Recent upward shift of the deep convection system in the Japan Sea, as inferred from the geochemical tracers tritium, oxygen, and nutrients

Gamo, Toshitaka; Momoshima, Noriyuki; Tolmachyov, Sergei

doi:10.1029/2001gl013367

Cited by 62 publications

(40 citation statements)

References 15 publications

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“…As shown in Fig. 18, the concentrations of PFOA were higher than those of PFOS, and a gradual decrease from the surface to the bottom was observed, similar to those of man-made materials in the Japan Sea such as tritium (Watanabe et al, 1991;Gamo et al, 2001;Postlethwaite et al, 2005) and chlorofluorocarbons (Tsunogai et al, 1993;Min and Warner, 2005). The deep convection or surface water sinking in the Japan Sea will transfer these PFASs to a deeper zone.…”

Section: Man-made Persistent Perfluoroalkyl Substancesmentioning

confidence: 81%

“…The tritium data in 1984 and 1998, together with the dissolved oxygen data described in Subsection 5.1, suggests that the thermohaline conveyor system of the Japan Sea was shifted sometime before 1977 from the previous mode (A) to the current mode (B) as shown in Fig. 12 (Gamo et al, 2001). Mode A, or the "total (overall) convection mode", is the normal abyssal circulation pattern in which the surface water is sufficiently cooled and sinks down to the bottom layer.…”

Section: Tritiummentioning

confidence: 96%

“…Mode A, or the "total (overall) convection mode", is the normal abyssal circulation pattern in which the surface water is sufficiently cooled and sinks down to the bottom layer. In contrast, Mode Gamo et al, 2001). The values in 1984 (Kaji et al, 1988) are decay-corrected to those in 1998.…”

Section: Tritiummentioning

confidence: 99%

“…Since the supply of tritium is limited to precipitation from the atmosphere to the ocean surface where tritium exists as tritiated water (HTO), the amount of tritium in subsurface and deep waters should reflect the magnitude of surface water sinking or convection to the deep layer. Tritium profiles in the Eastern Japan Basin and the Yamato Basin were measured in 1984 (Kaji et al, 1988) and 1998 (Gamo et al, 2001) during the KH-84-3 cruise and the KH-98-3 cruise, re- spectively. Figure 11 compares the tritium profiles in 1984 and 1998, with a statistical counting error (±σ ) of 0.01 Bq L −1 or less.…”

Section: Tritiummentioning

confidence: 99%

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The Sea of Japan and Its Unique Chemistry Revealed by Time-Series Observations over the Last 30 Years

Gamo¹,

Nakayama²,

Takahata³

et al. 2014

Monogr. Environ. Earth Planets

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Chemical tracers in seawater, as well as physical parameters such as temperature and salinity, have been measured to better characterize the dynamics of water convection and its spatiotemporal changes in the Sea of Japan (also called the Japan Sea), a semi-closed, hyperoxic marginal sea (maximum depth: ∼3,800 m) in the northwestern corner of the Pacific Ocean. Repeated conductivity, temperature, and depth (CTD) observations and measurements of dissolved oxygen, for more than 30 years, have confirmed that the bottom layer of the Japan Sea, with a thickness of ∼1 km below the boundary at a depth of ∼2,500 m, is characterized by vertical homogeneity with fluctuations of potential temperature and dissolved oxygen of <0.001• C and <0.5 µmol kg −1 , respectively. The timescale of the abyssal circulation in the Japan Sea has been estimated to be 100-300 years, using 14 C and other chemical tracers. Stable isotope analyses for dissolved He, O 2 and CH 4 have given us information on their unique geochemical cycles in the Japan Sea. Profiles of the short-lived radioisotope 222 Rn just above the sea bottom have brought new insights into the short-term lateral water movement with a timescale of several days in the Japan Sea bottom water. It is of special concern that the gradual deoxygenation and warming of the bottom water over the last 30 years have resulted in an ∼10% decrease in dissolved oxygen and ∼0.04• C increase in potential temperature, suggesting a change of the deep convection system in the Japan Sea. The temporal changes in the vertical profiles of tritium from 1984 to 1998 have suggested a shift of the abyssal circulation pattern from a "total (overall) convection mode" to a "shallow (partial) convection mode". It is likely that the global warming since the last century has hindered the formation of dense surface seawater and its ability to sink down to the bottom, isolating the bottom layer from the deep convection loop that is indispensable as the source of cold and oxygen-rich water. However, the decreasing trend of bottom dissolved oxygen between 1977 and 2010 was not monotonous; rather, it was interrupted by an occasional break in the winter of 2000-2001, when severely cold weather may have resulted in especially dense surface water to sink down to the bottom layer for its ventilation.

