Summer Melt Research Articles

Ship-based estimates of momentum transfer coefficient over sea ice and recommendations for its parameterization

Abstract. A major source of uncertainty in both climate projections and seasonal forecasting of sea ice is inadequate representation of surface–atmosphere exchange processes. The observations needed to improve understanding and reduce uncertainty in surface exchange parameterizations are challenging to make and rare. Here we present a large dataset of ship-based measurements of surface momentum exchange (surface drag) in the vicinity of sea ice from the Arctic Clouds in Summer Experiment (ACSE) in July–October 2014, and the Arctic Ocean 2016 experiment (AO2016) in August–September 2016. The combined dataset provides an extensive record of momentum flux over a wide range of surface conditions spanning the late summer melt and early autumn freeze-up periods, and a wide range of atmospheric stabilities. Surface exchange coefficients are estimated from in situ eddy covariance measurements. The local sea-ice fraction is determined via automated processing of imagery from ship-mounted cameras. The surface drag coefficient, CD10n, peaks at local ice fractions of 0.6–0.8, consistent with both recent aircraft-based observations and theory. Two state-of-the-art parameterizations have been tuned to our observations, with both providing excellent fits to the measurements.

A 10Be-dated record of glacial retreat in Connemara, Ireland, following the Last Glacial Maximum and implications for regional climate

Late Pleistocene stadials are traditionally viewed as periods of severe, year-round cooling centred on the North Atlantic, where the abrupt onset and termination of stadial conditions is widely, though not unequivocally, thought to reflect the impact on Atlantic Meridional Circulation of meltwater fluxes from fringing ice masses. Widespread subaerial melting of land-based ice, however, implies a state of glacier-climate disequilibrium that, according to some conceptual models, had to persist for the duration of each stadial event rather than immediately prior to it. Yet, to date, the spatial extent of any such melting remains unclear, as do the magnitude and duration of any cognate atmospheric warming. To help address this ambiguity, we reconstructed the timing and nature of deglaciation of the Connemara ice centre, Ireland, which, being located immediately downwind of the North Atlantic, affords an ideal location for assessing terrestrial expressions of stadial and non-stadial conditions. We report 15 new cosmogenic beryllium-10 ages of glacial erratic boulders that reveal the timing and magnitude of fluctuations in this sector of the former Irish ice sheet during Heinrich Stadial 1 (HS1). Coupled with geomorphic mapping, these results indicate rapid, widespread deglaciation of the Connemara ice centre at approximately 17 ka, under full stadial conditions, and that the ice margin retreated back to regional source areas rather than eastward towards the centre of the island. Recognising the potential divergence from the traditional view of cold North Atlantic stadials, we propose that the rate and nature of deglaciation in Connemara during HS1 likely reflects enhanced subaerial melting during the summer ablation season. • Fifteen new 10 Be dates constrain the deglaciation of an ice centre in Connemara, Ireland to Heinrich Stadial 1. • Our chronology contrasts with the current paradigm and suggests summer melting occurred despite anomalous winter cooling. • The Connemara deglacial record supports a broader pattern of enhanced seasonality in the North Atlantic during stadials.

