Origin and fate of the secondary nitrite maximum in the Arabian Sea

The Arabian Sea harbours one of the three major oxygen minimum zones (OMZs) in the world's oceans, and it alone is estimated to account for ~10–20 % of global oceanic nitrogen (N) loss. While actual rate measurements have been few, the consistently high accumulation of nitrite (NO2?) coinciding with suboxic conditions in the central-northeastern part of the Arabian Sea has led to the general belief that this is the region where active N-loss takes place. Most subsequent field studies on N-loss have thus been drawn almost exclusively to the central-NE. However, a recent study measured only low to undetectable N-loss activities in this region, compared to orders of magnitude higher rates measured towards the Omani Shelf where little NO2? accumulated (Jensen et al., 2011). In this paper, we further explore this discrepancy by comparing the NO2?-producing and consuming processes, and examining the relationship between the overall NO2? balance and active N-loss in the Arabian Sea. Based on a combination of 15N-incubation experiments, functional gene expression analyses, nutrient profiling and flux modeling, our results showed that NO2? accumulated in the central-NE Arabian Sea due to a net production via primarily active nitrate (NO3?) reduction and to a certain extent ammonia oxidation. Meanwhile, NO2? consumption via anammox, denitrification and dissimilatory nitrate/nitrite reduction to ammonium (NH4+) were hardly detectable in this region, though some loss to NO2? oxidation was predicted from modeled NO3? changes. No significant correlation was found between NO2? and N-loss rates (p>0.05). This discrepancy between NO2? accumulation and lack of active N-loss in the central-NE Arabian Sea is best explained by the deficiency of labile organic matter that is directly needed for further NO2? reduction to N2O, N2 and NH4+, and indirectly for the remineralized NH4+ required by anammox. Altogether, our data do not support the long-held view that NO2? accumulation is a direct activity indicator of N-loss in the Arabian Sea or other OMZs. Instead, NO2? accumulation more likely corresponds to long-term integrated N-loss that has passed the prime of high and/or consistent in situ activities

Nitrous oxide in the northern Gulf of Aqaba and the central Red Sea

Nitrous oxide (N2O) is a climate-relevant atmospheric trace gas. It is produced as an intermediate of the nitrogen cycle. The open and coastal oceans are major sources of atmospheric N2O. However, its oceanic distribution is still largely unknown. Here we present the first measurements of the water column distribution of N2O in the Gulf of Aqaba and the Red Sea. Samples for N2O depth profiles were collected at the time-series site Station A in the northern Gulf of Aqaba (June and September 2003, and February 2004) and at several stations in the central Red Sea (October 2014, January and August 2016). Additionally, we measured N2O concentrations in brine pool samples collected in the northern and central Red Sea (January 2005 and August 2016). In the Gulf of Aqaba, N2O surface concentrations ranged from 6 to 8 nmol L−1 (97–111% saturation) and were close to the equilibrium with the overlying atmosphere. A pronounced temporal variability of the N2O water column distribution was observed. We suggest that this variability is a reflection of the interplay between N2O production by nitrification and its consumption by N2 fixation in the layers below 150 m during summer. N2O surface concentrations and saturations in the central Red Sea basin ranged from 2 to 9 nmol L−1 (43–155% saturation). A pronounced temporal variability with significant supersaturation in October 2014 and undersaturation in January and August 2016 was observed in the surface layer. In October 2014, N2O in the water column seemed to result from production via nitrification. Low N2O water column concentrations in January and August 2016 indicated a significant removal of N2O. We speculate that either in-situ consumption or remote loss processes of N2O such as denitrification in coastal regions were responsible for this difference. Strong meso- and submesoscale processes might have transported the coastal signals across the Red Sea. In addition, enhanced N2O concentrations of up to 39 nmol L−1 were found at the seawater-brine pool interfaces which point to an N2O production via nitrification and/or denitrification at low O2 concentrations. Our results indicate that the Red Sea and the Gulf of Aqaba are unique natural laboratories for the study of N2O production and consumption pathways under extreme conditions in one of the warmest and most saline region of the global oceans

Outbreak of bovine viral diarrhoe on Dutch dairy farms induced by a BHV1 marker vaccine contaminated with BDVD type 2

