Atlantic Ocean Research Articles

Bacterial communities on giant kelp in the Magellan Strait: Geographical and intra-thallus patterns.

The giant kelp Macrocystis pyrifera is categorized as a keystone species, forming highly productive forests that provide ecosystem services and host a remarkable marine biodiversity of macro and microorganisms. The association of microorganisms with the algae is close and can be functionally interdependent. The Magellan Strait, a natural marine passage between the Atlantic and Pacific oceans, harbours extensive giant kelp forests. However, information related to the diversity of bacterial communities in this region is still scarce. In this study, 16S rRNA gene metabarcoding was used to characterize the diversity and composition of bacterial communities associated with apical blades and sporophylls of M. pyrifera from different sites (Bahía Buzo, San Gregorio, and Buque Quemado). Additionally, data from satellites and reanalysis, as well as tide data, were used to characterize the environmental variability. The findings revealed discernible local variations in bacterial taxa across sampling sites, with consistent dominance of Proteobacteria, Verrucomicrobia, Bacteroidetes, and Planctomycetes. Furthermore, a distinctive bacterial community structure was identified between apical and sporophyll blades of M. pyrifera. This research marks the inaugural characterization of bacterial community diversity and composition associated with M. pyrifera in the remote and understudied sub-Antarctic region of the Magellan Strait.

Cross-Time-Scale Analysis of Year-Round Atmospheric Circulation Patterns and Their Impacts on Rainfall and Temperatures in the Iberian Peninsula

Abstract This study presents a framework to assess climate variability and change through atmospheric circulation patterns (CPs) and their link with regional processes across time scales. We evaluate the CP impacts on daily rainfall and maximum and minimum temperatures in the Iberian Peninsula using sea level pressure (SLP) during 1950–2022. Different sensitivity analyses are performed, employing multiple spatial domains and number of patterns. An optimal classification is found in midlatitudes, centered over the Mediterranean basin and covering part of the North Atlantic Ocean, which can identify atmospheric configurations significantly related to discriminated rainfall and temperature anomalies, with clear seasonal behavior. The temporal variability of CPs is studied across time scales showing, e.g., that transitions between patterns are faster in autumn and spring, and that CPs exhibit distinct temporal variability at intraseasonal, seasonal, interannual, and decadal scales, including significant long-term trends on their frequency. CPs influence temperature and precipitation variations throughout the year. The winter season exhibits the largest atmospheric circulation variability, while the summer is dominated by persistent high-pressure structures—the subtropical Azores high—leading to warm and dry conditions. Based on an interannual correlation analysis, some CPs are significantly associated with the North Atlantic Oscillation (NAO), stronger during winter, indicating the NAO modulation on the regional-to-local climatic features. Overall, this approach arises as a dynamic cross-time-scale framework that can be adapted to specific user needs and levels of regional detail, being useful to study climate drivers for climate change and to perform a process-based evaluation of climate models.

The largest to the south? Assessment of the latitudinal variation in Mustelus schmitti (Chondrichthyes: Carcharhiniforms: Triakidae), an endemic coastal shark of the Southwest Atlantic Ocean

Abstract Relative growth and life history traits along latitudinal gradients have been widely examined in bony fishes, but chondrichthyans have received less attention. The present work focuses on testing whether southern distributed individuals of Mustelus schmitti sharks are larger and will mature at larger sizes than northern distributed individuals. We also show that intraspecific variation follows the latitudinal pattern and that body shape proportions are not altered by latitudinal distribution. The specimens come from two areas 1200 km apart [Puerto Quequén (PQ) and Ria Deseado (Deseado estuary) (PD)], which implies 9 degrees of latitudinal difference. For PQ, four allometric variables related to the trunk of the body showed secondary sexual dimorphism, while for PD this dimorphism was observed in a single variable. The females of PQ presented with a higher relative growth of the trunk than the females of PD. Males, by contrast, did not present a characteristic growth pattern that could differentiate specimens between the two areas. Specimens of both sexes in PD reached a larger average total length at first maturity (P < .05) than those in PQ.

