Oceanic profiles of dissolved silver: precise measurements in the basins of western North Pacific, Sea of Okhotsk, and the Japan Sea

doi:10.1016/S0304-4203(01)00035-4

Marine Chemistry

Volume 75, Issues 1–2, July 2001, Pages 151-163

https://doi.org/10.1016/S0304-4203(01)00035-4 Get rights and content

Abstract

We present here the detailed vertical profiles of dissolved (<0.04 μm) Ag in the three different oceanic basins in the western margin of the North Pacific. Those profiles confirmed that Ag is strongly involved in the biogeochemical cycling of biological uptake in the surface water, particulate sinking, and regeneration in the deep sea. The vertical profiles of Ag best resemble those of dissolved Si, but in detail there are differences between the two. In the western North Pacific, dissolved Ag reaches a maximum at 2500–3000 m, which is deeper than that of dissolved Si (∼2000 m). This implies that Ag is regenerated more slowly than Si. The greater inter-oceanic variation of Ag over Si in the deep waters between the North Atlantic and North Pacific is consistent with this interpretation. The other two profiles from the Sea of Okhotsk and the Japan Sea fit well in this biogeochemical and oceanographic trend.

Our dissolved Ag concentrations (4.2–8.0 pmol/kg) in the surface waters are significantly higher than those reported previously for other locations, and it appears that the variability of Ag in the surface waters is greater than an order of magnitude. Although many factors are involved in controlling the Ag concentration in the surface waters, removal by biological uptake appears to be particularly important. Although there may be some indication of anthropogenic sources in the surface waters, it seems to be local, and the large-scale contamination of Ag in the ocean is not seen in our data.

Introduction

Very few reliable measurements of Ag in seawater have been reported to date. The purpose of this paper is (1) to describe high-precision measurements of dissolved Ag in its water profiles of the Northwest Pacific, Sea of Okhotsk, and the Japan Sea, and (2) to elucidate the factors controlling the oceanic distributions. Murozumi (1981) first reported five data obtained from various depths in the mid South Pacific, based on isotope dilution thermal ionization mass spectrometry (ID-TIMS). The Ag concentration showed a systematic increase from <1 pmol/kg at the surface to ∼30 pmol/kg at 3000-m depth. Martin et al. (1983) confirmed the vertical profile showing an increase with depth in the eastern North Pacific using an atomic absorption technique, and suggested the involvement of Ag in the biogeochemical cycling much like Cu. Nevertheless, available data from Pacific deep waters below 1000 m to date are only six from three different locations, and therefore it is difficult to look into the vertical feature in detail.

More recently, Flegal et al. (1995) have measured four vertical profiles in the Atlantic during the IOC Baseline Study. They found the Ag concentrations in the deep waters are significantly lower that those in the Pacific, and postulated that Ag best resembles dissolved Si in the oceanic distribution. However, there are obvious exceptions in some coastal and oceanic margins where external inputs of Ag are significant. Anthropogenic sources have substantially increased dissolved Ag concentrations in the coastal waters of San Francisco Bay (Smith and Flegal, 1993) and the Southern California Bight (Sanudo-Wilhelmy and Flegal, 1992). Elevated Ag concentrations due to external inputs are also observed in the northern North Atlantic (Rivera-Duarte et al., 1999), although the relative importance of anthropogenic and natural sources is not well constrained there.

Obviously, further investigations are needed to better understand the global biogeochemical cycling of silver and the role and degree of anthropogenic perturbations in the ocean. We had an opportunity to collect water samples for Ag measurements in the western Pacific and its adjacent marginal basins during the R.V. Hakuho-Maru cruise in 1998. The results and their implications are described in this paper.

Section snippets

Methods

Fig. 1 shows the stations occupied by R. V. Hakuho-Maru during the “Canis Minor Expedition” July to August, 1998 where the water profiles of Ag were measured. The station CM-6 is located in the deepest part (>3000 m) of Kuril Basin of the Sea of Okhotsk, whereas CM-18 is located in the eastern margin of the Japan Sea Basin. The station CM-22 is located about 15 miles east of the Japan Trench axis. Our water collections were made by 12-l acid-precleaned Niskin bottles (lever action type) mounted

Hydrography

The station CM-22 in the western North Pacific is located in the Oyashio Current regime at ∼150 miles east from the Japanese coast. The potential temperature–salinity diagram is shown in Fig. 2. The North Pacific Deep Water (NPDW) occupies below ∼1200 m showing the linear trend of mixing in the diagram, and the North Pacific Intermediate Water characterized by the salinity minimum penetrating at around 450 m. There is a broad oxygen minimum centered at 1150 m typical for the western North

Data comparison for Pacific waters

Fig. 4a shows the vertical profiles of Ag and Si at CM-22 together with those reported previously in the Pacific. When compared to the Ag profile in the mid South Pacific (20°S, 160°W) by Murozumi (1981), our western North Pacific data are about 30% higher for the deep water. This difference can be attributed to the difference in location, since the North Pacific Deep Water contains more metabolized chemical constituents such as nitrate and silicate than the South Pacific deep water. This can

Acknowledgements

We would like to thank Captain H. Tanaka, the officers and crew of the R.V. Hakuho-Maru for their kind help in the sampling. We are also grateful to three anonymous reviewers for providing useful and constructive comments on the manuscript. This work was partially supported from the Ministry of Education, Science, Sports and Culture, Japan under the Grant-in-Aid No. 07041097 to the University of Tokyo (P.I., Y. Nozaki).

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Oceanic profiles of dissolved silver: precise measurements in the basins of western North Pacific, Sea of Okhotsk, and the Japan Sea

Abstract

Introduction

Section snippets

Methods

Hydrography

Data comparison for Pacific waters

Acknowledgements

Earth Planet. Sci. Lett.

Earth Planet. Sci. Lett.

Mar. Chem.

Mar. Chem.

Geochim. Cosmochim. Acta

Mar. Pollut. Bull.

Geochim. Cosmochim. Acta

Deep-Sea Res.

Earth Planet. Sci. Lett.

Geochim. Cosmochim. Acta

Determination of indium in natural waters by flow injection inductively coupled plasma mass spectrometry

Proc. Indian Acad. Sci. (Earth Planet. Sci.)

Atmospheric trace elements at Enewetak Atoll: 2. Transport to the ocean by wet and dry deposition

J. Geophys. Res.