Floral patterns in the California Current System off southern California: 1990–1996

In 1990, CalCOFI cruises began routine collection of samples for the enumeration of phytoplankton species. From each quarterly cruise, nearsurface samples from 34 stations are pooled into four regional samples prior to counting. This paper summarizes the first 6.5 years of the program in order to identify major large-scale patterns of species composition and fluctuations. A total of 312 species were recognized during this study. Recurrent group analysis defines two major floral clusters. The first is composed of diatoms characteristic of enriched regions. This cluster is most abundant in the northeastern region and often attains maximum abundances in the spring. Seventy-two percent of the variability of chlorophyll is accounted for by the variability of these species. The second cluster is composed of species common in the offshore central North Pacific. These species have relatively low spatial and temporal variability in the study region. There is no detectable seasonality. In neither cluster can interannual variability be detected above seasonal variability, spatial variability and error. These patterns differ from the geographic patterns of zooplankton species in the region, which are often dominated by fauna from the subarctic North Pacific and transition zone. The apparent absence of a similar subarctic flora is briefly discussed

Floral patterns in the California Current: The coastal-offshore boundary zone

This study quantified the vertical distributions of 294 taxa of phytoplankton from 112 samples in a vertical section across the California Current system off Southern California. The goal was to examine the relationship between coastal and offshore floras throughout the euphotic zone. The two associations were distinct throughout the upper 140 m. The coastal flora was found in water adjacent to and east of the Santa Rosa Ridge. The offshore flora occurred west of the California Current, and also at the station immediately east of the current, presumably the result of upstream entrainment across it. Both coastal and offshore floras were similar to the analogous floras described from the mixed layers in the springs of 1993 and 1995, in spite of different ENSO conditions prevailing during the three years.There were two unexpected results. Although the hydrographic characteristics of offshore water had been strongly modified by mixing with California Current water, the offshore flora remained similar to that of a central Pacific study site, 3000 km to the west. Clearly, the maintenance of this species association is not directly dependent upon temperature or salinity. In contrast, even though the temperature-salinity relationship of the California Current fell within the envelop of T-S relationships of source water to the north, the floristic analyses identified no flora unique to the California Current. Absence of oceanic subarctic species in the Current may be related to upstream depletion of nutrients

Environmental heterogeneity and plankton community structure in the central North Pacific

Spatial and temporal patterns of heterogeneity in nutrients (PO4, NO3), integrated water column chlorophyll, integrated water column primary production, and macrozooplankton biomass in the central North Pacific are described on spatial scales ranging from less than one to several thousand kilometers and on temporal scales from one day to 12 years. Fluctuations in these properties represent an index of the biological response of the ecosystem to physical forcing on various scales. These patterns are an important aspect of ecosystem structure because environmental perturbations may affect the outcome of biological interactions between populations. Heterogeneity in each property was low on all scales. Diel changes were evident only in macrozooplankton biomass, and no seasonal cycles were detected. This is consistent with a low overall level of physical forcing, little advection from outside the system into it, and lack of seasonal changes in nutrient flux to the euphotic zone. The central North Pacific shows relatively low heterogeneity, especially on mesoscales (tens to hundreds of kilometers), when compared to other pelagic ecosystems, suggesting that environmental disturbances do not have a major effect upon macrozooplankton and nekton populations

An unexpected nitrate distribution in the tropical North Atlantic at 18°N, 30°W—implications for new production

During a R.V. Meteor JGOFS-NABE cruise to a tropical site in the northeast Atlantic in spring 1989, three different vertical regimes with respect to nitrate distribution and availability within the euphotic zone were observed. Besides dramatic variations in the depth of the nitracline, a previously undescribed nose-like nitrate maximum within the euphotic zone was the most prominent feature during this study. Both the vertical structure of phytoplankton biomass and the degree of absolute and relative new production were related to the depth of the nitracline, which in turn was dependent on the occurrence/non-occurrence of the subsurface subtropical salinity maximum (S(max)). The mesoscale variability of the nitracline depth, as indicated from a pre-survey grid, and published data on the frequent occurrence of the S(max) in tropical waters suggest higher variability of new production and F-ratio than usually expected for oligotrophic oceans. The importance of salt fingering and double diffusion for nitrate transport into the euphotic zone is discussed

Ocean colour changes in the North Pacific since 1930

In this paper we present an analysis of historical ocean colour data from the North Pacific Ocean. This colour is described by the Forel-Ule colour index, a sea colour comparator scale that is composed of 21 tube colours that is routinely measured since the year 1890. The main objective of this research is to characterise colour changes of the North Pacific Ocean at a timescale of decades. Next to the seasonal colour changes, due to the yearly cycle of biological activity, this time series between 1930 and 1999 might contain information on global changes in climate conditions. From seasonal independent analyses of the long-term variations it was found that the greenest values, with mean Forel-Ule scale ((FU) ̅) of 4.1 were reached during the period of 1950-1954, with a second high ((FU) ̅ = 3) in the period 1980-1984. The bluest ocean was encountered during the years 1990-1994. The data indicate that after 1955 a remarkable long bluing took place till 1980

Temporal patterns of phytoplankton assemblages, size spectra and diversity during the wane of a Phaeocystis globosa spring bloom in hydrologically contrasted coastal waters

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