摘要:

Previous comprehensive investigations of the Canadian Arctic revealed that subsurface chlorophyll maxima (SCM) are widespread and long‐lived structures that can contribute significantly to daily primary production in the water column. However, estimating the annual contribution of SCM to production with in situ or remote‐sensing approaches is challenging in the high Arctic. For this reason and to estimate the impacts of fluctuating or changing environmental conditions on SCM, a numerical approach combining a turbulence model and an ecosystem model was implemented for the coastal Beaufort Sea. An ensemble analysis of simulations suggested that SCM contribute 65–90% of total annual primary production and that this proportion is weakly affected by ice regime, winter nitrogen (N) concentration, parameter values determining phytoplankton growth and decay or the physical forcing imposed, all varying within realistic values. Due to the persistent association between the SCM and the shallow nitracline, the pelagic ecosystem of the coastal Beaufort Sea is apparently characterized by a high ratio of new to total production, contrasting with the common assumption that oligotrophic systems are predominantly supported by recycled N and regenerated production. This study demonstrated that the use of a simple model in combination with in situ data leads to novel insights into biogeochemical processes that are otherwise very difficult to measure and

ISSN:0148-0227    

DOI:10.1002/2013JC008843

年代:2013

数据来源: WILEY

摘要:

In this paper, we assess the risk of future coastal flooding in the Severn Estuary, examining the contribution from low probability extreme sea level rise scenarios resulting from the possibility of increased rates of ice sheet mass loss in the coming century. A simple asymmetric probability distribution is constructed to include sea level rise scenarios of up to 1.9 m by 2100, based on recent assessments of future sea level rise in the UK. A regular sampling procedure, sampling every 1 mm, is used to increase the boundary water levels associated with a current 1:200 year event to force a two‐dimensional hydrodynamic model of coastal inundation to examine the influence of sea level rise on inundation of the Somerset Levels region. From the resulting ensemble of predictions an estimation of risk (conditioned upon the hazard and the probability of occurrence) by 2100 is established. The results indicate that although the likelihood of extreme sea level rise due to rapid ice sheet mass loss is low, the resulting hazard can be large, resulting in a significant (29.7%) increase to the projected risk. These findings clearly demonstrate that uncertainty in future sea level rise, mostly associated with the rate of ice sheet mass loss, is a vital component of coastal flood risk, and therefore, needs to be accounted for by decision makers when considering mitigation policies related to coastal floodin

ISSN:0148-0227    

DOI:10.1002/jgrc.20412

年代:2013

数据来源: WILEY

摘要:

We present airborne measurements to investigate the thickness of the western McMurdo Ice Shelf in the western Ross Sea, Antarctica. Because of basal accretion of marine ice and brine intrusions conventional radar systems are limited in detecting the ice thickness in this area. In November 2009, we used a helicopter‐borne laser and electromagnetic induction sounder (EM bird) to measure several thickness and freeboard profiles across the ice shelf. The maximum electromagnetically detectable ice thickness was about 55 m. Assuming hydrostatic equilibrium, the simultaneous measurement of ice freeboard and thickness was used to derive bulk ice densities ranging from 800 to 975 kg m−3. Densities higher than those of pure ice can be largely explained by the abundance of sediments accumulated at the surface and present within the ice shelf, and are likely to a smaller extent related to the overestimation of ice thickness by the electromagnetic induction measurement related to the presence of a subice platelet layer. The equivalent thickness of debris at a density of 2800 kg m−3is found to be up to about 2 m thick. A subice platelet layer below the ice shelf, similar to what is observed in front of the ice shelf below the sea ice, is likely to exist in areas of highest thickness. The thickness and density distribution reflects a picture of areas of basal freezing and supercooled Ice Shelf Water emerging from below the central ice shelf cavity into McMurdo

ISSN:0148-0227    

DOI:10.1002/2013JC009084

年代:2013

数据来源: WILEY

摘要:

A regional ocean circulation model (ROMS) is used to simulate the Chinese land‐derived sediment transport in the Bohai Sea, Yellow Sea, and East China Sea (BYECS). The model includes the effect of currents, tides, and waves on the sediment transport and is used to study the pathway and dynamic mechanisms of the fine‐grain sediment transport from the Huanghe River (Yellow River), the Old Huanghe Delta, and the Changjiang River (Yangtze River) in the BYECS. The seasonal variability of the sediment transport in the BYECS and the sources of the Yellow Sea Trough mud patch, the mud patch southwest of Cheju Island, the mud patch offshore from the Zhejiang and Fujian provinces and the Okinawa Trough mud patch are discussed. The results show that the Huanghe River sediment can be transported to the Yellow Sea Trough, but little makes it to the outer shelf while the Old Huanghe Delta sediment is mainly transported to the Yellow Sea Trough. Most of the sediment from the Changjiang River mouth is carried to the mud patch off the coast of the Zhejiang and Fujian provinces but with part of this sediment also transported to the Yellow Sea Trough. The model shows that it is difficult to transport land‐derived sediment to the Okinawa Trough mud patch under normal conditions. The model also has difficulty accounting for the deposition of sediment in the region to the southwest of Cheju Island and offshore from the Zhejiang and Fujian provinces, an issue requiring further

ISSN:0148-0227    

DOI:10.1002/2013JC009116

年代:2013

数据来源: WILEY

摘要:

The boundary layer above a 4569 m deep slope in the near‐equatorial N‐Atlantic Ocean Kane Gap, a throughflow for Antarctic Bottom Water (AABW), is characterized by two distinct turbulent regimes that differ by an order of magnitude in intensity depending on the direction of throughflow. During southward and downward flow, vertical mixing is vigorous. This is inferred from high‐resolution temperature observations between 6 and 132 m above the bottom. For a representative case study of 2 days, average values are found for dissipation rate ofε = 2.1 ± 1 × 10−9W kg−1and eddy diffusivity of Kz = 7 ± 4 × 10−4m2s−1. The mixing is across relatively large vertical overturns. During northward and upward flow, smaller overturns are more horizontal as in stratified shear flow (with representative 2 day meanε = 6 ± 3 × 10−11W kg−1, Kz = 4 ± 2 × 10−5m2s−1). Stratification is approximately the same during both flow directions. Although the different turbulence regimes are partially associated with frictional boundary layers of large‐scale flows above sloping topography, but not with those over flat bottoms, and partially with flow across a hill‐promontory, internal waves are a dominant process in promoting turbulence. In addition, internal waves are observed to push stratification towar

ISSN:0148-0227    

DOI:10.1002/2013JC009282

年代:2013

数据来源: WILEY

摘要:

In November 2005 off Cabo Corrientes, a cyclonic eddy was sampled from (i) remotely sensed data of sea level anomaly, near‐surface wind, chlorophyll‐aconcentration and sea surface temperature and (ii) direct observations from a lowered Acoustic Doppler profiler, and a conductivity, temperature, and depth sensor. The sea level anomaly data set and an automated eddy detection method showed that this vortex formed near the Mexican coast and traveled westward/northwestward, ∼1000 km into the open ocean for ∼8 months. Surface winds and currents indicated that the cyclone was generated during a coastal upwelling event that occurred simultaneously with an equatorward flow located close to the coast. During its growing phase, the eddy extended from the surface to 750 m depth and mixed the water column in the first ∼100 m, showing an eastward shift of the eddy axis toward the sea surface of 1.5° of longitude, that generated a southward meridional heat transport in the upper layers. Integrated in the vertical, this heat transport accounted for a total of −105 × 1012W, within the region of the eddy. The estimation of the available heat and salt anomaly contents revealed that the eddy transported relatively cold, salty, and anoxic waters associated with the Subtropical Subsurface water mass. While traveling offshore, the cyclonic eddy also exhibited relatively higher chlorophyllaconcentrations at the sea surface than its surroundings. Comparison of some surface properties estimated from satellite and in situ data showed that satellite data tend to underestimate its amplitude and orbital geostro

ISSN:0148-0227    

DOI:10.1002/2013JC009339

年代:2013

数据来源: WILEY

摘要:

