A large-scale transcontinental river system crossed West Antarctica during the Eocene.

Extensive ice coverage largely prevents investigations of Antarctica's unglaciated past. Knowledge about environmental and tectonic development before large-scale glaciation, however, is important for understanding the transition into the modern icehouse world. We report geochronological and sedimentological data from a drill core from the Amundsen Sea shelf, providing insights into tectonic and topographic conditions during the Eocene (~44 to 34 million years ago), shortly before major ice sheet buildup. Our findings reveal the Eocene as a transition period from >40 million years of relative tectonic quiescence toward reactivation of the West Antarctic Rift System, coinciding with incipient volcanism, rise of the Transantarctic Mountains, and renewed sedimentation under temperate climate conditions. The recovered sediments were deposited in a coastal-estuarine swamp environment at the outlet of a >1500-km-long transcontinental river system, draining from the rising Transantarctic Mountains into the Amundsen Sea. Much of West Antarctica hence lied above sea level, but low topographic relief combined with low elevation inhibited widespread ice sheet formation.

Ecophysiological and behavioural response of juveniles of the Chilean cold-water coral Caryophyllia (Caryophyllia) huinayensis to increasing sediment loads.

Chilean Patagonia is a hotspot of biodiversity, harbouring cold-water corals (CWCs) that populate steep walls and overhangs of fjords and channels. Through anthropogenic activities such as deforestation, roadworks, aquafarming and increased landslide frequency, sediment input increases in the fjord region. While the absence of CWCs on moderately steep slopes has been suggested to reflect high vulnerability to sedimentation, experimental evidence has been lacking. Here, we investigated the sensitivity of CWCs to sediment stress, using juvenile Caryophyllia (Caryophyllia) huinayensis as a model. A 12-week aquarium experiment was conducted with three sediment loads: the average natural sediment concentration in Comau Fjord, 100- and 1000-fold higher sediment levels, expected from gravel road use and coastal erosion. Changes in coral mass and calyx dimensions, polyp expansion, tissue retraction and respiration were measured. For CWCs exposed to two and three order of magnitude higher sediment concentrations, 32% and 80% of the animals experienced a decrease in tissue cover, respectively, along with a decrease in respiration rate of 34% and 66%. Under the highest concentration corals showed reduced polyp expansion and a significantly reduced growth of ~ 95% compared to corals at natural concentration. The results show that C. huinayensis is affected by high sediment loads. As human activities that increase sedimentation steadily intensify, coastal planners need to consider detrimental effects on CWCs.

Trophic ecology of Angolan cold-water coral reefs (SE Atlantic) based on stable isotope analyses.

Cold-water coral (CWC) reefs of the Angolan margin (SE Atlantic) are dominated by Desmophyllum pertusum and support a diverse community of associated fauna, despite hypoxic conditions. In this study, we use carbon and nitrogen stable isotope analyses (δ13C and δ15N) to decipher the trophic network of this relatively unknown CWC province. Although fresh phytodetritus is available to the reef, δ15N signatures indicate that CWCs (12.90 ± 1.00 ‰) sit two trophic levels above Suspended Particulate Organic Matter (SPOM) (4.23 ± 1.64 ‰) suggesting that CWCs are highly reliant on an intermediate food source, which may be zooplankton. Echinoderms and the polychaete Eunice norvegica occupy the same trophic guild, with high δ13C signatures (-14.00 ± 1.08 ‰) pointing to a predatory feeding behavior on CWCs and sponges, although detrital feeding on 13C enriched particles might also be important for this group. Sponges presented the highest δ15N values (20.20 ± 1.87 ‰), which could be due to the role of the sponge holobiont and bacterial food in driving intense nitrogen cycling processes in sponges' tissue, helping to cope with the hypoxic conditions of the reef. Our study provides first insights to understand trophic interactions of CWC reefs under low-oxygen conditions.

Multiscale mechanical consequences of ocean acidification for cold-water corals.

