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1.
A global in situ analysis and a global ocean simulation are used jointly to study interannual to decadal variability of temperature in the Bay of Biscay, from 1965 to 2003. A strong cooling is obtained at all depths until the mid-1970's, followed by a sustained warming over ～30 years. Strong interannual fluctuations are superimposed on this slow evolution. The fluctuations are intensified at the surface and are weakest at ～500 m. A good agreement is found between the observed and simulated temperatures, in terms of mean values, interannual variability and time correlations. Only the decadal trend is significantly underestimated in the simulation. A comparison to satellite sea surface temperature (SST) data over the last 20 years is also presented. The first mode of interannual variability exhibits a quasi-uniform structure and is related to the inverse winter North Atlantic Oscillation (NAO) index. Regarding the vertical structure, most cool and warm anomalies are generated at the surface, with the strongest ones penetrating down to 700 m and lasting up to 5 years. The complete heat budget from 1965 to 2004 is presented, including the contributions of vertical transport, freshwater flux and surface elevation. Interannual anomalies are mainly generated by the surface heat flux, while oceanic transports may become more important at longer time scales. 相似文献
2.
Relative sea level variations in the north-western part of the Arabian Gulf have been estimated in the past using no more than 10 to 15 years of observations. In this study, we have almost doubled the period to 28.7 years by examining all available tide gauge data in the area and constructing a mean gauge time-series from seven coastal tide gauges. We found for the period 1979–2007 a relative sea level rise of 2.2 ± 0.5 mm/year. Using the subsidence observed at 6 GPS stations within a radius of 100 km of the tide gauges as an indication of the vertical land motion, the corresponding absolute sea level rise is 1.5 ± 0.8 mm/year that is in agreement with the global estimate of 1.9 ± 0.1 mm/year (Church and White, 2011) for the same studied period. By taking into account the temporal correlations we conclude that previous published results underestimate the true sea level rate uncertainty in this area by a factor of 5–10. 相似文献
3.
An annual amplitude of ∼18 cm mass-induced sea level variations (SLV) in the Red Sea is detected from the Gravity Recovery and Climate Experiment (GRACE) satellites and steric-corrected altimetry from 2003 to 2011. The annual mass variations in the region dominate the mean SLV, and generally reach maximum in late January/early February. The annual steric component of the mean SLV is relatively small (<3 cm) and out of phase of the mass-induced SLV. In situ bottom pressure records at the eastern coast of the Red Sea validate the high mass variability observed by steric-corrected altimetry and GRACE. In addition, the horizontal water mass flux of the Red Sea estimated from GRACE and steric-corrected altimetry is validated by hydrographic observations. 相似文献
4.
In this review article, we summarize observations of sea level variations, globally and regionally, during the 20th century and the last 2 decades. Over these periods, the global mean sea level rose at rates of 1.7 mm/yr and 3.2 mm/yr respectively, as a result of both increase of ocean thermal expansion and land ice loss. The regional sea level variations, however, have been dominated by the thermal expansion factor over the last decades even though other factors like ocean salinity or the solid Earth's response to the last deglaciation can have played a role. We also present examples of total local sea level variations that include the global mean rise, the regional variability and vertical crustal motions, focusing on the tropical Pacific islands. Finally we address the future evolution of the global mean sea level under on-going warming climate and the associated regional variability. Expected impacts of future sea level rise are briefly presented. 相似文献
5.
