Oceanographic Variability induced by Tides, the Intraseasonal Cycle and Warm Subsurface Water intrusions in Maxwell Bay, King George Island (West-Antarctica)

Short-term glacier area changes, glacier geometry dependence, and regional climatic variations forcing, King George Island, Antarctica

This study investigates the transient snowline (TSL) altitude for summer 2020, as well as glacial area loss in King George Island Icefields since 1988 using Sentinel-1 and 2 and Landsat Thematic Mapper (TM) imagery. Trends and anomalies in atmospheric temperature, U-wind, and V-wind were examined using ERA5 solutions. Results show the wet-snow zone corresponds to values of ≤ -13dB, and 44.3% of the glacial area is located above the TSL (≥ 300 m). Glacial area for 2020 is 999.95 km², and losses in the period represent 104.9 km² (error <1%) - a retreat of 3.17 km² / year. Glaciers in Keller Peninsula and Bellingshausen Dome lost the most area (28% and 17%, respectively) and did not have a TSL in 2020; followed by Warszawa (15%), Kraków (13%), and Eastern (10%), where the TSL was verified. Percentage area loss values increased with decreases in dimensions, area above TSL, and maximum elevation. Calving glaciers with ice-flow toward deeper and steeper submarine sectors (Bransfield Strait) exhibited greater glacier variations. The trend in warming atmospheric temperature was greater in the Bransfield Strait than in the Drake Passage. TSL and retreat difference between glaciers were influenced by climatic and ocean input, as well as multiple environmental factors.

Seasonal variation of inorganic carbon parameters and air-sea exchange of CO2 in Marian Cove, King George Island, Western Antarctic Peninsula

Inorganic carbon parameters were observed in Marian Cove, King George Island, Western Antarctic Peninsula, to assess the impact of the Antarctic coastal regions on air-sea CO₂ exchange. The variations in total alkalinity (TA) and dissolved inorganic carbon (DIC) were caused by ice melting, formation, and biological activities. The net annual air-sea CO₂ flux (5.6 ± 11.8 mmol m^-2 d^-1) indicated that Marian Cove was a CO₂ source in the atmosphere, suggesting the opposite role of the Antarctic coastal regions to the Southern Ocean in CO₂ flux estimates. Finally, this study identified the controlling factors of the annual variation of TA and DIC for the first time through direct field observations in King George Island. This study indicated that Antarctic coastal regions can act as a CO₂ source to the atmosphere. Thus, further investigations and continuous monitoring are required in the coastal areas to improve our understanding of global carbon cycles.

Modeling of microplastics discharged from a station in Marian Cove, West Antarctica

Conspicuous amounts of microplastics have been discovered in bays near Antarctic research stations, including several types of microplastics in the water columns of Marian Cove. This study proposes an efficient operating strategy for a wastewater treatment plant to mitigate microplastic accumulations in the bay by assessing the transport and accumulation of microplastics using numerical simulations. Hence, microplastic particles were classified into falling and rising particles to find a mechanism for their vertical migration. The results showed that the characteristics of the vertical migration of the particles and flow conditions critically determined their traveling distance and accumulation location. Further, the amount of microplastics accumulated in the cove depended on the release time of the wastewater during the tidal cycle. Wastewater treatment plants need to be improved to reduce microplastics. However, it is necessary to adjust the location and schedule for releasing them into Marian Cove.

Biogeography of Southern Ocean Active Prokaryotic Communities Over a Large Spatial Scale

The activity of marine microorganisms depends on community composition, yet, in some oceans, less is known about the environmental and ecological processes that structure their distribution. The objective of this study was to test the effect of geographical distance and environmental parameters on prokaryotic community structure in the Southern Ocean (SO). We described the total (16S rRNA gene) and the active fraction (16S rRNA-based) of surface microbial communities over a ~6,500 km longitudinal transect in the SO. We found that the community composition of the total fraction was different from the active fraction across the zones investigated. In addition, higher α-diversity and stronger species turnover were displayed in the active community compared to the total community. Oceanospirillales, Alteromonadales, Rhodobacterales, and Flavobacteriales dominated the composition of the bacterioplankton communities; however, there were marked differences at the order level. Temperature, salinity, silicic acid, particulate organic nitrogen, and particulate organic carbon correlated with the composition of bacterioplankton communities. A strong distance–decay pattern between closer and distant communities was observed. We hypothesize that it was related to the different oceanic fronts present in the Antarctic Circumpolar Current. Our findings contribute to a better understanding of the complex arrangement that shapes the structure of bacterioplankton communities in the SO.

