Disentangling what controls the cadmium distribution in the Pacific Ocean

Sieber and his colleagues (2023, see reference below) established the distribution of dissolved cadmium (Cd) concentrations and isotopes at 23 stations (represented as δ114Cd) along the GEOTRACES GP15 section, a meridional transect along 152°W from Alaska to Tahiti.

Their data reveal an important disparity between northern Cd-rich high-nutrient low-chlorophyll waters and Cd-depleted waters of the subtropical and equatorial Pacific. In the open ocean, a biogeochemical model simulates the data in Cd-depleted surface waters, with the lowest Cd concentrations influenced by atmospheric inputs of isotopically light Cd. Below the surface (and surprisingly even in the North Pacific Ocean), Cd parameter distributions are essentially controlled by Southern Ocean processes, water mass mixing and regeneration. Indeed, Cd-depleted Antarctic Intermediate Water has a far-reaching effect on North Pacific intermediate waters as far as 47°N, contrasting with northern-sourced Cd signatures in North Pacific Intermediate Water. Last but not least, this study reveals that a correlation between the North Pacific phosphate maximum and a negative Cd* signal at depth in the North Pacific Ocean reflects a regeneration signal of Cd and PO4 at a slightly lower Cd:P ratio than the deep ocean ratio (0.35 mmol mol−1). This finding contradicts the hypothesis that this negative Cd* signal is due to in situ removal processes in low-oxygen waters.

Figure 1. The cruise track of the US GEOTRACES GP15 Pacific Meridional Transect from Alaska (St 1) to Tahiti (St 39), showing relevant surface currents.
Figure 2. Distribution of Cd* along GP15, overlain with oxygen contours (top) and phosphate contours (bottom). Note different depth scales. Cd* represents the deviation in samples from deep ocean Cd/P ratio, and is defined here as Cd* = [Cd] – ([PO4] x 0.35).
Figure 3. Dissolved Cd/phosphate relationship along GP15. Solid black lines represent slopes of data from this study (shallow slope = surface data, steeper slope = deep data). The dashed line represents a Cd* of 0 (global deep Cd/P relationship), where Cd* represents the deviation in samples from the deep ocean Cd/P ratio, and is defined as Cd* = [Cd] – ([PO4] x 0.35).

Reference:

Sieber, M., Lanning, N. T., Bunnell, Z. B., Bian, X., Yang, S., Marsay, C. M., Landing, W. M., Buck, C. S., Fitzsimmons, J. N., John, S. G., & Conway, T. M. (2023). Biological, Physical, and Atmospheric Controls on the Distribution of Cadmium and Its Isotopes in the Pacific Ocean. Global Biogeochemical Cycles, 37(2). Access the paper:10.1029/2022gb007441

Latest highlights

Science Highlights

Extremely high radioactive levels in the manganese nodules

Volz and co-authors demonstrate that radioisotopes in the manganese nodules mostly exceed exempt activity levels…

22.05.2023

Science Highlights

The North Pacific Ocean, a key actor for the zinc oceanic cycle

Sieber and his colleagues lift the veil on some of the mechanisms that control the behavior of zinc in the Pacific Ocean, and more globally.

17.05.2023

Science Highlights

Solid-solution distribution of the cosmogenic beryllium-7 in the water column

This work questions the validity and limits of the hypothesis that particulate beryllium-7 can be neglected in the oceanographic applications of this tracer.

12.05.2023

Science Highlights

Decoupling of barium and silicon at the Congo river-dominated Southeast Atlantic Margin: combined Barium and silicon isotope evidence

Zhang and co-authors conducted a comprehensive study to investigate the biogeochemical cycles of barium and silicon and their relationship…

09.05.2023

Rechercher