Supplemental description of Benedenia seriolae (Yamaguti, 1934) Meserve, 1938 (Monogenoidea: Capsalidae) and first record of the parasite infecting a wild greater amberjack, Seriola dumerili (Risso, 1810) Hureau and Tortonese, 1973 (Carangiformes: Carangidae) from the northern Gulf of Mexico

We herein provide a supplemental description of Benedenia seriolae (Yamaguti, 1934) Meserve, 1938 (Monogenoidea: Capsalidae Baird, 1853) based on specimens we collected from the skin of wild-caught greater amberjack (Seriola dumerili) in the northern Gulf of Mexico (GOM). Our specimens of B. seriolae from the GOM resemble those of Benedenia humboldti Baeza, Sepúlveda, and González, 2019 (from yellowtail amberjack, Seriola lalandi Valenciennes, 1833 [Carangidae] off Chile) by having a large body (>7000 μm in total length), non-overlapping anterior and posterior hamuli, an entirely sinistral and convoluted vas deferens, and a common genital pore as well as by lacking glands of Goto. It differs from B. humboldti by the shape of the penis tip. The 28S rRNA gene sequence differed from that of B. seriolae (from Japan) by 8 bp (1.1 %) and B. humboldti by 13 bp (2.8 %–1.7 %). The phylogenetic analysis recovered our sequences of B. seriolae sister to conspecific sequences from Japan, with that clade sister to B. humboldti from Chile. Benedenia was paraphyletic, suggesting some systematic revision to the genus could be warranted. Of 25 Benedenia spp., only Benedenia hendorffii (von Linstow, 1889) Odhner, 1905 had been reported previously from the GOM. Benedenia seriolae had previously not been reported from wild greater amberjack (previous records from greater amberjack were from sea cages only). This is also the first record of B. seriolae from the Northwestern Atlantic Ocean (GOM).

Morphosedimentary evolution of the Belgica Mound Drift: Controls on contourite depositional system development in association with cold-water coral mounds

Small-scale contourite drift is an important component of continental margins that can record information about complex oceanographic processes. The Belgica Mound Drift is one example of a small-scale contourite drift. It is formed under the influence of cold-water coral (CWC) mounds and represents one of the most distal contouritic expressions influenced by the Mediterranean Outflow Water (MOW) in the NE Atlantic Ocean. Three distinct evolutionary stages have been identified from new high-resolution pseudo-3D reflection seismic data, each associated with a significant change in paleoceanography, affecting both bottom-current intensity and sediment input. The pre-drift stage (Pliocene–Early Pleistocene) corresponds to the regional RD1 erosive event, which was caused by the reintroduction of the MOW in the Porcupine Seabight, creating a distinct paleotopography that will influence all ensuing sedimentary processes. The second stage (Early Pleistocene–Middle Pleistocene) is the contourite drift inception in two distinct centres of growth, strongly steered by topographic obstacles such as the CWC mounds. During the third and final stage (Middle Pleistocene–present day), the contourite drift is developed under a more stable but less dynamic environment, characterised by more continuous and mounded aggradational stratification. The final stage of the contourite drift is related to the Middle Pleistocene Transition, with a spatially variable reduction in the MOW-related bottom currents and sediment input. The spatial and temporal evolution of this drift shows that its present-day morphology is controlled by the location of initial growth. Evolving moat morphology indicates that the intensity of the bottom currents generally increases during the drift evolution.This research presents a crucial paradigm for advancing our knowledge of elucidating the complexities of smaller-sized contourite systems in diverse oceanic environments.

