Arctic Sea Ice Decline Research Articles

Isolating the Surface Type Influence on Arctic Low‐Clouds

AbstractInteractions between sea ice and clouds represent a mechanism through which sea ice influences climate. We composite cloud properties for ice‐free, marginal ice zone (MIZ), and ice‐covered surfaces during MIZ crossing events to analyze the cloud property differences between surface types. Restricting the analysis to MIZ crossing events enables the isolation of the sea ice effect on clouds from meteorological factors. We find larger cloud fraction (CF) and total water concentration below ∼1.5 km over ice‐free relative to ice‐covered surfaces during non‐summer months. During summer, the results suggest larger CF and total water concentration over ice‐free surfaces, however differences do not exceed observational uncertainty. Cloud property differences are linked to atmospheric thermodynamic profile differences, namely ice‐free surfaces are warmer, moister, less stable, and have more positive surface turbulent fluxes than ice‐covered surfaces. Ice‐free minus ice‐covered cloud property differences scale with surface temperature differences and are only found in the presence of a surface temperature difference. Our results suggest a 0.02 CF and 0.005 g m−3 total water concentration increase (∼5%) at the level of maximum CF between 2000 and 2021 due to the observed Arctic sea ice decline in fall, corresponding to ∼2 W m−2 increase in the net surface radiative flux. Our results support a positive sea ice‐cloud radiative feedback in fall and winter and a negative sea ice‐cloud radiative feedback in spring. We propose an updated conceptual model where the average surface type influence on cloud properties is mediated by surface temperature differences between ice‐free and ice‐covered surfaces.

Understanding Arctic Sea Ice Thickness Predictability by a Markov Model

Abstract The Arctic sea ice decline and associated change in maritime accessibility have created a pressing need for sea ice thickness (SIT) predictions. This study developed a linear Markov model for the seasonal prediction of model-assimilated SIT. It tested the performance of physically relevant predictors by a series of sensitivity tests. As measured by the anomaly correlation coefficient (ACC) and root-mean-square error (RMSE), the SIT prediction skill was evaluated in different Arctic regions and across all seasons. The results show that SIT prediction has better skill in the cold season than in the warm season. The model performs best in the Arctic basin up to 12 months in advance with ACCs of 0.7–0.8. Linear trend contributions to model skill increase with lead months. Although monthly SIT trends contribute largely to the model skill, the model remains skillful up to 2-month leads with ACCs of 0.6 for detrended SIT predictions in many Arctic regions. In addition, the Markov model’s skill generally outperforms an anomaly persistence forecast even after all trends were removed. It also shows that, apart from SIT itself, upper-ocean heat content (OHC) generally contributes more to SIT prediction skill than other variables. Sea ice concentration (SIC) is a relatively less sensitive predictor for SIT prediction skill than OHC. Moreover, the Markov model can capture the melt-to-growth season reemergence of SIT predictability and does not show a spring predictability barrier, which has previously been observed in regional dynamical model forecasts of September sea ice area, suggesting that the Markov model is an effective tool for SIT seasonal predictions.

Distinct Role of a Spring Atmospheric Circulation Mode in the Arctic Sea Ice Decline in Summer

