Continental Slope Waters Research Articles

Acoustic occurrence of beaked whales off eastern Canada, 2015-2017

Several beaked whale species occur off eastern Canada. However, except for the northern bottlenose whale (NBW; Hyperoodon ampullatus), their distribution and annual occurrence remain largely unknown, which complicates management efforts to assess the status of poorly known species and effectively protect those species considered at risk. The main objective of this paper is to provide a year-round and pluriannual description of the minimum acoustic occurrence of the NBW, Sowerby’s (SBW; Mesoplodon bidens), Cuvier’s (CBW; Ziphius cavirostris), True’s (TBW; M. mirus) and Gervais’ (GBW; M. europaeus) beaked whales. Twenty-five acoustic recorders were deployed off eastern Canada between May 2015 and November 2017. Beaked whale echolocation clicks were detected using a combination of automated detectors and manual validation at 12 of these stations. Detections were generally restricted to deep continental slope waters. All detected species occurred in the southern part of the study area (off the Scotian Shelf and southern Grand Banks), while only NBWs were detected at the northern edge, off southern Labrador. Clicks identified as TBW or GBW were restricted to, but occurred annually in, the southern areas. All other species were present, at least seasonally, east and north of the Grand Banks. NBWs occurred every day in the Gully Canyon, where SBWs also occurred regularly. While these results should be interpreted as minimum species presence and considered with regards to detector performance, they provide important information regarding beaked whales’ use of areas off eastern Canada where these species have generally received no or very limited monitoring effort.

Habitat and abundance of cetaceans in Atlantic Ocean continental slope waters off the eastern USA

This study quantifies the abundance and spatial distribution of the cetacean community occupying continental shelf edge and inner continental slope waters along the US southeast Atlantic coast. A shipboard visual line-transect survey was conducted between June and August of 2004 that included effort in waters >50m deep encompassing the shelf break and inner continental slope off the US east coast between 28°N and 38°N latitude. The abundance of nine cetacean taxa was estimated using line-transect distance analysis and an independent observer approach to correct for visibility bias. Canonical correspondence analysis was used to examine the spatial distribution of the cetaceans encountered during the survey as a function of surface temperature, surface salinity, surface fluorescence, bottom depth, and bottom slope. The abundance estimates for most species were much higher than those from a study of the area conducted in 1998. This is primarily due to increased coverage of the shelf-break region and correction for visibility bias. The multivariate analysis indicated four distinct groups of cetaceans that partitioned habitat as a function of salinity, depth, and a latitudinal gradient. These groups were associated with specific water masses and hydrographic features including mid-Atlantic shelf waters (Group I), the shelf break (Group II), mid-Atlantic slope waters (Group III), and south Atlantic slope water (Group IV). Areas where water masses converge such as the continental shelf break along the mid-Atlantic and near Cape Hatteras, North Carolina are therefore areas of both high diversity and density of cetaceans.

Field observations on rare or unnoticed dinoflagellates from the Argentine Sea

Background and aims: Planktonic dinoflagellates have a great ecological significance in marine environments. While some dinoflagellate species commonly reach bloom concentrations and are thus conspicuous components of marine phytoplankton, others occur in very low abundances which make them difficult to detect in field studies.Here we analyzed dinoflagellate composition and abundance in five oceanographic expeditions carried out in continental shelf and slope waters of the Argentine Sea.M&M: Plankton abundance was estimated by the Utermöhl method, using inverted microscopy, whereas further optical and scanning electron microscopy was applied for the identification of dinoflagellate species.Results: We focused on the occurrence of seven dinoflagellates that have been previously poorly documented or overlooked in marine environments worldwide: Dinophysis microstrigiliformis; Gyrodinium sp.; Karlodinium elegans; Oxytoxumlaticeps; Peridiniella danica; Peridiniella globosa and Prorocentrum nux. The latest and K. elegans are observed for the first time in field conditions after their original descriptions based on cell cultures. While most species were detected in low ormoderate abundances, P. nux, which is the smallest Prorocentrum species, reached 82,000 cells L-1 in slope waters. Very small Gyrodinium cells (11.5 µm long; 8.7 µm wide) with a distribution restricted to slope waters during spring, were not possible tobe accurately assigned to a species.Conclusions: This study contributes to the understanding of dinoflagellate diversity in the Argentine Sea and the worldwide distribution of little known species.

