An inventory of speleothems primarily composed of the closely related sulfate minerals baryte (BaSO4) and celestine (SrSO4) in Lechuguilla Cave (New Mexico, USA) has revealed an extraordinary variety. This includes subaerial stalactites, stalagmites, flowstone, coralloids, wall crusts, floor crystals, snow, frostwork, and subaqueous pool crystals. Large baryte and celestine crystals have also been documented in hydrothermal veins in the host rock, predating the cave and truncated when intersected by it. The respective carbonate mineral phases witherite (BaCO3) and strontianite (SrCO3), in contrast, were found to be rare in the studied speleothem samples, representing the first confirmed records from this cave. Baryte speleothems are typically composed of pure baryte, whereas celestine is usually syntactically intergrown with small baryte crystals and forms part of the most diverse assemblages of secondary cave minerals recorded in the cave to date, including species of the following mineral groups: carbonates (calcite, dolomite, aragonite, huntite, hydromagnesite, strontianite, and witherite), sulfates (gypsum), oxides and hydroxides (undetermined Mn/Fe-oxides or hydroxides), silicates (quartz, chalcedony, opal/cristobalite/tridymite, and montmorillonite), halogenides (fluorite), and vanadates (metatyuyamunite). Based on Th-230/U-series dating of directly associated carbonate minerals and gypsum, the age of formation of the various types of baryte and celestine speleothems was constrained to a range from the Middle Pleistocene to the Holocene. This confirms a formation during the ongoing post-hydrothermal and post-SAS (sulphuric acid speleogenesis) phase of epigenic normal temperature cave development. Six samples fall outside the dating range with close to secular equilibrium isotope ratios and are thus likely older than similar to 600 ka. While baryte stalactites, stalagmites, flowstone, and pool crystals are still forming, celestine minerogenesis, except for some of the coralloids, appears to have largely ceased in Lechuguilla Cave.

The discovery of non-hydrothermal baryte (BaSO4) speleothems in Lechuguilla Cave (New Mexico, USA) has raised the suspicion that speleothemic baryte in caves might be more common than previously recognized. This is primarily expected in caves with a similar geological setting in Paleozoic carbonate host rocks with tectonic fractures or paleokarst features that allowed hydrothermal fluids to mineralize veins and ore deposits that include baryte as a source of barium sulfate to form secondary cave minerals. To test this hypothesis, subaqueous and subaerial speleothems from caves in the Variscan Basement of Germany that match this geological context were examined. In all the caves investigated, calcite pool spar was found containing euhedral, tabular baryte crystals 5 to 300 μm in size. These were most abundant near the inflow of water and at the bottom of the pools, particularly on up-facing surfaces and in small cavities or intercrystalline voids. This distribution suggests a minerogenesis driven by a combination of episodic evaporation and density-driven processes, possibly involving meromixis. Water samples show elevated concentrations of barium as well as sulfate and saturation indices for barium sulfate are mostly positive (supersaturation with respect to baryte), indicating conditions favoring precipitation of baryte. Accessory baryte was also found in subaerial stalactites, helictites, coralloids, and wall crusts, with capillary seepage, surface diffusion, and evaporation considered the main processes of ion transport and supersaturation leading to mineral formation. Finally, baryte spherulites up to 400 μm in diameter were found in a deposit of cryogenic calcite formed during a Pleistocene glacial period. This extends the temperature range of speleothemic baryte to freezing conditions, when solute rejection during the formation of cave ice led to supersaturation of the residual water and triggered the minerogenesis of calcite and baryte, representing a climatically controlled endmember of baryte formation. Together, these findings confirm that accessory baryte in carbonate speleothems is common in non-hydrothermal, epigenic karst settings where baryte occurs in the host rock.

