摘要:

AbstractOngoing acoustic Doppler current profilers (ADCP) observation in the eastern equatorial Indian Ocean and a recentInternationalNusantaraStratificationandTransport (INSTANT) experiment in the Indonesian Throughflow (ITF) straits have shown coherent intraseasonal oceanic variations in this region. The intraseasonal variations are dominated by 30–70 day variations, with a tendency for the observed currents in the eastern equatorial Indian Ocean to lead those at the Lombok and Ombai Straits. Phase speed of these eastward propagating signals estimated using lag correlation analysis does not correspond to one particular baroclinic mode, though it is in the range expected for the first two baroclinic modes. In this study, the dynamics underlying this intraseasonal coherency is evaluated using output from a high‐resolution ocean general circulation model developed for the Earth Simulator (OFES). The results from model simulation of January 2001 through December 2007 show that the first two baroclinic modes dominate the intraseasonal variations in this region. While the first and second baroclinic modes have comparable contribution to the intraseasonal oceanic variations in the eastern equatorial Indian Ocean and in the Ombai Strait, the intraseasonal oceanic variations in the Lombok Strait are dominated by the first baroclinic mode. Moreover, the analysis reveals that the intraseasonal variability at all mooring sites is mostly confined in the upper layer above ∼100 m depth. Both equatorial wind from the Indian Ocean and alongshore winds off Sumatra and Java play important roles in generating intraseasonal variations in the Lombok and Ombai St

ISSN:0148-0227    

DOI:10.1002/2013JC009592

年代:2014

数据来源: WILEY

摘要:

AbstractAcceleration of the Greenland Ice Sheet (GrIS) tidewater outlet glaciers has increased the ice sheet's contribution to global sea level rise over the last two decades. Coincident increases in atmospheric temperatures around Greenland explain some of the increased ice loss, but warm Atlantic‐origin water (AW) is increasingly recognized as contributing to the accelerating ice‐mass loss, particularly, via the outlet glaciers of south‐east (SE) Greenland. However, there remains a lack of understanding of the variability in heat content of the water masses found to the east of Greenland and how this heat is communicated to the outlet glaciers of the GrIS. Here a new analysis is presented of ocean/GrIS interaction in which the oceanic heat flux toward the ice sheet in Kangerdlugssuaq Fjord (0.26 TW) is an order‐of‐magnitude greater than that reported for the other major outlet glacier of SE Greenland (Helheim). Heat delivered by AW to the calving front of Kangerdlugssuaq is equivalent to ∼10 m d−1melt (i.e., 30–60% of the ice flow speed), and thus is highly significant. During the observational campaign in September 2010 warm Polar Surface Water (PSWw) melted a substantial volume of ice within the fjord; equivalent to 25% of the volume melted by AW alone. Satellite‐derived sea surface temperatures show large interannual variability in PSWw over the 20 year period 1991–2011. Anomalously warm PSWw was observed within the fjord prior to the well‐documented major ice front retreats of May 2

ISSN:0148-0227    

DOI:10.1002/2013JC009295

年代:2014

数据来源: WILEY

摘要:

AbstractThe fugacity of CO2(fCO2) has been measured underway during three quasi‐synoptic cruises in the western tropical Atlantic in March/April 2009 and July/August 2010 in the region 6°S–15°N, 52°W–24°W. The distribution of fCO2is related to the main features of the ocean circulation. Temperature exerts a dominant control on the distribution of fCO2in March/April whereas salinity plays an important role in July/August due to the more developed North Equatorial Countercurrent (NECC) carrying Amazon water and to the high precipitation associated with the presence of the Intertropical Convergence Zone (ITCZ). The main surface currents are characterized by different fCO2. Overall, the NECC carries less saline waters with lower fCO2compared to the South Equatorial Current (SEC). The North Equatorial Current (NEC) is usually characterized by CO2undersaturation in winter and supersaturation in summer. Using empirical fCO2‐SST‐SSS relationships, two seasonal maps of fCO2are constructed for March 2009 and July 2010. The region is a sink of CO2of 0.40 mmol m−2d−1in March, explained by the winter cooling in the northern hemisphere, whereas it is a source of CO2of 1.32 mmol m−2d−1in July. The equatorial region is a source of CO2throughout the year due to the upwelling supplying CO2‐rich waters to the surface. However, the evolution of fCO2over time, determined from all the available cruises in a small area, 1°S–1°N, 32°W–28°W, suggests that the source of CO2has decreased in February‐March from 1983 to 2011 or has remained constant in O

