Boron isotope and B/Ca ratios of planktonic foraminifera

Here a new analytical methodology is described for measuring the isotopic composition of boron in foraminifera using multicollector inductively coupled plasma mass spectrometry (MC-ICPMS). This new approach is fast (~10 samples analysed in duplicate per analytical session) and accurate (to better than 0.25 per mil at 95% confidence) with acceptable sample size requirements (1-3 mg of carbonate). A core top calibration of several common planktic and two benthic species from geographically widespread localities shows a very close agreement between the isotopic composition measured by MC-ICPMS and the isotopic composition of B(OH)-4 in seawater (as predicted using the recently measured isotopic equilibrium factor of 1.0272) at the depth of habitat. A down core and core top investigation of boron concentration (B/Ca ratio) shows that the partition coefficient is influenced by [CO2-3] complicating the application of this proxy. Nevertheless, it is demonstrated that these two proxies can be used to fully constrain the carbonate system of surface water in the Caribbean Sea (ODP Site 999A) over the last 130 kyr. This reconstruction shows that during much of the Holocene and the last interglacial period surface water at Site 999A was in equilibrium with the atmosphere with respect to CO2. During the intervening colder periods although the surface water pCO2 was lower than the Holocene, it was a minor to significant source of CO2 to the atmosphere possibly due to either an expansion of the eastern equatorial Atlantic upwelling zone, or a more local expansion of coastal upwelling in the southern Caribbean. Such reorganisation of the oceanic carbonate system in favour of a larger source of CO2 to the atmosphere from the equatorial ocean may require mechanisms responsible for lowering atmospheric CO2 during glacial periods to be more efficient than previously supposed.

Seawater carbonate chemistry and elemental composition of purple sea urchin (Strongylocentrotus purpuratus) calcite in a laboratory experiment

Ocean acidification will likely have negative impacts on invertebrates producing skeletons composed of calcium carbonate. Skeletal solubility is partly controlled by the incorporation of "foreign" ions (e.g. magnesium) into the crystal lattice of these skeletal structures, a process that is sensitive to a variety of biological and environmental factors. Here we explore effects of life stage, oceanographic region of origin, and changes in the partial pressure of carbon dioxide in seawater (pCO2) on trace elemental composition in the purple sea urchin (Strongylocentrotus purpuratus). We show that, similar to other urchin taxa, adult purple sea urchins have the ability to precipitate skeleton composed of a range of biominerals spanning low- to high-Mg calcites. Mg / Ca and Sr / Ca ratios were substantially lower in adult spines compared to adult tests. On the other hand, trace elemental composition was invariant among adults collected from four oceanographically distinct regions spanning a range of carbonate chemistry conditions (Oregon, Northern California, Central California, and Southern California). Skeletons of newly settled juvenile urchins that originated from adults from the four regions exhibited intermediate Mg / Ca and Sr / Ca between adult spine and test endmembers, indicating that skeleton precipitated during early life stages is more soluble than adult spines and less soluble than adult tests. Mean skeletal Mg / Ca or Sr / Ca of juvenile skeleton did not vary with source region when larvae were reared under present-day, global-average seawater carbonate conditions (400 µatm; pHT = 8.02 ± 0.03 1 SD; Omega calcite = 3.3 ± 0.2 1 SD). However, when reared under elevated pCO2 (900 µatm; pHT = 7.73 ± 0.03; Omega calcite = 1.8 ± 0.1), skeletal Sr / Ca in juveniles exhibited increased variance across the four regions. Although larvae from the northern populations (Oregon, Northern California, Central California) did not exhibit differences in Mg or Sr incorporation under elevated pCO2 (Sr / Ca = 2.10 ± 0.06 mmol/mol; Mg / Ca = 67.4 ± 3.9 mmol/mol), juveniles of Southern California origin partitioned ~8% more Sr into their skeletons when exposed to higher pCO2 (Sr / Ca = 2.26 ± 0.08 vs. 2.09 ± 0.005 mmol/mol 1 SD). Together these results suggest that the diversity of carbonate minerologies present across different skeletal structures and life stages in purple sea urchins does not translate into an equivalent geochemical plasticity of response associated with geographic variation or temporal shifts in seawater properties. Rather, composition of S. purpuratus skeleton precipitated during both early and adult life history stages appears relatively robust to spatial gradients and predicted future changes in carbonate chemistry. An exception to this trend may arise during early life stages, where certain populations of purple sea urchins may alter skeletal mineral precipitation rates and composition beyond a given pCO2 threshold. This potential for geochemical plasticity during early development in contrast to adult stage geochemical resilience adds to the growing body of evidence that ocean acidification can have differing effects across organismal life stages.