The calcareous matrix of rhodoliths can be composed of one or more crustose coralline algae (CCA) taxa as well as a mixed assemblage of various encrusting organisms. Studies on modern and fossil rhodoliths assume such associations to vary with water depth. Our study explores the quantitative biological composition of calcareous rhodolith matrices along a bathymetric gradient at the Arctic Svalbard archipelago. Using a methodological combination of virtual micro-CT cross-sections with a modified point counting approach, we found five different taxonomic groups: CCA, bivalves, serpulids, bryozoans and balanids. While water depth does not influence the general taxon richness as well as the abundance of bivalves, it significantly affects the proportional matrix composition of encrusting organisms by a combination of environmental factors and biological interactions. The decrease in CCA skeletal material with increasing water depth is significantly governed by impaired irradiance conditions. Regular rhodolith movement in shallow waters fosters the proportion of CCA, while decreased movement in deeper waters spurs the proportion of other encrusters. This potentially results from post-mortem fouling of dead rhodolith parts followed by a recolonization with slow-growing CCA species Boreolithothamnion glaciale. Our results highlight mechanisms controlling the biogenic composition of calcareous rhodolith matrices and underline the potential of matrices compositions for palaeogeography and palaeobathymetry. Our study contributes to an improved understanding of the composition and developmental patterns of rhodoliths. This can add to a better comprehension of the respective ecosystems on a broader scale and be beneficial for conservation purposes.

Rhodoliths composed of crustose coralline algae (CCA) are marine calcifiers of global significance. Here, we investigate how floridean starch storage patterns of Arctic rhodoliths from Svalbard are affected by environmental conditions. Quantifying the amount of starch in photomosaic scans of rhodolith slabs via amylopectin-iodine complex formation, we found that shallow water rhodoliths contain significantly higher starch percentages compared to the deeper-water dwellers. We conclude that the observed starch patterns are mainly controlled by water depth because light and rhodolith turnover frequency both decrease in deeper waters. Regarding rhodolith turnover, the occasional burial of turned rhodoliths in deeper waters can result in a dieback of the outer CCA thallus areas, which contain important starch supplies. As rhodoliths are both calcifiers and photoautotrophs, we highlight their relevance in potentially contributing to global blue carbon, that is, their role as a marine carbon sink. In this context, our quantification approach of floridean starch patterns in rhodoliths provides a straightforward basis for further studies on this topic.

A new attachment trace belonging to the ichnogenus Centrichnus has been recognized on bivalve shells in a Pliocene coquina of the Pedra-que-Pica section in Santa Maria Island (Azores Archipelago). The new ichnospecies Centrichnus dentatus isp. nov. is characterized by an elliptical outline, bounded by a groove and/or a series of pits, and by having a more or less pronounced central to off-center depression surrounded by a flat area. Based on these new findings, the diagnosis of the ichnogenus Centrichnus is emended, as is the diagnosis of the ichnofamily Centrichnidae. The new trace fossil was produced by the barnacle Verruca spengleri, which was found in direct association with the trace. Some specimens of Centrichnus dentatus isp. nov. were found cross-cut by phoronid borings (Talpina isp.) or clionaid sponge borings (Entobia isp.), and they co-occur with polychaete borings (Maeandropolydora isp.) and bivalve borings (Gastrochaenolites isp.). The traces belong to the Gnathichnus ichnofacies, which refers to the early colonization of hard substrates taking place within months, even though the recorded ichnocoenoses suggest longer exposure and colonization by several generations of cirripeds, lasting several years rather than months.

Bedding planes of the early Tithonian lithographic limestone of Solnhofen (southern Germany) contain extensive networks of filiform tubular structures. The size of the irregularly distributed network polygons varies between several centimeters to few millimeters, and the diameter of the circular tunnels directionally decreases from millimetric to sub-millimetric. The network represents a bioerosion trace fossil (i.e. boring) and is interpreted to result from the bioeroding activity of plant roots and their symbiotic interaction with fungi (i.e. mycorrhiza). The traces are filled with an earthy substrate that is rich in iron minerals and has an ochre-brown color, and many of the tunnels were loci for manganese dendrites preferably forming in the bedding plane. It is assumed that the formation of the traces by plant colonization and bioerosion took place during the Paleogene to Neogene, when the area was affected by karstification. The networks are comparable with mycorrhizal networks of extant plants, which comprise a symbiotic association of plants and fungi. Although such symbioses are important for plant ecosystems and were crucial for evolutionary processes, only their body-fossil record has been traced back to the Ordovician, whereas their trace-fossils expression was hitherto unknown. The structures are described as Radixichnus reticularis igen. et isp. nov., which is the first ichnotaxon interpreted as terrestrial root bioerosion trace fossils.

