A method is described for the quantitative determination of adenosine triphosphate (ATP) in quantities as low as lo4 pg. Using sample volumes of less than 2 liters, two profiles of ATP concentration have been made down to 1,025 m off the California coast.

[1] Spectral ultraviolet (UV) and visible irradiance has been measured at the South Pole between 1991 and 2003 by a SUV-100 spectroradiometer, which is part of the U.S. National Science Foundation's UV Monitoring Network. Here we present a new data edition, labeled ''Version 2.'' The new version was corrected for wavelength shift errors and deviations of the spectroradiometer from the ideal cosine response. A comprehensive uncertainty budget of the new data set was established. Below 400 nm the expanded standard uncertainty (coverage factor 2) varies between 4.6 and 7.2%, depending on wavelength and sky condition. The uncertainty of biologically relevant UV irradiances is approximately 6%. Compared to the previously published data set, Version 2 UV data are higher by 5-14%, depending on wavelength, solar zenith angle (SZA), and year of observation. By comparing Version 2 data with results of a radiative transfer model, the good consistency and homogeneity of the new data set were confirmed. The data set is used to establish a UV climatology for the South Pole, focusing on the effects of aerosols, clouds, and total column ozone. Clouds are predominantly optically thin; 71% of all clouds have an optical depth between 0 and 1. The average attenuation of UV irradiance at 345 nm by clouds is less than 5% and no attenuations greater than 23% were observed. Attenuation by homogeneous clouds is generally larger in the visible than in the UV. The wavelength dependence of cloud attenuation is quantitatively explained with the wavelength-dependent radiance distribution on top of clouds and the incidence-angle dependence of cloud transmittance. Largest radiation levels occur in late November and early December when low stratospheric ozone amounts coincide with relatively small SZAs. Owing to the large effect of the ''ozone hole,'' short-and long-term variability of UV during the austral spring is very high. When the ozone hole disappears, DNA-damaging irradiance can decrease by more than a factor of two within 2 days. Typical summer UV index values range between 2 and 3.5 and vary by ±30% (±1s) between different years. Linear regression analyses did not indicate statistically significant UV trends owing to the large year-to-year variability and the fact that the network was established only after the first occurrence of the ozone hole. Current measurements therefore document variability on an elevated level.

A new optical instrument, designed specifically to measure the natural or solar-induced fluorescence of chlorophyll a, was deployed in the tropical and temperate waters of the western South Pacific gyre. During the 12 days of transit from Pajpeete, Tahiti, to Auckland, New Zealand, measurements were made of the vertical distribution of temperature, salinity, upwelling radiance and downwelling irradiance at selected wavelengths, the beam attenuation coefficient at 683 nm, the scalar irradiance of photosynthetically available radiation (PAR), and the nadir radiance at 683 nm, which is the wavelength of peak emission by Chl a. In addition, water samples were collected at regular depth intervals and analyzed for the concentration of Chl a and for the spectral absorption coefficient of cells and associated detrital particles. To examine the relationship between natural fluorescence and the size and photosynthetic rate of the phytoplankton crop, we derived several simple equations and applied them to the analysis of the data. One relates the nadir radiance at 683 nm to the total fluorescence emitted by the phytoplankton crop within the field ofview, another relates natural fluorescence to the concentration of Chl a, and a third relates natural fluorescence to the gross rate of photosynthesis of the crop.We found that even in the extremely oligotrophic waters of the central South Pacific gyre, natural fluorescence was easily measured throughout the euphotic zone at depths >6 m. As found in previous studies, the value of natural fluorescence varied spatially and temporally with ambient scalar irradiance of PAR and the concentration of Chl .a. The quantum yield of fluorescence, which varied fivefold, averaged about 0.035 photons emitted to photons absorbed and generally decreased with increasing levels of exciting irradiance. Most importantly, we found natural fluorescence covaried closely with calculated rates of photosynthesis. A linear regression of calculated photosynthetic rate on fluorescence yielded a correlation coefficient of 0.84 and a slope of 2.0 atoms of carbon fixed per photon emitted as fluorescence.

[1] Spectral ultraviolet (UV) and visible irradiance has been measured near Barrow, Alaska (71°N, 157°W), between 1991 and 2005 with a SUV-100 spectroradiometer. The instrument is part of the U.S. National Science Foundation's UV Monitoring Network. Here we present results based on the recently produced ''version 2'' data release, which supersedes published ''version 0'' data. Cosine error and wavelength-shift corrections applied to the new version increased biologically effective UV dose rates by 0-10%. Corrected clear-sky measurements of different years are typically consistent to within ±3%. Measurements were complemented with radiative transfer model calculations to retrieve total ozone and surface albedo from measured spectra and for the separation of the different factors influencing UV and visible radiation. A climatology of UV and visible radiation was established, focusing on annual cycles, trends, and the effect of clouds. During several episodes in spring of abnormally low total ozone, the daily UV dose at 305 nm exceeded the climatological mean by up to a factor of 2.6. Typical noontime UV Indices during summer vary between 2 and 4; the highest UV Index measured was 5.0 and occurred when surface albedo was unusually high. Radiation levels in the UV-A and visible exhibit a strong spring-autumn asymmetry. Irradiance at 345 nm peaks on approximately 20 May, 1 month before the solstice. This asymmetry is caused by increased cloudiness in autumn and high albedo in spring, when the snow covered surface enhances downwelling UV irradiance by up to 57%. Clouds reduce UV radiation at 345 nm on average by 4% in March and by more than 40% in August. Aerosols reduce UV by typically 5%, but larger reductions were observed during Arctic haze events. Stratospheric aerosols from the Pinatubo eruption in 1991 enhanced spectral irradiance at 305 nm for large solar zenith angles. The year-to-year variations of spectral irradiance at 305 nm and of the UV Index are mostly caused by variations in total ozone and cloudiness. Changes in surface albedo that may occur in the future can have a marked impact on UV levels between May and July. No statistically significant trends in monthly mean noontime irradiance were found.

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