Comparison of in vitro and in situ plankton production determinations

Plankton production was measured using 8 techniques at 4 stations in the Celtic Sea, North Atlantic Ocean, in April 2002. Primary production (PP) was derived from 14C incorporation into particulate carbon after 24 h simulated in situ, PP(14CSIS), and 2 h photosynthesis-irradiance incubations, PP(14CPUR), and from 2 published satellite algorithms, PP(VGPM) and PP (M91). Gross production (GP) was calculated from O2 evolution, GP(O2), and 18O enrichment of dissolved O 2, GP(18O), after 24 h simulated in situ incubations, and from in situ active fluorescence measured by fast repetition rate fluorometry (FRRF). Net community production (NCP) was determined from changes in in situ dissolved oxygen, NCP(?O2), and from changes in oxygen during 24 h simulated in situ incubations, NCP(O2). Dark community respiration (DCR) was derived from changes in oxygen during a 24 h dark incubation, DCR(O2), and daily oxygen uptake, DOU(18O, O2), was calculated from the difference between GP(18O) and NCP(O2). Three stations were dominated by picoautotrophs and the fourth station was dominated by diatoms. While most of the comparisons between techniques fell within previously published ranges, 2 anomalies occurred only at the diatom-dominated station. Rates of PP(14CPUR) were oxygen uptake in the dark. The low rates of PP( 14CPUR) in relation to PP(14CSIS) may have resulted from the heterogeneous nature of the bloom and differences in sampling time. However, it is also possible that dissolved organic material (DOM) released by the stressed diatom population restricted the diffusion of 14C into the cells, thereby causing a greater underestimate of PP by techniques using short incubations. The significantly higher rates of oxygen uptake in the light are difficult to reconcile, and we do not know whether the light enhanced oxygen uptake was directly linked to carbon fixation. However, the release of DOM may also have provided substrate for enhanced respiration in the light. These anomalies were only revealed through the concurrent measurement of plankton production by this wide range of techniques. Further investigation of DOM excretion and light-enhanced respiration during diatom blooms is warranted

Species-specific imprint of the phytoplankton assemblage on carbon isotopes and the carbon cycle in Lake Kinneret, Israel

Lakes undergoing major changes in phytoplankton species composition are likely to undergo changes in carbon (C) cycling. In this study we used stable C isotopes to understand how the C cycle of Lake Kinneret, Israel, responded to documented changes in phytoplankton species composition. We compared the annual δ13C cycle of particulate organic matter from surface water (POMsurf) between (1) years in which a massive spring bloom of the dinoflagellate Peridinium gatunense occurred (“Peridinium years”) and (2) years in which it did not (“non-Peridinium years”). In non-Peridinium years, the spring δ13C–POMsurf maxima were lower by 3.3‰. These spring δ13C maxima were even lower in POM sinking into sediment traps and in zooplankton (lower by 6.8 and 6.9‰, respectively). These differences in the isotopic composition of the major organic C components in the lake represent ecosystem-level responses to the presence or absence of the key blooming species P. gatunense . When present, the intensive, almost monospecific bloom lowers the concentrations of CO2(aq), causing a reduction in the isotopic fractionation of the algae (higher δ13C of POMsurf) and massive precipitation of calcium carbonate (CaCO3). In “non-Peridinium years, the phytoplankton cannot deplete CO2(aq) to similar levels; the algae maintain higher isotopic fractionation, leading to lower δ13C maxima. These changes are reflected higher up in the food web (zooplankton) and in sedimenting organic matter. The consequences for the ecosystem in non-Peridinium years are lower export of both organic and inorganic C

Evaluating triple oxygen isotope estimates of gross primary production at the Hawaii Ocean Time-series and Bermuda Atlantic Time-series Study sites

