An Examination of the Non-Formation of the North Water Polynya Ice Arch

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Article An Examination of the Non-Formation of the North Water Polynya Ice Arch

Ron F. Vincent

Department of Physics and Space Science, Royal Military College of Canada, Kingston, ON K7K 7B4, Canada; [email protected]

Received: 24 July 2020; Accepted: 19 August 2020; Published: 21 August 2020

Abstract: The North Water (NOW), situated between Ellesmere Island and Greenland in northern Baffin Bay, is the largest recurring polynya in the Canadian Arctic. Historically, the northern border of the NOW is defined by an ice arch that forms annually in Kane Basin, which is part of the Nares Strait system. In 2007 the NOW ice arch failed to consolidate for the first time since observations began in the 1950s. The non-formation of the NOW ice arch occurred again in 2009, 2010, 2017 and 2019. Satellite Advanced Very High Resolution Radiometry data shows that large floes broke off from the normally stable landfast ice in Kane Basin for each of these years, impeding ice arch formation. A closer analysis of a 2019 event, in which 2500 km2 of ice sheared away from Kane Basin, indicates that significant tidal forces played a role. The evidence suggests that thinning ice from a warming climate combined with large amplitude tides is a key factor in the changing ice dynamics of the NOW region. The non-formation of the NOW ice arch results in an increased loss of multiyear ice through Nares Strait.

Keywords: remote sensing; arctic waters; sea ice; marginal ice zones; tides

1. Introduction A polynya is an area of the polar ocean that remains relatively ice-free in climatic conditions that would normally result in thick ice cover. These anomalous areas, which significantly impact the biology, climate, and oceanography of a region, are broadly categorized as sensible or latent heat polynyas. For sensible heat polynyas, vertical mixing of warmer water from depth due to ocean current advection or wind-induced upwelling prevents the formation of sea ice. In the case of a latent heat polynya, ice is continually swept away from the region by winds and ocean currents. The subsequent formation of new ice releases energy into the environment through latent heat of fusion. During winter, polynyas have an ocean-to-atmosphere heat flux approximately two orders of magnitude greater than the surrounding ice pack and dominate the regional heat budget [1]. These high latitude oases are centers of considerable biodiversity and provide important habitats for marine mammals and birds [2]. Situated between Greenland and Ellesmere Island in northern Baffin Bay, the North Water (NOW) is the largest recurring polynya in the Canadian Arctic with a maximum area of approximately 80,000 km2 (Figure1a). Typically, the NOW forms when pack ice transported southward through Nares Strait becomes congested during winter and forms an ice arch just north of Smith Sound in Kane Basin. The configuration of the polynya is established as newly formed ice is continually swept southward from the ice arch by prevailing winds and ocean currents (Figure1b). Physical processes for NOW maintenance include latent heat of fusion, oceanic sensible heat, tidal influences and orographically channeled winds [3–12]. The ice arch generally breaks down in spring, allowing floes to enter Baffin Bay from the Arctic basin via Nares Strait.

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Figure 1. ((aa)) A A map map of of the the Nares Nares Strait Strait system system showing showing Kane Kane Basin, Basin, Smith Smith Sound Sound and and the the North North Water Water (NOW) polynya. ( (b)) Historically Historically the the northern northern border border of of the the NO NOWW is is defined deﬁned by by an an ice ice arch arch (red (red arrow) arrow) thatthat forms forms during winter winter in in Kane Basin. ( (cc)) Since Since 2007 2007 the the NOW NOW ice ice arch arch has failed to consolidate in fiveﬁve years, but relatively short-te short-termrm ice arches at the northern term terminusinus of Nares Strait have formed (blue arrow). As As shown shown in in ( (bb,,cc),), Nares Nares Strait Strait freezes freezes completely completely when when the the NOW NOW ice ice arch arch forms but remains comparatively ice ice free free along along with with the the NOW NOW when when only only the the northern northern ice ice arch arch consolidates. consolidates. (Satellite imagesimages in in (b (,bc),c are) are METOP-A METOP-A Advanced Advanced Very Very High High Resolution Resolution Radiometer Radiometer Channel Channel 4 thermal 4 thermalinfrared infrared with coastlines with coastlines outlined.) outlined.)