Anthropogenic microfibres flux in an Antarctic coastal ecosystem: The tip of an iceberg?

This study describes the occurrence of anthropogenic microfibres (AMFs) found in sediment trap samples collected at 25 m water depth in an Antarctic fjord (Potter Cove, King George/25 de Mayo Island) from 2012 to 2015. During visual sorting of samples, AMFs were detected and described, and a subset was confirmed, via FTIR (Fourier transform infrared) spectroscopy, as semi-synthetic cellulosic and polyacrylonitrile polymers. Estimated flux of AMF varied from 115 to 152,750 microfibres m^-2 throughout the studied period, with sizes ranging from 10 to 450 μm in length. Maximum AMFs fluxes occurred in summer months. Sediment traps allowed detecting temporal patterns of small (μm) AMFs, usually undersampled with nets or sieves, providing a new insight into microplastic pollution in Antarctica and its relation to environmental conditions.

Spatial distribution of microzooplankton in different areas of the northern Antarctic Peninsula region, with an emphasis on tintinnids

The Western Antarctic Peninsula (WAP) is experiencing rapid climate warming, resulting in affecting the marine food web. To investigate the microzooplankton spatial distribution and to assess how climate change could affect the tintinnids community, sea water samples were collected during late summer 2018 at 19 stations in three different areas: Deception Island, Elephant Island and Antarctic Sound. The microzooplankton community comprised mainly tintinnids, aloricate ciliates, heterotrophic dinoflagellates and micrometazoans. Microzooplankton abundance varied between 3 and 109 ind. L−1 and biomass ranged from 0.009 to 2.55 µg C L−1. Significant differences in terms of abundance and taxonomic composition of microzooplankton were found among the three sampling areas. Deception Island area showed 44% of tintinnids and the rest were heterotrophic dinoflagellate, aloricate ciliates and micrometazoans. In Elephant Island and Antarctic Sound areas, tintinnids reached, respectively, 73% and 83% of the microzooplankton composition, with all the other groups varying between 20 and 30%. Tintinnids were the most representative group in the area, with the species Codonellopsis balechi, Codonellopsis glacialis, Cymatocylis convallaria and Cymatocylis drygalskii. The highest amounts of tintinnids were found at the surface and 100 m depth. The above mentioned species may be considered key species for the WAP and therefore they can be used to track environmental and hydrographical changes in the area. In late summer, microzooplankton presented low abundances and biomass, nevertheless they represented an important fraction of the planktonic community in the area.

