摘要:

AbstractThe large‐scale boreal winter climatic patterns associated with interannual variability in a coral oxygen isotope (δ18O) record from the southern Red Sea covering most of the last century are investigated. From the early 1930s to the early 1960s, the winter coral δ18O record, reflecting temperature and salinity variations in southern Red Sea surface waters, is associated with global (or large scale) sea surface temperature (SST) and 850 mb geopotential height (Z850) anomalies which project on the corresponding patterns associated with the El Niño‐Southern Oscillation (ENSO). In contrast, since the early 1960s the winter coral δ18O record is related to a Z850 pattern that reflects the ENSO‐independent part of the East Asian Winter Monsoon (EAWM), which includes the Siberian High, the East Asian through, and the East Asian upper‐tropospheric Jet. Our results indicate a weakening of the ENSO control on interannual temperature/salinity variations in southern Red Sea surface waters in the early 1960s, due to the warming of the Indian Ocean, and suggest that information about the nonstationarity in the relationship between ENSO and two distinct modes of EAWM can be documented in southern Red Sea coral

ISSN:0148-0227    

DOI:10.1002/2013JC009203

年代:2014

数据来源: WILEY

摘要:

AbstractMeasurements were collected on a shallow estuarine mudflat in northern San Francisco Bay to examine the physical processes controlling waves, turbulence, sediment resuspension, and their interactions. Tides alone forced weak to moderate currents of 10–30 cm s−1in depths of 0–3 m, and maintained a background suspension of 30–50 mg L−1of fine sediment. In the presence of wind waves, bottom orbital velocities spanned 20–30 cm s−1, suspended‐sediment concentrations (SSC) at 15 and 30 cm above the bed (cmab) increased by 1–2 orders of magnitude, and vertical gradients in SSC were strong enough to produce turbulence‐limiting stratification, with gradient Richardson numbers exceeding 0.25. Simultaneously, turbulent stresses (decomposed from wave motions) increased by an order of magnitude. The apparent contradiction of energetic turbulence in the presence of strong stratification was reconciled by considering the turbulent kinetic energy (TKE) budget: in general, dissipation and buoyancy flux were balanced by local shear production, and each of these terms increased during wave events. The classic wave‐current boundary layer model represented the observations qualitatively, but not quantitatively since the velocity profile could not be approximated as logarithmic. Rather, the mean shear was elevated by the Stokes drift return flow and wind‐generated surface stress, which diffused sediment upward and limited stratification. Our findings highlight a pathway for waves to supply energy to both the production and destruction of turbulence, and demonstrate that in such shallow depths, TKE and SSC can be elevated over more of the water column than predicte

ISSN:0148-0227    

DOI:10.1002/2013JC009477

年代:2014

数据来源: WILEY

摘要:

AbstractTopographically generated eddies and internal waves have traditionally been studied separately even though bathymetry that creates both phenomena is abundant in coastal regions. Here a numerical model is used to understand the dynamics of eddy and wave generation as tidal currents flow past Three Tree Point, a 1 km long, 200 m deep, sloping headland in Puget Sound, WA. Bottom pressure anomalies due to vertical perturbations of the sea surface and isopycnals are used to calculate form drag in different regions of the topography to assess the relative importance of eddies versus internal waves. In regions where internal waves dominate, sea surface and isopycnal perturbations tend to work together to create drag, whereas in regions dominated by eddies, sea surface, and isopycnal perturbations tend to counteract each other. Both phenomena are found to produce similar amounts of form drag even though the bottom pressure anomalies from the eddy have much larger magnitudes than those created by the internal waves. Topography like Three Tree Point is common in high latitude, coastal regions, and therefore the findings here have implications for understanding how coastal topography removes energy from tidal currents.

ISSN:0148-0227    

DOI:10.1002/2013JC009757

年代:2014

数据来源: WILEY

摘要:

AbstractWe investigate how well methods based on empirical orthogonal functions (EOFs) can reconstruct global mean sea level (GMSL). We first explore the analytical solution of the method and then perform a series of numerical experiments using modeled data. In addition, we present a new GMSL reconstruction for the period 1900–2011 computed both with and without a spatially uniform EOF (EOF0). The method without the EOF0 uses global information, which leads to a better reconstruction of the variability, though with some underestimation. The trend, however, is not captured, which motivates the use of the EOF0. When the EOF0 is used the method reduces to the generalized weighted mean with regularization of altimetry records at tide‐gauge locations, and thus it uses no global information. This results in a poor reconstruction of the variability. Although the trend is better captured (biases smaller than ±25%) with the EOF0, using the covariance matrix of deseasonalized monthly time series as the basis for determining the contribution of each tide gauge to the trend is dubious because it assumes that the interannual variability and the trend are driven by the same mechanisms. A significant fraction of the interannual to decadal variability (∼4 mm peak‐to‐peak and ∼2 mm standard error) in the new GMSL reconstruction without the EOF0 is consistent with land hydrology changes associated with the El Niño‐Southern Oscillation (ENSO). When the EOF0 is used, we find no correlation with either the ENSO or land hydrology changes, and decadal fluctuations are

