Gulf Stream Water Research Articles

Ocean Circulation Causes Strong Variability in the Mid‐Atlantic Bight Nitrogen Budget

AbstractUnderstanding of nitrogen cycling on continental shelves, a critical component of global nutrient cycling, is hampered by limited observations compared to the strong variability on a wide range of time and space scales. Numerical models have the potential to partially alleviate this issue by filling spatiotemporal data gaps and hence resolving annual area‐integrated nutrient fluxes. In this study, a three‐dimensional biogeochemical‐circulation model was implemented to simulate the Mid‐Atlantic Bight (MAB) nitrogen budget. Model results demonstrate that, on average, MAB net community production (NCP) was positive (+0.27 Tg N/year), indicating net autotrophy. Interannual variability in NCP was strong, with annual values ranging between 0.19 and 0.41 Tg N/year. Along‐shelf and across‐shelf horizontal transport fluxes were the other dominant terms in the nitrogen budget and were primarily responsible for this NCP variability. The along‐shelf current transported nitrogen from the north (0.65 Tg N/year) into the MAB, supplementing the nitrogen entering from terrestrial inputs (0.27 Tg N/year). However, NCP was highest in the year when total water volume transport and inorganic nitrogen input was strongest across the continental slope in the southern MAB, rather than when terrestrial inputs were greatest. Interannual variability of NCP appears to be linked to changes in the positions of the Gulf Stream and Slope Water Gyre. Overall, the strong spatiotemporal variability of the nitrogen fluxes highlights the importance of observations throughout all seasons and multiple years in order to accurately resolve the current status and future changes of the MAB nitrogen budget.

Vertical mixing and elements of mesoscale dynamics over North Carolina shelf and contiguous Gulf Stream waters

Results of microstructure measurements conducted in October–November of 2015 as a part of the Coupled Air Sea Processes and Electromagnetic Ducting Research (CASPER) project are discussed. The measurements were taken on the North Carolina shelf and across the Gulf Stream front. On the shelf, the oceanic stratification was influenced by highly variable surface salinity and along-bottom advection. Vertical mixing was mostly governed by variable winds. The vertical eddy diffusivity was estimated using the VMP-based dissipation measurements, and the diffusivity values obtained during calm periods and stormy winds were compared. Parameterization of the diffusivity for various mesoscale dynamical conditions is discussed in terms of shear instabilities and internal wave-generated turbulence based on data obtained in deep waters of the Gulf Stream and on the continental slope.

First satellite tracks of the Endangered black-capped petrel

The black-capped petrel Pterodroma hasitata is an endangered seabird with fewer than 2000 breeding pairs restricted to a few breeding sites in Haiti and the Dominican Republic. To date, use areas at sea have been determined entirely from vessel-based surveys and opportunistic sightings and, as such, spatial and temporal gaps in our understanding of the species’ marine range are likely. To enhance our understanding of marine use areas, we deployed satellite tags on 3 black-capped petrels breeding on Hispaniola, representing the first tracking study for this species and one of the first published tracking studies for any breeding seabird in the Caribbean. During chick rearing, petrels primarily used marine habitats in the southern Caribbean Sea (ca. 18.0° to 11.5° N, 70.0° to 75.5° W) between the breeding site and the coasts of Venezuela and Colombia. Maximum distance from the breeding sites ranged from ca. 500 to 1500 km during the chick-rearing period. During the post-breeding period, each bird dispersed north and used waters west of the Gulf Stream offshore of the midand southern Atlantic coasts of the USA as well as Gulf Stream waters and deeper pelagic waters east of the Gulf Stream. Maximum distance from the breeding sites ranged from ca. 2000 to 2200 km among birds during the nonbreeding period. Petrels used waters located within 14 different exclusive economic zones, suggesting that international collaboration will benefit the development of management strategies for this species.

