Variation in upwelling intensity along the NorthWest Iberian Peninsula (Galicia)

Thermohaline variables were simultaneously measured, July 17, 2000, at four Galician rias under favourable upwelling conditions to analyse upwelling intensity. The intensity of coastal upwelling is shown to be strongly dependent on the wind pattern. The maximum amplitudes of wind stress were observed at the western coast (0.30 Nm^-2) with southward direction (favourable to upwelling) and these are shown to be related to low temperature (12°C) and high salinity (35.8) in the estuaries mouth. From Cape Finisterre to Cape Estaca de Bares the wind stress showed a lower magnitude (0.05-0.10 Nm^-2) with a direction oblique to the coast. The temperature showed an increase (14°C) and the salinity a decrease (35.4) because the lower upwelling intensity at this part of the coast. The observed decrease in upwelling from south to north is not an isolated event, since the measured wind conditions are persistent during summer months, at least in the period with available QuikSCAT data (1999-2004).     

The oxygen minimum zone (OMZ) off Chile as intense source of CO2 and N2O

The oxygen minimum zones (OMZs) are recognized as intense sources of N₂O greenhouse gas (GHG) and could also be potential sources of CO₂, the most important GHG for the present climate change. This study evaluates, for one of the most intense and shallow OMZ, the Chilean East South Pacific OMZ, the simultaneous N₂O and CO₂ fluxes at the air–sea interface. Four cruises (2000–2002) and 1 year of monitoring (21°–30°–36°S) off Chile allowed the determination of the CO₂ and N₂O concentrations at the sea surface and the analysis of fluxes variations associated with different OMZ configurations. The Chilean OMZ area can be an intense GHG oceanic local source of both N₂O and CO₂. The mean N₂O fluxes are 5–10 times higher than the maximal previous historical source in an OMZ open area as in the Pacific and Indian Oceans. For CO₂, the mean fluxes are also positive and correspond to very high oceanic sources. Even if different coupling and decoupling between N₂O and CO₂ are observed along the Chilean OMZ, 65% of the situations represent high CO₂ and/or N₂O sources. The high GHG sources are associated with coastal upwelling transport of OMZ waters rich in N₂O and probably also in CO₂, located at a shallow depth. The integrated OMZ role on GHG should be better considered to improve our understanding of the past and future atmospheric CO₂ and N₂O evolutions.     

基于镭同位素分布的黄海和东海垂直混合速率计算

在黄海和东海采样测定了水体中的镭同位素分布,用平流扩散模型描述镭同位素分布,最小二乘方法计算了垂直涡动扩散系数和上升流或下降流流速.结果给出北黄海中部、南黄海中部、浙江沿岸和台湾北部海域存在上升流,流速分别为0.46×10-3cm·s-1、0.17×10-3~1.39×10-3cm·s-1、2.02×10-3~3.04×10-3 cm·s-1和1.06×10-3~2.51×10-3 cm·s-1.北黄海中部和东海东北部存在下降流.流速分别为-2.30×10-3 cm·s-1和-0.61×10-3~-2.10×10-3 cm·s-1.计算同时给出的垂直涡动扩散系数为5.84~48.2 cm2·s-1,平均值为22.3 cm2·s-1.北黄海和浙江沿岸上升流流速与文献的结果一致;北黄海中部存在下降流与文献的结论一致.本研究结果与文献结果一致是对所建立的方法的肯定,也是对文献研究结果的支持.     

极隙区电子束流模电磁不稳定性

解析地研究了中高度（离他心3－4个地球半径）极隙区极低密度上行电子束流引起的沿磁力线传播的电磁个稳定性，上行电子束流和背景等离子体都考虑成冷等离子体．结果表明，上行电子引起的左旋和右旋圆偏振电磁来流模是不稳定的，当它与离子回旋模耦合时增长率达到最大值，频率色散关系仍为电子束流模特征这此结果对解释权隙区纬度地面站低频电磁波观测资料和理解极隙区动力学过程是很有益的．     

Biological response to coastal upwelling and dust deposition in the area off Northwest Africa

Nutrient supply in the area off Northwest Africa is mainly regulated by two processes, coastal upwelling and deposition of Saharan dust. In the present study, both processes were analyzed and evaluated by different methods, including cross-correlation, multiple correlation, and event statistics, using remotely sensed proxies of the period from 2000 to 2008 to investigate their influence on the marine environment. The remotely sensed chlorophyll-a concentration was used as a proxy for the phytoplankton biomass stimulated by nutrient supply into the euphotic zone from deeper water layers and from the atmosphere. Satellite-derived alongshore wind stress and sea-surface temperature were applied as proxies for the strength and reflection of coastal upwelling processes. The westward wind and the dust component of the aerosol optical depth describe the transport direction of atmospheric dust and the atmospheric dust column load.     

