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Almost all current climate models simplify the ocean surface albedo (OSA) by assuming the reflected solar energy without the ocean interior contribution. In this study, an improved ocean surface albedo scheme is incorporated into the Community Earth System Model version 2 (CESM2) to assess the sensitivity of Arctic surface temperature to including ocean interior reflectance to the OSA. Fully coupled CESM2 simulations with and without ocean interior reflectance are subsequently performed, we focus on the analysis of Arctic surface temperature responses. Incorporating ocean interior reflectance increases absorbed solar radiation and warms the ocean, enhancing seasonal heat storage and release across the Arctic Ocean, and increasing sea ice reduction and positive climate feedbacks that elevates Arctic surface temperature. Seasonal variations in air‐surface temperature differences induce changes in turbulent heat flux patterns, concurrently modifying dynamic advection and moisture processes that affect boundary layer humidity and low clouds, especially in winter. Based on partitioning physical processes in the thermodynamic energy equation, surface air warming is induced primarily through positive heating anomalies of vertical advection, latent heat release, and longwave radiative forcing. Through an examination of the surface energy budget, skin temperature warming is driven predominantly by increased downward longwave radiation, positive surface albedo feedback in summer, and increased conductive heat transport from the ocean particularly in winter. Significant effects of ocean interior reflectance on the Arctic Ocean, including sea surface warming and sea ice reduction, justify the importance of ocean interior reflectance in climate models for better understanding of ongoing Arctic climate changes. Plain Language Summary: The penetrated sunlight across the ocean surface is attenuated through the light absorption and scattering processes associated with oceanic optical constituents. The ocean attenuation of sunlight not only modifies the amount of solar energy reflected back to the atmosphere but also warms the seawater. Many climate models neglect the contribution of ocean interior reflectance to the ocean surface albedo (OSA) and hence simulate less accurate net heat flux through the air‐sea interface. In this study, sensitivity simulations were performed with and without ocean interior reflectance in the OSA calculation, respectively. When ocean interior reflectance is included, the Arctic surface shows warmings in both summer and winter, and the warming is stronger in winter, due to complex feedback mechanisms in the fully coupled model. The warmer Arctic surface is predominantly caused by changes in near‐surface vertical air motion, latent heat released during cloud formation, longwave radiative energy budget, and conductive heat transport from the ocean especially in winter. The changes in the drivers are related to seasonal variations in air‐surface temperature differences and heat storage‐release of the Arctic Ocean. To get a better understanding of climate responses associated with including ocean interior reflectance to the OSA, further investigations are necessary. Key Points: Arctic surface temperature changes are simulated to better understand the implication of the ocean interior reflectance in climate modelSimulation‐based increase in Arctic surface temperature is attributed to complex feedbacks inherent in the fully coupled modelClimate responses due to integrating ocean interior reflectance in the ocean surface albedo need more attention in earth system modeling [ABSTRACT FROM AUTHOR]

Hurricane Harvey deposited over 90×109 m 3 of rainwater over central Texas, USA, during late August/early September 2017. During four cruises (June, August, September and November 2017) we observed changes in hydrography and nutrient and oxygen concentrations in Texas coastal waters. Despite intense terrestrial runoff, nutrient supply to the coastal ocean was transient, with little phytoplankton growth observed and no hypoxia. Observations suggest this was probably related to the retention of nutrients in the coastal bays and rapid uptake by phytoplankton of nutrients washed out of the bays, as well as dilution by the sheer volume of rainwater and the lack of significant carbon reserves in the sediments, despite the imposition of a strong pycnocline. By the November cruise conditions had apparently returned to normal, and no long-term effects were observed. [ABSTRACT FROM AUTHOR]

Hurricane Harvey deposited over 90 billion cubic meters of rainwater over central Texas, USA, during late August/early September 2017. During four cruises (June, August, September and November 2017) we observed changes in hydrography, nutrient and oxygen concentrations in Texas coastal waters. Despite intense terrestrial runoff, nutrient supply to the coastal ocean was transient, with little phytoplankton growth observed and no hypoxia. Observations suggest this was probably related to the retention of nutrients in the coastal bays, rapid uptake by phytoplankton of nutrients washed out of the bays, as well as dilution by the sheer volume of rainwater, and the lack of significant carbon reserves in the sediments, despite the imposition of a strong pycnocline. By the November cruise conditions had apparently returned to normal and no long-term effects were observed. [ABSTRACT FROM AUTHOR]