Glaciers of the Olympic Mountains, Washington—The Past and Future 100 Years

AbstractIn 2015, the Olympic Mountains contained 255 glaciers and perennial snowfields totaling 25.34 ± 0.27 km2, half of the area in 1900, and about 0.75 ± 0.19 km3 of ice. Since 1980, glaciers shrank at a rate of −0.59 km2 yr−1 during which time 35 glaciers and 16 perennial snowfields disappeared. Area changes of Blue Glacier, the largest glacier in the study region, was a good proxy for glacier change of the entire region. Modeled glacier mass balance, based on monthly air temperature and precipitation, correlates with glacier area change. The mass balance is highly sensitive to changes in air temperature rather than precipitation, typical of maritime glaciers. In addition to increasing summer melt, warmer winter temperatures changed the phase of precipitation from snow to rain, reducing snow accumulation. Changes in glacier mass balance are highly correlated with the Pacific North American index, a proxy for atmospheric circulation patterns and controls air temperatures along the Pacific Coast of North America. Regime shifts of sea surface temperatures in the North Pacific, reflected in the Pacific Decadal Oscillation (PDO), trigger shifts in the trend of glacier mass balance. Negative (“cool”) phases of the PDO are associated with glacier stability or slight mass gain whereas positive (“warm”) phases are associated with mass loss and glacier retreat. Over the past century the overall retreat is due to warming air temperatures, +0.7°C in winter and +0.3°C in summer. The glaciers in the Olympic Mountains are expected to largely disappear by 2070.

North Atlantic Footprint of Summer Greenland Ice Sheet Melting on Interannual to Interdecadal Time Scales: A Greenland Blocking Perspective

AbstractRecent rapid melting of the summer Greenland ice sheet (GrIS) and its impact on Earth’s climate has attracted much attention. In this paper, we establish a connection between the melting of GrIS and the variability of summer sea surface temperature (SST) anomalies over the North Atlantic on interannual to interdecadal time scales through changes in subseasonal Greenland blocking (GB). It is found that the latitude and width of GB are important for the spatial patterns of the GrIS melting. The melting of the GrIS on interdecadal time scales is most prominent for the positive Atlantic multidecadal oscillation phase (AMO+) because the high-latitude GB and its large width, long lifetime, and slow decay are favored. However, the North Atlantic mid-high latitude warm–cold–warm (cold–warm–cold) tripole, referred to as the NAT+(NAT−) pattern, on interannual time scales tends to strengthen (weaken) the role of AMO+in the GrIS melting, especially on the northern or northeastern periphery of Greenland, by promoting (inhibiting) high-latitude GB and increasing (decreasing) its width. It is further revealed that AMO+(NAT+) favors the persistence and width of GB mainly through producing weak summer zonal winds and a small summer meridional potential vorticity gradient (PVy) in the North Atlantic mid-high latitudes at 55°–70°N (55°–65°N) compared to the role of negative AMO (NAT−). The event frequency and zonal width of GB events and their poleward shift are favored by the combination of NAT+with AMO+. In contrast, the combination of NAT−and AMO+tends to suppress reduced summer zonal winds and PVy, thus inhibiting the event frequency of GB events and their poleward shift and zonal width.Significance StatementRapid melting of the summer Greenland ice sheet (GrIS) has been observed to frequently occur, especially after the year 2000, leading to a rise in sea level and other effects on Earth’s climate. The physical cause of the rapid melting of the GrIS is an important area of research. We establish a connection between the summer melting of the GrIS and different sea surface temperature (SST) modes in the North Atlantic via changes in Greenland blocking. Although the positive Atlantic multidecadal oscillation (AMO+) phase favors the overall melting of GrIS, the phase of the North Atlantic tripole (NAT) SST pattern modulates the strength and location of the GrIS melting. The positive NAT phase (NAT+) with a warm–cold–warm tripole structure in the North Atlantic mid-high latitudes and AMO+combine to result in a strong warm SST anomaly in the high latitudes of the North Atlantic north of 60°N, which promotes the melting of GrIS on the western, northern, and northeastern peripheries of Greenland via high-latitude Greenland blocking with an increased zonal width. The combination of the negative NAT phase (NAT−) with a cold–warm–cold tripole structure and AMO+tends to suppress this effect. Thus, our results provide a new understanding of why the melting of GrIS shows a strong variability in strength and region.