AbstractA distinguishing feature of Arctic sea ice is the rapid declining in the Pacific Arctic Sector (PAS) in recent years. The atmospheric variability during spring (March‐May) plays a critical role in determining the sea ice extent (SIE) during the following summer. The summertime (June‐August) SIE reduction in the eastern part of PAS, including the East Siberian Sea and the Laptev Sea, is strongly related to the first two leading atmospheric circulation modes in spring, the Arctic Oscillation and the Arctic Dipole, retrieved from empirical orthogonal function analysis. Here, we show that the third leading mode of atmospheric circulation in spring, namely the Barents‐Beaufort Oscillation (BBO), can also change the summer SIE, especially on the western regime of the PAS across the Beaufort and Chukchi Seas. We find that a positive phase of springtime BBO (i.e., BBO+), relative to the BBO−, acts to decrease sea ice thickness via advection and generate sea ice deformation through divergence and shear processes, thereby preconditioning for a rapid sea ice loss within the PAS in the following summer. Furthermore, the occurrence of BBO is state‐dependent and potentially modulated by the phase shift of the Atlantic Multidecadal Oscillation (AMO) and the Pacific Decadal Oscillation (PDO). Since the mid‐1990s, the AMO (PDO) index has changed from a dominant negative (positive) to a positive (negative) phase. These phase shifts in AMO and PDO would have contributed to the subsequently increased appearance of anomalous BBO+ after 2000 and enhanced the summertime sea ice loss in the western regions of the PAS in recent years.

Comparing Arctic Surface Albedo Modification Geoengineering Solutions

As global warming continues, the trend of rapidly declining arctic sea ice is expected to increase. The albedo effect, a regulatory process in earth’s climate, has become a positive feedback loop under climate change conditions. Sea ice has a high albedo, reflecting the sun’s energy. As sea ice continuously melts, more energy is absorbed, reducing albedo and leading to increasing temperatures that continue to propel the cycle. With increasing concerns regarding the effects of climate change, focus has turned towards geoengineering solutions, which employ human intervention to slow or stop the effects of global warming. Regarding the decline in arctic sea ice, specific solutions that lower global albedo are examined. One of the first solutions was Arctic Ice Management (AIM), which proposed the use of wind-driven pumps to restore the thickness of melting sea ice. A more recent proposal was Glass Microsphere (GM) geoengineering, which involved the addition of reflective glass spheres to ice, increasing the albedo of the surface. Few studies have compared geoengineering solutions; a crucial step towards implementation. Using a mixed methodology of statistical and content analyses, GM and AIM surface albedo modification solutions were compared in terms of sea ice volume and risk factors. Results suggest that GM geoengineering displays a significantly higher capacity to preserve or increase sea ice volume, but is also associated with a higher number of risks compared to AIM. Further comparison of the two solutions is suggested, along with the implementation of climate solutions that combine both mitigation and geoengineering strategies.

Unraveling the Arctic Sea Ice Change since the Middle of the Twentieth Century

Changes in Arctic sea ice since the middle of the last century are explored in this study. Both observations and climate model simulations show an overall sea ice expansion during 1953–1970 but a general sea ice decline afterward. Anthropogenic aerosols, nature forcing and atmospheric ozone changes are found to contribute to the sea ice expansion in the early period. Their effects are strong generally in late boreal summer. On the other hand, greenhouse gas warming has a dominant effect on diminishing Arctic sea ice cover during 1971–2005, especially in September. Internal climate variability also plays a role in the Arctic sea ice change during 1953–1970. However, it cannot solely explain the Arctic sea ice decline since the 1970s.

A Review of Arctic–Subarctic Ocean Linkages: Past Changes, Mechanisms, and Future Projections

Arctic Ocean gateway fluxes play a crucial role in linking the Arctic with the global ocean and affecting climate and marine ecosystems. We reviewed past studies on Arctic–Subarctic ocean linkages and examined their changes and driving mechanisms. Our review highlights that radical changes occurred in the inflows and outflows of the Arctic Ocean during the 2010s. Specifically, the Pacific inflow temperature in the Bering Strait and Atlantic inflow temperature in the Fram Strait hit record highs, while the Pacific inflow salinity in the Bering Strait and Arctic outflow salinity in the Davis and Fram straits hit record lows. Both the ocean heat convergence from lower latitudes to the Arctic and the hydrological cycle connecting the Arctic with Subarctic seas were stronger in 2000–2020 than in 1980–2000. CMIP6 models project a continuing increase in poleward ocean heat convergence in the 21st century, mainly due to warming of inflow waters. They also predict an increase in freshwater input to the Arctic Ocean, with the largest increase in freshwater export expected to occur in the Fram Strait due to both increased ocean volume export and decreased salinity. Fram Strait sea ice volume export hit a record low in the 2010s and is projected to continue to decrease along with Arctic sea ice decline. We quantitatively attribute the variability of the volume, heat, and freshwater transports in the Arctic gateways to forcing within and outside the Arctic based on dedicated numerical simulations and emphasize the importance of both origins in driving the variability.