Resolving sea level contributions by identifying fingerprints in time-variable gravity and altimetry
We have studied the ability of the GRACE gravimetry mission and Jason-1 altimetry to resolve ice and glacier induced contributions to sea level rise, by means of a fingerprint method. Here, the signals from ice sheet and land glacier changes, steric changes, glacial isostatic adjustment and terrestrial hydrology are assumed to have fixed spatial patterns. In a joint inversion using GRACE and Jason-1 data the unknown temporal components can then be estimated by least-squares. In total, we estimate temporal components for up to ∼ 80 individual patterns. From a propagation of the full error-covariance from GRACE and a diagonal error-covariance from Jason-1 altimetry we find that: (1) GRACE almost entirely explains the mass related parameters in the joint inversion, (2) an inversion using only Jason-1 data has a marginal ability to estimate the mass related parameters, while the steric parameters have much better formal accuracy. In terms of mean sea level rise the steric patterns have a maximum formal accuracy of 0.01 mm for an 11 week running mean. In general, strong negative error correlations (ρ < − 0.9) exists between the high and low elevation parts of the ice sheet drainage basins, when those are estimated independently. The largest formal errors found are in the order of 40 Gton for small high elevation subbasins in the southern Greenland ice sheet, which are difficult to separate. In a simplified joint inversion, merging high and low elevation basins, we have investigated the ability of the GRACE and Jason-1 data to separate the geocenter motion into a present-day contribution and a contribution from glacial isostatic adjustment (GIA). We find that the GIA related signal is larger than the present-day component with a maximum of −0.71 mm/year in the Z direction. Total geocenter motion rates are found to be −0.28, 0.43, −1.08 mm/year for the X, Y and Z components, respectively. The inversion results have been propagated to the Jason-1 along-track measurements. Over the time period considered, we see that a large part of the variability in the Pacific, Atlantic and Indian ocean can be explained by our inversion results. The applied inversion method therefore seems a feasible way to separate steric from mass induced sea level changes. At the same time, the joint inversion would benefit from more advanced parameterizations, which may aid in fitting remaining signal from altimetry. 相似文献
6.
The mass-induced sea level variability and the net mass transport between Mediterranean Sea and Black Sea are derived for the interval between August 2002 and July 2008 from satellite-based observations and from model data. We construct in each basin two time series representing the basin mean mass signal in terms of equivalent water height. The first series is obtained from steric-corrected altimetry while the other is deduced from GRACE data corrected for the contamination by continental hydrology. The series show a good agreement in terms of annual and inter-annual signals, which is in line with earlier works, although different model corrections influence the consistency in terms of seasonal signal and trend.In the Mediterranean Sea, we obtain the best agreement using a steric correction from the regional oceanographic model MFSTEP and a continental hydrological leakage correction derived from the global continental hydrological model WaterGAP2. The inter-annual time series show a correlation of 0.85 and a root mean square (RMS) difference of 15 mm. The two estimates have similar accuracy and their annual amplitude and phase agree within 3 mm and 23 days respectively. The GRACE-derived mass-induced sea level variability yields an annual amplitude of 27 ± 5 mm peaking in December and a trend of 5.3 ± 1.9 mm/yr, which deviates within 3 mm/yr from the altimetry-derived estimate.In the Black Sea, the series are less consistent, with lower accuracy of the GRACE-derived estimate, but still show a promising agreement considering the smaller size of the basin. The best agreement is realized choosing the corrections from WaterGAP2 and from the regional oceanographic model NEMO. The inter-annual time series have a correlation and RMS differences of 0.68 and 55 mm, their annual amplitude and phase agree within 4 mm and 6 days respectively. The GRACE-derived seawater mass signal has an annual amplitude of 32 ± 4 mm peaking in April. On inter-annual time scales, the mass-induced sea level variability is stronger than in the Mediterranean Sea, with an increase from 2003 to 2005 followed by a decrease from 2006 to 2008.Based on mass conservation, the mass-induced sea level variations, river runoff and precipitation minus evaporation are combined to derive the strait flows between the basins and with the Atlantic Ocean. At the Gibraltar strait, the net inflow varies annually with an amplitude of 52 ± 10 × 10−3 Sv peaking end of September (1 Sv = 106 m3 s−1). The inflow through the Bosphorus strait displays an annual amplitude of 13 ± 3 ×10−3 Sv peaking in the middle of March. Additionally, an increase of the Gibraltar net inflow (3.4 ± 0.8 × 10−3 Sv/yr) is detected. 相似文献
7.
