Hiske G Fink

A slump in the trench: Tracking the impact of the 2011 Tohoku-Oki earthquake

We present differential bathymetry and sediment core data from the Japan Trench, sampled after the 2011 Tohoku-Oki (offshore Japan) earthquake to document that prominent bathymetric and structural changes along the trench axis relate to a large (∼27.7 km 2 ) slump in the trench. Transient geochemical signals in the slump deposit and analysis of diffusive re-equilibration of disturbed SO 4 2– profiles over time constrain the triggering of the slump to the 2011 earthquake. We propose a causal link between earthquake slip to the trench and rotational slumping above a subducting horst structure. We conclude that the earthquake-triggered slump is a leading agent for accretion of trench sediments into the forearc and hypothesize that forward growth of the prism and seaward advance of the deformation front by more than 2 km can occur, episodically, during a single-event, large mega-thrust earthquake.

Mediterranean cold-water corals - an important regional carbonate factory?

This study presents aggradation rates supplemented for the first time by carbonate accumulation rates from Mediterranean cold‐water coral sites considering three different regional and geomorphological settings: (i) a cold‐water coral ridge (eastern Melilla coral province, Alboran Sea), (ii) a cold‐water coral rubble talus deposit at the base of a submarine cliff (Urania Bank, Strait of Sicily) and (iii) a cold‐water coral deposit rooted on a predefined topographic high overgrown by cold‐water corals (Santa Maria di Leuca coral province, Ionian Sea). The mean aggradation rates of the respective cold‐water coral deposits vary between 10 and 530 cm kyr−1 and the mean carbonate accumulation rates range between 8 and 396 g cm−2 kyr−1 with a maximum of 503 g cm−2 kyr−1 reached in the eastern Melilla coral province. Compared to other deep‐water depositional environments the Mediterranean cold‐water coral sites reveal significantly higher carbonate accumulation rates that were even in the range of the highest productive shallow‐water Mediterranean carbonate factories (e.g. Cladocora caespitosa coral reefs). Focusing exclusively on cold‐water coral occurrences, the carbonate accumulation rates of the Mediterranean cold‐water coral sites are in the lower range of those obtained for the prolific Norwegian coral occurrences, but exhibit much higher rates than the cold‐water coral mounds off Ireland. This study clearly indicates that cold‐water corals have the potential to act as important carbonate factories and regional carbonate sinks within the Mediterranean Sea. Moreover, the data highlight the potential of cold‐water corals to store carbonate with rates in the range of tropical shallow‐water reefs. In order to evaluate the contribution of the cold‐water coral carbonate factory to the regional or global carbonate/carbon cycle, an improved understanding of the temporal and spatial variability in aggradation and carbonate accumulation rates and areal estimates of the respective regions is needed.

Evidence for Mass Transport Deposits at the IODP JFAST-Site in the Japan Trench

Several studies indicate that the 2011 Tohoku-Oki earthquake (Mw 9.0) off the Pacific coast of Japan has induced slip to the trench and triggered landslides in the Japan Trench. In order to better understand these processes, detailed mapping and shallow-coring landslides at the trench as well as Integrated Ocean Drilling Program (IODP) deep drilling to recover the plate boundary decollement (Japan Trench Fast Earthquake Drilling Project, JFAST) have been conducted. In this study we report sediment core data from the rapid response R/V SONNE cruise (SO219A) to the Japan Trench, evidencing a Mass Transport Deposit (MTD) in the uppermost section later drilled at this JFAST-site during IODP Expedition 343. A 8.7 m long gravity core (GeoB16423-1) recovered from ∼7,000 m water depth reveals a 8 m sequence of semi-consolidated mud clast breccias embedded in a distorted chaotic sediment matrix. The MTD is covered by a thin veneer of 50 cm hemipelagic, bioturbated diatomaceous mud. This stratigraphic boundary can be clearly distinguished by using physical properties data from Multi Sensor Core Logging and from fall-cone penetrometer shear strength measurements. The geochemical analysis of the pore-water shows undisturbed linear profiles measured from the seafloor downcore across the stratigraphic contact between overlying younger background-sediment and MTD below. This indicates that the investigated section has not been affected by a recent sediment destabilization in the course of the giant Tohoku-Oki earthquake event. Instead, we report an older landslide which occurred between 700 and 10,000 years ago, implying that submarine mass movements are dominant processes along the Japan Trench. However, they occur on local sites and not during each megathrust earthquake.