Properties of seawater and particulate matter from a FRRF instrument, operating in a flow-through mode on the continuous surface water sampling system during the Tara Oceans expedition 2009-2013

The Tara Oceans Expedition (2009-2013) sampled the world oceans on board a 36 m long schooner, collecting environmental data and organisms from viruses to planktonic metazoans for later analyses using modern sequencing and state-of-the-art imaging technologies. Tara Oceans Data are particularly suited to study the genetic, morphological and functional diversity of plankton. The present data set provides continuous measurements made with a FRRF instrument, operating in a flow-through mode during the 2009-2012 part of the expedition. It operates by exciting chlorophyll fluorescence using a series of short flashes of controlled energy and time intervals (Kolber et al, 1998). The fluorescence transients produced by this excitation signal were analysed in real-time to provide estimates of abundance of photosynthetic pigments, the photosynthetic yields (Fv/Fm), the functional absorption cross section (a proxy for efficiency of photosynthetic energy acquisition), the kinetics of photosynthetic electron transport between Photosystem II and Photosystem I, and the size of the PQ pool. These parameters were measured at excitation wavelength of 445 nm, 470nm, 505 nm, and 535 nm, allowing to assess the presence and the photosynthetic performance of different phytoplankton taxa based on the spectral composition of their light harvesting pigments. The FRRF-derived photosynthetic characteristics were used to calculate the initial slope, the half saturation, and the maximum level of Photosynthesis vs Irradiance relationship. FRRF data were acquired continuously, at 1-minute time intervals.

Investigation of manganese nodules from the Southern Tasman Sea

Two manganese nodules having a high clay content, a low Mn/Fe ratio, and low contents of valuable metals (Ni 0.25%, Cu 0.17%, Co 0.06%) were recovered in a grab sample during a short geological cruise in HMAS Kimbla in the southern Tasman Sea in May 1979. Five stations were occupied. Free-fall grabs recovered sediment or pumice from four stations; nothing was recovered from the fifth. The carbonate compensation depth in the region is about 4500 m. Reddish brown clay, but no manganese nodules, was recovered in the central southern Tasman Sea, from depths of 4900-5100 m. The nodules, together with grey calcareous mud, were obtained from a depth of 4300 m, farther to the northwest, near Gascoyne Seamount (250 n. miles SE of Sydney). The results suggest nodules with high metal values are likely to exist only in the broad and deep depression in the central southern Tasman Sea southeast of Gascoyne Seamount, where sedimentation rates are low and oxidising conditions prevail. Whether nodule fields are present or not will only be resolved by considerably more sampling.

Seawater carbonate chemistry and photosynthesis of a coccolithophorid in a laboratory experiment

Mixing of seawater subjects phytoplankton to fluctuations in photosynthetically active radiation (400-700 nm) and ultraviolet radiation (UVR; 280-400 nm). These irradiance fluctuations are now superimposed upon ocean acidification and thinning of the upper mixing layer through stratification, which alters mixing regimes. Therefore, we examined the photosynthetic carbon fixation and photochemical performance of a coccolithophore, Gephyrocapsa oceanica, grown under high, future (1,000 µatm) and low, current (390 µatm) CO2 levels, under regimes of fluctuating irradiances with or without UVR. Under both CO2 levels, fluctuating irradiances, as compared with constant irradiance, led to lower nonphotochemical quenching and less UVR-induced inhibition of carbon fixation and photosystem II electron transport. The cells grown under high CO2 showed a lower photosynthetic carbon fixation rate but lower nonphotochemical quenching and less ultraviolet B (280-315 nm)-induced inhibition. Ultraviolet A (315-400 nm) led to less enhancement of the photosynthetic carbon fixation in the high-CO2-grown cells under fluctuating irradiance. Our data suggest that ocean acidification and fast mixing or fluctuation of solar radiation will act synergistically to lower carbon fixation by G. oceanica, although ocean acidification may decrease ultraviolet B-related photochemical inhibition.

Photophysiological responses of Southern Ocean phytoplankton to changes in CO2 concentrations: Short-term versus acclimation effects

The present study examines how different pCO2 acclimations affect the CO2- and light-dependence of photophysiological processes and O2 fluxes in four Southern Ocean (SO) key phytoplankton species. We grew Chaetoceros debilis (Cleve), Pseudo-nitzschia subcurvata (Hasle), Fragilariopsis kerguelensis (O'Meara) and Phaeocystis antarctica (Karsten) under low (160 µatm) and high (1000 ?atm) pCO2. The CO2- and light-dependence of fluorescence parameters of photosystem II (PSII) were determined by means of a fluorescence induction relaxation system (FIRe). In all tested species, nonphotochemical quenching (NPQ) is the primary photoprotection strategy in response to short-term exposure to high light or low CO2 concentrations. In C. debilis and P. subcurvata, PSII connectivity (p) and functional absorption cross-sections of PSII in ambient light (sigma PSII') also contributed to photoprotection while changes in re-oxidation times of Qa acceptor (tQa) were more significant in F. kerguelensis. The latter was also the only species being responsive to high acclimation pCO2, as these cells had enhanced relative electron transport rates (rETRs) and sigma PSII' while tQa and p were reduced under short-term exposure to high irradiance. Low CO2-acclimated cells of F. kerguelensis and all pCO2 acclimations of C. debilis and P. subcurvata showed dynamic photoinhibition with increasing irradiance. To test for the role and presence of the Mehler reaction in C. debilis and P. subcurvata, the light-dependence of O2 fluxes was estimated using membrane inlet mass spectrometry (MIMS). Our results show that the Mehler reaction is absent in both species under the tested conditions. We also observed that dark respiration was strongly reduced under high pCO2 in C. debilis while it remained unaltered in P. subcurvata. Our study revealed species-specific differences in the photophysiological responses to pCO2, both on the acclimation as well as the short-term level.