ENSO and QBO modulation of the relationship between Arctic sea ice loss and Eurasian winter climate

The causality between Arctic sea ice decline and cold boreal winters has been widely debated recently and remains controversial. A major source of uncertainty in the sea ice-cold winter relationship originates from that the stratosphere polar vortex (SPV) is not only affected by Arctic sea ice anomaly but can also be modulated by El Niño-Southern Oscillation (ENSO) and quasi-biennial oscillation (QBO). Using reanalysis data and hindcasts from the decadal prediction system version 4, here we show that both cold and warm winters occur over Eurasia when the Barents–Kara Sea sea ice is abnormally low. Warm winters occur during the La Niña-easterly QBO-low sea ice (LANINA-EQBO-LICE) years and cold winters during the neutral ENSO-neutral QBO (NENSO-NQBO)-LICE and El Niño (ELNINO)-NQBO-LICE years. During the LANINA-EQBO-LICE years, weakened upward-propagating planetary waves from the troposphere to the stratosphere strengthen the Arctic SPV and then weaken the Aleutian low and Siberian high, creating conditions favorable for Eurasian warming. The atmospheric responses are opposite in the NENSO-NQBO-LICE and ELNINO-NQBO-LICE years. This implies that care should be taken in using Arctic sea ice alone as the precursor to predict boreal winter climate.

Impact of rapid Arctic sea ice decline on China's crop yield under global warming

AbstractFood is the material basis for human survival. Therefore, food security is a top priority for the people's livelihood and the sustainable development and future destiny of human beings. In the context of global warming in recent decades, the Arctic region has experienced more significant temperature anomalies than the midlatitudes due to the "Arctic amplification," and the rate of sea ice reduction has accelerated, which has an important impact on climate change in the middle and high latitudes, especially the frequent occurrence of extreme climate disasters that seriously affect food security and China's agricultural production. However, little research has been conducted on the role of changes in this important system of Arctic sea ice in China's agricultural production. Therefore, this paper analyzes the interannual variability and multi-year trends of Arctic sea ice concentration, CO2, air temperature, precipitation and China's major crop yield data to explore the possible effects and mechanisms of the rapid decrease in Arctic sea ice on China's grain production. From the analysis, it was found that the yield of major grains (rice, maize, wheat and soybean) in China was closely related to the Arctic sea ice anomaly in the previous summer and autumn, and the influence process was primarily through the dynamic process of the Arctic sea ice anomaly affecting the meridional temperature gradient and the positive and negative Arctic Oscillation phases, which in turn affected the air temperature anomalies in Eurasia and China, and finally led to the anomalous changes in Chinese grain yield. Based on this, a prediction model of China's major grain yield was established by stepwise nonlinear multiple regression analysis, which is a good fit and is expected to increase China's major crop yield by 11.4% in 2022 compared with last year. This presents new ideas and methods for future grain yield assessment in China and has far-reaching guidance for the stability and development of national and regional economies worldwide.

