Central North Atlantic Research Articles

Range Extension of Mesophotic Kelps (Ochrophyta: Laminariales and Tilopteridales) in the Central North Atlantic: Opportunities for Marine Forest Research and Conservation.

Kelp was first recorded for the remote warm-temperate Azores archipelago (central North Atlantic) in 1971, when a few Laminaria specimens were collected on the Formigas Bank at depths beyond conventional SCUBA diving reach. A shortage of technical means and projects targeting mesophotic environments has since kept this offshore marine protected area as the single known kelp occurrence site. Here, we present new kelp records collected on previously unexplored mesophotic reefs using remote imaging systems, open- and closed-circuit SCUBA diving, and fisheries bycatch information. The new data extend the known distribution range of kelp in the Azores 350km to the west and 25km to the southwest, henceforth including several island shelves in the eastern and central Azores. In addition to the previously recorded Laminaria ochroleuca, kelp specimens with a morphology akin to Phyllariopsis brevipes subsp. brevipes are also reported. For the first time, seabed imagery is used to document the depth-wise diversity of the Azores kelp beds and their associated biota. Our findings emphasize the poor knowledge that persists in regard to Macaronesia's mesophotic environments located beyond conventional SCUBA diving limits. The new on-shelf kelp occurrences add conservation value to coastal areas and should facilitate island-based research. However, their greater proximity to land-based impacts and exposure to climate change also raise management needs.

Magma-assisted fragmentation of Pangea: Continental breakup initiation and propagation

Pre-magmatic continental extension often precedes the major magmatic expulsion of large igneous provinces (LIPs). However, the cause-and-effect relationship between pre-magmatic rifting and the extrusion of large amount of magma is controversial. It remains unclear whether magmatism arises as a consequence of passive rifting or whether it is related to active upwelling of the mantle. In addition, the relationship between the pre-magmatic stages and the final breakup, with the onset of conjugate passive margins, is ambiguous. In this study, we compiled available data from six LIPs (Central Atlantic, Karoo, Parana-Etendeka, Deccan, North Atlantic, and Afar igneous provinces) that successively occurred during the fragmentation of Pangea and found that pre-magmatic rift trends may show a high obliquity or even be orthogonal with respect to the future passive margins. We conclude that syn-magmatic rifts should not be directly correlated, both structurally and dynamically, to the ancient pre-magmatic rift phase. Furthermore, following the breakup of a supercontinent, seafloor spreading usually initiates within volcanic passive margins (VPMs) and then propagates away to create non-volcanic passive margins (NVPMs) as a consequence of the consumption and cooling of a sub-lithospheric positive thermal anomaly. Major transform faults often exist between VPMs and NVPMs, acting as a mechanical barrier to mantle melting and magmatism transportation.

Impact of Intraseasonal Waves on Angolan Warm and Cold Events

AbstractThe intraseasonal variability of the tropical eastern boundary upwelling region in the Atlantic Ocean is investigated using multiyear mooring and satellite data. Pronounced oscillations of alongshore velocity and sea level off Angola at periods of about 90 and 120 days are observed. Similar spectral peaks are detected along the equator suggesting an equatorial forcing via equatorial and coastally trapped waves. Equatorial variability at 90 days is enhanced only in the eastern Atlantic likely forced by local zonal wind fluctuations. Variability at 120 days is generally stronger and linked to a second equatorial basin mode covering the whole equatorial basin. Besides forcing of the 120‐day variability by equatorial zonal winds, additional forcing of the resonant basin mode likely originates in the central and western tropical North Atlantic. The coastally trapped waves generated at the eastern boundary by the impinging equatorial Kelvin waves that are detected through their variations in sea level anomaly are associated with corresponding sea surface temperature anomalies delayed by about 14 days. Off Angola, those intraseasonal waves interfere with major coastal warm and cold events that occur every few years by either enhancing them as for the Benguela Niño in 1995 or damping them as for the warm event in 2001.

