Continental Margin Research Articles

Integrated physiological response by four species of Rhodophyta to submarine groundwater discharge reveals complex patterns among closely-related species

Algal physiological ecology on submarine groundwater discharge (SGD) influenced reefs is likely shaped by intermittent, tidally-driven estuarine conditions that occur with SGD fluxes of fresh-to-brackish groundwater from the subterranean estuary to reef ecosystems. SGD is a common inconspicuous feature worldwide on reefs of basaltic high islands and continental margins. Yet, SGD-driven dynamics of algal physiology are not well understood. To understand how invasive species have physiologically outcompeted native species on many SGD-influenced reefs, physiology in tissue water potential (TWP) regulation, photosynthesis, nitrogen storage, and cellular anatomy were measured across a gradient of SGD-influence, for four Rhodophyte species. Compared with non-SGD conditions, SGD was associated with higher TWP, larger medulla cells with thinner walls, and thinner cortical cell walls for two invasives, Gracilaria salicornia and Acanthophora spicifera, higher photosynthetic rates in G. salicornia, greater nitrogen concentration for A. spicifera and G. salicornia, and increased δ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\delta$$\\end{document}15N ratios for A. spicifera, G. salicornia, and native Laurencia dendroidea. Distinct physiological strategies were measured for the two invasive species across the gradient of SGD-influence, and for L. dendroidea and Gracilaria perplexa offshore. This study illuminates species-specific physiological response, and how introduced opportunistic species may outcompete native species under conditions of SGD.

Glacial interglacial variations in the natural iron fertilization during the low sea ice periods along the eastern continental margin of Antarctica

The Southern Ocean sequesters atmospheric CO2 through biological pumps, though its driving factors are debated. Modern productivity is regulated by natural iron fertilization from micronutrient influx through dust, regeneration, and Antarctic glaciers and sea ice melting (ice melt). The productivity along the eastern Antarctic continental margin was low during the last glacial period and gradually increased through the deglacial to Late Holocene, marked by distinct productivity peaks. The micronutrients also varied similarly, with reduced glacial influx and an increase in the Holocene, which may cause productivity peaks. Therefore, the coherence of enhanced productivity and micronutrient influx is considered as enhanced iron fertilization period. The productivity peaks declined within ∼1.5 kyr, mostly due to the Ekman transport and sea ice formation. Along with ice melt, the independent weathering pattern that responds with glacial- interglacial ice volume changes suggest the source of micronutrients is not terrigenous. Shelf interaction of oceanic currents can influence the water column nutrient stock significantly, while its utilization occurs during reduced ice periods (low sea ice and high glacier melting) for productivity. Therefore, enhanced natural iron fertilization periods are considered as ice low periods that occurred in a periodicity of 2 kyrs, at ∼7.5 kyr BP, ∼5.5 kyr BP, ∼4 kyr BP, ∼ 2.5 kyr BP, and ∼0.5 kyr BP, likely due to the combined effects of atmospheric and oceanographic factors driven by the high amplitude regional temperature variability during the mid to late Holocene.

Size-frequency distribution of submarine mass movements on the Palomares continental slope (W Mediterranean)

In this work, over 3620 km2 from the Palomares continental slope, which is located in the W. Mediterranean Sea, was analysed to quantify the impact of recent mass movements on this margin. A total of 936 landslides were identified, mapped and characterised by defining several morphometric variables that outline the accumulated impact of landslides equivalent to 918 km2 and 10.34 km3 of eroded sediment on the continental slope. The smallest event area was 0.0014 km2, whereas the largest event area was 32.48 km2. Smaller scars with a higher headwall gradient tend to dominate when the environment is steeper, and major mass movements are located on open slopes and structural highs. However, the slight or null correlations between variables indicate that a wide range of sizes may occur on any slope gradient and at any depth.The Palomares continental slope is intensively affected by mass movements. Compared with other passive margins (e.g., the U.S. Atlantic continental margin), landslides mobilised a limited amount of sediment, although it is comparable to other Mediterranean areas where small- to moderate-sized events are characteristic.The cumulative size distribution can be defined by a power-law function that describes events larger than 0.7 km2 with an exponent of α = 1.269. These results are consistent with those of other published inventories, including onshore cases. This result allows us to assume that the scale-invariant properties of the events are mapped. Scale-invariant properties can be explained by different models; self-organised criticality (SOC) is probably the most assumed by the scientific community, although alternative models may be nominated. Each model has important implications in terms of the landslide distribution and long-term landslide history of any slope. Alternative scenarios, such as submarine slopes, with more precise landslide inventories may contribute to new hazard assessment models that consider scaling exponents derived from size–frequency distributions.

