ALBERT

Description: In recent years, an increasing number of studies on phytoplankton in the tropical South China Sea (SCS) and Sulu Sea (SS) have been conducted. However, still little is known about the photophysiological state of natural phytoplankton communities under varying environmental conditions. This study investigates the photophysiological state of natural phytoplankton communities in the southern SCS and SS based on high horizontal and vertical resolution field observations collected during the SHIVA (Stratosphere ozone: Halogens in a Varying Atmosphere) cruise (SO 218) in November 2011 on board RV Sonne. At the surface, pigment results revealed that total chlorophyll a (TChl a ) concentrations at all offshore stations were low at the surface and were generally dominated by cyanobacteria. Enhanced concentrations of TChl a were only observed below the upper mixed layer and above the euphotic depth with haptophytes, prochlorophytes and prasinophytes contributing most of the biomass. At stations close to the coast and river outflows, surface phytoplankton blooms (between 1 to 2.2 mg m−3) dominated by diatoms were observed. Overall, the study region exhibited strong nitrate + nitrite (NOx, 〈 1 μmol L−1), and phosphate (PO4, 〈 0.2 μmol L−1) depletion from surface down to about 50–60 m. Silicate (Si) exhibited similar trends with the exception of some near shore stations in which high Si concentrations (〉 2 μmol L−1) were observed in conjunction with increased TChl a and diatoms concentrations. Surface NOx concentrations were observed to correlate positively with temperature (τ = 0.22, p 〈 0.05, n = 108), whereas negative correlations were reported between surface NOx (τ = −0.27, p 〈 0.05, n = 108), Si (τ = −0.68, p 〈 0.05, n = 108) and salinity indicating that the enhancement in nutrients at the surface was probably supplied through fresher and warmer river waters near the coast. In contrast, the opposite was observed between temperature, salinity and all nutrients in the water column suggesting that nutrients were supplied from the bottom through upwelling. Pigment gradients show that phytoplankton were optimising their pigment composition to acclimate to changes in the light climate and cells were in a competent state as suggested by high maximum photochemical efficiency values (Fv/ Fm, 〉 0.4).

Description: In recent years, an increasing number of studies on phytoplankton in the tropical South China Sea (SCS) and Sulu Sea (SS) have been conducted. However, still little is known about the photophysiological state of natural phytoplankton communities under varying environmental conditions. This study investigates the photophysiological state of natural phytoplankton communities in the southern SCS and SS based on high horizontal and vertical resolution field observations collected during the SHIVA (Stratosphere ozone: Halogens in a Varying Atmosphere) cruise (SO 218) in November 2011 on board RV Sonne. At the surface, pigment results revealed that total chlorophyll a (TChl a ) concentrations at all offshore stations were low at the surface and were generally dominated by cyanobacteria. Enhanced concentrations of TChl a were only observed below the upper mixed layer and above the euphotic depth with haptophytes, prochlorophytes and prasinophytes contributing most of the biomass. At stations close to the coast and river outflows, surface phytoplankton blooms (between 1 to 2.2 mg m−3) dominated by diatoms were observed. Overall, the study region exhibited strong nitrate + nitrite (NOx, 〈 1 μmol L−1), and phosphate (PO4, 〈 0.2 μmol L−1) depletion from surface down to about 50–60 m. Silicate (Si) exhibited similar trends with the exception of some near shore stations in which high Si concentrations (〉 2 μmol L−1) were observed in conjunction with increased TChl a and diatoms concentrations. Surface NOx concentrations were observed to correlate positively with temperature (τ = 0.22, p 〈 0.05, n = 108), whereas negative correlations were reported between surface NOx (τ = −0.27, p 〈 0.05, n = 108), Si (τ = −0.68, p 〈 0.05, n = 108) and salinity indicating that the enhancement in nutrients at the surface was probably supplied through fresher and warmer river waters near the coast. In contrast, the opposite was observed between temperature, salinity and all nutrients in the water column suggesting that nutrients were supplied from the bottom through upwelling. Pigment gradients show that phytoplankton were optimising their pigment composition to acclimate to changes in the light climate and cells were in a competent state as suggested by high maximum photochemical efficiency values (Fv/ Fm, 〉 0.4)

