Oceanographic Setting Research Articles

Evolution of a buried moat-drift system within the Ewing Terrace uncovering highly dynamic bottom currents at the Argentine Margin during Early Oligocene to Middle Miocene

The Ewing Terrace is a relatively flat surface formed by the action of bottom currents and part of a Contourite Depositional System (CDS) at the Argentine continental slope. It is situated in a highly complex oceanographic setting at the Brazil-Malvinas Confluence Zone. Located in water depths of approx. 1000 – 1200 m and incised by the Mar del Plata Canyon, the Ewing Terrace is separated into the Northern Ewing Terrace (NET) and the Southern Ewing Terrace (SET). The long-term variations in ocean circulation led to a complex internal architecture of the terrace. As a result, this region represents a unique archive for studying sedimentary features that were eroded, transported, and deposited by along- and down-slope processes. An in-depth data analysis of high-resolution multichannel seismic profiles exhibits a complex sequence of erosional and depositional contouritic features, namely buried moat-drift systems identified in depths of approx. 370-750 m below the seafloor. They are arranged in migrating sequences and clustered in the Early Oligocene to Middle Miocene. This pattern is probably attributable to the vertical shift of water masses and to a highly dynamic oceanographic setting with spatial changes influenced by the Brazil-Malvinas Confluence Zone over this particular geological time. The moat-drift systems reveal significant lateral changes from north to south. In the southern area of the SET the moats are constructional and the associated separated mounded drifts are well developed. In contrast, the northern area exhibits two types of moats, reminiscent of cut-and-fill structures that mirror the significant and rapid changes in bottom current dynamics. With these new insights, this study contributes to a better understanding of moat-drift systems and improves the knowledge about past oceanographic dynamics and sediment deposition at the northern Argentine margin.

Influence of changing water mass circulation on detrital component and carbon burial of late Pleistocene and Holocene sediments in the eastern-central Mid-Adriatic deep

A sediment core was retrieved in the eastern-central Mid-Adriatic Deep (MAD) to study the changes in the water mass circulation and their effect on carbon burial efficiency and the provenance of a detrital sediment component. An age-depth model of the sediment core POS-514-40-11 is based on radiocarbon dating and tephrochronology. Two tephra were correlated to the Neapolitan Yellow Tuff and Pomici di Mercato eruptions, extending the previously known distribution of Pomici di Mercato tephra. Based on the analysis of heavy mineral (HM) assemblages throughout the core, for the first time the occurrence of Eastern Adriatic current (EAC) was estimated at ca. 15 ka BP, i.e., at the beginning of the post last glacial maximum (LGM) transgression. During the late Pleistocene, the detrital component was dominated by Paleo-Po river sediments, which gradually shifted toward the Albanian province as a basin-wide counterclockwise circulation was established. Mass accumulation rates of organic carbon (OC), stable isotopes of carbon (δ 13C) and nitrogen (δ 15N) as well as C/N ratios, showed that carbon burial was affected by sea level rise and climatic changes. Climatic effects are observed during cold periods i.e., the Younger Dryas and the 8.4–7.9 ka cold period when terrestrial OC was dominant. In the latter case dominance of terrestrial carbon was due to the North Adriatic dense water (NAddW) influence. On the other hand, sea level rise increased MAD distance from the main river mouths/deltas, resulting in decreased influx of terrestrial organic carbon and lower accumulation rates of organic carbon in general. This reconstruction of the oceanographic setting is valuable considering that the Adriatic Sea is one of the key locations for the formation of DW and thus affects the overall Mediterranean circulation.

