两种测高重力异常反演海底地形方法比较

针对基于测高重力异常反演海底地形理论众多、选取标准无法确定的情况,利用中国南海海域内的测高重力异常和船测水深数据研究比较了重力地质法(GGM)和SmithSandwell (SAS)法两种精度高、计算速度相对较快的海底地形反演理论。其中,GGM方法的密度差异常数Δρ由向下延拓技术确定为2.15 g·cm-3,SAS方法采用移去-恢复技术得到反演波段内重力异常和水深数据。结果表明:测线分布条件一定时,水深多在-1 000 m左右或反演区域岛礁、海山等复杂海底地形较多时选取SAS方法,水深主要在-3 000 m以深的区域或海底地形复杂程度不高时选取GGM方法则能获取更好的效果,其效果最优处与船测水深在检核点处的差值最优平均值能达-0.61 m,标准差可达14.67 m。     

Crustal analysis of the Ulleung Basin in the East Sea (Japan Sea) from enhanced gravity mapping

To facilitate geological analyses of the Ulleung Basin in the East Sea (Japan Sea) between Korea and Japan, shipborne and satellite altimetry-derived gravity data are combined to derive a regionally coherent anomaly field. The 2-min gridded satellite altimetry-based gravity predicted by Sandwell and Smith [Sandwell DT, Smith WHF (1997) J Geophys Res 102(B5):10,039–10,054] are used for making cross-over adjustments that reduce the errors between track segments and at the cross-over points of shipborne gravity profiles. Relative to the regionally more homogeneous satellite gravity anomalies, the longer wavelength components of the shipborne anomalies are significantly improved with minimal distortion of their shorter wavelength components. The resulting free-air gravity anomaly map yields a more coherent integration of short and long wavelength anomalies compared to that obtained from either the shipborne or satellite data sets separately. The derived free-air anomalies range over about 140 mGals or more in amplitude and regionally correspond with bathymetric undulations in the Ulleung Basin. The gravity lows and highs along the basin’s margin indicate the transition from continental to oceanic crust. However, in the northeastern and central Ulleung Basin, the negative regional correlation between the central gravity high and bathymetric low suggests the presence of shallow denser mantle beneath thinned oceanic crust. A series of gravity highs mark seamounts or volcanic terranes from the Korean Plateau to Oki Island. Gravity modeling suggests underplating by mafic igneous rocks of the northwestern margin of the Ulleung Basin and the transition between continental and oceanic crust. The crust of the central Ulleung Basin is about a 14–15 km thick with a 4–5 km thick sediment cover. It may also include a relatively weakly developed buried fossil spreading ridge with approximately 2 km of relief.     

Crustal structure and tectonic provinces of the Riiser-Larsen Sea area (East Antarctica): results of geophysical studies

About 16,000 km of multichannel seismic (MCS), gravity and magnetic data and 28 sonobuoys were acquired in the Riiser-Larsen Sea Basin and across the Gunnerus and Astrid Ridges, to study their crustal structure. The study area has contrasting basement morphologies and crustal thicknesses. The crust ranges in thickness from about 35 km under the Riiser-Larsen Sea shelf, 26–28 km under the Gunnerus Ridge, 12–17 km under the Astrid Ridge, and 9.5–10 km under the deep-water basin. A 50-km-wide block with increased density and magnetization is modeled from potential field data in the upper crust of the inshore zone and is interpreted as associated with emplacement of mafic intrusions into the continental margin of the southern Riiser-Larsen Sea. In addition to previously mapped seafloor spreading magnetic anomalies in the western Riiser-Larsen Sea, a linear succession from M2 to M16 is identified in the eastern Riiser-Larsen Sea. In the southwestern Riiser-Larsen Sea, a symmetric succession from M24B to 24n with the central anomaly M23 is recognized. This succession is obliquely truncated by younger lineation M22–M22n. It is proposed that seafloor spreading stopped at about M23 time and reoriented to the M22 opening direction. The seismic stratigraphy model of the Riiser-Larsen Sea includes five reflecting horizons that bound six seismic units. Ages of seismic units are determined from onlap geometry to magnetically dated oceanic basement and from tracing horizons to other parts of the southern Indian Ocean. The seaward edge of stretched and attenuated continental crust in the southern Riiser-Larsen Sea and the landward edge of unequivocal oceanic crust are mapped based on structural and geophysical characteristics. In the eastern Riiser-Larsen Sea the boundary between oceanic and stretched continental crust is better defined and is interpreted as a strike-slip fault lying along a sheared margin.     