Dominant spring precipitation anomaly modes and circulation characteristics in the Tarim Basin, Central Asia

Recently, extreme precipitation has occurred frequently in the Tarim Basin, which has a fragile ecological environment, arousing widespread concern. Using daily precipitation observations from 42 stations in the Tarim Basin during the spring of 1980–2021 and monthly circulation reanalysis data from the European Center for Medium-Range Weather Forecasts Reanalysis v5, as well as statistical analyses and physical diagnostic methods, this study investigated the abnormal modes and the evolution characteristics and differences in atmospheric circulation. The results show that the spring precipitation anomalies in the Tarim Basin can be divided into two independent precipitation modes: the first (EOF1) is a precipitation pattern that is uniform throughout the region and the second (EOF2) is an east–west inverse pattern. Thus, there are distinct differences in the atmospheric circulation characteristics responsible for abnormal spring precipitation modes in the basin. When the precipitation across the entire basin is consistently excessive, the 500 hPa geopotential height is affected by the negative phase of the North Atlantic Oscillation related circulation, and the 700 hPa wind field is controlled by abnormal southwesterly winds. Water vapor transport is mainly driven by anomalous water vapor uplift along the terrain in the middle latitudes west of the Atlantic Ocean and south of the Arabian Sea. This leaves the Tarim Basin with a net water vapor budget and abnormally high atmospheric precipitable water. The opposite situation occurs when the precipitation across the entire basin is consistently lower than normal. When there is a west-to-east precipitation gradient, The western region of the Tarim Basin is dominated by upward airflow, whereas the eastern region is dominated by downward airflow, providing dynamic conditions for the west-to-east precipitation gradient. Under the influence of anomalous water vapor transport from the southwest and water vapor convergence, water vapor conditions favorable for precipitation can occur. The net water vapor in the basin also exhibited an abnormal west-to-east transport pattern. Moreover, the atmospheric precipitable water demonstrated an inverse phase distribution under the EOF2 atmospheric precipitation mode in the Tarim Basin.

Using DIC‐δ13C Pair to Constrain Anthropogenic Carbon Increase in the Southeastern Atlantic Ocean Over the Most Recent Decade (2010–2020)

AbstractThe southeastern Atlantic Ocean is a crucial yet understudied region for the ocean absorption of anthropogenic carbon (Canth). Data from the A12 (2020) and A13.5 (2010) cruises offer an opportunity to examine changes in dissolved inorganic carbon (DIC), its stable isotope (δ13C), and Canth over the past decade within a limited region (1∼3°E, 32∼42°S). For the decade of 2010–2020, Canth invasion was observed from the sea surface down to 1,200 m based on both DIC and δ13C data. The mean Canth increase rate (1.08 ± 0.26 mol m−2 yr−1) during this period accelerated from 0.87 ± 0.05 mol m−2 yr−1 during the previous period (1983/84–2010). The δ13C‐based Canth increase closely matches the DIC‐based estimation below 500 m but is 26% higher in the upper ocean. This discrepancy is likely due to δ13C's longer air‐sea exchange timescale, seasonal variability in the upper ocean, and the chosen ratio of anthropogenically induced changes in δ13C and DIC. Finally, column inventory changes based on the two methods also exhibit very similar mean Canth uptake rates. The paired DIC concentration and stable isotope dataset may enhance our ability to constrain Canth accumulation and its controlling mechanisms in the ocean.

Verification of Operational Forecast Models in Cases of Extratropical Transition of North Atlantic Hurricanes

Abstract Operational forecast models are necessary for the prediction of weather events in real time. Verification of these models must be performed to assess model skills and areas in need of improvement, particularly with different types of weather events that may occur. Despite the devastating impacts that can be caused by tropical cyclones (TCs) that undergo extratropical transition (ET) and become post-tropical cyclones (PTCs), these storms have not been extensively studied in the context of short-term weather prediction. This study completes the first analysis of the Global Forecast System (GFS) and a preoperational version of the newly operational Hurricane Analysis and Forecast System (HAFS) models in forecasting the occurrence of ET and the rainfall associated with ET storms in the North Atlantic basin. GFS’s skill exceeds that of HAFS in forecasting the occurrence of ET, but HAFS tends to have lower track and rain-rate errors in the fully tropical phase of ET storms’ life cycles. Both models simulate rain rates that are often too high near the storm center and fail to capture the larger area of moderate rain rates that greatly contributes to total rainfall accumulation. The discrepancies in rain rates between the models and Integrated Multi-satellitE Retrievals for GPM (IMERG) could be attributed to the models’ tendency to keep storms too intense and too compact with an overly strong warm core, even throughout the ET process.