Long-term trends of oxygen concentration in the waters in bank and shelves of the Southern Japan Sea

While multiple studies have investigated oxygen decrease in Japan Sea Proper Water (JSPW; > 300 m in depth), oxygen variation in continental slope and shelf waters (< 300 m) must also be investigated in order to assess its socioecological impacts. In this study, historical oxygen data in the waters of three continental shelves and a bank of Japan Sea, off-Awashima area (AW), Wakasa Bay (WB), East of Tsushima Straight (ETS), and Yamato Bank (YB), were collected and analyzed to assess temporal variation of oxygen in each region from 1960 to 2000s. Significant decreasing trends of oxygen were detected in the waters below 150 m depth in WB and YB, and below 300 m in AW, in the summer season. In winter, a decreasing trend of oxygen was detected throughout the water column from 300 m to the sea surface in WB and YB. In ETS, a deoxygenation trend was detected throughout the water column from the bottom to the sea surface in the summer season, while no trend was detected in winter. The results suggested that oxygen decreases in AW, WB, and YB were the consequence of the upward propagation of the deoxygenation signal from JSPW, while that of ETS was caused by horizontal propagation of deoxygenation signal from the East China Sea. Assuming that the observed trend will continue in future, it is predicted that part of the water in Tsushima Strait area will reach the general sublethal threshold of oxygen (134 μmol kg−1) by the end of this century.

Skin δ13C and δ15N reveal spatial and temporal patterns of habitat and resource use by free-ranging odontocetes from the southwestern Atlantic Ocean

Large diversity and abundance of cetacean species occur along the Brazilian outer continental shelf and slope waters. In the present study, we analyzed carbon (δ13C) and nitrogen (δ15N) stable isotopes in skin biopsies of ten odontocete species (Delphinidae and Physeteridae) to assess the intra- and inter-specific patterns in the use of resources along the region. Our isotopic analysis allowed us to identify two potential subpopulations of Stenella frontalis. High core isotopic niche overlap between S. frontalis from the southern range of the study area and Delphinus delphis, especially in spring, suggested that they share similar resources and rely on spatiotemporal segregation to achieve niche differentiation and to minimize competition. Our isotopic data also pointed to high similarity among Tursiops truncatus, S. frontalis, and Globicephala melas in the use of resources. Steno bredanensis had the highest δ15N and δ13C, which agrees with its occurrence in neritic waters. S. longirostris showed consistently low δ15N values, indicating that they feed at relatively lower trophic levels, and lack of niche overlap with most delphinid species, except S. attenuata. Orcinus orca and G. melas had very similar δ13C and δ15N values, that were consistent with feeding in offshore waters. δ13C and δ15N in Physeter macrocephalus suggested that individuals feed on similar trophic levels, but over a wide spatial range. The analyses of stable isotopes in skin biopsies helped us to refine our knowledge about the intra-specific resource and habitat use, ecological niches, and the trophic interactions amongst co-occurring cetaceans from the oceanic waters of the subtropical western South Atlantic.

Phytoplankton phenology in algerian continental shelf and slope waters using remotely sensed data

Understanding the dynamics of phytoplankton provides important information on the health and richness of a marine ecosystem. In the Mediterranean Sea, significant phytoplankton variability has been observed between the western and eastern basins and between open ocean and coastal waters. In this study, we used eleven years' (2003–2013) MERIS and MODIS sea surface chlorophyll-a (Chla) data to investigate the spatial and temporal variability of phytoplankton in the Algerian shelf and slope waters (ASW), in the southwestern part of the Mediterranean Sea. We assessed the inter-annual and seasonal variability of phytoplankton biomass, retrieved thirteen pixel-based phenology metrics using TIMESAT algorithms, and determined the influence of precipitation on phytoplankton dynamics. Our results reveal differences between the western and eastern parts of ASW. In the eastern part of the coast, the production season starts one month later than in the western region. It also peaks about 15 days earlier and ends one month earlier as compared to the west. As a result, the productive season is shorter in the east than in the west. The area between Béjaïa and Skikda stands out, with the highest Chla values and the highest variability. These findings show that the phytoplankton dynamics varies also at the scale of ASW in timing and magnitude, which is complementary with studies previously conducted at the Mediterranean Sea scale. Correlation analysis shows that rainfall influences phytoplankton biomass and some phenology metrics’ variability. However, other physical and biogeochemical variables should be investigated for a more complete understanding of the plankton dynamics and to assess the impact of this variability on species abundance and diversity.

