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By examining the sedimentary records from two new cores collected from the Sabrina Coast slope, we have developed an age model spanning from the late Pliocene to the present. From multiproxy sediment analyses of the piston and kasten core, PC03, and KC03, collected during the IN2017_V01 survey on the Sabrina Coast (East Antarctica) offshore the Totten Glacier, we here present the outcomes derived within the seismostratigraphic record coupled with the sedimentological, geochemical paleomagnetic, and biostratigraphic contexts. Our results highlight that the area has been affected by recurrent sediment slides facilitated by siliceous deposits, both biogenic and from an unprecedented tephra layer, during some of the major paleoclimatological events of the late Pliocene. Diatoms contributed not only to the biostratigraphic and depositional environmental definition but also to the instability of the slope, together with the tephra layer, as documented offshore the Sabrina–Aurora Basin for the first time. [ABSTRACT FROM AUTHOR]

With ongoing climate change, research into the biological changes occurring in particularly vulnerable ecosystems, such as Antarctica, is critical. The Totten Glacier region, Sabrina Coast, is currently experiencing some of the highest rates of thinning across all East Antarctica. An assessment of the microscopic organisms supporting the ecosystem of the marginal sea‐ice zone over the continental rise is important, yet there is a lack of knowledge about the diversity and distribution of these organisms throughout the water column, and their occurrence and/or preservation in the underlying sediments. Here, we provide a taxonomic overview of the modern and ancient marine bacterial and eukaryotic communities of the Totten Glacier region, using a combination of 16S and 18S rRNA amplicon sequencing (modern DNA) and shotgun metagenomics (sedimentary ancient DNA, sedaDNA). Our data show considerable differences between eukaryote and bacterial signals in the water column versus the sediments. Proteobacteria and diatoms dominate the bacterial and eukaryote composition in the upper water column, while diatoms, dinoflagellates, and haptophytes notably decrease in relative abundance with increasing water depth. Little diatom sedaDNA is preserved in the sediments, which are instead dominated by Proteobacteria and Retaria. We compare the diatom microfossil and sedaDNA record and link the weak preservation of diatom sedaDNA to DNA degradation while sinking through the water column to the seafloor. This study provides the first assessment of DNA transfer from ocean waters to sediments and an overview of the microscopic communities occurring in the climatically important Totten Glacier region. Plain Language Summary: Antarctica is highly vulnerable to climate change and research into how marine organisms around the continent will respond to warming conditions is important. Microscopic organism, such as bacteria and phytoplankton, are key in the marine ecosystems because they support the entire marine food web. In this study, we investigated the composition of these microorganisms in the climatically important East Antarctic Totten Glacier region. We profiled compositional changes throughout the water column and into underlying subseafloor sediments, which provided information on both actively living and long dead organisms, and thus modern and past environmental conditions, respectively. We used genetic techniques to compare these marine communities, focusing on the taxonomically informative small subunit ribosomal ribonucleic acid (SSU rRNA) gene. Our study provides an overview about the microorganisms that live in the modern ocean in the Totten Glacier region, and how well their genetic signatures preserve in the underlying sediments. This knowledge is important both for assessments of present‐day marine ecosystem health and functioning, and when reconstructing past ocean environments as analogs to ongoing climate change. Key Points: Genetic signals of marine prokaryotes and eukaryotes change considerably from surface to deep waters and into the sedimentsDNA of surface‐dwelling organisms in a deep water column degrades while sinking with little DNA preserved in the sedimentsOrganisms that are well represented in deeper waters appear to have a higher likelihood of becoming preserved in the sediments [ABSTRACT FROM AUTHOR]