How Rossby wave breaking modulates the water cycle in the North Atlantic trade wind region

Abstract. The interaction between low-level tropical clouds and the large-scale circulation is a key feedback element in our climate system, but our understanding of it is still fragmentary. In this paper, the role of upper-level extratropical dynamics for the development of contrasting shallow cumulus cloud patterns in the western North Atlantic trade wind region is investigated. Stable water isotopes are used as tracers for the origin of air parcels arriving in the sub-cloud layer above Barbados, measured continuously in water vapour at the Barbados Cloud Observatory during a 24 d measurement campaign (isoTrades, 25 January to 17 February 2018). These data are combined with a detailed air parcel back-trajectory analysis using hourly ERA5 reanalyses of the European Centre for Medium-Range Weather Forecasts. A climatological investigation of the 10 d air parcel history for January and February in the recent decade shows that 55 % of the air parcels arriving in the sub-cloud layer have spent at least 1 d in the extratropics (north of 35∘ N) before arriving in the eastern Caribbean at about 13∘ N. In 2018, this share of air parcels with extratropical origin was anomalously large, with 88 %. In two detailed case studies during the campaign, two flow regimes with distinct isotope signatures transporting extratropical air into the Caribbean are investigated. In both regimes, the air parcels descend from the lower part of the midlatitude jet stream towards the Equator, at the eastern edge of subtropical anticyclones, in the context of Rossby wave breaking events. The zonal location of the wave breaking and the surface anticyclone determine the dominant transport regime. The first regime represents the “typical” trade wind situation, with easterly winds bringing moist air from the eastern North Atlantic into the Caribbean, in a deep layer from the surface up to ∼600 hPa. The moisture source of the sub-cloud layer water vapour is located on average 2000 km upstream of Barbados. In this regime, Rossby wave breaking and the descent of air from the extratropics occur in the eastern North Atlantic, at about 33∘ W. The second regime is associated with air parcels descending slantwise by on average 300 hPa (6 d)−1 directly from the north-east, i.e. at about 50∘ W. These originally dry airstreams experience a more rapid moistening than typical trade wind air parcels when interacting with the subtropical oceanic boundary layer, with moisture sources being located on average 1350 km upstream to the north-east of Barbados. The descent of dry air in the second regime can be steered towards the Caribbean by the interplay of a persistent upper-level cut-off low over the central North Atlantic (about 45∘ W) and the associated surface cyclone underneath. The zonal location of Rossby wave breaking and, consequently, the pathway of extratropical air towards the Caribbean are shown to be relevant for the sub-cloud layer humidity and shallow-cumulus-cloud-cover properties of the North Atlantic winter trades. Overall, this study highlights the importance of extratropical dynamical processes for the tropical water cycle and reveals that these processes lead to a substantial modulation of stable water isotope signals in the near-surface humidity.

The Combined Effects of SST and the North Atlantic Subtropical High-Pressure System on the Atlantic Basin Tropical Cyclone Interannual Variability

The combined effect of the sea surface temperature (SST) and the North Atlantic subtropical high-pressure system (NASH) in the interannual variability of the genesis of tropical cyclones (TCs) and landfalling in the period 1980–2019 is explored in this study. The SST was extracted from the Centennial Time Scale dataset from the National Oceanic and Atmospheric Administration (NOAA), and TC records were obtained from the Atlantic Hurricane Database of the NOAA/National Hurricane Center. The genesis and landfalling regions were objectively clustered for this analysis. Seven regions of TC genesis and five for landfalling were identified. Intercluster differences were observed in the monthly frequency distribution and annual variability, both for genesis and landfalling. From the generalized least square multiple regression model, SST and NASH (intensity and position) covariates can explain 22.7% of the variance of the frequency of TC genesis, but it is only statistically significant (p < 0.1) for the NASH center latitude. The SST mostly modulates the frequency of TCs formed near the West African coast, and the NASH latitudinal variation affects those originated in the Lesser Antilles arc. For landfalling, both covariates explain 38.7% of the variance; however, significant differences are observed in the comparison between each region. With a statistical significance higher than 90%, SST and NASH explain 33.4% of the landfalling variability in the archipelago of the Bahamas and central–eastern region of Cuba. Besides, landfalls in the Gulf of Mexico and Central America seem to be modulated by SST. It was also found there was no statistically significant relationship between the frequency of genesis and landfalling with the NASH intensity. However, the NASH structure modulates the probability density of the TCs trajectory that make landfall once or several times in their lifetime. Thus, the NASH variability throughout a hurricane season affects the TCs trajectory in the North Atlantic basin. Moreover, we found that the landfalling frequency of TCs formed near the West Africa coast and the central North Atlantic is relatively low. Furthermore, the SST and NASH longitude center explains 31.6% (p < 0.05) of the variance of the landfalling intensity in the archipelago of the Bahamas, while the SST explains 26.4% (p < 0.05) in Central America. Furthermore, the 5-year moving average filter revealed decadal and multidecadal variability in both genesis and landfalling by region. Our findings confirm the complexity of the atmospheric processes involved in the TC genesis and landfalling.