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Nares Strait is approximately 500 km in length with depths varying from 200 m to 500 m. The northern section, which consists of Kennedy and Robeson Channels, varies from 30 to 50 km in width, while Kane Basin to the south widens to a maximum of 130 km. Prevailing winds funnel from the north through Nares Strait as a result of the orientation of the channel and mountainous topography of the region [13]. Arctic Ocean water flows southward through Nares Strait with a mean surface current speed ranging from 10 to 15 cm/s [14]. The highest tides in the Canadian Arctic occur in Kane Basin [15], which can reverse the Nares Strait current exiting Smith Sound and significantly change the ice dynamics on a diurnal basis [10]. The mean annual outflow of Arctic sea ice through Nares Strait is approximately 40,000 km2 [16] and is dominated by thick multiyear ice originating north of Ellesmere Island in the Last Ice Area [17]. The NOW was established approximately 4500 years ago as evidenced by prehistoric bird colonies. The rich biological diversity of the region has allowed human settlement since 1250 AD [18]. The annual consistency of the NOW ice arch was noted on air reconnaissance surveys beginning in the 1950s and continued to show remarkable stability with the advent of global multispectral satellite observation in the late 1970s [19]. Geophysical changes began to occur in the NOW during the 1990s. The amount of open water in the polynya during winter increased during the decade, which may be attributable to a predominantly more negative phase of the North Atlantic Oscillation resulting in warmer temperatures [20]. In 1993 the NOW ice arch consolidated for only 10 days, while the first known spatial deviation of the structure occurred in 1995 when it formed 100 km north of Kane Basin [21]. In 2007 the NOW ice arch failed to consolidate for the first time since observations began in the 1950s [19,21], allowing a record area (87,000 km2) and volume (254 km3) of Arctic Ocean ice to pass through Nares Strait in a season [16]. The NOW ice arch failed to form again in 2009, 2010, 2017 and 2019, but during these years an ice arch consolidated at the northern terminus of Nares Strait (Figure1c). During the five years in which the NOW ice arch failed to consolidate, Nares Strait was blocked for an average of 71 days each year by northern ice arches, which is significantly less than the 173-day average from 1979 to 2019 when the NOW ice arch formed [21]. Consequently, the non-formation of the NOW ice arch is a contributing factor to the dramatic loss of multiyear ice in the Arctic basin [22]. This paper examines the non-formation of the NOW ice arch using satellite data in the optical and thermal infrared (TIR) regime. Following an overview of the methods, the ice dynamics of Kane Basin are described using satellite data for the five years of ice arch non-formation. An in-depth analysis is then carried out for 2019 using satellite TIR imagery and ground based environmental information, including tidal data, sea ice classification, surface air temperature, and wind velocity. The final sections are a discussion of the results and conclusions.

2. Methods

2.1. Satellite Data This study uses Advanced Very High Resolution Radiometry (AVHRR) imagery obtained from National Oceanic and Atmospheric Administration (NOAA)-18 and European Space Agency METOP-A satellites. The AVHRR sensor images the Earth in visible and TIR wavelengths with a spatial resolution of 1.1 km at nadir. The large swath of the sensor in conjunction with the polar orbit of the host satellites allows Nares Strait and the NOW to be imaged seven times a day with a temporal resolution of approximately 100 min between successive passes. The study area is relatively close to satellite nadir for passes between 1500Z and 1800Z daily oﬀering good spatial resolution. Table1 contains pertinent information for the AVHRR sensor. All AVHRR data were retrieved online from NOAA’s Comprehensive Large Array-Data Stewardship System [23]. Remote Sens. 2020, 12, 2712 4 of 16

Table 1. Advanced Very High Resolution Radiometry (AVHRR) sensor information.

Parameter Comment Channel 1 0.58–0.68 µm (Visible) Channel 2 0.725–1.00 µm (Visible/Near Infrared) Channel 3a 1.58–1.64 µm (Near Infrared) Channel 3b 3.55–3.93 µm (Medium Infrared) Channel 4 10.30–11.30 µm (Thermal Infrared) Channel 5 11.50–12.50 µm (Thermal Infrared) Altitude 827 km (METOP-A), 858 km (NOAA-18) Orbit Type Sun Synchronous Orbital Period Approximately 100 min Spatial Resolution 1.1 km at nadir degrading to approximately 8 km at swath edge Swath Width Approximately 2900 km

Surface temperatures were determined for METOP-A AVHRR images using the single channel Composite Arctic Sea Surface Temperature Algorithm (CASSTA) [24]. In clear sky conditions CASSTA uses Channel 4 to determine the temperature of three regimes: sea surface, ice surface, and marginal ice zones containing a combination of seawater and ice. The single channel architecture mitigates inaccuracies of split window algorithms that generally overestimate surface temperatures in the Arctic environment by using the diﬀerence between Channel 4 and Channel 5 brightness temperatures as a proxy for atmospheric absorption of TIR energy [25]. AVHRR requires cloud-free conditions for surface analysis using visible and TIR wavelengths. The Arctic maritime environment typically experiences extensive cloud cover, particularly during the warmer months [26], which is a challenge for the analysis of AVHRR imagery. For this study the high number of daily satellite passes allowed suﬃcient assessment for 2007, 2009, 2010 and 2017, while unusually clear conditions from 19 to 26 February 2019 permitted a detailed analysis for that year. Clouds prevented a similar analysis for the other years. Data from a weather-independent high-resolution sensor such as synthetic aperture radar (SAR) was not available for this study.