Evaluating sea ice thickness simulation is critical for projecting a summer ice-free Arctic Ocean

The rapid decline of Arctic sea ice, including sea ice area (SIA) retreat and sea ice thinning, is a striking manifestation of global climate change. Analysis of 40 CMIP6 models reveals a very large spread in both model simulations of the September SIA and thickness and the timing of a summer ice-free Arctic Ocean. The existing SIA-based evaluation metrics are deficient due to observational uncertainty, prominent internal variability, and indirect Arctic response to global forcing. Given the critical roles of sea ice thickness (SIT) in determining Arctic ice variation throughout the seasonal cycle and the April SIT bridging the winter freezing and summer melting processes, we propose two SIT-based metrics, the April mean SIT and summer SIA response to April SIT, to assess climate models’ capability to reproduce the historical change of the Arctic sea ice area. The selected 11 good models reduce the uncertainty in the projected first ice-free Arctic by 70% relative to 11 poor models. The chosen models’ ensemble mean projects the first ice-free year in 2049 (2043) under the shared socio-economic pathways (SSP)2-4.5 (SSP5-8.5) scenario with one standard deviation of the inter-model spread of 12.0 (8.9) years.

Observed and forecasted changes in land use by polar bears in the Beaufort and Chukchi Seas, 1985–2040

Monitoring changes in the distribution of large carnivores is important for managing human safety and supporting conservation. Throughout much of their range, polar bears (Ursus maritimus) are increasingly using terrestrial habitats in response to Arctic sea ice decline. Their increased presence in coastal areas has implications for bear-human conflict, inter-species interactions, and polar bear health and survival. We examined observed trends in land use over three decades by polar bears in the southern Beaufort Sea (SB) and Chukchi Sea (CS) where bears have traditionally spent most of the year on the sea ice. Using data from 408 adult females fitted with satellite radio-collars, we examined trends in the annual proportion of bears coming onshore (hereafter referred to as “percent of bears”) during the summer for ≥ 21 days, arrival and departure dates, duration spent onshore and relationships with sea ice metrics. We then estimated future land use through 2040 by extrapolating trends and by combining observed relationships between land use and sea ice with projections of future sea ice from an ensemble of earth system models. The observed percent of bears summering onshore and their duration onshore was correlated with the percent of open water that occurred within their population’s range between July and October. As sea ice declined, the percent of bears summering onshore increased from ∼5–30% in the SB and ∼10–50% in the CS and duration onshore increased by > 30 days to 60–70 days in both populations. Using a range of greenhouse gas emission scenarios and adjustments for faster than forecasted sea ice loss we estimated that 50–62% of SB and 79–88% of CS bears will spend 90–108 and 110–126 days onshore during summer in the SB and CS, respectively, by 2040. Sea ice projections varied little between greenhouse gas emission scenarios prior to 2040 but diverged thereafter. Observed and forecasted increases in polar bear land occupancy puts more bears in proximity to human activities and settlements for longer durations while extending the lack of access to their primary prey. Because human conflict is one of the primary factors affecting the conservation of large carnivores worldwide, mitigation of bear-human interactions on land will be an increasingly important component of polar bear conservation.

An Optimal Atmospheric Circulation Mode in the Arctic Favoring Strong Summertime Sea Ice Melting and Ice–Albedo Feedback

Abstract The rapid decline of summer Arctic sea ice over the past few decades has been driven by a combination of increasing greenhouse gases and internal variability of the climate system. However, uncertainties remain regarding spatial and temporal characteristics of the optimal internal atmospheric mode that most favors summer sea ice melting on low-frequency time scales. To pinpoint this mode, we conduct a suite of simulations in which atmospheric circulation is constrained by nudging tropospheric Arctic (60°–90°N) winds within the Community Earth System Model, version 1 (CESM1), to those from reanalysis. Each reanalysis year is repeated for over 10 model years using fixed greenhouse gas concentrations and the same initial conditions. Composites show the strongest September sea ice losses are closely preceded by a common June–August (JJA) barotropic anticyclonic circulation in the Arctic favoring shortwave absorption at the surface. Successive years of strong wind-driven melting also enhance declines in Arctic sea ice through enhancement of the ice–albedo feedback, reaching a quasi-equilibrium response after repeated wind forcing for over 5–6 years, as the effectiveness of the wind-driven ice–albedo feedback becomes saturated. Strong melting favored by a similar wind pattern as observations is detected in a long preindustrial simulation and 400-yr paleoclimate reanalysis, suggesting that a summer barotropic anticyclonic wind pattern represents the optimal internal atmospheric mode maximizing sea ice melting in both the model and natural world over a range of time scales. Considering strong contributions of this mode to changes in Arctic climate, a better understanding of its origin and maintenance is vital to improving future projections of Arctic sea ice.