Holocene oceanographic changes in SW Labrador Sea, off Newfoundland

Benthic foraminiferal assemblages supported by selected geochemical data from three marine sediment cores collected in Placentia Bay, SE Newfoundland, are used to construct an ~13,000-year-long record of regional oceanographic changes in the SW Labrador Sea. The area is located in the boundary zone between the cold, ice-loaded Labrador Current (LC) in the north and the warm Gulf Stream (GS) waters to the south. After the Younger Dryas termination, the influence of GS-derived water increased and was further strengthened at 10.7 cal. kyr BP through enhanced northward flow of Atlantic water via the Slopewater Current. A short-term event of increased terrestrial input and water column stratification at 8.4 cal. kyr BP was likely linked to the distal drainage of glacial Lake Agassiz. After 7.3 cal. kyr BP, a stronger LC weakened the inflow of warmer subsurface waters from the GS. This may be explained by extensive meltwater release from ice sheets in Arctic Canada and is concurrent with a general shift in oceanographic conditions in the Labrador Sea region. Around 4.0 cal. kyr BP, conditions became more stable with a slight increase in salinity, indicating a decrease in meltwater transported via the LC. The Northern Hemisphere neoglacial cooling around 2.8 cal. kyr BP was characterized off SE Newfoundland by a further stabilization of the current system, dominated by the LC with some continued influx of GS water.

Low-Level Cloud Response to the Gulf Stream Front in Winter Using CALIPSO*

Abstract A sharp sea surface temperature front develops between the warm water of the Gulf Stream and cold continental shelf water in boreal winter. This front has a substantial impact on the marine boundary layer. The present study analyzes and synthesizes satellite observations and reanalysis data to examine how the sea surface temperature front influences the three-dimensional structure of low-level clouds. The Cloud–Aerosol Lidar and Infrared Pathfinder Satellite Observations (CALIPSO) satellite captures a sharp low-level cloud transition across the Gulf Stream front, a structure frequently observed under the northerly condition. Low-level cloud top (<4 km) increases by about 500 m from the cold to the warm flank of the front. The sea surface temperature front induces a secondary low-level circulation through sea level pressure adjustment with ascending motion over the warm water and descending motion over cold water. The secondary circulation further contributes to the cross-frontal transition of low-level clouds. Composite analysis shows that surface meridional advection over the front plays an important role in the development of the marine atmospheric boundary layer and low-level clouds. Under cold northerly advection over the Gulf Stream front, strong near-surface instability leads to a well-mixed boundary layer over the Gulf Stream, causing southward deepening of low-level clouds across the sea surface temperature front. Moreover, the front affects the freezing level by transferring heat to the atmosphere and therefore influences the cross-frontal variation of the cloud phase.

Surface and deep-water variability at the Blake Ridge, NW Atlantic during the Plio-Pleistocene is linked to the closing of the Central American Seaway

The closing of the Central American Seaway (CAS) during the late Pliocene played an important role in global climate change as well as variation in surface and deep ocean paleoceanography. Restriction in the mixing of Pacific Ocean water with Atlantic Ocean water through the CAS ultimately led to the enhanced production of high salinity warm Gulf Stream water which flowed poleward and caused the Northern Hemisphere Glaciation (NHG) as well as increased production of deep Northern Component Water (NCW). The timing of the final closure of the CAS is still a topic of debate. The present study pursued on planktic foraminifera and carbon isotopic variation in planktic foraminifera from the Blake Ridge to understand the variation in surface and deep ocean paleoceanography and their linkages to the timing of the closing of the CAS. Planktic faunal turnover at around 2.2Ma along with the increased production of NCW at around 2.4Ma is considered as the ceasing period of the CAS. Prior to 2.2Ma, the dominance of Globigerina bulloides, Orbulina universa and Globigerinoides ruber indicates the existence of the opening between the two Americas and invasion of Pacific surface water into the Atlantic through this gateway. It is proposed that during this time the studied ODP Hole 994C was under the influence of highly productive gyre water as observed by the dominance of G. bulloides and depleted δ13C of Neogloboquadrina dutertrei (δ13CNd). The dominance of N. dutertrei and Globorotalia truncatulinoides with enriched δ13CNd from 2.2 to 1.2Ma indicates the presence of high salinity-less productive surface water over the studied Hole 994C. The closing of the CAS restricted the mixing of two ocean waters and thus the intensity of the Gulf Stream increased significantly with the dominance of NCW at the deeper level. Increased cooling and intensified Gulf Stream shifted the gyre water eastward and deepened the thermocline, and thus the studied hole was under gyre margin/Gulf Stream water during 2.2–1.2Ma. The Mid Pleistocene Transition (1.2 to 0.8Ma) is marked by the presence of high productive gyre water (depleted δ13CNd) over Hole 994C. The dominance of all the species with highly variable δ13CNd and δ18ONd during the last 0.4Ma indicates that fluctuations in surface water perhaps are linked to increased NHG.

