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We present a complete description of the depth distribution of marine snow in Orca Basin (Gulf of Mexico), from sea surface through the pycnocline to within 10 m of the seafloor. Orca Basin is an intriguing location for studying marine snow because of its unique geological and hydrographic setting: the deepest ~200 m of the basin are filled with anoxic hypersaline brine. A typical deep ocean profile of marine snow distribution was observed from the sea surface to the pycnocline, namely a surface maximum in total particle number and midwater minimum. However, instead of a nepheloid (particle-rich) layer positioned near the seabed, the nepheloid layer in the Orca Basin was positioned atop the brine. Within the brine, the total particle volume increased by a factor of 2–3 while the total particle number decreased, indicating accumulation and aggregation of material in the brine. From these observations we infer increased residence time and retention of material within the brine, which agrees well with laboratory results showing a 2.2–3.5-fold reduction in settling speed of laboratory-generated marine snow below the seawater-brine interface. Similarly, dissolved organic carbon concentration in the brine correlated positively with measured colored dissolved organic matter (r2 = 0.92, n = 15), with both variables following total particle volume inversely through the pycnocline. These data indicate the release of dissolved organic carbon concomitant with loss in total particle volume and increase in particle numbers at the brine-seawater interface, highlighting the importance of the Orca Basin as a carbon sink.

Seafloor sediment resuspension events of different scales and magnitudes and the resulting deep (>1,000 m) benthic nepheloid layers were investigated in the northern Gulf of Mexico during Fall 2012 to Summer 2013. Time-series data of size-specific in-situ settling speeds of marine snow in the benthic nepheloid layer (moored flux cameras), particle size distributions (profiling camera), currents (various current meters) and stacked time-series flux data (sediment traps) were combined to recognize resuspension events ranging from small-scale local, to small-scale far-field to hurricane-scale. One small-scale local resuspension event caused by inertial currents was identified based on local high current speeds (>10 cm s–1) and trap data. Low POC content combined with high lithogenic silica flux at 30 m above bottom (mab) compared to the flux at 120 mab, suggested local resuspension reaching 30 mab, but not 120 mab. Another similar event was detected by the changes in particle size distribution and settling speeds of particles in the benthic nepheloid layer. Flux data indicated two other small-scale events, which occurred at some distance, rather than locally. Inertia-driven resuspension of material in shallower areas surrounding the traps presumably transported this material downslope leaving a resuspension signal at 120 mab, but not at 30 mab. The passage of hurricane Isaac left a larger scale resuspension event that lasted a few days and was recorded in both traps. Although hurricanes cause large-scale events readily observable in sediment trap samples, resuspension events small in temporal and spatial scale are not easily recognizable in trapped material as they tend to provide less material and become part of the background signal in the long-term averaged trap samples. We suggest that these small-scale resuspension events, mostly unnoticed in conventional time-series sampling, play an important role in the redistribution and ultimate fate of sediment distribution on the seafloor.

Hudson Canyon is the largest shelf-sourced canyon system off the east coast of the United States, and hosts a productive ecosystem that supports key fisheries. Here we report the results of a multi-year interdisciplinary study of the geological, geochemical, and physical oceanographic features and processes in the canyon that underpin that ecosystem. High-resolution multi-beam bathymetric and backscatter data show that the contrasting morphology of the two perpendicularly oriented branches at the head of the Hudson Canyon is indicative of different states of geomorphological activity and sediment transport. Tightly spaced ridges and gullies extend perpendicularly towards the canyon axis from the canyon walls. Numerous depressions are found at the base of the canyon walls or along the canyon axis at depths from 300 m to 600 m. Elevated concentrations of dissolved methane in the water column, where the highest density of depressions occur, suggests that methane is actively venting there. The topography and reflective floors of circular depressions in canyon walls and their association with methane maxima suggest that these represent active methane gas release-collapse pockmarks with carbonate floors. Patterns of irregular, low-relief, reflective depressions on the canyon floor may also represent methane release points, either as gas release or cold-seep features. The presence of methane maxima in a region of strong advective currents suggests continuous and substantial methane supply. Hydrographic observations in the canyon show that multiple layers of distinct inter-leaved shelf (cold, fresh) and slope (warm, salty) water masses occupy the head of the canyon during the summer. Their interactions with the canyon and with each other produce shifting fronts, internal waves, and strong currents that are influenced by canyon topography. Strong tidal currents with along-canyon-axis flow shear help to drive the advection, dispersion and mixing of dissolved materials in the water column that likely help support the rich canyon ecosystem.

Response management and damage assessment during and after environmental disasters such as the Deepwater Horizon (DWH) oil spill require an ecological baseline and a solid understanding of the main drivers of the ecosystem. During the DWH event, a large fraction of the spilled oil was transported to depth via sinking marine snow, a routing of spilled oil unexpected to emergency response planners. Because baseline knowledge of particle export in the Northern Gulf of Mexico and how it varies spatially and temporally was limited, we conducted a detailed assessment of the potential drivers of deep (~1400 m depth) particle fluxes during 2012–2016 using sediment traps at three contrasting sites in the Northern Gulf of Mexico: near the DWH site, at an active natural oil seep site, and at a site considered typical for background conditions. The DWH site, located ~70 km from the Mississippi River Delta, showed flux patterns that were strongly linked to the Mississippi nitrogen discharge and an annual subsequent surface bloom. Fluxes carried clear signals of combustion products, which likely originated from pyrogenic sources that were transported offshore via the Mississippi plume. The seep and reference sites were more strongly influenced by the open Gulf of Mexico, did not show a clear seasonal flux pattern, and their overall sedimentation rates were lower than those at the DWH site. At the seep site, based on polycyclic aromatic hydrocarbon data, we observed indications of three different pathways for “natural” oiled-snow sedimentation: scavenging by sinking particles at depth, weathering at the surface before incorporation into sinking particles, and entry into the food web and subsequent sinking in form of detritus. Overall, sedimentation rates at the three sites were markedly different in quality and quantity owing to varying degrees of riverine and oceanic influences, including natural seepage and contamination by combustion products.