2.2. Tidal Data Simulations indicate that ocean-ice stress caused by tides reduce the extent of landfast ice [27]. Additionally, it is estimated that over the past decade, tides have been responsible for an approximately 15% reduction in the volume of Arctic sea ice [28]. Another study found that tidal forcing decreased ice volume by 17.8% in the Canadian Arctic Archipelago due to the suppression of ice formation in winter [29]. Tides generally have small amplitudes in the Arctic, but Kane Basin is an exception. It has been observed that a standing wave forms in Nares Strait from barotropic semidiurnal tides, resulting in significant tidal amplitudes that may be important in the formation and breakup of ice arches to the north and south [15]. Tides near the NOW ice arch reach an amplitude greater than 4 m and may reverse the direction of the Nares Strait outflow at Smith Sound [10]. Figure2a shows Acoustic Data Current Profiler (ADCP) data of the near surface current in Smith Sound over a tidal cycle. As the tide builds the current reaches a maximum of 40 cm/s northward, reducing to zero at high tide before reaching a maximum of 80 cm/s southward as the tide ebbs. Tidal charts for the Pim Island tide station were used for the analysis of Kane Basin ice dynamics for 2019 [30]. Figure2b shows the average location of the NOW ice arch from 1979 to 2006 and 2007 to 2020 in relation to the ADCP and tidal data. Since 2007 there is a northern migration of the average position of the ice arch when compared to earlier years, which may be linked to climate change. The migration is approximately 30 km farther north, placing the eastern border of the ice arch an additional 30 km from the Greenland coast, which may affect the structural integrity of the formation. Remote Sens. 2020, 12, x FOR PEER REVIEW 5 of 16

Remoteis approximately Sens. 2020, 12, 2712 30 km farther north, placing the eastern border of the ice arch an additional 30 km5 of 16 from the Greenland coast, which may affect the structural integrity of the formation.

FigureFigure 2. 2.( a()a) Acoustic Acoustic DataData CurrentCurrent ProﬁlerProfiler (ADCP) data [10] [10] is is compared compared to to a atidal tidal cycle cycle in in the the North North WaterWater (NOW) (NOW) region region [10 [10].]. Tides Tides greater greater than than 4 m4 m can can reverse reverse the the Nares Nares Strait Strait outﬂow. outflow. The The ADCP ADCP data wasdata recorded was recorded on 30 March on 30 1998March at 1998 a depth at a ofdepth 108 mof as108 part m as of thepart International of the International Arctic PolynyaArctic Polynya Program andProgram is shown and hereis shown to illustrate here to illustrate current current reversal. reversal. (b) The (b location) The location of the of ADCP the ADCP and and Pim Pim Island Island tide stationtide station is shown is shown in relation in relation to the to average the averag positione position of the of NOW the NOW ice arch ice fromarch 1979from to1979 2006 to and2006 2007 and to 2020.2007 The to 2020. increased The increased distance ofdistance the eastern of the border eastern of bo therder ice of arch the fromice arch the fr Greenlandom the Greenland land mass land may havemass an may impact have on an ice impact arch stability.on ice arch stability.

2.3.2.3. Other Other Environmental Environmental Data Data AdditionalAdditional environmental environmental factorsfactors that may affect aﬀect the the movement movement of of sea sea ice ice include include surface surface air air temperaturetemperature and and wind wind velocity.velocity. Historic weather weather data data for for PIM PIM island island were were acquired acquired online online [31]. [31 ]. RegionalRegional weekly weekly ice ice charts charts forfor thethe EasternEastern ArcticArctic from the Environment Environment Canada Canada Ice Ice Service Service website website werewere used used to to determine determine ice ice type type and and thicknessthickness inin KaneKane Basin [32]. [32].