The inter-annual variability of the sea surface temperature (SST) was analyzed along the western Iberian Peninsula in the region ranging from 9.5 °W to 21.5 °W and from 37.5 °N to 42.5 °N with a spatial resolution of 1°×1° from 1900 to 2008. Both coastal and oceanic SST showed an overall increase with warming and cooling cycles similar to those observed in the North Atlantic region and in previous regional studies. In addition, the evolution of coastal and ocean water has been observed to be different. In general, ocean water is more affected by the different warming–cooling cycles than coastal water. In spite of coast and ocean are highly influenced by global changes affecting the whole North Atlantic region, near shore SST has been observed to be correlated with local wind regime, which is itself a manifestation of the Eastern Atlantic (EA) teleconnection pattern. 相似文献
8.
Oscillatory modes with the period of approximately 7–8 yr were detected in monthly time series of sunspot numbers, geomagnetic activity aa index, NAO (North Atlantic Oscillation) index and near-surface air temperature from several mid-latitude European locations. Instantaneous phases of the modes underwent synchronization analysis and their statistically significant phase coherence, beginning from 1950s, has been observed. Thus the statistical evidence for a coupling between solar/geomagnetic activity and climate variability has been obtained from continuous monthly data, independent of the season, however, confined to the temporal scale related to oscillatory periods about 7–8 yr. 相似文献
9.
Meltwater from the Greenland Ice Sheet (GIS) has been a major contributor to sea level change in the recent past. Global and regional sea level variations caused by melting of the GIS are investigated with the finite element sea-ice ocean model (FESOM). We consider changes of local density (steric effects), mass inflow into the ocean, redistribution of mass, and gravitational effects. Five melting scenarios are simulated, where mass losses of 100, 200, 500, and 1000 Gt/yr are converted to a continuous volume flux that is homogeneously distributed along the coast of Greenland south of 75°N. In addition, a scenario of regional melt rates is calculated from daily ice melt characteristics. The global mean sea level modeled with FESOM increases by about 0.3 mm/yr if 100 Gt/yr of ice melts, which includes eustatic and steric sea level change. In the global mean the steric contribution is one order of magnitude smaller than the eustatic contribution. Regionally, especially in the North Atlantic, the steric contribution leads to strong deviations from the global mean sea level change. The modeled pattern mainly reflects the structure of temperature and salinity change in the upper ocean. Additionally, small steric variations occur due to local variability in the heat exchange between the atmosphere and the ocean. The mass loss has also affects on the gravitational attraction by the ice sheet, causing spatially varying sea level change mainly near the GIS, but also at greater distances. This effect is accounted for by using Green's functions. 相似文献
10.
Estimation of ocean circulation is investigated via assimilation of satellite measurements of the dynamic ocean topography (DOT) into the global finite-element ocean model (FEOM). The DOT was obtained by means of a geodetic approach from carefully cross-calibrated multi-mission altimeter data and GRACE gravity fields. The spectral consistency was achieved by consistently filtering both, the sea surface and the geoid. The filter length is determined by the spatial resolution of the gravity field and corresponds to approximately 241 km half width for the GRACE-based gravity field model ITG-Grace03s.The assimilation of the geodetic DOT was performed by employing a local singular evolutive interpolated Kalman (SEIK) filter in combination with the method of weighting of observations. It is shown that this approach leads to a successful assimilation technique that reduced the RMS difference between the model and the data from 16 cm to 5 cm during one year of assimilation. The ocean model returns an optimized mean dynamic ocean topography. The effects of assimilation on transport estimates across several hydrographic World Ocean Circulation Experiment (WOCE) sections show improvements compared to the FEOM run without data assimilation. As a result of the assimilation, DOT estimates are available in the polar or coastal regions where the geodetic estimates from satellite data alone are not adequate. Furthermore, more realistic features of the ocean can be seen in these areas compared to those obtained using the filtered data fields. 相似文献
11.