U-Pb ages of pre- to post-salt carbonates, Santos and Campos basins, SE Brazil: Implications for the evolution of the South Atlantic

The exploration campaigns and independent studies conducted in the central South Atlantic basins after the discovery of giant oil accumulations in the Lower Cretaceous lacustrine carbonates sealed by the salt layer resulted in a new panorama of the tectonic framework, stratigraphic architecture, and petroleum systems of the investigated basins and passive margins in general. Despite these remarkable advances, the ages of the carbonate reservoirs and the sealing evaporites remain uncertain. Aiming to fill this gap, we present here the results of 30 U-Pb LA-ICP-MS calcite and dolomite age determinations representative of the depositional/eo-diagenetic processes and subsequent phases of carbonate cementation recorded by pre-to post-salt units of the Santos and Campos basins of southeastern Brazil. Microcrystalline calcite of a mudstone of the Itapema Formation (Santos Basin) yielded a minimum age of 126.8 ± 4.7 Ma. 19 depositional/eo-diagenetic ages obtained in mudstones, grainstones, shrubstones, spherulitestones, and travertines of the correlative Barra Velha and Macabu pre-salt lacustrine carbonates cluster around 124.1 ± 2.2 and 122.1 ± 2.3 Ma. Considering the errors, these results limit the deposition/eo-diagenesis of these units to the 126.2–120.0 Ma interval. Two determinations carried out in calcite laminae of a nodular anhydrite sample extracted from the lower portion of the Retiro Evaporite (Campos Basin) returned the ages of 119.2 ± 1.6 Ma and 119.18 ± 0.79 Ma, which we interpreted as the best approximation of the timing of the salt deposition. Analyses performed in 3 samples from the post-salt Quissamã carbonates (Campos Basin) provide a minimum age of 114.2 ± 2.8 Ma yielded by interparticle dolomite cement. Other phases of calcite and dolomite cements present in the investigated units were dated at ca. 119.4, 116.5, and 110.7 Ma. The stratigraphically coherent spectrum of ages obtained differs significantly from most available data, providing a new perspective for the ongoing discussions on the tectonic evolution of the South Atlantic and probably impacting the current views of the burial history and petroleum system of the Santos and Campos basins.

Arctic's hidden hydrocarbon degradation microbes: investigating the effects of hydrocarbon contamination, biostimulation, and a surface washing agent on microbial communities and hydrocarbon biodegradation pathways in high-Arctic beaches

BackgroundCanadian Arctic summer sea ice has dramatically declined due to global warming, resulting in the rapid opening of the Northwest Passage (NWP), slated to be a major shipping route connecting the Atlantic and Pacific Oceans by 2040. This development elevates the risk of oil spills in Arctic regions, prompting growing concerns over the remediation and minimizing the impact on affected shorelines.ResultsThis research aims to assess the viability of nutrient and a surface washing agent addition as potential bioremediation methods for Arctic beaches. To achieve this goal, we conducted two semi-automated mesocosm experiments simulating hydrocarbon contamination in high-Arctic beach tidal sediments: a 32-day experiment at 8 °C and a 92-day experiment at 4 °C. We analyzed the effects of hydrocarbon contamination, biostimulation, and a surface washing agent on the microbial community and its functional capacity using 16S rRNA gene sequencing and metagenomics. Hydrocarbon removal rates were determined through total petroleum hydrocarbon analysis. Biostimulation is commonly considered the most effective strategy for enhancing the bioremediation process in response to oil contamination. However, our findings suggest that nutrient addition has limited effectiveness in facilitating the biodegradation process in Arctic beaches, despite its initial promotion of aliphatic hydrocarbons within a constrained timeframe. Alternatively, our study highlights the promise of a surface washing agent as a potential bioremediation approach. By implementing advanced -omics approaches, we unveiled highly proficient, unconventional hydrocarbon-degrading microorganisms such as Halioglobus and Acidimicrobiales genera.ConclusionsGiven the receding Arctic sea ice and the rising traffic in the NWP, heightened awareness and preparedness for potential oil spills are imperative. While continuously exploring optimal remediation strategies through the integration of microbial and chemical studies, a paramount consideration involves limiting traffic in the NWP and Arctic regions to prevent beach oil contamination, as cleanup in these remote areas proves exceedingly challenging and costly.

