The sub‐Antarctic waters of South Georgia Island (Islas Georgias del Sur, SG/IG) are a regularly visited feeding ground for southern right whales ( Eubalaena australis , SRW) in the southwest Atlantic. Satellite telemetry and photo‐identification records were compared to better understand the role of SG/IG in the SRW migratory network. We present the first insights from SRW satellite‐tracked from the SG/IG feeding ground, habitat use patterns in the Scotia Arc, and movements to Antarctic habitats. Photo‐identification comparisons to calving and feeding areas across the South Atlantic and a review of sightings of cetaceans reported from Bird Island (west of SG/IG) since 1979 illuminate long‐term habitat use patterns in SG/IG. We present the first recorded migratory movement between SG/IG and multiple countries: Argentina, Uruguay, and Brazil. Photo‐identification (1) linked SG/IG to a female SRW with a long‐term sighting history in Brazil, and (2) provided the first match between SG/IG and the western Antarctic Peninsula, suggesting the latter could extend the feeding area for southwest Atlantic SRW. Satellite tracking and opportunistic sightings suggest that shelf and coastal waters west of SG/IG represent an important multi‐season SRW feeding habitat and add to our overall understanding of habitats and ranges occupied by recovering southwest Atlantic SRW.
Ocean iron fertilization (OIF) aims to remove carbon dioxide (CO2) from the atmosphere by stimulating phytoplankton carbon‐fixation and subsequent deep ocean carbon sequestration in iron‐limited oceanic regions. Transdisciplinary assessments of OIF have revealed overwhelming challenges around the detection and verification of carbon sequestration and wide‐ranging environmental side‐effects, thereby dampening enthusiasm for OIF. Here, we utilize five requirements that strongly influence whether OIF can lead to atmospheric CO2 removal (CDR): The requirement (a) to use preformed nutrients from the lower overturning circulation cell; (b) for prevailing iron‐limitation; (c) for sufficient underwater light for photosynthesis; (d) for efficient carbon sequestration; (e) for sufficient air‐sea CO2 transfer. We systematically evaluate these requirements using observational, experimental, and numerical data in an “informed back‐of‐the‐envelope approach” to generate circumpolar maps of OIF (cost‐)efficiency south of 60°S. Results suggest that (cost‐)efficient CDR is restricted to locations on the Antarctic Shelf. Here, CDR costs can be <100 US$/tonne CO2 while they are mainly >>1,000 US$/tonne CO2 in offshore regions of the Southern Ocean, where mesoscale OIF experiments have previously been conducted. However, sensitivity analyses underscore that (cost‐)efficiency is in all cases associated with large variability and are thus difficult to predict, which reflects our insufficient understanding of the relevant biogeochemical and physical processes. While OIF implementation on Antarctic shelves appears most (cost‐)efficient, it raises legal questions because regions close to Antarctica fall under three overlapping layers of international law. Furthermore, the constraints set by (cost‐)efficiency reduce the area suitable for OIF, thereby likely reducing its maximum CDR potential.
Between March 15-19, 2022, East Antarctica experienced an exceptional heatwave with widespread 30-40° C temperature anomalies across the ice sheet. In Part I, we assessed the meteorological drivers that generated an intense atmospheric river (AR) which caused these record-shattering temperature anomalies. Here in Part II, we continue our large, collaborative study by analyzing the widespread and diverse impacts driven by the AR landfall. These impacts included widespread rain and surface melt which was recorded along coastal areas, but this was outweighed by widespread, high snowfall accumulations resulting in a largely positive surface mass balance contribution to the East Antarctic region. An analysis of the surface energy budget indicated that widespread downward longwave radiation anomalies caused by large cloud-liquid water contents along with some scattered solar radiation produced intense surface warming. Isotope measurements of the moisture were highly elevated, likely imprinting a strong signal for past climate reconstructions. The AR event attenuated cosmic ray measurements at Concordia, something previously never observed. Finally, an extratropical cyclone west of the AR landfall likely triggered the final collapse of the critically unstable Conger Ice Shelf while further reducing an already record low sea-ice extent.
