摘要:

AbstractWave climate characterization at different time scales (long‐term historical periods, seasonal prediction, and future projections) is required for a broad number of marine activities. Wave reanalysis databases have become a valuable source of information covering time periods of decades. A weather‐type approach is proposed to statistically downscale multivariate wave climate over different time scales from the reanalysis long‐term period. The model calibration is performed using historical data of predictor (sea level pressure) and predictand (sea‐state parameters) from reanalysis databases. The storm activity responsible for the predominant swell composition of the local wave climate is included in the predictor definition.N‐days sea level pressure fields are used as predictor.K‐means algorithm with a postorganization in a bidimensional lattice is used to obtain weather patterns. Multivariate hourly sea states are associated with each pattern. The model is applied at two locations on the east coast of the North Atlantic Ocean. The validation proves the model skill to reproduce the seasonal and interannual variability of monthly sea‐state parameters. Moreover, the projection of wave climate onto weather types provides a multivariate wave climate characterization with a physically interpretable linkage with atmospheric forcings. The statistical model is applied to reconstruct wave climate in the last twentieth century, to hindcast the last winter, and to project wave climate under climate change scenarios. The statistical approach has been demonstrated to be a useful tool to analyze wave climate at differen

ISSN:0148-0227    

DOI:10.1002/2014JC010141

年代:2014

数据来源: WILEY

摘要:

AbstractWe investigated the spectral structure and source term balance of short gravity waves, based onin situobservations of wave number spectra retrieved by air‐sea interaction spar (ASIS) buoys. The behaviors of wave number spectra up to 10 rad/m (the gravity wave regime) were analyzed for a wide range of wind and wave conditions. The observed wave number spectra showed the spectral power laws described by Toba (1973) andPhillips(1958) in addition to the characteristic nodal point at ∼10 rad/m where spectral energy becomes constant over the entire wind speed range. We also improved the third‐generation wave model using the nonlinear dissipation term. The wave model reproduced the spectral form in the higher wave number domain. In the equilibrium range, nonlinear transfer played a major role in maintaining equilibrium conditions. On the other hand, in the saturation range, which starts at the upper limit of the equilibrium range, the nonlinear transfer tended to be out of balance with other source terms, and the dissipation term was in balance with wind

ISSN:0148-0227    

DOI:10.1002/2014JC009869

年代:2014

数据来源: WILEY

摘要:

AbstractEmploying continuous in situ measurements of dissolved O2/Ar and O2in the Arctic Ocean, we investigate the mechanisms controlling the physical (abiotic) and biological oxygen saturation state variability in the surface ocean beneath sea ice. O2/Ar measurements were made underway using Equilibrator Inlet Mass Spectrometry (EIMS) during an icebreaker survey transiting the upper Arctic Ocean across the North Pole in late summer 2011. Using concurrently collected measurements of total oxygen, we devolve biological oxygen saturation and physical oxygen (Ar) saturation signals at unprecedented horizontal resolution in the surface ocean. In the Nansen Basin, Ar is undersaturated up to −7% while biological oxygen supersaturation peaks at 18.4%. We attribute this to ice melt, Atlantic Water influence and/or cooling. In the Canadian Basin, Ar is supersaturated up to 3%, likely because of Ar injection from freezing processes and long residence times of gas under ice cover. The overall Canadian Basin to Eurasian Basin gradient of Ar supersaturation to undersaturation may reflect net freezing in the Canadian Basin and net melting in the Eurasian Basin over several seasons, either by Pacific to Atlantic sector ice transport or local changes over time. Ar saturation could thereby provide large‐scale high‐resolution estimates of current and future changes in these processes. O2/Ar supersaturation averages 4.9% with peaks up to 9.8% where first year ice and abundant melt ponds likely allow sufficient light for blooms in ice‐covered

ISSN:0148-0227    

DOI:10.1002/2014JC009816

年代:2014

数据来源: WILEY

摘要:

AbstractUpper ocean measurements of temperature and salinity obtained from profiling floats equipped with auxiliary surface temperature and salinity sensors (STS) are presented. Using these instruments, high vertical resolution (10 cm) measurements in the near‐surface layer were acquired to within 20 cm of the sea surface, allowing for an examination of the ocean's near‐surface structure and variability not usually possible. We examine the data from 62 Argo‐type floats equipped with STS units deployed in the Pacific, Atlantic, and Indian Oceans. The vertical variability of temperature and salinity in the near‐surface layer is characterized for each of these regions. While observations show the upper 4 m of the ocean are well mixed most of the time, this homogeneity is interrupted by significant and often short‐lived warming/cooling and freshening events. In addition to the presence of barrier layers, a strong diurnal signal in temperature is observed, with salinity exhibiting somewhat weaker diurnal variations. The magnitude of the upper ocean diurnal cycle in temperature and salinity is largest in areas with light winds and heavy precipitation and was found to decay rapidly with depth (∼50% over the top 2 m). Storm events, validated from meteorological data collected from nearby TAO moorings and the Tropical Rainfall Measuring Mission (TRMM) satellite, show downward mixing of rainfall‐derived freshwater to 10 m depth over only a few hours. Turner angle calculations show instability following

ISSN:0148-0227    

DOI:10.1002/2014JC010112

年代:2014

数据来源: WILEY

摘要:

AbstractA monthly time series of remotely sensed chlorophyll‐a(Chlars) over the Louisiana continental shelf (LCS) was developed and examined for its relationship to river discharge, nitrate concentration, total phosphorus concentration, photosynthetically available radiation (PAR), wind speed, and interannual variation in hypoxic area size. A new algorithm for Chlars, tuned separately for clear and turbid waters, was developed using field‐observed chlorophyll‐a(Chlaobs) collected during 12 cruises from 2002 to 2007. The new algorithm reproduced Chlaobs, with ∼40% and ∼60% uncertainties at satellite pixel level for clear offshore waters and turbid nearshore waters, respectively. The algorithm was then applied to SeaWiFS and MODIS images to calculate long‐term (1998–2013) monthly mean Chlarsestimates at 1 km resolution across the LCS. Correlation and multiple stepwise regression analyses were used to relate the Chlarsestimates to key environmental drivers expected to influence phytoplankton variability. The Chlarstime series covaried with river discharge and nutrient concentration, PAR, and wind speed, and there were spatial differences in how these environmental drivers influenced Chlars. The main axis of spatial variability occurred in a cross‐shelf direction with highest Chlarsobserved on the inner shelf. Both inner (<10 m depth) and middle‐shelf (10–50 m depth) Chlarswere observed to covary with interannual variations in the size of the hypoxic (O2 < 63 mmol m−3) area, and they explained ∼70 and ∼50% variability in interannu

ISSN:0148-0227    

DOI:10.1002/2014JC010084

年代:2014

数据来源: WILEY

摘要:

AbstractAir‐entraining breaking waves form oceanic whitecaps and play a key role in climate regulation through air‐sea bubble‐mediated gas transfer, and sea spray aerosol production. The effect of varying sea surface temperature on air entrainment, subsurface bubble plume dynamics, and surface foam evolution intrinsic to oceanic whitecaps has not been well studied. By using a breaking wave analog in the laboratory over a range of water temperatures (Tw = 5°C toTw = 30°C) and different source waters, we have examined changes in air entrainment, subsurface bubble plumes, and surface foam evolution over the course of a breaking event. For filtered seawater, air entrainment was estimated to increase by 6% betweenTw = 6°C andTw = 30°C, driven by increases of about 43% in the measured surface roughness of the plunging water sheet. After active air entrainment, the rate of loss of air through bubble degassing was more rapid at colder water temperatures within the first 0.5 s of plume evolution. Thereafter, the trend reversed and bubbles degassed more quickly in warmer water. The largest observed temperature‐dependent differences in subsurface bubble distributions occurred at radii greater than about 700 μm. Temperature‐dependent trends observed in the subsurface bubble plume were mirrored in the temporal evolution of the surface whitecap foam area demonstrating the intrinsic link between surface whitecap foam and the subsurface bubble plume. Differences in foam and plume characteristics due to different water sources were greater than the temperature dependencies for

ISSN:0148-0227    

DOI:10.1002/2014JC010351

年代:2014

数据来源: WILEY

摘要:

AbstractYear‐long time series of water level are analyzed at five locations along the St. Johns River Estuary, Florida, to investigate propagation of subtidal pulses. Hilbert‐transformed Empirical Orthogonal Functions (HEOFs) are obtained after a dominant seasonal signal is extracted from the data. These functions provide information on spatial structure and propagation phase of subtidal water level pulses. The first HEOF mode explains 96% of the subtidal variability and features an unusual spatial structure: amplitude attenuation (averaging 1 mm/km) to 55 km upstream, slight amplification (0.16 mm/km) over the middle 70 km, and attenuation (2.3 mm/km) over the final 18 km of the estuary. The phase suggests a shift from progressive to quasi‐standing wave behavior at 55 km from the estuary mouth. Additionally, local minima in the phase suggest two sources of subtidal forcing: the coastal ocean and the upstream end. An analytical model describing the evolution of long waves through a channel with frictional damping is fit to the amplitude of HEOF mode 1. Solutions are obtained as a function of two parameters: the nondimensional length of the basin,κ, and the nondimensional frictional depth,δ. Values ofκbetween 0.55 and 0.67 andδbetween 1.45 and 1.7 provide the best fit with the HEOF results (1% error or less). These values indicate a highly frictional environment in which the average subtidal wavelength is 10 times the basin length. Subtidal pulses in this estuary, therefore, behave as damped waves that can be represented with idealiz

ISSN:0148-0227    

DOI:10.1002/2014JC009829

年代:2014

数据来源: WILEY

摘要:

AbstractSea level variations prior to the launch of satellite altimeters are estimated by analyzing historic tide gauge records. Recently, a number of groups have reconstructed sea level by applying EOF techniques to fill missing observations. We complement this study with alternative methods. In a first step gaps in 178 records of sea level change are filled using the pattern recognition capabilities of artificial neural networks. Afterward satellite altimetry is used to extrapolate local sea level change to global fields. Patterns of sea level change are compared to prior studies. Global mean sea level change since 1900 is found to be1.77±0.38 mm yr−1on average. Local trends are essentially positive with the highest values found in the western tropical Pacific and in the Indian Ocean east of Madagascar where it reaches about+6 mm yr−1. Regions with negative trends are spotty with a minimum value of about−2 mm yr−1south of the Aleutian Islands. Although the acceleration found for the global mean,+0.0042 ± 0.0092 mm yr−2, is not significant, local values range from−0.1 mm yr−2in the central Indian Ocean to+0.1 mm yr−2in the western tropical Pacific and east of Japan. These extrema are associated with patterns of sea level change that differ significantly from the first half of the analyzed period (i.e., 1900–1950) to the second half (1950–2000). We take this as an indication of long period oceanic processes that are

ISSN:0148-0227    

DOI:10.1002/2014JC009900

年代:2014

数据来源: WILEY

摘要:

AbstractRegional and global trends of Sea Level Rise (SLR) owing to mass addition centered between 1996 and 2006 are assessed through a full‐depth SLR budget using full‐depth in situ ocean data and satellite altimetry. These rates are compared to regional and global trends in ocean mass addition estimated directly using data from the Gravity Recovery and Climate Experiment (GRACE) from 2003 to 2013. Despite the two independent methods covering different time periods with differing spatial and temporal resolution, they both capture the same large‐scale mass addition trend patterns including higher rates of mass addition in the North Pacific, South Atlantic, and the Indo‐Atlantic sector of the Southern Ocean, and lower mass addition trends in the Indian, North Atlantic, South Pacific, and the Pacific sector of the Southern Ocean. The global mean trend of ocean mass addition is 1.5 (±0.4) mm yr−1for 1996–2006 from the residual method and the same for 2003–2013 from the GRACE method. Furthermore, the residual method is used to evaluate the error introduced into the mass budget if the deep steric contributions below 700, 1000, 2000, 3000, and 4000 m are neglected, revealing errors of 65%, 38%, 13%, 8%, and 4% respectively. The two methods no longer agree within error bars when only the steric contribution shallower than 1000 m

ISSN:0148-0227    

DOI:10.1002/2014JC010180

年代:2014

数据来源: WILEY

摘要:

AbstractPacific Water flows northward through Bering Strait and penetrates the Arctic Ocean halocline throughout the Canadian Basin sector of the Arctic. In summer, Pacific Summer Water (PSW) is modified by surface buoyancy fluxes and mixing as it crosses the shallow Chukchi Sea before entering the deep ocean. Measurements from Ice‐Tethered Profilers, moorings, and hydrographic surveys between 2003 and 2013 reveal spatial and temporal variability in the PSW component of the halocline in the Central Canada Basin with increasing trends in integrated heat and freshwater content, a consequence of PSW layer thickening as well as layer freshening and warming. It is shown here how properties in the Chukchi Sea in summer control the temperature‐salinity properties of PSW in the interior by subduction at isopycnals that outcrop in the Chukchi Sea. Results of an ocean model, forced by idealized winds, provide support to the mechanism of surface ocean Ekman transport convergence maintaining PSW ventilation of the halocl

ISSN:0148-0227    

DOI:10.1002/2014JC010273

年代:2014

数据来源: WILEY