The blowout of the Macondo oil well in the Gulf of Mexico in April 2010 injected up to 500,000 tonnes of natural gas, mainly methane, into the deep sea1. Most of the methane released was thought to have been consumed by marine microbes between July and August 20102, 3. Here, we report spatially extensive measurements of methane concentrations and oxidation rates in the nine months following the spill. We show that although gas-rich deepwater plumes were a short-lived feature, water column concentrations of methane remained above background levels throughout the rest of the year. Rates of microbial methane oxidation peaked in the deepwater plumes in May and early June, coincident with a rapid rise in the abundance of known and new methane-oxidizing microbes. At this time, rates of methane oxidation reached up to 5,900 nmol l−1 d−1—the highest rates documented in the global pelagic ocean before the blowout4. Rates of methane oxidation fell to less than 50 nmol l−1 d−1 in late June, and continued to decline throughout the remainder of the year. We suggest the precipitous drop in methane consumption in late June, despite the persistence of methane in the water column, underscores the important role that physiological and environmental factors play in constraining the activity of methane-oxidizing bacteria in the Gulf of Mexico.

Three-dimensional (3D) fluorescence spectroscopy and parallel factor analysis (PARAFAC) were used to characterize oil components and to examine their fate and transformation processes during the unprecedented Deepwater Horizon oil spill in the Gulf of Mexico. Water samples were collected during two cruises in May and June 2010 soon after the spill began. Fluorescence excitation-emission matrix (EEM) spectra of seawater samples strongly resemble those of crude oil from the Macondo well and weathered oil collected from Gulf surface waters. This indicates the influence of oil on marine dissolved organic matter (DOM) which yielded elevated dissolved organic carbon (DOC) concentrations, higher UV–vis absorbance, and higher optically inferred molecular weight DOM in the water column. Two major types of DOM were found in the water column: one with low abundance but high optical activity and the other with high mass concentration yet low optical activity. Higher specific UV absorbance but lower spectral slope values observed for deep-water samples indicates the presence of less degraded or fresher crude oil in deep waters. Results of PARAFAC modeling revealed three oil-related components corresponding to crude and weathered oil in the water column: the most prominent one (namely C1) centered on Ex/Em 226/340 nm and the other two components (C2 and C6) centered on 236/360 and 252/311 nm, respectively. In addition, there is another DOM component (C3), partially representing chemically dispersed oil. Interestingly, the oil component ratios, an intensive property, varied with time and the degradation status of oil. We hypothesize that C2 (236/360 nm) is mostly a degraded product while C6 (252/311 nm) is a crude oil component with lower molecular weight, but at the same time, could be derived from oil degradation. Changes in fluorescence component ratios can thus be used as a compelling index to track the fate and transport of oil in marine environments.

The 2010 Deepwater Horizon oil spill resulted in 1.6-2.6 × 10(10) grams of petrocarbon accumulation on the seafloor. Data from a deep sediment trap, deployed 7.4 km SW of the well between August 2010 and October 2011, disclose that the sinking of spill-associated substances, mediated by marine particles, especially phytoplankton, continued at least 5 mo following the capping of the well. In August/September 2010, an exceptionally large diatom bloom sedimentation event coincided with elevated sinking rates of oil-derived hydrocarbons, black carbon, and two key components of drilling mud, barium and olefins. Barium remained in the water column for months and even entered pelagic food webs. Both saturated and polycyclic aromatic hydrocarbon source indicators corroborate a predominant contribution of crude oil to the sinking hydrocarbons. Cosedimentation with diatoms accumulated contaminants that were dispersed in the water column and transported them downward, where they were concentrated into the upper centimeters of the seafloor, potentially leading to sustained impact on benthic ecosystems.

The deep-sea oil spill in the Gulf of Mexico released large quantities of oil and gaseous hydrocarbons into the deep ocean. Calculations using published estimates of the volume of oil released suggest that up to 500,000 t of gases such as methane were released into the deep ocean.

The vertical flux of particulate matter from the surface of the Ross Sea, Antarctica, has been suggested as being large, with substantial seasonal and spatial variations. We conducted a study in which vertical flux was quantified using sediment traps deployed at 200 m and compared to estimates calculated from one-dimensional budgets of nutrients (nitrogen and silicon). Estimates of flux were collected at two locations in the southern Ross Sea from late December to early February during four years: 2001–2002, 2003–2004, 2004–2005, and 2005–2006. Phytoplankton biomass and vertical flux varied substantially seasonally and spatially between the two sites, and among years. The greatest flux was observed in 2001–2002, with a short-term maximum organic carbon flux of 3.13 mmol m−2 d−1, and the summer mean organic carbon flux equal to 0.93 mmol m−2 d−1. In contrast, the mean carbon flux at the same site in 2003–2004 was over an order of magnitude less, averaging 0.19 mmol m−2 d−1, despite the fact that productivity in that year was substantially greater. In 2005–206 the contribution of fecal pellets to flux was smallest among all years, and the pellet contribution ranged from

Phytoplankton fluorescence, temperature and salinity were measured from December through February using in situ instruments deployed at two locations in the southern Ross Sea, Antarctica during the austral summers of three consecutive years (2003–2004, 2004–2005, and 2005–2006) to assess the short-term, seasonal and interannual variations in phytoplankton biomass and oceanographic conditions. The seasonal climatologies of physical forcing variables were also determined from satellite measurements, and the data from the two sites compared to the 2000–2009 mean. In situ fluorometers were deployed at three depths at 77S, 172.7E and 77.5S, 180. Significant differences between the two sites were consistently observed, confirming the anticipated high level of spatial and temporal heterogeneity. Chlorophyll fluorescence was maximal in late December, and generally decreased rapidly to modest levels in January and February. However, during 1 year (2003–2004) a secondary bloom was found, with summer maxima being similar to those observed during spring. Fluorescence displayed a strong diel cycle, with strong quenching during periods of maximum irradiance. The magnitude of this reduction was large (the minimum average fluorescence was 25% of the daily mean) and decreased with depth. Fluorescence varied interannually, with the absolute levels and temporal patterns being different among years. The two sites had different temperature/salinity properties as measured at 24 m, and both variables changed with time. During 2004–2005 we were able to continuously measure the photosynthetic quantum efficiency of PSII (F v /Fm) at 11 m, which revealed a minimum in December, and an increase in January, whereas the absolute fluorescence (Fo) decreased simultaneously. We suggest that this reflected a mixing event, whereby available irradiance increased, allowing a short period of growth in a more favorable optical environment. While substantial variations from the mean physical forcing were observed, the linkage of these physical variations with fluorescence was not always clear. Short-term (over 24-h) changes in fluorescence occurred, and were likely related to advective events. Wind events altered fluorescence in the surface layer, and these redistributed phytoplankton in the surface. The variability in chlorophyll fluorescence and physical forcing over a variety of scales in the Ross Sea provides insights into temporal–spatial coupling of phytoplankton.