We present sea level observations derived from the analysis of signal-to-noise ratio (SNR) data recorded by five coastal GPS stations. These stations are located in different regions around the world, both in the northern and in the southern hemisphere, in different multipath environments, from rural coastal areas to busy harbors, and experience different tidal ranges.The recorded SNR data show periodic variations that originate from multipath, i.e. the interference of direct and reflected signals. The general assumption is that for satellite arcs facing the open sea, the rapid SNR variations are due to reflections off the sea surface. The SNR data recorded from these azimuth intervals were analyzed by spectral analysis with two methods: a standard analysis method assuming a static sea level during a satellite arc and an extended analysis method assuming a time dependent sea level during a satellite arc.The GPS-derived sea level results are compared to sea level records from co-located traditional tide gauges, both in the time and in the frequency domain. The sea level time series are highly correlated with correlation coefficients to the order of 0.89–0.99. The root-mean-square (RMS) difference is 6.2 cm for the station with the lowest tidal range of 165 cm and 43 cm for the station with the highest tidal range of 772 cm. The relative accuracy, defined as the ratio of RMS and tidal range, is between 2.4% and 10.0% for all stations.Comparing the standard analysis method and the extended analysis method, the results based on the extended analysis method agree better with the independent tide gauge records for the stations with a high tidal range. For the station with the highest tidal range (772 cm), the RMS is reduced by 47% when using the extended analysis method. Furthermore, the results also indicate that the standard analysis method, assuming a static sea level, can be used for stations with a tidal range of up to about 270 cm, without performing significantly worse than the extended analysis method.Tidal amplitudes and phases are derived by harmonic analysis of the sea level records. Again, a high level of agreement is observed between the tide gauge and the GPS-derived results. Comparing the GPS-derived results, the results based on the extended analysis method show a higher degree of agreement with the traditional tide gauge results for stations with larger tidal ranges. Spectral analysis of the residuals after the harmonic analysis reveals remaining signal power at multiples of the draconitic day. This indicates that the observed SNR data are to some level disturbed by additional multipath signals, in particular for GPS stations that are located in harbors. 相似文献
12.
《Journal of Geodynamics》2009,47(3-5):182-193
A new method to estimate the vertical crustal motion from satellite altimetry over land was developed. The method was tested around Hudson Bay, where the observed vertical motion is largely caused by the incomplete glacial isostatic adjustment (GIA) as a result of the Laurentide ice sheet deglaciation since the last glacial maximum (LGM). Decadal (1992–2003) TOPEX/POSEIDON radar altimetry data over land surfaces were used. The results presented here are improved compared to a previous study (Lee, H., Shum, C.K., Kuo, C.Y., Yi, Y., Braun, A., 2008. Application of TOPEX altimetry for solid Earth deformation studies. Terr. Atmos. Ocean. Sci. 19, 37–46. doi:10.3319/TAO.2008.19.1-2.37(SA).) which estimated vertical motion only over relatively flat land surfaces (standard deviation of the height variation <40 cm). In this study, we extended the concept of traditional 1-Hz (one-per-frame) radar altimeter ocean stackfiles to build 10-Hz (10-per-frame) land stackfiles over Hudson Bay land regions, and succeeded in obtaining vertical motion estimates over much rougher surfaces (standard deviation of the height variation <2 m). 90-m C-band Shuttle Radar Topography Mission (SRTM) Digital Elevation Model (DEM) is used as a reference surface to select an optimal waveform retracker, to correct surface gradient errors, and to calculate land surface anomalies. Here, we developed an alternative retracker, called the modified threshold retracker, resulting in decadal vertical motion time series over a 1500 km by 1000 km region covering northern Ontario, northeastern Manitoba, and the Great Lakes region which is at the margin of the former Laurentide ice sheet. The average of the estimated uncertainties for the vertical motion is 2.9 mm/year which is comparable to 2.1 mm/year of recent GPS solutions. The estimated vertical motion is compared with other geodetic observations from GPS, tide gauge/altimetry, GRACE, and several GIA models. The data agree best with the laterally varying 3D GIA model, RF3S20 (β = 0.4) whereas the combination of land altimetry solution with other measurements match best with the models RF3S20 (β = 0.0) or RF3S20 (β = 0.2) in terms of mean and standard deviation of the differences. It is anticipated that this innovative technique could potentially be used to provide additional constraints for GIA model improvement, and be applied to other geodynamics studies. 相似文献
13.