Marine CO<sub>2</sub> system variability along the northeast Pacific Inside Passage determined from an Alaskan ferry

Abstract. Information on marine CO2 system variability has been limited along the northeast Pacific Inside Passage despite the region's rich biodiversity, abundant fisheries, and developing aquaculture industry. Beginning in 2017, the Alaska Marine Highway System M/V Columbia has served as a platform for surface underway data collection while conducting twice weekly ∼1600 km transits between Bellingham, Washington, and Skagway, Alaska. Marine CO2 system patterns were evaluated using measurements made over a 2-year period, which revealed the seasonal cycle as the dominant mode of temporal variability. The amplitude of this signal varied spatially and was modulated by the relative influences of tidal mixing, net community production, and the magnitude and character of freshwater input. Surface water pHT (total hydrogen ion scale) and aragonite saturation state (Ωarag) were determined using carbon dioxide partial pressure (pCO2) data with alkalinity derived from a regional salinity-based relationship, which was evaluated using intervals of discrete seawater samples and underway pH measurements. High-pCO2, low-pHT, and corrosive Ωarag conditions (Ωarag<1) were seen during winter and within persistent tidal mixing zones, and corrosive Ωarag values were also seen in areas that receive significant glacial melt in summer. Biophysical drivers are shown to dominate pCO2 variability over most of the Inside Passage except in areas highly impacted by glacial melt. pHT and Ωarag extremes were also characterized based on degrees of variability and severity, and regional differences were evident. Computations of the time of detection identified tidal mixing zones as strategic observing sites with relatively short time spans required to capture secular trends in seawater pCO2 equivalent to the contemporary rise in atmospheric CO2. Finally, estimates of anthropogenic CO2 showed notable spatiotemporal variability. Changes in total hydrogen ion content ([H+]T), pHT, and Ωarag over the industrial era and to an atmospheric pCO2 level consistent with a 1.5 ∘C warmer climate were theoretically evaluated. These calculations revealed greater absolute changes in [H+]T and pHT in winter as opposed to larger Ωarag change in summer. The contemporary acidification signal everywhere along the Inside Passage exceeded the global average, with specific areas, namely Johnstone Strait and the Salish Sea, standing out as potential bellwethers for the emergence of biological ocean acidification (OA) impacts. Nearly half of the contemporary acidification signal is expected over the coming 15 years, with an atmospheric CO2 trajectory that continues to be shaped by fossil–fuel development.

Distributions of virio- and picoplankton and their relationships with ice-melting and upwelling in the Indian Ocean sector of East Antarctica

Ice melting in the Antarctic summer and upwelling of the Circumpolar Deep Water (CDW) near the Antarctic continent have been suggested to regulate the distributions of microbial communities. However, an understanding of these relationships in the Indian Ocean sector of East Antarctica is lacking. We report on the distribution and relationships of virio- and picoplankton at 77 stations (including 29 stations throughout the entire water column and 48 stations from the epipelagic zone) from 35° to 78°E and 62° to 70°S, covering the Cosmonaut Sea, Cooperation Sea and Prydz Bay. The epipelagic stations were grouped into four clusters based on the virio- and picoplankton composition and abundance. Clusters three and four, which corresponded with areas of upwelling and ice retreat, had high abundances of autotrophic picoeukaryotes; this resulted in subsequent high abundances of heterotrophic prokaryotes and virioplankton. Cluster one and two stations correspond with a high nutrient, low chlorophyll (HNLC) area, where the abundances of autotrophic and heterotrophic picoplankton are low. Viruses were significantly correlated with heterotrophic prokaryotes in the ice-covered areas but more strongly correlated with autotrophic picoeukaryotes in areas associated with ice-edge blooms. Throughout the water column in the Cooperation Sea, nutrient supply from the upwelling of the CDW induced an increased abundance of heterotrophic prokaryotes, particularly in the meso- and bathypelagic zones of stations in the northern part of the area. High viral abundances were detected in the meso- and bathypelagic zones of stations with high abundances of virio- and picoplankton in the epipelagic zone. This study shows that the summer distribution of virio- and picoplankton in the Indian Ocean sector of East Antarctica was mainly controlled by ice-melting and upwelling of the CDW.