3.3. Results Results

3.1.3.1. NOW NOW Ice Ice Arch Arch Formation Formation

RemoteThe Sens. formation 2020, 12, x; anddoi: FOR dissolution PEER REVIEW of the NOW ice arch has demonstrated www.mdpi.com/journal/remotesensing considerable temporal variability over the past 40 years. Satellite data since 1979 shows that the NOW ice arch may form as early Remote Sens. 2020, 12, x FOR PEER REVIEW 6 of 16 Remote Sens. 2020, 12, 2712 6 of 16 The formation and dissolution of the NOW ice arch has demonstrated considerable temporal variability over the past 40 years. Satellite data since 1979 shows that the NOW ice arch may form as as November or as late as April, while the breakdown of the structure varies from April to September. early as November or as late as April, while the breakdown of the structure varies from April to On average, the ice arch forms mid-January and persists until the end of June. Overall, ice arches in the September. On average, the ice arch forms mid-January and persists until the end of June. Overall, Nares Strait system, including both the NOW and northern ice arches, prevent the flow of multiyear ice arches in the Nares Strait system, including both the NOW and northern ice arches, prevent the ice from the Arctic basin for 161 days per season with a standard deviation of 76.7 days [21]. In this flow of multiyear ice from the Arctic basin for 161 days per season with a standard deviation of 76.7 context a season is considered the beginning of freezing in the fall and extending to the summer melt days [21]. In this context a season is considered the beginning of freezing in the fall and extending to the following year. the summer melt the following year. In the Nares Strait system, ice is normally first established in the sheltered waters of eastern Kane In the Nares Strait system, ice is normally first established in the sheltered waters of eastern Kane Basin. First year ice begins to build in September and by January the eastern portion of Kane Basin is Basin. First year ice begins to build in September and by January the eastern portion of Kane Basin is generally classified as landfast ice with a thickness more than 120 cm [32] that can persist well into the generally classified as landfast ice with a thickness more than 120 cm [32] that can persist well into melt season. The thick ice in Kane Basin serves as a solid anchor for the eastern side of the NOW ice the melt season. The thick ice in Kane Basin serves as a solid anchor for the eastern side of the NOW arch (Figure3), while the western edge is stabilized by thick landfast ice close to land. If the ice in ice arch (Figure 3), while the western edge is stabilized by thick landfast ice close to land. If the ice in eastern Kane Basin becomes unstable then the ice arch is unable to consolidate. eastern Kane Basin becomes unstable then the ice arch is unable to consolidate.

Figure 3. ((aa)) A A METOP-A METOP-A AVHRR AVHRR Channel 4 thermal in infraredfrared image of the NOW for 05 Jan 2020 1713Z and (b) the surface temperature ofof thethe samesame scenescene withwith aa land mask. Thick first ﬁrst year ice in Kane Basin (red arrows) provides a stable platform for thethe eastern edge of the ice arch. Sea and ice surface temperatures were determined with the Single Channel Composite Arctic Sea Surface Temperature Algorithm (CASSTA).

3.2. 2007 2007 Season Season It is reportedreported thatthat no no ice ice arches arches consolidated consolidated in in the the Nares Nares Strait Strait system system during during the 2007the 2007 season season [16], [16],although although a short-term a short-term northern northern ice arch ice appeared arch appeared from 30 from March 30to March 07 April. to 07 This April. was This the ﬁrstwas recorded the first recordedtime that time the NOW that the ice NOW arch did ice notarch form did innot a season.form in Ina season. late April In late it appeared April it appeared that the ice that arch the may ice

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Remote Sens. 2020, 12, x FOR PEER REVIEW 7 of 16 consolidate, but a large section of ice broke from eastern Kane Basin and prevented formation of the archstructure may (Figureconsolidate,4). but a large section of ice broke from eastern Kane Basin and prevented formation of the structure (Figure 4).

Figure 4. ((aa)) A A NOAA-18 NOAA-18 AVHRR AVHRR Channel 1 visible image with a land mask of the NOW for 07 April April 2007 and ( b)) 20 20 April April 2007. 2007. On On 07 07 April April the the short-term short-term northe northernrn ice ice arch arch is is intact, intact, and and ice ice is is becoming becoming congestedcongested in in Kane Basin where the ice appears solid to the east (red arrow). Thirteen days later the northern ice arch has collapsed and ice in Kane Kane Basin Basin has has fractured fractured into into several several floes, floes, the the largest largest more more 2 thanthan 2,000 2000 kmkm2 (blue arrow). 3.3. 2009 Season 3.3. 2009 Season The 2009 season was remarkable, with the first observed instance of an ice arch at the northern The 2009 season was remarkable, with the first observed instance of an ice arch at the northern terminus of Nares Strait in conjunction with the non-formation of the NOW ice arch in Kane Basin. terminus of Nares Strait in conjunction with the non-formation of the NOW ice arch in Kane Basin. The northern ice arch consolidated on 08 January and broke 184 days later on 12 July. The phenomenon The northern ice arch consolidated on 08 January and broke 184 days later on 12 July. The resulted in record low ice cover in the NOW and led to anomalously high sea surface temperatures phenomenon resulted in record low ice cover in the NOW and led to anomalously high sea surface during the summer [33]. Northern ice arches have occurred 17 times since 1979, however, until 2009, temperatures during the summer [33]. Northern ice arches have occurred 17 times since 1979, they preceded the formation of the NOW ice arch by an average of 30 days [21]. In 2009 the NOW ice however, until 2009, they preceded the formation of the NOW ice arch by an average of 30 days [21]. arch appeared to be consolidating within a week of the northern ice arch formation, but a significant In 2009 the NOW ice arch appeared to be consolidating within a week of the northern ice arch area of landfast ice in Kane Basin became unstable and broke away in the ensuing month (Figure5). formation, but a significant area of landfast ice in Kane Basin became unstable and broke away in the Extensive cloud cover prevented observation of the ice breakup in Kane Basin with AVHRR imagery. ensuing month (Figure 5). Extensive cloud cover prevented observation of the ice breakup in Kane Nares Strait remained uncharacteristically free of floes until the collapse of the northern ice arch in July. Basin with AVHRR imagery. Nares Strait remained uncharacteristically free of floes until the collapse of the northern ice arch in July.

