Description: During the RV Polarstern cruise ARK-XXVII/3 to the Arctic Ocean in summer 2012, when sea ice declined to a record minimum bottom, water and sediment pore water samples were collected with a TV-guided multicorer at stations in the Nansen and Amundsen basin. 50 ml sediment pore water samples were collected from 0-1, 1-5 and 5-10 cm sediment depths from up to 4 parallel sediment cores at each station. Additionally, overlying bottom waters were carefully collected from undisturbed sediment cores. Acidified pore water samples (pH2) were used for analysis of DOC and TDN concentrations. The measurements were performed by hand injection via catalytic oxidation at high temperature on a TOC-V Shimadzu instrument.

Description: Marine organic matter (OM) sinks from surface waters to the seafloor via the biological pump. Benthic communities, which use this sedimented OM as energy and carbon source, produce dissolved organic matter (DOM) in the process of remineralization, enriching the sediment porewater with fresh DOM compounds. We hypothesized that in the oligotrophic deep Arctic basin the molecular signal of freshly deposited primary produced OM is restricted to the surface sediment pore waters which should differ from bottom water and deeper sediment pore water in DOM composition. This study focused on: 1) the molecular composition of the DOM in sediment pore waters of the deep Eurasian Arctic basins, 2) whether the signal of marine vs. terrigenous DOM is represented by different compounds preserved in the sediment pore waters and 3) whether there is any relation between Arctic Ocean ice cover and DOM composition. Molecular data, obtained via 15 Tesla Fourier transform ion cyclotron resonance mass spectrometer, were correlated with environmental parameters by partial least square analysis. The fresher marine detrital OM signal from surface waters was limited to pore waters from 〈 5 cm sediment depth. The productive ice margin stations showed higher abundances of peptides, unsaturated aliphatics and saturated fatty acids formulae, indicative of fresh OM/pigments deposition, compared to northernmost stations which had stronger aromatic signals. This study contributes to the understanding of the coupling between the Arctic Ocean productivity and its depositional regime, and how it will be altered in response to sea ice retreat and increasing river runoff.

Description: Dissolved organic matter molecular analyses were performed on a Solarix FT-ICR-MS equipped with a 15 Tesla superconducting magnet (Bruker Daltonic) using a an electrospray ionization source (Bruker Apollo II) in negative ion mode. Molecular formula calculation for all samples was performed using an Matlab (2010) routine that searches, with an error of 〈 0.5 ppm, for all potential combinations of elements including including the elements C∞, O∞, H∞, N = 4; S = 2 and P = 1. Combination of elements NSP, N2S, N3S, N4S, N2P, N3P, N4P, NS2, N2S2, N3S2, N4S2, S2P was not allowed. Mass peak intensities are normalized relative to the total molecular formulas in each sample according to previously published rules (Rossel et al., 2015; doi:10.1016/j.marchem.2015.07.002). The final data contained 7400 molecular formulae.

Description: A high-resolution sea surface temperature and paleoproductivity reconstruction on a sedimentary record collected at 36°S off central-south Chile (GeoB 7165-1, 36°33'S, 73°40'W, 797 m water depth, core length 750 cm) indicates that paleoceanographic conditions changed abruptly between 18 and 17 ka. Comparative analysis of several cores along the Chilean continental margin (30°-41°S) suggests that the onset and the pattern of deglacial warming was not uniform off central-south Chile due to the progressive southward migration of the Southern Westerlies and local variations in upwelling. Marine productivity augmented rather abruptly at 13-14 ka, well after the oceanographic changes.We suggest that the late deglacial increase in paleoproductivity off central-south Chile reflects the onset of an active upwelling system bringing nutrient-rich, oxygen-poor Equatorial SubsurfaceWater to the euphotic zone, and a relatively higher nutrient load of the Antarctic Circumpolar Current. During the Last Glacial Maximum, when the Southern Westerlies were located further north, productivity off central-south Chile, in contrast to off northern Chile, was reduced due to direct onshore-blowing winds that prevented coastal upwelling and export production.

