摘要:

Mean sea level is one of the most important indicators for climate variability and change. Here, we use tide‐gauge data and satellite measurements to examine recent trends in the mean relative sea level (RSL) in the Northwest Atlantic. We then combine model output and satellite observations to provide sea level projections in the 21st century. The mean RSL trend based on historical tide‐gauge data shows large regional variations, from 2 to 4 mm/yr (above the global mean RSL rise rate) in the southeast to −2 mm/yr in the northwest along East Canada. This spatial difference can to a large degree be attributed to that in the vertical land motion measured by the Global Positioning System (GPS). The combination of altimeter‐measured sea level change with the GPS data can approximately account for tide‐gauge measurements at most stations over 1993–2011. When the GPS data are used, the projected mean RSL rise between 1980–1999 and 2090–2099 ranges from 38 to 63 cm along the Scotia‐Fundy and Newfoundland coasts and smaller along Labrador, the northern Gulf of St. Lawrence, and the St. Lawrence Estuary. In spite of considerable uncertainties the ocean steric and dynamical effect is the dominant contributor (35–70 cm) to the RSL rise along the Canadian east coast. The land‐ice (glaciers and ice sheets) melt contributes to the RSL rise by 10–15 cm except at Nain where it is negligible. The effect of the vertical land uplift is large (40–50 cm) at Nain, Sept‐iles and Rimouski, significantly reducing th

ISSN:0148-0227    

DOI:10.1002/2013JC009454

年代:2014

数据来源: WILEY

摘要:

In recent years, it has been observed that there are different types of El Niño events. The warm events can be divided into two categories: those centered in the central Pacific (CP) and those centered in the eastern Pacific (EP). We examined the variability of western Pacific warm pool (WPWP) horizontal migration and size from January 1982 to December 2011 by applying Ensemble Empirical Mode Decomposition (EEMD) and Hilbert‐Huang Spectrum (HHS) to the optimally interpolated sea surface temperature (OISST) data set. The analysis shows that the long‐term residual trend of the zonal centroid movement is migrating to the west by 3.78° from the mean location during the past 30 years. The size of the warm pool has also increased 18% during this period. These analysis techniques isolated two separate time series for the migration of the zonal component of the WPWP for both CP and EP events and showed that these two types of El Niño generally operate at different time scales. The EP time series shows the strong traditional EP El Niño and the transition between strong El Niño conditions and La Niña conditions. The CP time series shows that CP El Niños occur more often than EP El Niños. The changes of El Niño type in conjunction with westward drift and increasing warm pool size shows an interesting multidecadal change in the warm pool. Potential mechanisms relating the Pacific Decadal Oscillation to El Niño typologies were a

ISSN:0148-0227    

DOI:10.1002/2013JC009083

年代:2014

数据来源: WILEY

摘要:

Ensemble optimal interpolation technique has been used to blend winds for the years 2011–2012, derived by OSCAT, a scatterometer onboard the satellite Oceansat‐2, with winds from two different numerical weather prediction (NWP) centers, namely, National Center for Environmental Prediction (NCEP) and European Centre for Medium Range Weather Forecast (ECMWF). These blended winds, when compared with buoy winds, show higher correlations and lower root‐mean‐square errors (RMSE) than the standalone NWP winds. Analysis of divergence and curl of wind stresses also suggests that the blending is physically realistic. Comparisons of blended winds with buoy winds and analysis of divergence and curls as also the subsequent spectral analysis show that the blended ECMWF wind is the best among all the wind products. Consequent assessment of the impact of blended ECMWF wind product has been done using an ocean general circulation model (OGCM). The technique of empirical orthogonal function (EOF) analysis has been used to assess the impact on sea level and surface currents. The dominant modes of simulated variability in the case of forcing by blended winds are found to be more faithfully reproducing the well‐known features of global ocean circulation. Validation of the depth of the 20°C isotherm (D20) also establishes the relative superiority of the blended wi

ISSN:0148-0227    

DOI:10.1002/2013JC009406

年代:2014

数据来源: WILEY

摘要:

