The winter St. Helena climate index and extreme Benguela upwelling

Climate changes in the subtropical South-east Atlantic turn out to be well described by the St. Helena Island Climate Index (HIX) and observed fluctuations are in good agreement with inter-decadal variability of the entire South Atlantic Ocean. Year-to-year variations of the averaged austral winter HIX (July–September), representative of the main upwelling season, were compared with (i) corresponding averages of the geostrophic alongshore component of the south-east trade wind (SET) between St. Helena Island in the south-west and Luanda/Angola in the north-east, (ii) the meridional distribution of surface waters colder than 13 °C to characterise intense Benguela upwelling (IBU), and (iii) the meridional position of the Angola-Benguela Frontal Zone (ABFZ) determined by means of sea surface temperature images for offshore distances between 50 and 400 km. Temporal changes of these parameters were investigated and showed that the frequency of consecutive years of strong and relaxed Benguela upwelling is characterised by a quasi-cycle of about 11–14 years. It is proposed that the index of the winter HIX may be used as a ‘surveyor’s rod' to describe interannual changes in the Benguela upwelling regime as well as those of the embedded marine ecosystem.     

Variability in hydrographic conditions to the east and northwest of South Georgia, 1996–2001

Six years of high-resolution hydrographic data from the eastern and northwestern sides of South Georgia (southwest Atlantic) are used to study the changing circulation and water mass properties of the region. One year of data from these locations was used previously to describe the oceanographic conditions at those times; using the much greater volume of data now available, we identify which features appear temporally robust and which are transient, and begin addressing topics relating to the forcing of the inter-annual variability and the potential consequences for the local ecosystem. Waters on the shelf and those over the adjacent deep ocean invariably have different hydrographic properties, though the transition between them can be abrupt or gradual. The onshelf/offshelf differences vary greatly from year to year, due to the combined influences of local and remote processes. There are several instances of strong physical coupling between the eastern and northwestern sides of South Georgia; this offers potential for distinguishing physically-induced ecosystems changes separately from biologically-induced ecosystems changes. On the northeast side of the shelf, close to Cumberland Bay, there is evidence of an often intense, but variable, cyclonic circulation that is the result of interaction with the local bathymetry. This may act as a retention mechanism, and enhance local productivity. Two examples of extreme cold anomalies are present in the series of measurements. One of these (in 2000/2001) affected a limited area at the eastern side of the region surveyed and was due to an intrusion of the Southern Antarctic Circumpolar Current Front. The other (in early 1998) was due to the combined effects of the passage of a large-scale ocean anomaly that had its origins upstream in the Pacific Ocean, and strong air/sea interaction. Both of these were associated with the strong 1997/1998 El Niño event. Whilst previous studies have observed a link between El Niño forcing and ocean response around South Georgia with a temporal lag of around 3 years, we observe a much more rapid response to the extremely strong 1997/1998 El Niño event. This indicates that the ocean and ecosystem around South Georgia are more immediately susceptible to extreme instances of remote climatic forcing than had been supposed.     

Enrichment, concentration and retention processes in relation to anchovy (Engraulis ringens) eggs and larvae distributions in the northern Humboldt upwelling ecosystem

A Lagrangian model is used to simulate and quantify in the northern Humboldt upwelling ecosystem the processes of enrichment, concentration and retention, identified by Bakun [Bakun, A., 1996. Patterns in the ocean. Ocean processes and marine population dynamics. University of California Sea Grant, California, USA, in cooperation with Centro de Investigaciones Biologicas de Noroeste, La Paz, Baja California Sur, Mexico, 323 pp.] as being important for the survival and recruitment of early life stages of pelagic fish. The method relies on tracking the positions of particles within water velocity fields generated by a three-dimensional hydrodynamic model. Simple criteria for considering particles as participating to enrichment, concentration or retention are used to derive indices of the three processes. We analyse the spatial distribution of and seasonal variability in these indices. The results are discussed in relation to anchovy (Engraulis ringens) eggs and larvae distributions off Peru, and to a comparable study conducted in the southern Benguela upwelling ecosystem.     

Why is the southwest the most productive region of the East Sea/Sea of Japan?

