Northern Continental Shelf Research Articles

Changing phytoplankton phenology in the marginal ice zone west of the Antarctic Peninsula

Climate change is altering global ocean phenology, the timing of annually occurring biological events. We examined the changing phenology of the phytoplankton accumulation season west of the Antarctic Peninsula to show that blooms are shifting later in the season over time in ice-associated waters. The timing of the start date and peak date of the phytoplankton accumulation season occurred later over time from 1997 to 2022 in the marginal ice zone and over the continental shelf. A divergence was seen between offshore waters and ice-associated waters, with offshore bloom timing becoming earlier, yet marginal ice zone and continental shelf bloom timing shifting later. Higher chlorophyll a (chl a) concentration in the fall season was seen in recent years, especially over the northern continental shelf. Minimal long-term trends in annual chl a occurred, likely due to the combination of later start dates in spring and higher chl a in fall. Increasing spring wind speed is the most likely mechanism for later spring start dates, leading to deeper wind mixing in a region experiencing sea ice loss. Later phytoplankton bloom timing over the marginal ice zone and continental shelf will have consequences for surface ocean carbon uptake, food web dynamics, and trophic cascades.

Stratigraphic-sedimentary evolution of a mixed siliciclastic-carbonate system in the Huizhou Sag of the Pearl River Mouth Basin, Northern South China Sea

Mixed siliciclastic-carbonate systems are regulated interactively by factors such as siliciclastic sediment supply, carbonate production, sea-level change, tectonism, and climate conditions. These systems record vital information that aids in understanding ancient environments. This study used a merged 3D seismic volume, in conjunction with over 100 industrial wells, to systematically investigate the stratigraphic-sedimentary evolution of such a system within the Huizhou Sag of the Pearl River Mouth Basin, located on the northern continental shelf of the South China Sea. In total, six major sequence boundaries were identified for the Zhujiang Formation within the area, thus subdividing the interval into five typical third-order depositional sequences. Each of these sequences can be divided into a transgressive and a highstand systems tract. Lowstand or falling stage systems tracts were also recognized, the deposition of which was potentially in response to the uplifting process of the Dongsha Rise. During the deposition of the Zhujiang Formation, the Huizhou Sag may have undergone a sequential evolutionary history from delta-shore, to delta-shore-tidal-lagoon, to delta-shore-carbonate, and finally to delta-shore-shallow marine systems. This evolution responded to a varying degree of mixing processes, which was mainly regulated by siliciclastic sediment supply, confined paleomorphology, and local oceanic currents. Furthermore, the deposition of the Zhujiang Formation in the Huizhou Area was time-equivalent with the spreading process after the ridge jump of the South China Sea (23–16.5 Ma), providing valuable insights into sea-level fluctuations, provenance changes, and tectonic evolution. Our results may also shed light on the evaluation of lithologic traps and hydrocarbon sweet spots within mixed siliciclastic-carbonate systems.

Forward numerical investigation of potential tsunami deposits in the South China sea: A case study of Nan'ao Island

