Organic sulfur: a spatially variable and understudied component of marine organic matter

© The Author(s), 2020. This article is distributed under the terms of the Creative Commons Attribution License. The definitive version was published in Longnecker, K., Oswald, L., Soule, M. C. K., Cutter, G. A., & Kujawinski, E. B. Organic sulfur: a spatially variable and understudied component of marine organic matter. Limnology and Oceanography Letters, (2020), doi:10.1002/lol2.10149.Sulfur (S) is a major heteroatom in organic matter. This project evaluated spatial variability in the concentration and molecular‐level composition of organic sulfur along gradients of depth and latitude. We measured the concentration of total organic sulfur (TOS) directly from whole seawater. Our data reveal high variability in organic sulfur, relative to established variability in total organic carbon or nitrogen. The deep ocean contained significant amounts of organic sulfur, and the concentration of TOS in North Atlantic Deep Water (NADW) decreased with increasing age while total organic carbon remained stable. Analysis of dissolved organic matter extracts by ultrahigh resolution mass spectrometry revealed that 6% of elemental formulas contained sulfur. The sulfur‐containing compounds were structurally diverse, and showed higher numbers of sulfur‐containing elemental formulas as NADW moved southward. These measurements of organic sulfur in seawater provide the foundation needed to define the factors controlling organic sulfur in the global ocean.We thank Catherine Carmichael, Winifred Johnson, and Gretchen Swarr for assistance with sample collection and processing, and Joe Jennings for the analysis of inorganic nutrients. The help of the captain and crew of the R/V Knorr and the other cruise participants during the “DeepDOM” cruise is appreciated. Two anonymous reviewers and Patricia Soranno provided thorough comments that greatly improved the manuscript. The ultrahigh resolution mass spectrometry samples were analyzed at the WHOI FT‐MS Users' Facility that is funded by the National Science Foundation (grant OCE‐0619608) and the Gordon and Betty Moore Foundation (GMBF1214). This project was funded by NSF grants OCE‐1154320 (to EBK and KL), the W.M. Marquet Award (to KL), and OCE‐1435708 (to GAC). The authors declare no conflicts of interest

Metalloids in Wet Deposition on Bermuda: Concentrations, Sources, and Fluxes

The concentrations of antimony, arsenic, and selenium were determined in wet deposition samples collected on a daily (event) basis from 1988 to 1990 on Bermuda as a part of the Atmosphere/Ocean Chemistry Experiment (AEROCE). Isentropic back trajectories were used to identify air masses that passed over North America (59% of the events), Europe or North Africa (8%), or were largely marine in origin (33% of the events). The North American trajectories had the highest volume-weighted average (VWA) concentrations and crustal enrichment factors for the three metalloids; the As/Se ratio and good correlations with acidity suggest inputs from fossil fuel combustion. The Euro-African trajectories had the lowest VWA concentrations and enrichment factors that approached crustal values, indicating mineral aerosol inputs; values for marine events fell between these two extremes. The atmospheric flux of metalloids to the western Atlantic Ocean represents a major source of these elements in surface waters (up to 100% for Sb and Se; up to 61% for As) and a corresponding sink in their global atmospheric budgets

Intercalibraton in Chemical Oceanography-- Getting The Right Number

Intercalibration has a strict metrological definition, but in brief, it\u27s an open sharing of methods and results between laboratories to achieve the most accurate data with the fewest random and systematic errors. In the field of chemical oceanography where concentrations of many constituents can be in the nano- to picomolar range, the salt water matrix can be difficult to analyze, and knowing the exact concentrations, or even chemical forms, of biologically required elements is essential, intercalibration is a very relevant and needed tool. Implementing it is not simple because errors can occur at any step in the process of taking a water or particle sample, handling and processing it, and finally analyzing it and treating the resulting data. The international GEOTRACES program provides a good example of implementing intercalibration for studies of dissolved and particulate trace elements and isotopes, and is described here

Trace Elements in Estuarine and Coastal Waters: U.S. Studies from 1986-1990

The use of specialized analytical techniques, field studies, controlled laboratory experiments, and geochemical modeling have allowed U.S. investigators to expand our understanding of trace element cycling in coastal waters and estuaries. Considerable emphasis has been placed on quantifying the flux of trace elements within and through the coastal zone. In addition, substantial progress has been made in identifying the chemical speciation of many trace elements, providing a linkage between the geochemical and biochemical behavior of these elements. Another significant advance has been the use of trace elements as tracers of geochemical processes and water masses in the coastal environment

Divergent responses of Atlantic coastal and oceanic Synechococcus to iron limitation

