DOCSLIB.ORG

Satellite Observed Behavior of the Terra Nova Bay Polynya

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Satellite Observed Behavior of the Terra Nova Bay Polynya JOURNAL OF GEOPHYSICAL RESEARCH, VOL. 88, NO. C14, PAGES 9717-9722, NOVEMBER 20, 1983 Satellite Observed Behavior of the Terra Nova Bay Polynya DENNIS D. KURTZ AND DAVID H. BROMWICH Institute of Polar Studies,Ohio State University Infrared satelliteimages indicate that a polynya,surrounded by a zone of loosepack ice, persistedin Terra Nova Bay, Antarcticathrough the winter of 1979; the featuremay recur each year. The affected region(polynya and loosepack) occupied roughly 25000 km 2 of the westernRoss Sea. Throughout the winterthe area of openwater fluctuated quasi-periodically with a periodof 15-20 days.Average polynya areawas 1000 km2; maximum area was approximately 5000 km 2. Fluctuationswere associated with the magnitudeof the zonal geostrophicwind, with a closingpolynya being related to strong,persistent easterlies.An open,or opening,polynya was linkedwith persistentwesterly or weak easterlywinds and the probabledescent of adiabaticallywarming, drift-bearing air from the plateau.This air entersTerra Nova Bay throughthe ReevesGlacier valley,probably as katabaticsurface winds. Polynya formation wasprobably due to the actionof thesewinds on the coastalpack ice,while areal fluctuations reflected the interplaybetween the katabaticwinds and synopticscale motions advecting ice toward and away from the bay. INTRODUCTION must frequently cross Victoria Land farther south. Cyclones Many areas of wintertime open water are now known to be sometimes behave in this fashion when cyclogenesistakes presentwithin the Antarctic northern ice limit. Theseplay an place in the Victoria Land Trough [U.S. Navy Weather Ser- important role in the surfaceenergy balance of the pack ice vice, 1970]; however, this does not explain why winter open belt [Weller, 1980] and exist on a variety of temporal and water persistsonly in Terra Nova Bay. The presentcompari- spatialscales. The WeddellPolynya is a roughly3 x l0 s km2 son of this polynya's behavior with synopticscale conditions, area of open water which irregularlyforms during winter and through one winter, constitutes a needed test of Knapp's spring[Carsey, 1980; Martinsonet al., 1981]; this featuremay model for the geographicsetting of the westernRoss Sea. be a result of extensiveopen-ocean convection [Martinson et Wintertime open water has been known to exist in Terra al., 1981]. Much smaller polynyascan persistin coastalareas Nova Bay since 1912 when six men of Scott'sNorthern Party which are sheltered from drifting sea ice and can undergo were stranded on InexpressibleIsland [Priestley, 1914; Brom- substantial oscillations in size [Knapp, 1967, 1972; Streten, wich and Kurtz, 1982]. In the mid-1960's, Knapp [1972] noted 1973]. Theseare distinctfrom shoreleads which open tempor- this polynya in a generalsurvey of Antarctic coastalpolynyas, arily due to seawardadvection of seaice by strong winds and using experimentalNIMBUS 1 and 2 infrared photographs, which form partly by chance. and gave a sequenceof imagesillustrating its temporal varia- Knowledgeof Antarctic coastalpolynyas is limited because bility (his Figure 6). $zekielda [1974] probably examined it of the difficulty of observing small areas during the polar more recently using early operational infrared satellite ima- night. However, their extent can be approximatelyinferred gery. His geographiccoordinates are incorrect,but the profile from the ~ 30 km resolution microwave brightnesstemper- of the Drygalski Ice Tongue is apparent in his figure 3. Sze- ature distributions monitored since 1973 [Carsey, 1980; kielda noted that the polynya persistedthroughout the winter Weller, 1980]. Relatively high resolution (~3 km) infrared and