Arctic sea ice sensitivity to lateral melting representation in a coupled climate model

Abstract. The melting of sea ice floes from the edges (lateral melting) results in open-water formation and subsequently increases absorption of solar shortwave energy. However, lateral melt plays a small role in the sea ice mass budget in both hemispheres in most climate models. This is likely influenced by the simple parameterization of lateral melting in sea ice models that are constrained by limited observations. Here we use a coupled climate model (CESM2.0) to assess the sensitivity of modeled sea ice state to the lateral melt parameterization in preindustrial and 2×CO2 runs. The runs explore the implications of how lateral melting is parameterized and structural changes in how it is applied. The results show that sea ice is sensitive both to the parameters determining the effective lateral melt rate and the nuances in how lateral melting is applied to the ice pack. Increasing the lateral melt rate is largely compensated for by decreases in the basal melt rate but still results in a significant decrease in sea ice concentration and thickness, particularly in the marginal ice zone. Our analysis suggests that this is tied to the increased efficiency of lateral melting at forming open water during the summer melt season, which drives the majority of the ice–albedo feedback. The more seasonal Southern Hemisphere ice cover undergoes larger relative reductions in sea ice concentration and thickness for the same relative increase in lateral melt rate, likely due to the hemispheric differences in the role of the sea-ice–upper-ocean coupling. Additionally, increasing the lateral melt rate under a 2×CO2 forcing, where sea ice is thinner, results in a smaller relative change in sea ice mean state but suggests that open-water-formation feedbacks are likely to steepen the decline to ice-free summer conditions. Overall, melt processes are more efficient at forming open water in thinner ice scenarios (as we are likely to see in the future), suggesting the importance of accurately representing thermodynamic evolution. Revisiting model parameterizations of lateral melting with observations will require finding new ways to represent salient physical processes.

Distribution of dissolved organic carbon linked to bacterial community composition during the summer melting season in Arctic fjords

Distribution of dissolved organic carbon linked to bacterial community composition during the summer melting season in Arctic fjords

Influences of Hydrodynamic Force on Deep Relaxation Rockslide in Cold and Arid Areas of Langjia Reservoir in China

Abstract This research took the Langjia landslide in Qinghai Province of China as an example to explore the failure mechanism and mode of deep relaxation rockslide at cold and arid areas of the plateau under the influence of temperature difference, rainfall. Studies showed that deep relaxation tension cracks are the main precondition of the occurrence of the landslide, and the main triggering factor was the strong weathering and disintegration of argillaceous cemented conglomerate on sliding surface. Affected by rainfall, snow melting, and temperature, the water trapped in tensile cracks froze to ice in winter to accelerate the development of cracks and melt into water in spring and summer to accelerate the weathering process. The process led to forming a sliding surface of mud rock with gravel by weathering the argillaceous cemented conglomerate along the cracks, which was confirmed by field investigation after occurrence of the landslide. For this special failure type, calculation formula on considering rolling friction, sliding friction, and bottom shear stress was proposed, and the influence of shear stress on sliding surface on landslide stability under the seepage caused by rainfall and summer melt water when landslide occurred was discussed. The calculation results of three-dimensional numerical simulation and improved Sarma’s method on considering the hydrodynamic action on relaxation slope stability are consistent with the actual situation.

AN APPLICATION OF MACHINE LEARNING TO COLLEGE ADMISSIONS: THE SUMMER MELT PROBLEM

We present educational data mining research, specifically an application of machine learning to college admissions. Meeting targets for the number of students admitted and enrolled is crucial for many institutions of higher education since tuition-based income often serves as a major component of the operating revenue budget. Enrollment targets and diversity goals can be hampered by summer melt: the phenomenon in which students who, after being admitted and having committed to attend a college or university in the spring, do not actually enroll in the fall. Using 6 years of data from 2014 through 2019 of students admitted to a small liberal arts college in California, we investigate the application of supervised machine learning models to predict and identify those admitted students who will decline their admission offers, those that will accept their admission offers, and those students who are in danger of "melting away" over the summer. Institutions can use our summer melt model to estimate how many and identify which students will fail to enroll in order to implement activities and provide support to achieve their enrollment goals. The results of our research should encourage other institutions of higher education to apply machine learning algorithms to their admissions data to effectively estimate the size of the incoming student body and achieve other institutional goals.