Author Posting. © The Author(s), 2015. This is the author's version of the work. It is posted here by permission of National Academy of Sciences for personal use, not for redistribution. The definitive version was published in Proceedings of the National Academy of Sciences of the United States of America 112 (2015): 9944-9949, doi:10.1073/pnas.1509448112.Marine Synechococcus are some of the most diverse and ubiquitous phytoplankton, and iron (Fe) is an essential micronutrient that limits productivity in many parts of the ocean. To investigate how coastal and oceanic Atlantic Synechococcus strains acclimate to Fe availability, we compared the growth, photophysiology, and quantitative proteomics of two Synechococcus strains from different Fe regimes. Synechococcus strain WH8102, from a region in the southern Sargasso Sea that receives substantial dust deposition, showed impaired growth and photophysiology as Fe declined, yet utilized few acclimation responses. Coastal WH8020, from the dynamic, seasonally variable New England shelf, displayed a multi-tiered, hierarchical cascade of acclimation responses with different Fe thresholds. The multi-tiered response included changes in Fe acquisition, storage, and photosynthetic proteins, substitution of flavodoxin for ferredoxin, and modified photophysiology, all while maintaining remarkably stable growth rates over a range of Fe concentrations. Modulation of two distinct ferric uptake regulator (Fur) proteins that coincided with the multi-tiered proteome response was found, implying the coastal strain has different regulatory threshold responses to low Fe availability. Low nitrogen (N) and phosphorus (P) availability in the open ocean may favor the loss of Fe response genes when Fe availability is consistent over time, whereas these genes are retained in dynamic environments where Fe availability fluctuates and N and P are more abundant.This work was supported by a National Science Foundation Postdoctoral Research Fellowship in Biology to K.R.M.M. (NSF 1103575), National Science Foundation Oceanography grants OCE-1220484, OCE-0928414, OCE-1233261, OCE- 1155566, OCE-1131387, and OCE-0926092, as well as Gordon and Betty Moore Foundation grants 3782 and 3934

Sources And Cycling of Carbonyl Sulfide in the Sargasso Sea

The cycling of the radiatively important gas carbonyl sulfide (OCS) was studied in surface waters of the Sargasso Sea. In August 1999, surface OCS concentrations averaged 8.6 pmol L-1, showed minor diel variations, and varied little with depth. An OCS precursor, total dissolved organic sulfur (DOS), was lowest at the surface (40 nmol L-1) and increased with depth. The photoproduction rate of OCS from in situ incubations averaged 9.6 pmol L-1 h-1, whereas dark production was 7.0 pmol L-1 h-1. Apparent quantum yields were 10-5-10-7 from 313-436 nm and varied with the water depth irradiated. In March 2000, there were strong diel variations in surface OCS (highest in late afternoon; overall average, 16.9 pmol L-1). Depth profiles in the afternoon showed surface water maxima and decreases with depth, whereas DOS had a surface maximum of 419 nmol L-1 and decreased with depth. Dark production was 4.0 pmol L-1 h-1. Modeling of the diel cycle suggested a photoproduction rate of 16.4 pmol L-1 h-1. Overall, the photochemical production of OCS strongly depended on DOS and chromophoric dissolved organic matter, whereas dark production was influenced by the presence of particles and perhaps microbial respiration, showing a direct biotic influence on OCS cycling

High Resolution Determination of Nanomolar Concentrations of Dissolved Reactive Phosphate in Ocean Surface Waters Using Long Path Liquid Waveguide Capillary Cells (LWCC) and Spectrometric Detection

In the last decade, long path length, low volume, liquid waveguide capillary cells (LWCC) in conjunction with conventional nutrient auto-analyzers have been applied to determinations of nanomolar levels of phosphate, nitrate, and nitrite in oligotrophic waters. This article reports a high resolution, real-time, continuous method for nanomolar dissolved reactive phosphate measurements in ocean surface waters with data logging every 30 seconds for up to 16 consecutive hours. Surface seawater is pumped continuously from a shipboard underway tow-fish unit to a helium gas-segmented, continuous-flow, nutrient auto-analyzer modified with a 250 cm LWCC. To circumvent baseline instability due to reagents, a parallel channel with deionized water (DI) and reagents is run and later subtracted from the sample absorbances. The detection limit is 0.8 nmol/L. The precision (as relative standard deviation) at 5 nmol/L phosphate is 6.1% (n = 5) and 0.8% (n = 5) at 50 nmol/L. We also report an optimized method for discrete samples using a 200 cm LWCC. To minimize any background phosphate concentration in low nutrient seawater used as wash water solution, we use DI water, but increase sample and wash times to achieve plateau-shaped peaks after the transient wash/sample mixing period. The detection limit is 0.5 nmol/L. The precision at 10 nmol/L phosphate is 1.8% (n = 8) and 0.9% (n = 9) at 60 nmol/L. The two systems have successfully been deployed on the U.S. GEOTRACES 2010 cruise, transecting the upwelling area northwest of Africa and the highly stratified, oligotrophic, subtropical North Atlantic gyre