attributed its presenceto marine upwellingor submarine satelliteimagery permits daily observationof localizedsea ice volcanism.The nature and frequencyof polynya fluctuations behavior throughout the winter [e.g., Dey, 1981]. The present and their relationships to synoptic scale weather were not studyuses the latter to examinesea ice conditionsin the west- discussed. ern Ross Sea where a prominent feature is a polynya in Terra Information from sunlit periodsalso indicatesunusual con- Nova Bay (Figure 1). ditions in Terra Nova Bay. Sea ice charts from 1973 to present Knapp [1972], drawing on earlier work by Zubov, hypoth- [Fleet Weather Facility, 1975, 1977, 1979; Naval Polar Ocean- esizedthat Antarctic coastalpolynyas form when strong winds ographyCenter, 1981, 1983] consistentlyshow open water or associatedwith traveling cyclonescause net sea ice displace- reducedice concentrationsfrom October to early March. The ments away from stationary ice boundaries.Thus, zonally anomaly persistsin spring, surroundedby concentratedpack propagating storms north of an irregular east-westcoastline ice in the Ross Sea, during the summer when ice tends to (East Antarctica for instance)should generatepolynyas to the remain along the Victoria Land coast, and during fall when west of capelikeprojections and along the east cost of protec- pack ice is rapidly forming in the open sea.That the Antarctic ted bays.This situation was verified by Knapp's analysisfor 2 sea ice edge retreats to its most southerlypoint in the central winter months of variations in the area of open water west of and western Ross Sea [Streten and Pike, 1980] suggestsan the fast ice anchoredby Fram Bank (longitude ~ 70øE),about atypical characterfor this whole region. Prior to 1980, sea ice 70 km north of Cape Darnley. Knapp's model requires that chartslabel Terra Nova Bay as being filled with concentrated for a polynya to form in Terra Nova Bay depressioncenters pack from mid-March to early October. These charts were •1••.• 1111,•11• •. •,•11 •11 •,• 1,•• 1 • •.1•.• 11•1 o ffl.•o1 o • 11 •.•. o • ffl.• 1•1• • •,.•11 •.•.1 •.l •,.•l 1 o Ill that area during winter were not of navigational interest. Copyright 1983by the AmericanGeophysical Union. Newer charts are more detailed. For the period betweenmid Paper number 3C1039. March and late Septemberduring the years 1980-1982, 41% 0148-0227/83/003C- 1039505.00 of the analysesshow reduced ice concentrationsor new ice.in 9717 9718 KURTZ AND BROMWlCH' TERRA NOVA BAY POLYNYA -74•S 170øE •ooE study area .ova ROSS SEA Marble Pt. Cape Washington ROSS ICE SHELF 170øE .- .... TERRA ::: .......... - 75øS•/oo ø ii InexpressibleIslandNOVA :D Glaciers \ ..-"'""-') i........._............._...:.:•:•.••..:.....•:• •..... a FastIce t •!• 01 krn 5•0 •/• .;.• CONTOURINTERVAL1000m Fig. 1. Location map showingTerra Nova Bay and surroundingfeatures. Terra Nova Bay. These findings indicate that ice charts alone SATELLITE IMAGERY ANALYSIS cannot be used to derive ice concentrationsfor the inner pack during the polar night. Infrared positive transparencies were analyzed by using Western Ross Sea wind and ice conditions were compared straightforward photo-interpretive techniques.Original digital for March through October 1979 to elucidate mechanismsof information was not available. Although 64 gray shadesare polynya formation and maintenancein Terra Nova Bay. Sea present, the human eye can normally distinguish between ice behavior was monitored by using thermal infrared imagery about 14 shades [Dickinson et al., 1974] (i.e., objects of suf- from the two near polar-orbiting satellitesadministered by the ficient size with an equivalent temperature contrast of at least U.S. Air Force Defense Meteorological Satellite Program 7 K can be observed).The Drygalski Ice Tongue is a readily (DMSP). Images were selectedfrom 1979, the FGGE (First