Revealing the energy sources of alternating intensity regimes of the evolving Alberto tropical cyclone using microwave satellite sensing data

The trajectory characteristics and the intensity evolution of the Alberto tropical cyclone (TC) in the integral water-vapor field are analyzed in detail using a software-algorithmic complex designed for constructing highly detailed global radio-thermal fields of the ocean-atmosphere system based on microwave satellite measurements. This complex was developed by the authors earlier and allows one to obtain global animated radio-thermal fields with a time step of 1.5 h and a spatial resolution of 0.2°. Special attention is paid to the problem of revealing the energy sources of three consecutive intensifications of this TC. The analysis of satellite data with the use of the animation method developed by the authors shows for the first time that these sources are regions with an increased (exceeding the critical level) integral water-vapor content located in different geographical areas lying along the complex trajectory of the TC with a variable intensity. The first region was located in the equatorial intertropical convergence zone, the second was located above the Gulf Stream water area, and the third resided in the area affected by the Azores High.

Paralarval octopods of the Florida Current

Taxonomic and ecological aspects of paralarval octopods from the Florida Current (Gulf Stream) waters off Fort Pierce, Florida are reported. Nine external morphological features were analysed in each specimen, including chromatophore patterns and meristic characters. The relative abundance of each species present in the collections made at standard stations [2–26 nautical miles (nmi) offshore at 2-nmi intervals; 1 nmi = 1.8520 km] was determined in relation to seasonal occurrence, depth of capture, distance offshore and time of day/night. The most common species in the samples was Octopus “vulgaris”, followed by Amphioctopus burryi and Macrotritopus defilippi (two morphs). Two forms could not be verified to species, but they most closely resemble Scaeurgus unicirrhus and “Octopus” joubini. The seasonal distribution of the most commonly captured species showed peak relative abundance in the summer months. Paralarval octopods were captured most frequently in the standard stations between 18 and 22 nmi (29.6–40.7 km) offshore in the mid-depth stratum of the water column. Most of the species represented in this study were captured in higher numbers at night than during the day, with the exception of A. burryi.

Direct interaction between the Gulf Stream and the shelfbreak south of New England

Sea surface temperature imagery, satellite altimetry, and a surface drifter track reveal an unusual tilt in the Gulf Stream path that brought the Gulf Stream to 39.9°N near the Middle Atlantic Bight shelfbreak—200 km north of its mean position—in October 2011, while a large meander brought Gulf Stream water within 12 km of the shelfbreak in December 2011. Near-bottom temperature measurements from lobster traps on the outer continental shelf south of New England show distinct warming events (temperature increases exceeding 6°C) in November and December 2011. Moored profiler measurements over the continental slope show high salinities and temperatures, suggesting that the warm water on the continental shelf originated in the Gulf Stream. The combination of unusual water properties over the shelf and slope in late fall and the subsequent mild winter may affect seasonal stratification and habitat selection for marine life over the continental shelf in 2012.

Intrusions of Gulf Stream waters onto the South Atlantic Bight shelf

[1] Intrusions of Gulf Stream waters onto the South Atlantic Bight continental shelf are analyzed using historical observations spanning several decades. Intrusions of dense water near the bottom occur predominantly during summer, when they are observed 30% of the time at the middle and outer shelf, but less frequently (<10%) inshore of the 20 m isobath, where they are found predominantly following periods of strong upwelling favorable winds. Bottom intrusions can have an important effect on stratification, especially on the outer shelf, where the average near-bottom temperature is 2°C lower when bottom intrusions are present. Surface intrusions, on the other hand, occur more evenly distributed throughout the year, although they are more frequent during summer, when they also tend to reach farther onshore. Surface intrusions occur slightly more frequently during times when winds are downwelling favorable. Both surface and bottom intrusions are more frequently observed in the northern and southern South Atlantic Bight, where the shelf is narrowest, and less frequently in the wider central region.