The South China Sea (SCS) coastlines are particularly vulnerable to tsunamis due to rapid urbanization and dense infrastructures. However, whether the SCS has experienced ocean-wide tsunamis is still under debate. Some geological records from the offshore islands inside the SCS imply a regional tsunami event may have occurred approximately 1000-yr-ago. We address these questions for the first time using forward numerical simulations in the SCS: what source could be responsible for such deposits, how the deposits were formed and at what conditions do the deposits could be preserved? Here, we assume the validity of the tsunami deposit hypothesis and use the forward model COMCOT-SED to investigate if these tsunami deposits can be linked to potential seismogenic tsunami sources inside the SCS, including megathrust earthquakes (Mw8.8–9.2) from the Manila subduction zone (MSZ) and the 1918 Mw7.5 Nan'ao earthquake from the Littoral Fault Zone (LFZ) in the northern continental shelf of the SCS. We also utilize a reported tsunami deposit from Qing'ao Embayment, Nan'ao Island, China, to exemplify the deposit formation process in a typical barrier-low coastal plain system. Quantitative analysis suggests large earthquakes from the MSZ may account for the reported geological deposits. The full-rupture earthquake scenario could best explain the depositions if such extreme case is geophysically and geologically plausible. If not, earthquakes (∼ Mw 9.0) covering the northern (16–23.5°N) or southern portion (14–19°N) of the MSZ could also be suitable candidates. Such great earthquakes can generate large tsunami waves (>7 m) that inundate the Qing'ao Embayment, transporting sediments and leaving tsunami deposits in low-lying areas. Conversely, tsunamis triggered by nearshore earthquakes in the LFZ cannot cause deposition in Qing'ao Embayment. The barrier-low coastal plain system is well-suited for preserving tsunami deposits, which remain unaltered by subsequent tsunami waves. Our findings offer a quantitative reference for paleo-tsunami research in the SCS and enhance global understanding of the tsunami deposition process in barrier-low coastal plain systems.

Environmental controls on macrozooplankton and fish distributions over diurnal to seasonal time scales in the northern Barents Sea

We present acoustic observations obtained by bottom mounted echosounders at two locations in the northern Barents Sea and a third on the northern continental slope of the Barents Sea. Data collected over a period of approximately two years reveal significant variability in the density and depth distribution of pelagic macrozooplankton and fish. Variability over diurnal to seasonal timescales is related to light conditions, prevailing currents, water column characteristics (temperature, stability, and pycnocline depth) and to sea ice conditions. Of particular importance is the relative volume of Polar Water and Atlantic influenced water present at the mooring sites. On the northern continental shelf, above average concentrations of macrozooplankton and fish were observed during late summer and early autumn following ice melt, and during winter. Minimum densities of macrozooplankton and fish were observed during spring and early summer. These data demonstrate the persistent presence of a macrozooplankton community throughout the winter months in the northern Barents Sea. On the Great Bank full depth diel vertical migrations were observed throughout the Polar Night and under sea ice. At the two more northerly stations the density of the sound scattering layers performing diel vertical migrations and the vertical range of the migrations was greatest during the transition period between the polar night and mid-night sun periods. Superimposed on the seasonal variability in density distribution was significant shorter-term variability driven by hydrographic processes occurring over synoptic time scales. Significant mixing events, or changes in the prevailing current direction that lead to a change in water mass characteristics, forced changes in the concentration and depth distribution of macrozooplankton over periods of hours that were on occasion of similar magnitude to the seasonal variability. On the northern continental slope, a mesopelagic sound scattering layer more than 300 m thick at its seasonal maximum, was located for most of the year within the warm core of the Atlantic Water Boundary Current, ascending into the epipelagic zone for 5–6 weeks during summer. The density and thickness of this sound scattering layer were greatest during the late summer/early autumn and lowest during early spring. Fish-like scatterers were present, concentrated within the deeper regions of the sound scattering layer, during the winter months and during July.

Generation of nonlinear internal waves on the northern continental shelf south of Hainan Island

Nonlinear internal waves (NLIWs) are prevalent on the northern continental shelf south of Hainan Island in the South China Sea. However, our understanding of these NLIWs is still in a preliminary state. In the study, we take a step toward fully elucidating the generation and propagation process of the NLIWs on the northern continental shelf south of Hainan Island through a synergistic analysis of satellite observations, in situ measurements, and numerical simulations. Both mooring and satellite observations suggest that the Xisha Islands remotely generate the NLIWs on the northern continental shelf south of Hainan Island; moreover, more than one source exists in the Xisha Islands. Based on the realistic topography, stratification, and tidal forcing, two-dimensional numerical simulations using the MITgcm reveal that the NLIWs observed on the continental shelf can be generated from the Xisha Islands through the internal tidal beam regime. Furthermore, the internal tide energy flux estimation shows that the locally generated internal tides that arise from the continental shelf break mostly carry their energy toward the deep water and have little effect on the generation of NLIWs on the shelf.