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Figure 5. AA METOP-A METOP-A AVHRR AVHRR Channel 4 thermal infrared image with a land mask of the NOW for (a) 11 January 2009 and ( b) 19 February 2009. On On 11 11 January, January, th threeree days after the northern ice ice arch consolidated,consolidated, Kane Kane Basin Basin is is congested congested with with ice ice and and appears appears to to be be in in the early development of of an an ice arch. By By 19 19 February, February, the Kane Basin landfast landfast ice ice ha hass retreated retreated eastward and there are few floes ﬂoes in the Nares Strait system because of the northern ice arch.

3.4. 2010 2010 Season Season The 2010 seasonseason representedrepresented the the third third lowest lowest number numb ofer daysof days in the in satellitethe satellite record record in which in which Nares NaresStrait wasStrait blocked was blocked by ice arches by ice [21 arches]. A northern [21]. A icenorthern arch consolidated ice arch consolidated in mid-March in andmid-March collapsed and by collapsedmid-April, by while mid-April, an ice archwhile failed an ice to arch form failed in Kane to form Basin in for Kane a second Basin season for a second in a row. season The NOWin a row. ice Thearch NOW was in ice the arch process was in of the solidifying process of in solidifying mid-January in mid-January when ice in Kanewhen Basin ice in shatteredKane Basin into shattered several intolarge several ﬂoes that large destabilized floes that destabilized the landfast icethe (Figurelandfast6). ice The (Figure Kane Basin6). The ice Kane regenerated Basin ice over regenerated the next overtwo months,the next buttwo broke months, once but again broke in once April. again in April.

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FigureFigure 6. METOP-A 6. METOP-A AVHRR AVHRR Channel Channel 4 thermal thermal infrared infrared images images with with a land a mask land of mask the NOW of the for NOW (a) for 21 January 2010 and (b) 30 January 2010. On 21 January, Kane Basin ice appears stable (red arrow) (a) 21 January 2010 and (b) 30 January 2010. On 21 January, Kane Basin ice appears stable (red arrow) but is broken into several large floes nine days later (blue arrow). METOP-A AVHRR Channel 1 but is broken into several large floes nine days later (blue arrow). METOP-A AVHRR Channel 1 visible visible images with a land mask of the NOW for (c) 12 April 2010 and (d) 23 April 2010. The first-year imagesice within Kane a land Basin mask has regenerated of the NOW since for January (c) 12 April and appears 2010 and solid (d )on 23 12 April April. 2010. Eleven The days first-year later on ice in Kane23 Basin April, has Kane regenerated Basin ice has since broken January into andseveral appears floes in solid the ice on arch 12 April. region. Eleven The 23 days April later image on also 23 April, Kaneshows Basin that ice hasthe northern broken intoice arch several has collapsed floes in thesince ice 12 arch April. region. The 23 April image also shows that the northern ice arch has collapsed since 12 April.

3.5. 2017 Season Remote Sens. 2020, 12, x; doi: FOR PEER REVIEW www.mdpi.com/journal/remotesensing Following six seasons in which the NOW ice arch averaged 194.5 days of consolidation, 2017 featured a sole northern ice arch that persisted for 108 days between 23 January and 11 May [21]. Remote Sens. 2020, 12, x FOR PEER REVIEW 10 of 16

Remote3.5. 2017 Sens. Season2020, 12 , 2712 10 of 16 Following six seasons in which the NOW ice arch averaged 194.5 days of consolidation, 2017 featured a sole northern ice arch that persisted for 108 days between 23 January and 11 May [21]. Notably, a large ﬂoe 90 km by 25 km broke from the Kane Basin ice on 26 January (Figure7). The ice in Notably, a large floe 90 km by 25 km broke from the Kane Basin ice on 26 January (Figure 7). The ice the region did not fully regenerate for the rest of the season. in the region did not fully regenerate for the rest of the season.

FigureFigure 7.7. AA METOP-AMETOP-A AVHRR Channel 4 thermal infrared infrared image image with with a a land land mask mask of of the the NOW NOW for for (a(a)) 25 25 January January 2017 2017 and and ( b(b)) 26 26 January January 2017. 2017. In In a a 24-h 24-h period period a a large large ﬂoe floe breaks breaks from from the the Kane Kane Basin Basin ice inice the in criticalthe critical region region of NOW of NOW ice archice ar formationch formation (see (see red red and and blue blue arrows). arrows).

