Consequences of winter upwelling events on biogeochemical and phytoplankton patterns in a western Galician ria (NW Iberian peninsula)

The consequences of two upwelling events in mid- (MW) and late (LW) winter on biogeochemical and phytoplankton patterns were studied in the Pontevedra Ria and compared with the patterns measured under typical winter conditions and under a summer upwelling event. Thermohaline patterns measured during the mid-winter upwelling event (MW-up) revealed the intrusion of saltier seawater (35.9) into the ria associated with the Iberian Poleward Current (IPC). During the late-winter upwelling event (LW-up), the seawater which had welled up into the ria showed characteristics of the Eastern North Atlantic Central Water mass (ENACW). In both cases the measured water residence time (4 days during MW-up and 10 days during LW-up) was related to both meteorological and fluvial forcing. This residence time contrasts with that of summer upwelling (7 days) and with that estimated under unfavorable upwelling atmospheric conditions (2–4 weeks). During MW-up, the ria became poor in nutrients due to continental freshwater dilution, associated with the shorter residence time of the water, and the intrusion of IPC, which is a water body poor in nutrient salts: 2.9 μM of nitrate, 0.1 μM of phosphate and 1.5 μM of silicate. During this event, the ria exported 3.4 mol_DIN s⁻¹, compared with 6.9 mol_DIN s⁻¹ in non-upwelling conditions. Phytoplankton showed a uniform distribution throughout the ria, as during unfavorable upwelling conditions, and was characterized by the dominance of diatoms, mainly Nitzschia longissima and Skeletonema costatum. During LW-up, a nutrient depletion in the photic layer also occurred, but as a result of a phytoplankton spring bloom developing at this time. The ria was a nutrient trap where 4.1 mol_DIN s⁻¹ were processed by photosynthesis. This budget is three times higher than the one under non-upwelling conditions. In contrast with the MW-up, which had no effect on primary production, during LW-up the ria became more productive, although not as productive as during a summer upwelling event (9.9 mol_DIN s⁻¹). The taxonomic composition of the phytoplankton community did not change noticeably during LW-up and the summer upwelling, with the same species present and changing only in relative proportions. Diatoms were always the dominant microphytoplankton community, with Pseudonitzschia pungens, Thalassionema nitzschioides and several species of Chaetoceros as characteristic taxons.     

台湾海峡上升流区夏季溶解氧的特征

本文根据1983—1984年,1987—1988年台湾海峡中北部海域调查资料,着重讨论了该海域夏季溶解氧分布特征及其与上升流、生物活动的关系。该上升流区温度、盐度、溶解氧含量及其饱和度的特征值分别为24.4℃,34.3,4.49mlO_2/L和93％。溶解氧含量及其饱和度与温度呈正相关关系,与盐度呈负相关关系。     

台湾海峡中、北部及邻近海域夏季浮游动物总生物量的分布特点

台湾海峡中、北部夏季浮游动物（非胶质）总生物量较丰富，1983年夏季的总生物量高于其他季节，1987年7、8月和1988年7月则高于1983年同期的生物量，这3a的高生物量分布区，一般都连片出现在上升流锋面区，显然和上升流的出现有密切关系。构成高生物量的优势种以外海广高盐种为主，生物量和高生物量区的分布态势都存在年际变化，这可能和不同性质水系的消长，相互推移及被囊动物的摄食竞争有关。     

台湾海峡中、北部上升流区浮游有孔虫的生态研究

分析１９８７—１９８８年在台湾海峡中、北部用浮游生物网采集的水层中的浮游有孔虫标本，研究调查海区浮游有孔虫的生态分布特征及其与海水温度和盐度的关系。结果表明：该海区浮游有孔虫计有１６种，以泡抱球虫Ｇｌｏｂｉｇｅｒｉｎａｂｕｌｌｏｉｄｅｓ为主要优势种类，其次是袋拟抱球虫Ｇｌｏｂｉｇｅｒｉｎｏｉｄｅｓｓａｃｃｕｌｉｆｅｒ和红拟抱球虫Ｇ．ｒｕｂｅｒ。在夏季的７月和８月（特别是７月），浮游有孔虫密集在福建中部沿岸的南日岛至闽江口外海海域一带沿岸水域，其中９０％以上的个体由泡抱球虫组成。此现象推测与夏季出现在福建沿岸的上升流活动有关。     

南海东北部表层沉积中有孔虫的分布及其环境意义

为了探讨南海东北部表层沉积中有孔虫分布的规律，选取184个表层样进行分析，结果发现有孔虫的垂向分布与碳酸盐的溶解作用密切相关。在2300－2500m水深以下，浮游有孔虫丰度迅速减小，而底栖有孔虫占有孔虫全群的比值BF／（BF＋PF）以及底栖有孔虫胶结质壳类的百分含量则迅速增加，这三者随水深的变化在3400－3500m处有一明显的转变，被认为是南海东北部CCD面（碳酸盐补偿深度）所在的位置，且该研究区内碳酸盐补偿深度南部较北部深100m。浮游有孔虫水平分布除了受表层海水温度的的控制外，黑潮南海分支以及吕宋岛北端上升流区带来的富营养水体的存在也起很重要的作用。