In the study, the responses of chlorophyll to decadal oscillations of Kuroshio Extension (KE) between two dynamical states are investigated using satellite data. Associated with the KE stable and unstable states, the surface chlorophyll south of 35°N also undergoes two different contrast patterns: low (high) chlorophyll (∼12% relative to multiyear mean) corresponding to strengthened (weakened) KE jet, i.e., stable (unstable) KE. Two distinct seesaw patterns exist on the north and south side of 35°N for both chlorophyll and sea level anomaly and on the east and west side of 153°E for both chlorophyll and eddy kinetic energy. Similarly, the magnitude of spring bloom was also modulated by decadal variations of KE. The spring bloom was suppressed (enhanced) relative to the magnitude of climatological spring bloom south of 35°N during the KE stable (unstable) period. This change is significant and can reach 35% in extreme years of 2006 and 2009. The decadal variation of chlorophyll in the KE is likely modulated by vertical nutrient supply induced by divergences (convergences) associated with the westward propagation of wind‐induced Rossby waves in the central and eastern North Pacific Ocean, which are dynamically modulated by the North Pacific Gyre Oscillations (NPGO) or PDO (Pacific Decadal Oscill

ISSN:0148-0227    

DOI:10.1002/2013JC009359

年代:2014

数据来源: WILEY

摘要:

Increasing attention is dedicated to the implementation of suitable marine forecast systems for the estimate of the state of the ocean. Within the framework of the European MyOcean infrastructure, the pre‐existing short‐term Mediterranean Sea biogeochemistry operational forecast system has been upgraded by assimilating remotely sensed ocean color data in the coupled transport‐biogeochemical model OPATM‐BFM using a 3‐D variational data assimilation (3D‐VAR) procedure. In the present work, the 3D‐VAR scheme is used to correct the four phytoplankton functional groups included in the OPATM‐BFM in the period July 2007 to September 2008. The 3D‐VAR scheme decomposes the error covariance matrix using a sequence of different operators that account separately for vertical covariance, horizontal covariance, and covariance among biogeochemical variables. The assimilation solution is found in a reduced dimensional space, and the innovation for the biogeochemical variables is obtained by the sequential application of the covariance operators. Results show a general improvement in the forecast skill, providing a correction of the basin‐scale bias of surface chlorophyll concentration and of the local‐scale spatial and temporal dynamics of typical bloom events. Further, analysis of the assimilation skill provides insights into the functioning of the model. The computational costs of the assimilation scheme adopted are low compared to other assimilation techniques, and its modular structure facilitates further developments. The 3D‐VAR scheme results especially suitable for implementation within a biogeochemistry oper

ISSN:0148-0227    

DOI:10.1002/2013JC009277

年代:2014

数据来源: WILEY

摘要:

The temperature in the coastal ocean off the northeastern U.S. during the first half of 2012 was anomalously warm, and this resulted in major impacts on the marine ecosystem and commercial fisheries. Understanding the spatiotemporal characteristics of the warming and its underlying dynamical processes is important for improving ecosystem management. Here, we show that the warming in the first half of 2012 was systematic from the Gulf of Maine to Cape Hatteras. Moreover, the warm anomalies extended through the water column, and the local temperature change of shelf water in the Middle Atlantic Bight was largely balanced by the atmospheric heat flux. The anomalous atmospheric jet stream position induced smaller heat loss from the ocean and caused a much slower cooling rate in late autumn and early winter of 2011–2012. Strong jet stream intraseasonal oscillations in the first half of 2012 systematically increased the warm anomalies over the continental shelf. Despite the importance of advection in prior northeastern U.S. continental shelf interannual temperature anomalies, our analyses show that much of the 2012 warming event was attributed to local warming from the atmospher

ISSN:0148-0227    

DOI:10.1002/2013JC009393

年代:2014

数据来源: WILEY

摘要:

The narrow and deep Faroe Bank Channel (FBC) is an important pathway for cold, dense waters from the Nordic Seas to flow across the Iceland‐Scotland ridge into the North Atlantic. The swift, turbulent FBC overflow is associated with strong vertical mixing. Hydrographic profiles from a shipboard survey and two Slocum electric gliders deployed during a cruise in May–June 2012 show an intermediate water mass characterized by low salinity and low oxygen concentration between the upper waters of Atlantic origin and the dense overflow water. A weak low‐salinity signal originating north‐east of Iceland is discernible at the exit of the FBC, but smeared out by intense mixing. Further west (downstream) marked salinity and oxygen minima are found, which we hypothesize are indicators of a mixture of Labrador Sea Water and Intermediate Water from the Iceland Basin. Water mass characteristics vary strongly on short time scales. Low‐salinity, low‐oxygen water in the stratified interface above the overflow plume is shown to move along isopycnals toward the Iceland‐Faroe Front as a result of eddy stirring and a secondary, transverse circulation in the plume interface. The interaction of low‐salinity, low‐oxygen intermediate waters with the overflow plume already at a short distance downstream of the sill, here reported for the first time, affects the final properties of the overflow waters through entra