Water Mass Structure and Variability in the Kane Gap (Equatorial Atlantic Ocean)

Water Mass Structure and Variability in the Kane Gap (Equatorial Atlantic Ocean)

Distinct management units for the Critically Endangered angelshark (Squatina squatina) revealed in the Canary Islands

AbstractThe angelshark, Squatina squatina, is listed as Critically Endangered on the IUCN Red List of Threatened Species, and remaining populations are highly fragmented throughout its historical distribution. The Canary Islands archipelago in the North East Atlantic has been identified as a uniquely large stronghold for the species. In the present study, we compared the population genetic structure of S. squatina across different islands of the Canary Island archipelago using both microsatellite and single nucleotide polymorphism (SNP) markers. Both markers revealed significant differentiation of angelsharks between islands in the archipelago, with three main genetic units at: (1) Tenerife, (2) Gran Canaria and (3) the island group consisting of La Graciosa, Lanzarote and Fuerteventura. Our results imply a connectivity barrier between some adjacent islands, most likely driven by abyssal depths, and varying geological history and formation of each island and oceanographic patterns (i.e. seasonal coastal upwellings off the African coast). Therefore, we suggest that in the Canary Islands, S. squatina populations should be managed locally, with conservation and research priorities designed and implemented specifically for each of the three genetic units.

Fish distribution shifts due to climate change in the Northeast Atlantic: Using a hierarchical filtering approach on marine-estuarine opportunist species

Marine-estuarine opportunist (MEO) species are fish that occur in the continental shelf and use estuaries and/or shallow coastal areas as nurseries. These commercially important resources are facing significant environmental modifications caused by direct and/or indirect anthropogenic climate change effects. In this study, we investigated the directionality and the magnitude of the distribution shifts (i.e., range size, gravity centroids, and margins) in marine environment suitability for six main MEO fish species within the Northeast Atlantic expected for the end of the 21st century. In the framework of this study, we have distinguished ‘sub-boreal’ from ‘sub-tropical’ species. The ‘hierarchical filters’ concept was adopted for modelling the potential species distributions and combined the predictions of i) a bioclimatic model with ii) a habitat model. The bioclimatic model is based on large-scale and time-variant variables while variables of the habitat model are fine-grained and time-invariant. Two Intergovernmental Panel on Climate Change (IPCC) scenarios are tested: an intermediate (SSP2-4.5) and a pessimistic one (SSP5-8.5). We applied this framework using international databases of biodiversity occurrences, ensemble forecasting producing consensual predictions, and innovative indices of distribution shifts. A visible north-westward shift was predicted for all six species in our study area. However, the northward expansion was greater for ‘sub-tropical’ than for ‘sub-boreal’ species due to faster gravity centroid displacement shifts and faster margins shifts. These range shifts may lead to major ecological impacts (e.g., changes in recruitment to estuarine and coastal nurseries, as well as changes in spawning grounds) that may alter populations' connectivity.

Diving deeper into the taxonomy of the Neoscopelus species complex (Myctophiformes: Neoscopelidae) with the description of Neoscopelus serranoi sp. nov.

