Primary production and nutrient assimilation in the Iberian upwelling in August 1998

Primary production was measured during two Lagrangian experiments in the Iberian upwelling. The first experiment, in a body of upwelled water, measured day-to-day changes in phytoplankton activity as the water mass moved south along the shelf break. Nutrient concentrations decreased over a five day period, with concomitant increases in phytoplankton biomass. Initially the maximum phytoplankton biomass was in the upper 10m but after four days, a sub-surface chlorophyll maximum was present at 30m. Depth-integrated primary production at the beginning of the experiment was 70mmolC.m⁻².d⁻¹ (838mgC.m⁻².d⁻¹) and reached a maximum of 88mmolC.m⁻².d⁻¹ (1053mgC.m⁻².d⁻¹) on day 3. On day 1, the picoplankton fraction (<2μm) was slightly more productive than larger (>5μm) phytoplankton, but the increase in overall production during the drift experiment was by these larger cells. Nitrate was the dominant nitrogen source. As nutrient concentrations declined, ammonium became increasingly more important as a nitrogen source and the f-ratio decreased from 0.7 to 0.5. Picoplankton cells (<2μm) were responsible for most (65–80%) of the ammonium uptake. The C:N:P uptake ratios were very close to the Redfield ratio for the first four days but as nutrients became depleted high C:N uptake ratios (11 to 43) were measured. Over the period of the experiment, nitrate concentration within the upper 40m decreased by 47.91mmolN.m⁻². In vitro estimates, based on ¹⁵N nitrate uptake, accounted for 56% of the decrease in nitrate concentration observed in the drifting water mass. Ammonium uptake over the same four day period was 16.28mmolN.m⁻², giving a total nitrogen uptake of 43.18mmolN.m⁻².In the second experiment, an offshore filament was the focus and a water mass was sampled as it moved offshore. Nutrient concentrations were very low (nitrate was <10nmol l⁻¹ and ammonium was 20–40nmol l⁻¹). Primary production rate varied between 36mmolC.m⁻².d⁻¹ (436mgC.m⁻².d⁻¹) and 21mmolC.m⁻².d⁻¹ (249mgC.m⁻².d⁻¹). Picophytoplankton was the most productive fraction and was responsible for a constant proportion (ca 0.65) of the total carbon fixation. Uptake rates of both nitrate and ammonium were between 10 and 20% of those measured in the upwelling region. Urea could be a very significant nitrogen source in these waters with much higher uptake rates than nitrate or ammonium; urea turnover times were ca. one day but the source of the urea remains unknown. Urea uptake had a profound effect on calculated f ratios. If only nitrate and ammonium uptake was considered, f ratios were calculated to be 0.42–0.46 but inclusion of urea uptake reduced the f ratio to <0.1. The primary production of this oligotrophic off-shore filament was driven by regenerated nitrogen.     

AK Herculis — An atypical W UMa-type system

AK Herculis is a contact binary of spectral class F with a number of obvious peculiarities such as a displacement of secondary eclipse from phase 0 _. ^P 500, unequal heights of the maxima, and a possibly sinusoidal (60 yr) period variation. The light curve is variable and shows erratic short-term behavior, although the latter effects are not unusual for a short period contact binary. Here we present new photoelectric light curves in theB andV passbands and derive several new times of minima. The new observations are compared graphically with seven earlier light curves. We analyzed the new observations and those by Bookmyer (1972) by the method of differential corrections. We find that the temperature difference between components is too large (1000 K) for AK Her to be considered a normal W UMa-system, but too small to allow a detached configuration obeying the mass-luminosity law. The solutions of both series of observations clearly indicate a contact configuration. Other unusual findings include a bolometric albedo greater than 2, and rather low values for the limb-darkening coefficients. We offer some possible reasons for these peculiarities. The mass ratio seems well determined from the photometry and is about 0.26, which is much lower than assumed in most earlier papers. The brightness and color of the known visual companion, ADS 10408B, were found by the differential corrections program. They agree, within observational error, with values found directly at the 200-in. telescope by Eggen, despite the fact that the B component contributes only a few percent of the light of the multiple system. The suggestion by Schmidt and Herczeg (1959) that a fourth body is responsible for the sinusoidal period variation seems stronger now than when first proposed. To encourage a search for this hypothetical component, we have tabulated expected values for its angular separation and relative mass with respect to the eclipsing pair, as well as the amplitude of the expected variable proper motion of the eclipsing pair. Discovery as a visual component seems impossible with present means, but the variable proper motion should be detectable. Thus we suggest that ADS 10408A (AK Her) be observed astrometrically. If a search for the predicted variable proper motion proves negative, mass transfer would remain the only plausible mechanism to explain the period change. We advance a different reason than did Schmidt and Herczeg to explain the phase lag of secondary eclipse.     

Correlation of the Rockland ash bed,a 400,000-year-old stratigraphic marker in northern California and western Nevada,and implications for middle Pleistocene paleogeography of central California

Outcrops of an ash bed at several localities in northern California and western Nevada belong to a single air-fall ash layer, the informally named Rockland ash bed, dated at about 400,000 yr B.P. The informal Rockland pumice tuff breccia, a thick, coarse, compound tephra deposit southwest of Lassen Peak in northeastern California, is the near-source equivalent of the Rockland ash bed. Relations between initial thickness of the Rockland ash bed and distances to eruptive source suggest that the eruption was at least as great as that of the Mazama ash from Crater Lake, Oregon. Identification of the Rockland tephra allows temporal correlation of associated middle Pleistocene strata of diverse facies in separate depositional basins. Specifically, marine, littoral, estuarine, and fluvial strata of the Hookton and type Merced formations correlate with fluvial strata of the Santa Clara Formation and unnamed alluvium of Willits Valley and the Hollister area, in northwestern and west-central California, and with lacustrine beds of Mohawk Valley, fluvial deposits of the Red Bluff Formation of the eastern Sacramento Valley, and fluvial and glaciofluvial deposits of Fales Hot Spring, Carson City, and Washoe Valley areas in northeastern California and western Nevada. Stratigraphic relations of the Rockland ash bed and older tephra layers in the Great Valley and near San Francisco suggest that the southern Great Valley emerged above sea level about 2 my ago, that its southerly outlet to the ocean was closed sometime after about 2 my ago, and that drainage from the Great Valley to the ocean was established near the present, northerly outlet in the vicinity of San Francisco Bay about 0.6 my ago.