An analysis of the climate change signal for seasonal temperature and precipitation over the Northern Adriatic region is presented here. We collected 43 regional climate simulations covering the target area, including experiments produced in the context of the PRUDENCE and ENSEMBLES projects, and additional experiments produced by the Swedish Meteorological and Hydrological Institute. The ability of the models to simulate the present climate in terms of mean and interannual variability is discussed and the insufficient reproduction of some features, such as the intensity of summer precipitation, are shown. The contribution to the variance associated with the intermodel spread is computed. The changes of mean and interannual variability are analyzed for the period 2071–2100 in the PRUDENCE runs (A2 scenario) and the periods 2021–2050 and 2071–2100 (A1B scenario) for the other runs. Ensemble results show a major warming at the end of the 21st century. Warming will be larger in the A2 scenario (about 5.5 K in summer and 4 K in winter) than in the A1B. Precipitation is projected to increase in winter and decrease in summer by 20% (+0.5 mm/day and −1 mm/day over the Alps, respectively). The climate change signal for scenario A1B in the period 2021–2050 is significant for temperature, but not yet for precipitation. In summer, interannual variability is projected to increase for temperature and for precipitation. Winter interannual variability change is different among scenarios. A reduction of precipitation is found for A2, while for A1B a reduction of temperature interannual variability is observed. 相似文献
14.
The paper is focused on the global spatial structure, seasonal and interannual variability of the ～5-day Rossby (W1) and ～6-day Kelvin (E1) waves derived from the SABER/TIMED temperature measurements for 6 full years (January 2002–December 2007). The latitude structure of the ～5-day W1 wave is related to the gravest symmetric wave number 1 Rossby wave. The vertical structure of the ～5-day Rossby wave amplitude consists of double-peaked maxima centred at ～80–90 km and ～105–110 km. This wave has a vertically propagating phase structure from the stratosphere up to 120 km altitude with a mean vertical wavelength of ～50–60 km. The ～6-day E1 wave is an equatorially trapped wave symmetric about the equator and located between 20°N and 20°S. Its seasonal behaviour indicates some equinoctial and June solstice amplifications, while the vertical phase structure indicates that this is a vertically propagating wave between 20–100 km altitudes with a mean vertical wavelength of ～25 km. 相似文献
15.
Sea-Level Rise from the Late 19th to the Early 21st Century 总被引：9，自引：1，他引：8
We estimate the rise in global average sea level from satellite altimeter data for 1993?C2009 and from coastal and island sea-level measurements from 1880 to 2009. For 1993?C2009 and after correcting for glacial isostatic adjustment, the estimated rate of rise is 3.2 ± 0.4 mm year?1 from the satellite data and 2.8 ± 0.8 mm year?1 from the in situ data. The global average sea-level rise from 1880 to 2009 is about 210 mm. The linear trend from 1900 to 2009 is 1.7 ± 0.2 mm year?1 and since 1961 is 1.9 ± 0.4 mm year?1. There is considerable variability in the rate of rise during the twentieth century but there has been a statistically significant acceleration since 1880 and 1900 of 0.009 ± 0.003 mm year?2 and 0.009 ± 0.004 mm year?2, respectively. Since the start of the altimeter record in 1993, global average sea level rose at a rate near the upper end of the sea level projections of the Intergovernmental Panel on Climate Change??s Third and Fourth Assessment Reports. However, the reconstruction indicates there was little net change in sea level from 1990 to 1993, most likely as a result of the volcanic eruption of Mount Pinatubo in 1991. 相似文献
16.