New heat flow measurements in the Ulleung Basin, East Sea (Sea of Japan): relationship to local BSR depth, and implications for regional heat flow distribution

In July 2007, new marine heat flow data were collected at ten sites (HF01–10) in the central and southwestern sectors of the Ulleung Basin (East Sea or Sea of Japan) as part of regional gas hydrate research. In addition, cores were collected at five of these sites for laboratory analysis. The results show that the geothermal gradient ranged from 103–137 mK/m, and the in-situ thermal conductivity from 0.82–0.95 W/m·K. Laboratory measurements of thermal conductivity were found to deviate by as much as 40% from the in-situ measurements, despite the precautions taken to preserve the cores. Based on the in-situ conductivity, the heat flow was found to increase with water depth toward the center of the basin, ranging from 84–130 mW/m². Using a simple model, we estimated the heat flow from the depths of the BSR, and compared this with the observed heat flow. In our study area, the two sets of values were quite consistent, the observed heat flows being slightly higher than the BSR-derived ones. The evaluation of regional pre-1994 data revealed that the heat flow varied widely from 51–157 mW/m² in and around the basin. Due to a large scatter in these older data, a clear relationship between heat flow and water depth was not evident, in contrast to what would be expected for a rifted sedimentary basin. This raises the question as to whether the pre-1994 data represent the true background heat flow from the underlying basin crust since the basin opening, and/or whether they contain large measurement errors. In fact, evidence in support of the latter explanation exists. BSRs are generally found in the deep parts of the basin, and vary by only ±15 m in depth below the seafloor. From the average BSR depth, we inferred the background heat flow using a simple model, which in the case of the Ulleung Basin is approximately 120 and 80 mW/m² for 2.5 and 1 km below sea level, respectively.     

Particulate organic carbon (POC) in surface sediments of the Baltic Sea

In this study, particulate organic carbon (POC) contents and their distribution pattern in surficial sediments of the Baltic Sea are presented for 1,471 sampling stations. POC contents range from approx. 0.1% in shallow sandy areas up to 16% in deep muddy basins (e.g. Gotland Basin). Some novel relationships were identified between sediment mass physical properties (dry bulk density (DBD), grain size) and POC levels. Notably, the highest POC concentrations (about 10–17 mg cm^–3) occur in sandy mud to mud (60–100% mud content) with intermediate POC contents of about 3–7% and DBDs of 0.1–0.4 g cm^–3. Areas with this range in values seem to represent the optimum conditions for POC accumulation in the Baltic Sea. The maximum POC contents (8–16%) are found in fluid mud of the central Baltic Sea characterized by extremely low DBDs (<0.1 g cm^–3) and moderate POC concentrations (4–7 mg cm^–3). Furthermore, sediment mass accumulation rates (MAR), based on ²¹⁰Pb and ¹³⁷Cs measurements and available for 303 sites of the Baltic Sea, were used for assessing the spatial distribution of POC burial rates. Overall, these vary between 14 and 35 g m^–2 year^–1 in the mud depositional areas and, in total, at least 3.5 (±2.9) Mt POC are buried annually. Distribution patterns of POC contents and burial rates are not identical for the central Baltic Sea because of the low MAR in this area. The presented data characterize Baltic Sea sediments as an important sink for organic carbon. Regional differences in organic carbon deposition can be explained by the origin and transport pathways of POC, as well as the environmental conditions prevailing at the seafloor (morphology, currents, redox conditions). These findings can serve to improve budget calculations and modelling of the carbon cycle in this large brackish-water marginal sea.     

