Respiration rates and electron transport system activities of copepod species obtained during Maria S. Merian cruise MSM17/3

Respiration rates and electron transport system (ETS) activities were measured in dominant copepod species from the northern Benguela upwelling system in January-February 2011 to assess the accuracy of the ETS assay in predicting in vivo respiration rates. Individual respiration rates varied from 0.06 to 1.60 µL O2/h/ind, while ETS activities converted to oxygen consumption ranged from 0.14 to 4.46 µL O2/h/ind. ETS activities were significantly correlated with respiration rates (r**2 = 0.79, p = 0.0001). R:ETS ratios were lowest in slow-moving Eucalanidae (0.11) and highest in diapausing Calanoides carinatus copepodids CV (0.76) while fast-moving copepods showed intermediate R:ETS (0.23-0.37). 82% of the variance of respiration rates could be explained by differences in dry mass, temperature and the activity level of different copepod species. Three regression equations were derived to calculate respiration rates for diapausing, slow- and fast-moving copepods, respectively, based on parameters such as body mass and temperature. Thus, knowledge about the activity level and behavioral characteristics of copepod species can significantly increase the predictive accuracy of metabolic models, which will help to better understand and quantify the impact of copepods on nutrient and carbon fluxes in marine ecosystems.

Phosphorus components, CaCO3 and biogenic opal in sediments from ODP Leg 167 sites

The ocean history of reactive phosphorus (P) (i.e., dissolved P available to fuel oceanic primary productivity) is of interest because of the role of P as a biolimiting nutrient, and knowledge of P burial in marine sediments is key to testing hypotheses about temporal changes in P input or output fluxes. Our understanding of the history of the P cycle over the Cenozoic has increased substantially with temporal records of reactive P mass accumulation rates from open-ocean Pacific and Atlantic equatorial sites. However, questions about the relative importance of nutrient burial in ocean-margin sediments relative to burial in open-ocean sediments and about the extent of P remobilization in organic-rich, reducing environments characteristic of margin sediments remain unresolved. Nutrient burial in oceanic boundary current systems has been suggested to have a controlling role in oceanic nutrient budgets in certain time intervals (Vincent and Berger, 1985, doi:10.1029/GM032p0455), with higher sediment accumulation rates balancing the limited spatial extent of these sediments. Some investigators suggest that remobilization of P from reducing sediments in margin settings is a significant positive feedback to primary productivity (e.g., Van Cappellan and Ingall, 1994, doi:10.1029/94PA01455), whereas other results indicate that both P uptake and P release may occur in these settings depending on the balance of organic carbon and iron supply to the sediments and on the oxygenation of bottom waters (McManus et al., 1997, doi:10.1016/S0016-7037(97)00138-5). It is important to quantitatively understand the geochemistry of reactive P in margin sediments, where productivity and delivery of organic-rich material to the sediments in relatively shallow-water settings is often sufficient to promote anoxia in interstitial waters. To address these questions, we determined the P concentrations and geochemistry in sediment samples from eight sites drilled during Ocean Drilling Program (ODP) Leg 167, California margin (Sites 1010-1012, 1014, 1016-1017, and 1021-1022). These results are the first records of reactive P concentrations on long time scales-required for the calculation of P accumulation rates-for sediments from a highly productive eastern boundary current setting. In addition, we determined calcium carbonate contents and biogenic silica concentrations to define the environments of sedimentary production, burial, and diagenesis.