identifiablegeographic feature on satelliteimages. Its profile is GARP Global Experiment) year, and were used in conjunc- evident even when no open water is present.In addition, Cape tion with twice-daily (0000 and 1200 GMT) synoptic analyses Washington (Figure 1) and the outline of Terra Nova Bay for that year. The latter constitutethe best available record of us,uallyexhibit sufficient radiative contrast with openwater to the surface pressurefield over the Southern Ocean [Guyruer be discernable.Thermal featuresvisible on cloud-free images and Le Marshall, 1981] and enabled derivation of the western accurately reflect relative temperature distributions on the Ross Sea wind field. It is important to note, however, that the land, sea, or ice surface. Intervening cloud alters observed southernhemisphere circulation was highly anomalous during temperature, thereby modifying the appearanceof the surface. FGGE [van Loon and Rogers, 1981; Trenberth and van Loon, But, clouds and moving features in the pack ice could be 1981]. tracked by superimposingsuccessive images, eliminating much KURTZ AND BROMWICH' TERRA NOVA BAY POLYNYA 9719 TABLE 1. Estimatesof Monthly Mean Extent of Open Water in the Terra Nova Bay Polynya Mean Area of Number Maximum Area of Month, Open Water, of Open Water, 1979 km2 S S• Days km2 March 3300 2700 1100 6 April 900 900 220 17 3000 May 1000 800 160 23 3000 June 1100 1000 230 19 4500 July 1100 600 120 25 3000 August 1400 1100 230 23 5000 September 1500 800 200 16 3400 October 1400 900 210 18 4500 Total 1300 1100 90 147 5000 Values used in calculating the means are based upon minimum estimatesof open water extent on any given day. of the uncertainty associatedwith cloudy images.Interpreta- The most difficult distinction to make was that between tions are biased becausethe polynya could only be observed open and partly open water which presumably contained with cloud-free or partly cloudy conditions; however, accept- patchesof thin ice. The two situations differ little in temper- able imageswere
Load more

Recommended publications
  • Years at the Amery Ice Shelf in September 2019
    https://doi.org/10.5194/tc-2020-219 Preprint. Discussion started: 19 August 2020 c Author(s) 2020. CC BY 4.0 License. 1 Atmospheric extremes triggered the biggest calving event in more than 50 2 years at the Amery Ice shelf in September 2019 3 4 Diana Francis 1*, Kyle S. Mattingly 2, Stef Lhermitte 3, Marouane Temimi 1, Petra Heil 4 5 6 1 Khalifa University of Science and Technology, P. O. Box 54224, Abu Dhabi, United Arab 7 Emirates. 8 2 Institute of Earth, Ocean, and Atmospheric Sciences, Rutgers University, New Brunswick, NJ, 9 USA. 10 3 Department of Geoscience and Remote Sensing, Delft University of Technology, Mekelweg 5, 11 2628 CD Delft, Netherlands. 12 4 University of Tasmania, Hobart, Tasmania 7001, Australia. 13 14 * Corresponding Author: [email protected]. 15 16 Abstract 17 Ice shelf instability is one of the main sources of uncertainty in Antarctica’s contribution to future 18 sea level rise. Calving events play crucial role in ice shelf weakening but remain unpredictable and 19 their governing processes are still poorly understood. In this study, we analyze the unexpected 20 September 2019 calving event from the Amery Ice Shelf, the largest since 1963 and which 21 occurred almost a decade earlier than expected, to better understand the role of the atmosphere in 22 calving. We find that atmospheric extremes provided a deterministic role in this event. The calving 23 was triggered by the occurrence of a series of anomalously-deep and stationary explosive twin 24 polar cyclones over the Cooperation and Davis Seas which generated strong offshore winds 25 leading to increased sea ice removal, fracture amplification along the pre-existing rift, and 26 ultimately calving of the massive iceberg.