On the magnitude of upwelling fluxes in shelf-break canyons

A hydrodynamic model is employed to derive the magnitude of on-shelf fluxes through a shelf-break canyon for a wide range of canyon sizes and ambient oceanic conditions. Predicted canyon-upwelling fluxes are of the order of 0.05–0.1 Sv (1 Sv=1 million m³/s), being several orders of magnitude greater than upslope fluxes in the bottom Ekman layer on the ambient continental slope. On the basis of ∼150 simulations conducted, a bulk formula of upwelling flux in a submarine canyon is derived. For typical conditions, the upwelling flux varies quadratically with forcing strength (speed of incident flow), linearly with canyon depth, and is inversely proportional to the buoyancy frequency of the density stratification inside the canyon. Other parameters such as density stratification above shelf-break depth and bottom friction are found to have minor influences on the resultant canyon-upwelling flux.     

长江中下游成矿带三维S波速度结构及对深部过程的约束

利用73个固定台站记录的163个远震事件数据,采用多道互相关技术挑选了5524条S波到时数据,并对S波到时数据进行地壳校正,在此基础上采用天然地震层析成像方法和远震S波到时信息,获得了长江中下游成矿带上地幔的三维S波速度结构模型.研究结果表明:(1)研究区域上地幔存在着明显的低速异常,且走向与成矿带相同,可能为上涌的软流圈热物质;(2)研究区域地幔过渡带和上地幔底部存在着明显的高速异常,可能为俯冲的古太平洋板块和拆沉的岩石圈;(3)成矿带上地幔的低速异常呈现由南向北逐渐变浅的空间分布特征,该特征表明软流圈热物质由南向北上涌.综合分析认为,成矿带中生代大规模岩浆活动和成矿作用的深部过程主要与岩石圈的拆沉密切相关.     

Net ecosystem metabolism of a coastal embayment fertilised by upwelling and continental runoff

O₂, N, P and Si net ecosystem metabolism of the Ría de Ares-Betanzos (NW Iberian upwelling system) was estimated during two 3-wk periods of contrasting summer downwelling and autumn upwelling conditions by means of a transient 2-D kinematic box model. The subtidal circulation was positive in both situations, although it was depressed during downwelling and enhanced during upwelling. Concurrently, the ría was fertilised mainly by shelf bottom waters, which introduced from 69% (under downwelling) to almost 100% (under upwelling) of the limiting N nutrients. The ría was an efficient nutrient trap: about 70% of the N nutrients that entered the embayment were retained under downwelling conditions (average flushing time, 9 days) and about 50% under upwelling conditions (average flushing time 3 days). Although the trapping efficiency was lower, the net ecosystem production (NEP) was much higher under upwelling (from 1.0±0.3 to 1.5±0.4 g C m⁻² d⁻¹), than under downwelling favourable winds (from 0.2±0.1 to 0.3±0.1 g C m⁻²). The stoichiometry of NEP suggests that P and N compounds recycled faster than C compounds, specially in the inner segment of the ría. The net degree of silification was twice in the inner than in the outer segment of the ría.     

Surface circulation downstream of the Point Arena upwelling center

Measurements from recently installed 5 MHz high-frequency radar (CODAR) stations south of Point Arena, California, are used to describe surface current patterns during the upwelling season (June-August 2007). The systems provide hourly current maps on a 5-km grid, covering a region from approximately 10 to 150 km offshore (the continental shelf into the deep ocean). These HF-radar observations provide an unprecedented view of circulation in this “coastal transition zone”, between the wind-driven circulation over the shelf and the California Current circulation offshore. Circulation patterns include: (1) bifurcation of the coastal upwelling jet downstream of Point Arena into an along-shelf (down-coast) branch and an offshore branch, and (2) a large-scale anticyclonic meander that often develops into an eddy-like recirculation south of the bifurcation. The “recirculation” feature extends well offshore, with surface currents 50-100 km from the coast consistently opposing the wind stress. The spatial and temporal evolution of the surface current features during upwelling events affects surface transport from Point Arena to areas in the south, increasing the travel time of a substantial fraction of newly upwelled water from a few days to roughly two weeks. Thus, surface currents even far offshore influence coastal transport of nutrients, phytoplankton and larvae on ecologically relevant timescales, with resultant connectivity patterns very different than implied by a simple examination of the mean flow.     

Long-term global sea surface temperature fluctuations and their possible influence on atmospheric CO2 concentrations

Changes of atmospheric CO₂ concentration since 1958 are shown to be related to sea surface temperature changes. The largest contribution to changes arises from the Pacific equatorial upwelling region, with the Indian Ocean and Atlantic contributing only small fractions to the variance. It is hypothesized that the observed relationship is related to the nutrients that are brought up by upwelling cold water, with photosynthesis contributing to a lowering of the partial pressure of CO₂ in the sea and thus to a greater tendency for a flux from the air to the sea.Possible longer term variations of sea temperature and CO₂ are discussed.