Knowledge of spatial biodiversity patterns is important for ecosystem assessment. Rhodoliths, free-living calcareous algae, are biotic components that structure the sea floor through their complex calcareous skeletons and their tendency to accumulate in an area to form rhodolith beds. Thereby, rhodoliths are considered to act as ecosystem engineers promoting local biodiversity. In this study, the biodiversity of rhodolith beds in Mosselbukta, Svalbard, was investigated to analyse the proposed link between local biodiversity and the presence of rhodoliths by evaluating beam trawl and underwater video transect data. The comparative analysis of two sampling methods addressing the same research question allowed us to assess the suitability of these two methods. To test our hypothesis and the utility of the two methods, evaluations of the two data sets were carried out separately by using Bayesian statistics. The results confirm a positive relationship between the presence of rhodoliths and local biodiversity with a posterior probability of 70% for the video transects and 85% for the beam trawl data. The similarity of the results of the two methods suggests that both methods are well-suited for the analysis of local biodiversity patterns. The combination of the two methods, with their individual strengths and weaknesses, has provided stronger support for the results and a broader view on different components of the biodiversity in the Svalbard rhodolith beds.

Rhodoliths built by crustose coralline algae (CCA) are ecosystem engineers of global importance. In the Arctic photic zone, their three-dimensional growth emulates the habitat complexity of coral reefs but with a far slower growth rate, growing at micrometers per year rather than millimeters. While climate change is known to exert various impacts on the CCA's calcite skeleton, including geochemical and structural alterations, field observations of net growth over decade-long timescales are lacking. Here, we use a temporally explicit model to show that rising ocean temperatures over nearly 100 years were associated with reduced rhodolith growth at different depths in the Arctic. Over the past 90 years, the median growth rate was 85 μm year-1 but each °C increase in summer seawater temperature decreased growth by a mean of 8.9 μm (95% confidence intervals = 1.32-16.60 μm °C-1, p < .05). The decrease was expressed for rhodolith occurrences in 11 and 27 m water depth but not at 46 m, also having the shortest time series (1991-2015). Although increasing temperatures can spur plant growth, we suggest anthropogenic climate change has either exceeded the population thermal optimum for these CCA, or synergistic effects of warming, ocean acidification, and/or increasing turbidity impair rhodolith growth. Rhodoliths built by calcitic CCA are important habitat providers worldwide, so decreased growth would lead to yet another facet of anthropogenic habitat loss.

ABSTRACT Ooids are abundant carbonate grains throughout much of Earth's history, but their formation is not well understood. Here, an in‐depth study of microbial bioerosion features of Holocene ooids from the Schooner Cays ooid shoals (Great Bahama Bank, Eleuthera, Bahamas) and the Shalil al Ud ooid shoals in the Arabian/Persian Gulf (Abu Dhabi, United Arab Emirates) is presented. No obvious differences were found in ooid size distribution, cortex layer thickness, the composition of nuclei or euendolithic community when comparing ooids from both locations. Microendolithic borings are present in most studied ooid surfaces, but the intensity of (micro‐)bioerosion varies significantly. Applying an epoxy vacuum cast‐embedding technique allowed the identification of ichnotaxa and their inferred producers (various genera of diatoms, cyanobacteria, coccolithophores and unspecified bacteria). Euendolithic taxa have specific low‐light tolerances and light optima. This implies that information about the relative bathymetry (seafloor versus burial within an ooid shoal) and ecology for ooid cortex formation can be obtained via the presence or absence of their respective ichnotaxa. The history of a statistically significant number of ooid cortices can be translated into dune dynamics and the temporal variations thereof by allocating the inferred index producer to a defined burial or light penetration zone. In this context, ooid formation can be divided into four stages: (i) an agitation stage in the water column, characterized by the colonization of grains by photoautotrophs; (ii) a resting stage, characterized by temporary burial of the ooid, leading to immobilization and a shift towards heterotrophs; (iii) a sleeping stage, characterized by prolonged burial and colonization by organotrophs; and (iv) a reactivation stage, characterized by a resurfacing of the ooid and a subsequent shift towards photoautotrophs. The sleeping stage is presumably a stage of ooid degradation where bioerosion, mainly by heterotrophic fungi and bacteria is particularly active.