    [Show full text]
  • Open-Ocean Polynyas and Deep Convection in the Southern Ocean Woo Geun Cheon1 & Arnold L
    www.nature.com/scientificreports OPEN Open-ocean polynyas and deep convection in the Southern Ocean Woo Geun Cheon1 & Arnold L. Gordon 2 An open-ocean polynya is a large ice-free area surrounded by sea ice. The Maud Rise Polynya in the Received: 27 December 2018 Southern Ocean occasionally occurs during the austral winter and spring seasons in the vicinity of Maud Accepted: 18 April 2019 Rise near the Greenwich Meridian. In the mid-1970s the Maud Rise Polynya served as a precursor to Published: xx xx xxxx the more persistent, larger Weddell Polynya associated with intensive open-ocean deep convection. However, the Maud Rise Polynya generally does not lead to a Weddell Polynya, as was the situation in the September to November of 2017 occurrence of a strong Maud Rise Polynya. Using diverse, long- term observation and reanalysis data, we found that a combination of weakly stratifed ocean near Maud Rise and a wind induced spin-up of the cyclonic Weddell Gyre played a crucial role in generating the 2017 Maud Rise Polynya. More specifcally, the enhanced fow over the southwestern fank of Maud Rise intensifed eddy activity, weakening and raising the pycnocline. However, in 2018 the formation of a Weddell Polynya was hindered by relatively low surface salinity associated with the positive Southern Annular Mode, in contrast to the 1970s’ condition of a prolonged, negative Southern Annular Mode that induced a saltier surface layer and weaker pycnocline. In the Southern Ocean there are two modes in which surface water can attain sufcient density to descend into the deep ocean1.
    [Show full text]
  • The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation
    15 MARCH 2020 C H E O N A N D K U G 2111 The Role of Oscillating Southern Hemisphere Westerly Winds: Global Ocean Circulation WOO GEUN CHEON Maritime Technology Research Institute, Agency for Defense Development, Changwon, South Korea JONG-SEONG KUG School of Environmental Science and Engineering, Pohang University of Science and Technology (POSTECH), Pohang, South Korea (Manuscript received 23 May 2019, in final form 5 December 2019) ABSTRACT In the framework of a sea ice–ocean general circulation model coupled to an energy balance atmospheric model, an intensity oscillation of Southern Hemisphere (SH) westerly winds affects the global ocean circu- lation via not only the buoyancy-driven teleconnection (BDT) mode but also the Ekman-driven telecon- nection (EDT) mode. The BDT mode is activated by the SH air–sea ice–ocean interactions such as polynyas and oceanic convection. The ensuing variation in the Antarctic meridional overturning circulation (MOC) that is indicative of the Antarctic Bottom Water (AABW) formation exerts a significant influence on the abyssal circulation of the globe, particularly the Pacific. This controls the bipolar seesaw balance between deep and bottom waters at the equator. The EDT mode controlled by northward Ekman transport under the oscillating SH westerly winds generates a signal that propagates northward along the upper ocean and passes through the equator. The variation in the western boundary current (WBC) is much stronger in the North Atlantic than in the North Pacific, which appears to be associated with the relatively strong and persistent Mindanao Current (i.e., the southward flowing WBC of the North Pacific tropical gyre).
    [Show full text]
  • Chapter 32 Ice Navigation
    CHAPTER 32 ICE NAVIGATION INTRODUCTION 3200. Ice and the Navigator mate average for the oceans, the freezing point is –1.88°C. As the density of surface seawater increases with de- Sea ice has posed a problem to the navigator since creasing temperature, convective density-driven currents antiquity. During a voyage from the Mediterranean to are induced bringing warmer, less dense water to the sur- England and Norway sometime between 350 B.C. and 300 face. If the polar seas consisted of water with constant B.C., Pytheas of Massalia sighted a strange substance salinity, the entire water column would have to be cooled to which he described as “neither land nor air nor water” the freezing point in this manner before ice would begin to floating upon and covering the northern sea over which the form. This is not the case, however, in the polar regions summer sun barely set. Pytheas named this lonely region where the vertical salinity distribution is such that the sur- Thule, hence Ultima Thule (farthest north or land’s end). face waters are underlain at shallow depth by waters of Thus began over 20 centuries of polar exploration. higher salinity. In this instance density currents form a shal- Ice is of direct concern to the navigator because it low mixed layer which subsequently cannot mix with the restricts and sometimes controls vessel movements; it deep layer of warmer but saltier water. Ice will then begin affects dead reckoning by forcing frequent changes of forming at the water surface when density currents cease course and speed; it affects piloting by altering the and the surface water reaches its freezing point.