Biophysical Drivers of Zooplankton Variability on the Scotian Shelf Observed Using Profiling Electric Gliders

Variation in water mass transport is a key driver of variability in zooplankton ecology. Data distribution (e.g., sparseness) is often an important factor limiting robust delineation of zooplankton-water mass associations. Mobile autonomous profiling gliders can help address the sparseness issue because gliders can sample across water mass domains spanning tens to hundreds of kilometers at high frequency during a single deployment. The goal of our study was to research the use of gliders as a tool to increase the spatiotemporal scale and robustness of zooplankton-water mass datasets. An autonomous ocean glider was deployed in Roseway Basin, Scotian Shelf, Canada for 2 months along a set of transects that crossed two water masses, a cold-fresh coastal water mass, and a warm-salty continental slope water mass. Zooplankton biomass was measured with a single frequency Imagenex 300 kHz hydroacoustic echosounder mounted to the underside of the glider at an angle of 26°, such that it was directed vertically downward on the glider downcast. During the deployment, an unusual basin flushing event occurred, where the slope water mass that is typically present in the deep water of Scotian Shelf basins was almost completely replaced by coastal water at all depths. This unique event offered an opportunity to study how extreme changes in water mass affected zooplankton distribution. The impact of basin flushing on both diel- and non diel-vertically migrating zooplankton communities within the basin was investigated using General Linear Models. The analysis demonstrated some key relationships exist among zooplankton acoustic scattering layers, water mass properties, and basin bathymetry. Zooplankton biomass was higher in the slope water mass, and declined substantially during the basin flushing event, suggesting that coastal water is not zooplankton habitat for either community. Spatial gradients in the extent of flushing provided local refuge for zooplankton within one margin of the Basin. These patterns would be challenging to measure using conventional shipboard surveys. Our study provides guidance on the use of gliders to supplement shipboard research on biophysical coupling in the plankton, which is of value as the use of gliders for this purpose is proliferating.

Improved bromide measurements using chloramine-T shows, bromide depletion in the Gulf of Maine

The assay for bromide (Br−) based on bromination of phenol red using chloramine-T was tested with small volumes (0.3 ml or less) of seawater and had two confounding issues. High blanks (with no added bromide) occasionally occurred, and the reaction-derived color frequently was destroyed by coupled reactions within the assay. The method was modified by lowering the assay pH to 3.9, by reducing the assay temperature to 13C, and by keeping the reaction short (10 s). As a result, blank absorbances were very low, and reaction-produced color was not destroyed in routine assays. In addition, no interferences by ionic seawater constituents were found. The assay was tested on natural water samples from the Antarctic continental shelf and from the Gulf of Maine. The results were highly precise; duplicates of 32 samples from the Gulf of Maine had an average standard error of the mean of ± 2.26 μmol kg−1. Antarctic bottom waters had bromide concentrations of 834.1 and 831.9 μmol kg−1 and the Br−/Chl ratio, where Chl is the chlorinity in μmol chloride equivalents (kg of seawater)−1, statistically matched the previously determined ocean mean of 0.15410 mol %. In the Gulf of Maine, vertical profiles from the sea surface to the sea floor showed lower concentrations inshore near the surface (minimum of 762.2 μmol kg−1) and greater concentrations at depth (maximum of 837.3 μmol kg−1 in a basin containing continental slope water). At the offshore basin with slope water, the Br−/Chl ratio of all waters below 15 m matched the ocean mean. Sites near the Maine and New Hampshire coast had lower concentrations of bromide, and the station-averaged Br−/Chl ratios reached a minimum of 0.15283 mol %. A previous explanation for reduced Br−/Chl ratios in shallow seas was that the fresh water Br−/Chl ratio could be much less than the ocean mean. A two end-member mixing model of the Gulf of Maine showed that this mechanism could explain a reduction in bromide concentrations in coastal Maine of about 0.6 μmol kg−1, but this depletion is 10-fold low of the observed bromide reduction. The lowered bromide content in coastal waters could be due to 1) significant macroalgal uptake along the coastline, and 2) in situ bromination of dissolved organics and planktonic detritus via photochemical or peroxide oxidation.