Between March 15-19, 2022, East Antarctica experienced an exceptional heatwave with widespread 30-40° C temperature anomalies across the ice sheet. This record-shattering event saw numerous monthly temperature records being broken including a new all-time temperature record of -9.4° C on March 18 at Concordia Station despite March typically being a transition month to the Antarctic coreless winter. The driver for these temperature extremes was an intense atmospheric river advecting subtropical/mid-latitude heat and moisture deep into the Antarctic interior. The scope of the temperature records spurred a large, diverse collaborative effort to study the heatwave’s meteorological drivers, impacts, and historical climate context. Here we focus on describing those temperature records along with the intricate meteorological drivers that led to the most intense atmospheric river observed over East Antarctica. These efforts describe the Rossby wave activity forced from intense tropical convection over the Indian Ocean. This led to an atmospheric river and warm conveyor belt intensification near the coastline which reinforced atmospheric blocking deep into East Antarctica. The resulting moisture flux and upper-level warm air advection eroded the typical surface temperature inversions over the ice sheet. At the peak of the heatwave, an area of 3.3 million km2 in East Antarctica exceeded previous March monthly temperature records. Despite a temperature anomaly return time of about one hundred years, a closer recurrence of such an event is possible under future climate projections. In a subsequent manuscript, we describe the various impacts this extreme event had on the East Antarctic cryosphere.
The Southern Ocean surrounding Antarctica harbours some of the most pristine marine environments remaining, but is increasingly vulnerable to anthropogenic pressures, climate change, and invasion by non-native species. Monitoring biotic responses to cumulative impacts requires spatiotemporal baselines and ongoing monitoring - traditionally, this has been obtained by continuous plankton recorder (CPR) surveys. Here, we conduct a 3000 nautical mile environmental DNA (eDNA) transect from Hobart (Australia) to Davis Station (Antarctica). We evaluate eDNA sampling strategies for long-term open ocean biomonitoring by comparing two water volume and filter pore size combinations: large (12 L with 20 μm) and small (2 L with 0.45 μm). Employing a broad COI metabarcoding assay, we found the large sample/pore combination was better suited to open-ocean monitoring, detecting more target DNA and rare or low abundance species. Comparisons with four simultaneously conducted CPR transects revealed that eDNA detections were more diverse than CPR, with 7 (4 unique) and 4 (1 unique) phyla detections respectively. While both methods effectively delineated biodiversity patterns across the Southern Ocean, eDNA enables surveys in the presence of sea-ice where CPR cannot be conducted. Accordingly, 16 species of concern were detected along the transect using eDNA, notably in the Antarctic region (south of 60°S). These were largely attributed to hull biofouling, a recognized pathway for marine introductions into Antarctica. In a warming Southern Ocean, continued biomonitoring is vital for conserving Antarctic ecosystems. We advocate for the long-term implementation of eDNA metabarcoding alongside CPR surveys to facilitate ecosystem-based management of these vulnerable environments.
There are many advantages to transitioning from conducting marine wildlife surveys via human observers onboard light-aircraft, to capturing aerial imagery using drones. However, it is important to maintain the validity of long-term data series whilst transitioning from observer to imagery surveys. We need to understand how the detection rates of target species in images compare to those collected from observers in piloted aircraft, and the factors influencing detection rates from each platform. We conducted trial ScanEagle drone surveys of dugongs in Shark Bay, Western Australia, covering the full extent of the drone’s range (∼100 km), concurrently with observer surveys, with the drone flying above or just behind the piloted aircraft. We aimed to test the assumption that drone imagery could provide comparable detection rates of dugongs to human observers when influenced by same environmental conditions. Overall, the dugong sighting rate (i.e., count of individual dugongs) was 1.3 (95% CI [0.98–1.84]) times higher from the drone images than from the observers. The group sighting rate was similar for the two platforms, however the group sizes detected within the drone images were significantly larger than those recorded by the observers, which explained the overall difference in sighting rates. Cloud cover appeared to be the only covariate affecting the two platforms differently; the incidence of cloud cover resulted in smaller group sizes being detected by both platforms, but the observer group sizes dropped much more dramatically (by 71% (95% CI [31–88]) compared to no cloud) than the group sizes detected in the drone images (14% (95% CI [−28–57])). Water visibility and the Beaufort sea state also affected dugong counts and group sizes, but in the same way for both platforms. This is the first direct simultaneous comparison between sightings from observers in piloted aircraft and a drone and demonstrates the potential for drone surveys over a large spatial-scale.