Late glacial to Holocene sea-level changes in the Sea of Marmara: new evidence from high-resolution seismics and core studies

The late glacial to Holocene sedimentary record of the northern shelf of the Sea of Marmara (SoM) has been documented by detailed seismo-, chrono-, and biostratigraphic analyses using sub-bottom (Chirp) profiles and sediment cores. During MIS 3 and the main part of MIS 2 (60–15 ¹⁴C ka b.p.), disconnection from the Mediterranean and Black seas together with a dry climate resulted in a regression in the SoM, when the Sea was transformed into a brackish lake. The river incisions below 105 m water depth along the northern shelf took place during the last glacial maximum, when the lake level was modulated by stillstands at −98 and −93 m. The post-glacial freshwater transgressive stage of the Marmara ‘Lake’ occurred between 15 and 13.5 ¹⁴C ka b.p., leading to a rise in water level to −85 m by 13.0 ¹⁴C ka b.p., as evidenced by broad wave-cut terraces along the northern shelf. Since 12 ¹⁴C ka b.p., high-frequency sea-level fluctuations have been identified at the SoM entrance to the Strait of İstanbul (SoI). Thus, wave-cut terraces have been recorded at water depths of −76 and −71 m that, according to an age model for core MD04-2750, have ages of 11.5 and 10.5 ¹⁴C ka b.p., respectively. Ancient shoreline at −65 m along the northern shelf presumably formed soon after the Younger Dryas (YD) at ca. 10.1 ¹⁴C ka b.p. Moreover, there is compelling evidence of Holocene outflow from the Sea of Marmara to the Black Sea. At the SoM entrance to the SoI, the existence of bioherms on the reflector surface together with abundant Brizalina spathulata and Protoglobulimina pupoides in a core suggests a return to higher salinities due to strong Mediterranean water incursion into the SoM at ∼8.8 ¹⁴C ka b.p. This finding is consistent with earlier suggestions that, after the YD, the Black Sea was flooded by outflow from the SoM as a result of global sea-level rise.     

Evolution of errors in the altimetric bathymetry model used by Google Earth and GEBCO

We analyze errors in the global bathymetry models of Smith and Sandwell that combine satellite altimetry with acoustic soundings and shorelines to estimate depths. Versions of these models have been incorporated into Google Earth and the General Bathymetric Chart of the Oceans (GEBCO). We use Japan Agency for Marine-Earth Science and Technology (JAMSTEC) multibeam surveys not previously incorporated into the models as “ground truth” to compare against model versions 7.2 through 12.1, defining vertical differences as “errors.” Overall error statistics improve over time: 50th percentile errors declined from 57 to 55 to 49 m, and 90th percentile errors declined from 257 to 235 to 219 m, in versions 8.2, 11.1 and 12.1. This improvement is partly due to an increasing number of soundings incorporated into successive models, and partly to improvements in the satellite gravity model. Inspection of specific sites reveals that changes in the algorithms used to interpolate across survey gaps with altimetry have affected some errors. Versions 9.1 through 11.1 show a bias in the scaling from gravity in milliGals to topography in meters that affected the 15–160 km wavelength band. Regionally averaged (>160 km wavelength) depths have accumulated error over successive versions 9 through 11. These problems have been mitigated in version 12.1, which shows no systematic variation of errors with depth. Even so, version 12.1 is in some respects not as good as version 8.2, which employed a different algorithm.     

The Cosmonaut Sea Wedge

A set of multi-channel seismic profiles (∼15,000 km) is used to study the depositional evolution of the Cosmonaut Sea margin of East Antarctica. We recognize a regional sediment wedge, below the upper parts of the continental rise, herein termed the Cosmonaut Sea Wedge. The wedge is situated stratigraphically below the inferred glaciomarine section and extends for at least 1,200 km along the continental margin with a width that ranges from 80 to about 250 km. The morphology of the wedge and its associated depositional features indicate a complex depositional history, where the deep marine depositional sites were influenced by both downslope and alongslope processes. This interaction resulted in the formation of several proximal depocentres, which at their distal northern end are flanked by elongated mounded drifts and contourite sheets. The internal stratification of the mounded drift deposits indicates that westward flowing bottom currents reworked the marginal deposits. The action of these currents together with sea-level changes is considered to have controlled the growth of the wedge. We interpret the Cosmonaut Sea Wedge as a composite feature comprising several bottom current reworked fan systems. The wide spectrum of depositional geometries in the stratigraphic column reflects dramatic variations in sediment supply from the continental margin as well as varying interaction between downslope and alongslope processes.     

