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Abstract—The research was carried out on cruise 79 of the R/V Akademik Mstislav Keldysh. The variability of the chlorophyll a specific light absorption coefficient of phytoplankton and the correlation coefficient for the fluorescence intensity and chlorophyll a concentration at various optical depths under ambient light intensity and after dark adaptation was studied. It was shown that in the absence of water stratification, there was no vertical variability in the chlorophyll a specific light absorption coefficient of phytoplankton. It was found that when measuring the intensity of chlorophyll a fluorescence with a submersible sensor, without preliminary dark adaptation, a decrease in the fluorescence intensity signal in the upper layer of water was observed, which was associated with the effect of light on the fluorescence quantum yield. [ABSTRACT FROM AUTHOR]

Columnar aerosol loading and surface level atmospheric black carbon (BC) concentration over the Antarctic are examined using the measurements carried out at the Indian Antarctic stations, Bharati and Maitri, as part of the 36th Indian Scientific Expedition (2016–17) to Antarctica (ISEA). The mean aerosol optical depth (AOD) at wavelength 500 nm at Bharati is observed to be 0.101 ± 0.01, whereas that at Maitri is 0.047 ± 0.003. Columnar aerosol loading at Bharati is found to be more than two times that measured at Maitri. The daily mean surface level atmospheric BC concentration at Bharati in the Austral summer from December 2016 to February 2017 is 24 ± 16.5 ngm−3. Comparison of this measurement with earlier reported values over the same region indicates an increase in surface-level atmospheric BC concentration. Long-term (1997–2017) trend analysis carried out using MERRA-2 aerosol reanalysis data also corroborates the increasing trend in AOD and BC concentration with 0.005 (0.007) yr−1 and 0.3 (0.27) ngm−3 yr−1 over Bharati (Maitri) respectively. Spectral variations of aerosol absorption coefficients show absorption angstrom exponent values (AAE) close to unity (1.096 ± 0.029), which indicates that fossil fuel emission is the primary source of absorbing aerosols over this region. During the study period, air mass back trajectory analysis indicates that the sources are from the Antarctic, coastal, and southern ocean regions with no long-range transport from other continents in the southern hemisphere. [ABSTRACT FROM AUTHOR]

Dissolved organic carbon (DOC) is the largest organic carbon pool in the ocean, and is the most active component in respect to the ocean carbon cycling. However, its study in Antarctica has been limited due to challenges associated with sample collection. In this study, we conduct an investigation on the chromophoric dissolved organic matter (CDOM) in a highly productive Amundsen Sea Polynya (ASP), where phytoplankton blooms occur annually during the austral summer, serving as the primary source of DOC and CDOM. The relative abundances of CDOM, as indicated by the absorption coefficient at 254 nm (a 254), exhibit significant variability, reaching up to 6.34 m−1. Four fluorescent components, including two humic-like components (C1 and C4) and two protein-like components (C2 and C3), are identified by excitation emission matrix coupled with parallel factor analysis (EEM-PARAFAC). Our findings suggest that heterotrophic metabolism primarily contributes to the formation of humic-like fluorescent components and DOC removal. Water mass, solar radiation, primary productivity as well as microbial degradation are identified as the main factors influencing CDOM dynamics in ASP. This study bears significant implications for advancing our understandings of the CDOM and DOC dynamics in the coastal polynyas of Antarctica, thus facilitating improved evaluation of carbon cycle in the Antarctica. • The relative abundances of CDOM as indicated by the absorption coefficient at 254 nm (a 254) are highly variable. • Two humic-like components (C1 and C4) and two protein-like components (C2 and C3) are identified by EEM-PARAFAC. • Heterotrophic metabolism primarily contributes to the formation of humic-like fluorescent components and the DOC removal. • The CDOM dynamics in the ASP are influenced by water mass, solar radiation, primary productivity, and microbial degradation. [ABSTRACT FROM AUTHOR]

Microalgae use Antarctic sea ice as habitat and accumulate in spring, leading to significant early-season production in Southern Ocean ecosystems. As key contributors to the marine food web and carbon fixation within the Antarctic pack-ice zone, ice algae depend on the light environment and their adaptability to irradiance extremes. This study examines spectral ice algal and non-algal particulate absorption coefficients, pigments, and community composition in pack-ice cores sampled off East Antarctica and in the Weddell Sea during the winter-spring transitions in 2012 and 2013, respectively. Our results show that ice algae dominated particulate absorption in pack ice in both regions. From high- to low-light exposure in both East Antarctica and Weddell Sea, biomass-specific absorption decreased, suggesting strong pigment packaging with depth towards the ice-water interface. Ice algae also showed increased production of photoprotective pigments in the surface in comparison to the bottom of the sea ice, with flagellates being more dominant in the surface ice sections. Our results indicate species-specific light-acclimation and photoprotection through the ice profiles, and highlight the role of light conditions in influencing pigment production and shifts in community composition. • Ice algae implement photoprotective pigments early in the season. • Strong pigment packaging observed towards the ice-water interface. • Xanthophyll cycle plays a significant role in photoprotection of Antarctic ice algae. [ABSTRACT FROM AUTHOR]

Ice is a highly transparent material in the visible. According to the most widely used database (IA2008; Warren and Brandt, 2008), the ice absorption coefficient reaches values lower than 10-3 m-1 around 400 nm. These values were obtained from a vertical profile of spectral radiance measured in a single snow layer at Dome C in Antarctica. We reproduced this experiment using an optical fiber inserted in the snow to record 56 profiles from which 70 homogeneous layers were identified. Applying the same estimation method on every layer yields 70 ice absorption spectra. They present a significant variability but absorption coefficients are overall larger than IA2008 by 1 order of magnitude at 400-450 nm. We devised another estimation method based on Bayesian inference that treats all the profiles simultaneously. It reduces the statistical variability and confirms the higher absorption, around 2x10-2 m-1 near the minimum at 440 nm. We explore potential instrumental artifacts by developing a 3-D radiative transfer model able to explicitly account for the presence of the fiber in the snow. The simulation shows that the radiance profile is indeed perturbed by the fiber intrusion, but the error on the ice absorption estimate is not larger than a factor of 2. This is insufficient to explain the difference between our new estimate and IA2008. The same conclusion applies regarding the plausible contamination by black carbon or dust, concentrations reported in the literature are insufficient. Considering the large number of profiles acquired for this study and other estimates from the Antarctic Muon and Neutrino Detector Array (AMANDA), we nevertheless estimate that ice absorption values around 10-2 m-1 at the minimum are more likely than under 10-3 m-1. A new estimate in the range 400-600 nm is provided for future modeling of snow, cloud, and sea-ice optical properties. Most importantly, we recommend that modeling studies take into account the large uncertainty of the ice absorption coefficient in the visible and that future estimations of the ice absorption coefficient should also thoroughly account for the impact of the measurement method. [ABSTRACT FROM AUTHOR]