Fluvial transport in the deglaciated Antarctic catchment – Bohemian Stream, James Ross Island

ABSTRACT With the ongoing climate change and the prolongation of the summer melting season and increasing air temperature that this entails, fluvial transport is likely to become a more important process shaping the deglaciated areas of Antarctica. Quantification of suspended sediment transport in the deglaciated catchment of the Bohemian Stream is presented in this study. It was shown that a large amount of fine-grained material is being transported even in the relatively small catchment during the short period of the Antarctic summer. The average calculated suspended sediment concentration during the 2018 austral summer reached 274.6 mg l−1, which corresponded to an average suspended sediment load of 3662 kg day−1 and suspended sediment yield of 68 t km−2 year−1 when considering the flow season to be approximately 4 months per year. Such values are considerably higher than those reported from continental Antarctica; however, they are lower compared to most of the Arctic catchments.

Effects of sea ice decline and summer land use on polar bear home range size in the Beaufort Sea

AbstractAnimals responding to habitat loss and fragmentation may increase their home ranges to offset declines in localized resources or they may decrease their home ranges and switch to alternative resources. In many regions of the Arctic, polar bears (Ursus maritimus) exhibit some of the largest home ranges of any quadrupedal mammal. Polar bears are presently experiencing a rapid decline in Arctic sea ice extent and a change in sea ice composition. For the Southern Beaufort Sea subpopulation of polar bears, this has resulted in a divergent movement pattern where most of the subpopulation remains on the sea ice in the summer melt season while the remainder move to land. We evaluated the effects of summer land use and maternal denning on the annual and seasonal utilization distribution size (i.e., home range) of adult female polar bears in the Southern Beaufort Sea subpopulation over 30 yr (1986–2016) during a period of rapid sea ice decline. For bears that remained on the summer sea ice, model‐derived mean annual utilization distributions were 64% larger in 1999–2016 ( = 176,000 km2) relative to 1986–1998 ( = 107,000 km2). This increase was primarily driven by increases in summer utilization distributions that encompassed increased amounts of open water and decreased amounts of preferred sea ice. The mean centroid of summer utilization distributions for bears that remained on the sea ice was 193 km further north‐northeast in 1999–2016. In contrast, bears that summered on land during 1999–2016 exhibited 88% smaller mean annual utilization distribution sizes ( = 22,000 km2) relative to bears that remained on the summer sea ice during the same period. Our findings highlight the impacts of sea ice declines on polar bear space use and the increasing importance of land as an alternative summer refuge.

Meltwater sources and sinks for multiyear Arctic sea ice in summer

Abstract. On Arctic sea ice, the melt of snow and sea ice generate a summertime flux of fresh water to the upper ocean. The partitioning of this meltwater to storage in melt ponds and deposition in the ocean has consequences for the surface heat budget, the sea ice mass balance, and primary productivity. Synthesizing results from the 1997–1998 SHEBA field experiment, we calculate the sources and sinks of meltwater produced on a multiyear floe during summer melt. The total meltwater input to the system from snowmelt, ice melt, and precipitation from 1 June to 9 August was equivalent to a layer of water 80 cm thick over the ice-covered and open ocean. A total of 85 % of this meltwater was deposited in the ocean, and only 15 % of this meltwater was stored in ponds. The cumulative contributions of meltwater input to the ocean from drainage from the ice surface and bottom melting were roughly equal.