Radially symmetric coherence between satellite gravity and multibeam bathymetry grids

We compute the radially symmetric coherence between multibeam bathymetry and satellite gravity grids in 25 areas distributed around the world. In contrast to previous studies employing one-dimensional analysis of data along profiles, our results cannot be biased by unseen off-track topography. The mean coherence averaged over the 20?C160?km waveband, and the shortest wavelength at which coherence is above 0.5, vary with tectonic setting. Seamounts and slow spreading ridges have high (>0.7) mean coherence down to ~20?km wavelength, other spreading ridges and trenches have intermediate (0.5?C0.7) coherence down to ~20?C30?km wavelength, and continental shelves have low (<0.5) coherence at all wavelengths. In the areas with highest mean coherence, the shortest wavelength at which coherence is above 0.5 decreases as mean depth decreases. The filter employed in the bathymetric prediction method of Smith and Sandwell (J Geophys Res 99(B11):21803?C21824, 1994) selects the most coherent parts of the bathymetry and gravity spectrum.     

An integrated geophysical study of Vestbakken Volcanic Province, western Barents Sea continental margin, and adjacent oceanic crust

This paper describes results from a geophysical study in the Vestbakken Volcanic Province, located on the central parts of the western Barents Sea continental margin, and adjacent oceanic crust in the Norwegian-Greenland Sea. The results are derived mainly from interpretation and modeling of multichannel seismic, ocean bottom seismometer and land station data along a regional seismic profile. The resulting model shows oceanic crust in the western parts of the profile. This crust is buried by a thick Cenozoic sedimentary package. Low velocities in the bottom of this package indicate overpressure. The igneous oceanic crust shows an average thickness of 7.2 km with the thinnest crust (5–6 km) in the southwest and the thickest crust (8–9 km) close to the continent-ocean boundary (COB). The thick oceanic crust is probably related to high mantle temperatures formed by brittle weakening and shear heating along a shear system prior to continental breakup. The COB is interpreted in the central parts of the profile where the velocity structure and Bouguer anomalies change significantly. East of the COB Moho depths increase while the vertical velocity gradient decreases. Below the assumed center for Early Eocene volcanic activity the model shows increased velocities in the crust. These increased crustal velocities are interpreted to represent Early Eocene mafic feeder dykes. East of the zone of volcanoes velocities in the crust decrease and sedimentary velocities are observed at depths of more than 10 km. The amount of crustal intrusions is much lower in this area than farther west. East of the Kn?legga Fault crystalline basement velocities are brought close to the seabed. This fault marks the eastern limit of thick Cenozoic and Mesozoic packages on central parts of the western Barents Sea continental margin.     

Gravity effect of spreading ridges: comparison of 2D and spherical models

Because of its importance to many Earth science analyses, it is worth assessing whether gravity modelling can be simplified depending on the intended purpose and required precision. While it is obvious that large-scale gravity studies should account for the sphericity of the Earth, each case should be examined on its own merits. Demonstrations are useful for providing estimates of the errors in much simpler 2D modelling. The example of the Mid-Atlantic Ridge serves to compare “large” 2D and spherical 3D models. My model extends horizontally ±2,000 km (±18°) from the model profile across and along the straight ridge axis (along a great circle) and to a depth of 82 km across the axis. 3D modelling would generally be considered obligatory, but this is not clearly necessary from this study. The density structure is highly idealised, the asthenospheric uplift or lithosphere thinning is simplified. The Bouguer anomaly is fitted by least-squares for the density contrast, and the 2D–3D difference of the results is taken as the error. A lithosphere–asthenosphere density contrast of 86.56 kg/m³ was computed for the 2D model, and 84.14 kg/m³ for the spherical model. The difference is small, in the order of 3%, well within all the other uncertainties. My study shows that despite the significant sphericity of the structure, 2D models are well suited for such ridge studies, or generally for models with a laterally extended layered structure, and that spherical modelling can be applied discriminately.     