Amino acid δ13C and δ15N fingerprinting of sea ice and pelagic algae in Canadian Arctic and Subarctic Seas

The on-going decline in Arctic sea ice represents a significant loss of habitat for sea ice algae, which are a major contributor to primary production in the Arctic. Data on sea ice algal production is limited due to difficulties in both accessing sea-ice and sampling under-ice algae. Compound-specific isotope analysis (CSIA) of amino acids (AAs) is emerging as a powerful tool to trace element origins and biogeochemical processes in marine food webs and may address the knowledge gaps in sea ice algal productivity dynamics. Here we measured δ13C-AA and δ15N-AA in natural communities of sea ice and pelagic algae collected from regions offshore Labrador and Nunavut, Canada. Significant difference in δ13C-AA patterns between sea ice and pelagic algae was observed in different size classes. This difference was further supported by multivariate analyses based on normalized δ13C of essential amino acids (EAAs), which demonstrated a clear separation between sea ice and pelagic algae. Beta (β) values and trophic position (TP) calculated from δ15N of Glutamic Acid and Phenylalanine (Phe) and ∑V parameter for microbial resynthesis indicated a slightly higher heterotrophic biomass in pelagic and sea ice samples as compared to cultured samples. This finding is consistent with the Phe-normalized δ15N of Alanine and Threonine, which provided better separations between sea ice/pelagic algae and other end-member groups. Overall, our study provides first insights into the potential differences in δ13C-AA and δ15N-AA patterns between sea ice and pelagic algae and suggests carbon of sea ice origins may be distinguished from pelagic sources using CSIA-AA approach. These observations highlight the potential of CSIA-AA to estimate proportional contributions of sea ice and pelagic algae to export production and efficiency of benthic-pelagic coupling in polar marine environments.

GNSS Real–Time Precise Point Positioning in Arctic Northeast Passage

Human activities in the Arctic regions have been increasing in recent years due to the impacts of climate change, such as Arctic Sea ice decline. For example, there has been an increase in Arctic shipping routes. A robust navigation system with a high positioning accuracy is required when traversing the extremely challenging Arctic environment to ensure the safety of human activities. However, the high–precision GNSS navigation and the positioning method, e.g., real–time kinematic (RTK), is not available in the polar regions due to the accessibility issues of the required infrastructures. On the other hand, the International GNSS Service (IGS) enables real–time applications; additionally, quick and convenient satellite communication systems are also available. This offers the possibility of real–time precise point positioning (RT–PPP) with multi–GNSS for high-precision navigation in the Arctic. In our paper, we analyzed the performance of multi–GNSS RT–PPP in the Arctic Northeast Passage (NEP), highlighting the following contributions: First, a GNSS device is installed on the M/V TIANHUI, which passed through the NEP from 10 September to 20 September 2019; Second, we quantitatively evaluated the collected GNSS signals in terms of the maximum satellite elevations, number of visible satellites (NSAT), position dilution of precision (PDOP) values, signal–to–noise ratio (SNR), and multipath errors. Third, we evaluated the accuracy of the CLK93 real–time products compared with the Deutsches GeoForschungsZentrum (GFZ) final products GBM. Finally, we carried out experiments for both single– (SF) and dual–frequency (DF) RT–PPP in the NEP during the 11–day testing period. Our experimental results show that meter–level positioning accuracy can be achieved with SF RT–PPP, while the DF RT–PPP model reaches sub–decimeter values and even centimeter–level accuracy. In addition, using the multi–GNSS method, we showed that the average RMS values of DF RT–PPP in the horizontal and vertical directions are 0.080 m and 0.057 m, respectively, demonstrating an improvement of approximately 70% over single–GPS solutions.