Analysis of mooring-observed bottom current on the northern continental shelf of the South China Sea

The bottom current is an important component of the three-dimensional ocean circulation, which is of significance for the safeties of ocean bottom engineering and facilities, the research on sediment and pollutant transports, and the ecological environment. Due to the lack of observation data, research on the bottom current in the South China Sea (SCS) has been limited. This study systematically analyzes bottom currents from 0.5 to 5 m above the seafloor based on 20-month-long mooring observations on the shelf slope west of the Dongsha Atoll. The spectral analysis results indicate that currents induced by the internal tides and the internal solitary waves (ISWs) comprise dominant constituents of bottom currents with velocity amplitudes up to O(50–90) cm/s. Dominant internal tide-induced bottom currents of the velocity amplitude of O(50) cm/s occupy 53% of the total horizontal kinetic energy. The pulsating ISW-induced bottom currents reach a maximum amplitude of 93 cm/s, which has intrinsic relation to the amplitude of the ISWs, according to the soliton propagation speed solutions of the Korteweg–De Vries (KdV) equation. The background bottom current is strongest in winter, followed by spring, and weak in summer and autumn, which is closely correlated with the behavior of mesoscale eddies. These results are of significance for understanding the dynamics of the bottom boundary layer.

Evidence of upwelling on the Brazilian continental shelf of Rio Grande do Norte

This study evaluates Foraminiferal assemblages and their relation with grain size, calcium carbonate content, organic matter, and mineralogy of sediment samples collected at the sediment-water interface along a transect on the northern continental shelf of Rio Grande do Norte State, Brazil, adjacent to the city of Areia Branca. The sedimentary sequence of this shelf is represented by lithostratigraphic units of a marine regressive sequence dominated by four facies: Siliciclastic sand, Silicibioclastic Sand, carbonate mud, and Biosiliciclastic sand. The carbonate content ranged from 5.83% to 85% and the organic matter content from 1.16% to 27.05%. Mineralogical characters separated the predominant siliciclastic content (37% to 92%) from the bioclastic content (8% to 63%). We have identified 14 species out of 50 species of Foraminifera, associated to particular depths and sediment types as follows: (1)deeper-water sediments in the middle shelf contain Bolivina striatula, Bulimina marginata, Triloculina trigonula, Pyrgo ringens, Textularia gramen (2)the shallowest sediments in the inner shelf contain Ammonia tepida, Buccella peruviana, Miliolinella subrotunda, and Quinqueloculina patagonica, (3)the central parts of the transect, also in the inner shelf, provide habitats for Quinqueloculina lamarckiana, Textularia earlandi, Buliminella elegantissima, Discorbis peruvianus, and Pyrgo nasuta. The distribution of Uvigerina striata and Buccella peruviana is probably related to colder water temperatures and possibly the occurrence of an upwelling phenomenon for the deepest parts of the area rather than the sedimentological features discussed here.

The quantitative relationship between macrobenthic carbon and organic carbon in sediments: A case study of the northern continental shelf of the South China Sea