The cheilostome Bryozoa encrusting settlement panels deployed in the Azores between 0 and 500 m, which were retrieved after a time span of 1 and 2 years, are here described and figured. Of the 49 cheilostome species reported, 15 are new to science: Beania pauciserialis sp. nov., Caberea rylandi sp. nov., Micropora acorecia sp. nov., Cellaria acorensidolisi sp. nov., Hippothoa jakobseni sp. nov., Chorizopora lula sp. nov., Haplopoma freiwaldi sp. nov., Schizomavella ( Schizomavella ) reverteri sp. nov., Schizomavella ( Schizomavella ) kekrymmena sp. nov., Microporella avilai sp. nov., Microporella quadrispinosa sp. nov., Microporella lobopodia sp. nov., Microporella nodulifera sp. nov., Buffonellaria faialensis sp. nov., and Omalosecosa secunda sp. nov. The subspecies Glabrilaria orientalis azorensis (Harmelin, 1988) is here raised to species rank, resulting in Glabrilaria azorensis (Harmelin, 1988) comb. nov. Moreover, we designate a lectotype for Nimba praetexta Jullien in by Jullien & Calvet, 1903, type species of the genus Nimba Jullien in by Jullien & Calvet, 1903, redescribe the species based on scanning electron microscope inspection, and transfer the genus from the Lacernidae Jullien, 1888 to the Escharinidae Tilbrook, 2006. A lectotype is also designated for Schizobrachiella sanguinea (Norman, 1868). Based on the taxonomic account, we discuss changes concerning the recorded diversity of bryozoans in the Azores and their taxonomic assignment, now including 91 endemic species that account for 41% of a total of 221 bryozoan species reported from the archipelago. Finally, we discuss biogeographic relationships and the status of origin, including potential non-indigenous species, and demonstrate a strong relatedness with eastern Atlantic/Mediterranean faunas.

IntroductionCold-water coral reefs form complex benthic habitats, supporting thousands of species. The broadscale environmental tolerances of reef-forming species such as Lophelia pertusa are well studied, but small-scale differences between different reef settings have received little attention so far. The controlling factors of thriving cold-water coral reefs and how these habitats differ in terms of framework extent, coral colony morphology, and associated fauna could reveal how these benthic ecosystems form and expand. Information on the natural range of environmental fluctuations could provide a better understanding of the resilience of such ecosystems towards environmental changes. Our study aimed to elaborate small-scale forces on local hydrodynamics and oceanographic parameters at two geographically close but contrasting reef sites in mid-Norway.MethodsWe investigated natural fluctuations and the seasonal variability of environmental conditions of an inshore and an offshore Lophelia-dominated reef over an annual cycle by time series monitoring of physical properties by benthic landers and water sampling for biogeochemical variables using CTD casts.Results and discussionThe flow fields at the extensive reef on the offshore Sula Ridge and a bank reef at Nord-Leksa in a fjord-system differed regarding both short-term and seasonal levels. The inshore flow field was strong and tidally driven, whereas the offshore flow field was slower with large seasonal variability. The local flow regimes and the seasonal atmospheric forcing could explain the observed seasonality of the hydrographic variables and the observed inter-annual variability in biogeochemical variables. Comparison with a flow model showed that the natural short-term and seasonal variability are driven by small-scale forcing that is not represented in model analyses. These results suggest that local hydrodynamics together with sea-floor topography control the reef extent and the morphology of cold-water coral colonies.

Methane seeps are typified by the formation of authigenic carbonates, many of which exhibit corrosion surfaces and secondary porosity believed to be caused by microbial carbonate dissolution. Aerobic methane oxidation and sulfur oxidation are two processes capable of inducing carbonate corrosion at methane seeps. Although the potential of aerobic methanotrophy to dissolve carbonate was confirmed in laboratory experiments, this process has not been studied in the environment to date. Here, we report on a carbonate corrosion experiment carried out in the REGAB Pockmark, Gabon-Congo-Angola passive margin, in which marble cubes were deployed for 2.5 years at two sites (CAB-B and CAB-C) with apparent active methane seepage and one site (CAB-D) without methane seepage. Marble cubes exposed to active seepage (experiment CAB-C) were found to be affected by a new type of microbioerosion. Based on 16S rRNA gene analysis, the biofilms adhering to the bioeroded marble mostly consisted of aerobic methanotrophic bacteria, predominantly belonging to the uncultured Hyd24-01 clade. The presence of abundant 13 C-depleted lipid biomarkers including fatty acids (n-C16:1ω8c , n-C18:1ω8c , n-C16:1ω5t ), various 4-mono- and 4,4-dimethyl sterols, and diplopterol agrees with the dominance of aerobic methanotrophs in the CAB-C biofilms. Among the lipids of aerobic methanotrophs, the uncommon 4α-methylcholest-8(14)-en-3β,25-diol is interpreted to be a specific biomarker for the Hyd24-01 clade. The combination of textural, genetic, and organic geochemical evidence suggests that aerobic methanotrophs are the main drivers of carbonate dissolution observed in the CAB-C experiment at the REGAB pockmark.