The temporal variability in currents, temperature, and particulate matter concentration were measured in the Mississippi Canyon axis where the thalweg was 300 m deep from May–July and August–November 1998 using current meters, thermographs, a light-scattering sensor, and sediment traps. Canyon sediments were sampled by coring and observed using an ROV video camera. Currents in the upper Mississippi Canyon generally oscillated up/down canyon with diurnal periodicity and were bottom-intensified. Mean current speed at 3.5 mab was approximately 8 cm s −1 during both deployments, reaching maximum speeds of over 50 cm s −1 under normal conditions. Based on current velocities, critical bed shear stress for resuspension of canyon-floor sediments was exceeded about 30% of the time during both deployments. In late September, Hurricane Georges passed 150 km NE of the study site, significantly intensifying current velocities, bed shear stress, resuspension, trap fluxes and temperature fluctuations. As the hurricane passed, maximum current speed reached 68 cm −s and temperature decreased ∼7 °C in less than two hours. Critical bed shear stress for sediment resuspension was exceeded approximately 50% of the time during the five days of hurricane influence. Further evidence for sediment resuspension was the five-fold (and perhaps 70–130 fold) increase in trap fluxes and compositional similarities between canyon surface sediment and material collected by traps.

The vertical distribution and temporal changes in aggregate abundance and sizes were measured in the Ross Sea, Antarctica, during two field seasons, one in austral spring 1994 and one in early summer, 1995/96. Aggregate abundance, size and potential sinking rates were determined by photographic techniques. Measurements ofwater column parameters, including particulate organic carbon concentrations, were assessed simultaneously, as was the flux oforganic matter with floating sediment traps. The numbers ofaggregates (and to a lesser extent their size) increased with time, although there was substantial spatial variability in these variables at any point in time. Some aggregates appeared to sink extremely rapidly, and for these, our photographic measurements were able to estimate only a minimum sinking rate, which equaled 288 m d � 1 . Estimates ofaggregate organic carbon flux were compared to those determined by floating sediment traps. From these results, aggregate fluxes appear to have dominated the vertical export oforganic matter f the euphotic zone. The genesis and flux ofaggregates in the Ross Sea are the critical processes controlling the export of biogenic material from the surface layer. r 2003 Elsevier Science Ltd. All rights reserved.

Since the development of gliders, scientists have used them to collect high resolution data sets over long periods of time, weeks to months. For the majority of the time a glider is flown, scientists equip the glider with only the sensors needed to collect a limited data set specific to the scientist's research objective. Scientists can overload the glider with sensors, causing a shortening of the mission due to battery life. However, some glider missions include only the minimum of sensors, (e.g. CTD) which result in surplus battery life remaining after the mission completion. In these instances the battery life could provide additional data sets with minimal cost or interruption to the primary mission. Many opportunities for gliders to conduct multiple missions occur but decisions are required to manage the variety of sensors for optimum scientific and operational efficiency. In 2013 a joint glider mission with Shell Oil and NOAA's National Data Buoy Center was conducted in the Gulf of Mexico (GOM). This glider mission provides an example of sensors being deployed, yet data not collected. The main mission objective was to provide validation for the Ocean Heat Content being derived by satellites and augment existing in-situ data into the real time HWRF-HYCOM hurricane model. The mission was planned with coordination through the Environmental Modeling Center (EMC) to target features, such as eddies, in the GOM. The secondary objective included baseline sampling of water column dissolved oxygen and color dissolved organic matter (CDOM) in the Northern Gulf of Mexico. With the third mission objective to continually operate a glider in the GOM throughout the hurricane season, which limited sensor use in order to prolong the deployment. This creates additional and critical considerations among the piloting team to balance sampling rates of sensors with mission duration capabilities. This paper uses experiences from this 2013 glider mission, to discuss the possible gains and losses of including additional sensors on gliders for secondary mission objectives. In addition, this paper discusses the need to identify the scientific focus and sampling requirements and how to integrate the secondary requirements into flight operations.

In 2010-2011, three projects combined to characterize the temporal and spatial distributions of Modified Circumpolar Deep Water (MCDW) in the Ross Sea using icebreaker-based sampling, gliders, instrumented seals, and hindcasts from a numerical circulation model. The fieldwork clearly identified MCDW throughout the Ross Sea, and the data were used to determine its influence on potential heat and nutrient inputs and biotic distributions. Furthermore, the numerical simulations confirm its apparent trajectory and location. Substantial small-scale variability in oceanographic and biological distributions suggests that such variability may play an important role in biogeochemical cycles. Data from the three projects provide a view of hydrographic variability in the Ross Sea that is impossible to obtain using traditional sampling. Multiplatform investigations are promising approaches to future polar experiments where logistical considerations are of paramount importance. © 2014 by The Oceanography Society. All rights reserved.

In recent Black Sea sediments peculiar sediment layers occur which in sedimentological and geochemical composition differ from over- and underlying sediments. Originally described as turbidites they lack typical turbidite features. An alternative formation mechanism is proposed here and a conceptual model developed. This explains the occurrence of the so-called ‘Degens’-layers by density inversion eventually supported by exsolution of biogenic gas.