Planktonic foraminiferal assemblages as tracers of paleoceanographic changes within the northern Benguela current system since the Early Pleistocene

Abstract. The Benguela Upwelling System (BUS), located in the southeastern Atlantic Ocean, represents one of the world's most productive regions. This system is delimited to the south by the Agulhas retroflection region. The northern boundary of the BUS is, instead, represented by the Angola–Benguela Front (ABF), which is a thermal feature separating warm waters of the Angola Basin (including the South Atlantic Central Water; SACW) from the cooler Benguela Oceanic Current (BOC). We performed statistical analyses on planktonic foraminiferal assemblages in 94 samples from Holes U1575A and U1576A, cored during International Ocean Discovery Program (IODP) Expedition 391. Drilled sites are located along the Tristan–Gough–Walvis Ridge (TGW) seamount track in the northern sector of the BUS (offshore the Namibian continental margin). The analyzed stratigraphic intervals span the Early–Late Pleistocene, marked by the Early–Middle Pleistocene transition (EMPT; 1.40–0.40 Myr), during which important glacial–interglacial sea surface temperature (SST) variabilities occurred. This work provides novel insights on the local paleoceanographic evolution of the northern BUS and associated thermocline variability based on the ecological significance of the foraminiferal assemblages. Specifically, variations in the assemblage content allowed us to characterize the different water masses (BOC, SACW, and Agulhas waters) and reconstruct their interactions during the Quaternary. The interplay of the previously mentioned water masses induced perturbations in the BUS (ABF latitudinal shifts and input of tropical waters from the Agulhas retroflection region). Furthermore, we investigated the possible link between changes in the paleoceanographic conditions and climatic events (e.g., Benguela Niño-/Niña-like phases and deglaciation stages) recorded since the EMPT.

Spatial distribution and deposits of cliffs along the Brazilian semi-arid coast

Cliffed coasts are common landforms found worldwide, but their precise spatial distribution and the nature of associated deposits may present regional gaps. This works presents a geological and geomorphological study of the Brazilian semi-arid coast (∼900 km), which was carried out on coastal cliffs with the aim of addressing three important knowledge gaps: i) spatial distribution of coastal cliffs, analyzed using topographic data from SRTM, LiDAR and field surveys, ii) the lithology and ages of the deposits, investigated through sedimentological analysis and OSL dating, and iii) origin of the cliffs, explored through relations with global and regional sea-level curves. The supply of terrigenous sediments to the western equatorial Atlantic coast was also considered. Coastal cliffs were identified along 235 km of the coastline, represented mainly by inactive cliffs (∼170 km). These cliffed coasts are composed mainly by poorly sorted siliciclastic sandstones and conglomerates, deposited in the Late Pleistocene. The depositional phases correlate with abrupt climate changes, due to pulses of terrigenous supply to the continental margin during the Heinrich Events. The formation of marine cliffs in these deposits occurred in the mid-Holocene, as sea level reached current elevation (msl) in ∼7 ka and 2-4 m above in ∼5.5 ka. This previous higher sea-level supports the widespread occurrence of inactive cliffs. The findings in this work contribute to i) improved mapping of coastal landforms, with higher resolution data demonstrating that previous works underestimated the presence of coastal cliffs; ii) the coastal cliffs are cut in Pleistocene sediments instead of older, Miocene deposits of the Barreiras Formation as previously assumed; iii) cliff formation due to marine erosion occurred in the mid- to- late Holocene; iv) the siliciclastic sediments that compose the cliffs are correlatable to marine sediments found in adjacent offshore areas, highlighting the role of abrupt global climatic changes in the Pleistocene in shaping contemporary coastal landscapes.