Previous studies have highlighted possible cryptic biodiversity in the genus Neoscopelus. This hypothesis was tested using new morphological, molecular and biogeographical data on species of this genus caught in the north Atlantic between 2010 and 2022. The information obtained has been combined with available data in an integrative approach, including a review of morphological characters reported in the ichthyological literature and DNA-based species delimitation analyses. The main outcome of the present study is the description of Neoscopelus serranoi sp. nov. from the Atlantic and southwestern Indian Oceans. The new species is morphologically very similar to Neoscopelus microchir from which differs in having a shorter anal-fin base, a shorter pelvic fin, more dorsal and pectoral-fin rays, less anal-fin rays, fewer gillrakers and fewer isthmus and lateral photophores. They also differ in geographic distribution, with the new species occurring in the Atlantic Ocean and the near southwestern Indian Ocean, whereas N. microchir was originally described from Japanese waters of the Pacific Ocean. A literature review of available morphological data between geographic areas for Neoscopelus macrolepidotus and Neoscopelus microchir showed a large intraspecific overlap and no boundaries. However, molecular species delimitation based on the mitochondrial COI gene revealed the existence of cryptic diversity in both species, with eight to ten molecular operational taxonomic units (MOTU), compared to three valid species. Neoscopelus serranoi sp. nov. was considered an independent MOTU in all analyses performed, supporting the morphological identification as a new species. These results highlight that the taxonomy of Neoscopelus is far from settled and show that a greater sampling effort is needed to resolve the uncertainties and to describe unknown putative species. This also exemplifies the virtues of integrative taxonomy in delving into the systematics of deep-sea fishes.

Assessment of a Tropical Transition over the Southwestern South Atlantic Ocean: The Case of Cyclone Akará

Tropical cyclones are rare in the South Atlantic Ocean. Hurricane Catarina (2004), developed from a tropical transition, was the first documented case, followed by Iba (2019), which had a purely tropical genesis. In February 2024, the southeastern South Atlantic recorded its third tropical cyclone, Akará, initially a subtropical system. Due to the specific conditions required for tropical cyclones to develop in this ocean basin, the main purpose of this study is to describe the physical mechanisms that triggered the genesis of Akará’s precursor and its tropical transition. Data from various sources and methodologies, including the cyclone phase space diagram, are used in this study. Results show that the passage of a cold front created an environment with horizontal wind shear, contributing to most of the cyclonic relative vorticity in the genesis region. This was the primary driver of cyclogenesis at 1200 UTC on 15 February, along with other secondary processes. The tropical transition occurred as the vertical shear weakened, and turbulent heat fluxes from the ocean to the atmosphere increased, enhancing diabatic processes that warmed the atmosphere. This led to the tropical transition at 0600 UTC on 17 February.

Voucher Specimens in Taxonomy and Simpson’s Hypodigm

The problem of specifying representative specimens to serve as vouchers or ground truth specimens for species is viewed from a perspective of object recognition based on training using exemplars recognized by personal perception. In taxonomy, an ‘exemplar’ mirrors the hypodigm concept of Simpson, which refers to certain specimens being unequivocal members of a species. His concept has been discarded in most taxonomies because he did not provide procedures that distinguished it from ‘material’ or ‘sample’. However, his underlying view of a morphospecies was of a group united by shared character resemblances, probabilistically related. On this basis, the hypodigm of a taxonomic species is here restricted to specimens demonstrated as likely belonging to one population. To raise objectivity in this task, personal perception should be supplemented by morphometric analyses, several of which are demonstrated using living and Holocene samples of the oceanic zooplankter Truncorotalia crassaformis (Galloway and Wissler) from the Atlantic and Caribbean Oceans.

A checklist of marine phytoplankton species of Northeast Brazil

The oceanic zone of Northeast Brazil in the southwestern tropical Atlantic Ocean is characterised by the presence of a variety of current systems. Thus, it has the potential to host a large diversity of phytoplankton species. In this context, we propose a comprehensive checklist of documented marine phytoplankton species in this region. To this end, we have compiled all the published material and supplemented it with original data from two comprehensive surveys, the ABRAÇOS surveys, covering the shelf, slope, and offshore areas of Northeast Brazil. Even if few articles were atrieved from our review research, a total of 719 phytoplankton taxa are reported, including 98 new records plus 45 potential new records from the ABRACOS data. Most taxa are accompanied by a comprehensive library of illustrations. The two major phytoplankton groups, dinoflagellates and diatoms, contributed similarly to the total checklist richness, which is consistent with the global phytoplankton diversity. The contribution of nano- and microphytoplankton varies between areas. The shelf displays a greater diversity of pennate and small/medium-sized diatoms. This may be attributed to the inputs from estuarine rivers as well as the resuspension of benthic diatoms. Conversely, dinoflagellates are more prevalent offshore, demonstrating their adaptability to changing nutritional conditions, by employing numerous metabolic and growth strategies to survive. This checklist, which reveals an remarkable diversity of nano- and microphytoplankton in Northeast Brazil, provides a valuable reference for scientists and managers to monitor community evolution under global change.

