin

  Advances in Polar Science. 2018, 29(3): 181-189. https://doi.org/10.13679/j.advps.2018.3.00181

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  Melt ponds on Arctic sea ice are of great significance in the study of the heat balance in the ocean mixed layer, mass and salt balances of Arctic sea ice, and other aspects of the earth-atmosphere system. During the 7th Chinese National Arctic Research Expedition, aerial photographs were taken from an Unmanned Aerial Vehicle over an ice floe in the Canada Basin. Using threshold discrimination and three-dimensional modeling, we estimated a melt pond fraction of 1.63% and a regionally averaged surface roughness of 0.12 for the study area. In view of the particularly foggy environment of the Arctic, aerial images were defogged using an improved dark channel prior based image defog algorithm, especially adapted for the special conditions of sea ice images. An aerial photo mosaic was generated, melt ponds were identified from the mosaic image and melt pond fractions were calculated. Three-dimensional modeling techniques were used to generate a digital elevation model allowing relative elevation and roughness of the sea ice surface to be estimated. Analysis of the relationship between the distributions of melt ponds and sea ice surface roughness shows that melt ponds are smaller on sea ice with higher surface roughness, while broader or deeper melt ponds usually occur in areas where sea ice surface roughness is lower.
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  Extreme events as ecosystems drivers: Ecological consequences of anomalous Southern Hemisphere weather patterns during the 2001/2002 austral spring-summer

  Dana M. BERGSTROM, Eric J. WOEHLER, Andrew R. KLEKOCIUK, Michael J. POOK, Robert A. MASSOM

  Advances in Polar Science. 2018, 29(3): 190-204. https://doi.org/10.13679/j.advps.2018.3.00190

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  The frequency and severity of extreme events associated with global change are both forecast to increase with a concomitant increase expected in perturbations and disruptions of fundamental processes at ecosystem, community and population scales, with potentially catastrophic consequences. Extreme events should thus be viewed as ecosystem drivers, rather than as short term deviations from a perceived ‘norm’. To illustrate this, we examined the impacts associated with the extraordinary weather pattern of the austral spring/summer of 2001/2002, and find that patterns of ocean-atmosphere interactions appear linked to a suite of extreme events in Antarctica and more widely across the Southern Hemisphere. In the Antarctic, the extreme events appear related to particular ecological impacts, including the substantial reduction in breeding success of Adélie penguins at sites in the Antarctic Peninsula as well as for Adélie penguin and snow petrel colonies in East Antarctica, and the creation of new benthic habitats associated with the disintegration of the Larsen B Ice Shelf. Other major impacts occurred in marine and terrestrial ecosystems at temperate and tropical latitudes. The suite of impacts demonstrates that ecological consequences of extreme events are manifested at fundamental levels in ecosystem processes and produce long-term, persistent effects relative to the short-term durations of the events. Changes in the rates of primary productivity, species mortality, community structure and inter-specific interactions, and changes in trophodynamics were observed as a consequence of the conditions during the 2001/2002 summer. Lasting potential consequences include reaching or exceeding tipping points, trophic cascades and regime shifts.
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  Trends of summertime extreme temperatures in the Arctic

  SUI Cuijuan, YU Lejiang

  Advances in Polar Science. 2018, 29(3): 205-214. https://doi.org/10.13679/j.advps.2018.3.00205

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  Extreme temperature events can influence the natural environment and societal activities more so than mean temperature events. This study used daily data from 238 stations north of 60°N, obtained from the Global Summary of the Day dataset for the period 1979–2015, to investigate the trends of summertime extreme temperature. The results revealed most stations north of 60°N with trends of decrease in the number of cold days (nights) and increase in the number of warm days (nights). The regional average results showed trends of consistent decline (rise) of cold days and nights (warm days and nights) in Eurasia and Greenland. Similarly, the trends of the seasonal maximum and minimum values were most significant in these regions. In summer, of three indices considered (i.e., Arctic Oscillation, Arctic dipole, and El Niño–Southern Oscillation), the largest contributor to the trends of extreme temperature events was the Arctic dipole. Prevailing southerly winds in summer brought warm moist air across northern Eurasia and Greenland, conducive to increased numbers of warm days (nights) and decreased numbers of cold day (nights). Moreover, we defined extreme events using different thresholds and found the spatial distributions of the trends were similar.
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  The study of ice shelf-ocean interaction – techniques and recent results

  Keith W. NICHOLLS

  Advances in Polar Science. 2018, 29(3): 222-230. https://doi.org/10.13679/j.advps.2018.3.00222

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  Although the importance to global oceanography of ice shelf-ocean interactions has been recognized for many years, only more recently has its role in the control of ice flow from the interior, grounded ice sheet into the ocean been more clearly understood. The consequences for global sea level of increasing ice loss from the Antarctic and Greenland ice sheets has prompted rapidly growing research efforts in this area. Here we describe the different techniques commonly employed in the field study of ice shelf-ocean interactions. We focus on techniques used by the British Antarctic Survey, primarily on Filchner-Ronne Ice Shelf, and describe some recent results from instruments deployed both beneath the ice shelf and on its upper surface, which demonstrate variability at a broad range of time scales.