Ocean acidification is a threat to deep-sea corals and could lead to dramatic and rapid loss of the reef framework habitat they build. Weakening of structurally critical parts of the coral reef framework can lead to physical habitat collapse on an ecosystem scale, reducing the potential for biodiversity support. The mechanism underpinning crumbling and collapse of corals can be described via a combination of laboratory-scale experiments and mathematical and computational models. We synthesise data from electron back-scatter diffraction, micro-computed tomography, and micromechanical experiments, supplemented by molecular dynamics and continuum micromechanics simulations to predict failure of coral structures under increasing porosity and dissolution. Results reveal remarkable mechanical properties of the building material of cold-water coral skeletons of 462 MPa compressive strength and 45-67 GPa stiffness. This is 10 times stronger than concrete, twice as strong as ultrahigh performance fibre reinforced concrete, or nacre. Contrary to what would be expected, CWCs retain the strength of their skeletal building material despite a loss of its stiffness even when synthesised under future oceanic conditions. As this is on the material length-scale, it is independent of increasing porosity from exposure to corrosive water or bioerosion. Our models then illustrate how small increases in porosity lead to significantly increased risk of crumbling coral habitat. This new understanding, combined with projections of how seawater chemistry will change over the coming decades, will help support future conservation and management efforts of these vulnerable marine ecosystems by identifying which ecosystems are at risk and when they will be at risk, allowing assessment of the impact upon associated biodiversity.

Major environmental drivers determining life and death of cold-water corals through time.

Cold-water corals (CWCs) are the engineers of complex ecosystems forming unique biodiversity hotspots in the deep sea. They are expected to suffer dramatically from future environmental changes in the oceans such as ocean warming, food depletion, deoxygenation, and acidification. However, over the last decades of intense deep-sea research, no extinction event of a CWC ecosystem is documented, leaving quite some uncertainty on their sensitivity to these environmental parameters. Paleoceanographic reconstructions offer the opportunity to align the on- and offsets of CWC proliferation to environmental parameters. Here, we present the synthesis of 6 case studies from the North Atlantic Ocean and the Mediterranean Sea, revealing that food supply controlled by export production and turbulent hydrodynamics at the seabed exerted the strongest impact on coral vitality during the past 20,000 years, whereas locally low oxygen concentrations in the bottom water can act as an additional relevant stressor. The fate of CWCs in a changing ocean will largely depend on how these oceanographic processes will be modulated. Future ocean deoxygenation may be compensated regionally where the food delivery and food quality are optimal.

Subsurface aeration of tidal wetland soils: Root-system structure and aerenchyma connectivity in Spartina (Poaceae).

Root-aerenchyma in wetland plants facilitate transport of oxygen from aboveground sources (atmosphere and photosynthesis) to belowground roots and rhizomes, where oxygen can leak out and oxygenate the otherwise anoxic soils. In salt marshes, the soil oxygenation capacity varies among different Spartina-taxa, but little is known about structural pattern and connectivity of root-aerenchyma that facilitates this gas transport. Both environmental conditions and ploidy level play a role for the root-system morphology. Root-system morphology of polyploid Spartina-taxa was studied, quantifying root-tissue volume and root-aerenchyma volume of hexaploid Spartina alterniflora, Spartina maritima, and Spartina × townsendii as well as dodecaploid Spartina anglica from different habitats. Computed tomography (CT)-scan image analysis was applied to quantify the volume of roots and aerenchyma, and to determine the root-system structure (ratio of aerenchyma to root-tissue volumes) and aerenchyma connectivity. On average, Spartina-roots accounted for 12% (v/v) and root-aerenchyma accounted for 1% (v/v) of the soil volume in the pioneer marsh. About 90% (v/v) of all roots were associated with aerenchyma. Root-system structures of S. × townsendii and S. anglica differed and showed clear responses to habitat conditions, such as flooding regime and redox potential. The development of large well-connected aerenchyma fragments were specifically shown in S. anglica and to a minor extend in S. maritima. Aerenchyma in S. alterniflora and S. × townsendii consisted only of smaller fragments. Spartina-dominated tidal marsh soils show high connectivity with the atmosphere via root-aerenchyma. The high ploidy level in S. anglica comes along with high connectivity in root-aerenchyma.