The East Sea/Sea of Japan is a moderately productive sea that supports a wealth of living marine resources. Of the East Sea subregions, the southwest has the highest productivity. Various authors have proposed coastal upwelling, the Tsushima Current, the Changjiang Dilute Water, eddies, or discharge from the Nagdong River as potential sources of additional nutrients. In this paper, we propose, using satellite data from 1998 to 2006, that the biological productivity of the southwestern region is enhanced mainly by wind-driven upwelling along the Korean coast. Firstly, the climatology of seasonal patterns suggests that the enhanced chlorophyll a along the Korean coast is of local origin. Secondly, coastal upwelling is frequent in all seasons except winter. For example, along the coast of the Ulgi region, enhanced chlorophyll a due to coastal upwelling was observed for 25–92% of the time between Jun and Sep in the period 1998–2006. Thirdly, the advection of upwelled water through various pathways to the deeper basin was observed. Fourthly, there appeared to be a strong correlation between the interannual chlorophyll a variations of the coastal upwelling regions and the Ulleung Basin. The chlorophyll a patterns of both regions were closely related to the wind pattern in the upwelling regions, but not to that in the Ulleung Basin. Finally, changes in advection pathways also appeared to affect the productivity of the Ulleung Basin. Since 2004, there has been a shift in the pathways of upwelled water, and consequent increases in chlorophyll a in the Ulleung Basin were observed. This last observation requires further investigation.     

Hydrographic cruises off northwest Africa: the Canary Current and the Cape Ghir region

We present hydrographic data for several sections located along the African coastline and off Cape Ghir, carried out at times of weak surface winds (October 1995 and September 1997). The main sections are near the continental slope, at mean distances between 100 and 150 km from the coastline. North of Cape Ghir (31°N) the geostrophic transport (referenced to 650 m) of North Atlantic Central Water through these sections is 3.7 and 2.0 Sv for 1995 and 1997, respectively. This confirms that a major fraction of the water transport by the Canary Current flows east, into the continental slope off northwest Africa, at latitudes above Cape Ghir. Most of this flow continues south past Cape Ghir, along the coast and probably through the eastern passages of the Canary Archipelago. A significant fraction, however, may escape through surface Ekman transport (0.3–0.5 Sv during the early fall season) and by offshore flow at Cape Ghir (1.1 Sv in September 1997, referenced to 650 m). Despite the weak winds the Cape Ghir filament was clearly visible, characterized by localized coastal upwelling associated to a cyclonic shallow structure and cold (and fresh) waters stretching offshore as a very shallow feature (50–100 m deep). The satellite images show that the surface temperature field is highly variable, in rapid response to the surface winds, always with a core region of relatively cold water and commonly with one or two associated eddies. Our results support the existence of two recirculation cells in the area: a horizontal one that connects the interior eastern boundary currents with the coastal region and a vertical one related to both wind-induced and filament upwelling. The data also show a salinity subsurface maximum at the root of the filament, linked to water inflow from northern latitudes, and a subsurface anticyclonic eddy over the Agadir canyon, likely related to the poleward slope undercurrent.     

The West African coastal upwelling filaments and cross-frontal water exchange conditioned by them

One of the important problems in the oceanography of the wind-driven upwelling regions of the Ocean is the investigation of water exchange processes in the coastal zone. Satellite data (thermal and colour imagery) have changed our view on these processes after the relatively recent discovery of cold, chlorophyll-rich, narrow (< 50 km wide) offshore flowing filaments off the west coasts of North America, North and South Africa. On the basis of satellite IR images and oceanographic original and archive data we investigated systems of filaments in the northwest and southwest African upwelling regions. The spatial distribution of filaments was analyzed. It was found that seasonal variability of the filaments' location depends upon the general intensity of upwelling motion along the coast during the year. The main statistical characteristics of filaments were obtained. An example of the three-dimensional velocity structure of the filament was presented. In order to estimate the intensity of cross-frontal exchange process due to filaments, a special procedure was proposed. The values of the velocity of cross-frontal water exchange produced by filaments in these upwelling zones are obtained. It was shown that upwelling filaments play an important role in water exchange between the coastal zone and the open ocean. A non-dimensional parameter which characterizes the permeability of oceanic fronts for water exchange due to mesoscale dynamical structures was introduced and estimated.     