Centennial‐Scale Variability of the Atlantic Meridional Overturning Circulation in CMIP6 Models Shaped by Arctic–North Atlantic Interactions and Sea Ice Biases

AbstractClimate variability on centennial timescales has often been linked to internal variability of the Atlantic Meridional Overturning Circulation (AMOC). However, due to the scarceness of suitable paleoclimate proxies and long climate model simulations, large uncertainties remain on the magnitude and physical mechanisms driving centennial‐scale AMOC variability. For these reasons, we perform a systematic multi‐model comparison of centennial‐scale AMOC variability in pre‐industrial control simulations of state‐of‐the‐art global climate models. Six out of nine models in this study exhibit a statistically significant mode of centennial‐scale AMOC variability. Our results show that freshwater exchanges between the Arctic Ocean and the North Atlantic provide a plausible driving mechanism in a subset of models, and that AMOC variability can be amplified by ocean–sea ice feedbacks in the Labrador Sea. The amplifying mechanism is linked to sea ice cover biases, which could provide an observational constraint for centennial‐scale AMOC variability.

Arctic sea‐ice export as a mechanism for cold climate events during the last deglaciation

ABSTRACTRecently it was proposed that a sudden drainage of accumulated Arctic sea ice could have caused cold climate events during the last deglaciation. To explore this mechanism, we performed numerical experiments with an atmosphere–ocean–sea ice model. In these experiments, the impact of a large flush of Arctic sea ice was compared to a reference glacial state of the climate. In our results, the sea ice flush produces a major surface freshening of the North Atlantic Ocean and a 17% weakening of the strength of the Atlantic Meridional Overturning Circulation. Together with an increase in surface albedo, this weakening in ocean circulation leads to a cooling over the North Atlantic, extending to the downwind continents. Compared to our reference glacial state, the cooling reaches 5°C and lasts about 80 years. This climate anomaly is similar in magnitude and duration to relatively short cooling events during the last deglaciation, such as the Older Dryas, the Inter‐Allerød cold period and the Preboreal Oscillation. We thus conclude that the sea‐ice flush mechanism is consistent with the occurrence of such cooling events in the North Atlantic region. However, longer cooling events such as the Younger Dryas would require additional mechanisms.

Ichnotaxonomy of microboring traces in marine aphotic depths

Microboring traces in carbonate skeletal fragments deposited in aphotic depths of the oceans are studied, evaluated, and described with respect to their marine ecology and palaeoecology as well as ichnotaxonomy. Sand-size deep sea sediment particles dredged from depths ranging between 600 and 3266 m of the Bermuda Pedestal, Central Atlantic Ocean, the Florida Escarpment, the Mediterranean Sea, the Red Sea and the Indian Ocean were studied. Following ichnological rules, trace fossils are described as ichnogenera and ichnospecies, defined as products of organismal behaviour. This, in our view, refers to the growth habit of microboring organisms in response to environmental stimuli within the substrate they penetrate. The problem of palaeobathymetry is discussed in conjunction with the distinction between light-dependent and light independent microboring organisms, with the emphasis on the latter. We considered this distinction to be important because only the light-dependent microborers have been recognized as indicators of ancient depositional depths, whereas the light-independent ones are expected to occur at any depth, subject to the availability of organic nutrients. Microboring organisms often leave morphologically similar traces due to convergent evolution. Their responses may change during their life cycle; they may produce different traces when pursuing their vegetative vs. reproductive functions. New ichnotaxa are described. All are regarded as organotrophs given their aphotic zone deep sea origin. This work presents the most complete set of deep sea microbial euendolith traces, to date.