Estimates of non-tidal exchange transport between the Sea of Okhotsk and the North Pacific

The outflow from the Sea of Okhotsk to the North Pacific is important in characterising the surface-to-intermediate-depth water masses in the Pacific Ocean. The two basins are separated by the Kuril Islands with numerous straits, among which the Bussol and the Kruzenshterna Straits are deeper than 1000 m. The physics governing the transport between the two basins is complicated, but when the semidiurnal and diurnal tides are subtracted, the observed density and velocity structures across the Bussol Strait suggest a significant contribution from geostrophic balance. Using a two-layer model with the interface at 27.5σ _θ , part of the upper layer transport that is not driven by tides is estimated using two previously unexplored data sets: outputs from the Ocean General Circulation Model for Earth Simulator (OFES), and historical hydrographic data. The Pacific water flows into the Sea of Okhotsk through the northeastern straits. The greatest inflow is through the Kruzenshtern Strait, but the OFES results show that the contributions from other shallower straits are almost half of the Kruzenshtern inflow. Similarly, the outflow from the Sea of Okhotsk is through the southwestern straits of the Kuril Islands with the largest Bussol Strait contributing 60% of the total outflow. The OFES and hydrographic estimates agree that the exchange is strongest in February to March, with an inflow of about −6 to −12 Sv (negative indicates the flow from the North Pacific, 1 Sv = 10⁶ m³s⁻¹), and an outflow from the Sea of Okhotsk of about +8 to +9 Sv (positive indicates the flow from the Sea of Okhotsk), which is weakest in summer (−3 to +1 Sv through the northeastern straits and +0 to +3 Sv through the southwestern straits). The estimated seasonal variation is consistent with a simple analytic model driven by the difference in sea surface height between the two basins.     

Aliasing due to sampling of the Adriatic temperature, salinity and density in space

High-resolution underway temperature and conductivity measurements collected by R/V Knorr during winter and spring 2003 are used to characterize errors associated with spatial aliasing in the northern and central Adriatic Sea. During winter, 99th percentile temperature, salinity and density errors were 0.62 °C, 0.25 and 0.12 kg/m³ (0.25 °C, 0.10 and 0.05 kg/m³) for sampling at 10 km (5 km) horizontal resolution, respectively. The corresponding values in spring were 1.31 °C, 0.50 and 0.40 kg/m³ (0.93 °C, 0.25 and 0.22 kg/m³) for the 10 km (5 km) sample spacing, respectively. The largest errors were associated with energetic regions over the shallow, western Adriatic, in front of the Po River mouth and off the tip of the Istrian peninsula. The deeper eastern basin exhibited smaller errors. The variability of errors in time and space reflected the variability of small-scale density features, characterized by wavelengths as small as 2 km in winter and 1 km in spring and being more pronounced in the western and northern parts of the Adriatic. As these results indicate that errors associated with undersampling can be considerable, they should be taken into account while planning future CTD measurements in the region.     

Morpho-sedimentary evidence for a canyon�Cchannel�Ctrench interconnection along the Taiwan�CLuzon plate margin, South China Sea

Examining bathymetric and seismic reflection data collected from the deep-sea region between Taiwan and Luzon in 2006 and 2008, we identified a connection between a submarine canyon, a deep-sea channel, and an oceanic trench in the northern South China Sea. The seafloor of the South China Sea north of 21°N is characterized by two broad slopes: the South China Sea Slope to the west, and the Kaoping Slope to the east, intersected by the prominent Penghu Canyon. This negative relief axis parallels the strike of the Taiwan orogen, extends downslope in an approx. N–S direction, and eventually merges with the northern Manila Trench via a hitherto unidentified channel. The discovery of this channel is pivotal, because it allows connecting the Penghu Canyon to the Manila Trench. This channel is 80 km long and 20–30 km wide, with water depths of 3,500–4,000 m. The progressive morphological changes recorded in the aligned canyon, channel, and trench suggest that they represent three distinct segments of the same longitudinal sediment conduit from southern Taiwan to the northern Manila Trench. Major sediment input would be via the Kaoping Canyon and Kaoping Slope, with a smaller contribution from the South China Sea Slope. We determined the northern end of the Manila Trench to be located at about 20°15′N, 120°15′E, where sediment accumulation has produced a bathymetry shallower than 4,000 m, thereby abruptly terminating the trench morphology. Comparison with existing data reveals a similarity with, for example, the Papua New Guinea–Solomon Sea Plate convergent zone, another modern analog of a mountain source to oceanic sink longitudinal sediment transport system comprising canyon–channel–trench interconnections.     

