Dynamic land-plant carbon sources in marine sediments inferred from ancient DNA

Terrigenous organic matter in marine sediments is considered a significant long-term carbon sink, yet our knowledge regarding its source taxa is severely limited. Here, we leverage land-plant ancient DNA from six globally distributed marine sediment cores covering the Last Glacial–Holocene transition as a proxy for the share, burial rate, preservation, and composition of terrigenous organic matter. We show that the spatial and temporal plant composition as revealed by sedimentary ancient DNA records reflects mainly the vegetation dynamics of nearby continents as revealed by comparison with pollen from land archives. However, we also find indications of a global north-to-south translocation of sedimentary ancient DNA. We also find that plant sedimentary ancient DNA has a higher burial rate in samples from the Late Glacial, which is characterized by high runoff and mineral load. This study provides an approach to understanding the global linkages between the terrestrial and marine carbon cycle, highlighting the need for further research to quantify the processes of DNA preservation and dispersal in marine sediments

Non‐native species have higher consumption rates than their native counterparts

Non-native species can be major drivers of ecosystem alteration, especially through changes in trophic interactions. Successful non-native species have been predicted to have greater resource use efficiency relative to trophically analogous native species (the Resource Consumption Hypothesis), but rigorous evidence remains equivocal. Here, we tested this proposition quantitatively in a global meta-analysis of comparative functional response studies. We calculated the log response ratio of paired non-native and native species functional responses, using attack rate and maximum consumption rate parameters as response variables. Explanatory variables were consumer taxonomic group and functional feeding group, habitat, native assemblage latitude, and non-native species taxonomic distinctiveness. Maximum consumption rates for non-native species were 70% higher, on average, than those of their native counterparts; attack rates also tended to be higher, but not significantly so. The magnitude of maximum consumption rate effect sizes varied with consumer taxonomic group and functional feeding group, being highest in favour of non-natives for molluscs and herbivores. Consumption rate differences between non-native and native species tended to be greater for freshwater taxa, perhaps reflecting sensitivity of insular freshwater food webs to novel consumers; this pattern needs to be explored further as additional data are obtained from terrestrial and marine ecosystems. In general, our results support the Resource Consumption Hypothesis, which can partly explain how successful non-native species can reduce native resource populations and restructure food webs

Holocene onshore/offshore tephra correlation of Mt. Etna, Sicily

The volcanic history of Mt. Etna is mainly known from studies of subaerial deposits and stratigraphy. However, little is known about the offshore deposits, which can provide a more detailed insight into geological and sedimentological processes affecting the flanks of Mt. Etna. During RV Meteor Cruise M178, eight gravity cores were taken offshore across the continental margin east of the volcanic edifice to re-evaluate the volcanic history of pre-historic eruptions and mass wasting events in the area. In total, we investigated 87 marine tephra layers in order to build a marine tephrostratigraphic framework. Based on major element compositions of glass shards, sediment componentry, and petrographic characteristics, 27 layers were identified as primary pyroclastic flow and fall deposits, i.e., directly related to an explosive volcanic eruption. However, most of the remaining tephra layers are interpreted to represent deposits of secondary density currents and are not necessarily related to a volcanic eruption. The marine dataset is complemented by twelve onshore samples taken from major explosive eruptions. Applying geochemical fingerprinting of volcanic glass shard compositions, we correlated eleven marine tephra deposits to seven well-known Mt. Etna eruptions (FV, FF, FG, FL, FS, TV, and M1 eruptions) within the last 12 kyr, which provide valuable time markers in the marine sediment record. Furthermore, we correlated ten marine tephra layers between the marine cores (four individual eruptions) and identified another six primary layers in single cores. In total, we discovered 17 widespread volcanic events in the marine record, including four previously unknown eruptions between 10 and 7.7 ka, which indicate that Mt. Etna was more active than previously thought during this time period

Foraminiferal denitrification and deep bioirrigation influence benthic biogeochemical cycling in a seasonally hypoxic fjord