The Arctic Surface Heating Efficiency of Tropospheric Energy Flux Events

Abstract This paper examines the processes that drive Arctic anomalous surface warming and sea ice loss during winter-season tropospheric energy flux events, synoptic periods of increased tropospheric energy flux convergence (Ftrop), using the NASA MERRA-2 reanalysis. During an event, a poleward anomaly in Ftrop initially increases the sensible and latent energy of the Arctic troposphere; as the warm and moist troposphere loses heat, the anomalous energy source is balanced by a flux upward across the tropopause and a downward net surface flux. A new metric for the Arctic surface heating efficiency (Etrop) is defined, which measures the fraction of the energy source that reaches the surface. Composites of high-, medium-, and low-efficiency events help identify key physical factors, including the vertical structure of Ftrop and Arctic surface preconditioning. In high-efficiency events (Etrop ≥ 0.63), a bottom-heavy poleward Ftrop occurs in the presence of an anomalously warm and unstratified Arctic—a consequence of decreased sea ice—resulting in increased vertical mixing, enhanced near-surface warming and moistening, and further sea ice loss. Smaller Etrop, and thus weaker surface impacts, are found in events with anomalously large initial sea ice extent and more vertically uniform Ftrop. These differences in Etrop are manifested primarily through turbulent heat fluxes rather than downward longwave radiation. The frequency of high-efficiency events has increased from the period 1980–99 to the period 2000–19, contributing to Arctic surface warming and sea ice decline.

Slowdown and Recovery of the Atlantic Meridional Overturning Circulation and a Persistent North Atlantic Warming Hole Induced by Arctic Sea Ice Decline

AbstractWe investigate the impact of Arctic sea ice loss on the Atlantic meridional overturning circulation (AMOC) and North Atlantic climate in a coupled general circulation model (IPSL‐CM5A2) perturbation experiment, wherein Arctic sea ice is reduced until reaching an equilibrium of an ice‐free summer. After several decades we observe AMOC weakening caused by reduced dense water formation in the Iceland basin due to the warming of surface waters, and later compensated by intensification of dense water formation in the Western Subpolar North Atlantic. Consequently, AMOC slightly weakens in deep, dense waters but recovers through shallower, less dense waters overturning. In parallel, wind‐driven intensification and southeastward expansion of the subpolar gyre cause a depth‐extended cold anomaly ∼2°C around 50°N that resembles the North Atlantic “warming hole.” We conclude that compensating dense water formations drive AMOC changes following sea ice retreat and that a warming hole can develop independently of the AMOC modulation.

Correction to: Persistent freshening of the Arctic Ocean and changes in the North Atlantic salinity caused by Arctic sea ice decline

Correction to: Persistent freshening of the Arctic Ocean and changes in the North Atlantic salinity caused by Arctic sea ice decline

Arctic Sea Ice Decline and Geoengineering Solutions: Cascading Security and Ethical Considerations

Climate change is generating sufficient risk for nation-states and citizens throughout the Arctic to warrant potentially radical geoengineering solutions. Currently, geoengineering solutions such as surface albedo modification or aerosol deployment are in the early stages of testing and development. Due to the scale of deployments necessary to enact change, and their preliminary nature, these methods are likely to result in unforeseen consequences. These consequences may range in severity from local ecosystem impacts to large scale changes in available solar energy. The Arctic is an area that is experiencing rapid change, increased development, and exploratory interest, and proposed solutions have the potential to produce new risks to both natural and human systems. This article examines potential security and ethical considerations of geoengineering solutions in the Arctic from the perspectives of securitization, consequentialism, and risk governance approaches, and argues that proactive and preemptive frameworks at the international level, and especially the application of risk governance approaches, will be needed to prevent or limit negative consequences resulting from geoengineering efforts. Utilizing the unique structures already present in Arctic governance provides novel options for addressing these concerns from both the perspective of inclusive governance and through advancing the understanding of uncertainty analysis and precautionary principles.

