Boron concentration ocean

Boron concentrations and isotopes are also useful geochemical tracers of contamination in MORB. Boron concentrations are low (<2 ppm) in unaltered ocean floor basalt but high in altered basalts (>8 ppm B) (Spivack and Edmond 1987 Ryan and Langmuir 1993). Goldstein et al. (1989) measured B concentrations in their samples and found them to be less than 1.6 ppm, inconsistent with contamination. More recently, B isotopes have been used to assess contamination since large differences in 5 B are known to exist between seawater, sediments, and unaltered MORB. Sims et al. (2002) reported that 6 B for their 9°N EPR samples were inconsistent with incorporation of any seawater or seawater-derived material. 

The first studies of Li isotopes in subduction zones concentrated on young convergent margin lavas. Moriguti and Nakamura (1998b) reported correlated Li isotope and fluid-mobile element (notably boron) concentration variations in the Izu arc, southeastern Japan (8 Li = +1.1 to +7.6), consistent with significant incorporation of Li from altered oceanic crust into arc lava sources (Fig. 6). A similar trend has been reported in samples of basalts and basaltic andesites from Mt. Shasta, California (5 Li = +2.5 to +6.5 Magna et al. 2003). 

Since boron concentrations in mantle minerals are exceedingly low, boron isotope analysis of mantle minerals are very restricted. On the basis of a boron budget between mantle and crust, Chaussidon and Marty (1995) conclnded that the primitive mantle had a 5 B-value of-10 2%c.ForMORB Spivack and Edmond (1987) and Chaussidon and Marty (1995) reported a 5 B-value of aronnd -4%c. Higher and lower 5 B-values observed in some ocean island basalts shonld be due to crustal assimilation (Tanaka and Nakamura 2005). 

It is important to note that the presence of polyborate anions, as shown in Fignre 2, is only significant in relatively concentrated solutions. This is relevant to the enviromnental and biological aspects of boron chemistry, since boron is present in both natural waters and biological systems at low concentrations. Under these conditions, only B(OH)3 and B(0H)4 are significant species and at near neutral pH, the concentration of the B(OH)4 anion is minor. Ocean waters contain an average boron concentration of about 4.6 g p,g g , which is almost entirely present in the form of naturally occurring boric acid. Boron in plants and animals is also present mainly as boric acid, even if the dietary source of boron is a borate salt. 

Boron concentration in the analyzed DSDP cherts varies between 44 and 104 ppm and value between -9.3 1.6%o and +7.7 1.2%o (Table 1, Fig. 3). The range of values reported here overlaps and includes those observed in opal-A radiolarians and diatoms (+ 2.2 to + 4.5%c, IsHiKAWA and Nakamura, 1993). Some of the DSDP cherts analyzed by us have very low 8 B values lending further support to the general claim of Lemarchand et al (2002) that boron sinks from the ocean are B enriched. The two chert samples from Holes 169 and 195 have 8 B values within the range defined by cherts from Hole 167 but tend to have low B concentrations and low values. 

Pressurized Water Reactor. The PWR contains three coolant systems (1) the primary system, which removes heat from the reactor and partially controls nuclear criticality (2) the secondary system, which transfers the heat from the primary system via the steam generator to the turbine-driven electric generator (3) the service water system (the heat sink), which dumps the residual coolant energy from the turbine condenser to the environment. The service water is recirculated from a river, lake, ocean, or cooling tower. In the primary system (Fig. 31.21), dissolved boron is present to control nuclear criticality. Fixed-bed ion exchange units are used to maintain the water quality in both the primary and the secondary systems. In addition, the chemical and volume control system reduces boron concentration during the power cycle to compensate for fuel burnup. These operations are carried out continuously though bypass systems. A more complete... 

This approach has been not only used to directly estimate the ocean pH from 8 B of foraminifera but to estimate from the pn the past atmospheric CO2 concentrations (i.e. Pearson and Palmer 1999,2000 Pagani et al. 2005). An increase in atmospheric CO2 results in increased dissolved CO2 in ocean water, which in turn causes a reduction in oceanic pn- A note of caution was presented by Lemarchand et al. (2000) who suggested that boron isotope variations in foraminifera depend at least in part on variations in the supply of riverine boron to the ocean during the geologic past. And indeed the boron isotope composition of rivers can be extremely variable (Rose et al. 2000 Lemarchand et al. 2002). Joachimski et al. (2005) presented evidence... 