The distribution and movement of chloropigments (chlorophylls and associated degradation products) in the bottom boundary layer near Duck, North Carolina, were examined during July and August 1994. Time series of chloropigment fluorescence, current velocity, and surface wave properties were acquired from instruments mounted on a bottom tripod set at 20 m depth. These data were combined with moored current meter measurements, meteorological data, and shipboard surveys in a comparative assessment of physical processes and chloropigment distribution over a wide range of temporal and spatial scales. Two dominant scales of chloropigment variation were observed. On numerous occasions, small-scale (order m) structure in the near-bottom fluorescence field was observed, even in the absence of identifiable structure in the temperature and salinity fields. Over larger time-scales and space scales, variations in fluorescence were related to changes in water mass properties that could be attributed to alternating events of upwelling and downwelling. This view was reinforced by shipboard measurements that revealed correlations between fluorescence and hydrographic fields, both of which were modified by wind-forced upwelling and downwelling and by the advection of low-salinity water from Chesapeake Bay. Local resuspension of sediments did not contribute appreciably to the near-bottom pigment load seen at the tripod, because of low bottom stress. Estimates of chloropigment flux indicated a net shoreward transport of chloropigments in the lower boundary layer. However, the rapid fluctuations of currents and pigment concentrations gave rise to large and frequent variations in chloropigment fluxes, generating uncertainty in extrapolations of this finding to longer timescales.

To test the hypothesis that phytoplankton assemblages dominated by different taxa have distinct biogeochemical characteristics and cycles, the temporal and spatial variations in phytoplankton biomass and composition were studied within the Ross Sea polynya, where diatoms and the haptophyte Phaeocystis antarctica are thought to have spatially distinct distributions. Two cruises were completed, with the first conducted in spring, 1994, and the second in late spring–early summer, 1995/1996. Ice concentrations decreased substantially from spring to summer. Mixed layer depths for the region decreased markedly in early spring and were relatively invariant thereafter; the strength of the stratification varied both in time and space. Mixed layers were greater in spring in assemblages dominated by diatoms (as determined by HPLC pigment concentrations) than those dominated by Phaeocystis antarctica, whereas in summer no difference was observed. Nutrient concentrations were initially high and near winter values, but decreased throughout November and December. Nitrate : phosphate removal ratios varied widely, with ratios exceeding 20 in spring but decreasing below 14 in summer. N : P removal ratios at stations dominated by diatoms were less than the Redfield ratio in both spring and summer, and at those stations dominated by P. antarctica the N : P removal ratio was ca. 19 in both seasons. Chlorophyll and particulate matter concentrations increased as nutrients decreased. Spatial and temporal variations of phytoplankton pigments occurred, with 19′-hexanoylfucoxanthin, a pigment of P. antarctica, exceeding 3.9 μg l−1 during spring in the south-central polynya, and fucoxanthin, an accessory pigment of diatoms, found in concentrations >1 μg l−1 in the western Ross Sea. The distributions were not mutually exclusive, and concentrations of both pigments were greatest in spring. The early growth of P. antarctica appears to be related to earlier stratification and disappearance of ice from the south-central Ross Sea. Ratios of FUCO/CHL were relatively invariant, but substantial changes in the HEX/CHL and POC/CHL ratios were observed through time. A one-dimensional nitrogen budget for the spring–early summer period suggests that much of the surface production was partitioned into particles, most (53%) of which remained in the upper 200 m. The rest was partitioned into dissolved organic matter (14%), remineralized as ammonium (19%), or sank from the surface layer as particles (13%). The region may serve as a useful analog to other polar systems, and an understanding of the processes controlling assemblage composition, production, and biomass accumulation may provide insights into biogeochemical cycles of other Antarctic environments.

This study was motivated by the need to understand dispersion processes which affect the redistribution of nuclear wastes in the Arctic from dump sites in the Kara Sea and in the rivers which flow into the Kara Sea. We focus on vertical profiles of light beam transmission and fluorometry made over the delta region fronting the Ob and Yenisey Rivers and over the East Novaya Zemlya Trough (ENZT). The delta region fronting the Ob River Estuary contains a large repository of particles in a dense bottom nepheloid layer with a maximum centered ∼100 km in front of the estuary entrance and covering an area of roughly 200 km diameter. This suspended particle mass repository appears to contain both sediments and detritus and lends credence to the Lisitsyn [1995] concept of the marginal filter zone. In the deep water of the ENZT we found a strong increase of beam attenuation with depth, indicating a relatively large increase of particle mass concentration from ∼50 m to the bottom (depths in excess of 300 m). The strongest concentration was adjacent to the southeast coast of Novaya Zemlya. We suggest that a type of hyperpycnical flow occurs from accumulation of sediments in the bottom waters of Novaya Zemlya fjords which then cascades down the steep slopes adjacent to the island, producing the particle mass distribution as observed by the transmissometer. The accumulation of these repositories of high particle mass concentrations in suspension would suggest that the residence time is high but that storm-driven events could act to disperse the material.

The flux of particles from the euphotic zone through 200 m was investigated on the Ross Sea continental shelf during two cruises, the first in November-December 1994 and the second in December 1995 and January 1996. An assessment of surface layer phytoplankton biomass and productivity was made simultaneously. Particle flux was measured using floating sediment traps whose collection efficiency was assessed rigorously. Phytoplankton biomass and productivity increased rapidly in November-December, and biomass was maximal in mid-December. Thereafter productivity appeared to decline substantially. Biomass declined as well, but not as rapidly as productivity. Vertical flux rates were low early in the bloom period, averaging 457 mg m−2 d−1, but increased markedly in late December and January (mean = 1160 mg m−2 d−1). Daily losses due to vertical flux represented only 2.3% of the surface layer particulate organic carbon standing stock. Measured particle fluxes were greater than those observed previously, and this is attributed to the period and depths sampled as well as to the care taken to ensure accuracy of sample collection. As in other regions, vertical flux of biogenic material is coupled with surface layer production and biomass. In our study area, however, a distinct temporal lag is introduced between surface production and flux at depth as a result of the temporal characteristics of the dominant mechanism generating large particles (aggregation) as well as the characteristic species of the region (Phaeocystis antarctica).

