Penetration of Bomb ¹⁴C Into the Deepest Ocean Trench

Abstract

The food source of hadal endemic fauna provides an insight into the carbon cycle in trenches and a biological adaptation to the impoverished and harsh trench environment. Here, we present the first Δ14C results of hadal amphipods from three trenches in the Pacific to define the organic matter source in these remote ecosystems. Amphipod muscle tissues contain a bomb 14C signature (Δ14C from 10 ± 2‰ to 65 ± 2‰), thereby revealing a dietary preference for labile and fresh organic matter derived from the surface water. Thus, the carbon cycle in the deepest ocean trench has a tight linkage with the surface ocean via the food chain. The bomb 14C dating result suggests that hadal amphipods have a low tissue turnover rate and an unexpectedly long lifetime (>10 years), at more than 4 times higher than the common longevity (~2 years) of amphipods in shallow waters.

Mercury isotopes identify near-surface marine mercury in deep-sea trench biota

“…Hg isotope ratios of snailfish and amphipods from 6,000 to 10,250-m depth in the Mariana and Kermadec hadal trenches were measured and compared with Hg isotope measurements of a wide range of fish species in the central Pacific that feed at depths of 10–1,000 m. Based on odd-MIF and even-MIF isotopic signatures we conclude that the majority of Hg in the tissues of animals living in the hadal zone originates from the atmosphere, is methylated in the epipelagic (upper 200 m) and mesopelagic (200–1,000-m) zones, and is then delivered to the hadal zone (6,000–11,000 m) by the carcasses of fish, and to a lesser extent by particles ( 33 ). A near-surface source of Hg to hadal biota is consistent with recent documentation of “bomb 14 C” ( 59 ), lead ( 60 ), and persistent organic pollutants ( 61 ) in hadal biota. The importance of carrion to trench foodwebs is consistent with observations of seafloor communities of fish and amphipods that depend upon carrion for nutrition in other deep-sea regions (e.g., refs.…”

Methylmercury produced in upper oceans accumulates in deep Mariana Trench fauna

“…2) 6,7 . A study on amphipods from the Mariana Trench and two other Pacific trenches revealed that the bomb 14 C signals of the surface ocean could rapidly penetrate into the deepest ocean via fast sinking of surface POM 56 . It is thus likely that, similar to IHg(II), the MMHg produced in the surface and intermediate waters above the trenches transfers to the deep ocean through sinking of surface POM as well.…”

Bomb 137Cs in modern honey reveals a regional soil control on pollutant cycling by plants

“…In 1963, the Nuclear Test Ban Treaty effectively limited atmospheric testing with the exception of a few dozen smaller yield detonations that occurred primarily in China and Africa in the 1960s and 1970s 1 . The presence of radioactive pollution from nuclear testing is globally ubiquitous, and detectable on every continent and even in deep ocean trenches 4 . Earth scientists widely apply the “bomb spike” radionuclides as a global chronological marker based on the assumption of strong radionuclide associations with minerals, and there are thousands of published studies using weapons fallout to trace soil transport and for dating sediments deposited in the 1960s 5 , 6 .…”