Aquatic ectotherms often attain smaller body sizes at higher temperatures. By analysing ~15,000 coastal-reef fish surveys across a 15oC spatial sea surface temperature (SST) gradient, we found that the mean length of fish length in communities decreases by ~5% for each 1oC temperature increase across space. This equated to a 50% decrease in mean length from 14 to 29oC mean annual SST. We found that trophic guild composition shifts from domination by herbivores and planktivores in the tropics, to invertivores and piscivores in cooler waters. By investigating the contribution of trophic composition to community-level mean length, we show ~25% of temperature-related changes could be attributed to trophic composition at the warmest sites, but <1% at colder temperatures. Our findings suggest that small changes in temperature will lead to large changes in fish community body sizes, driven both by community trophic composition in warm waters and mean sizes within trophic guilds.
Due to its persistence and potential ecological and health impacts, mercury (Hg) is a global pollutant of major concern that may reach high concentrations even in remote polar oceans. In contrast to the Arctic Ocean, studies documenting Hg contamination in the Southern Ocean are spatially restricted and large-scale monitoring is needed. Here, we present the first circumpolar assessment of Hg contamination in Antarctic marine ecosystems. Specifically, the Adélie penguin (Pygoscelis adeliae) was used as a bioindicator species, to examine regional variation across 24 colonies distributed across the entire Antarctic continent. Mercury was measured on body feathers collected from both adults (n = 485) and chicks (n = 48) between 2005 and 2021. Because penguins’ diet represents the dominant source of Hg, feather δ13C and δ15N values were measured as proxies of feeding habitat and trophic position. As expected, chicks had lower Hg concentrations (mean ± SD: 0.22 ± 0.08 μg·g‒1) than adults (0.49 ± 0.23 μg·g‒1), likely because of their shorter bioaccumulation period. In adults, spatial variation in feather Hg concentrations was driven by both trophic ecology and colony location. The highest Hg concentrations were observed in the Ross Sea, possibly because of a higher consumption of fish in the diet compared to other sites (krill-dominated diet). Such large-scale assessments are critical to assess the effectiveness of the Minamata Convention on Mercury. Owing to their circumpolar distribution and their ecological role in Antarctic marine ecosystems, Adélie penguins could be valuable bioindicators for tracking spatial and temporal trends of Hg across Antarctic waters in the future.
Lanternfishes (Myctophidae) are key components of mesopelagic fish communities globally. In the Southern Ocean, incomplete information on myctophid diets limits our understanding of their energetics, interactions and wider ecosystem impact. Traditional microscopic methods of diet analysis have relatively coarse prey resolution and possible taxonomic and observer biases. DNA metabarcode sequencing promises higher taxonomic and temporal resolution, but uncertainty remains in comparing this is with microscopy-based analyses. Here, we applied 18S DNA metabarcode sequencing to stomach contents from twenty Electrona antarctica individuals which had previously been examined via microscopic analysis. Across all fish, crustacean and gastropod taxa dominated the prey identified via both methods, with broad agreement between methods on the relative abundance of different prey items. DNA metabarcode sequencing recovered greater taxonomic diversity and resolution, particularly for soft-bodied prey items and small crustaceans. DNA sequencing results also more clearly differentiated diet between individuals collected from different environments. Overall, our findings illustrate how DNA based methods are complementary to, and consistent with, traditional methods and can provide additional, high-resolution data on a range of trophic interactions.
The first year of life is critical for large mammals to acquire foraging and predator avoidance skills. Southern elephant seal (Mirounga leonina) pups wean at approximately three weeks of age and depart on their first foraging trips in midsummer, typically remaining at sea for three to four months before returning to their natal islands. We describe the foraging trips (n = 29) of 16 underyearling southern elephant seals from sub-Antarctic Marion Island and compare these with trips (n = 152) of 94 older seals from the same population. While subadults (prebreeding age) and adult females (breeding age) displayed directional travel, underyearlings traveled in multiple directions from the island with no evidence of repeatability of travel directions within or between individuals and years. Maiden trips took longer to complete than subsequent trips during the first year of life, but we found no evidence for significant changes in other track metrics between the first three foraging trips. The comparatively inconsistent movement patterns of underyearlings suggest that foraging strategies of individuals are influenced by their learning and/or success during the first year of life and that individual level consistency in successful foraging strategies only become apparent in subsequent years.