A Blended Sea Ice Concentration Product from AMSR2 and VIIRS

An effective blended Sea-Ice Concentration (SIC) product has been developed that utilizes ice concentrations from passive microwave and visible/infrared satellite instruments, specifically the Advanced Microwave Scanning Radiometer-2 (AMSR2) and the Visible Infrared Imaging Radiometer Suite (VIIRS). The blending takes advantage of the all-sky capability of the AMSR2 sensor and the high spatial resolution of VIIRS, though it utilizes only the clear sky characteristics of VIIRS. After both VIIRS and AMSR2 images are remapped to a 1 km EASE-Grid version 2, a Best Linear Unbiased Estimator (BLUE) method is used to combine the AMSR2 and VIIRS SIC for a blended product at 1 km resolution under clear-sky conditions. Under cloudy-sky conditions the AMSR2 SIC with bias correction is used. For validation, high spatial resolution Landsat data are collocated with VIIRS and AMSR2 from 1 February 2017 to 31 October 2019. Bias, standard deviation, and root mean squared errors are calculated for the SICs of VIIRS, AMSR2, and the blended field. The blended SIC outperforms the individual VIIRS and AMSR2 SICs. The higher spatial resolution VIIRS data provide beneficial information to improve upon AMSR2 SIC under clear-sky conditions, especially during the summer melt season, as the AMSR2 SIC has a consistent negative bias near and above the melting point.

Correction to: Are Artificially Intelligent Conversational Chatbots Uniformly Effective in Reducing Summer Melt? Evidence from a Randomized Controlled Trial

Correction to: Are Artificially Intelligent Conversational Chatbots Uniformly Effective in Reducing Summer Melt? Evidence from a Randomized Controlled Trial

Homo Sapiens Sapiens Progressive Defaunation During The Great Acceleration: The Cli-Fi Apocalypse Hypothesis

Homo Sapiens Sapiens Progressive Defaunation During The Great Acceleration: The Cli-Fi Apocalypse Hypothesis

Helheim Glacier diurnal velocity fluctuations driven by surface melt forcing

AbstractThe influence of surface melt on the flow of Greenland's largest outlet glaciers remains poorly known and in situ observations are few. We use field observations to link surface meltwater forcing to glacier-wide diurnal velocity variations on East Greenland's Helheim Glacier over two summer melt seasons. We observe diurnal variations in glacier speed that peak ~6.5 h after daily maximum insolation and extend from the terminus region to the equilibrium line. Both the amplitude of the diurnal speed variation and its sensitivity to daily melt are largest at the glacier terminus and decrease up-glacier, suggesting that the magnitude of the response is controlled not only by melt input volume and temporal variability, but also by background effective pressure, which approaches zero at the terminus. Our results provide evidence that basal lubrication by meltwater drives diurnal velocity variations at Greenland's marine-terminating glaciers in a similar manner to alpine glaciers and Greenland's land-terminating outlet glaciers.

Macro-Nutrient Stoichiometry of Glacier Algae From the Southwestern Margin of the Greenland Ice Sheet.

Glacier algae residing within the surface ice of glaciers and ice sheets play globally significant roles in biogeochemical cycling, albedo feedbacks, and melt of the world’s cryosphere. Here, we present an assessment of the macro-nutrient stoichiometry of glacier algal assemblages from the southwestern Greenland Ice Sheet (GrIS) margin, where widespread glacier algal blooms proliferate during summer melt seasons. Samples taken during the mid-2019 ablation season revealed overall lower cellular carbon (C), nitrogen (N), and phosphorus (P) content than predicted by standard microalgal cellular content:biovolume relationships, and elevated C:N and C:P ratios in all cases, with an overall estimated C:N:P of 1,997:73:1. We interpret lower cellular macro-nutrient content and elevated C:N and C:P ratios to reflect adaptation of glacier algal assemblages to their characteristic oligotrophic surface ice environment. Such lower macro-nutrient requirements would aid the proliferation of blooms across the nutrient poor cryosphere in a warming world. Up-scaling of our observations indicated the potential for glacier algal assemblages to accumulate ∼ 29 kg C km2 and ∼ 1.2 kg N km2 within our marginal surface ice location by the mid-ablation period (early August), confirming previous modeling estimates. While the long-term fate of glacier algal autochthonous production within surface ice remains unconstrained, data presented here provide insight into the possible quality of dissolved organic matter that may be released by assemblages into the surface ice environment.