Miocene marine macropaleontology of the fourth bore Caldecott Tunnel excavation, Berkeley Hills, Oakland, California, USA

Author(s): Powell, II, Charles L.; Clites, Erica C.; Poust, Ashley W. | Abstract: Excavation of the new fourth bore of the Caldecott Tunnel in the Berkeley Hills, Oakland, California reveals two faunas attributed to an unnamed glauconitic mudstone (=Sobrante Formation and mapped as Tsm) and the Claremont chert (both of Graymer 2000). The fossil assemblage from the unnamed glauconitic mudstone, referred to here as the Tsm Caldecott Tunnel fauna, consists of 32 taxa: one bryozoan, 22 Mollusca (16 Bivalvia, five Gastropoda and one Scaphopoda), two Arthropoda (one Decapoda and one Maxillopoda), two Echinodermata (one Crinoidae and one Echinoidea), and five Chordata. Mollusks indicate a middle Miocene age based on the co-occurrence of the provisionally identified bivalves Acila empirensis, Anadara osmonti, Yoldia submontereyensis, Y. supramontereyensis and the gastropod genera Bruclarkia and Trophoscyon. This fauna was likely deposited at water depths between 350 and 400 m. Although several taxa from shallower depths are present, these are assumed to have washed in from shallower depths. Only one taxon was found that typically occurs in deeper water. The fauna lived in a methane-rich environment based on the occurrence of vesicomyid bivalves and on a vesicomyid/lucinid bivalve association shown elsewhere to be associated with cold seep environments. Vertebrates include great numbers of small, pelagic fish and the piscivorous sharks and marine mammals which likely took advantage of them for food. The Tsm Caldecott Tunnel fauna represents the second fauna from a methane-rich environment from the greater San Francisco Bay area and the first attributed to a methane seep environment. In addition, this fauna contains the first reported Cenozoic crinoid from California and the new species Dentalium (Fissidentalium?) mcganna (Mollusca: Scaphopoda) is described. The fauna from the Claremont chert includes two bivalve mollusks, one scaphopod, one barnacle and three vertebrates. These taxa are all represented by single specimens. They represent a marine environment likely at continental shelf or slope water depths. The occurrence of the shark Carcharhinus obscurus may indicate water temperatures warmer than off the central California coast today.

Shionodiscus gaarderae sp. nov. (Thalassiosirales, Thalassiosiraceae), a bloom-producing diatom from the southwestern Atlantic Ocean, and emendation of Shionodiscus bioculatus var. bioculatus

The recently established diatom genus Shionodiscus is characterized as possessing a labiate process on the valve face and strutted processes with long internal and reduced, or no, external extensions. Many Thalassiosira species with these features were transferred to this new genus, as well as some with short internal, strutted process extensions. Examination of samples from the Argentine continental shelf and slope waters, and from the Beagle Channel, revealed the presence of a small centric diatom that formed an extensive bloom in slope waters during spring 2005 and 2006. Analysis by light and electron microscopy revealed high similarity to specimens previously referred as Thalassiosira bioculata var. raripora. This name was never effectively published; nevertheless, the name has been adopted and observations referring to it have been reported on several occasions. Here we trace the usage of the (nomenclaturally invalid) name Thalassiosira bioculata var. raripora in the literature, and formally describe the species as Shionodiscus gaarderae, based on our observations and comparison with previous reports. A morphological comparison of this and similar taxa is also provided. In addition, we offer an emended description of S. bioculatus var. bioculatus from Ostenfeld material sampled from the ‘Färöer Island Naströ Fjord Plankton (16.9.1902)’, held in the Hustedt collection. Finally, we propose the transfer of Thalassiosira rosulata to Shionodiscus.