On 23 February 1999, the Dutch Animal Health Service advised all Dutch veterinary practices to postpone vaccination against bovine herpesvirus 1 (BHV1) immediately. The day before severe disease problems were diagnosed on four dairy farms after vaccination with the same batch of BHV1 marker vaccine. Using monoclonal antibodies, bovine virusdiarrhoea virus (BVDV) type 2 was found in the vaccine batch. This paper describes an outbreak of BVDV type 2 infection caused by the use of a batch of modified live BHV1 marker vaccine contaminated with BDVD. Sources of information used were reports of farm visits, minutes of meetings, laboratory results, and oral communications from the people involved. The first symptoms of disease were observed on average six days after vaccination. Morbidity was high on 11 of the 12 farms. On five farms more than 70% of the animals became ill, while on one farm no symptoms could be detected. During the first week after vaccination, feed intake and milk production decreased. During the second week, some animals became clinically diseased having nasal discharge, fever, and diarrhoea. At the end of the second week and at the start of the third week, the number of diseased animals increased rapidly, the symptoms became more severe, and some animals died. Mortality varied among herds. Necropsy most often revealed erosions and ulcers of the mucosa of the digestive tract. In addition, degeneration of the liver, hyperaemia of the abomasum, and swollen mesenterial lymph nodes and swollen spleen were found. On 11 of the 12 farms all animals were culled between 32 and 68 days after vaccination after an agreement was reached with the manufacturer of the vaccine. This was the third outbreak of BVD in cattle after administration of a contaminated vaccine in the Netherlands. The possibilities to prevent contamination of a vaccine as a consequence of infection of fetal calf serum with BVDV are discussed. Improvement of controls to prevent contamination before and during vaccine production, and improvement of the monitoring of side-effects is necessary

FREMIX: a high power 8 GHz plasma heating experiment

A survey was made of the problems encountered in the assembly and the operation of the equipment used for the FREMIX expt. This expt. aims at resonant ion heating in a magnetic bottle at frequencies which are the product of nonlinear mixing of e cyclotron resonance waves. The problems can be divided into 3 categories: (1) Requirements for operation of 2 klystron amplifiers: power supplies with protective equipment, steering circuitry, and cooling water. (2) Wave-guide systems: are protection, circulators, and vacuum window. (3) Construction of the plasma chamber; introduction of diagnostic tools: 4-mm interferometry, x-ray detection of escaping particles, and detection of excited radiation and mixing products (1-5 MHz; 16 GHz). [on SciFinder (R)

Nitrous oxide in the northern Gulf of Aqaba and the central Red Sea

Nitrous oxide (N2O) is a climate-relevant atmospheric trace gas. It is produced as an intermediate of the nitrogen cycle. The open and coastal oceans are major sources of atmospheric N2O. However, its oceanic distribution is still largely unknown. Here we present the first measurements of the water column distribution of N2O in the Gulf of Aqaba and the Red Sea. Samples for N2O depth profiles were collected at the time-series site Station A in the northern Gulf of Aqaba (June and September 2003, and February 2004) and at several stations in the central Red Sea (October 2014, January and August 2016). Additionally, we measured N2O concentrations in brine pool samples collected in the northern and central Red Sea (January 2005 and August 2016). In the Gulf of Aqaba, N2O surface concentrations ranged from 6 to 8 nmol L−1 (97–111% saturation) and were close to the equilibrium with the overlying atmosphere. A pronounced temporal variability of the N2O water column distribution was observed. We suggest that this variability is a reflection of the interplay between N2O production by nitrification and its consumption by N2 fixation in the layers below 150 m during summer. N2O surface concentrations and saturations in the central Red Sea basin ranged from 2 to 9 nmol L−1 (43–155% saturation). A pronounced temporal variability with significant supersaturation in October 2014 and undersaturation in January and August 2016 was observed in the surface layer. In October 2014, N2O in the water column seemed to result from production via nitrification. Low N2O water column concentrations in January and August 2016 indicated a significant removal of N2O. We speculate that either in-situ consumption or remote loss processes of N2O such as denitrification in coastal regions were responsible for this difference. Strong meso- and submesoscale processes might have transported the coastal signals into the central Red Sea. In addition, enhanced N2O concentrations of up to 39 nmol L−1 were found at the seawater-brine pool interfaces which point to an N2O production via nitrification and/or denitrification at low O2 concentrations. Our results indicate that the Red Sea and the Gulf of Aqaba are unique natural laboratories for the study of N2O production and consumption pathways under extreme conditions in one of the warmest and most saline regions of the global ocean