3.6.3.6. 20192019 SeasonSeason DetailedDetailed Case Study InIn 20192019 the the northern northern ice ice arch arch solidified solidified on on 16 February16 February and and broke broke down down 32 days 32 days later onlater 20 on March. 20 FourMarch. days Four after days the northernafter the icenorthern arch formed, ice arch a crackformed, was a observedcrack was in observed the landfast in the ice landfast in eastern ice Kane in Basin.eastern Relatively Kane Basin. cloud-free Relatively weather cloud-free allowed weather a close examinationallowed a close of the examination event. On 19of February,the event. the On Kane 19 BasinFebruary, ice appears the Kane solid Basin on satelliteice appears imagery. solid on A smallsatellite crack imagery. in the iceA small is observed crack in on the 20 ice February is observed 1536Z andon 20 appears February to grow 1536Z by and the appears next satellite to grow pass by at the 1716Z. next Oversatellite the pass next at six 1716Z. days approximately Over the next six 2500 days km 2 ofapproximately ice is cleaved 2500 from km the2 Kaneof ice Basinis cleaved landfast from ice the and Kane flushed Basin through landfast Smith ice and Sound. flushed Figure through8 shows Smith the satelliteSound. imageryFigure 8 of shows the initial the cracksatellite in the imagery ice compared of the to initial tidal informationcrack in the at Pimice compared Island. Between to tidal the 1536Zinformation and 1716Z at Pim satellite Island. images Between on 20 the February 1536Z and a high 1716Z tide satellite of 4.61m images occurred on 20 at 1555ZFebruary [30]. a Weatherhigh tide at theof 4.61 time m of occurred the breakup at 1555Z was partly [30]. cloudyWeather with at the a temperature time of the ofbreakup39 and was winds partly from cloudy the eastwith at a 8 − ◦ kmtemperature/h [31]. Winds of –39° were and light winds during from thethe twoeast daysat 8 km/h prior [31]. to breakup Winds were and temperatureslight during the ranged two days from prior38 C to to breakup40 C. and Additionally, temperatures there ranged were from no –38 obvious °C to impacts–40 °C. Additionally, from southward there movingwere no floesobvious that − ◦ − ◦ couldimpacts have from weakened southward the moving ice in Kane floes Basin. that could Given ha theve weakened conditions, the the ice evidence in Kane suggests Basin. Given that tidalthe forcesconditions, were athe key evidence contributor suggests to the th iceat tidal breakup forces in were Kane a Basin. key contributor Figure9 shows to the the ice thermal breakup evolution in Kane of the ice breakup and illustrates southward movement of cold first year ice from Kane Basin and cold multiyear ice originating from the northern ice arch. Remote Sens. 2020, 12, x; doi: FOR PEER REVIEW www.mdpi.com/journal/remotesensing Remote Sens. 2020, 12, x FOR PEER REVIEW 11 of 16

Basin.Remote Sens.Figure2020 9, 12 shows, 2712 the thermal evolution of the ice breakup and illustrates southward movement11 of 16 of cold first year ice from Kane Basin and cold multiyear ice originating from the northern ice arch.

Figure 8. 8. (a()a )On On 19 19 February February 2019 2019 1737Z 1737Z the the ice icein Kane in Kane Basin Basin appears appears solid solid (yellow (yellow arrow). arrow). (b) Twenty-two(b) Twenty-two hours hours later a later small a crack small appears crack appears at the southwest at the southwest edge of the edge Kane of Basin the Kaneice (red Basin arrow), ice coinciding(red arrow), with coinciding a tidal height with a of tidal 4.5 m height as seen of 4.5on mthe as tide seen height on the chart. tide ( heightc) One chart.hundred (c) Oneminutes hundred later theminutes high tide later of the 4.61 high m tidehas passed of 4.61 mand has the passed crack andin the the ice crack has expanded in the icehas in Kane expanded Basin in(blue Kane arrow). Basin ((blued) Less arrow). than 24 (d )h Less later than a large 24 hfloe later has a broken large ﬂoe free has of broken Kane Basin free of (green Kane arro Basinw). (green All panels arrow). are All METOP- panels are METOP-A AVHRR Channel 4 thermal infrared image with coastlines outlined. Tidal height in (b) Remoteand Sens. (c 2020) is for, 12, Pim x; doi: Island FOR PEER 20 Feb REVIEW 1100 to 2200Z [30]. www.mdpi.com/journal/remotesensing Remote Sens. 2020, 12, x FOR PEER REVIEW 12 of 16

Remote Sens.A AVHRR2020, 12, Channel 2712 4 thermal infrared image with coastlines outlined. Tidal height in (b) and (c) is 12 of 16 for Pim Island 20 Feb 1100 to 2200Z [30].