Palaeoecological analysis of Sentolo Formation based on foraminifera fossil assemblage from stratigraphic cross-sectional measurements in Pengasih, Kulon Progo, Yogyakarta

Sentolo formation that is included in the Kulon Progo stratigraphic series has a wide distribution. Although there have been a number of studies on it, more detailed research is needed, as there are still many unexplored outcrop locations. Moreover, there are still a lot of questions about the stratigraphic relationship between Sentolo Formation and Oligocene-Miocene volcanic series of Kulon Progo. Based on this background, this study is focused on the existence of foraminifera fossil in Sentolo Formation as an indicator of palaeoecological conditions at the time Sentolo Formation was deposited. This research is very important to get a detail understanding about the indicators that are influential at the time of deposition process of Sentolo Formation in research area. Based on palaeoecological analysis, the palaeoecology at the time Sentolo Formation deposited was normal marine continental slope waters. Meanwhile, the community structure of foraminifera indicates a stable water conditions in a marine environment that was not disrupted by volcanism, so it becomes a good factor for the growth of foraminifera. Whereas the presence of volcaniclastic material mixed with carbonate which is occurred in the lower part of Sentolo Formation were interpreted as reworked of older volcanic rock.

The spatial and interannual dynamics of the surface water carbonate system and air–sea CO&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt; fluxes in the outer shelf and slope of the Eurasian Arctic Ocean

Abstract. The Arctic is undergoing dramatic changes which cover the entire range of natural processes, from extreme increases in the temperatures of air, soil, and water, to changes in the cryosphere, the biodiversity of Arctic waters, and land vegetation. Small changes in the largest marine carbon pool, the dissolved inorganic carbon pool, can have a profound impact on the carbon dioxide (CO2) flux between the ocean and the atmosphere, and the feedback of this flux to climate. Knowledge of relevant processes in the Arctic seas improves the evaluation and projection of carbon cycle dynamics under current conditions of rapid climate change. Investigation of the CO2 system in the outer shelf and continental slope waters of the Eurasian Arctic seas (the Barents, Kara, Laptev, and East Siberian seas) during 2006, 2007, and 2009 revealed a general trend in the surface water partial pressure of CO2 (pCO2) distribution, which manifested as an increase in pCO2 values eastward. The existence of this trend was defined by different oceanographic and biogeochemical regimes in the western and eastern parts of the study area; the trend is likely increasing due to a combination of factors determined by contemporary change in the Arctic climate, each change in turn evoking a series of synergistic effects. A high-resolution in situ investigation of the carbonate system parameters of the four Arctic seas was carried out in the warm season of 2007; this year was characterized by the next-to-lowest historic sea-ice extent in the Arctic Ocean, on satellite record, to that date. The study showed the different responses of the seawater carbonate system to the environment changes in the western vs. the eastern Eurasian Arctic seas. The large, open, highly productive water area in the northern Barents Sea enhances atmospheric CO2 uptake. In contrast, the uptake of CO2 was strongly weakened in the outer shelf and slope waters of the East Siberian Arctic seas under the 2007 environmental conditions. The surface seawater appears in equilibrium or slightly supersaturated by CO2 relative to atmosphere because of the increasing influence of river runoff and its input of terrestrial organic matter that mineralizes, in combination with the high surface water temperature during sea-ice-free conditions. This investigation shows the importance of processes that vary on small scales, both in time and space, for estimating the air–sea exchange of CO2. It stresses the need for high-resolution coverage of ocean observations as well as time series. Furthermore, time series must include multi-year studies in the dynamic regions of the Arctic Ocean during these times of environmental change.

Biology of the shrimp Oplophorus spinosus (Brullé, 1839) (Decapoda, Oplophoridae) in the continental slope waters of the coast of northwest Africa

The size-sex structure and reproduction of the pelagic shrimp Oplophorus spinosus (Brullé, 1839) in the northwestern African continental slope is described herein. A total of 175 males and 53 females were caught by pelagic and bottom trawls at depths of 354-913 m in October-May 2003-2005. Total body length (TL) was 20-55.5 mm in males and 28.5-54 mm in females. Female TL at first maturity was 31 mm, the TL of ovigerous females ranged from 39.5-54 mm. Fecundity varied from 5 to 25 eggs with an outer diameter of 3.21 ± 0.19 mm at the beginning of embryogenesis and 3.14 ± 0.16 mm at half-time. O. spinosus has a continuous spawning period with a possible peak in spring. Its main reproductive traits are similar to those of this species from the Pacific and are comparable with the other species of this genus. In general, Oplophorus spp. are typical K-strategists with large-sized eggs and low fecundity.