Decadal sea level trends in the Bay of Biscay from tide gauges, GPS and TOPEX

Sea level time series derived from TOPEX altimeter and from tide gauge measurements in the Bay of Biscay (Eastern North Atlantic Ocean) are used to investigate the regional sea level rise. Altimetry sea level anomalies are computed from TOPEX measurements and resampled into fixed along track bins in order to obtain consistent records and to approach as close as possible to the coast. Tidal corrections are critical in the estimation of sea level trends; therefore an additional analysis has been carried out in order to identify and correct for residual tidal signals. The obtained mean sea level rise in the region is + 3.09 ± 0.21 mm/year over the period 1993–2002. Tide gauges have been corrected for vertical land motions by means of collocated GPS measurements. GPS-corrected tide gauges and nearby altimetry trends are found to be statistically consistent. The relationship with the atmospheric forcing is also investigated revealing that 15% of this sea level rise is attributed to the atmospheric pressure effects.     

State ocean policy initiatives in Florida

Abstract

A territorial sea comprising 6.7 million acres of offshore lands extending three geographic miles into the Atlantic Ocean three marine leagues (nine geographic miles) into the Gulf of Mexico makes Florida the second largest “oceanowning”; state in the contiguous United States. Florida's history, climate, economic development, and worldwide reputation have evolved from the state's relationship with the sea. The state is now becoming aware that aggressive management of its ocean resources is necessary to preserve the future of that relationship. The purpose of this article is to present some of Florida's recent legal and policy initiatives that have been directed toward better understanding and management of ocean resources and uses.     

Numerical experiments on the prediction of sea surface temperature anomalies in the Gulf of Mexico

The conservation of thermal energy equation applied to the mixed layer of the ocean, has been used to predict the sea surface temperature anomalies (SSTA) and the month-to-month changes in the Gulf of Mexico. The model includes the horizontal transport of heat by mean ocean currents and by turbulent eddies, as well as the heating by short and long wave radiation, evaporation and sensible heat given off to the atmosphere. A comparative study is carried out on the relative importance of the heating and transport terms. An objective verification of the skill of the predictions is presented for each season and for the whole period from March 1986 to February 1987. The predictions using only the heating terms have some skill over the control predictions (persistence and return to normal). The skill is substantially increased when the horizontal transport of heat by turbulent mixing is included in the model. The incorporation in the model of the Ekman wind drift current anomalies computed from the anomalous surface geostrophic wind improves appreciably the skill of the predictions in winter and fall.The mixed layer depth computed using the Kraus and Turner theory with dissipation, shows that the depths in summer and fall are shallower than in spring and winter. The effect of the shallow mixed layer depth in the model becomes apparent in summer and fall, improving the skill of the predictions in these seasons, with respect to the skill obtained using a constant mixed layer depth of 60 m.The incorporation in the model of the cooling in the mixed layer by turbulent entrainment of colder water from the thermocline, does not improve in an appreciable way the average skill of the predictions.     

Characterization of fall–winter upwelling recurrence along the Galician western coast (NW Spain) from 2000 to 2005: Dependence on atmospheric forcing

Upwelling events driving ENACW (Eastern North Atlantic Coastal Water) into the Galician western coast rias had been considered typical spring–summer processes, according to the research developed in this area. However, they can also be observed in fall or winter under northerly winds blowing at shelf. Six different upwelling events were analyzed in the Ria of Pontevedra during the wet season (NDJF) from 2000 to 2005. These events were characterized by means of the zonal Ekman transport (Q_x) at four control points in front of the western rias (locally known as Rias Baixas) and thermohaline variables measured at a fixed station in the main mouth of the Ria of Pontevedra. The duration of the upwelling events ranged from 27 days (during February and March 2002) to 69 days (during November–December 2004 and January 2005). Upwelling events studied in the Ria of Pontevedra from 2000 to 2005 showed the similarity in upwelling features during both seasons (similar wind forcing and upwelled water). Finally, Q_x was correlated with the most representative atmospheric patterns in the Northern Hemisphere (EA, NAO, EA/WR, POL and SCA) from 1966 to 2005. The winter EA pattern has the most influence on Q_x showing an annual evolution with a prevalence of the positive phase from 1976 on. This positive phase is directly correlated with a prevalence of positive values of Q_x which are upwelling unfavorable in the Rias Baixas.     