Characterization of the Operability, Catch, and Fishing Effort of a Hake Trawling Vessel in Peru

In this study, the operational characteristics of the industrial hake fishing vessel "Santa Monica II" were characterized for the years 2020 and 2021, focusing on its catch production and fishing effort. A total of 234 trips and 1087 hauls were analyzed, considering a working depth of 100 fathoms on the continental shelf. Fishing effort was assessed based on years, seasonal periods, and months, allowing for a comparison of its productivity with 33 other vessels in the industrial fleet. The results revealed that the vessel caught 18% of the total catch of the industrial fleet in 2020 and 17% in 2021. Subarea A was the most frequented in 2020, with 66 trips, while in 2021, Subarea B led with 78 trips. The Catch per Unit Effort (CPUE) was 6.24 tons per hour and 8.99 tons per haul in 2020, and increased to 8.20 tons per hour and 10.75 tons per haul in 2021, highlighting its performance. Additionally, a significant concentration of hake resources was observed in the upper part of the continental slope during the study years.

Organic Carbon Reaction Kinetics in Bioturbated Sediments

AbstractMost organic carbon delivered to the seafloor is degraded within the bioturbated layer. Theory and empirical evidence have shown that organic carbon reactivity relates to the age of a particle. However, due to particle mixing, the age‐depth linear relation induced by sediment accretion is obfuscated. Here we combine a Lagrangian particle tracking model that resolves the age distribution of particles in the bioturbated zone and couple it to age‐dependent organic carbon degradation. Depth profiles for organic carbon concentration, reactivity and degradation rate are presented for sediments receiving low and high reactivity organic carbon in coastal, continental slope and deep‐sea environments. Our results show that a simple first‐order kinetics model suffices for well‐mixed sediments and systems receiving pre‐processed materials. A reactive continuum approach is needed for poorly mixed sediments receiving highly reactive organic carbon and for sediments below the bioturbated layer.

Mesoscale ocean eddies determine dispersal and connectivity of corals at the RMS Titanic wreck site

The sinking of the RMS Titanic on 15 April 1912 remains one of most iconic maritime disasters in history. Today, the wreck site lies in waters 3800 m deep approximately 690 km south southeast of Newfoundland, Atlantic Canada. The wreck and debris field have been colonized by many marine organisms including the octocoral Chrysogorgia agassizii. Because of the rapid deterioration of the Titanic and the vulnerability of natural deep-sea coral populations to environmental changes, it is vital to understand the role the Titanic as well as other such structures could play in connecting ecosystems along the North American slope. Based on Lagrangian experiments with more than one million virtual particles and different scenarios for larval behavior, given the uncertainties around the biology of chrysogorgiids, the dispersal of larvae spawned at the Titanic wreck is studied in a high-resolution numerical ocean model. While the large-scale bathymetry shields the Titanic from a strong mean flow, mesoscale ocean eddies can considerably affect the deep circulation and cause a significant speed up, or also a reversal, of the circulation. As a consequence, the position of upper and mid-ocean eddies in the model largely controls the direction and distance of larval dispersal, with the impact of eddies outweighing the importance of active larval swimming in our experiments. Although dependent on larval buoyancy and longevity, we find that the Titanic could be reached by larvae spawned on the upper slope east of the Grand Banks. Therefore, the Titanic could act as a stepping stone connecting the upper to the deep continental slope off Newfoundland. From the Titanic, larvae then spread into deep Canadian waters and areas beyond national jurisdiction.

Bedform generation beneath shoaling nonlinear internal waves on a mild slope

Subaqueous sand waves have been observed where nonlinear internal waves (NLIWs) shoal on continental margins. To investigate their generation mechanisms, we propagated periodic NLIWs of depression to shoal upon a sloping bed in a laboratory flume. Following fission of the incident waves, ripple-type bedforms were observed between the point of incipient suspension and interaction point (where the quiescent pycnocline intersects the sediment bed). The largest ripples were centered on the bolus birth point, where the NLIWs of elevation, generated by fission, transform into boluses and maximum near-bed velocities occurred. The ripple height and wavelength were consistent with fluvial scaling. In two experiments, where bedload transport was not predicted, the observations showed resuspension to influence ripple generation. Net upslope sediment movement was observed beyond the turning point.