    [Show full text]
  • Sea Ice and the Ocean Mixed Layer Over the Antarctic Shelf Seas
    The Cryosphere, 8, 761–783, 2014 Open Access www.the-cryosphere.net/8/761/2014/ doi:10.5194/tc-8-761-2014 The Cryosphere © Author(s) 2014. CC Attribution 3.0 License. Sea ice and the ocean mixed layer over the Antarctic shelf seas A. A. Petty1,*, P. R. Holland2, and D. L. Feltham3 1Centre for Polar Observation and Modelling, Department of Earth Sciences, University College London, London, WC1E 6BT, UK 2British Antarctic Survey, High Cross, Madingley Road, Cambridge CB3 0ET, UK 3Centre for Polar Observation and Modelling, Department of Meteorology, University of Reading, Reading, RG6 6BB, UK *now at: Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, USA Correspondence to: A. A. Petty ([email protected]) Received: 15 August 2013 – Published in The Cryosphere Discuss.: 30 August 2013 Revised: 28 February 2014 – Accepted: 12 March 2014 – Published: 29 April 2014 Abstract. An ocean mixed-layer model has been incorpo- The Weddell and Ross shelf seas show stronger spatial corre- rated into the Los Alamos sea ice model CICE to investi- lations (temporal mean – intra-regional variability) between gate regional variations in the surface-driven formation of the autumn/winter mixed-layer deepening and several atmo- Antarctic shelf waters. This model captures well the expected spheric variables compared to the Amundsen and Belling- sea ice thickness distribution, and produces deep (> 500 m) shausen. In contrast, the Amundsen and Bellingshausen shelf mixed layers in the Weddell and Ross shelf seas each winter. seas show stronger temporal correlations (shelf sea mean – This results in the complete destratification of the water col- interannual variability) between the autumn/winter mixed- umn in deep southern coastal regions leading to high-salinity layer deepening and several atmospheric variables.
    [Show full text]
  • Polynyas in the Southern Ocean They Are Vast Gaps in the Sea Ice Around Antarctica
    Polynyas in the Southern Ocean They are vast gaps in the sea ice around Antarctica. By exposing enormous areas of seawater to the frigid air, they help to drive the global heat engine that couples the ocean and the atmosphere by Arnold L. Gordon and Josefino C. (omiso uring the austral winter (the In these regions, called polynyas, the largest and longest-lived polynyas. It months between June and Sep­ surface waters of the Southern Ocean is not yet fully understood what forces Dtember) as much as 20 million (the ocean surrounding Antarctica) are create and sustain open-ocean polyn­ square kilometers of ocean surround­ bared to the frigid polar atmosphere. yas, but ship and satellite data gath­ ing Antarctica-an area about twice Polynyas and their effects are only ered by us and by other investigators the size of the continental U.S.-is cov­ incompletely understood, but it now are enabling oceanographers to devise ered by ice. For more than two cen­ appears they are both a result of the reasonable hypotheses. turies, beginning with the voyages of dramatic interaction of ocean and at­ Captain James Cook in the late 18th mosphere that takes place in the Ant­ n order to understand the specific century, explorers, whalers and scien­ arctic and a major participant in it. forces that create and sustain po­ tists charted the outer fringes of the The exchanges of energy, water and Ilynyas and the effects polynyas can ice pack from on board ship. Never­ gases between the ocean and the at­ have, one must first understand the theless, except for reports from the mosphere around Antarctica have a role the Southern Ocean plays in the few ships that survived after being major role in determining the large­ general circulation of the world ocean trapped in the pack ice, not much was scale motion, temperature and chemi­ and in the global climate as a whole.