Ocean surface albedo (OSA) is an important factor for the transfer of radiation in the coupled atmosphere-ocean system. By resolving the spectral variations of the reflective properties for incident direct and diffuse solar radiation, we develop an OSA computational scheme to study the impact of ocean biogeochemistry on the air-sea boundary condition of solar radiative transfer in the atmosphere. The new scheme is implemented for the General Circulation Model applications of the shortwave rapid radiative transfer model RRTMG_SW, a radiative transfer model used extensively in regional and global models. We show that a number of OSA schemes lead to underestimated results in comparison with in-situ measurements obtained at a site 25 km east of Virginia Beach. The scheme developed in this study considers multiple influential factors and is robust in terms of the mean absolute percentage error (MAPE) and the root mean square error in comparison with in-situ measurements. Furthermore, the new simulations are highly consistent with the Clouds and the Earth's Radiant Energy System (CERES) OSA distribution on a global scale. However, the theoretical results show slight differences compared with the CERES OSA under all sky conditions and overestimate the OSA in the subpolar Southern Ocean under clear sky conditions. The assumption of a uniform phase function, which neglects the spatial variability of the optical properties of oceanic particles, is largely responsible for the primary source of uncertainties in an OSA scheme. [ABSTRACT FROM AUTHOR]

We validate a new model for mass transfer and bubble transport for natural seeps on the continental margins using an integrated observation of a seep at 883 m in the Northern Gulf of Mexico. In the model, mass transfer is assumed to transition from clean to dirty bubble mass transfer rates following a characteristic hydrate formation time that depends on the initial bubble surface area and the hydrate subcooling. We show that buoyancy‐induced upwelling is negligible for the bubble stream. We initialize the model using precise data observed at the seafloor and validate the model results to optical and acoustic measurements within the bubble stream. The model accurately predicts the acoustic attenuation of the bubble flare by lateral spreading and bubble shrinkage throughout the water column. The model shows that up to 99.4% by mass of the released gases from this seep dissolves into the ocean within the hydrate stability zone. Plain Language Summary: Natural bubble seepage in the deep ocean is increasingly observed by shipboard surveys using sonars. These acoustic signals of these bubble flares are observed high into the ocean water column, raising the question of what the vertical distribution of natural seep gases, including methane, originating at natural seeps may be in the oceans. Present numerical models of natural seeps cannot consistently predict the observed rise heights of seep bubbles. Here, we validate a new model for natural seep bubbles to an integrated in situ and multibeam survey of a seep site in the Northern Gulf of Mexico. Our model assumes that bubbles initially dissolve following convective mass transfer until a hydrate coating slows the mass transfer to rates consistent with solid particles. The characteristic transition time for hydrate formation depends on the initial bubble surface area and a characteristic hydrate formation rate. The model shows that the bulk of the released gases (up to 99.4% by mass) dissolves in the deep ocean, within the hydrate stability zone, and that the model may justifiably neglect other aspects of gas hydrates or buoyancy effects of the rising bubbles. This work is important to understand the role of natural seeps in the oceanic biogeochemical cycling. Key Points: Hydrocarbon dissolution at seeps slows from clean to dirty bubble mass transfer coefficients after a characteristic hydrate formation timeSeep‐induced upwelling at natural seeps can be negligible, evidenced by both measurement and modelingThe model predicts nearly full dissolution of released hydrocarbons within the hydrate stability zone for a seep originating at 883 m depth [ABSTRACT FROM AUTHOR]