Author Posting. © American Geophysical Union, 2012. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research 117 (2012): C05012, doi:10.1029/2010JC006856.The triple oxygen isotopic composition of dissolved oxygen (17Δ) is a promising tracer of gross oxygen productivity (P) in the ocean. Recent studies have inferred a high and variable ratio of P to 14C net primary productivity (12–24 h incubations) (e.g., P:NPP(14C) of 5–10) using the 17Δ tracer method, which implies a very low efficiency of phytoplankton growth rates relative to gross photosynthetic rates. We added oxygen isotopes to a one-dimensional mixed layer model to assess the role of physical dynamics in potentially biasing estimates of P using the 17Δ tracer method at the Bermuda Atlantic Time-series Study (BATS) and Hawaii Ocean Time-series (HOT). Model results were compared to multiyear observations at each site. Entrainment of high 17Δ thermocline water into the mixed layer was the largest source of error in estimating P from mixed layer 17Δ. At both BATS and HOT, entrainment bias was significant throughout the year and resulted in an annually averaged overestimate of mixed layer P of 60 to 80%. When the entrainment bias is corrected for, P calculated from observed 17Δ and 14C productivity incubations results in a gross:net productivity ratio of 2.6 (+0.9 −0.8) at BATS. At HOT a gross:net ratio decreasing linearly from 3.0 (+1.0 −0.8) at the surface to 1.4 (+0.6 −0.6) at depth best reproduced observations. In the seasonal thermocline at BATS, however, a significantly higher gross:net ratio or large lateral fluxes of 17Δ must be invoked to explain 17Δ field observations.We acknowledge support from Center for Microbial Oceanography Research and Education (CMORE) (NSF EF-0424599) and NOAA Global Carbon Program (NA 100AR4310093). BL thanks the USA-Israel Binational Science Foundation for supporting his project at BATS.2012-11-0

Acquisition of isotopic composition for surface snow in East Antarctica and the links to climatic parameters

The isotopic compositions of oxygen and hydrogen in ice cores are invaluable tools for the reconstruction of past climate variations. Used alone, they give insights into the variations of the local temperature, whereas taken together they can provide information on the climatic conditions at the point of origin of the moisture. However, recent analyses of snow from shallow pits indicate that the climatic signal can become erased in very low accumulation regions, due to local processes of snow reworking. The signal-to-noise ratio decreases and the climatic signal can then only be retrieved using stacks of several snow pits. Obviously, the signal is not completely lost at this stage, otherwise it would be impossible to extract valuable climate information from ice cores as has been done, for instance, for the last glaciation. To better understand how the climatic signal is passed from the precipitation to the snow, we present here results from varied snow samples from East Antarctica. First, we look at the relationship between isotopes and temperature from a geographical point of view, using results from three traverses across Antarctica, to see how the relationship is built up through the distillation process. We also take advantage of these measures to see how second-order parameters (d-excess and O-17-excess) are related to delta O-18 and how they are controlled. d-excess increases in the interior of the continent (i.e., when delta O-18 decreases), due to the distillation process, whereas O-17-excess decreases in remote areas, due to kinetic fractionation at low temperature. In both cases, these changes are associated with the loss of original information regarding the source. Then, we look at the same relationships in precipitation samples collected over 1 year at Dome C and Vostok, as well as in surface snow at Dome C. We note that the slope of the delta O-18 vs. temperature (T) relationship decreases in these samples compared to those from the traverses, and thus caution is advocated when using spatial slopes for past climate reconstruction. The second-order parameters behave in the same way in the precipitation as in the surface snow from traverses, indicating that similar processes are active and that their interpretation in terms of source climatic parameters is strongly complicated by local temperature effects in East Antarctica. Finally we check if the same relationships between delta O-18 and second-order parameters are also found in the snow from four snow pits. While the d-excess remains opposed to delta O-18 in most snow pits, the O-17-excess is no longer positively correlated to delta O-18 and even shows anti-correlation to delta O-18 at Vostok. This may be due to a stratospheric influence at this site and/or to post-deposition processes