Rapid Holocene coastal change revealed by high-resolution micropaleontological analysis, Pamlico Sound, North Carolina, USA

Foraminiferal analyses of 404 contiguous samples, supported by diatom, lithologic, geochronologic and seismic data, reveal both rapid and gradual Holocene paleoenvironmental changes in an 8.21-m vibracore taken from southern Pamlico Sound, North Carolina. Data record initial flooding of a latest Pleistocene river drainage and the formation of an estuary 9000 yr ago. Estuarine conditions were punctuated by two intervals of marine influence from approximately 4100 to 3700 and 1150 to 500 cal yr BP. Foraminiferal assemblages in the muddy sand facies that accumulated during these intervals contain many well-preserved benthic foraminiferal species, which occur today in open marine settings as deep as the mid shelf, and significant numbers of well-preserved planktonic foraminifera, some typical of Gulf Stream waters. We postulate that these marine-influenced units resulted from temporary destruction of the southern Outer Banks barrier islands by hurricanes. The second increase in marine influence is coeval with increased rate of sea-level rise and a peak in Atlantic tropical cyclone activity during the Medieval Climate Anomaly. This high-resolution analysis demonstrates the range of environmental variability and the rapidity of coastal change that can result from the interplay of changing climate, sea level and geomorphology in an estuarine setting.

Warm and saline events embedded in the meridional circulation of the northern North Atlantic

Ocean state estimates from 1958 to 2005 from the Simple Ocean Assimilation System (SODA) system are analyzed to understand circulation between subtropical and subpolar Atlantic and their connection with atmospheric forcing. This analysis shows three periods (1960s, around 1980, and 2000s) with enhanced warm, saline waters reaching high latitudes, alternating with freshwater events originating at high latitudes. It complements surface drifter and altimetry data showing the subtropical -subpolar exchange leading to a significant temperature and salinity increase in the northeast Atlantic after 2001. The warm water limb of the Atlantic meridional overturning cell represented by SODA expanded in density/salinity space during these warm events. Tracer simulations using SODA velocities also show decadal variation of the Gulf Stream waters reaching the subpolar gyre and Nordic seas. The negative phase of the North Atlantic Oscillation index, usually invoked in such variability, fails to predict the warming and salinization in the early 2000s, with salinities not seen since the 1960s. Wind stress curl variability provided a linkage to this subtropical/subpolar gyre exchange as illustrated using an idealized two ]layer circulation model. The ocean response to the modulation of the climatological wind stress curl pattern was found to be such that the northward penetration of subtropical tracers is enhanced when amplitude of the wind stress curl is weaker than normal. In this case both the subtropical and subpolar gyres weaken and the subpolar density surfaces relax; hence, the polar front moves westward, opening an enhanced northward access of the subtropical waters in the eastern boundary current.

Cold winters from warm oceans

Winters are colder in northeastern North America and Asia than in other regions at the same latitude. Previous explanations may be incomplete, having overlooked the radiation of atmospheric wave energy. See Letter p.621 It is well known that the northeastern reaches of Asia and North America are far colder in the winter than western areas at similar latitudes. The generally accepted explanation is that the weather systems are influenced by elevated terrain and by the movement of prevailing atmospheric circulation over warm ocean currents. Yohai Kaspi and Tapio Schneider now show that oceans are indeed an important underlying cause for the temperature difference, but they identify a surprising mechanism for the phenomenon. Climate modelling suggests that paradoxically, the relative coldness of North America, not the warmth of Europe, arises because of the warm waters of the Gulf Stream. Warm Gulf Stream waters adjacent to the North American coast — and similarly warm ocean waters on Asia's Pacific coast — generate atmospheric waves that draw cold northern air to continental areas westward of the currents.