The boron isotope approach to pC02 estimation relies on the fact that a rise in the atmospheric CO2 concentration will increase pC02 of the surface ocean which in turn causes a reduction of its pH. By measuring the boron isotope composition of planktonic foraminifera Pahner et al. (1998) and Pearson and Palmer (2000) have reconstructed the pH-profile of Eocene sea water and estimated past atmospheric CO2 concentrations. However, Lemarchand et al. (2000) argued that 5 B records of planktonic foraminifera partly reflect changes in the marine boron isotope budget rather than changes in ocean pH. 

Spero HJ, Bijma J, Lea DW, Bemis BE (1997) Effect of seawater carbonate concentration on foraminiferal carbon and oxygen isotopes. Nature 390 497-500 Spivack AJ, Edmond JM (1986) Determination of boron isotope ratios by thermal ionization mass spectrometry of the dicesium metaborate cation. Anal Chem 58 31-35 Spivack AJ, Edmond JM (1987) Boron isotope exchange between seawater and the oceanic crust. Geochim Cosmochim Acta 51 1033-1043... 

The ratio of the boron isotopes and °B is known to depend on ambient pH in the boron incorporated in the carbonate shells of marine foraminifera (Sanyal et ai, 1996 Sanyal et al., 2001). The use of boron isotopes as an indicator for seawater paleo-pH has been extended to the calculation of past CO2 concentrations in ocean surface waters and in the atmosphere (Spivack, 1993 Sanyal et al., 1997 Pearson and Palmer, 1999, 2000 Sanyal and Bijma, 1999 Palmer and Pearson, 2003). Sources of uncertainty in these estimates include the fractionation of boron isotopes during incorporation in carbonate shells, effects of diagenesis, the assumptions needed to calculate CO2 concentrations from pH, and the influence of changing boron isotope ratios in ambient seawater (Lemarchand et al., 2000 Lemarchand et al., 2002). The latter problem is especially serious for estimates based on samples older than the 15 Myr residence time of boron in the oceans. 

The acid-hase pair with the second highest concentration and a pK near the pH of seawater is horic acid (Table 4.1). The carbonate system and boric acid turn out to be by far the most important contributors to the acid-base chemistiy of seawater, but they contrast greatly in their reactivity in the ocean carbon is involved in all metabohc processes and varies in concentration from place to place, whereas borate is conservative and maintains a constant ratio to salinity. The equih-brium reaction and total boron, Bj, equations are ... 

The alkalinity and DIC data were used to calculate the carbonate ion concentration and pH of the culture medium during the second half of the first experiment, and throughout the second experiment (Fig. 3). These calculations used the program C02SYS (Lewis Wallace 1998) with the carbonate dissociation constants of Roy et al. (1993), the calcite solubility of Mucci (1983), and the assumption that the boron/salinity ratio of the culture system water was equal to the seawater ratio. Because much of the culture system water in both years was Instant Ocean, it may not be correct to estimate the total borate concentration from the whole-ocean boron/salinity relationship. However, trends in the concentrations of carbonate system species during each year will be independent of the actual absolute total borate concentration. 

In ocean water, boron occurs in two dominant species, boric acid B(OH)j and borate B(OH). The relative concentration of these two species is pH dependent such that the boric acid B(OH)3 is dominant at pH < 9.0, whereas the tetrahedral complex of B(OH) dominates at pH >9.0 (Fig. 10.12 Hemming and Hanson 1992). The principal process that causes fractionation of boron isotopes in aqueous solutions is the following exchange reaction ... 

Last glacial boron isotope composition of planktonic foraminifers has been shown to be 2%o higher compared to the modern value of 23%o. What is the result for surface ocean pH during the last glacial What happened to the carbonate ion concentration and consequently to atmospheric pCO assuming the ECO to be the same as today (see chapter 9) ... 

If we compare the total amounts of trace elements present in solution in sea water with the annual levels of production (Table 40), it is clear that the total dissolution of the global annual production of most elements would have a negligible effect on their concentrations in the ocean. With the notable exception of the element lead, it would require the dissolution of over one hundred years production of every element to double its present concentration in sea water. For some elements like boron, fluorine, molybdenum and nickel, this level of enhancement would require the dissolution in the ocean of thousands of years of production at present levels. This is to say that any significant enhancement of the levels of these elements in ocean water as a result of human activity is impossible. 

Continuing in this vein, Hemming (this volume) considers more recent feedbacks between life and atmospheric changes that affect climate. He rrses boron isotopes, which serve as a proxy for ancient ocean pH. Because of interactions between the atmosphere and surface ocean, these isotopic data reveal natural variations in atmospheric CO2 concentrations. Understanding such natural co-variabihty in atmospheric composition and climate is essential if we are to document and predict the role of anthropogenic influences on present and future climates. 

Boron in seawater has a concentration of about 4.5ppm. It is supplied to the ocean by continental weathering and hydrothermal inputs, and has a residence... 

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