A case study of near-inertial oscillation in the South China Sea using mooring observations and satellite altimeter data

A near-inertial oscillation (NIO) burst event in the west South China Sea (SCS) was observed by an upward-looking mooring Acoustic Doppler Current Profiler (ADCP) in summer 2004. The mooring station was located at 13.99°N, 110.52°E. The spectral analysis reveals that typhoon Chanchu is a major mechanism in triggering the NIO burst event. Before typhoon Chanchu passed over, the NIO signals were quite weak. The NIO band becomes the most energetic constituent of the circulation during the typhoon-wake period. The average peak power density (PD) reaches (5.3 ± 2.6) × 10² cm² s⁻² (cycles per hour, cph)⁻¹ with a maximum value of 9.0 × 10² cm² s⁻² cph⁻¹, i.e., 3.1 times higher than that of diurnal tide (DT), (1.7 ± 0.5) × 10² cm² s⁻² cph⁻¹. At the upper (80 m) and sub-upper (208 m) layers, the central frequency of the NIO band is 0.022 cph with a blueshift of about 9% above the inertial frequency f (0.02015 cph). At the lower layer (400 m), the central frequency of the NIO band is 0.021 cph with a blueshift of about 4% above the inertial frequency. The blueshifts are explained partially by the Doppler shift induced by the vorticity of mesoscale eddies. During the after-typhoon period, a resonance-like process between NIO and DT is observed in the upper layer. As the NIO frequency approaches the DT subharmonic frequency (0.5K₁), the PD of the NIO band rises sharply accompanied by a sharp drop of the PD of the DT band. The PD ratio of the two bands increases from 4.5 during the typhoon-wake period to 8 during the after-typhoon period, indicating the effect of the parametric subharmonic instability (PSI) mechanism.     

Sandbank occurrence on the Dutch continental shelf in the North Sea

Sandbanks, the largest of bed patterns in shallow sandy seas, pose a potential risk to shipping. They are also valuable elements of natural coastal protection, dissipating the energy of waves. In the Southern Bight of the North Sea, several sandbank areas have been reported in the literature. However, based on an objective crest–trough analysis of the bathymetry of the Dutch continental shelf, the present study shows that sandbanks are more widespread than commonly considered. These banks are relatively low, presumably explaining why they have not been documented before. This widespread occurrence of sandbanks in the North Sea is in agreement with theoretical predictions based on stability analysis techniques. The possible interference between large-scale human activity and low-amplitude open-shelf ridges implies that one should be careful not to overlook these patterns if none should appear in a preliminary (visual) assessment. The only part of the Southern Bight in which no ridges can be seen is a circular area with a diameter of about 50 km near the mouth of the river Rhine. Here, freshwater outflow affects the direction of tidal ellipses and residual flow, and suppresses the formation of open ridges.     

Denitrification in the Arabian Sea: A 3D ecosystem modelling study

A three-dimensional hydrodynamic-ecosystem model was used to examine the factors determining the spatio-temporal distribution of denitrification in the Arabian Sea. The ecosystem model includes carbon and nitrogen as currencies, cycling of organic matter via detritus and dissolved organic matter, and both remineralization and denitrification as sinks for material exported below the euphotic zone. Model results captured the marked seasonality in plankton dynamics of the region, with characteristic blooms of chlorophyll in the coastal upwelling regions and central Arabian Sea during the southwest monsoon, and also in the northern Arabian Sea during the northeast monsoon as the mixed layer shoals. Predicted denitrification was 26.2 Tg N yr⁻¹,the greatest seasonal contribution being during the northeast monsoon when primary production is co-located with the zone of anoxia. Detritus was the primary organic substrate consumed in denitrification (97%), with a small (3%) contribution by dissolved organic matter. Denitrification in the oxygen minimum zone was predicted to be fuelled almost entirely by organic matter supplied by particles sinking vertically from the euphotic zone above (0.73 mmol N m⁻² d⁻¹) rather than from lateral transport of organic matter from elsewhere in the Arabian Sea (less than 0.01 mmol N m⁻² d⁻¹). Analysis of the carbon budget in the zone of denitrification (north of 10°N and east of 55°E) indicates that the modelled vertical export flux of detritus, which is similar in magnitude to estimates from field data based on the ²³⁴Th method, is sufficient to account for measured bacterial production below the euphotic zone in the Arabian Sea.     

