Preformed Nitrate Research Articles

Carbon utilization in the Eurasian sector of the Arctic Ocean

Production and remineralization of carbon in the Eurasian sector have been estimated based on a combined data set of the Oden—91 and Polarstern—93 (ARK IX—4) expeditions. This sector includes the deep Nansen and Amundsen Basins and their linked shelf seas, i.e., the Barents, Kara, and Laptev Seas. The water masses in this region are composed of Atlantic water, river runoff, and sea ice‐melt water. The fractionation between these source waters is elucidated from the δ18O—salinity relation and conservation of mass. By combining preformed nitrate concentrations of the source waters with the fractionation model and the measured nitrate concentrations, nitrate deficits and excesses are calculated. These concentrations are then converted to carbon equivalents by applying a C/N ratio, whereby a measure of apparent carbon utilization (ACU) is obtained. From the relative inventory of ACU along the slope and deep basin sections, we conclude that the shelf areas are the dominant productivity sites and that the productivity signal is transported to all water masses in the Eurasian Basin. The flux of utilized carbon from the Barents‐Kara and Laptev Seas is about 0.022 Gton C yr−1.

Chemical tracers of biological processes in shallow waters of North Pacific: Preformed nitrate distributions

Distributions of nitrate and Apparent Oxygen Utilization in the upper subtropical North Pacific Ocean reveal a layer with negative values of preformed nitrate. This layer occurs at depths just below the 1% light level and above the density of sigma theta 25.6. We show that large-scale spatial patterns in the distribution of this feature are determined by an interaction between light penetration and the depth of isopycnal surfaces which are ventilated in nutrient rich surface waters. Although the data alone are insufficient to distinguish between several possible causes, we believe the geographic and depth distributions of the negative preformed nitrate feature are most readily explained by respiration of nitrogen-poor dissolved organic matter (DOM) from the surface ocean with the possible accompaniment of nitrate uptake. Dissolved organic carbon gradients and transport calculations suggest that a significant fraction of the carbon flux out of the euphotic zone may be via DOM, indicating that the processes responsible for creating the negative preformed nitrate feature could alter the metabolite stoichiometry in upper subtropical Pacific Ocean.

Effect of cyanophage N-1 infection on the synthesis and stability ofNostoc muscorum nitrate reductase

The control operative on the nitrate reductase enzyme system of host cyanobacteriumNostoc muscorum was studied after being infected with the cyanophage N-1. Phage infection lifted the host nitrate reductase activity level via accelerating the enzyme synthesis. It was found that the phage-mediated increase in the molybdenum cofactor synthesis was a major contributing factor for apparent elevated nitrate reductase level of the host. This process was inhibited in the presence of erythromycin and tungsten, the inhibitors of protein synthesis and new nitrate reductase synthesis respectively. While the preformed nitrate reductase of healthy cyanobacterium was inhibited by hydrogen peroxide, an oxidizing photosynthetic product, the same enzyme of infected cells remained virtually insensitive to this inhibitor. These data suggest involvement of new nitrate reductase synthesis and its resistance to oxidative inactivation as joint factors controlling the characteristic high enzyme level of host cyanobacterium.

Calculating the oceanic CO2 increase: A need for caution

A number of workers have presented calculations attempting to show the anthropogenic CO2 increase in the ocean. These workers back‐calculate the CO2 concentration of a water parcel to when it was at the sea surface by using well‐known ratios to correct for chemical changes induced by biological decomposition. Because of the potential significance of these CO2 back‐calculations, their limitations are examined here. In the Antarctic Intermediate Water, which has served as a primary testing ground for these backcalculation models, mixing is seen to significantly alter chemical concentrations. However, previously used mixing corrections are shown to have little effect on an analogous back‐calculation of preformed nitrate. Additionally, the results of the CO2 back‐calculations are probably too high for the water mass in question. Thus the ability of these methods to provide reliable estimates of the oceanic CO2 increase is in doubt.