Madrepora oculata forms large frameworks in hypoxic waters off Angola (SE Atlantic).

This study aims to map the occurrence and distribution of Madrepora oculata and to quantify density and colony sizes across recently discovered coral mounds off Angola. Despite the fact that the Angolan populations of M. oculata thrive under extreme hypoxic conditions within the local oxygen minimum zone, they reveal colonies with remarkable heights of up to 1250 mm-which are the tallest colonies ever recorded for this species-and average densities of 0.53 ± 0.37 (SD) colonies m-2. This is particularly noteworthy as these values are comparable to those documented in areas without any oxygen constraints. The results of this study show that the distribution pattern documented for M. oculata appear to be linked to the specific regional environmental conditions off Angola, which have been recorded in the direct vicinity of the thriving coral community. Additionally, an estimated average colony age of 95 ± 76 (SD) years (total estimated age range: 16-369 years) indicates relatively old M. oculata populations colonizing the Angolan coral mounds. Finally, the characteristics of the Angolan populations are benchmarked and discussed in the light of the existing knowledge on M. oculata gained from the North Atlantic and Mediterranean Sea.

Orbital- and millennial-scale Antarctic Circumpolar Current variability in Drake Passage over the past 140,000 years.

The Antarctic Circumpolar Current (ACC) plays a crucial role in global ocean circulation by fostering deep-water upwelling and formation of new water masses. On geological time-scales, ACC variations are poorly constrained beyond the last glacial. Here, we reconstruct changes in ACC strength in the central Drake Passage in vicinity of the modern Polar Front over a complete glacial-interglacial cycle (i.e., the past 140,000 years), based on sediment grain-size and geochemical characteristics. We found significant glacial-interglacial changes of ACC flow speed, with weakened current strength during glacials and a stronger circulation in interglacials. Superimposed on these orbital-scale changes are high-amplitude millennial-scale fluctuations, with ACC strength maxima correlating with diatom-based Antarctic winter sea-ice minima, particularly during full glacial conditions. We infer that the ACC is closely linked to Southern Hemisphere millennial-scale climate oscillations, amplified through Antarctic sea ice extent changes. These strong ACC variations modulated Pacific-Atlantic water exchange via the "cold water route" and potentially affected the Atlantic Meridional Overturning Circulation and marine carbon storage.

Bacterial communities in temperate and polar coastal sands are seasonally stable.

Coastal sands are biocatalytic filters for dissolved and particulate organic matter of marine and terrestrial origin, thus, acting as centers of organic matter transformation. At high temporal resolution, we accessed the variability of benthic bacterial communities over two annual cycles at Helgoland (North Sea), and compared it with seasonality of communities in Isfjorden (Svalbard, 78°N) sediments, where primary production does not occur during winter. Benthic community structure remained stable in both, temperate and polar sediments on the level of cell counts and 16S rRNA-based taxonomy. Actinobacteriota of uncultured Actinomarinales and Microtrichales were a major group, with 8 ± 1% of total reads (Helgoland) and 31 ± 6% (Svalbard). Their high activity (frequency of dividing cells 28%) and in situ cell numbers of >10% of total microbes in Svalbard sediments, suggest Actinomarinales and Microtrichales as key heterotrophs for carbon mineralization. Even though Helgoland and Svalbard sampling sites showed no phytodetritus-driven changes of the benthic bacterial community structure, they harbored significantly different communities (p < 0.0001, r = 0.963). The temporal stability of benthic bacterial communities is in stark contrast to the dynamic succession typical of coastal waters, suggesting that pelagic and benthic bacterial communities respond to phytoplankton productivity very differently.

Temperate rainforests near the South Pole during peak Cretaceous warmth.

