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Abstract Using satellite-derived abundance indices over 20 years, we investigated population change among the seven Ross Sea emperor penguin (Aptenodytes forsteri) colonies. We found a 90% probability that the Ross Sea metapopulation had lower springtime attendance between 2005 and 2024 (mean change = −23%; 95% CI: −46 to +20%). We identified two distinct phases of change: slightly increasing 2005 to 2019/2020, followed by a steep decline 2020–2024, resulting in a decrease of approximately 23 000 birds in 5 years or approximately 32% of the regional population. Over the 20 years, the two southernmost colonies, Cape Crozier and Cape Colbeck, increased in size, yet Beaufort, Coulman, Roget and Washington declined, resulting in a negative population trend especially evident from 2021. Asynchronous population change suggests metapopulation dynamics, with immigration from western colonies possibly driving increases at Colbeck and Crozier. Winter and spring sea ice concentration anomalies (5 year lag) and El Niño phases (1 year lag) statistically explained the most variance in our time series. Our results indicate that emperor penguins may be sensitive to sea ice fluctuations, offering insight into how this species may have adapted throughout their history and emphasizing the need for timely re-evaluation of targeted conservation strategies in an era of sea ice change. 

Abstract The Western Antarctic Peninsula is undergoing rapid environmental change. Regional warming is causing increased glacial meltwater discharge, but the ecological impact of this meltwater over large spatiotemporal scales is not well understood. Here, we leverage 20 years of remote sensing data, reanalysis products, and field observations to assess the effects of sea surface glacial meltwater on phytoplankton biomass and highlight its importance as a key environmental driver for this region’s productive ecosystem. We find a strong correlation between meltwater and phytoplankton chlorophyll-a across multiple time scales and datasets. We attribute this relationship to nutrient fertilization by glacial meltwater, with potential additional contribution from surface ocean stabilization associated with sea-ice presence. While high phytoplankton biomass typically follows prolonged winter sea-ice seasons and depends on the interplay between light and nutrient limitation, our results indicate that the positive effects of increased glacial meltwater on phytoplankton communities likely mitigate the negative impact of sea-ice loss in this region in recent years. Our findings underscore the critical need to consider glacial meltwater as a key ecological driver in polar coastal ecosystems. 

The Southern Ocean plays a vital role in global CO₂uptake, but the magnitude and even the sign of the flux remain uncertain, and the influence of phytoplankton phenology is underexplored. This study focuses on the West Antarctic Peninsula, a region experiencing rapid climate change, to examine shifts in seasonal carbon uptake. Using 20 years of in situ air‐sea CO₂flux and satellite‐derived Chlorophyll‐a, we observe that the seasonal cycles of both air‐sea CO₂flux and Chlorophyll‐a intensify poleward. The amplitude of the seasonal cycle of the non‐thermal component of surface ocean pCO₂increases with increasing latitude, while the amplitude of the thermal component remains relatively stable. Pronounced biological uptake occurs over the shelf in austral summer despite reduced CO₂solubility in warmer waters, which typically limits carbon uptake through physical processes. These findings underscore the prominence of biological mechanisms in regulating carbon fluxes in this rapidly changing region. 

Abstract. The Amundsen Sea polynya hosts intense sea ice formation, but, due to the presence of relatively warm and salty modified Circumpolar Deep Water, the cold, brine-enriched water is not typically dense enough to sink to the deep ocean. A hydrographic survey of the Dotson Ice Shelf region in the Amundsen Sea using two ocean gliders identified and characterised subsurface lenses containing water with temperatures less than −1.70 °C. These lenses, located at depths between 240 to 500 m, were colder, saltier and denser than the overlying Winter Water (WW) layer. The pH of the lenses was 7.99, lower than WW by 0.02 and the dissolved inorganic carbon concentration was higher in the lenses than WW by approximately 10 µmol kg−1. The lenses were associated with a dissolved oxygen concentration greater than surrounding water at the same depth and density due to the cold temperatures increasing O2 solubility. We hypothesise that these lenses are a product of wintertime surface cooling and brine rejection in areas with intense sea ice formation. They may form in shallow regions, potentially around the Martin Peninsula and Bear Island, where intense upper ocean heat loss occurs, and then spill off into the deeper Dotson-Getz Trough to reach their neutrally-buoyant depth. This is supported by wintertime temperature and salinity observations. This study highlights the importance of shallow parts of shelf seas for generating cold dense water masses in the warm sector of Antarctica. These lenses are widespread in the region of the Dotson-Getz Trough and have the potential to sequester carbon deeper than typical in the region, alongside cooling the water impinging on the Dotson ice shelf base. 