Macrobenthos play an important role in global biogeochemical cycles and carbon energy exchange. Macrobenthic communities on continental shelves are alimented through the sedimentation of organic material. Sedimentary organic carbon is the key step for the carbon cycling within the continental shelf benthic trophic web. However, the quantitative relationship between the macrobenthos and sediments based on total organic carbon (TOC), and the trophic pathways of macrobenthos applied by stable carbon and nitrogen isotope data (δ13C and δ15N) on the continental shelf are still limited. Therefore, the continental shelf of the northern South China Sea (NSCS), with abundant macrobenthos, was chosen as the research area. In this paper, TOC, total nitrogen (TN), δ13C and δ15N of the macrobenthos and sediments, the eco-exergy (Ex), structural eco-exergy (Exst) of macrobenthos communities of the NSCS were analysed. The TOC and TN in macrobenthos varied widely between 1.05% and 71.08% and between 0.29% and 11.36%, respectively, which were much higher than those in sediments. Trophic pathways (food sources and trophic levels) were established by applying δ13C and δ15N values of the main macrobenthic species. The similar stable isotope ratios and the trophic levels of most macrobenthos (2.0–3.4) might indicate similar food compositions and living habits. Eco-exergy grades were positively correlated with the average trophic level value of macrobenthos (correlation coefficient R=0.79). The relationship between the Ex value and the weight of required sediments estimated by the average organic carbon showed a typical positive correlation (R=0.98). This establishment of quantitative relationship provides a useful method for evaluating the structural functions of the ecosystem and researching the carbon sequestration potential of the macrobenthos community.

Combining tracking with at-sea surveys to improve occurrence and distribution estimates of two threatened seabirds in Peru

SummarySeabirds are highly threatened, including by fisheries bycatch. Accurate understanding of offshore distribution of seabirds is crucial to address this threat. Tracking technologies revolutionised insights into seabird distributions but tracking data may contain a variety of biases. We tracked two threatened seabirds (Salvin’s AlbatrossThalassarche salvini n= 60 and Black PetrelProcellaria parkinsoni n= 46) from their breeding colonies in Aotearoa (New Zealand) to their non-breeding grounds in South America, including Peru, while simultaneously completing seven surveys in Peruvian waters. We then used species distribution models to predict occurrence and distribution using either data source alone, and both data sources combined. Results showed seasonal differences between estimates of occurrence and distribution when using data sources independently. Combining data resulted in more balanced insights into occurrence and distributions, and reduced uncertainty. Most notably, both species were predicted to occur in Peruvian waters during all four annual quarters: the northern Humboldt upwelling system for Salvin’s Albatross and northern continental shelf waters for Black Petrels. Our results highlighted that relying on a single data source may introduce biases into distribution estimates. Our tracking data might have contained ontological and/or colony-related biases (e.g. only breeding adults from one colony were tracked), while our survey data might have contained spatiotemporal biases (e.g. surveys were limited to waters <200 nm from the coast). We recommend combining data sources wherever possible to refine predictions of species distributions, which ultimately will improve fisheries bycatch management through better spatiotemporal understanding of risks.

Characteristics of astronomical tides and their modulation on sea level extremes along the Indian coast

In this study, long-term hourly sea-level records from 18 tide gauge stations during 1972–2007 were analyzed to study the characteristics of astronomical tides, sea-level trends, and extremes around India's mainland. The de-tided signals were used to estimate these parameters and study tide and surge interaction. The observed sea level depicts significant variability in daily, seasonal, and inter-annual time scales. Semidiurnal tides are the most dominant among the high-frequency tides, with an amplitude of up to 2.5 m for M2 and 0.75 m for S2 tides in the northwestern and northeastern continental shelf and reduced to 0.25 m in the south. The amplitude of diurnal tides (O1 and K1)is relatively weak (<0.25m) at all the stations. The annual harmonics dominate the seasonal cycle, with an amplitude of 0.7 m at Garden Reach in the northeastern continental shelf, decreases to 0.15 m at Tuticorin in the south, and remains small (<0.1 m) along the west coast of India. The amplitude of lunar nodal and perigee tides are significantly high (up to 25 mm) at several stations compared to the long-term global mean sea level trend (∼3.3 mm/y). The sea level trend is significantly positive (up to 4 mm/y) for Sagar Island, Diamond Harbor, Haldia, and Mangalore; negative (up to −3 mm/y) for Garden Reach and Okha, and in-significant (0.5 mm/y) for Mumbai, Vishakhapatnam, and Paradip. Interaction between the semidiurnal tides and surges was intense at most stations, with a high probability of surge peaks during the fall-tide conditions in the northern continental shelf, at rising-tidal conditions for the south-eastern and western peninsula, and co-occurring at high tide for southern stations. The degree of tide-surge interaction increases from south to north with an increase in tidal range and significant nodal and perigee tidal modulation.