Diverse bioerosion structures in lower Pliocene deposits from a volcanic oceanic island: Baía de Nossa Senhora section, Santa Maria Island, Azores (central North Atlantic)

Pliocene body fossils from Santa Maria Island, Azores, have been studied for decades, but only more recently have ichnofossils received their due attention. Calcareous Pliocene deposits from the Baía de Nossa Senhora section contain numerous, diverse, well-preserved natural casts of invertebrate borings. The study of this type of fossils adds to knowledge on the dispersal of benthic faunas across oceans to volcanic oceanic islands. The borings belong to seven ichnogenera and twenty-two ichnotaxa at the ichnospecies level with more than half pertaining to Entobia, which is produced by clionaid sponges. Other borings found were produced by bivalves (Gastrochaenolites), polychaete worms (Caulostrepsis and Maeandropolydora), sipunculid worms (Trypanites), phoronid worms (Talpina) and ctenostome bryozoans (Iramena). The occurrence, ichnogeny, distribution and preservational state of the borings suggest that the bearing bioclasts have been exposed for several years on the sea floor. The borings derive from different bathymetric zones on the shelf, and their formation took place during several bioerosional phases. The association of borings belongs to the Entobia ichnofacies, which is typical of carbonate rocky shores, and shows close similarity to those described from the Paratethys, Mediterranean and partly the eastern Atlantic regions. This fits the idea that most of the Neogene shallow-water marine fauna in the Azores is biogeographically related to the eastern Atlantic shores.

Assessment of a full-field initialized decadal climate prediction system with the CMIP6 version of EC-Earth

Abstract. In this paper, we present and evaluate the skill of an EC-Earth3.3 decadal prediction system contributing to the Decadal Climate Prediction Project – Component A (DCPP-A). This prediction system is capable of skilfully simulating past global mean surface temperature variations at interannual and decadal forecast times as well as the local surface temperature in regions such as the tropical Atlantic, the Indian Ocean and most of the continental areas, although most of the skill comes from the representation of the external radiative forcings. A benefit of initialization in the predictive skill is evident in some areas of the tropical Pacific and North Atlantic oceans in the first forecast years, an added value that is mostly confined to the south-east tropical Pacific and the eastern subpolar North Atlantic at the longest forecast times (6–10 years). The central subpolar North Atlantic shows poor predictive skill and a detrimental effect of initialization that leads to a quick collapse in Labrador Sea convection, followed by a weakening of the Atlantic Meridional Overturning Circulation (AMOC) and excessive local sea ice growth. The shutdown in Labrador Sea convection responds to a gradual increase in the local density stratification in the first years of the forecast, ultimately related to the different paces at which surface and subsurface temperature and salinity drift towards their preferred mean state. This transition happens rapidly at the surface and more slowly in the subsurface, where, by the 10th forecast year, the model is still far from the typical mean states in the corresponding ensemble of historical simulations with EC-Earth3. Thus, our study highlights the Labrador Sea as a region that can be sensitive to full-field initialization and hamper the final prediction skill, a problem that can be alleviated by improving the regional model biases through model development and by identifying more optimal initialization strategies.

Climatology, variability, and trends in near‐surface wind speeds over the North Atlantic and Europe during 1979–2018 based on ERA5

AbstractThis study presents the monthly 10‐m wind speed climatology, decadal variability and possible trends in the North Atlantic and Europe from ERA5 reanalysis from 1979 to 2018 and investigates the physical reasons for the decadal variability. Additionally, temporal time series are examined in three locations: the central North Atlantic, Finland and Iberian Peninsula. The 40‐year mean and the 98th percentile wind speeds emphasize a distinct land‐sea contrast and a seasonal variation with the strongest winds over the ocean and during winter. The strongest winds and the highest variability are associated with the storm tracks and local wind phenomena such as the mistral. The extremeness of the winds is examined with an extreme wind factor (the 98th percentile divided by mean wind speeds) which in all months is higher in southern Europe than in northern Europe. Mostly no linear trends in 10‐m wind speeds are identified in the three locations but large annual and decadal variability is evident. The decadal 10‐m wind speeds were stronger than average in the 1990s in northern Europe and in the 1980s and 2010s in southern Europe. These decadal changes were largely explained by the positioning of the jet stream and storm tracks and the strength of the north–south pressure gradient in the North Atlantic. The 10‐m winds have a positive correlation with the North Atlantic Oscillation in the central North Atlantic and Finland on annual scales and during cold season months and a negative correlation in Iberian Peninsula mostly from July to March. The Atlantic Multi‐decadal Oscillation has a moderate negative correlation with the winds in the central North Atlantic but no correlation in Finland and Iberian Peninsula. Overall, our results emphasize that while linear trends in wind speeds may show a general long‐term trend, more information on the changes is obtained by analysing long‐term variability.