Predicting species survival in the face of climate change requires understanding the drivers that influence their distribution. Emperor penguins ( Aptenodytes forsteri ) incubate and rear chicks on landfast sea ice, whose extent, dynamics, and quality are expected to vary substantially due to climate change. Until recently, this species’ continent-wide observations were scarce, and knowledge on their distribution and habitat limited. Advances in satellite imagery now allow their observation and characterization of habitats across Antarctica at high resolution. Using circumpolar high-resolution satellite images, unique fast ice metrics, and geographic and biological factors, we identified diverse penguin habitats across the continent, with no significant difference between areas with penguins or not. There is a clear geographic partitioning of colonies with respect to their defining habitat characteristics, indicating possible behavioral plasticity among different metapopulations. This coincides with geographic structures found in previous genetic studies. Given projections of quasi-extinction for this species in 2100, this study provides essential information for conservation measures.
The sponge microbiome underpins host function through provision and recycling of essential nutrients in a nutrient poor environment. Genomic data suggest that carbohydrate degradation, carbon fixation, nitrogen metabolism, sulphur metabolism and supplementation of B‐vitamins are central microbial functions. However, validation beyond the genomic potential of sponge symbiont pathways is rarely explored. To evaluate metagenomic predictions, we sequenced the metagenomes and metatranscriptomes of three common coral reef sponges: Ircinia ramosa , Ircinia microconulosa and Phyllospongia foliascens . Multiple carbohydrate active enzymes were expressed by Poribacteria, Bacteroidota and Cyanobacteria symbionts, suggesting these lineages have a central role in assimilating dissolved organic matter. Expression of entire pathways for carbon fixation and multiple sulphur compound transformations were observed in all sponges. Gene expression for anaerobic nitrogen metabolism (denitrification and nitrate reduction) were more common than aerobic metabolism (nitrification), where only the I. ramosa microbiome expressed the nitrification pathway. Finally, while expression of the biosynthetic pathways for B‐vitamins was common, the expression of additional transporter genes was far more limited. Overall, we highlight consistencies and disparities between metagenomic and metatranscriptomic results when inferring microbial activity, while uncovering new microbial taxa that contribute to the health of their sponge host via nutrient exchange.
We present a new global oxygen atlas. This atlas uses all of the available full water column profiles of oxygen, salinity, and temperature available as part of the World Ocean Database released in 2018. Instead of optimal interpolation, we use the Data Interpolating Variational Analysis (DIVA) approach to map the available profiles onto 108 depth levels between the surface and 6800 m, covering more than 99% of ocean volume. This 1/2° × 1/2° atlas covers the period 1955–2018 in 1-yr intervals. The DIVA method has significant benefits over traditional optimal interpolation. It allows the explicit inclusion of advection and boundary constraints, thus offering improvements in the representations of oxygen, salinity, and temperature in regions of strong flow and near coastal boundaries. We demonstrate these benefits of this mapping approach with some examples from this atlas. We can explore the regional and temporal variations of oxygen in the global oceans. Preliminary analyses confirm earlier analyses that the oxygen minimum zone in the eastern Pacific Ocean has expanded and intensified. Oxygen inventory changes between 1970 and 2010 are assessed and compared against prior studies. We find that the full ocean oxygen inventory decreased by 0.84% ± 0.42%. For this period, temperature-driven solubility changes explain about 21% of the oxygen decline over the full water column; in the upper 100 m, solubility changes can explain all of the oxygen decrease; for the 100–600 m depth range, it can explain only 29%, 19% between 600 and 1000 m, and just 11% in the deep ocean. Significance Statement The purpose of this study is to create a new oxygen atlas of the world’s oceans using a technique that better represents the effects of ocean currents and topographic boundaries, and to investigate how oxygen in the ocean has changed over recent decades. We find the total quantity of oxygen in the world’s oceans has decreased by 0.84% since 1970, similar to previous studies. We also examine how much of this change can be explained by changes in water temperature; we find that this can explain all the changes in the upper 100 m but only 21% of the oxygen decline over the whole water column.