Cenozoic Depositional Evolution and Stratal Patterns in the Western Pearl River Mouth Basin, South China Sea: Implications for Hydrocarbon Exploration

Investigating the deposition evolution and stratal stacking patterns in continental rift basins is critical not only to better understand the mechanism of basin fills but also to reveal the enrichment regularity of hydrocarbon reservoirs. The Pearl River Mouth Basin (PRMB) is a petroliferous continental rift basin located in the northern continental shelf of the South China Sea. In this study, the depositional evolution process and stacking pattern of the Zhu III Depression, western PRMB were studied through the integration of 3D seismic data, core data, and well logs. Five types of depositional systems formed from the Eocene to the Miocene, including the fan delta, meandering river delta, tidal flat, lacustrine system, and neritic shelf system. The representative depositional systems changed from the proximal fan delta and lacustrine system in the Eocene–early Oligocene, to the tidal flat and fan delta in the late Oligocene, and then the neritic shelf system in the Miocene. The statal stacking pattern varied in time and space with a total of six types of slope break belts developed. The diversity of sequence architecture results from the comprehensive effect of tectonic activities, sediment supply, sea/lake level changes, and geomorphic conditions. In addition, our results suggest that the types of traps are closely associated with stratal stacking patterns. Structural traps were developed in the regions of tectonic slope breaks, whereas lithological traps occurred within sedimentary slope breaks. This study highlights the diversity and complexity of sequence architecture in the continental rift basin, and the proposed hydrocarbon distribution patterns are applicable to reservoir prediction in the PRMB and the other continental rift basins.

Use of 223Ra and 224Ra as chronometers to estimate the residence time of Amazon waters on the Brazilian continental shelf

AbstractWhen rivers mix into the ocean, radium isotopes are released into the dissolved phase allowing us to apply these isotopes as powerful tracers of river plumes spreading into the ocean. We report 223Ra and 224Ra radium activities that were determined in the Amazon River mouth and along the Amazon plume that extends off the coasts of Brazil and French Guyana into the Atlantic Ocean. We summarize 223Ra and 224Ra data from AmasSeds (1991), AMANDES (GEOTRACES process study GApr01; 2007–2008) and M147 (2018) projects, which were conducted in different seasons corresponding to different Amazon discharge rates. We determined the 224Raex/223Ra activity ratios (AR) along the Amazon plume to derive apparent ages and to estimate the residence time of the Amazon waters on the Brazilian continental shelf. Our data suggest that it takes 9–14 d for the Amazon waters to reach the northern continental shelf off French Guyana and 12–21 d to reach the eastern part of the Brazilian continental shelf. These time scales are in good agreement with those derived from a high‐resolution numerical simulation of the regional ocean dynamics. We do not find any relationship between the discharge rate of the Amazon River and the residence time of the waters on the Brazilian continental shelf, suggesting that the residence time of the Amazon waters is primarily driven by the ambient northwestward current. Using the apparent ages along the plume, we estimate an average velocity of 26 cm s−1 for the northward transport of the Amazon waters on the continental shelf.

Coralligenous banks along the western and northern continental shelf of Sardinia Island (Mediterranean Sea)

ABSTRACT Mapping of coralligenous banks was carried out along the continental shelf of the northern and western margin of Sardinia Island (Italy, western Mediterranean Sea) in the context of the European Marine Strategy Framework Directive (MSFD, 2008/56/EC). Coralligenous banks are bioconstructions produced by calcareous coralline algae. Seafloor mapping was carried out through multibeam echosounder surveys and video transects, using a Remote Operating Vehicles (ROV), in areas not formerly explored. A high-resolution digital model of the seabed (DTM) was obtained from multibeam data. A total surface of 436 km2 of sparse patches of coralligenous banks was mapped in the depth range ~40-160 m. A final map of coralligenous habitat distributions along the western and northern continental shelf of Sardinia (scale 1:250,000) was produced. The base-map is formed by the shaded DTM of the seabed. Other mapped features include the edge of the continental shelf and the distribution of rocky seabed.