Interannual variation of the Polar Front in the Japan/East Sea from summertime hydrography and sea level data

The Polar Front in the Japan/East Sea separates the southern warm water region from the northern cold water region. A merged TOPEX/POSEIDON and ERS-1/2 altimeter dataset and upper water temperature data were used to determine the frontal location and to examine the structure of its interannual variability from 1993 to 2001. The identified frontal location, where sea surface height gradient has a maximum about 10–20 cm over the horizontal distance of 100 km, corresponds well to the maximum subsurface horizontal temperature gradient. The front migrates more widely (36°N–41°N) in the western part of the sea than in the eastern part. The interannual migration induces large variability in upper water temperatures and sea surface height in the western region. Responsible physical mechanisms were studied using a reduced-gravity model. Differences between inflow and outflow change the total volume of warm water, and total warm water volume change in the warm water region uniformly pushes the front in the meridional direction across its mean position in the model simulation. Interannual variation of wind stress causes relatively wide migration of the modeled front in the western part.     

Benthic megafauna communities under the influence of the South Atlantic Central Water intrusion onto the Brazilian SE shelf: A comparison between an upwelling and a non-upwelling ecosystem

The structure and dynamics of the benthic invertebrate megafauna of the Southeastern Brazilian shelf were studied over a 2-year period. Two regions presenting different oceanographic conditions, Ubatuba-SP and Cabo Frio-RJ were compared in terms of biomass, density of organisms and species richness. Two to three 30-min tows were undertaken at each of the stations, located at 40 and 100 m isobath, in a normal transect offshore of both regions. Faunal distributional patterns correlated with water mass dynamics, depth and sediment parameters. In the Cabo Frio region, subjected to a Ekman-driven seasonal coastal upwelling, the impact of the South Atlantic Central Water (SACW) on the inner shelf leads to a change in the benthic communities, with a high dominance of top carnivores such as the crab Portunus spinicarpus and the sea-star Astropecten brasiliensis, which accounted for the larger part of the total biomass. Distinct species associations were found in each of the two regions and the total biomass at Cabo Frio inner shelf was almost twice that of Ubatuba during the 2002 summer, when a marked upwelling was verified. The relationship between megabenthic biomass and input of organic matter to the sea floor during upwelling events is discussed.     

Oceanic CO2 uptake and biogeochemical variability during the formation of the Eastern North Atlantic Central water under two contrasting NAO scenarios

Long-term variability of the biogeochemical properties during the formation of central waters in the Eastern North Atlantic were analyzed between 42–47°N and 10–20°W from the dataset gathered during the Galicia VII (GVII) and C. Darwin 58/59 (CD58/59) cruises. These cruises that showed important changes in the thermohaline properties and the nutrient abundance of the upper layers were carried out under contrasting conditions of the North Atlantic Oscillation (NAO) index. The different climate forcing led a meridional shift of the transition zone between the formation regions of subpolar and subtropical Eastern North Atlantic Central Water (ENACWp and ENACWt, respectively). This displacement conditioned the presence of each ENACW in the study region and so the thermohaline and biogeochemical properties. The effect of the observed variability at decadal scale on the air–sea CO₂ gradient (ΔfCO₂) and exchange (F_CO2) was analyzed using 1D model approach throughout 11 weekly-steps that simulated the development of a spring bloom during the shoaling of the mixed layer. The outputs of the model showed an intensification of the ocean CO₂ uptake due to higher biological CO₂ drawdown, during positive NAO conditions and its weakening under negative NAO influence.     

Rates and mechanisms of climate change: Implications for ports and harbours

The paper explores some of the key ocean-atmosphere processes relevant to the themes of ‘global warming“ and ‘sea level rise“ addressing some of issues that form the basis of the science. It is shown that both processes as well as the data used to characterise such processes demonstrate that a) there is no such thing as a single global sea level and b) changes in extreme storminess are not uniform worldwide. Instead, trends in storminess (including Asian typoon and Atlantic hurricane activity) exhibit marked regional variability with strong regional signature linked to episodes of major El Niño and La Niña activity. Similarly, satellite data demonstrates that whereas some ocean areas have recently experienced sea level rise caused principally by thermal expansion effects, other ocean areas have been subject to cooling and sea level lowering. This account provides an introductory account that discusses the rationale for understanding the regional variability in the nature of coastal flood risk to the world’s ports and harbours.     