Acoustic imaging of stable double diffusion in the Madeira abyssal plain

Sub-mesoscale and mesoscale (i.e., 1–10 km and 10–200 km, respectively) ocean processes are highly relevant for the understanding of global circulation, mixing of water masses and energy exchange between ocean layers. However, the processes happening at these scales are hard to be characterized using direct measurements of temperature and salinity. Direct measurements are obtained from vertical probes and/or autonomous vehicles, which, despite their high vertical resolution, are sparsely located in space and therefore unable to capture spatial details at these scales. Seismic oceanography (SO) data have been successfully used to imaging and characterize the ocean at these spatial scales. These data represent indirect measurements of the ocean temperature and salinity along kilometric transects with high horizontal resolution (i.e., a near-synaptic view of the system under investigation), but lower vertical resolution when compared with direct observations. Despite its complex oceanographic setting, the Madeira Abyssal Plain is still largely uncharacterized due to the lack of direct observations. We show for the first time a comprehensive processing, modelling and interpretation of three 2-D seismic oceanography sections from this region. The data show coherent seismic reflection in space, depth and time and shed light into this oceanographic setting with an unprecedent horizontal resolution. The SO modelling and interpretation are combined with existing direct measurements and a quantitative method to correlate thermohaline staircases interpreted from conductivity-temperature-depth casts and seismic reflections is proposed. The results show the relatively stable presence of thermohaline staircases in simultaneously time and space between 1200 and 2000 m of water depth and their spatial variability and contribute to the generalization of SO in physical oceanography.

The dynamic ocean redox evolution during the late Cambrian SPICE: Evidence from the I/Ca proxy

The late Cambrian Steptoean positive carbon isotope excursion (SPICE) is a distinct chemostratigraphic feature of the Paleozoic, marked by a 4–5‰ shift in carbonate δ13C that has been recognized across the globe during the Paibian Stage. The SPICE may be related to enhanced burial of organic matter and pyrite during the expansion of marine euxinia, which as a source of O2 also results in a pulse of atmospheric oxygen. However, geochemical proxies have not clearly illustrated how the ocean redox evolved with atmospheric oxygen changes during the SPICE. This study presents new carbonate I/Ca data, a redox proxy for the upper ocean, from three basins. I/Ca values are low at Great Basin and South China from early into the peak of SPICE, indicating generally anoxic conditions in shallow waters. The overall increasing trend in I/Ca through the peak and recovery phase of the SPICE roughly correlates with the previously modeled rise in atmospheric oxygen. Spatially, the Georgina Basin (Mt. Whelan) might have recorded a relatively more oxic upper ocean compared to the Great Basin and South China. Earth system model simulations also demonstrate the importance of paleogeographic and oceanographic settings on local redox conditions, highlighting the redox heterogeneity during the SPICE.

Spatial and temporal patterns of scyphozoan jellyfish abundance and growth in Icelandic coastal waters – a climate change perspective

ABSTRACT Scyphozoan jellyfish in Icelandic waters have received limited attention, despite apparent recent increases in blooms and changes in the regional oceanographic setting. The objectives of this study were to describe the species composition, abundance, phenology, and growth of scyphomedusae around Iceland and explore changes by comparing our findings with reports from the 1930s. Specimens were collected with a Bongo net in five regions around Iceland in the spring, summer, and autumn of 2008. Three jellyfish species were collected in the study, Aurelia aurita, followed by Cyanea capillata, and C. lamarckii. In the western and northwestern parts of Iceland, A. aurita abundance was highest in spring and summer, whereas in the North and East, abundances were highest in autumn. Cyanea capillata was not encountered in the Southwest, but in the west, Northwest, and North. There, numbers were highest in spring, whereas in the East, abundance was highest in autumn. Clockwise coastal current dispersal and regional interconnectivity are indicated. Weight-specific growth rates varied between 7.0 and 8.5% d−1 for A. aurita and 11.1 and 15.7% d−1 for C. capillata and are comparable to rates from often food-limited ecosystems at temperate latitudes. Presented evidence suggests that ephyrae and small medusae appear earlier in the season and in previously (in the 1930s) not occupied regions, while some regions (Southwest for C. capillata) were not populated anymore.