River runoff in Switzerland in a changing climate – changes in moderate extremes and their seasonality

Abstract. Future changes in river runoff will impact many sectors such as agriculture, energy production, or ecosystems. Here, we study changes in the seasonality, frequency, and magnitude of moderate low and high flows and their time of emergence. The time of emergence indicates the timing of significant changes in the flow magnitudes. Daily runoff is simulated for 93 Swiss catchments for the period 1981–2099 under Representative Concentration Pathway 8.5 with 20 climate model chains from the most recent transient Swiss Climate Change Scenarios. In the present climate, annual low flows typically occur in the summer half-year in lower-lying catchments (<1500 m a.s.l.) and in the winter half-year in Alpine catchments (>1500 m a.s.l.). By the end of the 21st century, annual low flows are projected to occur in late summer and early autumn in most catchments. This indicates that decreasing precipitation and increasing evapotranspiration in summer and autumn exceed the water contributions from other processes such as snowmelt and glacier melt. In lower-lying catchments, the frequency of annual low flows increases, but their magnitude decreases and becomes more severe. In Alpine catchments, annual low flows occur less often and their magnitude increases. The magnitude of seasonal low flows is projected to decrease in the summer half-year in most catchments and to increase in the winter half-year in Alpine catchments. Early time of emergence is found for annual low flows in Alpine catchments in the 21st century due to early changes in low flows in the winter half-year. In lower-lying catchments, significant changes in low flows emerge later in the century. Annual high flows occur today in lower-lying catchments in the winter half-year and in Alpine catchments in the summer half-year. Climate change will change this seasonality mainly in Alpine catchments with a shift towards earlier seasonality in summer due to the reduced contribution of snowmelt and glacier melt in summer. Annual high flows tend to occur more frequent, and their magnitude increases in most catchments except some Alpine catchments. The magnitude of seasonal high flows in most catchments is projected to increase in the winter half-year and to decrease in the summer half-year. However, the climate model agreement on the sign of change in moderate high flows is weak.

Antarctic Peninsula Regional Circulation and its Impact on the Surface Melt of Larsen C Ice Shelf

AbstractEnhanced surface melt over the ice shelves of the Antarctic Peninsula (AP) is one of the precursors to their collapse, which can be proceeded by accelerated ground glacier flow and increased contribution to sea level rise. With the collapse of Larsen A and B, and the major 2017 calving event from Larsen C, whether Larsen C is bound for a similar fate has received increasing attention. Here, the interannual variation of regional circulation over the AP region is studied using the Empirical Orthogonal Function (EOF) / Principal Component (PC) analysis on the sea level pressure of ERA5 reanalysis. The EOF modes capture the variations of depth, location and extent of Amundsen Sea Low and Weddell Sea Low in each season. Statistically significant positive correlations exist between Larsen C surface temperature and the PC time series of EOF mode 1 in winter and spring through northerly/northwesterly wind anomalies west of the AP. The PC time series of EOF mode 2 is negatively correlated with Larsen C surface temperature in autumn and summer and surface melt in summer, all due to southerly wind anomalies east of the AP. Surface energy budget analysis associated with EOF mode 2 shows that downwelling longwave radiation over Larsen C is negatively statistically significantly, correlated with EOF mode 2 and is the major atmospheric forcing regulating the variation of Larsen C surface melt. Positively enhanced EOF mode 2 since 2004 is responsible for the recent cooling and decline of surface melt over Larsen C.