Methane seeps are typified by authigenic carbonate formation. Many seep carbonates exhibit corrosion surfaces and secondary porosity, which are believed to be caused by microbial carbonate dissolution. Aerobic methane oxidation and sulfur oxidation are the two most likely processes capable of inducing carbonate corrosion at methane seeps. Although the potential of aerobic methanotrophy to dissolve carbonate was confirmed in laboratory experiments, this process has not been studied in the environment to date. Here, we report on a carbonate corrosion experiment carried out in the REGAB Pockmark, Gabon-Congo-Angola passive margin, in which marble cubes were deployed for 2.5 years at two sites (CAB-B and CAB-C) with apparent active methane seepage and one site (CAB-D) without methane seepage. Marble cubes exposed to active seepage (experiment CAB-C) were found to be affected by a new type of microbioerosion. Based on 16S rRNA gene analysis, the biofilms adhering to the bioeroded marble mostly consisted of aerobic methanotrophic bacteria, predominantly belonging to the uncultured Hyd24-01 clade. The presence of abundant 13C-depleted lipid biomarkers including fatty acids (n-C16:1ω8c, n-C18:1ω8c, n-C16:1ω5t), various 4-mono- and 4,4-dimethyl sterols, and diplopterol agrees with the dominance of aerobic methanotrophs in the CAB-C biofilms. Among the lipids of aerobic methanotrophs, the uncommon 4α-methylcholest-8(14)-en-3β,25-diol is interpreted to be a specific biomarker for the Hyd24-01 clade. The combination of textural, genetic, and organic geochemical evidence suggests that aerobic methanotrophs are the main drivers of carbonate dissolution observed in the CAB-C experiment at the REGAB pockmark.

The fossil record yields a peculiar phenomenon in different kinds of molluscan shells: bioclaustrations formed around (epi)symbionts during growth of the hosts' shell margin. Four morphologies, two of them formerly considered bioerosion traces, are here united in the parataxonomy of bioclaustration structures under the revised cecidogenus Rodocanalis. These are: (1) simple linear grooves (Rodocanalis linearis csp. nov.) formed below the periostracum in Pleistocene to Recent endobenthic bivalves; (2) series of distally ramifying grooves (Rodocanalis runicus) in Silurian orthoconic nautiloids; (3) irregular networks of grooves (Rodocanalis reticulatus) in Jurassic to Cretaceous bivalves and gastropods; and (4) regular reticulate networks (Rodocanalis geometricus csp. nov.) in Jurassic to Cretaceous gastropods. The linear grooves might be associated with commensal worms, while multiple lines of reasoning point towards hydrozoan symbionts in the case of the branched and anastomosing grooves. After the hydrozoan larva settles and the first polyp becomes fixed on the calcareous ostracum at the shell margin, the process of bioclaustration commences when the periostracum surrounds the base of the polyp, which moves towards the external shell surface, while the hydrorhizae develop in the only possible direction: towards the shell growth margin. This enables new polyps to originate at the shell edge by budding, while the bioclaustration of the stolonial hydrorhizae advances. We consider the nature of this symbiotic relationship as mutualism, with the hydrozoan symbiont taking advantage of the host's feeding current or food debris, and the molluscan host profiting from the defensive capability of the hydrozoan's cnidocysts.