Occurrence characteristics of authigenic pyrite in the deep-sea environment and its paleoceanographic implications based on core sediments from IODP Expedition 342 Site U1406

Although authigenic pyrite (FeS2) in marine sediment is an important proxy for oxygen conditions and microbial activities at its formation site, very little is known about its morphological characteristics in the deep-sea (> 3500 m) environment and their paleoceanographic implications. Here, we report the occurrence characteristics of authigenic pyrite including texture, size distribution, and relative content in North Atlantic deep-sea sediments from Integrated Ocean Drilling Program (IODP) Expedition 342 Site U1406. The results of electron microscopy show octahedral pyrite microcrystals of 1.5–4.0 μm, the spherical texture of greigite (Fe3S4), and large pyrite framboids (average, 25 μm) relative to those of the continental margin. These features may demonstrate an unchanged supersaturation level of the pore water for octahedral pyrite after its initial formation, replacement of the precursor greigite by pyrite, and an expanded pyrite framboid formation zone with a low sulfate reduction rate in deep-sea sediments, respectively. Although the size distribution of pyrite framboids measured in this study falls into the range of pyrites formed in the sulfate–methane transition zone, based on onboard geochemical data and previous research, these pyrites most likely formed through organoclastic sulfate reduction during diagenesis. We assessed the implications of these findings for paleoceanographic changes, as the formation of diagenetic pyrite is controlled by the supply rate and reactivity of organic matter, which are closely related to ocean productivity and circulation. A comparison between the profiles of relative pyrite content and benthic foraminiferal oxygen isotope (δ18Obf) values indicated that these factors were anti-phased during the late Oligocene. Based on our results, we conclude that the formation of diagenetic pyrite was favored during interglacial periods due to increases in the amount and reactivity of organic matter driven by more energetic formation of proto-North Atlantic Deep Water. Our findings provide new insights into the formation of authigenic pyrite in deep-sea environments and its potential as a paleoceanographic proxy.

Chemical and isotopic investigation of the I-type Bega Batholith, southeastern Australia: Implications for batholith compositional zoning and crustal evolution in accretionary orogens

Cordilleran granitic batholiths represent significant episodes of crustal growth and differentiation, and commonly display lateral isotopic and chemical variations. Establishing the tectono-magmatic processes responsible for generating this compositional asymmetry is important for understanding crustal evolutionary processes throughout the Phanerozoic. The Bega Batholith, an example of a ‘Cordilleran style’ granite batholith, is the largest I-type Siluro-Devonian granite complex in the Lachlan Fold Belt (LFB) of southeastern Australia and comprises seven granite supersuites that display systematic lateral isotopic and chemical asymmetry. From west to east towards the present-day continental margin, an increase in the content of Na2O, Sr, Al2O3, and P2O5, with concomitant decreases in CaO, Sc, Rb, and V are observed. In the same direction, whole-rock initial 87Sr/86Sr decreases from 0.7098 to 0.7039, εNd values increase from −8.3 to +4.4, and δ18O decreases from 10.2 ‰ to 7.9 ‰. Depleted-mantle model ages also decrease from ca. 1800 Ma in the west to 600 Ma in the east. Here, we address whether these chemical and isotopic variations were generated by interaction between two distinct components (mantle-derived magmas and supracrustal sources) or were alternatively produced by partial melting of infracrustal source rocks formed sequentially by much earlier episodes of crustal underplating. Combined whole-rock Nd-Sr-O isotopic and geochemical analyses indicate that several I-type supersuites exhibit chemical and isotopic correlations consistent with two-component magma mixing. This new evidence challenges the long-held view that I-type granites derive exclusively from the melting of infracrustal sources, and that granite terranes represent wholesale crustal reworking rather than new crustal growth. Our results show that the compositional zoning within the Bega Batholith is multifaceted. Firstly, the presence of two discrete mantle sources endows chemically and isotopically distinct eastern and western segments in the batholith. Secondly, within these compositionally distinct regions the lateral compositional changes across supersuites derives from mixing between mantle-derived and supracrustal sources. Finally, progressive extension within a developing back-arc environment regulates the ratio of crust-mantle contributions and compositional architecture of each I-type supersuite.

Major tunnel valleys and sedimentation changes document extensive Early Pleistocene glaciations of the Barents Sea