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Section: Man-made Persistent Perfluoroalkyl Substancesmentioning

confidence: 81%

Section: Tritiummentioning

confidence: 96%

Section: Tritiummentioning

confidence: 99%

Section: Tritiummentioning

confidence: 99%

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The Sea of Japan and Its Unique Chemistry Revealed by Time-Series Observations over the Last 30 Years

Gamo¹,

Nakayama²,

Takahata³

et al. 2014

Monogr. Environ. Earth Planets

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“…As inferred from extremely high organic matter inputs to the bottom layer, a 'micro reducing environment̓ may be formed in the bottom layer (Wolgast et al 1998), enabling an upward extension of denitrifying bacterial activity from the sediments to the bottom waters above. Recent increases in atmospheric nitrogen deposition flux to the EJS (Kim et al 2011), warming of the water column (Gamo et al 2001;Kim et al 2001Kim et al , 2004Min and Kim 2006), oxygen content decreases (Kim and Kim 1996;Chen et al 1999;Gamo 1999;Kang et al 2004), and high deposition rates of organic matter (Cha et al 2007;Tishchenko et al 2007;Lee et al 2008Lee et al , 2010Hyun et al 2010) might have created a favorable environment for denitrification in the bottom layer at the two basins in the EJS in recent years.…”

Section: Extended Benthic Denitrification To Bottom Waters Vs 'Aerobmentioning

confidence: 99%

Deep Nitrate Deficit Observed in the Highly Oxygenated East/Japan Sea and Its Possible Cause

Kim¹,

Min²,

Lee³

2012

Terr. Atmos. Ocean. Sci.

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We present evidence of denitrification on the continental slopes of the Ulleung Basin (UB) and the Eastern Japan Basin (EJB) near the Tatar Strait (TtS) in the East/Japan Sea (EJS), despite its high water column dissolved oxygen concentrations. Some nutrient concentration data deviate significantly from the fitted regression line of nitrate (N) vs. phosphate (P) in deep waters, indicating a loss of nitrate in the region. The EJS has a lower N/P ratio (ca. 12.4 below 300 dbar) than a traditional Redfield ratio (16). The N/P ratio and oxygen concentration are substantially lower at several locations whose depths are close to the sediment-water interface, near TtS (500 -1100 dbar) and in UB (1100 -2200 dbar). The decreased nitrate concentration is smaller than the expected nitrate level (a low N/P ratio of < 12.4), and a secondary nitrite peak near the bottom of these two regions: taken collectively, both indicate the presence of denitrification in the bottom layer. It is speculated that active re-mineralization and denitrification may occur simultaneously along the rich organic matter bottom layer on the slope environment. Denitrification rates are estimated at ~3 -33 μmol N m -2 d -1 . Current estimates do not support the previous idea of basin-wide denitrification in EJS, although the N/P ratio is low like in other hypoxic/anoxic seas. A better understanding of the denitrification process is necessary for predicting future changes of nitrogen cycle in the well-oxygenated EJS considering the decadal-scale physical and biogeochemical changes that have occurred.

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Significant anaerobic production of fluorescent dissolved organic matter in the deep East Sea (Sea of Japan)

Kim

2016

Geophysical Research Letters

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The distribution of fluorescent dissolved organic matter (FDOM) in the East Sea (Sea of Japan) was examined by excitation‐emission matrix spectroscopy with parallel factor analysis (PARAFAC). Humic‐like FDOM (FDOMH) increased with depth and was significantly correlated with Apparent Oxygen Utilization (AOU), indicating that FDOMH in the deep water is mainly produced by oxidation of organic matter. In addition, a surprisingly large excess of FDOMH relative to that expected from the observed AOU was found from 1000 m to the bottom (up to 3500 m). Based on the high‐resolution geographical distribution and characteristics of FDOM in the East Sea, we conclude that this excess likely originates from anaerobic FDOMH production in subsurface bottom sediments. This FDOMH flux accounts for 8–15% of the total FDOM production in the water column. Our results suggest that anaerobic activities in subsurface sediments are an important hidden source of FDOM in the ocean.

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Recent upward shift of the deep convection system in the Japan Sea, as inferred from the geochemical tracers tritium, oxygen, and nutrients

Cited by 62 publications

References 15 publications

The Sea of Japan and Its Unique Chemistry Revealed by Time-Series Observations over the Last 30 Years

The Sea of Japan and Its Unique Chemistry Revealed by Time-Series Observations over the Last 30 Years

Deep Nitrate Deficit Observed in the Highly Oxygenated East/Japan Sea and Its Possible Cause

Significant anaerobic production of fluorescent dissolved organic matter in the deep East Sea (Sea of Japan)

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