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The Labrador Sea and contiguous Baffin Bay play an important role in the formation of the upper layer of the North Atlantic Deep Water, an essential component of the Atlantic Meridional Ocean Circulation. The hydrography of these two seas is strongly influenced by the melting of sea-ice and glacier-ice, which has likely been affected by long-term climate changes. In this study, we use historical data of ocean temperature and salinity from 1950 to 2022 to estimate the summer freshwater volume (SFV) in Baffin Bay and the Labrador Sea, establish climatologies, and assess the impact of multi-decadal climate change. The SFV climatology (1956 km3)and the summer freshwater budget (2286 km3)estimated from various components are in good agreement. Sea ice and glacial melt account for 37 % and 26 % of the freshwater budget, respectively. SFV climatologies before and after 1995 reveal an increase in Baffin Bay (+226 km3) because of enhanced glacier melting, and a decline (-112 km3) in the Labrador Sea because of recent sea ice volume decreases. The time series of Labrador Sea SFV and total freshwater content are uncorrelated at the multi-decadal scale possibly because the influx of freshwater from the Beaufort Sea dominates the long-term variability. [ABSTRACT FROM AUTHOR]

Landfast sea ice (fast ice) is an important though poorly understood component of the cryosphere on the Antarctic continental shelf, where it plays a key role in atmosphere–ocean–ice-sheet interaction and coupled ecological and biogeochemical processes. Here, we present a first in-depth baseline analysis of variability and change in circum-Antarctic fast-ice distribution (including its relationship to bathymetry), based on a new high-resolution satellite-derived time series for the period 2000 to 2018. This reveals (a) an overall trend of -882±824 km 2 yr -1 (-0.19±0.18 % yr -1) and (b) eight distinct regions in terms of fast-ice coverage and modes of formation. Of these, four exhibit positive trends over the 18-year period and four negative. Positive trends are seen in East Antarctica and in the Bellingshausen Sea, with this region claiming the largest positive trend of +1198±359 km 2 yr -1 (+1.10±0.35 % yr -1). The four negative trends predominantly occur in West Antarctica, with the largest negative trend of -1206±277 km 2 yr -1 (-1.78±0.41 % yr -1) occurring in the Victoria and Oates Land region in the western Ross Sea. All trends are significant. This new baseline analysis represents a significant advance in our knowledge of the current state of both the global cryosphere and the complex Antarctic coastal system, which are vulnerable to climate variability and change. It will also inform a wide range of other studies. [ABSTRACT FROM AUTHOR]

Landfast sea ice (fast ice) is an important component of the Antarctic nearshore marine environment, where it strongly modulates ice sheet–ocean–atmosphere interactions and biological and biogeochemical processes, forms a key habitat, and affects logistical operations. Given the wide-ranging importance of Antarctic fast ice and its sensitivity to climate change, improved knowledge of its change and variability in its distribution is a high priority. Antarctic fast-ice mapping to date has been limited to regional studies and a time series covering East Antarctica from 2000 to 2008. Here, we present the first continuous, high-spatio-temporal resolution (1 km, 15 d) time series of circum-Antarctic fast-ice extent; this covers the period March 2000 to March 2018, with future updates planned. This dataset was derived by compositing cloud-free satellite visible and thermal infrared imagery using an existing methodology, modified to enhance automation and reduce subjectivity in defining the fast-ice edge. This new dataset has wide applicability and is available at 10.26179/5d267d1ceb60c. The new algorithm presented here will enable continuous large-scale fast-ice mapping and monitoring into the future. [ABSTRACT FROM AUTHOR]

Rare CO2 flux measurements from Arctic pack ice show that two types of ice contribute to the release of CO2 from the ice to the atmosphere during winter and spring: young, thin ice with a thin layer of snow and older (several weeks), thicker ice with thick snow cover. Young, thin sea ice is characterized by high salinity and high porosity, and snow-covered thick ice remains relatively warm (>-7.5 °C) due to the insulating snow cover despite air temperatures as low as -40 °C. Therefore, brine volume fractions of these two ice types are high enough to provide favorable conditions for gas exchange between sea ice and the atmosphere even in mid-winter. Although the potential CO2 flux from sea ice decreased due to the presence of the snow, the snow surface is still a CO2 source to the atmosphere for low snow density and thin snow conditions. We found that young sea ice that is formed in leads without snow cover produces CO2 fluxes an order of magnitude higher than those in snow-covered older ice (+1.0±0.6 mmol C m-2day-1 for young ice and +0.2 ±0.2 mmolCm-2 day-1 for older ice). [ABSTRACT FROM AUTHOR]

We show that young, snow-covered ice has a potential for sea-ice-to-air CO2 release during winter and spring in the Arctic Ocean north of Svalbard. Young thin sea ice was characterized by high salinities and thus porosity, while the surface of thicker sea ice was relatively warm (> -7.5 °C), due to a thick insulating snow cover, even though air temperatures were as low as -40 °C. During these conditions, brine volume fractions of sea ice were high, providing potentially favorable conditions for gas exchange between sea ice and overlying air even in mid-winter. Although the potential CO2 flux through the sea ice decreased due to the presence of the snow, the snow surface still is a CO2 source to the atmosphere for low snow density and thin snow conditions. Especially young ice formed in leads, without snow cover, is important for the CO2 flux from the ice pack as the fluxes are an order of magnitude higher than for snow-covered older ice. [ABSTRACT FROM AUTHOR]

Knowledge of wintertime sea-ice production in polynyas is an important aspect ofatmosphere – sea-ice – ocean interactions in high latitudes, and a precise quantification canbe for instance utilized to verify frequently used climate and ocean models. This studyfeatures a high-resolution (2km) MODIS thermal infrared satellite data set with spatial andtemporal characteristics of 17 coastal polynya regions over the entire Arctic basin for2002/2003 to 2017/2018, as well as a similar data set based on lower resolution (6.25km)AMSR-E passive microwave satellite data for a nine-year overlapping comparison period (upto 2010/2011). The MODIS data set is relying on a 1D energy balance model, where quasi-dailythin-ice thickness composites (up to 20cm) are directly derived from ice-surfacetemperature swath-data and ERA-Interim atmospheric reanalysis data. Dedicated cloudscreening and spatial/temporal interpolation techniques are therein applied to effectivelyaccount for sensor-specific drawbacks. In case of the AMSR-E data set, thin-icethicknesses are derived using an empirical approach that utilizes a characteristicpolarization ratio (PR) – ice thickness relationship. In both data sets, the daily pan-Arcticmapping of thin-ice thicknesses allows for a long-term derivation of important polynyaproperties such as polynya area (POLA) and potential thermodynamic ice production(IP). It shows that the average POLA (average accumulated IP) for all Arctic polynyascombined is 1.99 x 105 km2 (1.34 x 103 km3) when derived from MODIS data and 2.23 x105 km2 (1.29 x 103 km3) in case of AMSR-E data. Although the two data sets areindependently derived, they show quite similar spatial and temporal variations of POLA andIP, which suggests a high reliability of both data sets. Hence, despite all methodicaldifferences, both data sets are to a large degree coherent in terms of capturing the generalspatial and temporal characteristics of Arctic polynyas for the overlapping 9-yr period.Emerging positive trends in POLA and IP over the long 16-yr period of the MODIS data setare mainly visible in the Eastern Arctic and are potentially related to large-scaleatmospheric modes and/or changing characteristics of the Transpolar drift system. [ABSTRACT FROM AUTHOR]