FigureFigure 9. METOP-A9. METOP-A AVHRR AVHRR Composite Composite Arctic Arctic Sea Sea Surface Surface Temperature Temperature Algorithm Algorithm (CASSTA) (CASSTA) images of theimages NOW of the for NOW February for February 2019. (a) 2019. On 19 (a February) On 19 February eastern eastern Kane BasinKane isBasin covered is covered with with thick thick first year ice,first which year has ice, a which very cold has a signature. very cold (signature.b) The first (b) crack The first in the crack Kane in the Basin Kane ice Basin is observed ice is observed on 20 February on during20 February high tide, during which high is tide followed, which byis followed (c) the removal by (c) the of removal a large of flow a large on flow 21 February. on 21 February. (d–f) Between (d– 24 andf) Between 26 February 24 and several 26 February large floes several break large from floes the br landfasteak from ice the in Kanelandfast Basin ice andin Kane are flushedBasin and southward are throughflushed Smith southward Sound. through The four Smith large Sound. floes inThe (d )four are large approximately floes in (d) 2500 are approximately km2 in total (red 2500 arrow). km2 in total (red arrow). 4. Discussion 4. Discussion Over the past four decades, there has been a significant reduction of sea ice in the Arctic because of surface air temperatures that are increasing quicker than the global average, a phenomenon known Remote Sens. 2020, 12, x; doi: FOR PEER REVIEW www.mdpi.com/journal/remotesensing as Arctic Amplification [34]. More than 50% of multiyear ice has been lost in the past two decades, leaving more than two thirds of the Arctic Ocean covered by seasonal ice [35]. In the Arctic Basin there is a trend toward younger, thinner ice that is more easily melted and broken up [36]. With respect to the NOW, there has been an expansion of open water during winter since the mid-1990s and an increased Remote Sens. 2020, 12, 2712 13 of 16 prominence of thinner ice [20]. After many years of noted stability and recurrence, the NOW ice arch has failed to consolidate in five seasons since 2007. Although there is significant variability between years making it difficult to predict ice arch formation in any one season, there is a downward trend of 2.1 days of ice arch consolidation per season in the Nares Strait system since 1979 [21]. The recent variability in the NOW ice arch is likely a response to Arctic Amplification. Satellite imagery indicates that the non-formation of the NOW ice arch is associated with a destabilization of ice in Kane Basin that serves as the eastern anchor of the structure. The surface flow in Kane Basin is reduced as the channel widens from approximately 40 km to 130 km [37], allowing the formation of thick first year ice in the calmer waters on the eastern side. Since 2007, the average latitude of the NOW ice arch has moved further north compared to previous years [21]. This northward migration of the ice arch requires greater stability of the Kane Basin landfast ice since the eastern part of the arch is farther from land (Figure2b). It is notable that the northern ice arch has formed in 40% of the seasons since 1979 but occurred in each of the five years in which the NOW ice arch failed to consolidate. For three of these years the northern ice arch was intact when ice in Kane Basin became unstable. In 2009 and 2017 it may be argued that the NOW ice arch did not consolidate, since the long-term northern arches in those years prevented the multiyear ice contribution to the structure. While this is likely a factor, similar configurations prior to 2009 allowed the NOW ice arch to form as late as 93 days after the northern arch formation. As such, there is no clear correlation between the non-formation of the NOW ice arch and the existence of the northern ice arch. The observed breakage of ice in Kane Basin prior to ice arch formation could be the combination of several physical factors, including warm temperatures, winds, thinning ice, impact from southerly moving floes and tidal fluctuations. In 2019 there is compelling evidence that tidal forces played an important role in breaking up ice in Kane Basin, thereby destabilizing the eastern boundary of the ice arch. During the 2019 event the winds were calm, surface air temperatures very cold and satellite imagery shows no obvious impacts from floes moving through Nares Strait. Conversely, the first observable crack in the ice coincided with a high tide of 4.61 m at nearby Pim Island. This represented the highest local tide in February and the second highest tide for the entire year (Figure 10)[30]. The section of ice that broke away from Kane Basin was reported as 3/10 vast floe, thin first year ice (30 to 70 cm thick) and 7/10 landfast, thick first year ice (>120 cm thick) [32]. The section of thinner ice may have been a contributing factor in the Kane Basin breakup. The overall thinning ice in the Arctic because of risingRemote temperatures Sens. 2020, 12, x FOR and PEER longer REVIEW melting seasons makes the ice more prone to ocean-ice tidal 14 of stresses. 16

Figure 10. Maximum tide heights for February 2019. The highest tide of the month at nearby Pim Island Figure 10. Maximum tide heights for February 2019. The highest tide of the month at nearby Pim occurredIsland on occurred the same on daythe same that aday crack that wasa crack observed was observed in the in Kane the Kane Basin Basin ice onice 20on February20 February (red (red arrow). The 4.61arrow). m tide The represented4.61 m tide represented the second the highest second tidehighest of thetide yearof the for year Pim forIsland Pim Island [30]. [30].