Sedimentary evolution and controlling factors of Early-Mid Miocene Deltaic systems in the Northern Pearl River Mouth Basin, South China Sea

The Pearl River Mouth Basin is located at the northern continental shelf of the South China Sea. Since the early Miocene, the Paleo-pearl river transported a large amount of sediments to the northwest of the basin and resulted in the formation of a large-scale river-delta depositional system, which has become an important oil and gas reservoir in the study area. In the current paper, we investigate the characteristics and evolution of fluvial-deltaic depositional systems and their controlling factors, including sea level change, tectonic subsidence and sediment supply on the basis of 3D seismic, well logging and core data. Early-Mid Miocene succession can be divided into two second-order sequences (CS1–CS2) and eight third-order sequences (S1–S8). Deltaic systems developed in S1–S2 are relatively coarse in grain size, and the delta plain deposits are dominated by thickly stacked (100–180 m) distributary channel sand bodies and interpreted as braided delta depositional system. In the early stage (S1–S2), the braided delta systems mainly distributed in the west of the Baiyun Sag, which were proceeded by a retreat to the south of the Enping Sag along with sharply rising sea level. Following the transgression of S2, the provenance of the Paleo-Pearl River extended to the coastal region of South China, and the papleoclimate changed from warm and humid to dry and cold in the early Miocene, leading to the development of transition of braided river delta to meandering river delta, which was characterized by relatively fine grain deposits. During the deposition of S3–S6, well sorted and rounded fine sandstones of deltaic front deposits accumulated in the study area. The retrogradation to accretion and subsequent progradation of these meander delta systems are attributed to the sea level change in the study area. During the deposition of S7–S8, the delta front retreated to the south of the Enping depression as a result of minor sea level rise, reduction in sediment input, and subsidence rate. This resulted in the development of a wave-controlled deltaic depositional system.

Spatio-Temporal Assessment of the European Hake (Merluccius merluccius) Recruits in the Northern Iberian Peninsula

The protection of fish nurseries has been recognized as a useful tool to efficiently manage fisheries given that protected areas enhance the recruitment of target species. To identify and locate potential nursery areas, a solid understanding of species-environment relationships and their spatio-temporal dynamics is needed. Within this context, in this study we assess where European hake (Merluccius merluccius) recruits persistently aggregate in the northern continental shelf of the Iberian Peninsula. Hake recruit data collected during scientific trawl surveys between 2005 and 2016 were analyzed using Bayesian hurdle hierarchical spatio-temporal models, considering the environmental variables bathymetry, sea bottom temperature and salinity. Additionally, three different spatio-temporal structures (i.e., persistent, progressive, or opportunistic) were compared to assess the temporal persistence of nurseries over time. Among all the environmental variables analyzed, bathymetry was the most important. The preferential habitat of recruits was found to be within a bathymetric range of 120–200 m. Our findings clearly show that there is a temporally persistent main nursery located along the continental shelf of the Artabrian gulf (off La Coruña) in addition to several areas with high aggregations of hake recruits but with strong inter-annual variability. We argue that the analytical framework applied in this study allowed us to identify European hake nurseries in the northern continental shelf of the Iberian Peninsula, as well as their spatio-temporal fluctuations throughout the study period (2005–2016), and to assess which environmental factors, among bathymetry, sea bottom temperature and salinity, influence the occurrence and abundance of recruits in the study area. Results of our models also produce a new abundance index that could be useful for improving traditional stock assessment models.