An in situ multisensor fiber-optic fluorometer (MFF) has been developed to acquire long-term chlorophyll fluorescence measurements in the oceanic bottom boundary layer to characterize the finescale pigment structure at vertical spatial scales comparable to physical measurements. The eight fluorescence sensors of the MFF are composed of dual optical fibers of varying lengths (1.5–8 m), with the fiber ends oriented at 30° to each other and enclosed by a small light baffle. Strobe excitation blue light is passed through one of each pair of optical fibers and stimulated chlorophyll fluorescence is carried back to a photomultiplier. Two sets of four fluorescence sensors assigned to high- and low-sensitivity photomultiplier detectors enable chlorophyll a measurements in two ranges, 0–50 mg m−3 and 0–200 mg m−3, respectively. Aspects of the design of the fiber-optic sensor are described that were intended to optimize detection of fluorescence signals and minimize interference by ambient light. The fiber...

Abstnct-Zn situ settling speeds of marine snow aggregates were determined with the Marine Aggregate Settling Collector and Observation Tower (MASCOT) in the central Black Sea and in the northern Gulf of Mexico. The Black Sea data showed a wide distribution in size and settling speeds of marine snow aggregates (0.5-55 mm diameter and 1.3-280 m/d) with an average settling speed of 11.7 m/d over all size classes. However, these settling speeds might have been inlhtenced by the addition of salt (0.9% above the background seawater) plus formalin to the water in one side of the acrylic chamber of the MASCOT. Data from the Gulf of Mexico had a smaller range in terms of size and speed (0.5-3.5 mm diameter and IO-89 m/d). The average settling speed over all size classes was approximately three times higher (33.8 m/d) than for aggregates measured in the Black Sea. Stokes’ Law predicts that settling speeds are determined by both density and volume of an aggregate. For both study sites no statistically significant correlation of settling speed with the equivalent spherical diameter (ESD) of the aggregates was found. It was therefore concluded that variations in density controlled the aggregate settling speeds measured in these two study areas. 0 1997 Elsevier Science Ltd

Profiles made during the JGOFS EgPac October 1992 time series cruise to the equator with a Large Aggregate Profiling System (LAPS) recorded the concentration and size distribution of particles in the marine snow size range ( > 0.5 mm diameter). Profiles were made routinely at local midnight during the twenty day occupation of the time series station on the equator. The LAPS data set, when combined with the CTD/transmissometer data set from the EgPac program's intensive profiling operation, reveals a complex dynamic of particle production and aggregation driven by the equatorial flow field. During the cruise, the influence of the passage of a Tropical Instability Wave (TIW) was observed in the transmissometer/aggregate and temperature/salinity data sets. A peak in particle production rate occurred in conjunction with the maximum shoaling of the thermocline and a minimum in the aggregate volume concentration. Subsequently, the particle load in the surface water increased followed by an increase in the aggregate abundance. Quasi -oligotrophic conditions on the equator (subsurface particle and aggregate maxima and decreased particle production rates) toward the end of the time series corresponded to the appearance of stratified low salinity water characteristic of more northerly conditions. The variations in temperature and salinity fields are ascribed to the passage of a TIW; in sequence: the trailing edge, the northwestward-flowing cool cusp water and the convergent front. Current meters at the equator recorded a rotational flow at 80 m, with a shift from southeastward to northeastward flow during this sequence. A simple conceptual model of meridional flow field is presented in which poleward transport of the upwelled water from the equator returns at shallow depths to mix with the EUC. The signature of this return flow is reflected in the decrease in the vertical gradients of nutrients and oxygen at the equator with respect to the poleward gradients, and a subsurface particle maximum below the EUC. The flow field's effect on the distribution of particles is reflected in the meridional pattern of the sediment accumulation rate ( Murray and Leinen, 1996 ). The return flow of particles to the equator is reflected in the maximum in accumulation rate near the equator. The longterm influence of TIW's is reflected in the asymmetry of the accumulation rates across the equator as described by Murray and Leinen (1996) , with the maximum accumulation rate found south of the equator, a local minimum in accumulation rate at approximately 2°N, and a local maximum near 4°N.

The National Institute for Undersea Science and Technology operates two AUVs, Eagle Ray and Mola Mola that are primarily tasked with performing seafloor surveys. Upcoming missions will require surveys at 1200 to 1600 meters depth, so the vehicles are being prepared with new and updated systems and software. Recently, Eagle Ray was equipped with new batteries and a subbottom profiler. A descent weight system was added to Mola Mola, along with a revised power system and new mission capabilities.

Over the last several decades, numerous approaches have been used to observe the rapid development of the annual phytoplankton bloom in the Ross Sea, including ship-based sampling, moored instrumentation, satellite images, and computer modeling efforts. In the Austral Spring of 2010, our group deployed a pair of iRobot Seagliders equipped with fluorometers, oxygen sensors and CTDs in order to obtain data on this phenomenon over the entire duration of the bloom. Data from these deployments will be used, along with samples from the recovery cruise and satellite data, to model and better understand the dynamics of this phytoplankton bloom.

Monitoring and M A Record-Breakin Geophysical Mon Copyright 2011 b 10.1029/2011GM Surface and subsurface water samples were collected in the vicinity of the Deepwater Horizon (DWH) wellhead in the Gulf of Mexico. Samples were extracted with dichloromethane and analyzed for a toxic component, polycyclic aromatic hydrocarbons (PAHs), using total scanning fluorescence (TSF) and by gas chromatography/mass spectrometry (GC/MS). An aliquot of fresh, floating oil from a surface sample was used as a DWH oil reference standard. Twelve of 19 samples collected from 24 May 2010 to 6 June 2010 on the R/V Walton Smith cruise contained TSF maximum intensities above background (0.7 μg L 1 based on 1 L sample size). These 12 samples had total petroleum hydrocarbon (TPH) concentrations as measured by quantitative gas chromatography flame ionization detector (FID) ranging from 2 to 442 μg L . Quantitative GC/MS analysis of these 12 samples resulted in total PAH concentrations ranging from 0.01 to 59 μg L . Low molecular weight, more water-soluble naphthalene and alkylated naphthalene dominated the PAH composition patterns for 11 of the 12 water samples. Sample 12 exhibited substantially reduced concentrations of naphthalenes relative to other PAH compounds. The total PAH concentrations were positively correlated (R = 0.80) with the TSF maximum intensity (MI). TSF is a simple, rapid technique providing an accurate prediction of the amount of PAH present in a sample. TSFderived estimates of the relative contribution of PAH present in the oil provided evidence that PAH represented ~10% of the higher molecular weight TPH. The subsurface oil plume was confirmed by the analyses of discrete water samples for TSF, TPH, and PAH.

