An improved method for the determination of dissolved nitric oxide (NO) in seawater samples

Nitric oxide (NO) is a short-lived intermediate of the oceanic nitrogen cycle, however, due to its high reactivity, measurements of dissolved NO in seawater are rare. Here we present an improved method to determine NO concentrations in discrete seawater samples. The set-up of our system consisted of a chemiluminescence NO analyser connected to a stripping unit. The limit of detection for our method was 5 pmol NO in aqueous solution which translates into 0.25 nmol L−1 when using a 20 mL seawater sample volume. Our method was applied to measure high resolution depth profiles of dissolved NO during a cruise to the eastern tropical South Pacific Ocean. Our method is fast and comparably easy to handle thus it opens the door for deciphering the distribution of NO in the ocean and it facilitates laboratory studies on NO pathways

Nitric oxide (NO) in the oxygen minimum zone off Peru

Nitric oxide (NO) is a short-lived compound of the marine nitrogen cycle. However, measurements of NO in seawater are analytically challenging and our knowledge about its oceanic distribution is, therefore, rudimentary. NO was measured in the oxygen minimum zone (OMZ) of the eastern tropical South Pacific Ocean (ETSP) off Peru during R/V Meteor cruise M93 in February/March 2013. NO concentrations ranged from close to or below the detection limit (0.5nmolL-1) in the surface layer to 9.5nmolL-1 in the OMZ. NO concentrations increased significantly when oxygen (O2) concentrations dropped below 1-2μmolL-1. We found positive correlations between NO and NO2 - as well as between NO and the abundance of archaeal amoA, a marker gene for archaeal nitrifiers. No trends between NO and nirS and hzo, marker genes for canonical denitrification and anammox, respectively, were found. To this end, we conclude that NO off Peru was mainly produced by archaeal nitrifier-denitrification at low O2 concentrations in the OMZ

A novel method for the measurement of VOCs in seawater using needle traps devices and GC-MS

Highlights: • Development/evaluation of a ‘needle trap device’ (NTD) method for the analysis of VOC in seawater. • First field application of the NTD method in a Norwegian Fjord during a CO2 enrichment study. • Identification and quantification of DMS, isoprene and α-pinene under various pCO2 levels. • In field NTD GC-MS and P&T GC-FPD method comparison for the DMS datasets (r2 = 0.8). Abstract: A novel analytical method using newly developed needle trap devices (NTDs) and a gas chromatograph–mass spectrometer (GC–MS) system was developed. It has been applied for the first time on seawater samples to quantify marine volatile organic compounds (VOCs) relevant to atmospheric chemistry and climate. By purging gases from small water volumes (10 ml) onto sealable NTDs and then desorbing them thermally within the GC injection port, an effective analysis of a wide range of VOCs (isoprene to α-pinene) was achieved within 23 min. Good repeatability (RSDs < 16 %), linearity (r2 = 0.96–0.99) and limits of detection in the range of pM were obtained for all examined compounds. Following laboratory validation, the NTD method was applied in a mesocosm field study in a Norwegian Fjord. Nine individual mesocosm ecosystems under different CO2 regimes were examined. Dimethyl sulfide (DMS), isoprene and monoterpenes were identified and quantified in mesocosm seawater. The DMS measurements are compared with parallel measurements provided by an independent P&T GC–FPD system showing good correlation, r2 = 0.8. Our study indicates that the NTD method can be used successfully in place of the traditionally used extraction techniques (P&T, SPME) in marine environments to extend the suite of species typically measured and improve detection limits

Sovereignty at Sea: The law and politics of saving lives in mare liberum

This article analyses the interplay between politics and law in the recent attempts to strengthen the humanitarian commitment to saving lives in mare liberum. Despite a long-standing obligation to aid people in distress at sea, this so-called search and rescue regime has been marred by conflicts and political standoffs as states were faced with a growing number of capsising boat migrants potentially claiming international protection once on dry land. Attempts to provide a legal solution to these problems have resulted in a re-spatialisation of the high seas, extending the states’ obligations in the international public domain based on geography rather than traditional functionalist principles that operated in the open seas. However, inadvertently, this further legalisation has equally enabled states to instrumentalise law to barter off and deconstruct responsibility by reference to traditional norms of sovereignty and maritime law. In other words, states may be able to reclaim sovereign power by becoming increasingly norm-savvy and successfully navigating the legal playing field provided by the very expansion of international law itself. Thus, rather than being simply a space of non-sovereignty per se, mare liberum becomes the venue for a complex game of sovereignty, law and politics