The East Australian Current, upwellings and downwellings off eastern-most Australia in summer

The complex influences of the East Australian Current (EAC) and winds on the waters of the continental shelf were addressed with a ship survey, moored and drifting instruments, satellite images and wind and sea level measurements. The study revealed intrusions of continental slope water reaching the inner continental shelf when the EAC was near the shelf edge and wind stress was near zero or upwelling favourable (northerly). The process was the onshore movement of a southward flowing stream of water originally from the continental slope. One event was captured near Cape Byron and Evans Head when these waters upwelled to the surface. When the wind stress turned northward, it reversed the inner shelf current and drove downwelling. Variations in the wind stress also modulated the strength of the EAC out across the shelf to the upper slope. The strength of the EAC per se varied with a time scale of 2–3 months; these variations decreased in amplitude westward until they were undetectable at the inner shelf. The EAC had a subsurface speed maximum of up to 1.6ms–1 at 100–150-m depth above the continental slope and was seen to accelerate with both time and distance southward along the 190-km length surveyed by the ship.

Видовой состав и численность метазойного микрозоопланктона в водах северо-восточной части Чёрного моря летом 2013 г.

Метазойный микрозоопланктон играет решающую роль в питании личинок и мальков многих видов рыб, в том числе промысловых. Целью работы являлось исследование обилия и видового состава микрометазоопланктона в водах северо-восточной части Чёрного моря, для которой подобные сведения единичны. Батометрические пробы воды для исследований взяты на двух полигонах в прикерченском районе моря: над шельфом (I) и над континентальным склоном (II). Над большими глубинами концентрация планктона в поверхностном слое была почти в 2 раза выше, а доля неритических видов — значительно ниже по сравнению с концентрацией в акватории над шельфом. Характер вертикального распределения численности микрометазоопланктона зависел от выраженности градиентов температуры и солёности. Общее снижение численности в прибрежных водах южного берега Крыма с глубиной гораздо сильнее выражено над континентальным склоном. В верхних слоях воды доминировали копеподы рода Acartia и Centropages ponticus; в шельфовых водах существенную долю составлял также недавний вселенец в Чёрное море Oithona davisae. В слое термоклина и под ним массовыми были копеподы Oithona similis, Acartia clausi, Paracalanus parvus; из нерачкового планктона преобладали Rotifera. Вновь полученные и ранее опубликованные данные свидетельствуют о тенденции увеличения общего обилия микрометазоопланктона в крымских акваториях Чёрного моря в последние годы.

First report of dwarf monocle bream Parascolopsis capitinis (Teleostei: Nemipteridae) from South-west coast of India

The dwarf monocle breams of Genus Parascolopsis are bottom living small fishes generally seen in the outer shelf and continental slope waters and are represented worldwide by 12 species. Morphometric measurements, meristic counts and identification of the specimens follows standard methods. Parascolopsis capitinis Russell (J South Asian Nat Hist. 2:63–6, 1996), is reported for the first time from Indian waters based on 22 specimens (192–232 mm total length) collected from Cochin fisheries harbour in the South-west coast of India on 5 November 2012. This is the first report of the fish from Indian waters and adds to the five species already reported from this genus from Indian waters. Full description of the species is provided.

Oceanographic constraints on seafloor surveys of the New England continental shelf

In July 2015, a seafloor survey of a 30 km x 10 km area of the New England continental shelf, centered at about 40.4750 N, 70.6030 W with an average depth of 74 m, highlighted constraints imposed by the locally dynamic oceanography. Variability in time and space of the water column in the survey area was observed in CTD casts, in underway temperature and salinity data, and in pervasive refraction correction errors symptomatic of internal waves. Depth profiles of temperature and practical salinity show evidence of sporadic continental slope water intrusion on the shelf between 50 m below sea level and the bottom. Underway data reveal a front responsible for an abrupt 10-m/s drop in sound speed along track at 5-m depth. Short of restricting soundings to ±300 about nadir, there is no mitigation for seafloor surveying through internal waves because frequent sampling of the sound-speed profile along track, e.g., with an underway sound-speed profiling system, provides no information on the water masses on eithe...