Integrated statistical analysis of calcareous nannofossil and elemental geochemistry of an outcrop from of the eastern Cenomanian Western Interior Seaway: Novel insights of shallow marine paleoceanography and nannoplankton paleoecology

Phytoplankton assemblages in shallow marine environments are being impacted by anthropogenic climate change, but long-term outcomes of these changes are uncertain. Investigation of past neritic calcareous nannoplankton can help us understand the fate these ecosystems face. In this study, a Canonical Correspondence Analysis (CCA) of calcareous nannofossils and X-ray fluorescence geochemistry was used to determine how past planktonic ecosystems were influenced by paleoenvironmental parameters on the eastern side of the Late Cretaceous Western Interior Seaway in the Cenomanian (ca. 95–93 Ma). Samples were collected every 10 cm from the Graneros Shale Greenhorn Formation at an outcrop in northwestern Iowa to determine high resolution changes in assemblages and paleoenvironments. Nannofossil diversity outside of a few small intervals ranges is high (generally 30–60 species) with abundant small Biscutum constans, confirming other publications that show elevated diversity in Cretaceous nearshore settings. The CCA results imply assemblages were most influenced by terrigenous influence, wet vs. dry climate, and changes in water mass source. Cretaceous nannofossil paleoecology was also revised based on the CCA results. Size differentiation of nannofossil taxa may highlight more complexity in environmental preferences that have been largely overlooked. After the initial transgression of the Greenhorn Sea into the region, the climate became wetter and terrigenous influence in the area was high. The peak of terrigenous influence corresponds with elevated nannofossil diversity but a lack of microfauna, which may indicate a similar oceanographic setting to the modern Gulf of Mexico nearshore dead zone. As sea level continued to rise above this point, nannoplankton assemblages indicate a potential shift to a higher productivity, stratified water column. As the muddy Graneros Shale transitioned to a further offshore chalky Greenhorn Formation, a normal marine, cosmopolitan nannofloral assemblage became established. Nannofossil and geochemical evidence indicates high productivity from upwelling might be related to the change of deposition to chalk in the Greenhorn Formation. While only a single outcrop was investigated, the novel use of an integrated micropaleontological and geochemical analysis has shed light on the dynamics of how phytoplankton ecosystems were established and modified in shallow marine environments of the Cretaceous and could have important implications on modern shallow marine settings.

Integration of empirical and modelled data unravels spatiotemporal distribution and connectivity patterns of Fuegian sprat early life stages

The distribution patterns of fish early life stages are critical to recruitment success and closely related to major oceanographic circulation patterns. We explored the spatiotemporal distribution of early life stages of Fuegian sprat Sprattus fuegensis, a key trophic species in the Southwestern Atlantic Ocean (SWAO), in a complex oceanographic setting. Samples were collected during austral spring, summer, and autumn, from 2014 to 2017, across areas with distinct biophysical properties between Tierra del Fuego (TDF) and the marine protected area ‘Namuncurá’ at Burdwood Bank (BB) (ca. 54°S). Results revealed significant seasonal fluctuations in abundance, distribution, and ontogenetic composition across habitats. High egg and early larval abundances at Isla de los Estados (IE) suggest it is an additional spawning ground to those previously identified at TDF and BB. However, only the latter appear to be suitable nursery areas. Particle-tracking simulations based on egg abundance and spawning dates were conducted for the first time using results from a high-resolution hydrodynamic model. Particle transport provides evidence of connectivity between IE and neighbouring areas—enhanced when horizontal diffusivity is incorporated into the model—but not between TDF and BB. Simulated distributions closely resembled empirical patterns from this and other studies, allowing the integration of empirical and modelled data to schematize the species’ dispersal pathways in the study area. These results offer new insights into distribution and connectivity patterns among spawning grounds and highlight the potential use of hydrodynamic models for future assessments of Fuegian sprat and other planktonic species’ dispersal and recruitment in the SWAO.