The coastal Gulf of Mexico (GOM) and coastal sea off the Korean Peninsula (CSK) both suffer from human-induced eutrophication. We used a nitrogen (N) mass balance model in two different regions with different nitrogen input sources to estimate organic carbon fluxes and predict future carbon fluxes under different model scenarios. The coastal GOM receives nitrogen predominantly from the Mississippi and Atchafalaya rivers and atmospheric nitrogen deposition is only a minor component in this region. In the CSK, groundwater and atmospheric nitrogen deposition are more important controlling factors. Our model includes the fluxes of nitrogen to the ocean from the atmosphere, groundwater and rivers, based on observational and literature data, and identifies three zones (brown, green and blue waters) in the coastal GOM and CSK with different productivity and carbon fluxes. Based on our model results, the potential primary production rate in the inner (brown water) zone are over 2 gC m -2 d -1 (GOM) and 1.5 gC m -2 d -1 (CSK). In the middle (green water) zone, potential production is from 0.1 to 2 (GOM) and 0.3 to 1.5 gC m -2 d -1 (CSK). In the offshore (blue water) zone, productivity is less than 0.1 (GOM) and 0.3 (CSK) gC m -2 d -1. Through our model scenario results, overall oxygen demand in the GOM will increase approximately 21 % if we fail to reduce riverine N input, likely increasing considerably the area affected by hypoxia. Comparing the results from the USA with those from the Korean Peninsula shows the importance of considering both riverine and atmospheric inputs of nitrogen. This has direct implications for investigating how changes in energy technologies can lead to changes in the production of various atmospheric contaminants that affect air quality, climate and the health of local populations. [ABSTRACT FROM AUTHOR]

The extent of hypoxia on the Louisiana shelf has been measured during July since 1985. The measured area was assumed to represent the seasonal maximum each year and was related to the Mississippi‐Atchafalaya riverine May NO2+3 loading and May–June total nitrogen loading, for planning management strategies. In this study, we analyze 25 years of simulations from a coupled physical‐biogeochemical model. An empirical orthogonal function analysis of the hypoxia frequency reveals that the dominant pattern is east‐west, with the seasonal maximum occurring in June, July, or August. This indicates that the July hypoxic area may or may not always be the largest of the year. A simple linear regression model was constructed to examine the explained variance of hypoxia attributable to nutrients. Results reveal that the May NO2+3 (May–June total nitrogen) loading can explain 35% ± 7% (54% ± 7%) of the maximum cumulative hypoxic area in contrast to 22% ± 9% (48% ± 12%) of the July cumulative hypoxic area. Our results suggest that the current nitrogen loading reduction suggested by the Hypoxia Task Force 2013 is not sufficient to reduce the 5‐year moving average Gulf's hypoxic zone to less than 5,000 km2. A reduction of at least 66% (48%) of May NO2+3 (May–June total N) loading is needed when using July hypoxic area as the criterion, while a reduction of 77% (60%) of May NO2+3 (May–June total N) loading is needed when using maximum hypoxic area. Plain Language Summary: Shelf‐wide surveys of hypoxia have been conducted in July since 1985 over the Texas‐Louisiana shelf. The measured hypoxic area has been used as the metric for hypoxia severity. Management practices have been designed based on this metric to control the amount of nitrogen loading to the Mississippi River Basin. Our analysis of 25 years of model output reveals that the reported measured area may not always be the largest of the year. Therefore, using July hypoxic area will underestimate the reduction in nutrient loading required to achieve a 5,000‐km2 area required reduction in nitrogen. Key Points: Monthly hypoxia frequency is predominantly east‐west, with seasonal maximum occurring in June, July, or AugustSatellite sea surface salinity, Chl a, and wind can be used with empirical relations to map spatiotemporally continuous bottom dissolved oxygen fieldsMore nitrogen reduction will be needed to reduce hypoxic area to 5,000‐km2 target once the maximum hypoxic area could be known [ABSTRACT FROM AUTHOR]