Description: Oceanic dissolved organic carbon (DOC) is an important carbon pool, similar in magnitude to atmospheric CO2, but the fate of its oldest forms is not well understood (Dittmar and Stubbins, 2014; Hansell, 2013, doi:10.1146/annurev-marine-120710-100757). Hot hydrothermal circulation may facilitate the degradation of otherwise un-reactive dissolved organic matter, playing an important role in the long-term global carbon cycle. The oldest, most recalcitrant forms of DOC, which make up most of oceanic DOC, can be recovered by solid-phase extraction. Here we present measurements of solid-phase extractable DOC from samples collected between 2009 and 2013 at seven vent sites in the Atlantic, Pacific and Southern oceans, along with magnesium concentrations, a conservative tracer of water circulation through hydrothermal systems. We find that magnesium and solid-phase extractable DOC concentrations are correlated, suggesting that solid-phase extractable DOC is almost entirely lost from solution through mineralization or deposition during circulation through hydrothermal vents with fluid temperatures of 212-401 °C. In laboratory experiments, where we heated samples to 380 °C for four days, we found a similar removal efficiency. We conclude that thermal degradation alone can account for the loss of solid-phase extractable DOC in natural hydrothermal systems, and that its maximum lifetime is constrained by the timescale of hydrothermal cycling, at about 40 million years (Elderfield and Schultz, 1996, doi:10.1146/annurev.earth.24.1.191).

Description: Molecular analysis of dissolved organic matter in overlying bottom water and porewater was performed on a Solarix FT-ICR-MS equipped with a 15 Tesla superconducting magnet (Bruker Daltonic) using an electrospray ionization source (Bruker Apollo II) in negative ion mode. Molecular formula calculation for all samples was performed using a Matlab (2010) routine that searches, with an error of 〈 0.5 ppm, for all potential combinations of elements including the elements C∞, O∞, H∞, N ≤ 4; S ≤ 2 and P ≤ 1. Combination of elements NSP, N2S, N3S, N4S, N2P, N3P, N4P, NS2, N2S2, N3S2, N4S2, S2P was not allowed. Mass peak intensities are normalized relative to the total molecular formulas in each sample according to previously published rules (Rossel et al., 2015; doi:10.1016/j.marchem.2015.07.002). Additionally, the contribution of molecular formulas with different elemental composition (carbon = C; hydrogen = H; oxygen = O; nitrogen = N; sulfur = S; phosphorus = P) is expressed as a percentage of the total intensity in each sample. Furthermore, in this table,Molecular weight~wa~ was calculated considering the intensity of the mass peak in each sample (i.e. wa stands for intensity weighted-average).

Description: Contribution of different molecular categories, H/Cwa and O/Cwa elemental ratios, aromaticity index (Aimodwa) and double bond equivalents (DBEwa) and indices of degradation (Ideg) and lability (MLBwl; Ibioprod). The contribution of each molecular category is expressed as a percentage of the total formulas in each sample obtained after normalization. Molecular formulas were additionally associated with different molecular categories because less than 6% of the DOM has been identified on a molecular level. Molecular categories are defined as follow: 1) condensed aromatics, with an AImod ≥ 0.67 (Koch and Dittmar, 2006, doi:10.1002/rcm.2386) was separated in 3 different subgroups, either 〈15 (condensed aromatics 〈15C), or ≥15 (condensed aromatics ≥15C) C atoms both without heteroatoms, or containing heteroelements (condensed aromatics-CHOx); 2) polyphenols, with an AImod 〉0.5 but 〈0.67; 3) highly unsaturated formulas, with an AImod 〈0.5, H/C 〈1.5; 4) formulas of unsaturated aliphatics, with an 1.5〈 H/C 〈2, O/C 〈0.9, N = 0; 5) saturated fatty acids, with an H/C 〉2, O/C 〈0.9 and with either no heteroatoms (sat. fatty acids) or with heteroatoms (sat. fatty acids-CHOx); 6) formulas of sugars, with an O/C 〉0.9 and with either no (sugars) or with heteroatoms (sugars-CHOx) and 7)unsaturated with N (unsaturated-N) molecular formulas, with 1.5 〈 H/C 〈2, O/C 〈 0.9 and N 〉0. Additionally, polyphenols, highly unsaturated and unsaturated aliphatics were further separated in oxygen rich (-O-rich) and oxygen poor (-O-poor) if the element ratio O/C was 〉 0.5 or 〈 0.5 respectively.