The mid-Cretaceous period was one of the warmest intervals of the past 140 million years1-5, driven by atmospheric carbon dioxide levels of around 1,000 parts per million by volume6. In the near absence of proximal geological records from south of the Antarctic Circle, it is disputed whether polar ice could exist under such environmental conditions. Here we use a sedimentary sequence recovered from the West Antarctic shelf-the southernmost Cretaceous record reported so far-and show that a temperate lowland rainforest environment existed at a palaeolatitude of about 82° S during the Turonian-Santonian age (92 to 83 million years ago). This record contains an intact 3-metre-long network of in situ fossil roots embedded in a mudstone matrix containing diverse pollen and spores. A climate model simulation shows that the reconstructed temperate climate at this high latitude requires a combination of both atmospheric carbon dioxide concentrations of 1,120-1,680 parts per million by volume and a vegetated land surface without major Antarctic glaciation, highlighting the important cooling effect exerted by ice albedo under high levels of atmospheric carbon dioxide.

Exploring computed tomography in ichnological analysis of cores from modern marine sediments.

Ichnological analysis is considered a very useful tool in several disciplines of Earth Sciences, including palaeoenvironmental studies and hydrocarbon exploration. Sediment cores provide excellent records, despite difficulties encountered during study runs due to specific core features. Previous studies using 2D images have proven the benefits of high-resolution image treatment in improving the visibility of ichnological features, but with limitations. 3D computed tomography (CT) techniques were applied to palaeoichnological studies in lithified cores and other disciplines of palaeontology to solve these limitations, but not used for ichnological studies in unconsolidated sediments due to the low density contrast between host sediment and trace fossils. In this study, a CT processing technique, previously tested in coral research, is applied to facilitate the characterisation of the ichnological signature of cores from modern marine soft sediments. This technique allows for the first time the isolation of burrows within these kinds of sediments and the differentiation of intervals based on burrow orientation. Data obtained from the technique are complemented with the ichnological information from conventional core description, thus providing a more complete characterisation of the trace fossil assemblage with additional ichnological properties such as burrow orientation and branching. This will improve palaeoenvironmental interpretations related to changes in energy or oxygenation, and the analysis of reservoir quality given the impact of burrows on porosity and permeability. Therefore, adopting CT to complement visual core description in the ichnological analysis of soft modern marine cores is a very informative approach.

In situ growth and bioerosion rates of Lophelia pertusa in a Norwegian fjord and open shelf cold-water coral habitat.

Coral reef resilience depends on the balance between carbonate precipitation, leading to reef growth, and carbonate degradation, for example, through bioerosion. Changes in environmental conditions are likely to affect the two processes differently, thereby shifting the balance between reef growth and degradation. In cold-water corals estimates of accretion-erosion processes in their natural habitat are scarce and solely live coral growth rates were studied with regard to future environmental changes in the laboratory so far, limiting our ability to assess the potential of cold-water coral reef ecosystems to cope with environmental changes. In the present study, growth rates of the two predominant colour morphotypes of live Lophelia pertusa as well as bioerosion rates of dead coral framework were assessed in different environmental settings in Norwegian cold-water coral reefs in a 1-year in situ experiment. Net growth (in weight gain and linear extension) of live L. pertusa was in the lower range of previous estimates and did not significantly differ between inshore (fjord) and offshore (open shelf) habitats. However, slightly higher net growth rates were obtained inshore. Bioerosion rates were significantly higher on-reef in the fjord compared to off-reef deployments in- and offshore. Besides, on-reef coral fragments yielded a broader range of individual growth and bioerosion rates, indicating higher turnover in live reef structures than off-reef with regard to accretion-bioerosion processes. Moreover, if the higher variation in growth rates represents a greater variance in (genetic) adaptations to natural environmental variability in the fjord, inshore reefs could possibly benefit under future ocean change compared to offshore reefs. Although not significantly different due to high variances between replicates, growth rates of orange branches were consistently higher at all sites, while mortality was statistically significantly lower, potentially indicating higher stress-resistance than the less pigmented white phenotype. Comparing the here measured rates of net accretion of live corals (regardless of colour morphotype) with net erosion of dead coral framework gives a first estimate of the dimensions of both processes in natural cold-water coral habitats, indicating that calcium carbonate loss through bioerosion amounts to one fifth to one sixth of the production rates by coral calcification (disregarding accretion processes of other organisms and proportion of live and dead coral framework in a reef). With regard to likely accelerating bioerosion and diminishing growth rates of corals under ocean acidification, the balance of reef accretion and degradation may be shifted towards higher biogenic dissolution in the future.