The coastal Gulf of Mexico (GOM) and Coastal Sea off Korea (CSK) both suffer from human-induced eutrophication. We used a N-mass balance model in two different regions with different nitrogen input sources to estimate organic carbon fluxes and predict future carbon fluxes under different model scenarios. The coastal GOM receives nitrogen predominantly from the Mississippi and Atchafalaya Rivers and atmospheric nitrogen deposition (AN-D) is only a minor component in this region. However, in the CSK, groundwater and atmospheric nitrogen deposition are more important controlling factors. Our model includes the fluxes of nitrogen to the ocean from the atmosphere, groundwater, and rivers, based on observational and literature data, and identifies three zones (brown, green and blue waters) in the coastal GOM and CSK with different productivity and carbon fluxes. Based on our model results, the potential primary production rate in the inner (brown water) zone are more than 2 (GOM) and 1.5 gC m-2 day-1 (CSK). In the middle (green water) zone, potential production is between 0.1 to 2 (GOM) and 0.3 to 1.5 gC m-2 day-1 (CSK). In the offshore (blue water) zone, productivity is less than 0.1 (GOM) and 0.3 (CSK) gC m-2 day-1. Through our model scenario results, overall oxygen demand in the GOM would increase approximately 21 % if we fail to reduce riverine N input, likely increasing considerably the area affected by hypoxia. Comparing the results from the U.S. with those from Korea shows the importance of considering both riverine and atmospheric inputs of nitrogen. This has direct implications for investigating how changes in energy technologies can lead to changes in the production of various atmospheric contaminants that affect air quality, climate and the health of local populations. [ABSTRACT FROM AUTHOR]

Harvey entered the Gulf of Mexico as a tropical depression on 23 August 2017; two days later it had strengthened to a category 1 hurricane. Over the following 30 hr Harvey rapidly intensified, reaching the Texas Bight as a category 3 storm. This intensification continued while Harvey crossed the shelf, making landfall as a category 4 storm 60 km east of Corpus Christi, TX on 26 August. A hydrographic survey two weeks prior to landfall shows that the tropical cyclone heat potential across the Texas Bight was approximately 35 kJ/cm2, which is 55 kJ/cm2 less than the amount of upper ocean heat normally associated with intensification. Combined with buoy, float, and satellite data, we use hydrographic surveys to study the conditions of the Texas Bight that contributed to Harvey's rapid intensification. We find that, at the time of landfall, the Texas Bight was well mixed with very warm water extending from the surface to bottom. As a consequence, mixing induced by Harvey had a small impact on surface temperatures which remained high and supported continued intensification. The results show that tropical cyclone heat potential is not an effective metric for hurricane intensity prediction in shallow water, and illustrate the need for continuous subsurface monitoring in order to improve hurricane forecasts. Plain Language Summary: Hurricanes rely on heat extracted from the upper ocean as their energy source. When the ocean is warm conditions are more favorable and hurricanes are often stronger. Hurricanes also mix the ocean which brings cold water from greater depth and can lead to intensity reduction. Tropical cyclone heat potential is a measure of heat in the upper ocean which is available as an energy source for hurricanes. In shallow water tropical cyclone heat potential is typically low because there is not as much water to store heat; therefore, hurricanes are not expected to intensify over shallow water. In this paper we show that hurricane Harvey did intensify over the shallow water off the Texas coast despite having low heat potential. Using ocean measurements, we found that the reason was because the ocean was very warm from the surface to the seabed. Therefore, when Harvey mixed the ocean very little cold water was brought up from below and the surface remained warm which allowed Harvey to continue to strengthen. Results suggest that tropical cyclone heat potential is ineffective for estimating hurricane strength in shallow water and demonstrates the importance of knowing subsurface temperatures if we want to improve hurricane forecasts. Key Points: Hurricane Harvey intensified over the shallow water of the Texas Bight despite being a region of low tropical cyclone heat potentialPeak season, warm, well‐mixed shelf water limits sea surface cooling and helps contribute to hurricane intensificationTropical cyclone heat potential has limited usefulness in shallow water; therefore, subsurface ocean observations are essential for increasing the accuracy of hurricane intensity forecasts [ABSTRACT FROM AUTHOR]