Abstract The mixed layer of polynyas is vital for local climate as it determines the exchange of properties and energy between ocean, sea ice, and atmosphere. However, its evolution is poorly understood, as it is controlled by complex interactions among these components, yet highly undersampled, especially outside summer. Here, we present a 2-month, high vertical-resolution, full-depth hydrographic dataset from the southeastern Amundsen Sea polynya in austral autumn (from mid-February to mid-April 2014) collected by a recovered seal tag. This novel dataset quantifies the changes in upper-ocean temperature and salinity stratification in this previously unobserved season. Our seal-tag measurements reveal that the mixed layer experiences deepening, salinification, and intense heat loss through surface fluxes. Heat and salt budgets suggest a sea ice formation rate of ∼3 cm per day. We use a one-dimensional model to reproduce the mixed layer evolution and further identify key controls on its characteristics. Our experiments with a range of reduced or amplified air–sea fluxes show that heat loss to the atmosphere and related sea ice formation are the principal determinants of stratification evolution. Additionally, our modeling demonstrates that horizontal advection is required to fully explain the mixed layer evolution, underlining the importance of the ice-covered neighboring region for determining sea ice formation rates in the Amundsen Sea polynya. Our findings suggest that the potential overestimation of sea ice production by satellite-based methods, due to the absence of oceanic heat flux, could be offset by horizontal advection inhibiting mixed layer deepening and sustaining sea ice formation. 

In the Western Antarctic Peninsula (WAP), marine plankton dynamics are tightly linked to the interannual variability in environmental conditions, including phenological shifts in sea‐ice seasonality. To explore these linkages, we use a 1‐dimensional vertical ocean‐ice‐ecosystem model (KPP‐Eco‐Ice, or KEI) that simulates physical and ecosystem conditions at a continental shelf mooring location in the Palmer Long Term Ecological Research program sampling grid. KEI allows for year‐round examination of the ecosystem in a region where in situ observations on the shelf are limited to January. Comparisons are made between seasonal sea‐ice retreat, mixed layer depth, primary productivity, and phytoplankton relative abundance, grazing, and loss rates. KEI successfully captures seasonal patterns in the WAP, demonstrating that total seasonal primary production was highest following a winter with late sea‐ice retreat. Stability in the surface mixed layer enables high photosynthetic rates by alleviating light limitation, while wind‐induced surface mixing results in lower phytoplankton production and biomass in years with early sea‐ice retreat. However, mixing reduces iron limitation in surface waters, which may influence phytoplankton species composition. Small, non‐diatom phytoplankton are better‐adapted to high light and low iron conditions, thriving longer in a year with late sea‐ice retreat and higher seasonal primary production, while larger diatoms are more abundant in the years with early sea‐ice retreat and lower seasonal production. These findings have implications for grazer populations and subsequent carbon export from the surface to depth in the WAP region. This study validates the role that sea ice plays in shaping Antarctic ecosystem dynamics. 

Satellite images from Antarctica reveal important changes in the coastal icescape (fast-ice, icebergs and ice shelves) but these yearly changes and their impacts on the coastal circulation and ice shelf basal melt rates are not represented in the Earth System Models used to project future sea level rise. The impacts of these yearly icescape changes are thus investigated using a high-resolution regional ocean-ice shelves-sea ice coupled model of the Amundsen Sea (Antarctica). A set of nine semi-idealized experiments were designed to highlight the impacts of (a) the collapse of the Thwaites Glacier Tongue, (b) the disappearance of the Bear Ridge Iceberg Chain and tabular iceberg B22, and (c) presence/absence of a fast-ice cover between Thwaites and Pine Island ice shelves, in both cold and warm background hydrological conditions. The dataset features the results of the nine experiments and reveals changes in sea ice concentrations, coastal oceanic circulation and oceanic heat supply to the ice shelf cavities, ice shelf basal melt rates, hydrological conditions, and fluxes of heat/freshwater at the sea surface. These model results are archived in self-documented NetCDF files with the appropriate metadata for each variable. The dataset includes a 'readme file' providing an overview of the archive as well as additional information regarding the model results. 

The northwestern Antarctic Peninsula is an important spawning, recruitment, and overwintering ground for Antarctic krill. The region is warming rapidly, and the current impacts of climate and environmental variability on the reproductive cycle of krill remain unclear. Here, we examine the reproductive stage of female krill in the austral winter from 2012 to 2016 in relation to climate and environmental data to assess what factors influence the timing of reproductive development. We observed significant interannual variability in the degree of maturation in female krill, ranging from 48% of female krill measured at a station in 2016 to a maximum of 94% of female krill measured at a station in 2014. On average, across all five years, three-quarters of the female krill sampled were in the stage known as previtellogenesis, the point at which the onset of sexual maturity begins. The preceding spring, summer, and autumn Southern Annular Mode and the Multivariate El Niño Index explained most of the variance in the data and indicated a strong, preconditioning storm-related effect on environmental conditions leading up to winter, affecting krill maturation status at the end of the winter season. Results from our study can be used to improve krill population models that are necessary for the management of the krill fishery and for conservation at the northwestern Antarctic Peninsula.