Sedimentary records of Early Pleistocene (~2.6–0.8 Ma) glaciations are sparse on shelves, yet trough mouth fans on adjacent continental slopes provide a continuous record of ice-sheet and climate development throughout the Quaternary. Here, we interpret high-quality 3D seismic reflection data combined with borehole and chronostratigraphic information from a shelf-slope setting in the southwestern Barents Sea to study meltwater and sediment inputs to the deep ocean, focusing on the onset of Pleistocene glaciations. Sandy deposits were brought to the slopes of the high-latitude Bear Island Fan by a preglacial contourite-turbidite system from ⁓2.6–2.4 Ma. Muddy glacigenic debris flows document the first shelf-edge glaciation at ⁓2.4 Ma. From 1.78–0.78 Ma, muddy turbidity-current- and debris-flow-derived sediments were delivered from shelf to slope via six tunnel valleys measuring up to 12 km in width and 200 m in depth. These tunnel valleys and associated downslope deposits formed during the 41-kyr climate cycles of the Early Pleistocene, and evidence abundant channelized, meltwater discharges from these glaciations. Following the mid-Pleistocene transition to 100-kyr cycles, a change in the style of glaciation is suggested by a change in landform and facies associations consistent with a reduced meltwater contribution. This study shows that the Norwegian-Barents shelf was extensively glaciated in the Early Pleistocene, with a first shelf-edge glaciation from ~2.4 Ma.

Evolution process of chemical weathering and sediment sources in the Makran Continental margin since the Younger Dryas

The chemical weathering processes and sedimentary source evolution since the Younger Dryas (YD) in the low-latitude arid continental margin have been investigated. Two sediment cores, MK07G and MK09G, were retrieved from the Makran continental margin in the northern Arabian Sea and subjected to analyses of major and trace elements, along with AMS14C dating. The results show that since the YD, the weathered parent rocks of Makran sediments have remained relatively stable, predominantly consisting of felsic rocks, with some contributions from mafic rocks. The Makran sediments exhibit initial to moderate weathering, with no discernible effects from grain size sorting or disturbances from sediment recycling, indicating primary deposition. Significant contributions of terrigenous eolian dust from surrounding continents (e.g., the Indian subcontinent, Arabian Peninsula, and northeastern Africa) were identified, along with riverine inputs from the Dasht River and fine-grained components from the Late Pleistocene Indus delta sediment, as well as proximal basin sedimentation. The evolution of sediment sources in the study area is significantly influenced by the Indian Monsoon and westerly wind systems, with intensified monsoon phases and westerly conditions correlating with increased fluvial input. Furthermore, chemical weathering processes since the YD are closely linked to local precipitation patterns, where intensified rainfall enhances weathering intensity. Records from the Makran continental margin indicate a teleconnection between chemical weathering and sedimentary processes in the Arabian Sea and Bond events in the North Atlantic, highlighting the extensive influence of Northern Hemisphere climate fluctuations.

Controls on the Stratigraphic Architecture of the US Atlantic Margin: Processes Forming the Accommodation Space

AbstractAccommodation space governs the spatial and temporal distributions of sediments in continental margins. Mapping the sedimentation patterns, therefore, offers insights into the solid‐Earth processes that shape accommodation space. We assembled an unprecedented amount of seismic and borehole data along the Eastern North American Margin and used it to divide the margin's sedimentary package into eight chronostratigraphic intervals, identifying temporal shifts in depocenters under the continental shelf, slope, and rise. The Jurassic depocenters follow the syn‐rift structure and its thermal subsidence loci. The Long Island Platform is the only margin segment where the early post‐rift sediment thickness matches subsidence predictions from uniform‐stretching models, whereas in Georges Bank Basin (GBB) and Baltimore Canyon Trough (BCT), sediment thickness is 1.5–3 times higher than predicted, pointing to other factors at play. A margin‐wide Jurassic transient shoulder uplift is inferred from the occurrence of stratigraphic onlaps above thinned crust. Unlike the Jurassic, the Cretaceous and Cenozoic depocenters disregard the inherited subsidence pattern. The accommodation space over the shelf and coastal plain during the Cretaceous was affected by regional isostatic compensation of the sedimentary loads accumulated on the shelf and rise. Accommodation space development in the GBB was interrupted during the Cretaceous after the margin crossed the Great Meteor Hotspot track, resulting in a widespread permanent uplift, erosion, and sediment redistribution. The distribution of anomalous Neogene subsidence in the BCT challenges previous suggestions of mantle dynamic control on the accommodation space and favors flexural downwarping of the shelf by sediment accumulation on the rise.