Channel inception through bottom‐current erosion of pockmarks revealed by numerical simulation

AbstractIn deep‐marine environments, the inception of channels can be induced by the interaction between bottom currents and rough topography. However, it is still unclear under which conditions such features can form and what happens in the earliest phase of channel development. In this study, based on the morphological, sedimentary and oceanographic settings of a pockmark field in the NW South China Sea, we reveal the process of channel inception through the erosion of pockmarks by bottom currents. Using numerical simulations, we show that an appropriate current velocity can induce the erosion of pockmark trains in cohesive sediments, leading to the coalescence of discrete pockmarks and the formation of a channel with a rough thalweg. The interaction of bottom currents with the pockmarks induces a significant erosion along the pockmarks axis. Bottom‐current erosion is strongest at the downstream edges of pockmarks, where the horizontal velocity reaches a maximum and an upwelling forms. Erosion increases as the distance between pockmarks reduces. In our simulation results, a channel is only formed by the coalescence of pockmarks if the distance between pockmarks is <6 times the diameter of the pockmark. This study provides evidence of the formation of channels by bottom currents, which helps reconstruct palaeoceanographic conditions based on sediment architecture. It also shows the complex hydrodynamics at these structures that strongly control sedimentary processes and may affect distribution of benthic ecosystems in marine environments.

Paleoceanographic Implications of Diatom Seasonal Laminations in the Upper Miocene Pisco Formation (Ica Desert, Peru) and Their Clues on the Development of the Pisco Fossil‐Lagerstätte

AbstractThe detailed study of diatom laminations conducted by means of backscattered electron imaging serves as tool to unravel details of past ocean dynamics. In this paper we apply this method to the analysis of the diatomites of Cerro Los Quesos, Upper Miocene Pisco Fm, Peru. Numerous studies have been conducted on the Pisco Fm; however, a focus on its paleoceanographic significance is still lacking. In this work, we provide information on the oceanographic setting in the area at the time of diatomites deposition. The high abundance of deep‐living Coscinodiscus laminae, proceeded by either a mixed lamina or a terrigenous one, let us hypothesize a deep position of the thermocline during the deposition of the Pisco diatomites; together with the scarcity of Chaetoceros Hyalochaete spp. resting spores, this evidence confutes the belief that equals high biogenic silica content in marine sediments with enhanced upwelling. Conversely, the depositional setting of the Pisco Fm diatomites is more similar to what is known as “permanent El Niño” (or “El Padre”) state, meaning a constant weakened upwelling (or upwelling of nutrients‐poor waters). Climate modeling warns that an increase in atmospheric CO2 may lead to this mean state in the near future. Thanks to this study we also obtained refined information on the diatomites sedimentations rates. The comparison of the Pisco diatomites sedimentation rates with those of Quaternary diatomites gave strength to the hypothesis that the formation of the vertebrate Lagerstätte may have been enhanced, among others, by the so‐called “impact‐burial” mechanism.

Testing the potential of Serpulidae tubes as an indicator of past relative sea-level collected from shored wave dissipating blocks along the Pacific and Japan sea coast of northeastern Japan

Relative sea-levels (RSL) in the past can be used to understand crustal movements, as paleo-shoreline elevations can be modified by seismic activities [1]. To assess short-term crustal movements, reliable RSL proxies are key in age determination to derive precise tectonic activities. The Tohoku region in northern Japan has complex oceanographic setting since two currents, cold Oyashio and warm Kuroshio being merged in the region. Here, we assessed the potential of Hydroides ezoensis (HE), as a new proxy of RSL. The 14C concentrations of HE collected in the Tohoku region were measured and compared with previous studies that reported radiocarbon values of the surface ocean. Results showed HE possesses summer surface 14C. This suggests that HE is suitable to be used as a reliable RSL proxy that can reliably provide age information without having influences from radiocarbon depleted Oyashio. Thus, HE could be used as a reliable proxy to understand paleo-RSL.

Evolution of complex giant seafloor depressions at the northern Argentine continental margin (SW Atlantic Ocean) under the influence of a dynamic bottom current regime