A critical reassessment of foraminiferan parasitism on echinoid hosts, past and present, identifies all previous records as doubtful and circumstantial evidence as being limited to possible foraminiferan bioerosion traces on a Late Cretaceous Echinocorys perconicus host from Northern Germany.Here, we report on a second type of putative foraminiferan attachment trace fossils found on a Late Cretaceous Echinocorys jaekeli from the Danish Basin, and establish the new ichnogenus and ichnospecies Solichnus aestheticus within the ichnofamily Centrichnidae.These delicate sun-shaped etchings are diagnosed as bowl-shaped circular depressions, wider than deep, from which numerous open canals radiate in a meandering fashion, ramify, and thin out.The canals indicate a mutual avoidance pattern with those of neighbouring specimens and they circumvent the areoles of the echinoid's primary tubercles.We interpret the central depression as anchoring site of a foraminiferan test and the radiating canals, formed right at the interface of the stereom and epithelium, as the work of its long and ramifying pseudopodia.The symbiotic relationship was probably of parasitic nature (sensu stricto), with the foraminiferan feeding on the organic tissue of the epithelium (epithelium browsing) and profiting from protection offered by the host's spines and defensive pedicellariae.The echinoid survived the infestation and formed skeletal regeneration textures that clearly identify the association as syn vivo.The high degree of specialisation required to infest an echinoid host and form the complex attachment trace might suggest that the pronounced rarity of the trace is not a case of a false host but of host specificity.The identity of the foraminiferan parasite remains unknown, although the bioerosion traces show some affinity to those of the extant species Cymbaloporella tabellaeformis and Gypsina vesicularis.

In the peaceful days before Christmas 2021, fate struck hard on fellow ichnologist Markus Bertling (Figure 1), when he learned of a devastating diagnosis that gave him very little chance to turn the tide. On February 13, 2022, Markus passed away, leaving behind a painful void in his family and the ichnologic community alike. Starting off in 1985 with research on Upper Jurassic coral reef palaeoecology and sedimentology in northern Germany, Markus received his doctoral degree in 1990 and quickly picked upon an interest in the trace fossils he found in Jurassic reef settings and established his f irst new ichnogenus, Arachnostega Bertling, 1992. In the following years, it was the bioerosion trace fossils and the lessons to learn from the bioerosion at Mesozoic coral reef settings that caught his particular interest (e.g., Bertling, 1995, 1997a, 1999a, 1999b, 1999c, 2002; Perry & Bertling, 2000). Since 1998, Markus was curator for palaeontology at the Institute of Palaeontology of the Westphalian Wilhelm’s University in Münster, Germany, and in 2007 he became one of the heads of the University’s Geomuseum. For the past decade, Markus was heavily involved in the complete refurnishing and modernization of the museum and had less valency to follow his scientific passion in ichnology and ichnotaxonomy. Nevertheless, he sustained his interest in this field of science and was involved, for instance, in various case studies on bioerosion traces in osteic and xylic substrates (e.g., Feng et al., 2019; Höpner & Bertling, 2017; Mikuláš et al., 2020) and contributed with this expertise to an extensive review and annotated list of all the known bioerosion ichnotaxa (Wisshak et al., 2019). Aside from Arachnostega gastrochaenae, Markus co-authored the erection of at least three ichnospecies, three ichnogenera and fourteen ichnofamilies (Höpner & Bertling, 2017; Wisshak et al., 2019). Markus was best known to the ichnologic research community as a leading authority when it came to both the nomenclature of trace fossils and ichnotaxonomic principles. His effort helped to implement the rules established in the International Code of Zoological Nomenclature and to advocate their application in all kinds of ichnotaxonomic work. This, in turn, enabled the ichnotaxonomist to apply ichnotaxobases more consistently, to focus on the erection of ichnotaxa by a valid procedure and avoiding the erection of too many monotypic taxa. Whenever there was a problem to solve on how to apply the Code, the trickier the better, it became a reflex for many ichnologists to send an e-mail to Markus, asking for his advice. His in-depth knowledge of the Code put him into the position to lead or contribute to several comments on the draft proposal to emend the Code with respect to trace fossils (Bertling et al., 2003, 2004; Genise et al., 2004). From 2017 onward, Markus himself served as a commissioner on the Internat ional Commission for Zoologica l Nomenclature, striving to foster the status of ichnotaxonomy in zoological nomenclature and contributing to the ongoing revision of the Code. His involvement with the ICZN was much appreciated by the broader taxonomic community and to honour his work, the vertebrate genus Bertlinggekko was named after him. Markus’ engagement in improving the Code testifies to his great talent and profound interest in sound (methodo)logical thinking and theories of scientific cognition – an invaluable trait he brought into the admittedly chaotic situation that was ichnotaxonomy in the 1990s. Markus became central to the ichnotaxonomic community in 1998 when spearheading