Sediment Corrections for Distributed Acoustic Sensing

AbstractOn continental margins, sediments cause significant and spatially variable delays in seismic phase arrival times. The strong impedance contrast of the sediment‐bedrock interface causes P‐wave splitting that is clearly seen on distributed acoustic sensing recordings of earthquakes, resulting in additional phase arrivals that must be picked separately. We introduce sediment corrections to correctly account for those additional phases in the hypocenter localization procedure. Conceptually, the sediment correction method differs from the commonly‐used station corrections; instead of introducing a mathematically optimal constant time delay for each station and each phase, the corrections are derived from a physical, first‐order modeling of the wave propagation in the sediments. To calibrate the sediment corrections, a two‐step procedure is adopted: (a) the delay between the P‐phase and the converted Ps‐phase is taken as a proxy of the sediment thickness; (b) the P‐ and S‐wave speeds are determined through inversion. We show that sediment corrections are able to account for most of the observed bias while considerably reducing the number of free parameters compared to classical station correction. Moreover, the observed local delays are almost fully explained by the presence of the sedimentary layer, rather than by the 3D velocity variations of the bedrock. We retrieve and values that are compatible with values commonly found for sediments. Given the simplicity and physical foundation of the proposed method, we recommend the use of sediment corrections over station corrections whenever significant P‐wave splitting can be observed.

Mechanism and controlling factors of mass transport complexes migration: A case study of the mass transport complexes in the taranaki deep water basin, New Zealand

Mass transport Complexes (MTCs) form significant sediment accumulations in continental slopes, hold key insights for natural hazard prediction and offshore oil exploration. This paper uses high-definition 3D seismic data to reconstruct the seismic geomorphology and sedimentary dynamics of MTCs, meticulously exploring the depositional systems of the Tanaraki Basin, New Zealand. It deciphers by kinematic notation, seismic faciess, quantifies megaclast morphological characteristics, in conjunction with the basal slope and channel structure development as the migration or kinematics of MTCs. Five seismic facies categories and dynamic traits—compression ridges, thrust faults, slides, grooves and slope terraces are distinguished in MTCs. Based on attributes maps and geomorphological interpretations, MTCs is segmented into four zones, showing combined effects of levée, basal slopes, and megaclast clusters on its migration. Lithological and topographical variations along these features modulate erosion properties and MTCs mobility, with base height shifts guiding local migration trajectories. The results of megaclast parameters in Zones 1 and 3 tune our understanding of stress patterns and directionality shifts, highlighting the complex dynamics at play. Notably, the differential motion triggered by levees instigates longitudinal shear zones. At critical migration disparities, MTCs fracture at these weak points, discharging pore pressure and filling fractures with fines, birthing “promontory” formations marked by low-amplitude fills. This work, therefore, establishes a groundbreaking migratory model that synthesizes the impacts of levees height, rock type variability, and megaclasts accumulation intensity, depicting a fragmented migration pattern. This study not only enriches our grasp of MTCs behavior in deep-water contexts but also furnishes a robust scientific foundation and predictive tool for gauging the hazards that MTCs may pose to underwater structures, thus carrying substantial theoretical and applied significance.

Observations of Sea Ice Edge Position in the Barents and Greenland Seas: Temporal Variability and Long‐Term Changes

AbstractSea ice edges play an essential role in the Earth's climate and weather systems through active atmosphere‐ice‐ocean interactions. However, our understanding of the observed positions of sea ice edges remains limited. The present study investigated, on seasonal and longer timescales from 1979 to 2023, the variability in sea ice edge positions in the Barents and Greenland Seas. We objectively derived the positions of sea ice edges based on satellite‐derived sea ice concentration gridded on a 25‐km resolution. In the Barents Sea, warm, narrow currents flow eastward along the northern and southern rims of the Central Bank. Until the mid‐2000s, sea ice edges fluctuated between these currents interannually during December–June, depending on the surface wind direction. However, after the mid‐2000s, the sea ice edges were mostly positioned near the northern current or farther to the north. Furthermore, sea ice edges during October–March were identified frequently near the warm current flowing along the continental slope in the northern Barents Sea after the mid‐2000s. In the Greenland Sea, sea ice edges were typically positioned near the East Greenland Current (EGC) throughout the year until 2006. However, sea ice edges in summer were located far to the west of the EGC after 2006. These observations suggest that the geographical relationship between sea ice edges and ocean currents has changed due to global warming.

