摘要:

AbstractFor this paper, a coupled physical‐biological model was developed in order to study the mechanisms of the winter bloom in the Luzon Strait (referred as LZB). Based on a simulation for January 2010, the results showed that the model was capable of reproducing the key features of the LZB, such as the location, inverted‐V shape, twin‐core structure and bloom intensity. The simulation showed that the LZB occurred during the relaxation period of intensified northeasterly winds, when the deepened mixed layer started to shoal. Nutrient diagnostics showed that vertical mixing was responsible for the nutrient supply to the upper ∼40 m layer, while subsurface upwelling supplied nutrients to the region below the mixed layer. Hydrodynamic diagnostics showed that the advection of relative vorticity (RV) primarily contributed to the subsurface upwelling. The RV advection was resulted from an offshore jet, which was associated with a northeasterly wind, flowed across the ambient R

ISSN:0148-0227    

DOI:10.1002/2014JC010218

年代:2015

数据来源: WILEY

摘要:

AbstractThe waters of the Weddell‐Scotia Confluence (WSC) lie above the rugged topography of the South Scotia Ridge in the Southern Ocean. Meridional exchanges across the WSC transfer water and tracers between the Antarctic Circumpolar Current (ACC) to the north and the subpolar Weddell Gyre to the south. Here, we examine the role of topographic interactions in mediating these exchanges, and in modifying the waters transferred. A case study is presented using data from a free‐drifting, intermediate‐depth float, which circulated anticyclonically over Discovery Bank on the South Scotia Ridge for close to 4 years. Dimensional analysis indicates that the local conditions are conducive to the formation of Taylor columns. Contemporaneous ship‐derived transient tracer data enable estimation of the rate of isopycnal mixing associated with this column, with values of O(1000 m2/s) obtained. Although necessarily coarse, this is of the same order as the rate of isopycnal mixing induced by transient mesoscale eddies within the ACC. A picture emerges of the Taylor column acting as a slow, steady blender, retaining the waters in the vicinity of the WSC for lengthy periods during which they can be subject to significant modification. A full regional float data set, bathymetric data, and a Southern Ocean state estimate are used to identify other potential sites for Taylor column formation. We find that they are likely to be sufficiently widespread to exert a significant influence on water mass modification and meridional fluxes across the southern edge of the ACC in this sector of the Souther

ISSN:0148-0227    

DOI:10.1002/2014JC010462

年代:2015

数据来源: WILEY

摘要:

AbstractA 15 year time series (1999–2014) from the 0°, 23°W Prediction and Research Moored Array in the Tropical Atlantic (PIRATA) mooring, which includes an 8 month record (October 2008 to June 2009) of high‐resolution near‐surface velocity data, is used to analyze the diurnal variability of sea surface temperature, shear, and stratification in the central equatorial Atlantic. The ocean diurnal cycle exhibits pronounced seasonality that is linked to seasonal variations in the surface wind field. In boreal summer and fall, steady trade winds and clear skies dominate, with limited diurnal variability in sea surface temperature. Diurnal shear layers, with reduced Richardson numbers, are regularly observed descending into the marginally unstable equatorial undercurrent below the mixed layer, conditions favorable for the generation of deep‐cycle turbulence. In contrast, in boreal winter and spring, winds are lighter and more variable, mixed layers are shallow, and diurnal variability of sea surface temperature is large. During these conditions, diurnal shear layers are less prominent, and the stability of the undercurrent increases, suggesting seasonal covariance between diurnal near‐surface shear and deep‐cycle turbulence. Modulation of the ocean diurnal cycle by tropical instability waves is also identified. This work provides the first observational assessment of the diurnal cycle of near‐surface shear, stratification, and marginal instability in the equatorial Atlantic, confirming previous modeling results and offering a complementary perspective on similar work in the equ

ISSN:0148-0227    

DOI:10.1002/2014JC010504

年代:2015

数据来源: WILEY

摘要:

AbstractIn this study, we propose a new algorithm for estimating the annual maximum mixed layer depth (M2LD) analogous to a full range of local “ventilation” depth, and corresponding to the deepest surface to which atmospheric influence can be “felt.” Two “seasonality indices” are defined, respectively, for temperature and salinity through Fourier analysis of their time series using Argo data, on the basis of which a significant local minimum of the index corresponding to a maximum penetration depth can be identified. A final M2LD is then determined by maximizing the thermal and haline effects. Unlike most of the previous schemes which use arbitrary thresholds or subjective criteria, the new algorithm is objective, robust, and property adaptive provided a significant periodic geophysical forcing such as annual cycle is available. The validity of our methodology is confirmed by the spatial correlation of the tropical dominance of saline effect (mainly related to rainfall cycle) and the extratropical dominance of thermal effect (mainly related to solar cycle). It is also recognized that the M2LD distribution is characterized by the coexistence of basin‐scale zonal structures and eddy‐scale local patches. In addition to the fundamental buoyancy forcing caused mainly by latitude‐dependent solar radiation, the impressive two‐scale pattern is found to be primarily attributable to (1) large‐wave climate due to extreme winds (large scale) and (2) systematic eddy shedding as a result of persistent winds (mesoscale). Moreover, a general geographical consistency and a good quantitative agreement are found between the new algorithm and those published in the literature. However, a major discrepancy in our result is the existence of a constantly deeper M2LD band compared with other results in the midlatitude oceans of both hemispheres. Given the better correspondence of our M2LDs with the depth of the oxygen saturation limit, it is argued that there might be a systematic underestimation with existing criteria in these regions. Our results demonstrate that the M2LD may serve as an integrated proxy for studying the coherent multidisciplinary variabilities of the coupled oc

ISSN:0148-0227    

DOI:10.1002/2014JC010383

年代:2015

数据来源: WILEY

ISSN:0148-0227    

DOI:10.1002/jgrc.20857

年代:2015

数据来源: WILEY