    [Show full text]
  • Trends in the Stability of Antarctic Coastal Polynyas and the Role of Topographic Forcing Factors
    remote sensing Article Trends in the Stability of Antarctic Coastal Polynyas and the Role of Topographic Forcing Factors Liyuan Jiang 1,2, Yong Ma 1, Fu Chen 1,*, Jianbo Liu 1, Wutao Yao 1,2 , Yubao Qiu 1 and Shuyan Zhang 1,2 1 Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100094, China; [email protected] (L.J.); [email protected] (Y.M.); [email protected] (J.L.); [email protected] (W.Y.); [email protected] (Y.Q.); [email protected] (S.Z.) 2 School of Electronic, Electrical and Communication Engineering, University of Chinese Academy of Sciences, Beijing 100049, China * Correspondence: [email protected]; Tel.: +86-010-8217-8158 Received: 2 February 2020; Accepted: 18 March 2020; Published: 24 March 2020 Abstract: Polynyas are an important factor in the Antarctic and Arctic climate, and their changes are related to the ecosystems in the polar regions. The phenomenon of polynyas is influenced by the combination of inherent persistence and dynamic factors. The dynamics of polynyas are greatly affected by temporal dynamical factors, and it is difficult to objectively reflect the internal characteristics of their formation. Separating the two factors effectively is necessary in order to explore their essence. The Special Sensor Microwave/Imager (SSM/I) passive microwave sensor has been making observations of Antarctica for more than 20 years, but it is difficult for existing current sea ice concentration (SIC) products to objectively reflect how the inherent persistence factors affect the formation of polynyas. In this paper, we proposed a long-term multiple spatial smoothing method to remove the influence of dynamic factors and obtain stable annual SIC products.
    [Show full text]
  • Weddell Sea Phytoplankton Blooms Modulated by Sea Ice Variability
    RESEARCH LETTER Weddell Sea Phytoplankton Blooms Modulated by Sea Ice 10.1029/2020GL087954 Variability and Polynya Formation Key Points: Lauren vonBerg1, Channing J. Prend2 , Ethan C. Campbell3 , Matthew R. Mazloff2 , • Autonomous float observations 2 2 are used to characterize the Lynne D. Talley , and Sarah T. Gille evolution and vertical structure of 1 2 phytoplankton blooms in the Department of Computer Science, Princeton University, Princeton, NJ, USA, Scripps Institution of Oceanography, Weddell Sea University of California, San Diego, La Jolla, CA, USA, 3School of Oceanography, University of Washington, Seattle, • Bloom duration and total carbon WA, USA export were enhanced by widespread early ice retreat and Maud Rise polynya formation in 2017 Abstract Seasonal sea ice retreat is known to stimulate Southern Ocean phytoplankton blooms, but • Early spring bloom initiation depth-resolved observations of their evolution are scarce. Autonomous float measurements collected from creates conditions for a 2015–2019 in the eastern Weddell Sea show that spring bloom initiation is closely linked to sea ice retreat distinguishable subsurface fall bloom associated with mixed-layer timing. The appearance and persistence of a rare open-ocean polynya over the Maud Rise seamount in deepening 2017 led to an early bloom and high annual net community production. Widespread early ice retreat north of Maud Rise in 2017, however, had a similar effect, suggesting that the polynya most impacted the timing Supporting Information: of bloom initiation. Still, higher productivity rates at Maud Rise relative to the surrounding region are • Supporting Information S1 observed in all years, likely supported by flow-topography interactions. The longer growing season in 2017–2018 also allowed for separation of distinct spring and fall bloom signals, the latter of which was primarily subsurface and associated with mixed-layer deepening.
