The pH dependency of the boron isotopic composition of diatom opal (Thalassiosira weissflogii)

The high-latitude oceans are key areas of carbon and heat exchange between the atmosphere and the ocean. As such, they are a focus of both modern oceanographic and palaeoclimate research. However, most palaeoclimate proxies that could provide a long-term perspective are based on calcareous organisms, such as foraminifera, that are scarce or entirely absent in deep-sea sediments south of 50∘ S in the Southern Ocean and north of 40∘ N in the North Pacific. As a result, proxies need to be developed for the opal-based organisms (e.g. diatoms) found at these high latitudes, which dominate the biogenic sediments recovered from these regions. Here we present a method for the analysis of the boron (B) content and isotopic composition (δ11B) of diatom opal. We apply it for the first time to evaluate the relationship between seawater pH, δ11B and B concentration ([B]) in the frustules of the diatom Thalassiosira weissflogii, cultured across a range of carbon dioxide partial pressure (pCO2) and pH values. In agreement with existing data, we find that the [B] of the cultured diatom frustules increases with increasing pH (Mejía et al., 2013). δ11B shows a relatively well defined negative trend with increasing pH, completely distinct from any other biomineral previously measured. This relationship not only has implications for the magnitude of the isotopic fractionation that occurs during boron incorporation into opal, but also allows us to explore the potential of the boron-based proxies for palaeo-pH and palaeo-CO2 reconstruction in high-latitude marine sediments that have, up until now, eluded study due to the lack of suitable carbonate material

Porewater oxygen profiles in surface sediments of the North Atlantic Basin during RV Maria S. Merian cruise MSM96

Vertical profiles of dissolved oxygen (O2) concentrations in the surface sediment of the North Atlantic Basin were acquired during MSM96 through ex-situ voltametric measurements during this research cruise. For every multicorer station, one liner was selected and transported to the on-board cool room immediately for analysis at 5°C. At some stations, a second core was analyzed for validation and to achieve better measurement resolution. Measurements were carried out through cyclic voltammetry (start: -100 mV, vertex: -1900 mV, start: -100 mV, scan rate: 500 mv/s) with Hg/Au microelectrodes (100 µm diameter) in a 3-electrode configuration with an Ag/AgCl pseudoreference electrode and a Pt counter electrode using a modified custom version of the DStat open source potentiostat (Dryden & Wheeler, 2015; doi:10.1371/journal.pone.0140349). Working electrodes were polished and Hg-plated prior to the research cruise according to the method by Brendel & Luther III (1995; doi:10.1021/es00003a024) and repolished (using diamond polishing plates of 5, 1 and 0.25 µm grit) and plated (180s at -100mV in 0.1M Hg(NO3)2 solution) on board when degradation of the signal was detected (twice over the duration of the cruise). Measurements were calibrated to 100% O2 saturation in bottom water at equilibrium with the atmosphere after recording air pressure and temperature to calculate dissolved O2 concentration as well as 0% O2 saturation in bottom water that was purged of oxygen by bubbling with nitrogen (N2) gas. The sensor was moved vertically on a linear axis with a stepper motor through an automated control system hosted on a Raspberry Pi control unit

Rare Earth Element and yttrium (REY) concentrations from SONNE cruise SO253

Rare Earth Element and yttrium (REY) concentrations measured with ICP-MS in hydrothermal fluids from the Kermadec intraoceanic arc. Seawater from 1000 m water depth, values for SW are * 100 (SW data from Alibo and Nozaki (1999; doi:10.1016/S0016-7037(98)00279-8))

Overview of all fluid samples collected during SONNE cruise SO253

Overview of all fluid samples collected during SO253 along the Kermadec intraoceanic arc together with parameters that were analyzed directly onboard.Fe were determined by a visual Fe CHEMets© field kit

Major, minor and trace element concentrations from SONNE cruise SO253

Major, minor and trace element concentrations measured with ICP-OES, ICP-MS and data for SO42- in hydrothermal fluids from the Kermadec intraoceanic arc

Comparison of Brothers hydrothermal fluid composition

Comparison of Brothers hydrothermal fluid composition collected by de Ronde et al. (2011; doi:10.1007/s00126-011-0345-8) with data collected during this study. In this study, only samples taken with IGT and Major samplers with end-member concentrations greater than 50% are shown. The three samples from the Upper Caldera Site are not included within this data set

End-member compositions of hydrothermal fluids from SONNE cruise SO253

Calculated end-member compositions of hydrothermal fluids (for samples that have at least ≥ 85 % end-member) from Haungaroa, Brothers Upper Caldera and NW Caldera Wall, Kermadec intraoceanic arc. Ambient background seawater concentrations are given for comparison