Current glacier melt rates in West Antarctica substantially exceed those around the East Antarctic margin. The exception is Wilkes Land, where for example Totten Glacier underwent significant retreat between 2000 and 2012, underlining its sensitivity to climate change. This process is strongly influenced by ocean dynamics, which in turn changes in accordance with the evolution of the ice caps. Here, we present new oceanographic data (temperature, salinity, and dissolved oxygen) collected during austral summer 2017 offshore the Sabrina Coast (East Antarctica) from the continental shelf break to ca 3000 m depth. This area is characterized by very few oceanographic in situ observations. The main water masses of the study area, identified by analysing thermohaline properties, are the Antarctic Surface Water with potential temperature θ>-1.5 ∘C and salinity S<34.2 (σθ<27.55 kgm-3), the Winter Water with -1.92<θ<-1.75 ∘C and 34.00 ∘C and S>34.5 (σθ>27.7 kgm-3), and Antarctic Bottom Water with -0.50<θ<0 ∘C and 34.6328.30 kgm-3). The latter is a mixture of dense waters from the Ross Sea and Adélie Land continental shelves. Such waters are influenced by the mixing processes they undergo as they move westward along the Antarctic margin, also interacting with the warmer Circumpolar Deep Water. The spatial distribution of water masses offshore the Sabrina Coast also appears to be strongly linked with the complex morpho-bathymetry of the slope and rise area, supporting the hypothesis that downslope processes contribute to shaping the architecture of the distal portion of the continental margin. Oceanographic data presented here can be downloaded from 10.25919/yyex-t381 (CSIRO; Van Graas, 2021). [ABSTRACT FROM AUTHOR]

Radiolarians (holoplanktonic protozoa) preserved in marine sediments are commonly used as palaeoclimate proxies for reconstructing past Southern Ocean environments. Generating reconstructions of past climate based on microfossil abundances, such as radiolarians, requires a spatially and environmentally comprehensive reference dataset of modern census counts. The Southern Ocean Radiolarian (SO-RAD) dataset includes census counts for 238 radiolarian taxa from 228 surface sediment samples located in the Atlantic, Indian, and southwest Pacific sectors of the Southern Ocean. This compilation is the largest radiolarian census dataset derived from surface sediment samples in the Southern Ocean. The SO-RAD dataset may be used as a reference dataset for palaeoceanographic reconstructions, or for studying modern radiolarian biogeography and species diversity. As well as describing the data collection and collation, we include recommendations and guidelines for cleaning and subsetting the data for users unfamiliar with the procedures typically used by the radiolarian community. The SO-RAD dataset is available to download from 10.1594/PANGAEA.929903 (Lawler et al., 2021). [ABSTRACT FROM AUTHOR]

Current glacier melt rates in West Antarctica substantially exceed those around the East Antarctic margin. The exception is Wilkes Land where, e.g., Totten Glacier, underwent significant retreat between 2000 and 2012, underlining its sensitivity to climate change. This process is strongly influenced by ocean dynamics, which in turn changes in accordance with the evolution of the ice caps. Here, we present oceanographic data (temperature, salinity, density, dissolved oxygen) collected for the first time offshore the Sabrina Coast (East Antarctica), from the continental shelf break to ca 3000 m depth during austral summer 2017. The main water masses are identified by analysing thermohaline properties: the Antarctic Surface Water with θ > −1. 5 °C and S < 34.2 (σθ < 27.55 kg m−3), the Winter Water with −1.92 < θ < −1.75 °C and 34.0 < S < 34.5 (27.55 < σθ < 27.7 kg m−3), the modified Circumpolar Deep Water with θ > 0 °C and S > 34.5 (σθ > 27.7 kg m−3), and Antarctic Bottom Water with −0.50 < θ < 0 °C and 34.63 < S < 34.67 (27.83 < σθ < 27.85). The latter in this region is a mixture of dense waters originating from the Ross Sea and Adélie Land continental shelves, and is affected by the mixing process they undergo as they move westward along the Antarctic margin and interact with the locally formed dense waters, and with the warmer and saltier Circumpolar Deep Water. The spatial distribution of water masses offshore the Sabrina Coast also appears to be strongly linked with the complex morpho-bathymetry of the slope and rise area, supporting the hypothesis that downslope processes contribute to shaping the architecture of the distal portion of the continental margin. [ABSTRACT FROM AUTHOR]