Seafloor depressions (SD) are features commonly observed on the ocean floor. They often occur as circular, small-sized (up to 10 s of m) incisions caused by fluid expulsion. Larger depressions (100s m to km) are considerably less abundant, and their origin and development have been scarcely studied. This study investigated two giant morphological depressions (>5 km) using recently acquired multibeam bathymetry and backscatter, sediment echosounder, and high-resolution seismic data. An arc-shaped (SD-N) and a sub-circular depression (SD-S) are located on the Ewing Terrace at the Argentine Continental Margin north and south of the Mar del Plata Canyon, respectively. The study area is influenced by the Brazil-Malvinas Confluence, where major counterflowing ocean currents affect sedimentation, and northward flowing currents form a large contourite depositional system. Using an existing seismo-stratigraphy, the onset of SD-N was dated to the middle Miocene (∼15–17 Ma), whereas SD-S started developing at the Miocene/Pliocene boundary (∼6 Ma). Acoustic anomalies indicate the presence of gas and diffuse upward fluid migration, and therefore seafloor seepage is proposed as the initial mechanism for SD-S, whereas we consider a structural control for SD-N to be most likely. Initial depressions were reworked and maintained by strong and variable bottom currents, resulting in prograding clinoform reflection patterns (SD-N) or leading to the build-up of extensive cut-and-fill structures (SD-S). Altogether, this study highlights the evolution of two unique and complex seafloor depressions throughout the geologic past under intense and variable bottom current activity in a highly dynamic oceanographic setting.

Distinguishing the influence of sediments, the Congo River, and water-mass mixing on the distribution of iron and its isotopes in the Southeast Atlantic Ocean

Iron (Fe) is an essential micronutrient for primary production, and Fe isotopic composition (δ56Fe) has become a widely used oceanographic tool for determining sources and evaluating the biogeochemical cycling of dissolved Fe (dFe) in the oceans. Here, we present dFe concentrations and δ56Fe from three unique oceanographic settings (a river dominated margin, a highly productive coastal upwelling margin, and a meridional open ocean transect) collected during the South Atlantic GEOTRACES cruise GA08 along the Namibian-Congo margin. In the North, the offshore Congo River plume dominates the surface ocean, resulting in elevated surface dFe concentrations up to 1000 km from the river mouth, corresponding to increasing δ56Fe values (+0.33 to +0.95‰) with distance from the river outlet. We attribute this unusual and extensive offshore delivery of heavy Fe to dFe preservation by complexation with organic ligands, coupled with rapid off-shelf advection. In the South, the highly productive Benguela Upwelling System produces oxygen depleted to seasonally anoxic bottom waters on the continental shelf, resulting in extremely high subsurface dFe concentrations (up to 42 nmol kg-1) and remarkably light δ56Fe values (as low as -3.31‰), characteristic of dFe(II) production and mobilization via reductive dissolution of Fe oxyhydroxides in sediments. Away from the continental margins, surface waters carry predictably low dFe concentrations (∼0.1 nmol kg-1), associated with isotopically heavy Fe linked to dust deposition and biological uptake. In subsurface waters, and away from Fe sources, we find a remarkably coherent relationship between water masses and dissolved δ56Fe signatures along the GA08 section. Using δ56Fe data from GA08 and water mass analysis, we assign endmember signatures of -0.12 ± 0.02‰ for AAIW, +0.71 ± 0.09‰ for NADW, and +0.35 ± 0.12‰ for AABW. Overall, we find that the distribution of δ56Fe in the South Atlantic can largely be explained by water mass mixing, with some overprinting by local processes and sources, suggesting that dissolved δ56Fe signatures can be used as tracers of deep ocean Fe transport.

Plio-Pleistocene Planktic Foraminiferal Biochronology of ODP Site 762B, Exmouth Plateau, Southeast Indian Ocean