ISSN:0148-0227    

DOI:10.1002/2013JC009248

年代:2014

数据来源: WILEY

摘要:

AbstractConcurrent observations of inner shelf near bed hydrodynamics and acoustic imagery of the seabed are used to relate wave‐induced ripple geometry (wavelength and orientation) to near bed directional wave velocities. The observations were collected on the continental shelf of the South Atlantic Bight at water depths of 9.5 and 30 m off the coasts of South Carolina (median size 177 µm) and Georgia (388 µm), respectively. 2‐D spectral analysis techniques are performed on the imagery to automate detection of ripple wavelength, orientation, and irregularity. Our analysis shows that ripple irregularity is a time‐dependent process dependent on magnitude, direction, and duration of wave forcing. During energetic events, ripple geometry changes rapidly and the ripples align with the main wave direction. During periods of low energy, close to the critical conditions for initiation of sediment motion, ripple evolution occurs at a much slower rate often leading to irregularities such as terminations and bifurcations along the ripple crest. Under constantly changing wave direction, the rippled bed becomes highly disorganized. Six types of ripples are defined based on newly developed irregularity parameters: linear, bifurcating‐linear, linear‐bifurcating, bifurcating and cross, irregular, and disorganized beds. Ripple irregularity depends on the time history of the bed; ripples remain irregular until their wavelength and orientation attain a nearly equilibrium geometry. The observations collected provide significant information on the response of the seabed to wave forcing and identify processes that should be reproduced by any time‐dependent ripple prediction model. Ripple irregularity can only be predicted using such time‐d

ISSN:0148-0227    

DOI:10.1002/2013JC009020

年代:2014

数据来源: WILEY

摘要:

AbstractThe Kerama Gap, near the middle of the Ryukyu Island chain, is the deepest channel with a sill depth of 1050 m connecting the East China Sea (ECS) to the Northwestern Pacific. We measured the flow through the Kerama Gap from June 2009 to June 2011. The 2 year mean transport, 2.0 ± 0.7 Sv, is into the ECS from the Northwestern Pacific; it contributes about 11% of the mean Kuroshio transport in the ECS at the PN line. Subtidal standard deviation of the transport through the Kerama Gap is 3.2 Sv, comparable to that of the PN‐line Kuroshio transport (4.0 Sv), suggesting a significant effect of Kerama Gap transport on temporal variability of the Kuroshio transport in the ECS. Comparison with time series of satellite‐measured sea surface height maps reveals that temporal variability of the Kerama Gap transport is related to the arrival of mesoscale eddies from the east: high (low) transport into the ECS is associated with the presence of a cyclonic (anticyclonic) eddy south of the Ke

ISSN:0148-0227    

DOI:10.1002/2013JC008899

年代:2014

数据来源: WILEY

摘要:

AbstractThe potential for a dynamical impact of Saharan mineral dust on the North Atlantic Ocean large‐scale circulation is investigated. To this end, an ocean general circulation model forced by atmospheric fluxes is perturbed by an idealized, seasonally varying, net shortwave flux anomaly, as it results from remote sensing observations of aerosol optical thickness representing Saharan dust load in the atmosphere. The dust dynamical impact on the circulation is assessed through a comparison between perturbed and an unperturbed run. Results suggest that, following the dust‐induced shortwave irradiance anomaly, a buoyancy anomaly is created in the Atlantic offshore the African coast, which over the course of the time propagates westward into the interior Atlantic while progressively subducting. Changes in the large‐scale barotropic and overturning circulations are significant after 3 years, which coincides with the elapsed time required by the bulk of the buoyancy perturbation to reach the western boundary of the North Atlantic. Although small in amplitude, the changes in the meridional overturning are of the same order as interannual‐to‐decadal variability. Variations in the amplitude of the forcing lead to changes in the amplitude of the response, which is almost linear during the first 3 years. In addition, a fast, but dynamically insignificant, response can be observed to propagate poleward along the eastern boundary of the North Atlantic, which contributes to a nonlinear response in the subpolar region nort

ISSN:0148-0227    

DOI:10.1002/2013JC009274

年代:2014

数据来源: WILEY

摘要:

AbstractThis article presents the results of a high‐resolution (1/12°), two‐way nested simulation of the oceanic circulation in the southwestern Atlantic region. A comparison between the model results and extant observations indicates that the nested model has skill in reproducing the best‐known aspects of the regional circulation, e.g., the volume transport of the ACC, the latitudinal position of the BMC, the shelf break upwelling of Patagonia, and the Zapiola Anticyclone. Sensitivity experiments indicate that the bottom stress parameterization significantly impacts the mean location of the Brazil/Malvinas Confluence and the transport of the Zapiola Anticyclone. The transport of the Brazil Current strengthens during the austral summer and weakens during the austral winter. These variations are driven by the wind stress curl over the southwestern Atlantic. The variations of the transport of the Malvinas Current are out of phase with those of the Brazil Current. Most of the seasonal variability of this current is concentrated in the offshore portion of the jet, the inshore portion has a weak seasonality that modulates the magnitude of the Patagonian shelf break upwelling. Using passive tracers we show that most of the entrainment of deep waters into the shelf occurs in the southernmost portion of the Patagonian shelf and along the inshore boundary of the Brazil Current. Shelf waters are preferentially detrained near the Brazil/Malvinas Confluence. Consistent with previous studies, our simulation also shows that south of ∼42°S the Malvinas Current is composed of two jets, which merge near 42°S to form a single jet far

ISSN:0148-0227    

DOI:10.1002/2013JC009498

年代:2014

数据来源: WILEY

摘要:

AbstractBubble size distributions ranging from 0.5 to 125 μm radius were measured optically during high winds of 13 m s−1and large‐scale wave breaking as part of the Southern Ocean Gas Exchange Experiment. Very small bubbles with radii less than 60 µm were measured at 6–9 m depth using optical measurements of the near‐forward volume scattering function and critical scattering angle for bubbles (∼80°). The bubble size distributions generally followed a power law distribution with mean slope values ranging from 3.6 to 4.6. The steeper slopes measured here were consistent with what would be expected near the base of the bubble plume. Bubbles, likely stabilized with organic coatings, were present for time periods on the order of 10–100 s at depths of 6–9 m. Here, relatively young seas, with an inverse wave age of approximately 0.88 and shorter characteristic wave scales, produced lower bubble concentrations, shallower bubble penetration depths, and steep bubble size distribution slopes. Conversely, older seas, with an inverse wave age of 0.70 and longer characteristic wave scales, produced relatively higher bubble concentrations penetrating to 15 m depth, larger bubble sizes, and shallower bubble size distribution slopes. When extrapolated to 4 m depth using a previously published bubble size distribution, our estimates suggest that the deeply penetrating small bubbles measured in the Southern Ocean supplied ∼36% of the total void fraction and likely contributed to the transfer and supersaturation of lo

ISSN:0148-0227    

DOI:10.1002/2013JC009227

年代:2014

数据来源: WILEY

摘要:

AbstractThe impacts of canonical and Modoki El Niño on tropical Atlantic sea surface temperature (SST) are quantified using composite analysis. Results show that El Niño Modoki fails to produce significant warming in the tropical Atlantic, in contrast to the well known warming following canonical El Niño events. El Niño Modoki instead induces significant cooling in the northeastern tropical Atlantic and near‐neutral conditions elsewhere in the tropical Atlantic. It is shown that the difference in SST response stems primarily from a much stronger Pacific/North American (PNA) teleconnection pattern and stronger atmospheric Kelvin wave response during canonical events compared to Modoki. The stronger PNA pattern and Kelvin waves during canonical events generate anomalously weak surface winds in the tropical North Atlantic, driving anomalously weak evaporative cooling and warmer SSTs. Past research has shown significant decadal variability in the frequency of noncanonical El Niños relative to canonical events. If such variability continues, it is likely that the impact of El Niño on tropical Atlantic SST will also fluctuate from one decade to t

ISSN:0148-0227    

DOI:10.1002/2013JC009476

年代:2014

数据来源: WILEY

摘要:

AbstractDeep water circulation in the Luzon Strait, which connects the Pacific deep circulation with the South China Sea throughflow, is investigated using a set of oceanographic observations combined with results from three numerical experiments. Both the in situ observations and the model show a deep water overflow in the Luzon Strait. Their results suggest that the deep Pacific water first flows into the Luzon Strait through the Bashi Channel (1.2 Sv, 1 Sv = 1 × 106m3s−1) and the Taltung Canyon (0.4 Sv), then turns southward along the Luzon Trough, and finally enters the South China Sea primarily through two gaps in the Heng‐Chun Ridge. Overall, the mean transport of the Luzon Strait overflow is about 1.5 Sv. Results from numerical experiments suggest that strong diapycnal mixing in the South China Sea and Luzon Strait, which sustains the baroclinic pressure gradient across the Luzon Strait, is the primary driving mechanism of the deep circulation in the Luzo

ISSN:0148-0227    

DOI:10.1002/2013JC009587

年代:2014

数据来源: WILEY