Polar Research Institute of China

Abstract. Improving the spatial and temporal coverage of volcanic records is essential to accurately quantify volcanic forcing and to provide reliable references for climate models validation. In this study, we present a new volcanic record derived from a 133 m ice core (DA2009) drilled at Dome A, Antarctica. Based on measurements of non-sea-salt sulfate concentrations, 95 volcanic events are identified. Using 15 volcanic age markers aligned with the West Antarctic Ice Sheet (WAIS) Divide ice core (WDC) record, the DA2009 core is dated to cover the past 3951 years, from 1951 BCE to 2000 CE. By comparing the DA2009 record with three Antarctic ice cores from WAIS Divide, Dome C and South Pole, 12 prominent volcanic events are recognized. The period between 1000 and 2000 CE exhibits the most intense volcanic activity of the past 4000 years. The mean snow accumulation rates calculated between adjacent age markers indicate a marked decline in accumulation at Dome A since the 13th century CE. This low-accumulation interval coincides with a pronounced cold phase on the East Antarctic Plateau, suggesting a potential connection between regional climate variability and local accumulation rates at Dome A.

Poleward Boundary Intensifications (PBIs) are transient auroral brightenings at the poleward edge of the auroral oval that serve as optical tracers of nightside plasma transport and energy deposition. However, their statistical properties and coupling with solar wind and geomagnetic activity remain insufficiently understanding. Using the observations from Yellow River Station auroral All-Sky Imager during 2012–2024, we identified 1,225 PBIs that were specifically associated with nightside polar cap patches touching the poleward boundary of the auroral oval. This study investigated the spatiotemporal characteristics of PBIs and their relationship with interplanetary magnetic field (IMF) conditions and geomagnetic indexes. The key findings include: (1) PBIs predominantly occur between 21 and 01 magnetic local time (MLT), with a clear pre-midnight distribution; (2) Due to the modification by IMF By, PBIs occurrence exhibits a dawn-dusk asymmetry near 23 MLT, indicating a systematic longitudinal shift of the nightside ionospheric convection; (3) relative to substorm onset, the PBIs occurrence rate peaks within the 20–40 min window thereafter. These results provide quantitative evidence of IMF By modulating the MLT distribution of PBIs and establish PBIs as optical tracers of nightside plasma transport and energy deposition.

Abstract A new Earth system reanalysis framework is being introduced consisting of the intermediate complexity coupled CESAM model together with its adjoint. The results presented are a first pilot demonstration of an Earth system reanalysis that shows the potential of such an approach to (a) improving model biases through parameter estimation and (b) accomplishing a fully coupled reanalysis over long time windows. Variational data assimilation applied to nonlinear chaotic atmospheric models is limited by predictability, and therefore restricted to short assimilation windows. Applications with ocean models, however, require much longer assimilation windows to propagate sparse data information through time and space efficiently. To overcome this contradiction we employ the adjoint method together with synchronization to atmospheric data. The first application presented requires nearly complete information on the atmospheric state for synchronization, for which it relies on European Centre for Medium‐Range Weather Forecasts Reanalysis v5 data, and a simple nudging technique to achieve synchronization. We demonstrate that, over 39 years, efficient assimilation of in‐situ and satellite ocean data and atmospheric reanalysis data is possible by adjusting the surface fluxes and internal model parameters. Given the coarse resolution of the model of , overturning and meridional transports of heat and fresh water are less realistic than previous higher resolution ocean syntheses based on the adjoint method. However, unsynchronized model runs with adjusted parameters show an improved climate and circulation consistent with the reanalysis, suggesting low initialization shocks if the reanalysis is used for initializing decadal predictions.

<strong class="journal-contentHeaderColor">Abstract.</strong> The spatial distribution of geothermal heat flow (GHF) beneath the Antarctic Ice Sheet is a major source of uncertainty in projections of ice sheet dynamics and sea-level rise. Direct measurements are sparse, necessitating robust modeling approaches. In this study, we developed a neural network framework whose architecture and hyperparameters are optimized using a particle swarm optimization (PSO) algorithm. Trained on a global heat flow compilation and a suite of geophysical datasets, our model generates a new GHF map for the entire continent. The model's accuracy in regions lacking direct measurements was confirmed through training density validation, with prediction errors constrained to within 20 %. The resulting map delineates a distinct dichotomy: East Antarctica exhibits predominantly low GHF values (&lt;60 mW m^-2) with notable exceptions of high heat flow (&gt;80 mW m^-2) in the Vostok Subglacial Highlands and Gamburtsev Subglacial Mountains. In contrast, West Antarctica is characterized by widespread high heat flow (&gt;60 mW m^-2), especially in tectonically active regions like the Transantarctic Mountains and the Amundsen Sea sector. These predictions show agreement when compared with direct borehole measurements. Our work offers a new, robust estimate of Antarctic GHF, providing a critical boundary condition for ice sheet models. We suggest that future improvements in accuracy and interpretability can be gained by assimilating more high-resolution drilling data and integrating physical constraints into the model framework.