Variability of sea surface temperature and warm pool area in the South China Sea and its relationship to the western Pacific warm pool

Sea surface temperature (SST) data derived from satellite and in situ measurements are used to study the thermal variability in the South China Sea (SCS). Time–frequency–energy distributions, periods of variability, and trends are computed by the Hilbert–Huang transform method. The SST trend from 1982 to 2005 is 0.276°C per decade in the SCS which is higher than 0.144°C per decade in the western Pacific warm pool (WPWP). The warm pool (SST ≥ 28°C) area in the SCS has increased by 0.20 × 10⁶ km² per decade. The SST and area of the warm pool in the SCS are strongly correlated, respectively, with the SST and area of the WPWP with a time lag of 1 month, suggestive of a strong connection between these two warm pools. Once the annual cycle is eliminated, decadal oscillations dominate the variability of SST and warm pool area in the SCS.     

Circulation in the Gulf of Aqaba (Red Sea) during winter—spring

This study is devoted to oceanographic features of the semi-enclosed Gulf of Aqaba, Red Sea. The data were recorded in winter—spring 1999 on the R/V Meteor cruise leg 44/2. Temperature and salinity profiles were measured at six positions (I—VI). The shipboard NarrowBand Acoustic Doppler Current Profiler (NB ADCP) 150 kHz continuously recorded current profiles down to 350 m en route. The research revealed that the current near the Strait of Tiran front (position VI) represents a semidiurnal signal of an internal tide wave (∼12 h period; 0.2 ms⁻¹ amplitude) that might be generated by the barotropic tide at the sill of the Strait. A sequence of cyclonic and anticyclonic eddy pairs is found along the axis of the Gulf of Aqaba during winter-spring seasons. These sub-mesoscale signals are dominant above the main thermocline and might be caused by wind forcing and the narrowness of the Gulf; it might remain in other seasons with different dimensions in relation to the depth of thermocline. The total diameter of each pair was twice the baroclinic Rossby radius (R ≈ 10 km). A single anti-cyclonic eddy was observed in the upper 300 m in the northern tip of the Gulf with a diameter of about 5–8 km.     

Factors influencing the abundance of deep pelagic bioluminescent zooplankton in the Mediterranean Sea

Measurements of the density of deep pelagic bioluminescent zooplankton (BL) were made with the Intensified Silicon Intensifier Target (ISIT) profiler in the Ligurian, Tyrrhenian, Adriatic, Ionian Seas and the Strait of Sicily from ～300 m to near seafloor. Mean BL densities ranged from 2.61 m^?3 at 500–1000 m depth in the Adriatic Sea to 0.01 m^?3 at 4000–5000 m depth in the E Ionian Sea. We investigated drivers of spatial variation of deep pelagic BL density. Linear regression was applied between surface chlorophyll a (Chl a) concentration and underlying BL density. Chl a values were determined from satellite derived 100 km radius composites (six 10-day means per ISIT deployment, over preceding 60 days). At 500–1000 m depth we found a significant positive relationship between mean BL density and mean Chl a in the period prior to 0–10 days (at 1% level) and prior to 10–40 days (at 5% level). Beyond 40 days no relationship between BL density and Chl a was found at this depth. At depths 1000–1500 m BL density values were low and no significant relationship with Chl a was detected. Generalised additive modelling (GAM) was used to assess the influence of benthic hotspots (seamount; cold water coral mound; mud volcano) on overlying BL density. A reduction in BL density was found downstream of the Palinuro seamount from 300 to 600 m. No effect on BL density in the overlying water column was detected from the presence of cold water corals. Higher BL densities were detected over the W Madonna dello Ionio mud volcano than at other sites sampled in the NW Ionian Sea. We find surface Chl a to be a good predictor of BL density in the mesopelagic zone; below this depth we hypothesise that processes affecting the efficiency of particle export to deep water may exert greater influence on BL density.