Microbes play a critical role in the development and health of marine invertebrates, though microbial dynamics across life stages and host generations remain poorly understood in most reef species, especially in the context of climate change. Here, we use a 4‐year multigenerational experiment to explore microbe–host interactions under the Intergovernmental Panel on Climate Change (IPCC)‐forecast climate scenarios in the rock‐boring tropical urchin Echinometra sp. A . Adult urchins (F 0 ) were exposed for 18 months to increased temperature and p CO 2 levels predicted for years 2050 and 2100 under RCP 8.5, a period which encompassed spawning. After rearing F 1 offspring for a further 2 years, spawning was induced, and F 2 larvae were raised under current day and 2100 conditions. Cross‐generational climate effects were also explored in the microbiome of F 1 offspring through a transplant experiment. Using 16S rRNA gene sequence analysis, we determined that each life stage and generation was associated with a distinct microbiome, with higher microbial diversity observed in juveniles compared to larval stages. Although life‐stage specificity was conserved under climate conditions projected for 2050 and 2100, we observed changes in the urchin microbial community structure within life stages. Furthermore, we detected a climate‐mediated parental effect when juveniles were transplanted among climate treatments, with the parental climate treatment influencing the offspring microbiome. Our findings reveal a potential for cross‐generational impacts of climate change on the microbiome of a tropical invertebrate species.
Antarctic precipitation remains poorly characterised and understood, especially within the boundary layer. This is due in part to a still‐limited amount of surface‐based remote sensing observations. A suite of cloud and precipitation remote‐sensing instruments including a W‐band cloud radar and a K‐band Micro Rain Radar (MRR) were used to characterise snowfall over Davis (69°S, 78°E). Surface snowfall events occurred when boundary layer wind speeds were weaker, temperatures were warmer, and relative humidity over ice higher than when virga were present. The presence of virga is associated with Föhn winds due to the location of Davis in the lee of an ice ridgeline. Dual wavelength ratio values from the summer indicate particle aggregation at temperatures of −14°C to −10°C, consistent with observations made elsewhere, including in the Arctic. Riming frequency increases for temperatures above −10°C and reaches 6.5% at −3°C. No temperature dependence of rime mass fraction was found. Sublimation of snowfall mass aloft was 50% between the snow peak at 1.2 km and 205 m altitude, which occurs within CloudSat’s ‘blind zone’. Given the common prevailing wind direction and numerous ice ridgelines along much of the East Antarctic coastline, these Davis results can be used as a basis to further understand snowfall across the Antarctic region.
Improving our understanding of the effects of satellite tags on large whales is a critical step in ongoing tag development to minimise potential health effects whilst addressing important research questions that enhance conservation management policy. In 2014, satellite tags were deployed on 9 female southern right whales Eubalaena australis accompanied by a calf off Australia. Photo-identification resights (n = 48) of 4 photo-identified individuals were recorded 1 to 2894 d (1-8 yr) post-tagging. Short-term (<22 d) effects observed included localised and regional swelling, depression at the tag site, blubber extrusion, skin loss and pigmentation colour change. Broad swelling observable from lateral but not aerial imagery (~1.2 m diameter or ~9% of body length) and depression at the tag site persisted up to 1446 d post-tagging for 1 individual, indicating a persistent foreign-body response or infection. Two tagged individuals returned 4 yr post-tagging in 2018 with a calf, and the medium-term effects were evaluated by comparing body condition of tagged whales with non-tagged whales. These females calved in a typical 4 yr interval, suggesting no apparent immediate impact of tagging on reproduction for these individuals, but longer-term monitoring is needed. There was no observable difference in the body condition between the 2 tagged and non-tagged females. Ongoing monitoring post-tagging is required to build on the sample size and statistical power. We demonstrate the value of long-term monitoring programmes and a collaborative approach for evaluating effects from satellite-tagging cetaceans to support species management.