The Gulf of Mexico Coastal Hypoxia Glider Experiment was designed to assess the feasibility of using ocean glider technology in the coastal hypoxic zone of the northern Gulf of Mexico in Summer/Fall 2014. The objectives were (1) to coordinate and operate multiple autonomous buoyancy ocean gliders in depths less than 50 m and (2) to determine how close to the bottom gliders can reliably reach without making contact. Strong vertical and horizontal stratification gradients, strong coastal currents, and the low-oxygen conditions that occur within the lower water column characterize the coastal area of the northern Gulf of Mexico. These environmental conditions combine with the presence of more than 5,000 surface piercing oil/gas structures to make piloting and navigation in the region challenging. We quantify glider performance to assess the usefulness of buoyancy gliders to address the National Oceanic and Atmospheric Administration Action Plan goal to monitor the spatial extent, duration, and severity of the Gulf hypoxic zone. We find that the gliders, despite the operational challenges, were consistently able to travel from the surface to the oxygen-depleted depths of subpycnocline waters, that is, within 2 m of the ocean bottom. Our assessment is that gliders are able to provide real-time observations suitable to monitor coastal hypoxia. [ABSTRACT FROM AUTHOR]

Moored ADCP data collected in the northern Gulf of Mexico are analyzed to examine near-inertial internal waves and their contribution to subthermocline diapycnal mixing based on a finescale parameterization of deep ocean mixing. The focus of the study is on the impact of near-inertial internal waves generated by an extreme weather event-that is, Hurricane Katrina-and by month-to-month variation in weather patterns on the diapycnal mixing. The inferred subthermocline diapycnal mixing exhibits pronounced elevation in the wake of Katrina. Both the increased near-inertial (0.8-1.8 f, where f is the Coriolis frequency) and superinertial (>1.8 f) shear variances contribute to the elevated diapycnal mixing, but the former plays a more dominant role. The intense wind work on near-inertial motions by the hurricane is largely responsible for the energetic near-inertial shear variance. Energy transfer from near-inertial to superinertial internal waves, however, appears to play an important role in elevating the superinertial shear variance. The inferred subthermocline diapycnal mixing in the region also exhibits significant month-to-month variation with the estimated diffusivity in January 2006 about 3 times the values in November and December 2005. The subseasonal change in the diapycnal mixing mainly results from the subseasonal variation of the near-inertial wind work that causes intensification of the near-inertial shear in January 2006. [ABSTRACT FROM AUTHOR]

Most commercially, important food fishes in the tropics reproduce in spawning aggregations, which serve to replenish their populations via larval dispersal. Dispersal pathways are not well understood. This study examines the dispersal hypothesis assumed for most dispersal modeling studies, i.e. that prevailing currents transport freshly released eggs offshore and away from spawning sites, where they are advected into far-field ocean currents and contribute to long-distance larval transport. We used GPS-tracked surface drifters, quantitative ichthyoplankton tows, and microsatellite DNA markers to assess egg dispersal pathways from a well-documentedLutjanus cyanopterusspawning aggregation site. We conducted and plotted 95 drifter tracks over a bathymetric map of the study area and used geoprocessing techniques to determine the direction, speed, and variability of these tracks. Our field-collected data do not support the hypothesis that surface currents transport Cubera snapper gametes offshore during peak spawning. Eggs were transported onshore toward the barrier reef and potentially through the channel, supporting the idea that local retention may be more important than long-distance transport. These results are highly relevant for parameterizing larval connectivity models. Furthermore, we demonstrate the use of a low-cost and easily replicable method to track currents and egg dispersal from spawning aggregation sites. [ABSTRACT FROM PUBLISHER]

The article discusses the results of a study that examined the potential for gastropod and bivalve shells to serve as proxies for benthic respiration and hypoxia in the Gulf of Mexico during three periods from 1964 to 2009. The mollusks shells were analyzed for oxygen and carbon stable isotopes. The study showed a correlation between carbon stable isotopes of dissolved inorganic carbon and dissolved oxygen.