Proteorhodopsin Phototrophy in Antarctic Coastal Waters

Microbial proton-pumping rhodopsins are considered the simplest strategy among phototrophs to conserve energy from light. Proteorhodopsins are the most studied rhodopsins thus far because of their ubiquitous presence in the ocean, except in Antarctica, where they remain understudied. We analyzed proteorhodopsin abundance and transcriptional activity in the Western Antarctic coastal seawaters. Combining quantitative PCR (qPCR) and metagenomics, the relative abundance of proteorhodopsin-bearing bacteria accounted on average for 17, 3.5, and 29.7% of the bacterial community in Chile Bay (South Shetland Islands) during 2014, 2016, and 2017 summer-autumn, respectively. The abundance of proteorhodopsin-bearing bacteria changed in relation to environmental conditions such as chlorophyll a and temperature. Alphaproteobacteria, Gammaproteobacteria, and Flavobacteriia were the main bacteria that transcribed the proteorhodopsin gene during day and night. Although green light-absorbing proteorhodopsin genes were more abundant than blue-absorbing ones, the latter were transcribed more intensely, resulting in >50% of the proteorhodopsin transcripts during the day and night. Flavobacteriia were the most abundant proteorhodopsin-bearing bacteria in the metagenomes; however, Alphaproteobacteria and Gammaproteobacteria were more represented in the metatranscriptomes, with qPCR quantification suggesting the dominance of the active SAR11 clade. Our results show that proteorhodopsin-bearing bacteria are prevalent in Antarctic coastal waters in late austral summer and early autumn, and their ecological relevance needs to be elucidated to better understand how sunlight energy is used in this marine ecosystem. IMPORTANCE Proteorhodopsin-bearing microorganisms in the Southern Ocean have been overlooked since their discovery in 2000. The present study identify taxonomy and quantify the relative abundance of proteorhodopsin-bearing bacteria and proteorhodopsin gene transcription in the West Antarctic Peninsula's coastal waters. This information is crucial to understand better how sunlight enters this marine environment through alternative ways unrelated to chlorophyll-based strategies. The relative abundance of proteorhodopsin-bearing bacteria seems to be related to environmental parameters (e.g., chlorophyll a, temperature) that change yearly at the coastal water of the West Antarctic Peninsula during the austral late summers and early autumns. Proteorhodopsin-bearing bacteria from Antarctic coastal waters are potentially able to exploit both the green and blue spectrum of sunlight and are a prevalent group during the summer in this polar environment.

Interrelation of quality parameters of surface waters in five tidewater glacier coves of King George Island, Antarctica

For further understanding of glacial meltwater's (GMW) impacts on marine environments, five coves adjacent to diverse glaciers of King George Island, Antarctica were investigated through surface measurements of water quality parameters. Measurements were conducted 49 times during January, February and March of 2019, with sampling performed in unprecedently close proximity to glacial fronts (<50 m distance from glacier termini in each cove) to create a unique dataset. Four out of five of the coves were inspected through vertical profiling to show water-column stratification. The findings showed synchronized GMW influence causing decreases of salinity, temperature, and dissolved organic matter contents, combined with increased pH, turbidity, and dissolved oxygen values. GMW presence was most correlated with dissolved organic matter content (93% of the cases >0.5 correlation noted with either turbidity or salinity) and least correlated with water temperature (from 22% to 77% of the cases with >0.5 correlation, dependent on the cove). In contrast to previous studies, the pH values of seawater infused with GMW were higher than those of the surrounding water. GMW was shown to stay in the boundary surface layer of the water column. Phytoplankton pigment quantities depending on the localization, time and distance from the glacial termini presented varied response to GMW (positive, negative or ambivalent with hotspots of simultaneous high GMW and phytoplankton quantities). The positive response to glacial water input was more often noted in measurements of phycoerythrin (from 0 to 80% of the cases depending on the cove) rather than chlorophyll A (from 0 to 25%) and maximum quantities of both biological pigments were found at a depth of approximately 5-10 m.

Biodiversity of an Antarctic rocky subtidal community and its relationship with glacier meltdown processes

Glacier meltdown is a major environmental response to climate change in the West Antarctic Peninsula. Yet, the consequences of this process for local biodiversity are still not well understood. Here, we analyse the diversity and structure of a species-rich marine subtidal macrobenthic community (consumers and primary producers) across two abiotic environmental gradients defined by the distance from a glacier (several km) and depth (between 5 and 20 m depth) in Fildes Bay, King George Island. The analysis of spatially extensive records of seawater turbidity, high-frequency temperature and salinity data, and suction dredge samples of macrobenthic organisms revealed non-linear and functional group-dependent associations between biodiversity, glacier influence, and depth. Turbidity peaked in shallow waters and in the nearby of the glacier. Temperature and salinity, on the other hand, slightly decreased in the proximity of the glacier relative to reference sites. According to the spatial pattern in turbidity, species richness of consumers was lowest in shallow waters and near to the glacier. Also, Shannon's diversity of consumers significantly decreased in the nearby of glacier across depths. Moreover, the spatial variation in community structure of consumers and primary producers depended on both glacier distance and depth. These results suggest that glacier melting can have significant effects on diversity and community structure. Therefore, the accelerated glacier meltdown may have major consequences for the biodiversity in this ecosystem.