Abstract With the rapid loss of Arctic sea ice in recent decades, the pack ice zone (PIZ) is gradually transitioning to the marginal ice zone (MIZ), but its impacts on heat exchanges within the atmosphere‐sea ice‐ocean system remain unquantified. This study identifies the transition region from PIZ to MIZ using a positive difference in MIZ occurrence frequency between 1979–2010 and 1992–2023, and compares changes in heat exchanges in this region to those over the pan Arctic Ocean. The transition from PIZ to MIZ in summer increases shortwave radiation absorption by the ice‐ocean surface (0.7 W m −2 yr −1 , P &lt; 0.05), further increasing upper ocean heat content (0.04 × 10 8 J m −2 yr −1 , P &lt; 0.05); while that in winter enhances the exchanges of longwave radiation (about 0.8 W m −2 yr −1 , P &lt; 0.05) and surface upward latent and sensible heat fluxes (0.4 and 0.5 W m −2 yr −1 , P &lt; 0.05), partly leading to an increase in 2‐m air temperature (about 0.2 K yr −1 , P &lt; 0.05), more than twice the average of the pan Arctic Ocean, although the transition region occupies less than 25% of the pan Arctic Ocean. The amplification of heat exchanges is more pronounced in the transition region from PIZ to MIZ than in the MIZ defined by ice concentration between 15% and 80%. Results highlight that the transition process from PIZ to MIZ is more critical for the thermodynamic coupling of the Arctic atmosphere‐sea ice‐ocean system, compared to changes in the location and extent of MIZ.

Atmospheric mercury depletion events (AMDEs) are a unique phenomenon in polar mercury cycling, involving intense atmospheric mercury oxidation and deposition that amplify marine mercury sinks. The Southern Ocean, a critical hotspot for environmental mercury exposure, exhibits AMDEs whose characteristics and distribution patterns remain unclear. This study presents the observational dataset of atmospheric gaseous elemental mercury (GEM) across the circum-Antarctic Southern Ocean. We observed pronounced summertime AMDEs that drove high spatial heterogeneity in circumpolar GEM distribution. By combining Generalized Additive Models (GAM) simulations with multi-platform observational evidence, we demonstrate that the Antarctic continental outflow largely shapes the circumpolar distribution of summertime AMDEs, concentrating these events within the convergence zones of katabatic winds. This work highlights the critical role of land-sea coupling effects in Antarctic atmospheric chemistry, and underscores the need to systematically assess the implications of these processes for mercury bioavailability across Southern Ocean ecosystems.

<strong class="journal-contentHeaderColor">Abstract.</strong> Transparent exopolymer particles (TEP) play a crucial role in marine carbon cycling. While phytoplankton are known to be the primary contributors to TEP, the impact of changes in phytoplankton community structure on TEP production in natural aquatic environments remains incompletely understood. This study employed multiple linear regression (MLR) modeling to quantify the contributions of two dominant phytoplankton groups, diatoms and haptophytes (primarily<em> Phaeocystis antarctica</em>), to TEP production in the surface waters of the Cosmonaut Sea, antarctica during the austral summer. Results demonstrate that in situ TEP production by each group can be estimated by scaling laboratory-derived theoretical values with an environmentally adjusted correction factor. These factors, primarily governed by phytoplankton community structure, reveal taxon-specific discrepancies between field and laboratory TEP production capacities. Notably, temperature, ammonium, and polysaccharide composition act as secondary modifiers of through indirect physiological effects. This study revealed that when the chlorophyll <em>a</em> concentration (Chl <em>a</em>) of <em>P. antarctica </em>exceeds 0.5 &mu;g/L in the Cosmonaut Sea, its TEP production capacity surpasses that of diatoms<em> </em>at equivalent biomass levels &ndash; challenging the paradigm of diatom-dominated TEP contributions. In the research area, <em>P. antarctica</em> contributed 14.6&ndash;82.5 % (mean: 48.6 &plusmn; 15.4 %) to total TEP production, while diatoms contributed 31.0&ndash;112.0 % (mean: 55.1 &plusmn; 21.2 %; values &gt;100 % reflect co-occurring group contributions). This highlights the pivotal role of <em>P. antarctica</em> in Southern Ocean carbon cycling and provides mechanistic insights for refining polar carbon budget models.

During Antarctic scientific expeditions, it is essential to ensure a stable supply of fresh water on board the polar icebreaking vessel when it docks at Zhongshan Station. The seawater desalination system and its associated batteries must operate within a temperature range of 2°C to 10°C, otherwise their performance will significantly decline. To address the issues of thermal load fluctuations and energy instability in low-temperature environments, this paper proposes a thermoelectric collaborative energy management system centered around thermal control of the desalination system. Based on meteorological data from Zhongshan Station, typical meteorological weeks are extracted using K-means clustering to establish a thermal management model for the desalination system, and a multi-source energy allocation strategy prioritizing thermal management is formulated. The system integrates wind energy, solar energy, diesel generators, and battery energy storage, achieving precise temperature control and energy efficiency optimization through dynamic scheduling. An improved particle swarm optimization algorithm is employed to perform multi-objective optimization of wind turbine, photovoltaic, and battery capacities, balancing temperature stability and fuel economy. Simulations indicate that the system can control temperature fluctuations within the desalination system within ±2°C, reduce diesel consumption by 18%-25%, and optimize energy storage configuration. This study provides a practical reference for thermal management and energy optimization of seawater desalination in polar icebreaking vessels operating in extreme environments.