(Table 1) Biological and chemical characteristics of surface water stations during Nathaniel B. Palmer cruise NBP06-08 to the Ross Sea

We present results from a field study of inorganic carbon (C) acquisition by Ross Sea phytoplankton during Phaeocystis-dominated early season blooms. Isotope disequilibrium experiments revealed that HCO3? was the primary inorganic C source for photosynthesis in all phytoplankton assemblages. From these experiments, we also derived relative enhancement factors for HCO3?/CO2 interconversion as a measure of extracellular carbonic anhydrase activity (eCA). The enhancement factors ranged from 1.0 (no apparent eCA activity) to 6.4, with an overall mean of 2.9. Additional eCA measurements, made using membrane inlet mass spectrometry (MIMS), yielded activities ranging from 2.4 to 6.9 U/[?g chl a] (mean 4.1). Measurements of short-term C-fixation parameters revealed saturation kinetics with respect to external inorganic carbon, with a mean half-saturation constant for inorganic carbon uptake (K1/2) of ~380 ?M. Comparison of our early springtime results with published data from late-season Ross Sea assemblages showed that neither HCO3? utilization nor eCA activity was significantly correlated to ambient CO2 levels or phytoplankton taxonomic composition. We did, however, observe a strong negative relationship between surface water pCO2 and short-term 14C-fixation rates for the early season survey. Direct incubation experiments showed no statistically significant effects of pCO2 (10 to 80 Pa) on relative HCO3? utilization or eCA activity. Our results provide insight into the seasonal regulation of C uptake by Ross Sea phytoplankton across a range of pCO2 and phytoplankton taxonomic composition.

Organic carbon and nitrogen concentrations in surface waters of the North Atlantic along 20°E in July-August 1996

Redfield stoichiometry has proved a robust paradigm for the understanding of biological production and export in the ocean on a long-term and a large-scale basis. However, deviations of carbon and nitrogen uptake ratios from the Redfield ratio have been reported. A comprehensive data set including all carbon and nitrogen pools relevant to biological production in the surface ocean (DIC, DIN, DOC, DON, POC, PON) was used to calculate seasonal new production based on carbon and nitrogen uptake in summer along 20°W in the northeast Atlantic Ocean. The 20°W transect between 30 and 60°N covers different trophic states and seasonal stages of the productive surface layer, including early bloom, bloom, post-bloom and non-bloom situations. The spatial pattern has elements of a seasonal progression. We also calculated exported production, i.e., that part of seasonal new production not accumulated in particulate and dissolved pools, again separately for carbon and nitrogen. The pairs of estimates of 'seasonal new production' and 'exported production' allowed us to calculate the C : N ratios of these quantities. While suspended particulate matter in the mixed layer largely conforms to Redfield stoichiometry, marked deviations were observed in carbon and nitrogen uptake and export with progressing season or nutrient depletion. The spring system was characterized by nitrogen overconsumption and the oligotrophic summer system by a marked carbon overconsumption. The C : N ratios of seasonal new as well as exported production increase from early bloom values of 5-6 to values of 10-16 in the post-bloom/oligotrophic system. The summertime accumulation of nitrogen-poor dissolved organic matter can explain only part of this shift.

Seawater carbonate chemistry and biological processes of Mytilus edulis during experiments, 2010

Marine organisms are exposed to increasingly acidic oceans, as a result of equilibration of surface ocean water with rising atmospheric CO2 concentrations. In this study, we examined the physiological response of Mytilus edulis from the Baltic Sea, grown for 2 months at 4 seawater pCO2 levels (39, 113, 243 and 405 Pa/385, 1,120, 2,400 and 4,000 µatm). Shell and somatic growth, calcification, oxygen consumption and excretion rates were measured in order to test the hypothesis whether exposure to elevated seawater pCO2 is causally related to metabolic depression. During the experimental period, mussel shell mass and shell-free dry mass (SFDM) increased at least by a factor of two and three, respectively. However, shell length and shell mass growth decreased linearly with increasing pCO2 by 6-20 and 10-34%, while SFDM growth was not significantly affected by hypercapnia. We observed a parabolic change in routine metabolic rates with increasing pCO2 and the highest rates (+60%) at 243 Pa. excretion rose linearly with increasing pCO2. Decreased O:N ratios at the highest seawater pCO2 indicate enhanced protein metabolism which may contribute to intracellular pH regulation. We suggest that reduced shell growth under severe acidification is not caused by (global) metabolic depression but is potentially due to synergistic effects of increased cellular energy demand and nitrogen loss.