ABSTRACTThe Indonesian Throughflow region connects the tropical Pacific Ocean with the eastern Indian Ocean, and variability of the Throughflow during the Plio-Pleistocene has been related to major climate shifts at the global level. Planktic foraminiferal biostratigraphy integrated with magnetochronology provides a robust time framework for assigning age control to major paleoceanographic events. Understanding of the coupled histories of the El Niño Southern Oscillation, Western Pacific Warm Pool, Indonesian Throughflow, and the eastern Indian Ocean has greatly benefitted from the chronological framework provided by planktic foraminiferal biostratigraphies from these regions. Ocean Drilling Program (ODP) Hole 762 lies under the influence of the Leeuwin Current, originating from the Indonesian Throughflow. Multiproxy data have been collected from Hole 762B and other nearby sites for paleoceanographic interpretation. However, a detailed planktic foraminiferal biostratigraphy integrated with magnetochronology is not available from this site. We provide here the sequential order of planktic foraminiferal First Occurrence (FO) and Last Occurrence (LO) events, which allowed us to divide the examined section into seven biostratigraphic zones. The biostratigraphy was integrated with magnetostratigraphy using revised ages of magnetochrons, which yielded biochronological age estimates for planktic foraminiferal events. A major planktonic faunal turnover between 3.4 and 2.7 Ma is probably related to the onset of the Northern Hemisphere glaciation and related changes in the Indonesian Throughflow. We have compared our numerical age estimates with published ages from other parts of the world. The diachronism observed probably is related to the local oceanographic setting of ODP Hole 762B, which has been alternatively influenced by changing strengths of the warm Leeuwin Current and the cold west Australian Current. The biochronology established here will be useful for correlating paleoceanographic events in the region.

Controls on large-scale architecture and facies distribution of an oolitic-microbial carbonate shelf margin, Nanpanjiang Basin, south China

Carbonate factory types and facies architecture of carbonate depositional systems result from complex interactions among several space- and time-dependent variables, including paleobathymetry, tectonic setting, water chemistry and oceanographic setting, clastic sediment influx, and accommodation. Whereas tropical factories that dominate modern settings have been documented and modelled extensively, microbial-oolitic systems, which are very common throughout the Paleozoic and Mesozoic, have received less attention.Continuous exposures along a platform-to-basin transect of an Early Triassic (Induan) microbial-oolitic carbonate ramp to shelf system in the Nanpanjiang Basin, South China, serves as a viable analogue to similar systems, including the Jurassic Smackover Formation of the Gulf of Mexico, and provide a natural laboratory to test these variables. Carbonate deposition following end-Permian regional drowning and retreat of the Yangtze Platform resulted in low-angle margin-slope systems during the Early Triassic. Lower Triassic carbonate systems display shifts in carbonate factory types, including skeletal, microbial, and abiotic factories, and lateral and vertical architectural variability.We applied stratigraphic forward modelling using DIONISOSFLOW, calibrated with detailed stratigraphic sections and facies mapping, to assess the impact of carbonate factory type, antecedent topography, and variations in accommodation on facies distribution and large-scale geometries of the carbonate shelf margin. Results from model simulations suggest that in the absence of skeletal carbonates in the Lower Triassic, the architecture of the carbonate margin is mainly controlled by rate of microbial growth along the slope.

Contourite and Turbidite Features in the Middle Caspian Sea and Their Connection to Geohazards Derived from High-Resolution Seismic Data

High fluvial input combined with specific topographic and oceanographic settings in the Caspian Sea create favorable conditions for contourite deposition. For the first time in its middle portion, contourite deposits have been observed in high-resolution seismic profiles. Various types of contourite drifts and mixed depositional systems have been revealed on the lower slope and in the adjacent basin, some of which are accompanied by sediment wave fields. The deposition of contourites or turbidites and their lateral distribution is controlled by sea-floor topography and oceanographic processes, as well as the modern activity of gravity flows downslope on the western Caucasian slope and in the channel system on the Mangyshlak Sill. The contourite drifts and sediment wave fields form several contourite depositional systems, which seem to merge in the Caspian contourite depositional complex. This occurs near the foot of slopes of the Derbent Basin and is related to the counterclockwise circum-Caspian current in the Middle Caspian Sea. The fact that the Caspian Sea is the largest lake in the world makes this region a significant area for research into the “lake contourites” issue. The Caspian Sea is an important oil-producing area, and sedimentary processes related to the contourite and turbidite can be a source of potential geohazards in the construction and exploitation of underwater engineering structures

Revised ΔR values for the Barents Sea and its archipelagos as a pre-requisite for accurate and robust marine-based 14C chronologies

