PLANKTONIC FORAMINIFERA: DIFFERENTIAL PRODUCTION AND EXPATRIATION OFF BAJA CALIFORNIA1

• Published in: Limnology and Oceanography
• Main Author: Berger, Wolfgang H.
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 1970
• Subjects: Aquatic Science; Oceanography; Planktonic foraminifera
• Online Access: http://dx.doi.org/10.4319/lo.1970.15.2.0183; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.4319%2Flo.1970.15.2.0183; https://aslopubs.onlinelibrary.wiley.com/doi/pdf/10.4319/lo.1970.15.2.0183

The species composition, living: dead ratios, morphology, and size distribution of planktonic foraminifera were studied in 54 depth‐controlled tow samples using a 333‐ µ net (0– 3,000 m) from northwest of Guadalupe Island, Baja California. Paired sampling and replicate tows permitted the determination of confidence limits on concentration and percentage estimates. Average concentrations of living foraminifera range from about 1/m 3 in shallow water to less than 1/1,000 m 3 at depth. Concentrations of empty shells are between 3 to 10/1,000 m 3 throughout. The depth of equal standing stock for live and empty individuals is between 5,000 and 10,000 in. The minimum replacement time for the living populations corresponds to the settling time through this column and is between 5 and 40 days. The apparent replacement times vary considerably between species and between sizes within species. The living assemblage consists of a mixture of northern, central, and southern species dominated by northern ones. Central water species are relatively abundant immediately below the surface water. The southern element has a maximum at about 1,000‐m depth. This distribution is in agreement with physical measurements, suggesting shallow entrainment of central water into the California Current and indicating a countercurrent at depth. It is suggested that the fauna contained in the oxygen‐poor intermediate water is expatriated and that its great proportion of specimens with small terminal chambers (“kummerforms”) is due to unfavorable living conditions during submergence. The notion that kummerform development indicates termination or slowing of growth is supported by a trend toward increase of kummerform proportions in living populations in large shell sizes and at subsurface depths and by the relatively high empty shell output of kummerforms. Oceanic stability of past ages may be recognized in fossil foraminiferal deposits if oceanic mixing enhances kummerform development and if the effects of differential preservation can be ...