Benthic macro- and micro-biota often play significant roles in controlling the biogeochemical dynamics in sediments. Their activity can be influenced by oxygen availability and impacted by the rise in global hypoxia in coastal regions over the last decades. To understand how these organisms interact with coastal hypoxia and influence sediment biogeochemistry, we undertook a study of early diagenesis in Bedford Basin, a seasonally hypoxic fjord on the West Atlantic coast in Nova Scotia, Canada, using a combination of observations and reaction-transport modeling. We observed that the seafloor was a source of ammonium and sink of nitrate with average fluxes of 2.2 ± 1.8 and −0.9 ± 0.7 mmol m−2 d−1 respectively. The diffusive oxygen uptake was 14 ± 4.6 mmol m−2 d−1 and the total organic carbon content in collected sediment cores was 5–7 % with a C/N ratio of ∼10. The pyrite content increased steadily from 0.5 wt% Fe at surface to ∼2 wt% Fe at 20 cm depth. Hydrogen sulfide was negligible down to 25 cm depth most of the time. The sediment was inhabited by tube-forming polychaete Spiochaetopterus sp. that formed tubes up to ∼30 cm in length. The living foraminiferal assemblage in the top 5 cm sediment was found to be dominated (>85 %) by nitrate-storing and denitrifying benthic foraminifera Stainforthia fusiformis. These observations were used to develop and constrain a biogeochemical reaction-transport model. The model results suggest that the observed decrease in porewater concentrations of ammonium and dissolved inorganic carbon below 5 cm depth, was due to deep bioirrigation by tubeworms, accounting for almost 50 % of the benthic efflux. The model further revealed that the deep bioirrigation along with bioturbation and iron cycling prevented accumulation of free sulfide in the top 25 cm sediment despite oxygen penetration depths of ∼1 mm. Modelled organic carbon and nitrogen deposition was 25.2 and 2.9 mmol m−2 d−1 with burial efficiencies of 23 % and 17 %, respectively. The model indicated a total denitrification rate of 1.3 mmol N m−2 d−1 that was largely (∼70 %) driven by benthic foraminifera. This study reports the first evidence of foraminiferal denitrification in western Atlantic coastal sediments, and suggests that eukaryote mediated denitrification is an important driver of sediment N-loss in seasonally hypoxic environments, a process that has been traditionally assumed to be carried out by prokaryotic microbes

Impact of Greenland Ice Sheet disintegration on atmosphere and ocean disentangled

We analyze the impact of a disintegrated Greenland Ice Sheet (GrIS) on the climate through steady-state simulations with the global Max Planck Institute for Meteorology Earth System Model (MPI-ESM). This advances our understanding of the intricate feedbacks between the GrIS and the full climate system. Sensitivity experiments enable the quantification of the individual contributions of altered Greenland surface elevation and properties (e.g., land cover) to the atmospheric and oceanic climate response. Removing the GrIS results in reduced mechanical atmospheric blocking, warmer air temperatures over Greenland and thereby changes in the atmospheric circulation. The latter alters the wind stress on the ocean, which controls the ocean-mass transport through the Arctic gateways. Without the GrIS, the upper Nordic Seas are fresher, attenuating deep-water formation. In the Labrador Sea, deep-water formation is weaker despite a higher upper-ocean salinity, as the inflow of dense overflow from the Denmark Strait is reduced. Our sensitivity experiments show that the atmospheric response is primarily driven by the lower surface elevation. The lower Greenland elevation dominates the ocean response through wind-stress changes. Only in the Labrador Sea do altered Greenland surface properties dominate the ocean response, as this region stores excessive heat from the Greenland warming. The main drivers vary vertically: the elevation effect controls upper-ocean densities, while surface properties are important for the intermediate and deep ocean. Despite the confinement of most responses to the Arctic, a disintegrated GrIS also influences remote climates, such as air temperatures in Europe, the Atlantic Meridional Overturning Circulation (AMOC) and the subtropical gyre. These interactions and feedbacks between ice sheets and the other climate components highlight the necessity of including dynamic ice sheets in climate models that are used for future projections

Shift in trophic strategy of coral holobionts exposed to internal waves in the Andaman Sea may contribute to higher bleaching resilience

Large amplitude internal waves (IW) of high frequencies break at the continental shelf in the Andaman Sea. These breaking waves travel upslope and periodically introduce cold, nutrient-rich, hypoxic subpycnocline water into shallow-water reefs while increasing organic matter flux. Locally, western island shores are exposed to IW-induced physicochemical variations, while eastern island shores are sheltered from these variations. Exposed reefs harbor corals with increased heat resistance, but the underlying mechanisms remain yet undiscovered. Heterotrophic feeding can play an important role in coral bleaching resilience, thus, a shift in trophic strategy through IW-enriched nutrients and organic matter flux may contribute to thermal resistance. Here we analyzed the fatty acid (FA) profiles of hosts and symbionts of two crucial reef-building species, Porites sp. and Pocillopora sp. from both shore sides. Preliminary results show that host and symbiont FA profiles were coral speciesspecific despite similar total lipid concentrations. Coral hosts and symbionts can transfer lipids from one to another. Nevertheless, in both species, symbiont FA compositions were distinct from host FA. This difference was considerably larger in the more heterotrophic coral Porites, likely because they exchange fewer lipids with their symbionts. Furthermore, Porites coral hosts on IW-exposed reefs showed a FA composition with a more heterotrophic signature than those on IW-sheltered sites. This suggests coral holobionts on IW-exposed reefs were likely able to utilize enriched nutrients and plankton delivery by IW and this could contribute to their improved bleaching resistance. Ongoing stable isotope analysis will provide further insights into IW-induced shifts in trophic strategy