Description: Marine brominated and iodinated halocarbons participate in catalytic ozone destruction and aerosol formation in the troposphere and they also have a significant impact on stratospheric ozone. While the tropical oceans are a known source of these very short lived substances (VSLS), including e.g. bromoform (CHBr3) and methyliodide (CH3I), the tropical Western Pacific waters are largely uncharacterized for these compounds. Coastal macro algae, regionally enhanced phytoplankton abundance, photochemical reactions and local anthropogenic sources are expected to contribute to strong marine emissions. As high convective activity with fast efficient uplift takes place throughout the year, the western Pacific is projected to be a hot spot for oceanic VSLS supply to the stratosphere. In this study, we present first results from the SHIVA Sonne expedition to the South China Sea during November 2011. The research cruise was embedded within the framework of the EU-project SHIVA (Stratospheric ozone: Halogen Impacts in a Varying Atmosphere). During the cruise we investigated the large variability of the VSLS concentrations in both ocean and atmosphere using several methods, including in-situ atmospheric measurements, air canister sampling, purge and trap gas chromatography with electron capture and mass spectrometric detection. We will intercompare the results from various methods and present highlights from the expedition including atmospheric and oceanic VSLS data, as well as first estimates of emissions.

Description: A field intercomparison was conducted at the Acqua Alta Oceanographic Tower (AAOT) in the northern Adriatic Sea, from 9 to 19 July 2018 to assess differences in the accuracy of in- and above-water radiometer measurements used for the validation of ocean colour products. Ten measurement systems were compared. Prior to the intercomparison, the absolute radiometric calibration of all sensors was carried out using the same standards and methods at the same reference laboratory. Measurements were performed under clear sky conditions, relatively low sun zenith angles, moderately low sea state and on the same deployment platform and frame (except in-water systems). The weighted average of five above-water measurements was used as baseline reference for comparisons. For downwelling irradiance ( Ed ), there was generally good agreement between sensors with differences of 〈6% for most of the sensors over the spectral range 400 nm–665 nm. One sensor exhibited a systematic bias, of up to 11%, due to poor cosine response. For sky radiance ( Lsky ) the spectrally averaged difference between optical systems was 〈2.5% with a root mean square error (RMS) 〈0.01 mWm−2 nm−1 sr−1. For total above-water upwelling radiance ( Lt ), the difference was 〈3.5% with an RMS 〈0.009 mWm−2 nm−1 sr−1. For remote-sensing reflectance ( Rrs ), the differences between above-water TriOS RAMSES were 〈3.5% and 〈2.5% at 443 and 560 nm, respectively, and were 〈7.5% for some systems at 665 nm. Seabird-Hyperspectral Surface Acquisition System (HyperSAS) sensors were on average within 3.5% at 443 nm, 1% at 560 nm, and 3% at 665 nm. The differences between the weighted mean of the above-water and in-water systems was 〈15.8% across visible bands. A sensitivity analysis showed that Ed accounted for the largest fraction of the variance in Rrs , which suggests that minimizing the errors arising from this measurement is the most important variable in reducing the inter-group differences in Rrs . The differences may also be due, in part, to using five of the above-water systems as a reference. To avoid this, in situ normalized water-leaving radiance ( Lwn ) was therefore compared to AERONET-OC SeaPRiSM Lwn as an alternative reference measurement. For the TriOS-RAMSES and Seabird-HyperSAS sensors the differences were similar across the visible spectra with 4.7% and 4.9%, respectively. The difference between SeaPRiSM Lwn and two in-water systems at blue, green and red bands was 11.8%. This was partly due to temporal and spatial differences in sampling between the in-water and above-water systems and possibly due to uncertainties in instrument self-shading for one of the in-water measurements.