The Marine Biogeochemistry of Selenium: A Re-Evaluation

Vertical and horizontal profiles from the North and South Pacific Oceans demonstrate the existence of three species of dissolved selenium: selenite, selenate, and organic selenide (operationally defined). In surface waters, organic selenide makes up about 80% of the total dissolved selenium, selenite concentrations are uniformly low, and selenate concentrations rise with increased vertical mixing. The organic selenide maximum (thought to consist of seleno-amino acids in peptides) coincides with the maxima of primary productivity, pigments, bioluminescence, and dissolved free amino acids. Deep ocean waters are enriched in selenite and selenate, while organic selenide is nondetectable. In suboxic waters of the tropical northeastern Pacific, organic selenide concentrations rise, while selenite values decrease. The downward flux of particulate selenium generally decreases with depth, and fluxing particulate selenium is found to be primarily in the (-2) oxidation state. These data allow a re-evaluation of the internal biogeochemical cycle of selenium. This cycle includes selective uptake, reductive incorporation, particulate transport, a multistep regeneration, and kinetic stabilization of thermodynamically unstable species

Evaluating the Biogeochemical Cycle of Selenium in San Francisco Bay Through Modeling

A biogeochemical model was developed to simulate salinity, total suspended material, phytoplankton biomass, dissolved selenium concentrations (selenite, selenate, and organic selenide), and particulate selenium concentrations (selenite + selenate, elemental selenium, and organic selenide) in the San Francisco Bay estuary. Model-generated estuarine profiles of total dissolved selenium reproduced observed estuarine profiles at a confidence interval of 91- 99% for 8 different years under various environmental conditions. The model accurately reproduced the observed dissolved speciation at confidence intervals of 81-98% for selenite, 72-91% for selenate, and 60-96% for organic selenide. For particulate selenium, model-simulated estuarine profiles duplicated the observed behavior of total particulate selenium (76-93%), elemental selenium (80-97%), selenite + selenate (77-82%), and organic selenide (70-83%). Discrepancies between model simulations and the observed data provided insights into the estuarine biogeochemical cycle of selenium that were largely unknown (e.g., adsorption/desorption). Forecasting simulations investigated how an increase in the discharge from the San Joaquin River and varying refinery inputs affect total dissolved and particulate selenium within the estuary. These model runs indicate that during high river flows the refinery signal is undetectable, but when river flow is low (70- day residence time) total particle-associated selenium concentrations can increase to \u3e2 µg g-1 . Increasing the San Joaquin River discharge could also increase the total particle-associated selenium concentrations to \u3e1 µg g-1 . For both forecasting simulations, particle-associated selenium was predicted to be higher than current conditions and reached levels where selenium could accumulate in the estuarine food web

A Tribute to Thomas M. Church: Exploring Chemical Oceanography in the Coastal Zone-The History and Future

( First paragraph) One can find different historical perspectives on the development of studying the chemistry of oceans as well as names for this study—marine chemistry, chemistry of the sea, marine aquatic chemistry, marine biogeochemistry, or chemical oceanography. It could be argued that chemical oceanography is the most inclusive for an earth science since oceanography itself is an integrated discipline that links the biology, chemistry, geology, and physics together. Regardless of the name, perhaps the first intensive, modern/post-nineteenth century study of the ocean’s chemistry was the GEOSECS Program from ca. 1970–1978. The significance of GEOSECS was that it examined the chemistry of the world’s oceans from nutrients to radionuclides, and even a few trace elements, but in a physical context of ocean circulation (e.g., Craig 1972). Thomas M. Church (Figs. 1 and 2) was ‘‘born’’ into the GEOSECS world, receiving his Ph.D. in 1970 from Scripps Institution of Oceanography in the laboratory of Edward Goldberg with the first examination of marine barite in the world’s oceans. GEOSECS was a ‘‘blue water’’ program, but Tom Church decided to take the road less travelled at the time to examine chemical processes in the coastal zone. The coastal zone has been described, both then and now and always somewhat facetiously, as the ‘‘brown ring around the bathtub,’’ but many would argue that this minimizes its importance since it is here where continental weathering products are primarily introduced to the ocean and where many of these same products are also removed. Primary productivity is at a maximum in coastal waters, and human populations and effects are also concentrated here