Distribution and Abundance of Killer Whales in the Central North Atlantic, 1987-2015

The North Atlantic Sightings Surveys (NASS), covering a large but variable portion of the Central and Eastern North Atlantic, were conducted in 1987, 1989, 1995, 2001, 2007 and 2015. Sightings of killer whales (Orcinus orca), a non-target species, were relatively rare in the Central Atlantic (Icelandic and Faroese) portions of the survey area. In cases where sighting numbers were insufficient, we pooled sightings over several surveys to derive a distance detection function and used this to estimate abundance using standard Distance Sampling methodology. Uncorrected estimates were produced for all surveys, and estimates corrected for perception bias were produced for the 2001 and 2015 surveys. Killer whales were sighted in all areas but were most common in the eastern part of the survey area. Uncorrected abundance in the NASS core area ranged from a low of 4,736 (95% CI: 1,842–12,176) in 1995 to a maximum of 15,142 (95% CI: 6,003–38,190) in 2001. The low precision of the estimates makes the detection of temporal trends unlikely. In 2007 an extension survey revealed relatively high numbers of killer whales to the east of the survey area, in conformity with Norwegian survey estimates in this area. The NASS and other surveys conducted over the period indicate that killer whales number in the low tens of thousands in the Central and Eastern North Atlantic.

Recent Weakening in Interannual Variability of Mean Tropical Cyclogenesis Latitude over the Western North Pacific during Boreal Summer

The intensity of the interannual variability (IIV) of the mean tropical cyclone (TC) genesis latitude over the western North Pacific (WNP) has been weakening significantly since the late 1990s. It is found that the IIV of the mean TC genesis latitude depends largely on the strength of the out-of-phase relationship between TC genesis numbers in the north (north of 15°N) and south (south of 15°N) of the WNP. A weaker (stronger) north–south TC see-saw has led to a smaller (larger) IIV of the mean TC genesis latitude after (before) the late 1990s. Different configurations of sea surface temperature (SST) anomalies are found to be responsible for the decadal changes in the north–south TC see-saw and dipole structure. Before the late 1990s, the joint effect of SST anomalies over the tropical Pacific and tropical North Indian Ocean dominated, rendering the obvious north–south TC see-saw and larger IIV of the mean TC genesis latitude. After the late 1990s, however, the dominant SST anomalies associated with TC genesis shift to the tropical central Pacific (CP) and tropical North Atlantic Ocean, which have weakened the north–south TC seesaw and reduced the IIV of the mean TC genesis latitude. These observed decadal changes in the configuration of SST anomalies are considered to be closely associated with the shift of the El Niño–Southern Oscillation (ENSO) from eastern Pacific (EP) type to the CP type during the recent decades. The results suggest that the increased influences from the tropical Atlantic Ocean have become more important to the variations of TC activity in the WNP during the recent decades. These results may have important implications for assessing the latitudinal distributions of TC-induced hazards.

Characteristics and Possible Sources of the Intraseasonal South Asian Jet Wave Train in Boreal Winter

