Grand challenges in marine biogeochemistry

The ocean plays a central role in our earth's climate system and also provides a range of important ecosystem services, including food, energy, transport, and nutrient cycling. Marine biogeochemistry focuses on the study of complex biological, chemical, and physical processes involved in the cycling of key chemical elements within the ocean, and between the ocean and the seafloor, land and atmosphere. The ocean is increasingly perturbed by human induced alterations to our planet, including anthropogenic emissions of nitrogen, phosphorus, carbon and trace elements, and climate change. The establishment of a detailed understanding of biogeochemical processes, including their rates, is essential to the identification and assessment of climatic and chemical feedbacks associated with changes in the chemical and physical environment that are mediated through ocean biology, chemistry and physics. Important research areas in marine biogeochemistry involve the cycling of organic and inorganic forms of carbon, nitrogen and phosphorus, the cycling and biological roles of essential trace elements, and the fate and climatic impact of marine produced trace gases

Chemistry and mineralogy of clay minerals in Asian and Saharan dusts and the implications for iron supply to the oceans

Mineral dust supplied to remote ocean regions stimulates phytoplankton growth through delivery of micronutrients, notably iron (Fe). Although attention is usually paid to Fe (hydr)oxides as major sources of available Fe, Fe-bearing clay minerals are typically the dominant phase in mineral dust. The mineralogy and chemistry of clay minerals in dust particles, however, are largely unknown. We conducted microscopic identification and chemical analysis of the clay minerals in Asian and Saharan dust particles. Cross-sectional slices of dust particles were prepared by focused ion beam (FIB) techniques and analyzed by transmission electron microscopy (TEM) combined with energy dispersive X-ray spectroscopy (EDXS). TEM images of FIB slices revealed that clay minerals occurred as either nano-thin platelets or relatively thick plates. Chemical compositions and lattice fringes of the nano-thin platelets suggested that they included illite, smectite, illite–smectite mixed layers, and their nanoscale mixtures (illite–smectite series clay minerals, ISCMs) which could not be resolved with an electron microbeam. EDXS chemical analysis of the clay mineral grains revealed that the average Fe content was 5.8% in nano-thin ISCM platelets assuming 14% H2O, while the Fe content of illite and chlorite was 2.8 and 14.8%, respectively. In addition, TEM and EDXS analyses were performed on clay mineral grains dispersed and loaded on micro-grids. The average Fe content of clay mineral grains was 6.7 and 5.4% in Asian and Saharan dusts, respectively. A comparative X-ray diffraction analysis of bulk dusts showed that Saharan dust was more enriched in clay minerals than Asian dust, while Asian dust was more enriched in chlorite. Clay minerals, in particular nanocrystalline ISCMs and Fe-rich chlorite, are probably important sources of Fe to remote marine ecosystems. Further detailed analyses of the mineralogy and chemistry of clay minerals in global mineral dusts are required to evaluate the inputs of Fe to surface ocean microbial communities

1. Wochenbericht Poseidon Cruise 527 [POS527]

Poseidon Cruise 527 to Goldeneye region in North Se

Analysis of longitudinal variations in North Pacific alkalinity to improve predictive algorithms

The causes of natural variation in alkalinity in the North Pacific surface ocean need to be investigated to understand the carbon cycle and to improve predictive algorithms. We used GLODAPv2 to test hypotheses on the causes of three longitudinal phenomena in Alk*, a tracer of calcium carbonate cycling. These phenomena are (a) an increase from east to west between 45°N and 55°N, (b) an increase from west to east between 25°N and 40°N, and (c) a minor increase from west to east in the equatorial upwelling region. Between 45°N and 55°N, Alk* is higher on the western than on the eastern side, and this is associated with denser isopycnals with higher Alk* lying at shallower depths. Between 25°N and 40°N, upwelling along the North American continental shelf causes higher Alk* in the east. Along the equator, a strong east-west trend was not observed, even though the upwelling on the eastern side of the basin is more intense, because the water brought to the surface is not high in Alk*. We created two algorithms to predict alkalinity, one for the entire Pacific Ocean north of 30°S and one for the eastern margin. The Pacific Ocean algorithm is more accurate than the commonly used algorithm published by Lee et al. (2006), of similar accuracy to the best previously published algorithm by Sasse et al. (2013), and is less biased with longitude than other algorithms in the subpolar North Pacific. Our eastern margin algorithm is more accurate than previously published algorithms

Characterization of a Time-Domain Dual Lifetime Referencing pCO2 Optode and Deployment as a High-Resolution Underway Sensor across the High Latitude North Atlantic Ocean