[1] Here, we report the initial observations of distributions of polycyclic aromatic hydrocarbons (PAH) in subsurface waters near the Deepwater Horizon oil well site (also referred to as the Macondo, Mississippi Canyon Block 252 or MC252 well). Profiles of in situ fluorescence and beam attenuation conducted during 9-16 May 2010 were characterized by distinct peaks at depths greater than 1000 m, with highest intensities close to the wellhead and decreasing intensities with increasing distance from the wellhead. Gas chromatography/mass spectrometry (GC/MS) analyses of water samples coinciding with the deep fluorescence and beam attenuation anomalies confirmed the presence of polycyclic aromatic hydrocarbons (PAH) at concentrations reaching 189 μg L−1 (ppb). Subsurface exposure to PAH at levels considered to be toxic to marine organisms would have occurred in discrete depth layers between 1000 and 1400 m in the region southwest of the wellhead site and extending at least as far as 13 km.

Mola is a seafloor mapping AUV owned and operated by the National Institute for Undersea Science and Technology (NIUST). Since its initial sea trials in May of 2009, effort has been applied to enhancing the navigation and imaging systems for high-resolution surveys of specific targets in depths up to 2000 meters. These surveys require accurate positioning during the initial dive to the seafloor, and smooth navigation once the survey begins. To work toward this goal, an inertial navigation system with position and velocity aiding has been integrated with the vehicle software, and it is currently being field tested. The imaging system has also been modified by adding LED arrays to provide more consistent lighting and by merging navigation data with the images for georeferencing. The above system enhancements have forced changes in the vehicle's layout, and operational experiences have led to improvements in the vehicle's mechanical systems.

The National Institute of Undersea Science and Technology (NIUST)'s Underwater Vehicle Technology Center (UVTC) expanded their operational capabilities by acquiring a SeaBED class AUV in early 2009. This vehicle dubbed, Mola Mola after the Ocean Sunfish, is a superb addition to the UVTC, as it adds photographic capabilities at very slow moving speeds to the centers repertoire. The vehicle is designed to fly at speeds of 0.2 ms−1 about 3m above the seafloor, snapping high resolution digital images of the seafloor at preset intervals of 4 to 5 seconds. Normal mission behavior, programmed prior to launch of the vehicle, is to cover a certain area on the seafloor in a lawn mowing track, with parallel lines covering the entire area. At the end of the mission, geo-referenced photo mosaic maps of the target of interest on the sea floor are computed. The vehicle was deployed for several missions on the NASA vessel Liberty Star in the Bahamas. High resolution imagery of the bottom fauna and flora from depths too deep for deep divers to reach, provided insight into the distribution of Lion Fish in the coral reefs of the Bahamas. At the end of the field season engineering efforts were started to reorganize and replace certain hardware components to allow for improved navigation and data handling within the vehicles software architecture. They vehicle itself has since been modified from its original design, adding guided inertial navigation and improvements in its image acquisition process. Changes further include obstacle avoidance, GPS positioning and addition of a VHF radio beacon.

In May 2010, the National Institute for Undersea Science and Technology (NIUST) had a 17-day research cruise aboard the UNOLS vessel R/V Pelican scheduled. NIUST is a partnership of the University of Mississippi, the University of Southern Mississippi and NOAA. Before sailing, the Deepwater Horizon oil platform burned and sank, resulting in an uncontrolled oil spill at a depth of 5000 ft at Mississippi Canyon Block 252. Subsequently, the decision was made to abort the planned hydrate and ship wreck research in favor of an oil spill response. The primary goals of the redefined cruise were to acquire baseline and early impact data for seafloor sediments and subsurface distribution of oil and gas hydrates as close as possible in time and space to the origin of the oil spill.

This project describes the effectiveness of using standard Moderate Resolution Imaging Spectroradiometer (MODIS) imagery and products, produced by NASA and distributed through the Distributed Active Archive Centers (DAACs), to monitor and map oil on the surface of the Gulf of Mexico from the oil release at the Deepwater Horizon site. With twice daily coverage of the Gulf of Mexico and the rest of the world, MODIS is well suited to monitor the effects of these types of incidents on the sea surface. MODIS imagery has been widely used by many federal, state, and local agencies, as well as the media and non-government groups to illustrate the distribution and movement of surface oil. The MODIS products evaluated for their effectiveness in mapping and monitoring oil and the sea surface include: imagery, sea surface temperature (available for nighttime and daytime temperatures), chlorophyll concentration, particulate organic/inorganic carbon, chromophoric dissolved organic matter index, diffuse attenuation coefficient, and remote sensing reflectance. These products were chosen because they are available on a daily basis. Some MODIS standard products are only available as eight-day composites which would not be as useful for monitoring a feature as dynamic as oil moving on the sea surface. MODIS standard products are produced by applying atmospheric corrections and algorithms to selected bands of MODIS data. The bands primarily used for ocean products are bands 8–16 which have a spatial resolution of 1 km. Additional products may be evaluated. The Deepwater Horizon oil rig exploded and caught fire on April 20, 2010. The drilling platform sank several days later. The well ruptured at the seafloor, 5000 feet below the sea surface, and began leaking a combination of crude oil and natural gas. As of July 15, 2010, the oil leak was capped. The Deepwater Horizon site is located approximately 58 miles southeast of the mouth of the Mississippi River in southeastern Louisiana. The effectiveness of the MODIS products was determined by comparing the MODIS data with surface water samples and digital photography taken aboard the research vessel Pelican between May 5 and May 15, 2010 within the Gulf of Mexico. During that scientific mission, the presence or lack of surface oil was reported, coordinate locations were recorded, and water and oil samples were collected. The majority of these samples were taken within 10 miles of the Deepwater Horizon site, while some were taken up to 72 miles away. During the research trip aboard the Pelican, the surface oil was not consistently present in some areas, but tended to shift due to wind and currents. Particular sites have a useful temporal aspect since they were repeatedly visited for sampling. Sun glint areas on MODIS true color imagery make surface oil especially evident. It is anticipated that the MODIS standard products will detect the oil on the sea surface that is not evident in the visible portion of the imagery spectra.