5. Conclusions The NOW ice arch in Kane Basin has failed to consolidate in five seasons (2007, 2009, 2010, 2017, 2019), a phenomenon that had not been observed prior to 2007 dating back to ice reconnaissance flights in the 1950s. In each of these years an ice arch formed at the northern terminus of Nares Strait for periods ranging from 7 to 184 days. The formation of ice arches in the Nares Strait system serve an important function in preventing the southward movement of multiyear ice from the Arctic Basin into Baffin Bay. The non-formation of the NOW ice arch reduces the seasonal blockage of Nares Strait by 102 days when compared to years that it consolidated. This leads to an increased loss of multiyear ice from the Arctic Basin southward through Nares Strait. Based on Nares Strait ice flux rates [16], the non-formation of the NOW ice arch corresponds to an average additional seasonal ice loss from the Arctic basin in the order of 20,000 to 30,000 km2, most of which is multiyear ice [17]. However, the inherent unpredictability of the NOW ice arch formation makes it difficult to incorporate this information in Arctic climate models. Structurally, the NOW ice arch requires stable ice on the eastern edge in Kane Basin. During the years in which the NOW ice arch failed to form there were events when large floes broke off from the normally strong first year ice in Kane Basin. There are several factors that could cause the weakening and breaking of ice in Kane Basin. Arctic Amplification has led to an overall thinning of polar ice in recent years and has affected the ice dynamics of the Nares Strait system [21]. The average position of the NOW ice arch has migrated northward since 2007, which means that the eastern edge is further from land and more susceptible to breakage. Clear skies allowed for a detailed analysis of the February 2019 breakup of ice in Kane Basin with AVHRR visible and TIR data. The satellite imagery indicates that tidal forces in the region, which are the strongest in the Arctic, caused large floes to break off from the Kane Basin ice. Newly formed cracks in the ice were concurrent with the highest tide of the month and second highest of the year. The evidence suggests that the combination of a warming climate and strong local tides are significant factors in the changing ice dynamics of the NOW region. For future work, archival SAR data could potentially be used for 2007, 2009, 2010 and 2017 to find similar correlations between ice breakup in Kane Basin and tidal forcing.

Remote Sens. 2020, 12, x; doi: FOR PEER REVIEW www.mdpi.com/journal/remotesensing Remote Sens. 2020, 12, 2712 14 of 16

5. Conclusions The NOW ice arch in Kane Basin has failed to consolidate in five seasons (2007, 2009, 2010, 2017, 2019), a phenomenon that had not been observed prior to 2007 dating back to ice reconnaissance flights in the 1950s. In each of these years an ice arch formed at the northern terminus of Nares Strait for periods ranging from 7 to 184 days. The formation of ice arches in the Nares Strait system serve an important function in preventing the southward movement of multiyear ice from the Arctic Basin into Baffin Bay. The non-formation of the NOW ice arch reduces the seasonal blockage of Nares Strait by 102 days when compared to years that it consolidated. This leads to an increased loss of multiyear ice from the Arctic Basin southward through Nares Strait. Based on Nares Strait ice flux rates [16], the non-formation of the NOW ice arch corresponds to an average additional seasonal ice loss from the Arctic basin in the order of 20,000 to 30,000 km2, most of which is multiyear ice [17]. However, the inherent unpredictability of the NOW ice arch formation makes it difficult to incorporate this information in Arctic climate models. Structurally, the NOW ice arch requires stable ice on the eastern edge in Kane Basin. During the years in which the NOW ice arch failed to form there were events when large floes broke off from the normally strong first year ice in Kane Basin. There are several factors that could cause the weakening and breaking of ice in Kane Basin. Arctic Amplification has led to an overall thinning of polar ice in recent years and has affected the ice dynamics of the Nares Strait system [21]. The average position of the NOW ice arch has migrated northward since 2007, which means that the eastern edge is further from land and more susceptible to breakage. Clear skies allowed for a detailed analysis of the February 2019 breakup of ice in Kane Basin with AVHRR visible and TIR data. The satellite imagery indicates that tidal forces in the region, which are the strongest in the Arctic, caused large floes to break off from the Kane Basin ice. Newly formed cracks in the ice were concurrent with the highest tide of the month and second highest of the year. The evidence suggests that the combination of a warming climate and strong local tides are significant factors in the changing ice dynamics of the NOW region. For future work, archival SAR data could potentially be used for 2007, 2009, 2010 and 2017 to find similar correlations between ice breakup in Kane Basin and tidal forcing.

Author Contributions: The author, R.F.V., searched and retrieved all satellite data, conducted the analysis and wrote the paper. Satellite imagery in this research was analyzed by the author using Harris Geospatial ENVI software, http://www.harrisgeospatial.com. Author has read and agreed to the published version of the manuscript. Funding: The Article Process Charge was funded by the Canadian Defence Academy Research Program. Conﬂicts of Interest: The author declares no conﬂict of interest.

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