The ocean is a major sink for anthropogenic carbon dioxide (CO2), with the CO2 uptake causing changes to ocean chemistry. To monitor these changes and provide a chemical background for biological and biogeochemical studies, high quality partial pressure of CO2 (pCO2) sensors are required, with suitable accuracy and precision for ocean measurements. Optodes have the potential to measure in situ pCO2 without the need for wet chemicals or bulky gas equilibration chambers that are typically used in pCO2 systems. However, optodes are still in an early developmental stage compared to more established equilibrator-based pCO2 systems. In this study, we performed a laboratory-based characterization of a time-domain dual lifetime referencing pCO2 optode system. The pCO2 optode spot was illuminated with low intensity light (0.2mA, 0.72 mW) to minimize spot photobleaching. The spot was calibrated using an experimental gas calibration rig prior to deployment, with a determined response time (t63) of 50 s at 25◦C. The pCO2 optode was deployed as an autonomous shipboard underway system across the high latitude North Atlantic Ocean with a resolution of ca.10 measurements per hour. The optode data was validated with a secondary shipboard equilibrator-based infrared pCO2 instrument, and pCO2 calculated fromdiscrete samples of dissolved inorganic carbon and total alkalinity. Further verification of the pCO2 optode data was achieved using complimentary variables such as nutrients and dissolved oxygen. The shipboard precision of the pCO2 sensor was 9.5μatmdetermined both from repeat measurements of certified reference materials and from the standard deviation of seawater measurements while on station. Finally, the optode deployment data was used to evaluate the physical and biogeochemical controls on pCO2

Abundance of the iron containing biomolecule, heme b, during the progression of a spring phytoplankton bloom in a mesocosm experiment

Concentrations of heme b were determined in a mesocosm experiment situated in Gullmar Fjord off Sweden. The mesocosm experiment lasted for ca. one hundred days and was characterised by the growth of a primary nutrient replete and a secondary nutrient deplete phytoplankton bloom. Heme b varied between 40 ± 10 pmol L-1 in the prebloom period up to a maximum of 700 ± 400 pmol L-1 just prior to the time of the primary chlorophyll a maximum. Thereafter, heme b concentrations decreased again to an average of 120 ± 60 pmol L-1. When normalised to total particulate carbon, heme b was most abundant during the initiation of the nutrient replete spring bloom, when ratios reached 52 ± 24 μmol mol-1; ten times higher than values observed both pre and post the primary bloom. Concentrations of heme b correlated with those of chlorophyll a. Nevertheless, differences were observed in the relative concentrations of the two parameters, with heme b concentrations increasing relative to chlorophyll a during the growth of the primary bloom, decreasing over the period of the secondary bloom and increasing again through the latter period of the experiment. Heme b abundance was therefore influenced by nutrient concentrations and also likely by changing community composition. In half of the mesocosms, pCO2 was elevated and maintained at ca.1000 μatm, however we observed no significant differences between heme b in plus or ambient pCO2 mesocosms, either in absolute terms, or relative to total particulate carbon and chlorophyll a. The results obtained in this study contribute to our understanding of the distribution of this significant component of the biogenic iron pool, and provide an iron replete coastal water end member that aids the interpretation of the distributions of heme b in more iron deplete open ocean waters

Spread, Behavior, and Ecosystem Consequences of Conventional Munitions Compounds in Coastal Marine Waters

Coastal marine environments are contaminated globally with a vast quantity of unexploded ordnance and munitions from intentional disposal. These munitions contain organic explosive compounds as well as a variety of metals, and represent point sources of chemical pollution to marine waters. Most underwater munitions originate from World Wars at the beginning of the twentieth century, and metal munitions housings have been impacted by extensive corrosion over the course of the following decades. As a result, the risk of munitions-related contaminant release to the water column is increasing. The behavior of munitions compounds is well-characterized in terrestrial systems and groundwater, but is only poorly understood in marine systems. Organic explosive compounds, primarily nitroaromatics and nitramines, can be degraded or transformed by a variety of biotic and abiotic mechanisms. These reaction products exhibit a range in biogeochemical characteristics such as sorption by particles and sediments, and variable environmental behavior as a result. The reaction products often exhibit increased toxicity to biological receptors and geochemical controls like sorption can limit this exposure. Environmental samples typically show low concentrations of munitions compounds in water and sediments (on the order of ng/L and μg/kg, respectively), and ecological risk appears generally low. Nonetheless, recent work demonstrates the possibility of sub-lethal genetic and metabolic effects. This review evaluates the state of knowledge on the occurrence, fate, and effect of munition-related chemical contaminants in the marine environment. There remain a number of knowledge gaps that limit our understanding of munitions-related contaminant spread and effect, and the need for additional work is made all the more urgent by increasing risk of release to the environment

Automation of a flow injection system for the determination of dissolved silver at picomolar concentrations in seawater with inductively coupled plasma mass spectrometry

An automated flow injection system for the determination of dissolved silver at ultratrace concentrations in seawater, and controlled under LabVIEW™, is described. The flow injection system allows online processing of seawater samples before their analysis using a magnetic sector inductively coupled plasma mass spectrometry (MS-ICP-MS) instrument. Samples were analysed with a minimum amount of manipulation, thereby reducing the risk of contamination. In addition, the flow injection approach with incorporation of an anion exchange minicolumn allowed ready removal of analytical interferences caused by the saline matrix. The software allowed full control of all flow injection components (valves and pumps) and removed manual time control and, therefore, operator errors. The optimized system was capable of five sample injections per h, including preconcentration and wash steps. The limit of detection was 0.5 pM for a 240-s sample load time, which allowed the determination of dissolved silver in open ocean waters, where picomolar concentration levels are typically encountered