Geochemistry on core 202-1240A

The modern Eastern Equatorial Pacific (EEP) Ocean is a large oceanic source of carbon to the atmosphere1. Primary productivity over large areas of the EEP is limited by silicic acid and iron availability, and because of this constraint the organic carbon export to the deep ocean is unable to compensate for the outgassing of carbon dioxide that occurs through upwelling of deep waters. It has been suggested that the delivery of dust-borne iron to the glacial ocean could have increased primary productivity and enhanced deep-sea carbon export in this region, lowering atmospheric carbon dioxide concentrations during glacial periods. Such a role for the EEP is supported by higher organic carbon burial rates documented in underlying glacial sediments but lower opal accumulation rates cast doubts on the importance of the EEP as an oceanic region for significant glacial carbon dioxide drawdown. Here we present a new silicon isotope record that suggests the paradoxical decline in opal accumulation rate in the glacial EEP results from a decrease in the silicon to carbon uptake ratio of diatoms under conditions of increased iron availability from enhanced dust input. Consequently, our study supports the idea of an invigorated biological pump in this region during the last glacial period that could have contributed to glacial carbon dioxide drawdown. Additionally, using evidence from silicon and nitrogen isotope changes, we infer that, in contrast to the modern situation, the biological productivity in this region is not constrained by the availability of iron, silicon and nitrogen during the glacial period. We hypothesize that an invigorated biological carbon dioxide pump constrained perhaps only by phosphorus limitation was a more common occurrence in low-latitude areas of the glacial ocean.

Production, oxygen uptake, and sinking velocity of copepod fecal pellets originated from the central North Sea

Production, oxygen uptake, and sinking velocity of copepod fecal pellets egested by Temora longicornis were measured using a nanoflagellate (Rhodomonas sp.), a diatom (Thalassiosira weissflogii), or a coccolithophorid (Emiliania huxleyi) as food sources. Fecal pellet production varied between 0.8 pellets ind**-1 h**-1 and 3.8 pellets ind**-1 h**-1 and was significantly higher with T. weissflogii than with the other food sources. Average pellet size varied between 2.2 x 10**5 µm**3 and 10.0 x 10**5 µm**3. Using an oxygen microsensor, small-scale oxygen fluxes and microbial respiration rates were measured directly with a spatial resolution of 2 µm at the interface of copepod fecal pellets and the surrounding water. Averaged volume-specific respiration rates were 4.12 fmol O2 µm**-3 d**-1, 2.86 fmol O2 µm**-3 d**-1, and 0.73 fmol O2 µm**-3 d**-1 in pellets produced on Rhodomonas sp., T. weissflogii, and E. huxleyi, respectively. The average carbon-specific respiration rate was 0.15 d**-1 independent on diet (range: 0.08-0.21 d**-1). Because of ballasting of opal and calcite, sinking velocities were significantly higher for pellets produced on T. weissflogii (322 +- 169 m d**-1) and E. huxleyi (200 +- 93 m d**-1) than on Rhodomonas sp. (35 +- 29 m d**-1). Preservation of carbon was estimated to be approximately 10-fold higher in fecal pellets produced when T. longicornis was fed E. huxleyi or T. weissflogii rather than Rhodomonas sp. Our study directly demonstrates that ballast increases the sinking rate of freshly produced copepod fecal pellets but does not protect them from decomposition.

Accumulation rates of dinoflagellate cysts at trap sites CB2, CB3, CB4, and CB9 off Cape Blanc

A 5-year sediment trap survey in the upwelling area off Cape Blanc (NW Africa) provides information on the seasonal and annual resting cyst production of dinoflagellates, their sinking characteristics and preservation potential. Strong annual variation in cyst production characterizes the region. Cyst production of generally all investigated species, including Alexandrium pseudogonyaulax (Biecheler) T. Horig. ex T. Kita et Fukuyo (cyst genus Impagidinium) and Gonyaulax spinifera (Clap. et J. Lachm.) Diesing (cyst genus Nematosphaeropsis) was enhanced with increasing upper water nutrient and trace-element concentrations. Cyst production of Lingulodinium polyedrum (F. Stein) J. D. Dodge was the highest at the transition between upwelling and upwelling-relaxation. Cyst production of Protoperidinium americanum (Gran et Braarud) Balech, Protoperidinium monospinum (Paulsen) K. A. F. Zonn. et B. Dale, and Protoperidinium stellatum (D. Wall) Balech, and heterotrophic dinoflagellates forming Brigantedinium spp. and Echinidinium aculeatum Zonn., increased most pronouncedly during upwelling episodes. Production of Protoperidinium conicum (Gran) Balech and Protoperidinium pentagonum (Gran) Balech cysts and total diatom valves were related, providing evidence of a predator-prey relationship. The export cyst-flux of E. aculeatum, P. americanum, P. monospinum, and P. stellatum was strongly linked to the flux of total diatom valves and CaCO3, whereas the export production of Echinidinium granulatum Zonn. and Protoperidinium subinerme (Paulsen) A. R. Loebl. correlated with total organic carbon, suggesting potential consumption of diatoms, prymnesiophytes, and organic matter, respectively. Sinking velocities were at least 274 m · d**-1, which is in range of the diatom- and coccolith-based phytoplankton aggregates and "slower" fecal pellets. Species-selective degradation did not occur in the water column, but on the ocean floor.