Migration Pathways, Behavioural Thermoregulation and Overwintering Grounds of Blue Sharks in the Northwest Atlantic

The blue shark Prionace glauca is the most abundant large pelagic shark in the Atlantic Ocean. Although recaptures of tagged sharks have shown that the species is highly migratory, migration pathways towards the overwintering grounds remain poorly understood. We used archival satellite pop-up tags to track 23 blue sharks over a mean period of 88 days as they departed the coastal waters of North America in the autumn. Within 1–2 days of entering the Gulf Stream (median date of 21 Oct), all sharks initiated a striking diel vertical migration, taking them from a mean nighttime depth of 74 m to a mean depth of 412 m during the day as they appeared to pursue vertically migrating squid and fish prey. Although functionally blind at depth, calculations suggest that there would be a ∼2.5-fold thermoregulatory advantage to swimming and feeding in the markedly cooler deep waters, even if there was any reduced foraging success associated with the extreme depth. Noting that the Gulf Stream current speeds are reduced at depth, we used a detailed circulation model of the North Atlantic to examine the influence of the diving behaviour on the advection experienced by the sharks. However, there was no indication that the shark diving resulted in a significant modification of their net migratory pathway. The relative abundance of deep-diving sharks, swordfish, and sperm whales in the Gulf Stream and adjacent waters suggests that it may serve as a key winter feeding ground for large pelagic predators in the North Atlantic.

From the redwood forest to the Gulf Stream waters: human signature nearly ubiquitous in representative US landscapes

What landscapes best represent the land uses and land covers (LU/LC) of the continental United States? Would the set include a cornfield? A forest? A backyard? Combining principles of landscape ecology and computer science, we identified a small set of “exemplar landscapes”, representing distinct LU/LC pattern types of the conterminous US. We first partitioned the 1992 US National Land Cover Dataset into 193 705 landscapes, and quantified patterns with standard measures of LU/LC composition and configuration. Using the values to estimate similarity of LU/LC patterns between landscapes, we applied an algorithm developed to find representatives in large sets. In the resulting 17‐member set of exemplar landscapes, patterns created and managed by human activity are by far the most evident features. This set of representatives summarizes the nation's LU/LC, demonstrating the degree to which human‐influenced patterns dominate: aggregations of rectangular fields, farmlands within cleared forests, shrublands/pasture, and suburbs. The algorithm's selection of an exemplar for each group may have other ecological applications when an objectively determined subset of representative items is needed.