    [Show full text]
  • ASPECT: Antarctic Sea Ice Processes & Climate
    ASPeCt Antarctic Sea-Ice Processes and Climate Science and Implementation Plan 1998-2008 TABLE OF CONTENTS EXECUTIVE SUMMARY 1. OVERVIEW 1.1 Introduction 1.2 History of the ASPeCt Programme 1.3 Rationale 1.4 Overall Objectives of ASPeCt 2. KEY SCIENTIFIC QUESTIONS FOR ASPeCt 3. IMPLEMENTATION STRATEGY 3.1 Climatology 3.1.1. Reconstruction of 1980-1997 Climatology 3.1.2. Climatology Studies in the Implementation Period 1998-2008 3.1.2.1. Snow and ice thickness distributions 3.1.2.2. Snow and ice properties surveys 3.2 Process Studies 3.2.1. Short Time Series Experiments 3.2.2. Coastal Polynyas 3.2.3. Long Time Series Experiments 3.2.4. Ice Edge Experiments 3.3 Long Term Observations: Landfast Ice 4. RELATED DATA SETS AND PROGRAMME COORDINATION 4.1 Satellite Data Records 4.2 World Climate Research Programme (WCRP) 4.2.1. International Programme on Antarctic Buoys (IPAB) 4.2.2. Antarctic Ice Thickness Measurement Programme (AnITMP) 4.3 International Antarctic Zone (IAnZone) 5. REFERENCES APPENDICES A. ASPeCt Science Steering Group B. ASPeCt Activities and Schedule C. Ice Observation Protocols D. Snow and Ice Properties-Survey Protocols E. Antarctic Coastal Polynas: Candidates for ASPeCt Study F. List of Acronyms and Abbreviations FIGURES EXECUTIVE SUMMARY With the growth of activities in Global Change research in the Antarctic, both by SCAR programmes and by other international programmes such as IGBP and WCRP, key deficiencies in our understanding and lack of data from the sea ice zone have been identified. Important problems remaining to be adequately covered by Antarctic sea ice research programmes include: 1.
    [Show full text]
  • Modeling the Influence of the Weddell Polynya on the Filchner–Ronne Ice
    15 AUGUST 2019 N AUGHTEN ET AL. 5289 Modeling the Influence of the Weddell Polynya on the Filchner–Ronne Ice Shelf Cavity KAITLIN A. NAUGHTEN,ADRIAN JENKINS,PAUL R. HOLLAND,RUTH I. MUGFORD, KEITH W. NICHOLLS, AND DAVID R. MUNDAY British Antarctic Survey, Cambridge, United Kingdom (Manuscript received 13 March 2019, in final form 21 May 2019) ABSTRACT Open-ocean polynyas in the Weddell Sea of Antarctica are the product of deep convection, which trans- ports Warm Deep Water (WDW) to the surface and melts sea ice or prevents its formation. These polynyas occur only rarely in the observational record but are a near-permanent feature of many climate and ocean simulations. A question not previously considered is the degree to which the Weddell polynya affects the nearby Filchner–Ronne Ice Shelf (FRIS) cavity. Here we assess these effects using regional ocean model simulations of the Weddell Sea and FRIS, where deep convection is imposed with varying area, location, and duration. In these simulations, the idealized Weddell polynyas consistently cause an increase in WDW transport onto the continental shelf as a result of density changes above the shelf break. This leads to saltier, denser source waters for the FRIS cavity, which then experiences stronger circulation and increased ice shelf basal melting. It takes approximately 14 years for melt rates to return to normal after the deep convection ceases. Weddell polynyas similar to those seen in observations have a modest impact on FRIS melt rates, which is within the range of simulated interannual variability. However, polynyas that are larger or closer to the shelf break, such as those seen in many ocean models, trigger a stronger response.