The calibration of marine 14C dates requires the incorporation of regionally specific marine reservoir offsets known as ΔR, essential for accurate and meaningful inter-archive comparisons. Revised, regional ΔR (‘ΔRR’) values for the Barents Sea are presented for molluscs and cetaceans for the two latest iterations of the marine calibration curve, based on previously published pre-bomb live-collected and radiocarbon-dated samples (‘ΔRL’; molluscs: n = 16; cetaceans: n = 18). Molluscan ΔRR, determined for four broad regional oceanographic settings, are: western Svalbard (including Bjørnøya), −61 ± 37 14C yrs (Marine20), 94 ± 38 14C yrs (Marine13); Franz Josef Land, −277 ± 57 14C yrs (Marine20), −122 ± 38 14C yrs (Marine13); Novaya Zemlya, −156 ± 73 14C yrs (Marine20), 0 ± 76 14C yrs (Marine13); northern Norway, −86 ± 39 14C yrs (Marine20), 74 ± 24 14C yrs (Marine13). Molluscan ΔRR values are considered applicable to other marine carbonate materials (e.g., foraminifera, ostracods). Cetacean ΔRR are determined for toothed (n = 10) and baleen (n = 8) whales, and a combined toothed-baleen group (n = 18): toothed, −161 ± 41 14C yrs (Marine20), 1 ± 41 14C yrs (Marine13); baleen, −158 ± 43 14C yrs (Marine20), 8 ± 41 14C yrs (Marine13); combined baleen-toothed whales, −160 ± 41 14C yrs (Marine20), 4 ± 49 14C yrs (Marine13). Where identification and separation of baleen and toothed whales is impossible the combined ΔRR term may be used. However, we explicitly discourage the application of existing cetacean ΔRR terms to other marine mammals. Our new ΔRR values are applicable for as long as those broad oceanographic conditions (circulation and ventilation) have persisted, i.e., through the Holocene. We recommend using the latest iteration of the marine calibration curve, Marine20, which seems to better capture the time-variant nature of R compared to Marine13. More ΔRL datapoints for both molluscs and cetaceans would improve the accuracy and precision of ΔRR. In the meantime, our new ΔR terms facilitate the calibration of marine 14C dates across the region, paving the way for meaningful and accurate late Quaternary histories and inter-regional comparisons.

Oceanographic setting influences the prokaryotic community and metabolome in deep-sea sponges

Marine sponges (phylum Porifera) are leading organisms for the discovery of bioactive compounds from nature. Their often rich and species-specific microbiota is hypothesised to be producing many of these compounds. Yet, environmental influences on the sponge-associated microbiota and bioactive compound production remain elusive. Here, we investigated the changes of microbiota and metabolomes in sponges along a depth range of 1232 m. Using 16S rRNA gene amplicon sequencing and untargeted metabolomics, we assessed prokaryotic and chemical diversities in three deep-sea sponge species: Geodia barretti, Stryphnus fortis, and Weberella bursa. Both prokaryotic communities and metabolome varied significantly with depth, which we hypothesized to be the effect of different water masses. Up to 35.5% of microbial ASVs (amplicon sequence variants) showed significant changes with depth while phylum-level composition of host microbiome remained unchanged. The metabolome varied with depth, with relative quantities of known bioactive compounds increasing or decreasing strongly. Other metabolites varying with depth were compatible solutes regulating osmolarity of the cells. Correlations between prokaryotic community and the bioactive compounds in G. barretti suggested members of Acidobacteria, Proteobacteria, Chloroflexi, or an unclassified prokaryote as potential producers.

A comparison of orbital-resolution, Late Pleistocene Alkenone and foraminiferal assemblage-based sea surface temperature reconstructions from the Southwest Pacific