WATER TREATMENT: Sweeteners Persist in Waterways

Artificial sweeteners are widespread in European sewage treatment plant effluent, waterways, groundwater, and even drinking water, a growing body of research demonstrates. One of the latest studies, published in the July 2009 issue of Analytical and Bioanalytical Chemistry, presents data on four common sweeteners found in German water and demonstrates the persistence of these additives. Two, acesulfame and sucralose, were remarkably resistant to treatment by conventional sewage treatment plants as well as by a more advanced soil aquifer treatment plant, report environmental engineer Marco Scheurer and colleagues from the Water Technology Center in Karlsruhe. In samples taken from four German rivers, concentrations of ace‐sulfame exceeded 2 μg/L, whereas concentrations of sucralose, cyclamate, and saccharin were an order of magnitude lower. Coauthor Frank T. Lange, an analytical chemist, notes that a person would have to drink 2–3 L of water with sweetener concentrations similar to those of the German rivers every day for years before they would consume the amount contained in a single sweetener tablet (the concentrations detected in water were well below human taste thresholds). Three other sweeteners—aspartame, neotame, and neohesperidin dihydrochalcone—were not detected in any of the samples. The findings echo those of four recent studies documenting artificial sweeteners in sewage treatment plant effluent and waterways throughout Europe. Preliminary results from two separate studies—one unpublished and one accepted 11 September 2009 for publication in Marine Chemistry—also show sucralose in Arizona wastewater treatment plant effluent and several downstream rivers, as well as in coastal and Gulf Stream waters off the southeastern United States. Acesulfame and sucralose, which is sold in the United States as Splenda®, have proven to be the most commonly found and resilient sugar substitutes. They are added to a wide variety of foods, beverages, pharmaceuticals, and toiletries, and they pass through the human body virtually unchanged. Cyclamate and saccharin are much less persistent. Cyclamate has been banned in the United States since 1970 as a possible human carcinogen, but the Food and Drug Administration is considering reapproval. And although saccharin has been found to cause cancer in rats, it is considered safe for human consumption. All the sources interviewed for this article agree there’s little risk that acesulfame and sucralose in drinking water will cause human health problems. The implications for the aquatic environment are less clear, however. Because these sweeteners have been classified as safe for human consumption, they have undergone virtually no environmental testing. Yet the remarkable persistence of acesulfame and sucralose gives some experts pause, given that environmental concentrations will likely rise over time with continued consumption. Henrik Kylin, an environmental chemist at the Norwegian Institute for Air Research and a coauthor of a study on sucralose presented at the Society of Environmental Toxicology and Chemistry Europe 17th Annual Meeting in 2007, points out that sucralose mimics sucrose, a structurally similar molecule involved in biological functions from the regulation of genes related to photosynthesis to feeding cues in zooplankton. “If those [functions] are affected, you may end up with serious ecosystem effects,” he says. Kylin is also concerned by the finding, reported in the October 2006 issue of Plant, Cell & Environment, that sucralose at least partially inhibited sucrose transport in sugarcane. “There are very many vascular plants in the aquatic ecosystem,” he says, “and if they are [similarly] affected, it would affect very many other organisms.” Rosa Krajmalnik‐Brown, an assistant professor of environmental biotechnology at Arizona State University, has been working for more than two years to identify a microorganism that can degrade sucralose and hasn’t found one yet—although she says she’s not giving up. Still, there may be a bright side to sweeteners’ persistence: Scheurer and other researchers have proposed using them as markers for detecting wastewater spills—a welcome finding for scientists who have long sought a failsafe marker.

Shelfbreak frontal eddies over the continental slope north of Cape Hatteras

Shelfbreak and slope eddies have been implicated as important agents in the exchange of water between the shelf and slope domains of the Middle Atlantic Bight (MAB). Here we present temperature, salinity, and velocity data from a series of shipboard transects that intercepted a rich eddy field over the slope of the southern MAB. Attention is focused on a well‐sampled cyclonic eddy, of roughly 60‐km diameter and 300‐m depth, that translated southward at 0.1 m s−1. The eddy was composed of a mix of water masses including MAB shelf and slope water, Gulf Stream water, and water from the MAB shelfbreak front. Gradient Richardson numbers suggest that these water masses were subject to vigorous turbulent vertical mixing. The transport of shelfbreak frontal water contained within the eddy was substantial. In the upper 100 m, shelfbreak frontal water comprised ∼75% of the eddy's volume. This frontal water fraction moved southward with a transport of ∼0.4 Sv, comparable with the volume transport within the shelfbreak frontal jet. A number of factors indicate that this highly energetic eddy, with maximum azimuthal velocity of 0.7 m s−1, was generated through instability of the shelfbreak frontal jet. The eddy had apparently developed rapidly (in &lt;3 days), consistent with models of eddy generation through baroclinic instability of the shelfbreak frontal jet. The eddy's potential temperature/salinity (θ/S) properties and energy density closely matched the θ/S properties and energy density found in the frontal jet to the north of the eddy.

Characterization of dissolved organic matter fluorescence in the South Atlantic Bight with use of PARAFAC model: Interannual variability