Near the vicinity of 30° latitude, the coincidence of the period of sea breeze and the inertial period of the ocean leads to a maximum near-inertial ocean response to sea breeze. This produces a propagating inertial internal (Poincare) wave response that transfers energy laterally away from the coast and provides significant vertical mixing. In this paper, the latitudinal dependence of this wave propagation and its associated vertical mixing are investigated primarily using a nonlinear numerical ocean model. Three-dimensional idealized simulations show that the coastal oceanic response to sea breeze is trapped poleward of 30° latitude; however, it can propagate offshore as Poincare waves equatorward of 30° latitude. Near 30° latitude, the maximum oceanic response to sea breeze moves offshore slowly because of the near-zero group speed of Poincare waves at this latitude. The lateral energy flux convergence plus the energy input from the wind is maximum near the critical latitude, leading to increased local dissipation by vertical mixing. This local dissipation is greatly reduced at other latitudes. The implications of these results for the Gulf of Mexico (GOM) at ∼30°N is considered. Simulations with realistic bathymetry of the GOM confirm that a basinwide ocean response to coastal sea-breeze forcing is established in form of Poincare waves. Enhanced vertical mixing by the sea breeze is shown on the model northern shelf, consistent with observations on the Texas–Louisiana shelf. Comparison of the three-dimensional and one-dimensional models shows some significant limitations of one-dimensional simplified models for sea-breeze simulations near the critical latitude. [ABSTRACT FROM AUTHOR]

The spatial structure and temporal characteristics of sea breeze and the associated coastal ocean response in the northwest Gulf of Mexico are investigated using moored instruments, hydrographic stations, and wind measurements. Near the study area of 30°N, motions in the diurnal–inertial band (DIB) may be significantly enhanced by a near-resonant condition between local inertial and diurnal forcing frequencies. Wavelet analysis is used to quantify the results. Results indicate that diurnal sea-breeze variability peaks in summer and extends at least 300 km offshore with continuous seaward phase propagation. The maximum DIB oceanic response occurs in June when there is a shallow mixed layer, strong stratification, and an approximately 10-day period of continuous sea-breeze forcing. DIB current variance decreases in July and August as the consequence of the deepening of the mixed layer and a more variable phase relationship between the wind and current. River discharge varies interannually and can significantly alter the oceanic response during summer. The “great flood” of the Mississippi River in 1993 deepened the summer mixed layer and reduced the sea-breeze response during that year. Vertically, DIB currents are surface intensified, with a first baroclinic modal structure. The significance of these DIB motions on the shelf is that they can provide considerable vertical mixing in summer, as seen by the suppression of the bulk Richardson number (by a factor of 30) during strong DIB events. This provides a potential mechanism to ventilate seasonally occurring near-bottom hypoxic waters of the coastal ocean. [ABSTRACT FROM AUTHOR]

Abstract: The circulation and distribution of water properties in the water column of the Gulf of Mexico influence the flux of carbon to the benthic environment. The eddy field of the upper 1000m creates environmental conditions that are favorable for biological productivity in an otherwise oligotrophic subtropical ocean. This eddy field results in the transport of nutrients and organic matter into the photic zone through cross-margin flow of shelf waters, upwelling in cyclones, and uplift from the interaction of anticyclones with bathymetry. These conditions then allow the productivity that becomes a possible source of carbon to the benthos. Data from four cruises during summers of 2000–2002 are used to describe the currents and water property distributions in the deepwater Gulf of Mexico, which consists of water depths greater than 400m. Comparisons are made to historical data sets to provide an understanding of the persistence of the characteristics of the Gulf and the processes that occur there. The currents in the Gulf are surface intensified, have minimum in 800–1000m depths, and also exhibit bottom intensification, especially near sloping topography. Historical time series records show current speeds near-bottom reach 50–100cms−1. At basin scales, these currents tend to flow cyclonically (counter-clockwise) along the bathymetry. These near-bottom, episodic, high-speed currents provide a mechanism for the transport of organic material, in both large and small particle sizes, from one benthic area to another. The distributions of temperature, salinity, nutrients, and dissolved oxygen during the study appear to be unchanged from historical findings. The source waters for the deep Gulf are the water masses brought into the Gulf by the Loop Current system. The properties in the upper 100–200m are the most variable of the water column, consistent with their proximity to wind mixing, river discharge mixing, and atmospheric influences. Below 1500m, there are no major horizontal variations in these water properties. [Copyright &y& Elsevier]