AbstractThe characteristics and possible energy sources of the South Asian jet wave train in winter are analyzed, with the intraseasonal signal emphasized. The wave train is equivalently barotropic and strongest in the upper troposphere, with its daily evolution dominated by the intraseasonal (10–30 day) time scale. Along the wave train, the propagation of disturbances from the North Atlantic to the western North Pacific takes around 8 days, which is much faster than the eastward migration of activity centers. The energy sources of the intraseasonal wave train are complicated and can be separated into three categories depending on the role of the North Atlantic Oscillation (NAO). When NAO− precedes the wave train, it is northwest–southeast oriented. The energy is rooted in the lower troposphere over the high-latitude North Atlantic, and excites the Rossby wave source (RWS) over the western Mediterranean Sea via vortex stretching by abnormal divergence. When NAO+ precedes the wave train, it is southwest–northeast oriented. The energy rooted in the northeastern activity center excites RWS over the eastern Mediterranean Sea. Additionally, disturbances from the western North Atlantic and southwestern activity center of NAO+ excite the RWS over the western Mediterranean Sea. Hence, both NAO− and NAO+ can excite the same wave train, but with different orientation and via different paths. Without the NAO, the wave train can also be stimulated by enhanced disturbances over the midlatitude central North Atlantic. The signal lies mainly in the middle-upper troposphere, which might be related to atmospheric internal dynamic processes, such as kinetic energy conversion from synoptic disturbances.

Deep structure of the Demerara Plateau: From a volcanic margin to a Transform Marginal Plateau

The Demerara Plateau (offshore Suriname and French Guiana) is located at the junction of the Jurassic Central Atlantic and the Cretaceous Equatorial Atlantic Oceans. The study of its crustal structure is fundamental to understanding its tectonic history, its relationship with the adjacent oceanic domains and to enlightening the formation of Transform Marginal Plateaus (TMPs). This study presents two wide-angle seismic velocity models from the MARGATS cruise seismic experiment, and adjacent composite seismic reflection lines. The plateau itself is characterized by a 30 km thick crust, subdivided into three layers, including a high velocity lower crust (HVLC). The velocities and velocity gradients do not fit values of typical continental crust but could fit with volcanic margin or Large Igneous Province (LIP) type crusts. We propose that the, possibly continental, lower crust is intruded by magmatic material and that the upper crustal layer is likely composed of extrusive volcanic rocks of the same magmatic origin, forming thick seaward dipping reflector sequences tilted to the west. This SDR complex was emplaced during hotspot related volcanic rifting preceding the Jurassic opening of the Central North Atlantic and forming the present-day western margin of the plateau. The internal limit of the SDR complex corresponds to the future limit of the eastern margin. The Demerara Plateau would therefore be an inherited Jurassic volcanic margin boarding the Central Atlantic. This margin was reworked during the Cretaceous at the eastern limit of the Jurassic SDR complex, creating the present-day northern transform margin and the eastern divergent margin along the Equatorial Atlantic. This study also highlights the major contribution of thermal anomalies such as hotspots and superposed tectonic phases in the history of TMPs, which share a great number of characteristics with Demerara.

Increasing energy transfer over Eurasia and the North Atlantic enhancing the Eurasian low‐frequency wave and boreal summer droughts in China

AbstractThe prolonged droughts that frequently occur in northern China are related to persistent anomalies of circulation and the low‐frequency waves. To explore the formation of the low‐frequency waves and the related internal variability and external forcing, the intra‐seasonal kinetic energy (KE) and the corresponding energy transfer terms are investigated algorithmically with multiscale energy and vorticity analysis. The results show two major energy sources located over the central North Atlantic (NA) and Europe, with increasing baroclinicity and energy conversion. The major energy conversion is from basic flow to intra‐seasonal KE, which corresponds to a southeastern extension of NA jet stream (JS) exit and the northward shift in the entrance of Afro Asian JS. JS shifts are helpful to the conjunction of both JS, and thereby enhance JS waveguide and wave energy dispersion. In addition, with increasing surface temperature and diabatic heating over Europe and the Mediterranean Sea, there are increase baroclinicity that facilitates the buoyancy energy conversion, ascending KE flux and positive pressure flux in the lower troposphere, those result in higher mid‐upper‐troposphere KE. The divergent energy contributes to the development and enhancement of the low‐frequency waves, favouring the extratropical eddy, wave structure, and quasi‐stationary waves amplitude, which is thereby conducive to magnified wave amplitude and extreme droughts in northern China. The results emphasize the internal dynamics and local forcing and provide prediction reference for extratropical extremes.