Geological characteristics and seismic identification of reservoirs in the Colorado Basin off the Atlantic coast of Argentina

Abstract The Colorado Basin is a hot exploration frontier basin conjugated with the southwest coast of Africa which has undergone four evolutionary stages: Carboniferous-Jurassic pre-rift, Jurassic-Early Cretaceous rift, Late Cretaceous transition and passive marginal drift since Paleocene. Major oil and gas discoveries have been made in the conjugated Orange Basin in recent years, including the Graff field and Venus field discovered in 2022 with recoverable reserves of 550 Mboe and 2.3 Bboe, respectively. This indicates that the basin has good oil and gas exploration potential. Based on the analysis of drilling data and seismic data, it is concluded that the basin has a mature oil-gas generation system and better reservoir conditions. The pre-rift and syn-rift source rocks are confirmed by 5 Wells with oil and gas shows in the shallow water shelf, and all have entered the hydrocarbon generation threshold. Reservoir distribution and trap-sealing conditions have become key factors in oil and gas exploration. this paper describes the reservoir characteristics in the drilling data, and extrapolates the seismic reflection characteristics of the same strata, and predicts the reservoir distribution in the unexplored area of the basin. The reservoir lithology and sedimentary facies are analyzed based on the gamma logging curves. Reservoir identification and reasonable prediction on seismic profile are mainly determined by seismic reflection amplitude and horizon calibration. The basin has three sets of reservoirs, namely, pre-rift Permian underwater fan sandstone, Lower Cretaceous alluvial fan sandstone of syn-rift period and Upper Cretaceous Colorado Formation shallow marine sandstone of transitional period. Among them, Colorado Formation sandstone reservoir has the best physical property conditions, with a maximum porosity of 32% and a thickness of 1000m. The Cretaceous and Paleogene turbidite sandstone of slope fan facies are potential reservoir in the deep waters, which mainly form litho-stratigraphic traps in the continental slope.

The marine methane cycle in the Canadian Arctic Archipelago during summer.

In the Arctic Ocean, methane concentrations surpassing global averages are prevalent, especially along sub-Arctic and Arctic continental shelf margins. Despite elevated dissolved methane levels, the Arctic Ocean exhibits minimal methane fluxes to the atmosphere, indicating a potential role of water column oxidation in methane processing. During the Northwest Passage Project in the summer of 2019, we integrated thermohaline, chemical, and biological data with in-situ and in-vitro methane data in Canadian Arctic Archipelago (CAA) waters. Elevated in-situ dissolved methane was prominent in near-surface Pacific waters (between 2 and 7m), particularly in meltwater regions, with av. concentrations of 5.8±2.5 nM within the upper 30m. While methane oxidation constants were generally low (av. 0.006±0.002 d-1), surface waters in Wellington Channel and Croker Bay exhibited higher rates (av. 0.01±0.0004 d-1), associated with Pacific-origin microbial taxa like Oleispira and Aurantivirga. Deeper layers (>200m) displayed lower methane concentrations (av. 3.1±1.1 nM) and oxidation rates (av. 0.005±0.001 d-1). Sea ice showed elevated dissolved methane concentrations (av. 9.2±5 nM). Waters in the western CAA exhibited a 25% increase in methane concentrations compared to ice-free areas. The overall picture suggested supersaturation of in-situ methane in shallow waters (between 2 and 50m), coupled with faster oxidation rates in meltwater and Pacific dominant layers, suggesting rapid seasonal cycling of methane and prevention of the methane migration into the atmosphere.

Subsurface Temperature Anomalies Off Central Oregon During 2014–2021

AbstractWe use moored observations in 80 m water depth at the NH‐10 site along the historic Newport Hydrographic Line from 1999 to 2021 to calculate water temperature anomalies at the surface, near surface, and bottom. Analysis is focused on the subsurface temporal and spatial characteristics of marine heatwaves (MHWs) during 2014–2016 and 2019–2020 on the continental shelf and slope. Warm anomalies extend throughout the water column in fall/winter 2014–2016 when winds are predominantly downwelling‐favorable, while the 2019–2020 period is characterized by shallower summer and fall anomalies on the shelf. Sustained temperature anomalies during the bottom MHW in late 2016 are the largest in the NH‐10 time series. Analysis of temporal patterns in wind stress during MHW and non‐MHW periods shows the onset of upwelling‐favorable winds interrupts warm events. Indices of cumulative upwelling and annual spring transition dates reveal the spring transition was unusually late in 2014, with only five years with later spring transitions since the upwelling index record began in 1967. In 2015 and 2019, in contrast, spring transition is close to the climatological mean of April 15. In 2016 and 2020, anomalous warming is observed when cumulative upwelling decreases after an early spring transition.