The geology of Wilkes Land, East Antarctica, is masked by kilometers of ice and remains largely unexplored. Defining the sediment provenance adjacent to this hidden region is important for distinguishing the proximal subglacial basement terranes and refining the dynamic regional glaciological history. This study presents a detrital sediment provenance record spanning c. 23.5 ka from the continental slope of central Wilkes Land. Sediment provenance was characterized using U‐Pb geochronology and trace element geochemistry from detrital zircon, titanite and apatite, and Pb isotopic signatures from detrital feldspar. These data were compared with new feldspar Pb‐isotopic signatures and existing U‐Pb zircon data sets from rare nearby coastal outcrop. A principally igneous source was revealed with dominant age populations between c. 1,360‐1,100 Ma and c. 1,620‐1,490 Ma, characteristic of rocks of the proximal Wilkes and Banzare provinces, respectively. Minor detritus was additionally sourced from the proximal Nuyina Province (c. 1,450‐1,390 Ma). Temporal variation in the climate and ice sheet configuration are likely responsible for subtle downcore changes observed in detrital sediment provenance. High sedimentation rates during the glacial period suggest reworking of continental shelf sediments and downslope transport in debris flows during ice sheet advance. Glacial meltwater fluxes fed largely by the Totten Glacier were responsible for supplying detritus during deglaciation. During interglacials, detritus was derived from a broad coastal region and delivered to the slope via multiple glacial outlets. These results present the first substantial offshore evidence to support recent interpretations that the subglacial crust of central Wilkes Land has a dominantly Mesoproterozoic history. Plain Language Summary: The geology underlying the Antarctic ice cap is poorly known due to thick and extensive ice cover. Understanding the composition of the rock types beneath the ice and how they are eroded and transported to the ocean is important for establishing the regional glaciological and tectonic histories. This study analyzes the age and composition of grains in marine sediment originally eroded from Wilkes Land, East Antarctica, to determine the source rock type, age, and likely provenance region. The composition of detritus is compared to that of nearby coastal rocks and the geology of southern Australia that was once adjacent to East Antarctica during past supercontinents. The detrital composition and age signature match the proximal Banzare, Nuyina, and Wilkes provinces in East Antarctica, validating the use of marine sediment records as a window into the hidden Antarctic bedrock. During glacial periods, detritus was scoured from the continental shelf and redeposited downslope. As the ice sheet began to retreat, fluxes of sediment‐laden meltwater were largely supplied by Totten Glacier. Detritus is sourced from a broad region of the coast during warm interglacials. This record provides the first substantial physical evidence to support former interpretations of the subglacial terrain in central Wilkes Land. Key Points: Multitracer provenance study offshore central Wilkes Land, East Antarctica, supports former interpretations of the subglacial geologyAge and composition of the detritus matches basement rocks of the proximal onshore Wilkes, Nuyina, and Banzare provincesChanges in detrital sediment provenance over c. 23.5 ka are associated with variation in climate and ice sheet configuration [ABSTRACT FROM AUTHOR]

Analysis of multichannel seismic profiles collected on the continental rise off the Sabrina Coast, East Antarctica, has allowed the determination of the acoustic features that are indicative of major evolution steps of the East Antarctic Ice Sheet (EAIS) and highlights the role of meltwater that originated from Totten Glacier in shaping the margin architecture. The arrival of marine-terminating glaciers into the coastal region was recorded by an enhanced sediment input on the continental rise and the nucleation of channel-levees. Downslope sedimentary processes were dominant throughout the Late Cenozoic, testifying to the progressive growth of a highly dynamic, temperate ice sheet on the continent. The last evolutionary step marks the transition to when a full polar glacial regime occurred. The development of a prograding wedge with steeply dipping foresets on the continental shelf and slope exemplifies sedimentation at this time. Other sub-sea-floor observations indicate that downslope fluxes, triggered by glacial meltwater, were still able to deeply erode and deliver sediments to the rise area. This study's findings have led to the identification of expanded and well-preserved sedimentary successions, which we suggest should be considered as priority targets for future International Ocean Discovery Program deep drilling due to the sensitivity of the ice sheet in this area. [ABSTRACT FROM AUTHOR]

Some aspects of the life cycle of the Southern Ocean diatom Fragilariopsis kerguelensis have been investigated previously, but many of its details have not been surveyed in nature. We investigated material from a two-year sediment trap time series by high-throughput imaging and image analysis, looking for morphometric signals of life cycle stages. Valve length distributions appeared close to unimodal but positively (right-) skewed. Size cohorts resulting from synchronized sexual reproduction events were not clearly distinguishable. Nevertheless, based on changes in valve length distributions, we found three general seasonal phases. These corresponded to periods of proliferation (with higher proportions of smaller cells during late spring/early summer), cessation of growth (relative loss of smaller cells during late summer/early autumn), and overwintering (little change in size distributions, with an increased proportion of large cells). We discuss possible causes of these signals, and their relevance to growth, sexual activity and adaption to environmental conditions, such as grazing pressures and the need for an overwintering strategy. [ABSTRACT FROM AUTHOR]