A Synthesis of the Upper Arctic Ocean Circulation During 2000–2019: Understanding the Roles of Wind Forcing and Sea Ice Decline

Major changes have occurred in the Arctic Ocean during 2000–2019, including the unprecedented spin-up of the Beaufort Gyre and the emergence of Arctic Atlantification in the eastern Eurasian Basin. We explored the main drivers for these changes by synthesizing numerical simulations and observations in this paper. The Arctic atmospheric circulation was unusual in some years in this period, with strongly negative wind curl over the Canada Basin. However, the wind-driven spin-up of the Beaufort Gyre would have been much weaker had it not been for Arctic sea ice decline. The sea ice decline not only fed the ocean with meltwater, but also made other freshwater components more available to the Beaufort Gyre through mediating the ocean surface stress. This dynamical effect of shifting surface freshwater from the Eurasian Basin towards the Amerasian Basin also resulted in the Arctic Atlantification in the eastern Eurasian Basin, which is characterized by halocline salinification and the uplift of the boundary between the halocline and the Atlantic Water layer. Contemporarily, the sea ice decline caused a strong warming trend in the Atlantic Water layer. The Empirical Orthogonal Function (EOF) analysis of Arctic annual sea surface height for this period reveals that the first two modes of the upper ocean circulation have active centers associated with the Arctic Oscillation and Beaufort High variability, respectively. In the presence of sea ice decline the first two EOFs can better distinguish the ocean variability driven by the two atmospheric circulation modes. Therefore, the major changes in the Arctic Ocean in the past two decades are indicators of climate change as is the sea ice retreat. Our synthesis could help assess how the Arctic Ocean might change in future warming climate.

Climate Change Fosters Competing Effects of Dynamics and Thermodynamics in Seasonal Predictability of Arctic Sea Ice

Abstract The fast decline of Arctic sea ice necessitates a stronger focus on understanding the Arctic sea ice predictability and developing advanced forecast methods for all seasons and for pan-Arctic and regional scales. In this study, the operational forecasting system combining an advanced eddy-permitting ocean–sea ice ensemble reanalysis ORAS5 and state-of-the-art seasonal model-based forecasting system SEAS5 is used to investigate effects of sea ice dynamics and thermodynamics on seasonal (growth-to-melt) Arctic sea ice predictability in 1993–2020. We demonstrate that thermodynamics (growth/melt) dominates the seasonal evolution of mean sea ice thickness at pan-Arctic and regional scales. The thermodynamics also dominates the seasonal predictability of sea ice thickness at pan-Arctic scale; however, at regional scales, the predictability is dominated by dynamics (advection), although the contribution from ice growth/melt remains perceptible. We show competing influences of sea ice dynamics and thermodynamics on the temporal change of ice thickness predictability from 1993–2006 to 2007–20. Over these decades, there was increasing predictability due to growth/melt, attributed to increased winter ocean heat flux in both Eurasian and Amerasian basins, and decreasing predictability due to advection. Our results demonstrate an increasing impact of advection on seasonal sea ice predictability as the region of interest becomes smaller, implying that correct modeling of sea ice drift is crucial for developing reliable regional sea ice predictions. This study delivers important information about sea ice predictability in the “new Arctic” conditions. It increases awareness regarding sea ice state and implementation of sea ice forecasts for various scientific and practical needs that depend on accurate seasonal sea ice forecasts.

Persistent freshening of the Arctic Ocean and changes in the North Atlantic salinity caused by Arctic sea ice decline

Persistent freshening of the Arctic Ocean and changes in the North Atlantic salinity caused by Arctic sea ice decline