    [Show full text]
  • The Relationship of Weddell Polynya and Open-Ocean Deep Convection to the Southern Hemisphere Westerlies
    694 JOURNAL OF PHYSICAL OCEANOGRAPHY VOLUME 44 The Relationship of Weddell Polynya and Open-Ocean Deep Convection to the Southern Hemisphere Westerlies WOO GEUN CHEON The 6th R&D Institute-1, Agency for Defense Development, Jinhae, South Korea YOUNG-GYU PARK Ocean Circulation and Climate Research Division, Korea Institute of Ocean Science and Technology, Ansan, South Korea J. R. TOGGWEILER NOAA/Geophysical Fluid Dynamics Laboratory, Princeton, New Jersey SANG-KI LEE Cooperative Institute for Marine and Atmospheric Studies, University of Miami, and NOAA/Atlantic Oceanographic and Meteorological Laboratory, Miami, Florida (Manuscript received 26 May 2013, in final form 3 October 2013) ABSTRACT The Weddell Polynya of the mid-1970s is simulated in an energy balance model (EBM) sea ice–ocean coupled general circulation model (GCM) with an abrupt 20% increase in the intensity of Southern Hemi- sphere (SH) westerlies. This small upshift of applied wind stress is viewed as a stand in for the stronger zonal winds that developed in the mid-1970s following a long interval of relatively weak zonal winds between 1954 and 1972. Following the strengthening of the westerlies in this model, the cyclonic Weddell gyre intensifies, raising relatively warm Weddell Sea Deep Water to the surface. The raised warm water then melts sea ice or prevents it from forming to produce the Weddell Polynya. Within the polynya, large heat loss to the air causes surface water to become cold and sink to the bottom via open-ocean deep convection. Thus, the underlying layers cool down, the warm water supply to the surface eventually stops, and the polynya cannot be main- tained anymore.
    [Show full text]
  • The Weddell Gyre, Southern Ocean: Present Knowledge and Future Challenges
    Vernet Maria (Orcid ID: 0000-0001-7534-5343) Hoppema Mario (Orcid ID: 0000-0002-2326-619X) Geibert Walter (Orcid ID: 0000-0001-8646-2334) Brown Peter (Orcid ID: 0000-0002-1152-1114) Haas Christian (Orcid ID: 0000-0002-7674-3500) Hellmer Hartmut, Heinz (Orcid ID: 0000-0002-9357-9853) Jokat Wilfried (Orcid ID: 0000-0002-7793-5854) Jullion Loïc (Orcid ID: 0000-0001-6269-6750) Mazloff Matthew, R. (Orcid ID: 0000-0002-1650-5850) Bakker Dorothee, C. E. (Orcid ID: 0000-0001-9234-5337) Brearley J., Alexander (Orcid ID: 0000-0003-3700-8017) Hattermann Tore (Orcid ID: 0000-0002-5538-2267) Hauck Judith (Orcid ID: 0000-0003-4723-9652) Hillenbrand Claus-Dieter (Orcid ID: 0000-0003-0240-7317) Huhn Oliver (Orcid ID: 0000-0003-3626-9135) Koch Boris, Peter (Orcid ID: 0000-0002-8453-731X) Lechtenfeld Oliver (Orcid ID: 0000-0001-5313-6014) Meredith Michael (Orcid ID: 0000-0002-7342-7756) Naveira Garabato Alberto, C. (Orcid ID: 0000-0001-6071-605X) Peeken Ilka (Orcid ID: 0000-0003-1531-1664) Rutgers van der Loeff Michiel (Orcid ID: 0000-0003-1393-3742) Schmidtko Sunke (Orcid ID: 0000-0003-3272-7055) Strass Volker, H. (Orcid ID: 0000-0002-7539-1400) Torres-Valdés Sinhué (Orcid ID: 0000-0003-2749-4170) Verdy Ariane (Orcid ID: 0000-0002-2774-2691) This article has been accepted for publication and undergone full peer review but has not been through the copyediting, typesetting, pagination and proofreading process which may lead to differences between this version and the Version of Record. Please cite this article as doi: 10.1029/2018RG000604 © 2019 American Geophysical Union.
    [Show full text]