High N2 Fixation in and Near the Gulf Stream Consistent with a Circulation Control on Diazotrophy

AbstractThe stoichiometry of physical nutrient supply may provide a constraint on the spatial distribution and rate of marine nitrogen (N2) fixation. Yet agreement between the N2 fixation rates inferred from nutrient supply and those directly measured has been lacking. The relative transport of phosphate and nitrate across the Gulf Stream suggests that 3–6 Tg N year−1 must be fixed to maintain steady nutrient stoichiometry in the North Atlantic subtropical gyre. Here we show direct measurements of N2 fixation consistent with these estimates, suggesting elevated N2 fixation in and near the Gulf Stream. At some locations across the Gulf Stream, we measured diazotroph abundances and N2 fixation rates that are 1–3 orders of magnitude greater than previously measured in the central North Atlantic subtropical gyre. In combination, rate measurements and gene abundances suggest that biogeochemical budgets can be a robust predictive tool for N2 fixation hot spots in the global ocean.

Tracking Atlantic bluefin tuna from foraging grounds off the west coast of Ireland

Abstract Pop-up archival tags (n = 16) were deployed on Atlantic bluefin tuna (ABT) off the west coast of Ireland in October and November 2016 (199–246 cm curved fork length), yielding 2799 d of location data and 990 and 989 d of depth and temperature time-series data, respectively. Most daily locations (96%, n = 2651) occurred east of 45°W, the current stock management boundary for ABT. Key habitats occupied were the Bay of Biscay and the Central North Atlantic, with two migratory patterns evident: an east-west group and an eastern resident group. Five out of six tags that remained attached until July 2017 returned to the northeast Atlantic after having migrated as far as the Canary Islands, the Mediterranean Sea (MEDI) and the Central North Atlantic. Tracked bluefin tuna exhibited a diel depth-use pattern occupying shallower depths at night and deeper depths during the day. Four bluefin tuna visited known spawning grounds in the central and western MEDI, and one may have spawned, based on the recovered data showing oscillatory dives transecting the thermocline on 15 nights. These findings demonstrate the complexity of the aggregation of ABT off Ireland and, more broadly in the northeast Atlantic, highlighting the need for dedicated future research to conserve this important aggregation.

Wind Stress‐Induced Multiyear Predictability of Annual Extratropical North Atlantic Sea Surface Temperature Anomalies

AbstractLong‐term predictability of the North Atlantic sea surface temperature (SST) is commonly attributed to buoyancy‐forced changes of the Atlantic Meridional Overturning Circulation. Here we investigate the role of surface wind stress forcing in decadal hindcasts as another source of extratropical North Atlantic SST predictability. For this purpose, a global climate model is forced by reanalysis (ERA‐interim) wind stress anomalies over the period 1979–2017. The simulated climate states serve as initial conditions for decadal hindcasts. Significant skill in predicting detrended observed annual SST anomalies is observed over the extratropical central North Atlantic with anomaly correlation coefficients exceeding 0.6 at lead times of 4 to 7 yrs. The skill is insensitive to the calendar month of initialization and primarily linked to upper ocean heat content anomalies that lead anomalous SSTs by several years.

Geochemical characterization of deep-sea sediments on the Azores Plateau – From diagenesis to hydrothermal activity

The Azores Plateau is an active magmatic region in the Central North Atlantic Ocean. In this study, we present a comprehensive data set of major element compositions and 87Sr/86Sr ratios of pore waters from surface sediments (0–9 mbsf) of the Azores Plateau. Based on distinct geochemical signatures we can separate normal marine from hydrothermally affected sediments. Normal marine sediments can further be differentiated by their ash content. Pore waters of ash rich gravity cores (GCs) do not show any deviations from seawater values except of a minor increase in Sr. In contrast, ash poor GCs generally show a trend for decreasing Ca with increasing depth, accompanied by a minor SO4 decrease and a more pronounced Sr increase. We suggest that these deviations are caused by processes such as anaerobic oxidation of methane and carbonate recrystallization. At four additional sample locations we observed a decrease in Mg and SO4 accompanied by a Ca increase in the pore waters, a pattern typical for hydrothermal fluids. The existence of hydrothermal systems in this region are corroborated by multi-channel seismic data, suggesting that sill or dyke intrusions are present in the subsurface close to the core locations. Overall, our observations offer preliminary indications for the existence of submarine hydrothermal systems on the Azores Plateau away from the Mid- Atlantic Ridge.