This study examines the recent evolution of the Greenland ice sheet and its six major drainage basins. Based on laser altimetry data acquired by the Ice, Cloud and Land Elevation Satellite (ICESat), covering the period September–November 2003 to February–March 2008, ice surface height changes and their temporal variations were inferred. Our refined repeat track analysis is solely based on ICESat data and is independent of external elevation models, since it accounts for both ice height changes and the local topography. From the high resolution ice height change pattern we infer an overall mean surface height trend of −0.12 ± 0.006 m yr−1. Furthermore, the largest changes could be identified at coastal margins of the ice sheet, exhibiting rates of more than −2 m yr−1. The total ice volume change of the entire ice sheet amounts to −205.4 ± 10.6 km3 yr−1. In addition, we assessed mass changes from 78 monthly Gravity Recovery and Climate Experiment (GRACE) solutions. The Release-04 gravity field solutions of GeoForschungsZentrum Potsdam cover the period between August 2002 and June 2009. We applied an adjusted regional integration approach in order to minimize the leakage effects. Attention was paid to an optimized filtering which reduces error effects from different sources. The overall error assessment accounts for GRACE errors as well as for errors due to imperfect model reductions. In particular, errors caused by uncertainties in the glacial isostatic adjustment models could be identified as the largest source of errors. Finally, we determined both seasonal and long-term mass change rates. The latter amounts to an overall ice mass change of −191.2 ± 20.9 Gt yr−1 corresponding to 0.53 ± 0.06 mm yr−1 equivalent eustatic sea level rise. From the combination of the volume and mass change estimates we determined a mean density of the lost mass to be 930 ± 11 kg m−3. This value supports our applied density assumption 900 ± 30 kg m−3 which was used to perform the volume–mass-conversion of our ICESat results. Hence, mass change estimates from two independent observation techniques were inferred and are generally in good agreement. 相似文献
17.
Pascal Lazure Valérie Garnier Franck Dumas Christelle Herry Marina Chifflet 《Continental Shelf Research》2009,29(8):985-997
The hydrology of the Bay of Biscay was investigated using the regional ocean model MARS3D (Model for Application at Regional Scale). The simulated hydrology is compared to a set of various data encompassing monthly climatology, remote sensing SST, CTD casts, and coastal salinity measurements. Special focus was put on the validation over the continental shelf. This paper reports that despite some misfits, the climatological hydrology and its seasonal variability are correctly simulated. Various statistics computed over the period from 1999–2004 highlight different aspects of the hydrology. The biases and root mean square errors (RMSE) remain very weak at all depths when comparing salinity (<0.1 and <0.6 psu respectively). The predicted temperature shows a global overestimation of temperature (bias of around 0.8 °C) and the maximum errors are located near the thermocline (rmse of 1 °C at 20–40 m). The model is shown to properly reproduce the annual dynamics of sea surface temperature, as well as the dynamics of large river plumes observed by high frequency time series from coastal salinity gauges. The misfits highlighted by these various comparisons between model and observations are attributed to heat fluxes and mixing parameterisation. 相似文献
18.
In this study, the Navidad current, which flows along the northern coast of Spain in winter, is observed and characterized
using coastal altimetry data over the period 1992–2002. This coastal current, marked by a strong interannual variability,
is associated with eastward transport of warm waters along the shelf slope. Specific data editing and processing strategies
have been applied to the along-track altimeter data, which allows us to retrieve altimetric sea level anomalies closer to
the coast, with a better spatial coverage and improved quality when compared with standard altimetric products. The current
variability observed upstream by in situ time series after November 1996 is well reproduced by the satellite across-track
surface geostrophic current anomalies up until September 1999; this agreement degrades later in time. The combined use of
satellite-derived current anomalies and sea-surface temperature anomalies allows us to develop indices of Navidad occurrences,
in the first long-term, systematic survey of that current based on a multi-sensor approach. The satellite analyses confirm
the previously identified Navidad occurrences in winter of 1995–1996, 1997–1998, and 2000–2001. Furthermore, a weak Navidad
event was identified in winter 1996–1997. These four winters are associated with a negative North Atlantic Oscillation index
in the previous fall, but the intensity of the Navidad is not correlated to the amplitude of that index. 相似文献
19.