Seismic geomorphology of three types of deepwater fans and their relationship with slope morphology: Qiongdongnan Basin, northern South China Sea

Analyses of high-resolution seismic reflection, drilling, and well-log data were combined to identify and investigate deepwater fans developed in the eastern part of the Qiongdongnan Basin, South China Sea, during the Middle Miocene and their relationship to slope morphology. We identified three types of deepwater fans that developed on the northern continental margin of the South China Sea during the Middle Miocene: (1) those consisting of small canyons and depositional lobes; (2) those consisting of large canyons and depositional lobes; and (3) those consisting of distributary channels without depositional lobes. Sourced from deltaic sediments deposited on the northern continental shelf margin, the lithologies of the sediments in all fans are dominated by siltstone. The scale of development and the internal features are mainly controlled by the slope topography. The deepwater fans consisting of small canyons and depositional lobes developed on slopes with low gradient, caused by the continuous progradation of the shelf-edge towards the basin centre due to sediment transport in high-speed flows. The canyon heads developed in this setting are located below the shelf-break; these canyons are narrower, shallower, and shorter than those of the deepwater fans consisting of large canyons. Thus, the scale of the depositional lobes deposited by gravity flow through such canyons is smaller than that of deepwater fans with large depositional lobes. Deepwater fans consisting of large canyons and depositional lobes developed on steep narrow slopes, caused by rising shelf-edge trajectories due to the equilibrium between the sediment supply and subsidence rates. The canyon heads developed in this setting are located upon the shelf-break and extend toward the toe of the slope, incising the shelf-break; these canyons are wider, deeper, and longer than those of the deepwater fans consisting of small canyons. The scale of the depositional lobes deposited by gravity flows transported through such canyons is correspondingly larger than that of deepwater fans with small depositional lobes. Deepwater fans consisting of distributary channels without depositional lobes developed on gentler and wider slopes than slopes where small canyons and depositional lobes formed, owing to the low sediment supply. The deepwater distributary channels have a long transportation distance and wider distribution area, enabling the formation of large-scale deepwater fans. Depositional models for all three types of deepwater fans were postulated.

Geolocator tagging links distributions in the non-breeding season to population genetic structure in a sentinel North Pacific seabird.

We tested the hypothesis that segregation in wintering areas is associated with population differentiation in a sentinel North Pacific seabird, the rhinoceros auklet (Cerorhinca monocerata). We collected tissue samples for genetic analyses on five breeding colonies in the western Pacific Ocean (Japan) and on 13 colonies in the eastern Pacific Ocean (California to Alaska), and deployed light-level geolocator tags on 12 eastern Pacific colonies to delineate wintering areas. Geolocator tags were deployed previously on one colony in Japan. There was strong genetic differentiation between populations in the eastern vs. western Pacific Ocean, likely due to two factors. First, glaciation over the North Pacific in the late Pleistocene might have forced a southward range shift that historically isolated the eastern and western populations. And second, deep-ocean habitat along the northern continental shelf appears to act as a barrier to movement; abundant on both sides of the North Pacific, the rhinoceros auklet is virtually absent as a breeder in the Aleutian Islands and Bering Sea, and no tagged birds crossed the North Pacific in the non-breeding season. While genetic differentiation was strongest between the eastern vs. western Pacific, there was also extensive differentiation within both regional groups. In pairwise comparisons among the eastern Pacific colonies, the standardized measure of genetic differentiation (FꞌST) was negatively correlated with the extent of spatial overlap in wintering areas. That result supports the hypothesis that segregation in the non-breeding season is linked to genetic structure. Philopatry and a neritic foraging habit probably also contribute to the structuring. Widely distributed, vulnerable to anthropogenic stressors, and exhibiting extensive genetic structure, the rhinoceros auklet is fully indicative of the scope of the conservation challenges posed by seabirds.