Nitrate reductase activity in Paul's scarlet rose suspension cultures and the differential role of nitrate and molybdenum in induction

Induction of nitrate reductase (EC 1.6.6.1) activity was measured in Paul's Scarlet rose cell suspensions cultured in media containing nitrate (NO 3 (-) ) or urea (U) as nitrogen source, and with (+Mo) or without molybdenum (-Mo). There was a lag of 30 min during induction by NO 3 (-) in +Mo cultures but no lag occurred during induction after adding Mo to NO 3 (-) -Mo or to U-Mo cultures preincubated with NO 3 (-) . Actinomycin D, cycloheximide, and puromycin completely blocked induction by NO 3 (-) , but had no effect on the initial rate of induction by Mo. Cycloheximide and puromycin blocked induction by NO 3 (-) more quickly than actinomycin D. Induction by NO 3 (-) appeared to involve mRNA-dependent synthesis of apoprotein followed by rapid activation with molybdenum in intact cells independently of protein synthesis. Nitrate-induced apoprotein appeared less stable than the holoenzyme. When induced by NO 3 (-) in the absence of Mo, apoprotein concentration was about half the amount of maximally induced nitrate reductase. Cycloheximide stabilised preformed nitrate reductase which disappeared steadily in the presence of puromycin. Apoprotein was not stabilised by either antimetabolite.

“NO”, a conservative water-mass tracer

A composite property, 9NO 3 + O 2, is proposed as a conservative water-mass tracer. The coefficient 9 is chosen so that the increase in “NO” resulting from nitrate introduction during respiration just balances the consumption of dissolved oxygen gas. Because of the pronounced difference in the preformed nitrate content of deep water produced at the northern and southern ends of the Atlantic Ocean “NO” provides an independent means of disentangling the degree of mixing of various water types in the deep sea. Evidence based on data obtained during the Atlantic Geosecs program is presented to demonstrate the sensitivity and reliability of this conservative tracer.

Formation of Antarctic bottom water in the Weddell Sea

During the austral summers of 1968 and 1969, the USCGC Glacier penetrated the pack ice of the Weddell Sea to over 75°S in support of the International Weddell Sea Oceanographic Expedition (IWSOE). A total of 83 hydrographic stations were conducted during the two expeditions for analysis of temperature, salinity, dissolved oxygen, and nutrients. The data revealed a cold (−1.9°C) saline (>34.60‰) layer of water on the continental shelf below a depth of 200 meters in the southwestern Weddell Sea. We hypothesize that this water mass is formed by alteration of coastal current water as it flows along and beneath the vast ice shelves in the southern Weddell Sea. The altered coastal current water then mixes with warm deep water (>0.2°C, >34.67‰) along the continental slope in approximately 1∶2 to form antarctic bottom water (−0.4°C, 34.66‰). The mixing ratio is confirmed by using core values of preformed phosphate and preformed nitrate concentrations as conservative properties. Antarctic bottom water then flows out of the Weddell Sea between 50° and 15°W longitudes and 60° and 65°S latitudes. Bottom water (−0.26°C, 34.66‰) flows into the Weddell Sea from the east near the Coats Land coast and is entrained into the antarctic bottom water flowing out.

Chemical Features of the Subarctic Boundary Near 170°W

During the Yaloc 66 cruise of R/V Yaquina, the vertical distribution of nutrients, pH alkalinity, apparent oxygen utilization, preformed phosphate, preformed nitrate, and specific alkalinity across the subarctic boundary near 170°W were studied. In addition to use of salinity to identify the subarctic boundary, the surface distributions of nutrients, pH, and preformed nutrients were found to be useful. Both the density-apparent oxygen utilization relationships and the specific alkalinity pattern indicated upward divergence of subsurface water having salinity greater than 34.0‰ on the north side of the boundary. A high specific alkalinity of about 0.129 immediately north of the boundary was probably due to the transport of upwardly diverged water having high specific alkalinity to near the boundary. Values for preformed phosphate and preformed nitrate gave supporting evidence that the origin of the salinity-minimum water located south of the boundary is in the subarctic region.