Semiautomated methods for microscopic image acquisition, image analysis, and taxonomic identification have repeatedly received attention in diatom analysis. Less well studied is the question whether and how such methods might prove useful for clarifying the delimitation of species that are difficult to separate for human taxonomists. To try to answer this question, three very similar Fragilariopsis species endemic to the Southern Ocean were targeted in this study: F. obliquecostata, F. ritscheri, and F. sublinearis. A set of 501 extended focus depth specimen images were obtained using a standardized, semiautomated microscopic procedure. Twelve diatomists independently identified these specimen images in order to reconcile taxonomic opinions and agree upon a taxonomic gold standard. Using image analyses, we then extracted morphometric features representing taxonomic characters of the target taxa. The discriminating ability of individual morphometric features was tested visually and statistically, and multivariate classification experiments were performed to test the agreement of the quantitatively defined taxa assignments with expert consensus opinion. Beyond an updated differential diagnosis of the studied taxa, our study also shows that automated imaging and image analysis procedures for diatoms are coming close to reaching a broad applicability for routine use. [ABSTRACT FROM AUTHOR]

Diatoms are siliceous phytoplankton that play a major role in global carbon fixation, as well as forming the basis of most marine food webs. In the Southern Ocean, diatoms are responsible for significant volumes of carbon export and sequestration in the deep sea. Diatoms are unicellular and microscopic, thus diatom taxonomy has naturally progressed as imaging and molecular technologies have developed. Despite recent advancements, some aspects of diatom taxonomy remain unclear. The genusShionodiscuswas separated fromThalassiosirain 2006, and possesses, as a group, internal extensions of the marginal strutted processes as well as a labiate process on the valve face, usually distant from the margin. The features distinguishingShionodiscusfromThalassiosira, andShionodiscusspp. from each other, are difficult to examine under light microscopy, and most taxonomists will group similarShionodiscusspecies together when encountered, rather than discriminating species. As a result, the full extent ofShionodiscusdiversity is rarely examined in individual studies. In this study, sediment trap material captured in the Australian sector of the Subantarctic Zone was examined using both light and scanning electron microscopy, and compared to known measurements onShionodiscusspecies and varieties. This study had two aims; to catalogue for the first time the diversity ofShionodiscusspp. within the Australian sector, and to create a formalized set of criteria for groupingShionodiscusspecies, when only light microscopy analysis is possible. By documentingShionodiscusdiversity in the Australian sector and establishing a standard identification protocol, researchers will be better able to determine the ecological significance of the genus in diatom assemblages. [ABSTRACT FROM AUTHOR]

In the naturally iron-fertilized surface waters of the northern Kerguelen Plateau region, the early spring diatom community composition and contribution to plankton carbon biomass were investigated and compared with the high nutrient, low chlorophyll (HNLC) surrounding waters. The large iron-induced blooms were dominated by small diatom species belonging to the genera Chaetoceros (Hyalochaete) and Thalassiosira, which rapidly responded to the onset of favorable light-conditions in the meander of the Polar Front. In comparison, the iron-limited HNLC area was typically characterized by autotrophic nanoeukaryote-dominated communities and by larger and more heavily silicified diatom species (e.g. Fragilariopsis spp.). Our results support the hypothesis that diatoms are valuable vectors of carbon export to depth in naturally iron-fertilized systems of the Southern Ocean. Furthermore, our results corroborate observations of the exported diatom assemblage from a sediment trap deployed in the iron-fertilized area, whereby the dominant Chaetoceros (Hyalochaete) cells were less efficiently exported than the less abundant, yet heavily silicified, cells of Thalassionema nitzschioides and Fragilariopsis kerguelensis. Our observations emphasize the strong influence of species-specific diatom cell properties combined with trophic interactions on matter export efficiency, and illustrate the tight link between the specific composition of phytoplankton communities and the biogeochemical properties characterizing the study area. [ABSTRACT FROM AUTHOR]

