Significance: Seawater elemental composition, namely Mg:Ca and Sr:Ca ratios are widely used in marine sciences. Our new single-laboratory global dataset, combined with past data of seawater Mg:Ca and Sr:Ca ratios, suggests that modern ocean variability is significant across different environments, being similar to the changes during the Neogene Period (20 Ma). Because there is large variability in seawater ratios, we cannot assume that secular changes derived from fossilized taxa with varied ecological niches and from diverse ecosystems provide an unbiased representation of past global seawater chemistry. We suggest that the problem of inconsistencies in previous studies of, for example, paleo conditions from different fossil taxa may be reduced by accounting for taxonomic differences, ecosystems, and abiotic processes to overcome the regional environmental effect.

Danshuei River in the northwestern tip of Taiwan discharges into the boundary coastal waters between the East China Sea and the Taiwan Strait. We conducted a 5-year study between October 1998 and September 2003 to assess the influence of the northeast (NE) and the southwest (SW) monsoons on copepod assemblages in the area. A total of 110 copepod species were identified. Temora turbinata, Paracalanus aculeatus, Acrocalanus gibber, Parvocalanus crassirostris and Oithona rigida comprised 80% of the copepod assemblages that consisted of coastal species from the East China Sea and species associated with the Kuroshio Branch Current. The effect of the NE monsoon was observed during a short period of each winter when species such as Calanus sinicus were transported into the study area by the China Coastal Current. In summer, species such as A. gibber, Acrocalanus gracilis and Canthocalanus pauper may be transported into the study area from Southern Taiwan by the combined effect of the SW monsoon and the Kuroshio Current. Influence of the NE monsoon on the copepod assemblages in terms of introduction of species from the Yellow Sea and the East China Sea during winter was observed every year but was unlikely to represent an important carbon source into the region due to its short-term nature. Local species such as T. turbinata, P. crassirostris and O. rigida form a major component of the copepod assemblage. The high copepod diversity in the area was caused by the year-round presence of many local species and the aggregation of different species from subtropical, tropical, and temperate water masses. Monsoon-driven water currents and the Kuroshio Branch Current appeared to mask the effect of river discharge in the region.

Taiwan waters are oceanographically complex, being characterized by different water masses in the East China Sea, the South China Sea, the Pacific Ocean and the Taiwan Strait, which form contiguous but distinct ecosystems. These ecosystems interact one with another through complex and strong water circulations. The present work investigates the relatively few studied interactions between the local copepod communities and the heterogeneous hydrodynamical regimes. Gathering data from 53 cruises carried out since June 1998 to October 2004 all around Taiwan, this study leads to the mapping of eleven local calanoid assemblages taking into account the physical properties of the environment in which they appeared and the characteristics of their indicator species. Three of these identified assemblages were located in the tropical waters, southwest of Taiwan. First, the assemblage of the 2001 South China Sea sampling cruises revealed a tropical community dominated by Acrocalanus gracilis and Undinula vulgaris. In the other cluster, tropical calanoid species such as Labidocera detruncata, Centropages calaninus and A. monachus were found. The eight other assemblages were associated with the seasonal dynamics of the water masses north of Taiwan. Although the seasonal characteristics in the north can be subtle, the demarcation between these assemblages was clear. The early spring community is dominated by Calanus sinicus and followed by Temora turbinata since the beginning of summer. September marks a transition period to a new community characterized by the indicator species A. gibber. When the north-easterly monsoon prevails in winter, it is the turn of the community of northern common species such as Paracalanus parvus and Euchaeta concinna to prevail. In the mean time, C. sinicus starts its intrusion from the Yellow Sea and the East China Sea towards the northwest of Taiwan. Thus, according to our results, identified assemblages appear to be good indicators of different, distinctive, water masses.