The long-term variability of sea level and surface flows in the Gulf of Mexico (GOM) is studied using global monthly sea level reconstruction (RecSL) for 1900–2015. The study explored the long-term relation between the dynamics of the GOM and inflows/outflows through the Yucatan Channel (YC) and the Florida Straits (FS). The results show a century-long trend of increased mean velocity and variability in the Loop Current (LC); however, no significant upward trend was found in the YC and FS flows, only increased variability. Empirical orthogonal function (EOF) analysis of sea surface height found spatial patterns dominated by variations in the LC and temporal variations on time scales ranging from a few months to multidecadal. The time evolution of each EOF mode of sea level is correlated with the velocity of either the LC, the YC, or the FS or some combination of the different flows. The mean sea level difference between the GOM and the northwestern Caribbean Sea was found to be influenced by the North Atlantic Oscillation (NAO), with unusually high differences during the 1970s when the NAO index was low and the Atlantic Ocean circulation was weak. Extreme peaks in SL difference coincide with the extension of the LC and the seasonal eddy shedding pattern. The observed seasonal cycle in the extension area of the LC as obtained from 20 years of altimeter data is significantly correlated (R = 0.63; confidence level = 98%) with the seasonal YC flow obtained from 116 years of the RecSL data. However, the same LC extension record had lower correlation (R = 0.45; confidence level = 90%) with the observed YC transport obtained from direct moored measurements over ~ 5 years, indicating the need for much longer measurements, since the LC extension and the YC flow are strongly affected by interannual and decadal variations. The study demonstrates the usefulness of even a coarse-resolution reconstruction for studies of regional ocean variability and climate change over longer time scales than current direct observations allow.
相似文献20.
《Continental Shelf Research》2006,26(17-18):2050-2072
A 5-yr data set of near-bed current and suspended-sediment concentration measured within 2 m of the seabed in 60-m water depth has been analyzed to evaluate the interannual variability of physical processes and sediment transport events on the Eel River continental shelf, northern California. This data set encompasses a wide range of shelf conditions with winter events characterized as: Major Flood (1996/97), strong El Niño (1997/98), strong La Niña (1998/99), and Major Storm (1999/00). Data were collected at a site located 25 km north of the Eel River mouth, on the landward edge of the mid-shelf mud deposit. During the winter months sediment resuspension is forced primarily by near-bed oscillatory flows, and sediment transport occurs both as suspended load and as gravity-driven (fluid-mud) flows. Winter conditions that caused periods of increased sediment transport existed on average for 142 d yr−1 over the total record, ranging between 89 d in the Major Flood year (1996/97) and 171 d in the La Niña year (1998/99). Hourly averaged values of significant wave height varied between 0.5 and 10.7 m and hourly averaged values of near-bed orbital velocities ranged between 0 and 125 cm s−1. During the five winters, sediment threshold conditions were exceeded an average of 35% of the time, ranging from 19% in the Major Flood year (1996/97) to 52% in the La Niña year (1998/99). Mean concentration of suspended sediment, measured at 30 cmab, ranged from values close to 0–8 g l−1. Among winters, major sediment flux events exhibited different patterns due to varying combinations of physical processes including river floods, waves, and shelf circulation. Within winters, the major period of sediment flux varied from a 3-d fluid mud event (Major Flood winter) to a 50-d period of persistent southerlies (El Niño winter) and a winter of continuous storm cycles (La Niña winter). Winter-averaged suspended-sediment concentration appeared to vary in response to river discharge, while total sediment flux responded to storm intensity. The net sediment flux appeared to depend on timing of river discharge and shelf conditions. On the Eel River shelf, the mid-shelf mud deposit apparently is not emplaced by deposition from the river plume, but by secondary processes from the inner shelf including off-shelf transport of sediment suspensions and gravity-driven fluid-mud flows. Thus, these inner-shelf processes redistribute sediment supplied by the Eel River (a point source) making the inner shelf a line source of sediment that forms and nourishes the mid-shelf deposit. Large-scale shelf circulation patterns and interannual variability of the physical forcing are also important in determining the locus of the mid-shelf deposit, and both are influenced by climate variations. Post-depositional alteration of the deposit also depends on the subsequent shelf conditions following major floods. 相似文献