Mode ofextension during the Xisha Trough rift in the South China Sea

A seismic transect across the Xisha Trough failed rift provides information on processes active during the opening of the South China Sea (SCS). The rift basement gradually thins at the conjugate flanks from ∼25 to 15 km toward the central sector, where it abruptly thins to ∼10–6 km in thickness. The seismic velocity model supports that 6.5 km/s velocity separates an upper from a lower crust layer, where Vp reaches 7.1 km/s above Moho. The upper crust extends across the entire rift, but the lower crust layer does not occur in the thin crust of the central sector, which is underlain by mantle with anomalously low Vp, indicating serpentinization. Changes in tectonic structure mimic the Vp distribution. The rift flanks have comparatively small faults associated to gradual thinning, whereas the central sector has larger faults that possibly reach the mantle. The faulting in the central sector thus indicates whole-crust embrittlement, which possibly led to synrift mantle serpentinization. Despite the weaker rheology, serpentinized mantle did not result in the development of low-angle faulting or continental break-up. Furthermore, the rift overall thinning and faulting structure is asymmetric with respect to the rift center, supporting an initial widespread moderate extension creating the flanks. When extension thinned the crust to <15 km, the whole crust was brittle and deformation first focused and subsequently laterally migrated to create the central sector. The continental Xisha Trough rift evolution is similar to classical magma-poor margins, but synrift magmatism described in adjacent regions indicate abrupt segmentation of the rift system. Key Points Xisha Trough rift continental extension evolved from initially distributed pure shear to focused simple shear Asymmetric flanks support initial moderate extension followed by deformation focusing in a central sector underlaid by serpentinized mantle Xisha Trough evolution resembles magma-poor margins, but adjacent magmatism indicates abrupt rift segmentation Plain Language Summary Continental rifting, breakup, and subsequent seafloor spreading represent a continuous evolutionary sequence. The South China Sea (SCS) experienced al steps until seafloor spreading, with much of the existing research focused on the continent-ocean transition (COT) zone. However, there is limited understanding of the structures emerged during the continental rifting. The Xisha Trough, an abandoned rift of the SCS, preserves features formed during continental extension. In this study, we revealed the velocity structure, tectonic features, and density distribution of the profile across Xisha Trough using wide-angle seismic data, multi-channel seismic data, and gravity data. Our results revealed that crustal structure is asymmetric, with distributed small faults at the beginning, and the extension concentrated in the axial region with evolution, where crust experienced significant thinning with the absence of lower crust, and hydration of the upper-most mantle rocks. Our findings indicate that the extension pattern in the Xisha Trough closely resembles that of magma-poor margins. Furthermore, when combined with insights from previous studies in the SCS, our research implies that the rheological behavior throughout the evolution of the SCS exhibits substantial lateral variability

Assessing the potential physiological impacts of urban development around lemon shark (Negaprion brevirostris) nurseries: effects on neonate and juvenile health

Highlights: • Urbanization threatens critical lemon shark nurseries in The Bahamas. • Degraded nurseries show elevated stress markers in neonate and juvenile sharks. • Community-based conservation is vital to preserve mangroves and nursery habitats. • Strengthened legal frameworks are needed to mitigate urbanization impacts. Urbanization driven by population growth, development and tourism increasingly threatens even remote areas, potentially impacting biodiversity. This is particularly concerning given the ecological and economic importance of biodiversity, especially for island nations, where ecotourism plays a crucial role in the economy. This study examines urban-driven degradation effects on the nurseries of lemon sharks, a predator with strong site fidelity to its birthing and nursery areas. Six sites in South Eleuthera, The Bahamas, were assessed, analyzing proxies indicative of body condition (triglycerides/cholesterol ratio, body condition index) and energetic stress markers (glucose, β-hydroxybutyrate, triglycerides, total cholesterol) in neonates and juveniles compared across nurseries relative to degradation scores. While TAG/CHOL and BCI were not significantly different between nurseries, energetic markers were overall higher in more degraded nurseries. Moreover, total urban score was a significant predictor for glucose, β-hydroxybutyrate, and triglyceride ciruclating concentrations. These findings, coupled with prior studies carried out in Bimini, suggest that urban development around lemon shark nurseries in The Bahamas may negatively impact shark health. Cooperative monitoring, community initiatives for mangrove preservation, and stronger urbanization laws are required to mitigate these impacts. As urbanization and environmental degradation are universal threats to mangroves worldwide, this approach can be adapted to study urbanization impacts on other species in regions such as Southeast Asia, the Caribbean, the Pacific Islands, and the coasts of Africa and South America, which face similar urban encroachment, habitat degradation, and biodiversity loss challenges

Reflections on delivering place-based climate risk data in support of local adaptation decisions

Strengthening the adaptive capacity of the UK, via national plans and local-scale interventions, requires easy access to climate risk information and adaptation scenarios. Stakeholder engagement can ensure the right balance between top-down prescriptive modelling, and bottom-up, solution-focussed and lived experience approaches. National-scale, spatially-explicit, integrated climate risk frameworks can help inform the needs of localised climate risk assessments, but there are barriers to local actors accessing the information