Strengths of numerical relationships between phytoplankton abundance estimates made by microscopy and CHEMTAX have often been tested using regression analysis. To specifically test agreement, where data points lie along a line of equality, the Bland and Altman technique is commonly used in the medical literature and applied here to phytoplankton analysis for the first time (simultaneously with regression). Our analyses are based on a sample set collected off Coffs Harbour (∼ 30°S), Eastern Australia. While comparing abundance estimates of different phytoplankton pigment-types derived from microscopy and CHEMTAX we specifically aim at: (1) determining the usefulness of the Bland and Altman technique in comparing phytoplankton abundance estimates made by both quantification techniques, and (2) identifying the lowest taxonomic level (i.e., interclass or intraclass level) at which phytoplankton abundance estimates agree. Our results suggest that Bland and Altman analysis is highly suited to compare phytoplankton abundance estimates made by microscopy and CHEMTAX. It delivered a quantifiable difference of chlorophyll a concentrations between abundance estimates, which may benefit the future calibration of phytoplankton quantification techniques. Both Bland and Altman and regression analyses were suited to resolve imbalances between phytoplankton abundance estimates made by microscopy and CHEMTAX. Best agreement was found within dinoflagellates (class-level), poor agreement within three diatom pigment-types (intraclass level). We attributed the poor agreement within diatom abundance estimates to classification errors of microscopically determined taxa into pigment-types. Intraspecific pigment composition seems more variable than generally assumed, calling for studies resolving this variation to further conform abundance estimates made by microscopy and CHEMTAX. [ABSTRACT FROM AUTHOR]

Species belonging to the potentially harmful diatom genus Pseudo-nitzschia, isolated from 16 localities (31 sampling events) in the coastal waters of south-eastern Australia, were examined. Clonal isolates were characterized by (i) light and transmission electron microscopy; (ii) phylogenies, based on sequencing of nuclear-encoded ribosomal deoxyribonucleic acid ( rDNA) regions and, (iii) domoic acid ( DA) production as measured by liquid chromatography-mass spectrometry ( LC- MS/ MS). Ten taxa were unequivocally confirmed as Pseudo-nitzschia americana, P. arenysensis, P. calliantha, P. cuspidata, P. fraudulenta, P. hasleana, P. micropora, P. multiseries, P. multistriata, and P. pungens. An updated taxonomic key for south-eastern Australian Pseudo-nitzschia is presented. The occurrence of two toxigenic species, P. multistriata (maximum concentration 11 pg DA per cell) and P. cuspidata (25.4 pg DA per cell), was documented for the first time in Australia. The Australian strains of P. multiseries, a consistent producer of DA in strains throughout the world, were nontoxic. Data from 5,888 water samples, collected from 31 oyster-growing estuaries (2,000 km coastline) from 2005 to 2009, revealed 310 regulatory exceedances for 'Total Pseudo-nitzschia,' resulting in six toxic episodes. Further examination of high-risk estuaries revealed that the ' P. seriata group' had highest cell densities in the austral summer, autumn, or spring (species dependent), and lowest cell densities in the austral winter, while the ' P. delicatissima group' had highest in winter and spring. [ABSTRACT FROM AUTHOR]

Pseudo-nitzschia H. Peragallo is a marine diatom genus found worldwide in polar, temperate, subtropical and tropical waters. It includes toxigenic representatives that produce domoic acid ( DA), a neurotoxin responsible for Amnesic Shellfish Poisoning. In this study we characterized two species of Pseudo-nitzschia collected from Port Stephens and the Hawkesbury River (south eastern Australia) previously unreported from Australian waters. Clonal isolates were sub-sampled for (i) light and transmission electron microscopy; (ii) DNA sequencing, based on the nuclear-encoded partial large subunit ribosomal RNA gene and internal transcribed spacer ( ITS)- ITS1, 5.8S and ITS2 rDNA regions and, (iii) DA production as measured by liquid chromatography-mass spectrometry. Morphological and molecular data unambiguously revealed the species to be Pseudo-nitzschia micropora Priisholm, Moestrup & Lundholm ( Port Stephens) and Pseudo-nitzschia hasleana Lundholm ( Hawkesbury River). This is the first report of the occurrence of these species from the Southern Hemisphere and the first report of P. micropora in warm-temperate waters. Cultures of P. micropora, tested for DA production for the first time, proved to be non-toxic. Similarly, no detectable toxin concentrations were observed for P. hasleana. Species resolution and knowledge on the toxicity of local Pseudo-nitzschia species has important implications for harmful algal bloom monitoring and management. [ABSTRACT FROM AUTHOR]

The article focuses on understanding Antarctic sea ice dynamics during the last glacial-interglacial transition. Topics include the role of sea ice reduction in Antarctic climate warming, molecular biomarker-based sea ice records indicating rapid sea ice reduction, and the relationship between sea ice changes, Southern Ocean overturning, and CO2 outgassing and provides empirical evidence supporting an initiation of deglacial Antarctic sea ice reduction driven by increasing local insolation.