The formation of a cold-core eddy in the East Australian Current

Cold-core eddies (CCEs) frequently form in western boundary currents and can affect continental shelf processes. It is not always clear, however, if baroclinic or barotropic instabilities contribute more to their formation. The Regional Ocean Modelling System (ROMS) is used to investigate the ocean state during the formation of a CCE in the East Australian Current (EAC) during October 2009. The observed eddy initially appeared as a small billow (approx. 50km in length) that perturbed the landward edge of the EAC. The billow grew into a mesoscale CCE (approx. 100km in diameter), diverting the EAC around it. A ROMS simulation with a realistic wind field reproduced a similar eddy. This eddy formed from negative vorticity waters found on the continental shelf south of the EAC separation point. A sensitivity analysis is performed whereby the impact of 3 different wind forcing scenarios, upwelling, downwelling, and no winds, are investigated. A CCE formed in all wind scenarios despite the wind induced changes in hydrographic conditions in the continental shelf and slope waters. As such, the source of energy for eddy formation did not come from the interactions of wind with the continental shelf waters. Analysis of strain and energy transformation confirms this by showing that the prevailing source of CCE energy was kinetic energy of the offshore EAC. These results clearly link the formation of the CCE to the swift flowing EAC and barotropic instabilities.

The biology of Benthosema glaciale and Ceratoscopelus maderensis (Myctophidae) in the Slope Sea off Nova Scotia, Canada

The myctophid species Benthosema glaciale and Ceratoscopelus maderensis were predominant in the catches of 10 mesopelagic fish surveys conducted in the Slope Sea, south and southeast of Nova Scotia. The area surveyed included both cold northeastern (Labrador Slope Water – LSW) and warm southwestern (Warm Slope Water – WSW) components of this water mass. The sub-polar-temperate species, B. glaciale, was found to be only about 15% as abundant in WSW as in LSW. Nonetheless, it occurred throughout WSW and reproduced there, maturing at a younger age than in LSW. The temperate species, C. maderensis, the predominant myctophid caught in WSW, had a life cycle of 1yr in most cases, but a small proportion lived for a second year and these occurred primarily in LSW. These larger animals matured sexually and contributed to spawning in the LSW/WSW boundary area, but their reproductive contribution elsewhere in LSW and in continental slope waters remains to be established. Both species had diverse diets, the taxonomic compositions of which overlapped substantially.

Interannual variation in diapausing copepods and associated water masses in a continental shelf basin, and implications for copepod buoyancy

Oceanographic surveys were conducted in Roseway Basin, western Scotian Shelf, during late-summer from 2007 through 2009 to measure the magnitude of interannual variation in the spatial distribution of diapausing copepods Calanus finmarchicus and C. hyperboreus and associated water mass characteristics. Calanus spp. abundance, energy density and hydrography were measured at depths >50m along transects using a Towed Underwater Biological Sampling System equipped with an Optical Plankton Counter (OPC) and a conductivity-temperature-depth (CTD) sensor, as well as at fixed stations using a Biological Net and Environmental Sampling System equipped with nets, OPC and CTD. Water mass density and in some cases salinity explained variation in the deep copepod layer across both time and space, whereas temperature did not. Water mass density, copepod energy density and thickness of the copepod layer were statistically lower during 2008 than 2007 or 2009. The copepod layer was absent from the western Basin margin during 2008 where low density continental water resided that year, whereas during 2007 and 2009 higher density continental slope water and copepods were each present along the western margin. Our results suggest that water mass density is an important characteristic defining the spatial and interannual ecology of the deep copepod layer in Roseway Basin. The 26 σt isopycnal may be a lower density limit to diapausing Calanus spp. habitat on continental shelves with shallow bathymetry, that helps the animals maintain neutral buoyancy during diapause.