Carbon uptake rate calculated for melt pond water samples during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012

Net Primary Production was measured using the 14**C uptake method with minor modifications. Melt pond samples were spiked with 0.1µCi ml**-1 of 14**C labelled sodium bicarbonate (Moravek Biochemicals, Brea, USA) and distributed in 10 clear bottles (20 ml each). Subsequently they were incubated for 12 h at -1.3°C under different scalar irradiances (0-420 µmol photons m**-2 s**-1) measured with a spherical sensor (Spherical Micro Quantum Sensor US-SQS/L, Heinz Walz, Effeltrich, Germany). At the end of the incubation, samples were filtered onto 0.2 µm nitrocellulose filters and the particulate radioactive carbon uptake was determined by liquid scintillation counting using Filter count scintillation cocktail (Perkin Elmer, Waltham, USA). The carbon uptake values in the dark were subtracted from the carbon uptake values measured in the light incubations. Dissolved inorganic carbon (DIC) was measured for each sample using the flow injection system (Hall and Aller, 1992). The DIC concentration was taken into account to calculate the amount of labeled bicarbonate incorporated into the cell. Carbon fixation rates were normalized volumetrically and by chlorophyll a. Photosynthesis-irradiance curves (PI curves) were fitted using MATLAB® according to the equation proposed by Platt et al. (1980) including a photoinhibition parameter (beta) and providing the main photosynthetic parameters: maximum Chla normalized carbon fixation rate if there were no photoinhibition (Pb) and the initial slope of the saturation curve (alpha). The derived parameters: light intensity at which photosynthesis is maximal (Im), the carbon fixation rate at that maximal irradiance (Pbm) and the adaptation parameter or photoacclimation index (Ik) were calculated according to Platt et al. (1982).

Carbon uptake rate calculated for CTD water samples during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012

Net Primary Production was measured using the 14**C uptake method with minor modifications. Seawater samples were spiked with 0.1µCi ml**-1 of 14**C labelled sodium bicarbonate (Moravek Biochemicals, Brea, USA) and distributed in 10 clear bottles (20 ml each). Subsequently they were incubated for 12 h at -1.3°C under different scalar irradiances (0-420 µmol photons m**-2 s**-1) measured with a spherical sensor (Spherical Micro Quantum Sensor US-SQS/L, Heinz Walz, Effeltrich, Germany). At the end of the incubation, samples were filtered onto 0.2 µm nitrocellulose filters and the particulate radioactive carbon uptake was determined by liquid scintillation counting using Filter count scintillation cocktail (Perkin Elmer, Waltham, USA). The carbon uptake values in the dark were subtracted from the carbon uptake values measured in the light incubations. Dissolved inorganic carbon (DIC) was measured for each sample using the flow injection system (Hall and Aller, 1992). The DIC concentration was taken into account to calculate the amount of labeled bicarbonate incorporated into the cell. Carbon fixation rates were normalized volumetrically and by chlorophyll a. Photosynthesis-irradiance curves (PI curves) were fitted using MATLAB® according to the equation proposed by Platt et al. (1980) including a photoinhibition parameter (beta) and providing the main photosynthetic parameters: maximum Chla normalized carbon fixation rate if there were no photoinhibition (Pb) and the initial slope of the saturation curve (alpha). The derived parameters: light intensity at which photosynthesis is maximal (Im), the carbon fixation rate at that maximal irradiance (Pbm) and the adaptation parameter or photoacclimation index (Ik) were calculated according to Platt et al. (1982).