Experiment: Influence of CO2 and nitrogen limitation on the coccolith volume of Emiliania huxleyi (Haptophyta)

Coccolithophores, a key phytoplankton group, are one of the most studied organisms regarding their physiological response to ocean acidification/carbonation. The biogenic production of calcareous coccoliths has made coccolithophores a promising group for paleoceanographic research aiming to reconstruct past environmental conditions. Recently, geochemical and morphological analyses of fossil coccoliths have gained increased interest in regard to changes in seawater carbonate chemistry. The cosmopolitan coccolithophore Emiliania huxleyi (Lohm.) Hay and Mohler was cultured over a range of pCO2 levels in controlled laboratory experiments under nutrient replete and nitrogen limited conditions. Measurements of photosynthesis and calcification revealed, as previously published, an increase in particulate organic carbon production and a moderate decrease in calcification from ambient to elevated pCO2. The enhancement in particulate organic carbon production was accompanied by an increase in cell diameter. Changes in coccolith volume were best correlated with the coccosphere/cell diameter and no significant correlation was found between the coccolith volume and the particulate inorganic carbon production. The conducted experiments revealed that the coccolith volume of E. huxleyi is variable with aquatic CO2 concentration but its sensitivity is rather small in comparison with its sensitivity to nitrogen limitation. Comparing coccolith morphological and geometrical parameters like volume, mass and size to physiological parameters under controlled laboratory conditions is an important step to understand variations in fossil coccolith geometry.

Nitrogen isotope gradients off Peru and Ecuador related to upwelling, productivity, nutrient uptake and oxygen deficiency

We present new nitrogen isotope data from the water column and surface sediments for paleo-proxy validation collected along the Peruvian and Ecuadorian margins between 1°N and 18°S. Productivity proxies in the bulk sediment (organic carbon, total nitrogen, biogenic opal, C37 alkenone concentrations) and 15N/14N ratios were measured at more than 80 locations within and outside the present-day Peruvian oxygen minimum zone (OMZ). Microbial N-loss to N2 in subsurface waters under O2 deficient conditions leaves a characteristic 15N-enriched signal in underlying sediments. We find that phytoplankton nutrient uptake in surface waters within the high nutrient, low chlorophyll (HNLC) regions of the Peruvian upwelling system influences the sedimentary signal as well. How the d15Nsed signal is linked to these processes is studied by comparing core-top values to the 15N/14N of nitrate and nitrite (d15N[NOx]) in the upper 200 m of the water column. Between 1°N and 10°S, subsurface O2 is still high enough to suppress N-loss keeping d15NNOx values relatively low in the subsurface waters. However d15N[NOx] values increase toward the surface due to partial nitrate utilization in the photic zone in this HNLC portion of the system. d15N[sed] is consistently lower than the isotopic signature of upwelled [NO3]-, likely due to the corresponding production of 15N depleted organic matter. Between 10°S and 15°S, the current position of perennial upwelling cells, HNLC conditions are relaxed and biological production and near-surface phytoplankton uptake of upwelled [NO3]- are most intense. In addition, subsurface O2 concentration decreases to levels sufficient for N-loss by denitrification and/or anammox, resulting in elevated subsurface d15N[NOx] values in the source waters for coastal upwelling. Increasingly higher production southward is reflected by various productivity proxies in the sediments, while the north-south gradient towards stronger surface [NO3]- utilization and subsurface N-loss is reflected in the surface sediment 15N/14N ratios. South of 10°S, d15N[sed] is lower than maximum water column d15N[NOx] values most likely because only a portion of the upwelled water originates from the depths where highest d15N[NOx] values prevail. Though the enrichment of d15N[NOx] in the subsurface waters is unambiguously reflected in d15N[sed] values, the magnitude of d15N[sed] enrichment depends on both the depth of upwelled waters and high subsurface d15N[NOx] values produce by N-loss. Overall, the degree of N-loss influencing subsurface d15N[NOx] values, the depth origin of upwelled waters, and the degree of near-surface nitrate utilization under HNLC conditions should be considered for the interpretation of paleo d15N[sed] records from the Peruvian oxygen minimum zone.