Antarctic Bottom Water (AABW) forms the deepest limb of the meridional overturning circulation (MOC) and is a key control on global exchanges of heat, freshwater, and carbon. Density differences that drive the MOC have their origin, in part, in coastal polynyas. Prydz Bay polynyas in East Antarctica are a key source of Dense Shelf Water (DSW) that feeds AABW to the Atlantic and Indian Oceans. However, several poorly understood mechanisms influence the pathways and change water mass properties of the DSW on its way to the abyss. To better understand these mechanisms, we release Lagrangian particles in a 10 km resolution simulation of the Whole Antarctic Ocean Model and analyze the resulting tracks using novel cluster analysis. Our results highlight the role of mixing with other water masses on the shelf in controlling the fate of DSW and its eventual contribution to AABW. When advected beneath the ice shelf, DSW can mix with fresh Ice Shelf Water (ISW), becoming less dense and making future AABW formation less likely. This study confirms that towards the shelf break along the Antarctic Slope Current, mixing with circumpolar deep water (CDW) forms modified circumpolar deep water (mCDW) and influences DSW export as AABW. Our findings indicate that the pathway from DSW to AABW is sensitive to mixing with ambient waters on the shelf. An important implication is that with future increase in ice shelf melt and CDW warming, AABW production is likely to decline, even if DSW production in coastal polynyas remains constant.
Shallow cloud decks residing in or near the boundary layer cover a large fraction of the Southern Ocean (SO) and play a major role in determining the amount of shortwave radiation reflected back to space from this region. In this article, we examine the macrophysical characteristics and thermodynamic phase of low clouds (tops < 3 km) and precipitation using ground‐based ceilometer, depolarization lidar and vertically‐pointing W‐band radar measurements collected during the Macquarie Island Cloud and Radiation Experiment (MICRE) from April 2016‐March 2017. During MICRE, low clouds occurred ∼65% of the time on average (slightly more often in austral winter than summer). About 2/3 of low clouds were cold‐topped (temperatures ≤ 0°C). These were thicker and had higher bases on average than warm‐topped clouds. 83‐88% of cold‐topped low clouds were liquid phase at cloud base (depending on the season). The majority of low clouds had precipitation in the vertical range 150 to 250 meters below cloud base, a significant fraction of which did not reach the surface. Phase characterization is limited to the period between April 2016 and November 2016. Small‐particle (low‐radar‐reflectivity) precipitation (which dominates precipitation occurrence) was mostly liquid below‐cloud, while large‐particle precipitation (which dominates total accumulation) was predominantly mixed/ambiguous or ice phase. Approximately 40% of cold‐topped clouds had mixed/ambiguous or ice phase precipitation below (with predominantly liquid phase cloud droplets at cloud base). Below‐cloud precipitation with radar reflectivity factors below about ‐10 dBZ were predominantly liquid, while reflectivity factors above about 0 dBZ were predominantly ice.
Oxygen isotope ratios (δ¹⁸O) of foraminifera in marine sediment records have fundamentally shaped our understanding of the ice ages and global climate change. Interpretation of these records has, however, been challenging because they reflect contributions from both ocean temperature and ice volume. Here, instead of disentangling, we reconstruct global benthic foraminiferal δ¹⁸O across the last deglaciation (18–11.5 ka) with ice volume constraints from fossil corals and ocean temperature constraints from ice core noble gases. We demonstrate that, while ocean temperature and ice volume histories are distinct, their summed contributions to δ¹⁸O agree remarkably well with benthic δ¹⁸O records. Given the agreement between predicted and observed δ¹⁸O, we further build upon recent insight into global energy fluxes and introduce a framework to quantitively reconstruct top-of-atmosphere net radiative imbalance, or Earth’s energy imbalance, from δ¹⁸O. Finally, we reconstruct 150,000 years of energy imbalance, which broadly follows Northern Hemisphere summer insolation but shows millennial-scale energy gain during the cold intervals surrounding Heinrich events. This suggests that, in addition to external forcing, internal variability plays an important role in modifying the global energy budget on long (millennial-plus) timescales.
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