The Deep Adda-1 well in the Danish Central Graben, North Sea, provides a record of mid-Cretaceous sedimentation on the eastern flank of the intrabasinal Adda–Tyra inversion high. An upper Hauterivian – lower Barremian core in the Tuxen Formation spans the lower boundary of the laminated organic-rich Munk Marl Bed (MMB), a key marker bed in North Sea Cretaceous stratigraphy. Multidisciplinary sedimentological–biostratigraphic–palaeoecological data document the abrupt environmental shift at this boundary. The upper Hauterivian – lowermost Barremian lower Tuxen Formation (nannozones BC10 – lowermost BC14), beneath the MMB, represents a well-ventilated, current-swept setting supporting a diverse benthic fauna and characterized by a condensed succession with hardgrounds, at one level defining a biostratigraphic hiatus, and stacked, thin shallowing-upward parasequences. The succeeding lower Barremian MMB (nannozone BC14) attests to poorly oxygenated bottom waters and a total lack of epi- and infauna; the calm, inhospitable sea floor was intermittently disturbed by muddy turbidity currents and debris flows. The base-MMB surface is a complex fractured hardground indicative of relative sea-level fall and protracted winnowing of the cemented sea floor. The Deep Adda-1 core thus records a sea-level excursion that accompanied the onset of early Barremian oxygen depletion in concert with additional potential forcing factors such as coeval volcanism and watermass warming.

Physiological sensitivity of cold-water corals to ocean change is far less understood than of tropical corals and very little is known about the impacts of ocean acidification and warming on degradative processes of dead coral framework. In a 13-month laboratory experiment, we examined the interactive effects of gradually increasing temperature and pCO(2) levels on survival, growth, and respiration of two prominent color morphotypes (colormorphs) of the framework-forming cold-water coral Lophelia pertusa, as well as bioerosion and dissolution of dead framework. Calcification rates tended to increase with warming, showing temperature optima at similar to 14 degrees C (white colormorph) and 10-12 degrees C (orange colormorph) and decreased with increasing pCO(2). Net dissolution occurred at aragonite undersaturation (Omega(Ar) < 1 ) at similar to 1000 mu atm pCO(2). Under combined warming and acidification, the negative effects of acidification on growth were initially mitigated, but at similar to 1600 mu atm dissolution prevailed. Respiration rates increased with warming, more strongly in orange corals, while acidification slightly suppressed respiration. Calcification and respiration rates as well as polyp mortality were consistently higher in orange corals. Mortality increased considerably at 14-15 degrees C in both colormorphs. Bioerosion/dissolution of dead framework was not affected by warming alone but was significantly enhanced by acidification. While live corals may cope with intermediate levels of elevated pCO(2) and temperature, long-term impacts beyond levels projected for the end of this century will likely lead to skeletal dissolution and increased mortality. Our findings further suggest that acidification causes accelerated degradation of dead framework even at aragonite saturated conditions, which will eventually compromise the structural integrity of cold-water coral reefs.

Studies of marine microbioerosion in polar environments are scarce. They include our recent investigations of bioerosion traces preserved in sessile balanid skeletons from the Arctic Svalbard archipelago and the Antarctic Ross Sea. Here, we present results from a third study site, Frobisher Bay, in the eastern Canadian Arctic, together with a synthesis of our current knowledge of polar bioerosion in both hemispheres. Barnacles from 62 to 94 m water depth in Frobisher Bay were prepared using the cast-embedding technique to enable visualization of microboring traces by scanning electron microscopy. In total, six ichnotaxa of traces produced by organotrophic bioeroders were found. All recorded ichnotaxa were also present in Mosselbukta, Svalbard, and most in the Ross Sea. Frobisher Bay contrasts with Mosselbukta in that it is a siliciclastic-dominated environment and shows a lower ichnodiversity, which may be accounted for by the limited bathymetrical range and a high turbidity and sedimentation rate. We evaluate potential key ichnotaxa for the cold-temperate and polar regions, of which the most suitable are Flagrichnus baiulus and Saccomorpha guttulata, and propose adapted index ichnocoenoses for the interpretation of palaeobathymetry accordingly. Together, the three studies allow us to make provisional considerations about the biogeographical distribution of polar microbioerosion traces reflecting the ecophysiological limits of their makers.