ISSN:0148-0227    

DOI:10.1002/2013JC009437

年代:2014

数据来源: WILEY

摘要:

The waters around South Georgia are among the most productive in the Southern Ocean, with zooplankton populations close to the island, in particular Antarctic krill, supporting vast colonies of higher predators. However, our understanding of the processes governing variability in the supply of these food resources is limited by the poor spatial and temporal resolution of available data. Here, we use a numerical modeling approach to examine the underlying physical processes driving the recruitment and retention of zooplankton to the South Georgia shelf. Variability in the magnitude and spatial distribution of recruitment was dominated by the proximity and orientation of the southern Antarctic Circumpolar Current front to the shelf edge. Shelf retention was highest for source sites on the southwest shelf, with the main transport routes off the shelf to the north and northwest. Retention was lowest in the austral summer and winter; in summer increased glacial melt drives stronger off‐shelf near‐surface currents, while in winter, stronger winds lead to an increase in off‐shelf transport. Of particular note was the prediction of a significant increase in retention for particles released throughout the shelf in April and July 2000. This period coincided with the development of pronounced anticlockwise shelf flows, associated with horizontal density gradients due to reduced wind mixing of shelf waters, and differences between shelf and oceanic waters, which significantly reduced off‐shelf transport rates. Such findings are crucial for understanding the influence of variability in physical processes on the ecosystem at South

ISSN:0148-0227    

DOI:10.1002/2013JC009348

年代:2014

数据来源: WILEY

摘要:

Satellite imagery and oceanographic data collected between 2003 and 2009 were used to examine factors controlling the onset timing and magnitude of spring algal blooms in the northwestern North Pacific. Consistent with the critical depth hypothesis, the spring bloom onsets coincided with the mixed layer depth (MLD) shoaling in the north of the Kuroshio extension and in Oyashio, where complex frontal physical structures and turbulence weakening, respectively, would be responsible for the MLD shoaling. In contrast, in the formation regions of the dense central mode water (D‐CMW) and the transition region mode water (TRMW), bloom onsets coincided with possible turbulence weakening but not with MLD shoaling. The peak of chlorophyllain the formation regions of the D‐CMW (0.44 ± 0.23 mg m−3) and the TRMW (0.58 ± 0.34 mg m−3) were ca. 5 times lower than that in the Oyashio (2.54 ± 0.74 mg m−3), despite the fact that nitrate concentration during the prebloom period was high (∼10 µM) and MLDs became shallow enough at the bloom peak in all the three regions. These observations indicated that light conditions and nitrate concentration did not explain the regional variability in the magnitude of spring blooms. The bloom magnitude west of ca. 150°E and in the north Kuroshio extension was increased relative to that in the eastern region, suggesting a chemical property in the water delivered from the Okhotsk Sea that would influence the western bloom. Our results demonstrated that factors controlling the timing and magnitude of spring algal blooms depend on the physicochemical regime in th

ISSN:0148-0227    

DOI:10.1002/2013JC009187

年代:2014

数据来源: WILEY

摘要:

Decadal sea‐level variability along the coast of Japan and its relation to large‐scale ocean circulation changes from 1993 to 2010 was investigated using tide‐gauge and satellite‐derived sea‐level data. A singular value decomposition (SVD) analysis is performed between coastal sea levels of Japan and sea levels in the western North Pacific. The first SVD mode reveals that the northward shifts of the Kuroshio Extension (KE) jet and the Kuroshio southeast of Japan accompany the coastal sea‐level rise in the early 2000s and 2010, and their southward shifts accompany the coastal sea‐level fall in the late 1990s and the late 2000s. The shifts of the KE jet are induced by westward propagating Rossby wave from the eastern North Pacific, which is concentrated along the KE jet axis as jet‐trapped Rossby waves. The resulting sea‐level changes along the coast of Japan show a strong spatial contrast. The sea‐level fluctuation is quite large along the southeastern coast of Japan that is under the direct influence of the jet‐trapped Rossby waves, and also large in the western coast of Japan, probably due to coastal waves that are excited by the incoming Rossby waves, but is small north of the KE jet latitude. Hence, the nature of the wave trapped by the KE jet produces an “active zone” and a “shadow zone” of coastal sea‐level variability of Japan. Our results indicate that the correct representation of western boundary currents is necessary for reliable prediction of f

ISSN:0148-0227    

DOI:10.1002/2013JC009327

年代:2014

数据来源: WILEY