Global and regional reconstructions of past climate conditions often incorporate sea surface temperature (SST) estimates from multiple proxies because not every paleotemperature proxy is applicable in all geographic locations. This practice of assimilating estimates from different proxies in global or regional temperature syntheses makes the implicit assumption that estimates derived from different proxies can be meaningfully intercompared. However, evidence to support the validity of this assumption is limited. Using paleotemperature data from sediments collected from ODP Site 1125 in the Southwest Pacific, we conduct a ∼1 Myr, orbital-scale SST proxy comparison of a recently published alkenone-derived SST record with a previously published foraminiferal assemblage-based SST record. These alkenone and foraminiferal assemblage SST datasets show strong structural similarity and yield remarkably similar estimates for basic climate metrics, including mean, median, standard deviation, and range. Statistical analysis indicates that the correlation between the two SST records is highly significant. In the spectral domain, the records share the same dominant 100 kyr beat, are coherent and in phase with each other at this frequency, and have the same coherence and phase relationship with benthic foraminiferal δ18O. Results from this work demonstrate that these two proxies would yield very similar estimates for the paleoclimate metrics most commonly used in empirical paleoclimate reconstructions that seek to document the evolution of climate over this interval. However, significant disparities between SST estimates derived from the two proxies exist for some time periods, particularly during glacial and interglacial extrema. This comparison suggests that treating estimates from these proxies as equivalent in studies that focus on short time windows (e.g. a few thousand to tens-of-thousands of years), particularly in investigations that seek to characterize glacial or interglacial extrema, could be potentially problematic. However, the sensitive location of Site 1125, just north of the Subtropical Front, likely accentuates the difference between temperature estimates from these proxies, which may be attenuated in other oceanographic settings. We attribute the discrepancies between the two SST records to two main causes: seasonal leakages of cold water across the Subtropical Front during glacial extrema and differential seasonality of maximum alkenone and foraminiferal production.

Seafloor pockmarks on the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand

ABSTRACT Enclosed depressions, termed pockmarks, are widespread seafloor morphologies, commonly associated with fluid seepage. This study provides the first detailed documentation of pockmarks offshore the South Westland margin of the South Island/Te Waipounamu, Aotearoa New Zealand. Pockmarks are identified from multibeam bathymetry (25-m grid) through manual and semi-automated selection in water depths of 100–2600 m. Pockmarks are most concentrated at 400–850 m water depth on continental slope areas between submarine canyons. A continuum of pockmark morphologies includes – (1) large (>0.5 km2 area) and irregularly shaped pockmarks above partially infilled channels; (2) small and circular pockmarks (∼100–200 m diameter; ∼0.008–0.03 km2 area) occurring between canyons; and (3) elongated and intermediate size pockmarks, generally oriented along-slope and often occurring above buried sediment waves. Elongated pockmarks appear to have been modified by near-seafloor oceanographic and/or turbidity current flows. Pockmark features occur across many locations around Aotearoa, including both the eastern and western margins. Some similar pockmark morphologies are identified in these different tectonic, sedimentary, and oceanographic settings, suggesting that there may be some similarity in formative mechanisms, but clear mechanisms leading to their formation remain enigmatic.

From Siliciclastic to Bioclastic Deposits in the Gulf of Naples: New Highlights from Offshore Ischia and Procida–Pozzuoli Based on Sedimentological and Seismo-Stratigraphic Data

This study discusses the siliciclastic to bioclastic deposits (in particular, the rhodolith deposits) in the Gulf of Naples based on sedimentological and seismo-stratigraphic data. The selected areas are offshore Ischia Island (offshore Casamicciola, Ischia Channel), where a dense network of sea-bottom samples has been collected, coupled with Sparker Multi-tip seismic lines, and offshore Procida–Pozzuoli (Procida Channel), where sea-bottom samples are available, in addition to Sparker seismic profiles. The basic methods applied in this research include sedimentological analysis, processing sedimentological data, and assessing seismo-stratigraphic criteria and techniques. In the Gulf of Naples, and particularly offshore Ischia, bioclastic sedimentation has been controlled by seafloor topography coupled with the oceanographic setting. Wide seismo-stratigraphic units include the bioclastic deposits in their uppermost part. Offshore Procida–Pozzuoli, siliciclastic deposits appear to prevail, coupled with pyroclastic units, and no significant bioclastic or rhodolith deposits have been outlined based on sedimentological and seismo-stratigraphic data. The occurrence of mixed siliciclastic–carbonate depositional systems is highlighted in this section of the Gulf of Naples based on the obtained results, which can be compared with similar systems recognized in the central Tyrrhenian Sea (Pontine Islands).