Thorium-Protactinium fate across the tropical Atlantic Ocean: what reveals the water column-sediment coupling

Twenty seawater profiles and twenty core-top 231-protactinium (231Pa) and 230-thorium (230Th) analyses were realised by Ng and colleagues (2020, see reference below) along five depth transects across the northern tropical Atlantic open ocean.  Among them, eighteen seawater-sediment pairs from nearby sites were compared. A thorough examination of this coupling associated to published data of 231Pa and 230Th in the North Atlantic Ocean, allow the authors to i) confirm the dominance of the 231Pa-export signal in the deep Atlantic associated with the southward advection of North Atlantic Deep Water (NADW) but also ii) observe contrasting local increases of sedimentary 231Pa/230Th above the production ratio, with higher values at intermediate depths (0.5–1.5 km) and in the eastern and mid-Atlantic sites. These last observations reflect either an additional input of 231Pa to the intermediate depths, or enhanced 231Pa scavenging at the eastern and mid-Atlantic sites, and/or the influence of boundary scavenging near the eastern margin.

Figure (modified from Ng, et al. 2020): Tropical Atlantic seawater 231Pa/230Th data and recently-deposited seafloor sediment 231Pa/230Th data. The map on the left shows the locations of seawater (square symbols) and sediment (circle symbols) data, and the red lines mark the boundary of the East-West depth section plotted on the right. The colour map in the depth section represents interpolated seawater 231Pa/230Th data, while the sediment 231Pa/230Th data is plotted overlain the seawater data as coloured circles. Seawater 231Pa/230Th is typically higher than the sediment 231Pa/230Th of a given site, reflecting the greater solubility of the 231Pa isotope. Sediment 231Pa/230Th values lower than the production ratio (0.093) indicate a net export of 231Pa, while sediment values higher than 0.093 reflect a net input of 231Pa, relative to 230Th. Sediment data may appear to be ‘below’ or ‘floating above’ the seafloor drawn in dark grey, because they are superimposed on a representative section across the Atlantic, rather than the overlying bathymetry measured at the actual sites.


Ng, H. C., Robinson, L. F., Rowland, G. H., Chen, S. S., & McManus, J. F. (2020). Coupled analysis of seawater and sedimentary 231Pa/230Th in the tropical Atlantic. Marine Chemistry, 227, 103894. DOI:

Latest highlights

Science Highlights

A new proxy for ocean iron bioavailability

The approach established and verified in this study, opens a new way for determining dissolved iron bioavailability in samples across the ocean.


Science Highlights

Scavenging differentiates the distribution of cadmium, nickel, zinc and copper in the North Pacific Ocean

Zheng and co-authors observed sectional distributions of cadmium, nickel, zinc, and copper in the North Pacific Ocean during three GEOTRACES related cruises…


Science Highlights

Surprising conservativity of trace metals along a costal embayment salinity gradient

Chen and co-workers analyzed an array of trace metals together with Rare Earth Elements in a salinity gradient in the Jinhae Bay, the largest semi-enclosed bay in South Korea…


Science Highlights

Measuring actinium-227 by mass spectrometry is feasible, sensitive and reliable!

Levier and co-authors have developed a new protocol measurement of the dissolved actinium in seawater.