Wave and wind measurements at Ocean Weather Station P (OWS‐P, 50°N 145°W) are used to evaluate the equilibrium range of surface wave energy spectra. Observations are consistent with a local balance between wind input and breaking dissipation, as described by Philips (1985). The measurements include direct covariance wind stress estimates and wave breaking dissipation rate estimates during a 3 week research cruise to OWS‐P. The analysis is extended to a wider range of conditions using observations of wave energy spectra and wind speed during a 2 year mooring deployment at OWS‐P. At moderate wind speeds (5–15 m/s), mooring wave spectra are in agreement, within 5% uncertainty, with the forcing implied by standard drag laws and mooring wind measurements. At high wind speeds (>15 m/s), mooring wave spectra are biased low, by 13%, relative to the forcing implied by standard drag laws and mooring wind measurements. Deviations from equilibrium are associated with directionality and variations at the swell frequencies. A spectral wave hindcast accurately reproduces the mooring observations, and is used to examine the w

ISSN:0148-0227    

DOI:10.1002/2013JC008837

年代:2013

数据来源: WILEY

摘要:

A time‐dependent, 1‐D coupled ice‐ocean model is used to quantify the impact of ocean stratification on the Arctic ice cover. The model results show that the ice growth during winter equals the ice melt in summer for areas with a well‐developed cold halocline layer (CHL), provided that the initial ice thickness is around 3 m, while thinner initial ice thickness results in net growth. Areas with weak salt stratification can have a negative annual thickness change irrespective of the initial ice thickness and are thus dependent on ice import in order to remain ice covered. The model results also show that ocean stratification is mostly important for ice‐thickness development during the growing season. Areas with weak stratification have an ocean heat flux up to 8 W m−2reaching the ice during the growing season, while areas with a CHL have an average of about 0.7 W m−2. In the extreme area, north of Svalbard, the ocean heat fluxes are typically around 25 W m−2but can be up to 400 W m−2during the initial adjustment, when the warm Atlantic water has direct contact with the ice. A general outcome of the study is that, depending on ocean stratification, the ice cover of Arctic Ocean can be divided into one part with net ice growth (the major part) and another part with net ice melt (mainly in

ISSN:0148-0227    

DOI:10.1002/jgrc.20409

年代:2013

数据来源: WILEY

摘要:

Several mechanisms can drive vertical velocities in the coastal ocean, including wind‐forcing and through gradients in the vorticity field generated by flow‐topography interactions. A two‐layer, steady, wind‐driven, analytical model is applied to the major upwelling systems of Brazil: Cabo Frio (CF) and Cabo de Santa Marta (CSM) regions. Comparisons are made between the relative roles of wind and flow‐topography interaction in inducing upwelling over these regions. Ekman pumping is the weakest mechanism over the shelf, but does influence the along‐shelf temperature in the CF area. Away from coastline irregularities, wind‐driven upwelling (Ekman transport) dominates over all mechanisms. However, in the vicinity of capes and coastal features, topographically driven upwelling plays a significant role, and its transports may vary from 43% to 94% of wind‐driven upwelling. Upstream of capes, topographically driven vertical motions are downwelling favorable and act against the wind‐driven coastal upwelling, while downstream of capes, they are upwelling favorable, where all mechanisms add up to create strong upwelling. Peaks in total upwelling in the CF region are about twice as large as those in the CSM area because the CF region has stronger winds and larger coastline perturbations than in the CSM region. Observed sea surface temperatures (SST) agree well with variability in the vertical transports where upwelling peaks are in phase with low temperature peaks along the coast. Results suggest that on larger scales, the SST variability along the coast is mainly controlled by wind‐driven upwelling, while upwelling due to flow‐topography interaction is responsible for the smaller

ISSN:0148-0227    

DOI:10.1002/2013JC008924

年代:2013

数据来源: WILEY

摘要:

Field measurements of the diffusive boundary layer (DBL) and bottom boundary layer (BBL) in two distinctly different coastal ocean environments are analyzed. The dynamic conditions of the BBL have a strong influence on the DBL thickness (δDBL) and oxygen diffusive fluxes at the sediment‐water interface. Three different estimates of the Batchelor length (LB) in the BBL are obtained from the measured dissipation rate of turbulent kinetic energy (εm), turbulent friction velocity (u*), and tidal velocity (Um) and bottom roughness length (z0). The two estimates ofLBfromεmandu*have low correlations withδDBL. The estimate ofLBfromUmandz0has a higher correlation withδDBLat both sites, suggesting a simple estimation

ISSN:0148-0227    

DOI:10.1002/2013JC008900

年代:2013

数据来源: WILEY