Strong shift from HCO3- to CO2 uptake in Emiliania huxleyi with acidification: new approach unravels acclimation versus short-term pH effects

Effects of ocean acidification on Emiliania huxleyi strain RCC 1216 (calcifying, diploid life-cycle stage) and RCC 1217 (non-calcifying, haploid life-cycle stage) were investigated by measuring growth, elemental composition, and production rates under different pCO2 levels (380 and 950 µatm). In these differently acclimated cells, the photosynthetic carbon source was assessed by a (14)C disequilibrium assay, conducted over a range of ecologically relevant pH values (7.9-8.7). In agreement with previous studies, we observed decreased calcification and stimulated biomass production in diploid cells under high pCO2, but no CO2-dependent changes in biomass production for haploid cells. In both life-cycle stages, the relative contributions of CO2 and HCO3 (-) uptake depended strongly on the assay pH. At pH values =< 8.1, cells preferentially used CO2 (>= 90 % CO2), whereas at pH values >= 8.3, cells progressively increased the fraction of HCO3 (-) uptake (~45 % CO2 at pH 8.7 in diploid cells; ~55 % CO2 at pH 8.5 in haploid cells). In contrast to the short-term effect of the assay pH, the pCO2 acclimation history had no significant effect on the carbon uptake behavior. A numerical sensitivity study confirmed that the pH-modification in the (14)C disequilibrium method yields reliable results, provided that model parameters (e.g., pH, temperature) are kept within typical measurement uncertainties. Our results demonstrate a high plasticity of E. huxleyi to rapidly adjust carbon acquisition to the external carbon supply and/or pH, and provide an explanation for the paradoxical observation of high CO2 sensitivity despite the apparently high HCO3 (-) usage seen in previous studies.

Carbon uptake rate calculated for sea-ice core samples during POLARSTERN cruise ARK-XXVII/3 (IceArc) in 2012

Net Primary Production was measured using the 14**C uptake method with minor modifications. Melted sea ice samples were spiked with 0.1µCi ml**-1 of 14**C labelled sodium bicarbonate (Moravek Biochemicals, Brea, USA) and distributed in 10 clear bottles (20 ml each). Subsequently they were incubated for 12 h at -1.3°C under different scalar irradiances (0-420 µmol photons m**-2 s**-1) measured with a spherical sensor (Spherical Micro Quantum Sensor US-SQS/L, Heinz Walz, Effeltrich, Germany). At the end of the incubation, samples were filtered onto 0.2 µm nitrocellulose filters and the particulate radioactive carbon uptake was determined by liquid scintillation counting using Filter count scintillation cocktail (Perkin Elmer, Waltham, USA). The carbon uptake values in the dark were subtracted from the carbon uptake values measured in the light incubations. Dissolved inorganic carbon (DIC) was measured for each sample using the flow injection system (Hall and Aller, 1992). The DIC concentration was taken into account to calculate the amount of labeled bicarbonate incorporated into the cell. Carbon fixation rates were normalized volumetrically and by chlorophyll a. Photosynthesis-irradiance curves (PI curves) were fitted using MATLAB® according to the equation proposed by Platt et al. (1980) including a photoinhibition parameter (beta) and providing the main photosynthetic parameters: maximum Chla normalized carbon fixation rate if there were no photoinhibition (Pb) and the initial slope of the saturation curve (alpha). The derived parameters: light intensity at which photosynthesis is maximal (Im), the carbon fixation rate at that maximal irradiance (Pbm) and the adaptation parameter or photoacclimation index (Ik) were calculated according to Platt et al. (1982).