基于Vega的虚拟海洋视景仿真研究

虚拟海洋视景仿真系统足虚拟现实技术在军事领域中的应用.由于海浪运动的随机性,虚拟海洋的计算机生成成为视景仿真领域的研究难点.文中详细讨论了两种海浪模型,重点研究Vega中海浪原理和海洋模块的计算机实现,基于Vega软件生成海浪.从效果图中可以看出,模拟的海浪效果比较好,能够满足实际应用的需求.     

Mesoscale high-frequency variability in the Alboran Sea and its influence on fish larvae distributions

This work analyses a multidisciplinary data set including hydrological and meteorological data, satellite images, and fish larvae abundance from a high-frequency experiment conducted along a north–south transect across the Western Alboran Sea anticyclonic gyre. Four consecutive occupations of the transect, crossing the frontal area, evidenced the high-frequency variability of hydrological structures and its influence on the latitudinal and vertical distribution of fish larvae in a period of a few days. The influence of dynamical processes on fish larvae depends on the location of the spawning as well as on the larval fish position in the water column. Wind induced upwelling and/or the southward drift of the Atlantic current transport larvae of neritic species, such as Sardina pilchardus and Engraulis encrasicolus to open sea areas. At the same time, these events bring about alterations in the latitudinal and vertical distributions of mesopelagic fish larvae. The species with a relatively surface distribution, as Ceratoscopelus maderensis, were transported and accumulated to the south of the Atlantic Jet (AJ), while those with a deeper distribution in the water column, as Maurolicus muelleri or Benthosema glaciale, would be upwelled and concentrated to the north. This study shows that it is difficult to extract conclusions about the mean or preferential distributions of fish larvae when one single/synoptic survey is considered and that time evolution of hydrological structures has to be considered in order to conclude.     

Integrating Climate and Ocean Change Vulnerability into Conservation Planning

Tropical coastal and marine ecosystems are particularly vulnerable to ocean warming, ocean acidification, and sea-level rise. Yet these projected climate and ocean change impacts are rarely considered in conservation planning due to the lack of guidance on how existing climate and ocean change models, tools, and data can be applied. Here, we address this gap by describing how conservation planning can use available tools and data for assessing the vulnerability of tropical marine ecosystems to key climate threats. Additionally, we identify limitations of existing tools and provide recommendations for future research to improve integration of climate and ocean change information and conservation planning. Such information is critical for developing a conservation response that adequately protects these ecosystems and dependent coastal communities in the face of climate and ocean change.     

Dissolved organic matter in shelf waters off the Ría de Vigo (NW Iberian upwelling system)

Net in situ production and export of dissolved organic carbon (DOC) and nitrogen (DON) have been studied in shelf waters off the Ría de Vigo (NW Spain), as part of a comprehensive hydrographic survey carried out from September 1994 to September 1995 with a fortnight periodicity. DOC and DON correlated well (r=+0.78), the slope of the regression line being 12.0±0.7 mol-C mol-N⁻¹, about twice the Redfieldian slope of particulate organic matter, 6.5±0.2 mol-C mol-N⁻¹ (r=+0.95). Labile DOC and DON accumulated in the upper 50 m during the upwelling season (March–September), mainly after prolonged periods of wind relaxation, when horizontal flows were reduced. This labile material represented 50% and 35% of the total (dissolved+particulate) organic carbon and nitrogen susceptible of microbial utilisation, which assert the key contribution of dissolved organic matter (DOM) to the export of new primary production in the NW Iberian upwelling system. This surface excess in shelf waters appeared to be formed into the highly productive Ría de Vigo (a large coastal indentation) at net rates of 4.4 μM-C d⁻¹ and 1.3 μM-C d⁻¹ in the inner and outer segments of the embayment respectively, and subsequently exported to the shelf. Once in the shelf, simple dilution with the inert DOM pool of recently upwelled Eastern North Atlantic Central Water (ENACW) occurred. Eventually, the DOM excess produced during the upwelling season is exported to the adjacent open ocean waters by the coastal circulation. Conversely, during the unproductive downwelling season (October–February), the lowest DOC and DON levels were recorded and export was prevented by the characteristic downwelling front associated to the seasonal poleward slope current.     

动态定位系统在深海钻井船上的应用

随着海洋石油工业由浅海向深海的转移,动态定位系统在海洋工程船舶中的应用越来越广泛,动态定位的级别也越来越高。本文就世界首艘圆筒形钻井平台某深海钻井平台的动态定位系统进行简单的阐述。