Transport, Fate and Impacts of the Deep Plume of Petroleum Hydrocarbons Formed During the Macondo Blowout

The 2010 Macondo oil well blowout consisted in a particularly intense, localized infusion of petroleum hydrocarbons to the deepwaters of the Gulf of Mexico. A substantial amount of these hydrocarbons did not reach the ocean surface but remained confined at depth within an intrusion layer at about 1000 m of depth. This layer, or plume, impacted the Gulf's benthic, mesopelagic and pelagic ecosystems, damaging also fish and mammals. This review outlines the challenges the science community overcame since 2010, the discoveries and the remaining open questions in interpreting and predicting the distribution, fate and impact of the Macondo oil in the deepwater plume. In the past ten years, the scientific community supported by, among others, the Gulf of Mexico Research Initiative, has achieved key milestones in observing, conceptualizing and understanding the physical oceanography of the Gulf of Mexico, not only at the surface but also along its northern continental shelf and slope. Major progress has been made also in modeling the transport, evolution and degradation of hydrocarbons. Here we review this new knowledge and modelling tools, how our understanding of the deep plume has evolved, and how research in the past decade may help preparing in the event of a future spill in the Gulf or elsewhere. Observational, theoretical, and modelling limitations, however, still constrain our ability to predict the three-dimensional movement of water in this basin, and the fate and impacts of the hydrocarbons they may carry.

Update on crustaceans known from the Amazonian continental shelf and adjacent oceanic areas

Abstract The major biodiversity on the planet is present in coastal and oceanic environments, despite this, on the northern continental shelf of Brazil, data on most of the marine groups still are deficient, especially in areas deeper than 20 m and in the continental slope area. This lack of data is aggravated by high fisheries exploitation, which causes a decline in large, abundant populations, even leading them to threat of extinction. Among that marine biodiversity, no group has a larger morphological variety than crustaceans. In this scenario, knowledge about the local biodiversity, its richness and seasonality, is essential for a qualified fisheries management. The Amazon continental shelf has one of the largest shrimp fisheries in the country, and due to the ecological and economic importance that crustaceans have in the region, a detailed study on their diversity is necessary. In this article, we use data collected in the Revizee Program. We identified 91 species: crabs (32.97%), shrimp (28.57%), anomurans (10.99%), soft crabs (10.99%), lobsters (9.89%), stomatopods (4.40%) and isopods (2.20%). The State of Amapá had fewer species () compared to Pará (). The data analysis shows there is a lack of knowledge about the real biodiversity present on the Amazon continental shelf.

Circulation in a Short, Microtidal Submarine Canyon in the Alborán Sea

Serrano, M.A.; Diez-Minguito, M.; Valle-Levinson, A., and Ortega-Sanchez, M., 2020. Circulation in a short, microtidal submarine canyon in the Alboran Sea. In: Malvarez, G. and Navas, F. (eds.), Global Coastal Issues of 2020. Journal of Coastal Research, Special Issue No. 95, pp. 1531–1535. Coconut Creek (Florida), ISSN 0749-0208.This study analyzes the circulation of a short, microtidal submarine canyon from observations and an analytical model. The Jolucar submarine canyon is located near the Carchuna beach (Granada, southern Spain) in the northern continental shelf of the Alboran Sea. Observations were analyzed with harmonic and spectral analyses techniques. Observations showed two layers flowing in opposite directions: down-canyon in the bottom layer and up-canyon in the upper layer. This suggest that the canyon might flush out dense materials form the nearshore. Moevoer, observed currents were mainly driven by tidal (10%) and, more significantly, by atmospheric forcing, i.e., by wind stress and local atmospheric pressure gradients, as shown by cross-spectral analysis. In order to explore the dynamics associated with these results, a classical analytical solution of wind-induced current profile in a non-homogeneous water column was extended to include the influence of pressure gradients. This result demonstrated that the circulation in Jolucar canyon could be influenced by atmospheric pressure gradients.