Mola Mola is a seafloor mapping AUV owned and operated by the National Institute for Undersea Science and Technology (NIUST). Its primary sensor is a downward-facing camera producing color-corrected seafloor imagery which, with proper navigation and post processing, can be converted to a photo mosaic. It also uses a multibeam sonar to gather bathymetry encompassing the photo coverage. Since its delivery in May of 2009 Mola Mola has been modified in the areas of its imaging and navigation systems as well as several mechanical systems.

In October 2009 two autonomous underwater vehicles (AUV's), the explorer class Eagle Ray and the seabed class Mola Mola, were launched from the NOAA ship Nancy Foster to locate and retrieve information about sunken ships of historic interest, some of which had disappeared below the water surface of the northern Gulf of Mexico, almost 200 years ago. In a collaboration between the National Institute for Undersea Science and Technology (NIUST,) the US Bureau of Ocean Energy Management, Regulation and Enforcement (BOEMRE) and the US NOAA Office of Ocean Exploration and Research (OER), targets identified in side scan sonar images, were selected and investigated by the AUVs. Eagle Ray, due to its large size and design features, performed initial multibeam surveys of the target areas, producing high-resolution maps of the seafloor. These maps were used to determine safe working areas for the Mola Mola, which was subsequently launched to take a continuous series of photographs in close proximity to the seafloor, producing a photo-mosaic map of the target area. Operational procedures and results from these dives will be presented, showing the complementing features of these two very different AUVs in operation.

The relationship between primary production and sediment trap-derived downward flux of particulate organic matter was characterized over a 2 year period at the U.S. JGOFS Bermuda Atlantic Time-series Study (BATS) site to evaluate the importance of temporal variations in upper ocean biogeochemical processes. Water column-integrated primary production (∫PP), determined once each cruise using 14C incubations (in situ dawn-to-dusk), peaked in late winter/early spring of both 1989 and 1990. Smaller increases in ∫PP also occured in July 1989 and October–December 1990. Annual ∫PP was 9.2 mol C m−2 y−1 in 1989 and 12 mol C m−2 y−1 in 1990. This was higher than the 1959–1963 annual average (6.8 mol C m−2 y−1) determined at Station “S” located approximately 50 km northwest of the BATS site. Fluxes associated with sinking of total particulate mass, particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured at 150, 200, 300 and 400 m using a free-floating sediment trap array generally deployed once each cruise for 72 h. Fluxes varied seasonally, and within our ability to resolve differences (i.e. monthly sampling), there was no distinguishable time offset between peaks in ∫PP and corresponding peaks in elemental flux. Fluxes generally decreased with increasing depth, and fluxes of POC and PON were positively correlated with particulate mass flux at all depths. POC/PON (C/N) ratios at 150 m during periods of high ∫PP were generally characteristics of live planktonic biomass. Higher C/N ratios in material collected by the deeper traps were consistent with more rapid losses of PON than POC from sinking particles. POC and PON fluxes at 150 m, nominally the base of the euphotic zone, were positively correlated with ∫PP. The fraction of ∫PP leaving the euphotic zone in the form of sinking particles (i.e. collected in traps) varied seasonally and was inversely proportionato ∫PP. Surface export of organic matter estimated by sediment traps at 150m was 0.78 mol C m−2y−1 (0.10 mol N m−2y−1) in 1989 and 0.77 mol C m−2y−1 (0.11 mol N m−2y−1) in 1990.

The National Institute for Undersea Science and Technology (NIUST) owns and operates two Autonomous Underwater Vehicles, an International Submarine Engineering built Explorer class AUV and a Woods Hole Oceanographie Institution built Seabed AUV These two AUVs have completely different operational requirements and tasks based on their physical layout and propulsion. The torpedo-shaped explorer class AUV is used for multibeam mapping and carrying third-party or experimental instrument payloads. The Seabed AUV, propelled by three independent thrusters, is used for close-up sub-sea photographic and multi-beam site investigation which takes advantage of its slow speed and maneuverability. The high resolution digital photography can be used to construct spatial photomosaicis of the target area. Both vehicles will be introduced during this talk, highlighting their operational parameters and presenting some of the data collected with each results from previous deployments of the systems.

The demand for deepwater (>1000 m) autonomous underwater vehicles is increasing but scientific applications are restricted due to complexity and cost of development and operation. We have acquired a commercially-available deep- water AUV and are presently operating it from vessels of opportunity. Experiences gained from both the development process and field operations are discussed and generally applicable recommendations are abstracted from specific events.

A large population of a previously unreported jellyfish occurred across the northern Gulf of Mexico (USA) from May through September of 2000. The jellyfish, identified as Phyllorhiza punctata by von Lendenfeld (1884), is not indigenous to the Gulf of Mexico or to the Atlantic Basin. Current theory states that this invasive species was introduced into the Atlantic from the Pacific Ocean through the Panama Canal about 45 years ago, and several confirmed reports indicated that a cryptic population may have existed in the northern Gulf since 1993. However, mesoscale hydrographic anomalies in spring 2000 may have directly transported the population from the Caribbean Sea where populations of P. punctata have been reported previously in Puerto Rico. We undertook a rapid-response sampling program from June through September to obtain ecological information regarding P. punctata in the highly productive northern Gulf waters. Jellyfish bell diameter increased by about 50% (from an average of 32 ±12 to 45 ± 6 cm) as animals invaded nearshore waters during July. As the summer progressed, a net westerly distribution shift followed nearshore currents to an accumulation point near the mouth of Lake Borgne, Louisiana, in the far western Mississippi Sound. In the Lake Borgne aggregation, we estimated 5.37 × 106 medusae over an area of about 150 km2. All of the medusae appeared to lack the symbiotic algae that are present in all other described populations, and therefore must have depended solely on planktivory for their nutrition. Clearance rates estimated from ambient zooplankton, gut contents and published digestion times ranged from