A Modern Analog Technique (MAT5201/31) has been applied to fossil diatom assemblages to provide down-core estimates of February sea-surface temperatures (SSTs) and of sea ice duration over the past 220 000 years at 56°40′S, 160°14′E. At the core location, sea ice progression lagged the SST drop by ∼1 ka at interglacial–glacial transitions, and sea ice retreat was almost synchronous to the SST increase at glacial–interglacial terminations. Sea ice increased continuously during glacial periods to reach its maximum extent at the end of glacial times, although SSTs were almost constant during glacials. This indicates that SSTs are the major parameter determining the advance and retreat of sea ice at transitions, but that the sea ice advance during glacial conditions may be related to positive feedbacks of the ice on albedo, air temperature and meridional wind stress. The strong correlation (r=0.75) between sea ice duration at the core location and the Vostok CO2 record argues for a control of Antarctic sea ice extent on atmospheric CO2 concentration via the modification of the ocean-to-atmosphere gas balance. [Copyright &y& Elsevier]

Semiautomated methods for microscopic image acquisition, image analysis, and taxonomic identification have repeatedly received attention in diatom analysis. Less well studied is the question whether and how such methods might prove useful for clarifying the delimitation of species that are difficult to separate for human taxonomists. To try to answer this question, three very similar Fragilariopsis species endemic to the Southern Ocean were targeted in this study: F. obliquecostata, F. ritscheri, and F. sublinearis. A set of 501 extended focus depth specimen images were obtained using a standardized, semiautomated microscopic procedure. Twelve diatomists independently identified these specimen images in order to reconcile taxonomic opinions and agree upon a taxonomic gold standard. Using image analyses, we then extracted morphometric features representing taxonomic characters of the target taxa. The discriminating ability of individual morphometric features was tested visually and statistically, and multivariate classification experiments were performed to test the agreement of the quantitatively defined taxa assignments with expert consensus opinion. Beyond an updated differential diagnosis of the studied taxa, our study also shows that automated imaging and image analysis procedures for diatoms are coming close to reaching a broad applicability for routine use. [ABSTRACT FROM AUTHOR]

The Earth is currently experiencing climatic changes that will result in similar environmental conditions to those experienced during the mid-Pliocene (5.3–3.6 million years ago [Ma]), such as similar atmospheric CO 2 concentrations, elevated sea surface temperature, and higher sea-levels due to polar ice melt. Studying the temporal distribution of Antarctic diatoms and silicoflagellates from this epoch provides insights into environmental conditions and sea-ice configurations during that time, and remains the only way to realistically estimate future phytoplankton community responses and Southern Ocean sea-ice extent during large-scale transient changes of similar magnitude to that anticipated by anthropogenic causes. In this study, we identified and quantified diatoms and silicoflagellates in a sediment core section obtained from the Antarctic Wilkes Land margin (IODP Expedition 318, Hole U1361A), spanning four glacial and interglacial cycles around the Gauss/Gilbert geochron boundary (3.6 Ma) between about 3.69 and 3.56 Ma. Two major abundance peaks (around 79.66 and 76.86 mbsf; representing time intervals around 3.65 Ma and 3.58 Ma, respectively) were identified. Both peaks temporally match previously determined high productivity warm intervals (interglacials). Diatom and silicoflagellate assemblages in these two interglacial periods differed: the abundance peak in the older sediments is dominated by the pennate diatoms Fragilariopsis barronii , Rouxia naviculoides and Rouxia antarctica ; indicative of seasonal, meltwater associated stratification. The abundance peak in the younger sediments is composed principally of Chaetoceros resting spores, suggesting higher productivity, strong stratification and prolonged ice-free, open water conditions. Analysing highly abundant diatoms and environmental indicator species from this IODP Site in relation to the previously determined palaeo-productivity proxy Ba/Al allowed us to refine the age model. Our study provides orbital-scale insights into the variability of Antarctic diatom and silicoflagellate assemblages during the mid-Pliocene, thereby offering a reference for future predictions of extant diatom responses to ongoing climate change. [ABSTRACT FROM AUTHOR]