Chemical composition and phytoplankton characteristics of water samples obtained during POLARSTERN cruise ANT-XXIV/3

The fixation of dissolved inorganic carbon (DIC) by marine phytoplankton provides an important feedback mechanism on concentrations of CO2 in the atmosphere. As a consequence it is important to determine whether oceanic primary productivity is susceptible to changing atmospheric CO2 levels Among numerous other factors, the acquisition of DIC by microalgae particularly in the polar seas is projected to have a significant effect on future phytoplanktonic production and hence atmospheric CO2 concentrations. Using the isotopic disequilibrium technique the contribution of different carbon species (CO2 and bicarbonate) to the overall DIC uptake and the extent to which external Carbonic Anhydrase (eCA) plays a role in facilitating DIC uptake was estimated. Simultaneous uptake of CO2 and HCO3- was observed in all cases, but the proportions in which different DIC species contributed to carbon assimilation varied considerably between stations. Bicarbonate as well as CO2 could be the major DIC source for local phytoplankton assemblages. There was a positive correlation between the contribution of CO2 to total DIC uptake and ambient concentration of CO2 in seawater suggesting that Southern Ocean microalgae could increase the proportion of CO2 uptake under future high atmospheric CO2 levels. Results will be discussed in view of metabolic costs related to DIC acquisition of Southern Ocean phytoplankton.

(Tables 1-3) Geochemical composition of seepage water in soils obtained in Schleswig-Holstein, Germany

Under defined laboratory and field conditions, the investigation of percolating water through soil columns (podsol, lessive and peat) down to groundwater table shows that the main factors which control the chemical characteristics of the percolates are: precipitation, evaporation, infiltration rate, soil type, depth and dissolved organic substances. Evaporation and percolation velocity influences the Na+, SO4**2- and Cl- concentrations. Low percolation velocity leads also to longer percolation times and water logging in less permeable strata, which results in lower Eh-values and higher CO2-concentrations due to low gas exchange with the atmosphere. Ca2+ and Mg2+ carbonate concentration depends on soil type and depth. Metamorphism and decomposition of organic substances involve NO3 reduction and K+, Mg2+, SO4**2-, CO2, Fe2+,3+ transport. The analytical data were evaluated with multi variate statistical methods.

Pore water measurements of sediment cores from the Helgoland mud area, North Sea

Iron reduction in subseafloor sulfate-depleted and methane-rich marine sediments is currently a subject of interest in subsurface geomicrobiology. While iron reduction and microorganisms involved have been well studied in marine surface sediments, little is known about microorganisms responsible for iron reduction in deep methanic sediments. Here, we used quantitative PCR (Q-PCR)-based 16S rRNA gene copy numbers and pyrosequencing-based relative abundances of bacteria and archaea to investigate covariance between distinct microbial populations and specific geochemical profiles in the top 5 m of sediment cores from the Helgoland mud area, North Sea. We found that gene copy numbers of bacteria and archaea were specifically higher around the peak of dissolved iron in the methanic zone (250-350 cm. The higher copy numbers at these depths were also reflected by the relative sequence abundances of members of the candidate division JS1, methanogenic and Methanohalobium/ANME-3 related archaea. The distribution of these populations was strongly correlated to the profile of pore-water Fe2+ while that of Desulfobacteraceae corresponded to the pore-water sulfate profile. Furthermore, specific JS1 populations also strongly co-varied with the distribution of Methanosaetaceae in the methanic zone. Our data suggest that the interplay among JS1 bacteria, methanogenic archaea and Methanohalobium/ANME-3-related archaea may be important for iron reduction and methane cycling in deep methanic sediments of the Helgoland mud area and perhaps in other methane-rich depositional environments. .