A prototype in situ multi-sensor fiber optic fluorometer is described which was designed to acquire long term time-series fluorescence measurements. The multi-sensor system uses dual detectors with four excitation sources, thereby providing for independent measurements at eight sensor locations. Strobe excitation light of wavelength < 500 nm is passed through one of each pair of optical fibers and stimulated chlorophyll fluorescence is carried back to a photomultiplier tube. The excitation and detection hardware are enclosed in a pressure case along with a battery operated 500 kHz data acquisition/storage system. Aspects of the design of the fiber optic sensor are described which were intended to optimize detection of fluorescence signals and minimize interference by ambient light. An illustration of the utility of fiber optics for fluorescence measurements was made by comparing a prototype fiber optic profiling fluorometer with a commercial fluorometer. Time series fluorescence measurements were made with the multi-sensor fluorometer in the Gulf of Mexico, and revealed chlorophyll variability in the benthic boundary layer.

Large amorphous aggregates (LAA), frequently called ‘marine snow’, may accelerate the flux of fine particles and dissolved matter in the ocean by adsorption. The aggregates are extremely fragile, and their sampling with conventional towing and casting is impossible. To assess the size and spatial distribution of such aggregates we have developed a photographic system that can be lowered to full ocean depth. The system, based on light scattering in water, uses a well-collimated beam pointed downward from the verticle at an angle of 45°. The beam is produced by placing high-powered stroboscopic lights at the back focal plane of a Fresnel lens system. Illuminated aggregates in the light are photographed from a direction perpendicular to the beam axis. The photographed volume, 0.66 m3, is 106 × 156 × 40 cm. The resolution of the instrument is about 0.2 mm. Aggregates were distributed throughout the water column at all stations along a 200-km transect off Monterey Bay. The abundance of macroscopic aggregates (>0.5 mm) ranged from several per liter near the surface to 1 or less at depth.

The flux and concentration of large amorphous aggregates (marine snow) were measured using a combination camera and sediment trap deployed at 380 m (390 m water depth) in the Panama Basin in April 1985. Results at this site indicate that essentially all settling particles arrive at the sea floor as components of large aggregates, with insignificant contributions of solitary fecal pellets. The observed flux of any particle divided by its concentration gives an estimate of a model parameter which can be interpreted as particle settling speed. Application of this method to marine snow indicates that, on average, larger aggregates (4–5 mm) settle more slowly (1 m day−1) than smaller aggregates (1–2.5 mm, 36 m day-1). These sinking speed estimates represent the average sinking speed of all aggregates photographed in the water column at the depth of the sediment trap. As such, these numbers may reflect the relative abundances of fast and slow-sinking aggregates rather than the absolute sinking speed of material entering the trap. Particles were observed to change positions or disappear between photographs, indicating water movement which may have been associated with the activity of grazing organisms within the sediment trap.

Samples from time-series sediment traps deployed in three distinct oceanographic settings (North Pacific, Panama Basin, and Black Sea) provide strong evidence for rapid settling of marine particles by aggregates. Particle water column residence times were determined by measuring the time lag between the interception of a flux event in a shallow trap and the interception of the same event in a deeper trap at the same site. Effective sinking speeds were determined by dividing the vertical offset of the traps (meters) by the interception lag time (days). At station Papa in the North Pacific, all particles settle at 175 m day-1, regardless of their composition, indicating that all types of material may be settling in common packages. Evidence from the other two sites (Panama Basin and Black Sea) shows that particle transport may be vertical, lateral, or a combination of directions, with much of the Black Sea flux signal being dominated by lateral input. In order to ascertain whether marine snow aggregates represent viable transport packages, surveys were conducted of the abundance of these aggregates at several stations in the eastern North Atlantic and Panama Basin using a photographic technique. Marine snow aggregates were found in concentrations ranging from ~1 mm3 liter-1 to more than 500 mm3 liter-1. In open ocean environments, abundances are higher near the surface (production) and decline with depth (decomposition). However, in areas near sources of deep input of resuspended material, concentrations reach mid-water maxima, reflecting lateral transport. A model is proposed to relate the observed aggregate abundances, time series sediment flux and inferred circulation. In this model, depthwise variations in sediment flux and aggregate abundance result from suspension from the sea floor and lateral transport of suspended aggregates which were produced or modified on the sea floor. Temporal changes in sediment flux result from variations in the input of fast-sinking material which falls from the surface, intercepts the suspended aggregates, and transports them to the sea floor. A new combination sediment trap and camera system was built and deployed in the Panama Basin with the intent of measuring the flux of marine snow aggregates. This device consists of a cylindrical tube which is open at the top and sealed at the bottom by a clear plate. Material lying on the bottom plate is illuminated by strobe lights mounted in the wall of the cylinder and photographed by a camera which is positioned below the bottom plate. Flux is determined as the number of aggregates arriving during the time interval between photographic frames (# area-1 time-1). Results show that essentially all material arrives in the form of aggregates with minor contributions of fecal pellets and solitary particles. Sinking speeds (m day-1), calculated by dividing the flux of aggregates (# m-2 day-1) by their abundance (# m-3), indicate that the larger (4-5mm) aggregates are flocculent and sink slowly (~1m…

Annual particle fluxes were measured by sediment traps deployed at a station about 40 km north of Amasra, Southern Black Sea, by an international team of oceanographers from Germany, Turkey, and the United States. This experiment continuously monitored oceanic particle flux for two and a half years at approximately two-week intervals at 250 m and 1200 m below the surface using 1.2sq.m Mark 5-12 time-series sediment traps. The water depth at this station was about 2,000 m and both traps were situated within the anoxic layer of the Black Sea. The collected flux samples were analyzed at the Wood Hole Oceanographic Institution to document the basic sedimentary characteristics using a quarter of each sample split. In the first data file from this experiment, total mass, carbonate, noncombustible, combustible, opal (biogenic silica), organic carbon, and organic nitrogen fluxes data are presented in bar graphs and detailed tables, in unit samples covering a two-week period at each depth. The Black Sea Sedimentation Data FIle is intended to provide source data on particle fluxes from this unique ocean environment for further investigation and for planning advanced research programs