Testing the applicability of a benthic foraminiferal-based transfer function for the reconstruction of paleowater depth changes in Rhodes (Greece) during the early Pleistocene.

We present paleo-water depth reconstructions for the Pefka E section deposited on the island of Rhodes (Greece) during the early Pleistocene. For these reconstructions, a transfer function (TF) using modern benthic foraminifera surface samples from the Adriatic and Western Mediterranean Seas has been developed. The TF model gives an overall predictive accuracy of ~50 m over a water depth range of ~1200 m. Two separate TF models for shallower and deeper water depth ranges indicate a good predictive accuracy of 9 m for shallower water depths (0-200 m) but far less accuracy of 130 m for deeper water depths (200-1200 m) due to uneven sampling along the water depth gradient. To test the robustness of the TF, we randomly selected modern samples to develop random TFs, showing that the model is robust for water depths between 20 and 850 m while greater water depths are underestimated. We applied the TF to the Pefka E fossil data set. The goodness-of-fit statistics showed that most fossil samples have a poor to extremely poor fit to water depth. We interpret this as a consequence of a lack of modern analogues for the fossil samples and removed all samples with extremely poor fit. To test the robustness and significance of the reconstructions, we compared them to reconstructions from an alternative TF model based on the modern analogue technique and applied the randomization TF test. We found our estimates to be robust and significant at the 95% confidence level, but we also observed that our estimates are strongly overprinted by orbital, precession-driven changes in paleo-productivity and corrected our estimates by filtering out the precession-related component. We compared our corrected record to reconstructions based on a modified plankton/benthos (P/B) ratio, excluding infaunal species, and to stable oxygen isotope data from the same section, as well as to paleo-water depth estimates for the Lindos Bay Formation of other sediment sections of Rhodes. These comparisons indicate that our orbital-corrected reconstructions are reasonable and reflect major tectonic movements of Rhodes during the early Pleistocene.

Two new species of erect Bryozoa (Gymnolaemata: Cheilostomata) and the application of non-destructive imaging methods for quantitative taxonomy.

Two new species of cheilostome Bryozoa are described from continental-slope habitats off Mauritania, including canyon and cold-water coral (mound) habitats. Internal structures of both species were visualised and quantified using microcomputed tomographic (micro-CT) methods. Cellaria bafouri n. sp. is characterised by the arrangement of zooids in alternating longitudinal rows, a smooth cryptocyst, and the presence of an ooecial plate with denticles. Smittina imragueni n. sp. exhibits many similarities with Smittina cervicornis (Pallas, 1766), but differs especially in the shape and orientation of the suboral avicularium. Observations on Smittina imragueni and material labelled as Smittina cervicornis suggest that the latter represents a species group, members of which have not yet been discriminated, possibly because of high intracolony variation and marked astogenetic changes in surface morphology. Both new species are known only from the habitats where they were collected, probably reflecting the paucity of bryozoan sampling from this geographic area and depth range. Both species are able to tolerate low oxygen concentration, which is assumed to be compensated by the high nutrient supply off Mauritania. The application of micro-CT for the semiautomatic quantification of zooidal skeletal characters was successfully tested. We were able to automatically distinguish individual zooidal cavities and acquire corresponding morphological datasets. Comparing the obtained results with conventional SEM measurements allowed ascertaining the reliability of this new method. The employment of micro-CT allows the observation and quantification of previously unseen characters that can be used in describing and differentiating species that were previously indistinguishable. Furthermore, this method might help elucidate processes of colony growth and the function of individual zooids during this process.