ISSN:0148-0227    

DOI:10.1002/2013JC009298

年代:2014

数据来源: WILEY

摘要:

AbstractHourly sea level records from 1954 to 2012 at 20 tide gauges at and adjacent to the Chinese coasts are used to analyze extremes in sea level and in tidal residual. Tides and tropical cyclones determine the spatial distribution of sea level maxima. Tidal residual maxima are predominantly determined by tropical cyclones. The 50 year return level is found to be sensitive to the number of extreme events used in the estimation. This is caused by the small number of tropical cyclone events happening each year which lead to other local storm events included thus significantly affecting the estimates. Significant increase in sea level extremes is found with trends in the range between 2.0 and 14.1 mm yr−1. The trends are primarily driven by changes in median sea level but also linked with increases in tidal amplitudes at three stations. Tropical cyclones cause significant interannual variations in the extremes. The interannual variability in the sea level extremes is also influenced by the changes in median sea level at the north and by the 18.6 year nodal cycle at the South China Sea. Neither of PDO and ENSO is found to be an indicator of changes in the size of extremes, but ENSO appears to regulate the number of tropical cyclones that reach the Chinese coasts. Global mean atmospheric temperature appears to be a good descriptor of the interannual variability of tidal residual extremes induced by tropical cyclones but the trend in global temperature is inconsistent with the lack of trend in the residual

ISSN:0148-0227    

DOI:10.1002/2013JC009607

年代:2014

数据来源: WILEY

摘要:

AbstractFrom October 2008 to November 2010, CH3I concentrations were measured in the Kiel Fjord together with potentially related biogeochemical and physical parameters. A repeating seasonal cycle of CH3I was observed with highest concentrations in summer (ca. 8.3 pmol L−1; June and July) and lowest concentrations in winter (ca. 1.5 pmol L−1; December to February). A strong positive correlation at zero lag between [CH3I] and solar radiation (R2 = 0.93) was observed, whereas correlations with other variables (SST, Chlorophylla) were weaker, and they lagged CH3I by ca. 1 month. These results appear consistent with the hypothesis that SSR is the primary forcing of CH3I production in surface seawater, possibly through a photochemical pathway. A mass balance of the monthly averaged data was used to infer mean rates of daily net production (Pnet) and losses for CH3I over the year. The sea‐to‐air flux of CH3I in the Kiel Fjord averaged 3.1 nmol m−2d−1, the mean chemical loss rate was 0.047 pmol L−1d−1, and Pnetvaried systematically from winter to summer (from 0 to 0.6 pmol L−1d−1). Pnetwas correlated at zero lag with SST, SSR, and Chla(R2 = 0.55, 0.67, and 0.73, respectively, p<<0.01). The lagged cross‐correlation analysis indicated that SSR led Pnetby 1 month, whereas the strongest cross correlations with Chlawere at lags of 0 to +1 month, and SST lagged Pnetby 1 month. The broad seasonal peak of Pnetmakes it difficult to determine the key factor controlling CH3I net production using in

ISSN:0148-0227    

DOI:10.1002/2013JC009328

年代:2014

数据来源: WILEY

摘要:

AbstractNew mechanisms for stratification and upwelling in the southern Great Barrier Reef (GBR) are identified, and dynamic details of Capricorn Eddy, a transient feature located off the shelf at the southern extremity of the GBR, are revealed using the newly available surface current from High Frequency (HF) radar combined with other remote sensing and mooring data. The HF radar surface currents were used for tidal harmonic analysis and current‐wind correlation analysis. These analyses, combined with Sea Surface Temperature (SST) data, mooring data, and altimetry‐based geostrophic currents, enabled the effects of forcing from the large‐scale oceanic currents (including the East Australian Current (EAC)), wind, and tides in a topographically complex flow regime to be separately identified. Within the indentation region where the width of the shelf abruptly narrows, current is strongly coupled with the EAC. Here strong residual flows, identified on current maps and SST images, fall into three patterns: southward flow, northwestward flow, and an eddy. Multiple data sets shed light on the prerequisite for the formation of the eddy, the reasons for its geometric variation, and its evolution with time. Intrusions of the eddy onto the shelf result in stratification characterized by a significant increase of surface temperature. Upwelling driven by wind or oceanic inflow is shown to cause stratification of previously well‐mixed shelf water. The upwelling appears to be associated with equatorward‐traveling coastal‐trapped waves. The integrative method of analysis embodied here is applicable to other coastal regions with complex

ISSN:0148-0227    

DOI:10.1002/2013JC009397

年代:2014

数据来源: WILEY

摘要:

AbstractThe deep water formation in the Labrador Sea is simulated with the Finite‐Element Sea‐Ice Ocean Model (FESOM) in a regionally focused, but globally covered model setup. The model has a regional resolution of up to 7 km, and the simulations cover the time period 1958–2009. We evaluate the capability of the model setup to reproduce a realistic deep water formation in the Labrador Sea. Two classes of modeled Labrador Sea Water (LSW), the lighter upper LSW (uLSW) and the denser deep LSW (dLSW), are analyzed. Their layer thicknesses are compared to uLSW and dLSW layer thicknesses derived from observations in the formation region for the time interval 1988–2009. The results indicate a suitable agreement between the modeled and observational derived uLSW and dLSW layer thicknesses except for the period 2003–2007 where deviations in the modeled and observational derived layer thicknesses could be linked to discrepancies in the atmospheric forcing of the model. It is shown that the model is able to reproduce four phases in the temporal evolution of the potential density, temperature, and salinity, since the late 1980s, which are known in observational data. These four phases are characterized by a significantly different LSW formation. The first phase from 1988 to 1990 is characterized in the model by a fast increase in the convection depth of up to 2000 m, accompanied by an increased spring production of deep Labrador Sea Water (dLSW). In the second phase (1991–1994), the dLSW layer thickness remains on a high level for several years, while the third phase (1995–1998) features a gradual decrease in the deep ventilation and the renewal of the deep ocean layers. The fourth phase from 1999 to 2009 is characterized by a slowly continuing decrease of the dLSW layer thickness on a deeper depth level. By applying a composite map analysis between an index of dLSW and sea level pressure over the entire simulation period from 1958 to 2009, it is shown that a pattern which resembles the structure of the North Atlantic Oscillation (NAO) is one of the main triggers for the variability of LSW formation. Our model results indicate that the process of dLSW formation can act as a low‐pass filter to the atmospheric forcing, so that only persistent NAO events have an effect, whether uLSW or dLSW is formed. Based on composite maps of the thermal and haline contributions to the surface density flux we can demonstrate that the central Labrador Sea in the model is dominated by the thermal contributions of the surface density flux, while the haline contributions are stronger over the branch of the Labrador Sea boundary current system (LSBCS), where they are dominated by the haline contributions of sea ice melting and formation. Our model results feature a shielding of the central Labrador Sea from the haline contributions by the LSBCS, which only allows a minor haline interaction with the central Labrador Sea by lateral mixing. Based on the comparison of the simulated and measured LSW layer thicknesses as well as vertical profiles of potential density, temperature, and salinity it is shown that the FESOM model is a suitable tool to study the regional dynamics of LSW formation and its impact on a global, not regional re

ISSN:0148-0227    

DOI:10.1002/2013JC009232

年代:2014

数据来源: WILEY

摘要:

AbstractThe present work investigates the structure of the near‐bed flow below irregular surfzone breaking waves inducing light‐weight sheet flow particle transport. The experiments are carried out in the LEGI flume under steady equilibrium conditions between the wave forcing and the underlying bed morphology. Synchronized ACVP and video images provide detailed information about the mean wave and current characteristics and the coupled flow regimes across the entire wave breaking region including the outer and the inner surfzones. An analysis of the impact of breaking eddies in the Wave Boundary Layer (WBL) is undertaken at the beginning of the inner surfzone. Subsequently, the intrawave variation of several contributions of the total shearing force per unit area and the net values of the Reynolds stress related to phase‐averaged velocities are analyzed. It is found that−ρu∼w∼is the dominant term. The turbulent Reynolds stress, the low frequency, and the mean terms are at least 1 order of magnitude lower. Due to the irregular wave forcing, the net values are separated into the net wave‐by‐wave Reynolds stress and the wave Reynolds stress averaged over the entire irregular wave sequence. All these measured bed shear stress terms are then compared to estimations obtained with two different parameterized models in order to evaluate their prediction performances. The values of the model parameters are discussed in comparison to those found in the literature. Finally, the vertical profile of net Reynolds shear stress exhibits a nearly constant value across the

ISSN:0148-0227    

DOI:10.1002/2013JC009338

年代:2014

数据来源: WILEY

摘要:

AbstractThe distribution and thickness of sea ice in the Arctic is changing rapidly, resulting in changes to Arctic marine ecosystems. Seabirds are widely regarded as indicators of marine environmental change, and understanding their distribution patterns can serve as a tool to monitor and elucidate biological changes in the Arctic seas. We examined the at‐sea distribution of seabirds in the North American Arctic in July and August, 2007–2012, and marine areas of high density were identified based on bird densities for four foraging guilds. Short‐tailed shearwaters (Puffinus tenuirostris) were the most abundant species observed. Northern fulmars (Fulmarus glacialis), thick‐billed murres (Uria lomvia), and dovekies (Alle alle) were also sighted in large numbers. Few birds were sighted between Dolphin and Union Strait and King William Island. Areas of high density over multiple years were found throughout the entire western portion of the study area (Bering Sea, Bering Strait, and Chukchi Sea), Lancaster Sound, Baffin Bay, Davis Strait, and the low Arctic waters off Newfoundland. These waters are characterized by high primary productivity. This study is the first to document the marine distribution of seabirds across the entire North American Arctic within the same time period, providing a critical baseline for monitoring the distribution and abundance of Arctic seabirds in a changing Arctic s

ISSN:0148-0227    

DOI:10.1002/2013JC009198

年代:2014

数据来源: WILEY