Global scale distribution, seasonal changes and long-range transport potentiality of endosulfan in the surface seawater and air

Endosulfan I, II, and sulfate were detected in the atmosphere and surface seawater on a global scale during three Chinese National Arctic-Antarctic Research Expeditions in 2016 and 2017. Concentrations of the three species displayed seasonal variations in seawater in the Northern Hemisphere but remained steadily low on Antarctic coasts. Endosulfan sulfate was predominant in the Northern Hemisphere, whereas isomer I was more abundant in the Southern Hemisphere. Endosulfan was detected in the atmosphere over the western Pacific Ocean but rarely in the central Arctic and North Atlantic oceans. Its concentration in seawater increased with increasing latitude in the Southern Ocean. Although fugacity ratios indicate a strong potential for deposition of endosulfan, air-seawater exchange may be slow, as suggested by the large differences between atmospheric and seawater concentrations. Ocean current endosulfan loads varied markedly between seasons. Three-day backward trajectories indicate that Northeast Asia is the major source of atmospheric endosulfan in the western Pacific Ocean, whereas the central Arctic and North Atlantic oceans are affected more by local air masses.

Low Molecular Weight Dissolved Organic Carbon: Aging, Compositional Changes, and Selective Utilization During Global Ocean Circulation

AbstractThe composition and cycling dynamics of marine dissolved organic carbon (DOC) have received increased interest in recent years; however, little research has focused on the refractory, low molecular weight (LMW) component that makes up the majority of this massive C pool. We measured stable isotopic (δ13C), radioisotopic (Δ14C), and compositional (C/N, 13C solid‐state NMR) properties of separately isolated high molecular weight (HMW) and LMW DOC fractions collected using a coupled ultrafiltration and solid phase extraction approach from throughout the water column in the North Central Pacific and Central North Atlantic. The selective isolation of LMW DOC material allowed the first investigation of the composition and cycling of a previously elusive fraction of the DOC pool. The structural composition of the LMW DOC material was homogeneous throughout the water column and closely matched carboxylic‐rich alicyclic material that has been proposed as a major component of the marine refractory DOC pool. Examination of offsets in the measured parameters between the deep waters of the two basins provides the first direct assessment of changes in the properties of this material with aging and utilization during ocean circulation. While our direct measurements largely confirm hypotheses regarding the relative recalcitrance of HMW and LMW DOC, we also demonstrate a number of novel observations regarding the removal and addition of DOC during global ocean circulation, including additions of fresh carbohydrate‐like HMW DOC to the deep ocean and large‐scale removal of both semilabile HMW and recalcitrant LMW DOC.

Estimates of the Abundance of Cetaceans in the Central North Atlantic from the T-NASS Icelandic and Faroese Ship Surveys Conducted in 2007

The Trans-North Atlantic Sightings Survey (T-NASS) carried out in June-July 2007 was the fifth in a series of large-scale cetacean surveys conducted previously in 1987, 1989, 1995 and 2001. The core survey area covered an area of about 1.8 million nm² spanning from the Eastern Barents Sea at 34°E to the east coast of Canada, and between 52°N and 78°N in the east and south to 42°N in the west. We present design-based abundance estimates from the Faroese and Icelandic vessel survey components of T-NASS, as well as results from ancillary vessels which covered adjoining areas. The 4 dedicated survey vessels used a Buckland-Turnock (B-T) mode with a tracker platform searching an area ahead of the primary platform and tracking sightings to provide data for bias correction. Both uncorrected estimates, using the combined non-duplicate sightings from both platforms, and mark-recapture estimates, correcting estimates from the primary platform for bias due to perception and availability, are presented for those species with a sufficient number of sightings. Corrected estimates for the core survey area are as follows: fin whales (Balaenoptera physalus): 30,777 (CV=0.19); humpback whales (Megaptera novaeangliae): 18,105 (CV=0.43); sperm whales (Physeter macrocephalus): 12,268 (CV=0.33); long-finned pilot whales (Globicephala melas): 87,417 (CV=0.38); white-beaked dolphins (Lagenorhynchus albirostris): 91,277 (CV=0.53); and white-sided dolphins (L. acutus): 81,008 (CV=0.54). Uncorrected estimates only were possible for common minke whales (B. acutorstrata): 12,427 (CV=0.27); and sei whales (B. borealis): 5,159 (CV=0.47). Sighting rates from the ancillary vessels, which used a single platform, were lower than those from the dedicated vessels in areas where they overlapped. No evidence of responsive movement by any species was detected, but there was some indication that distance measurements by the primary platform may have been negatively biased. The significance of this for the abundance estimates is discussed. The relative merits of B-T over other survey modes are discussed and recommendations for future surveys are provided.