Reply to comment by Martin F. Miller on “Record of δ 18 O and 17 O-excess in ice from Vostok Antarctica during the last 150,000 years”

International audienc

Combined Analysis of Water Stable Isotopes (H216O,H217O,H218O,HD16OH_{2}^{16}O, H_{2}^{17}O, H_{2}^{18}O, HD^{16}O) in Ice Cores

Water stable isotopes are currently measured in polar ice cores. The long records of $δ_{18}O$ and δD provide unique information on the past polar temperature while the combination of $δ_{18}O$ and δD constrains the evolution of the oceanic evaporative regions. Recently, new analytical developments have made it possible to measure with high precision a new isotopic ratio in water, $δ_{17}O$. As for δD and $δ_{18}0$, the combination of $δ_{17}0$ and $δ_{18}0$ shows a high dependence with the climatic conditions during evaporation. Based on measurements of the different isotopic ratios in Antarctica surface snow, we show that while the combination of $δ_{18}0$ and δD in the so-called d-excess displays variation with local climatic conditions in the polar regions in addition to the influence of the evaporative regions, the combination of $δ_{17}0$ and $δ_{18}0$ in the so-called $^{17}O_{excess}$ is not modified during the air mass transportation above the polar regions. This makes $^{17}O_{excess}$ a simpler parameter than d-excess to constrain the evolution of the oceanic evaporative regions. Finally, records of d-excess and $^{17}O_{excess}$ over the deglaciation in the Vostok ice core suggest significant changes in the evaporative regions. Our interpretation is that the relative humidity over the ocean was higher during the glacial period than today and that reevaporation increased over the deglaciation.IV. Chemical properties and isotope

Record of δ18^{18}O and 17^{17}O-excess in ice from Vostok Antarctica during the last 150,000 years

International audienceWe measured δ$^{17}$O and $^{18}$O in recent Antarctic snow and down the Vostok ice core and calculated the excess of $^{17}$O with respect to VSMOW. The magnitude of the $^{17}$O excess in the Holocene and the last interglacial is ~45 per meg, and it remains constant in a transect from the coast to the continental interior. Analysis of the transect data shows that the $^{17}$O-excess is not sensitive to temperature variations over the continent. There are significant shifts in $^{17}$O-excess from low values in glacial to high values in interglacial times. The observed shifts suggest higher normalized relative humidity and/or wind speeds over the source oceanic regions in glacial times

Fractionation of the Three Stable Oxygen Isotopes by Oxygen-Producing and Oxygen-Consuming Reactions in Photosynthetic Organisms

The triple isotope composition (δ(17)O and δ(18)O) of dissolved O(2) in the ocean and in ice cores was recently used to assess the primary productivity over broad spatial and temporal scales. However, assessment of the productivity with the aid of this method must rely on accurate measurements of the (17)O/(16)O versus (18)O/(16)O relationship in each of the main oxygen-producing and -consuming reactions. Data obtained here showed that cleavage of water in photosystem II did not fractionate oxygen isotopes; the δ(18)O and δ(17)O of the O(2) evolved were essentially identical to those of the substrate water. The fractionation slopes for the oxygenase reaction of Rubisco and respiration were identical (0.518 ± 0.001) and that of glycolate oxidation was 0.503 ± 0.002. There was a considerable difference in the slopes of O(2) photoreduction (the Mehler reaction) in the cyanobacterium Synechocystis sp. strain PCC 6803 (0.497 ± 0.004) and that of pea (Pisum sativum) thylakoids (0.526 ± 0.001). These values provided clear and independent evidence that the mechanism of O(2) photoreduction differs between higher plants and cyanobacteria. We used our method to assess the magnitude of O(2) photoreduction in cyanobacterial cells maintained under conditions where photorespiration was negligible. It was found that electron flow to O(2) can be as high as 40% that leaving photosystem II, whereas respiratory activity in the light is only 6%. The implications of our findings to the evaluation of specific O(2)-producing or -consuming reactions, in vivo, are discussed