MagNetZ With Usui Yoichi (2022/07/06) - Magnetic mineralogy of pelagic sediment in the North Pacific
Channel: MagNetZ
Date: 2022-07-06

Three (five) components of magnetic mineralogy of Cenozoic pelagic sediment in the North Pacific

The video is also available for download at: https://earthref.org/ERDA/2535/
and can be referenced with the doi: 10.7288/V4/ERDA/2535

Title: Three (five) components of magnetic mineralogy of Cenozoic pelagic sediment in the North Pacific
Author: Usui Yoichi from Kanazawa University, Japan

Detailed environmental magnetic variations have been reported from many marine sediments. However, relatively little attention has been paid to a commonality among sites, partly because hemipelagic sediments collect regional magnetic signatures from nearby land. Also, variations over tens of millions of years timescale have remained elusive. 
In this talk, I compare magnetic records in pelagic red clay from the North Pacific, where distant terrigenous sources dominate, to show first-order variations of magnetic components. There are abundant magnetofossils (magnetite from magnetic bacteria). Most of the examined sediments contain only one magnetofossil component. The magnetic and microscopic characteristics of the magnetofossil components are similar among different sites, suggesting similar deep-sea conditions. In contrast, the terrigenous (non-biogenic) fraction can be divided into two components, with the proportion of the higher coercivity component has increased since ~1 Ma. Even though Asian dust flux to the North Pacific has increased significantly since ~25 Ma, and though geochemical data from some sites have suggested that American dust was dominant before that time, a corresponding change is not resolved in terrigenous magnetic signature due to an overwhelming magnetofossil contributions. 
Occasionally there are additional magnetofossil components with higher and lower coercivities. The higher coercivity component represents bullet-shaped crystals, and the lower coercivity one is probably from non-chained crystals. It has been speculated that these may correspond to higher and lower nutrient conditions, respectively. Their spatial and temporal distributions should be investigated to test the speculation. 



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00:00 - Intro
00:56 - Presentation
23:46 - Questions
29:25 - Announcements