Systematic water sampling for characterization of chromophoric dissolved organic matter (CDOM) in the coastal South Atlantic Bight, was conducted as part of the long term Coastal Ocean Research and Monitoring Program (CORMP). Water samples were collected during a 3.5 year period, from October 2001 until March 2005, in the vicinity of the Cape Fear River (CFR) outlet and in adjacent Onslow Bay (OB). During this study there were two divergent hydrological and meteorological conditions in the CFR drainage area: a severe drought in 2002, followed by the very wet year of 2003. CDOM was characterized optically by the absorption coefficient at 350 nm, the spectral slope coefficient ( S), and by Excitation Emission Matrix (EEM) fluorescence. Parallel Factor Analysis (PARAFAC) was used to assess CDOM composition from EEM spectra and six components were identified: three terrestrial humic-like components, one marine humic-like component and two protein-like components. Terrestrial humic-like components contributed most to dissolved organic matter (DOM) fluorescence in the low salinity plume of the CFR. The contribution of terrestrial humic-like components to DOM fluorescence in OB was much smaller than in the CFR plume area. Protein-like components contributed significantly to DOM fluorescence in the coastal ocean of OB and they dominated DOM fluorescence in the Gulf Stream waters. Hydrological conditions during the observation period significantly impacted both concentration and composition of CDOM found in the estuary and coastal ocean. In the CFR plume, there was an order of magnitude difference in CDOM absorption and fluorescence intensity between samples collected during the drought compared to the wet period. During the drought, CDOM in the CFR plume was composed of equal proportions of terrestrial humic-like components (ca. 60% of the total fluorescence intensity) with a significant contribution of proteinaceous substances (ca. 20% of the total fluorescence). During high river flow, CDOM was composed mostly of humic substances (nearly 75% of total fluorescence) with minor contributions by proteinaceous substances. The impact of changes in fresh water discharge patterns on CDOM concentration and composition was also observed in OB, though to a lesser degree.

Sunlight-Induced Photochemical Decay of Oxidants in Natural Waters: Implications in Ballast Water Treatment

The transport and discharge of ship ballast water has been recognized as a major vector for the introduction of invasive species. Chemical oxidants, long used in drinking water and wastewater treatment, are alternative treatment methods for the control of invasive species currently being tested for use on ships. One concern when a ballasted vessel arrives in port is the adverse effects of residual oxidant in the treated water. The most common oxidants include chlorine (HOCl/OCl-), bromine (HOBr/OBr-), ozone (03), hydrogen peroxide (H2O2), chlorine dioxide (ClO2), and monochloramine (NH2Cl). The present study was undertaken to evaluate the sunlight-mediated photochemical decomposition of these oxidants. Sunlight photodecomposition was measured at various pH using either distilled water or oligotrophic Gulf Stream water for specific oxidants. For selected oxidants, quantum yields at specific wavelengths were obtained. An environmental photochemical model, GCSOLAR, also provided predictions of the fate (sunlight photolysis half-lives) of HOCI/OCl-, HOBr/OBr-, ClO2, and NH2Cl for two different seasons at latitude 40 degrees and in water with two different concentrations of chromophoric dissolved organic matter. These data are useful in assessing the environmental fate of ballast water treatment oxidants if they were to be discharged in port.

On micronekton and ichthyoplankton of the frontal zone of the gulf stream and subpolar waters (Polygone “Titanic”)

Results of studies of the species composition of micronektonic fish and ichthyoplankton in the frontal zone of the Gulf Stream and subpolar waters at the stationary polygone “Titanic” performed in years with different hydrological situations (2000 and 2003) are provided. In July through August of 2000 during the penetration in the polygone of warm waters of the Gulf Stream, a considerable (almost by an order of magnitude) increase in the species composition of fish due to numerous tropical and subtropical species was recorded in comparison with the period of studies in 2003, close by dates, when the region was occupied by the cold waters of the Labrador Current. In the summer of 2000, of the 80 taxonomic forms found on the polygone, 48 were represented only by larval stages of development; 27, only by juvenile and adult specimens; and 5, by both larvae and juvenile and adult specimens. The last five species include Ceratoscopelus maderensis and Lampanyctus pusillus (Myctophidae), Arctozenus risso (Paralepididae), Stomias boa (Stomiidae), and Gonostoma elongatum (Gonostomatidae). In the summer of 2003, larval fish were absent in collections, and only juvenile and adult specimens of eight species from ten families were found. The bulk of the population of micronektonic fish in this period, as in the summer of 2000, was formed by the same arcto-boreal species of myctophids Benthosema glaciale.