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Title: Paleoenvironmental Change Recorded in the Magnetic Properties of Marine Sediments Cored Off the Margin of Spain and Portugal During IODP Expedition 339
Integrated Ocean Drilling Program (IODP) Expedition 339 cored multiple sites along the Iberian Margin to investigate the paleoclimatic influence of discharge of warm and salty Mediterranean Outflow Water (MOW) into the Atlantic Ocean. As the MOW current flowed out of the Straits of Gibraltar and along the Iberian Peninsula, it deposited sediments, which have accumulated over the past 5 million years into thick sedimentary sections. The strength and position of the MOW current through time can be reconstructed using proxy data such as changes in sediment grain size and composition. In this study, we use magnetic susceptibility, anhysteretic remanent magnetization, and hysteresis properties of samples from drill cores collected at Sites U1386 and U1387 to estimate how magnetic grain size, magnetic concentration, and magnetic composition changes through time at these sites. Magnetic concentration highs correlate with Heinrich events and the lows correlate with Greenland interstadials. These peaks and troughs can be further correlated among the other Expedition 339 sites down to depths of about 100 meters below seafloor, spanning about the past 250 k.y., allowing comparison of paleocurrent strength and position along the Iberian Margin through time. As with the physical grain size, coarser magnetic grain sizes are associated with turbiditic intervals, which are deposited when MOW current speeds were high. Superparamagnetic grains, which have diameters less than about 30 nanometers, only have significant concentrations in the upper 30 m or so of the stratigraphic sections. Their abundance appears to be controlled mostly by reduction diagenesis, which acts progressively downhole eventually altering a significant proportion of iron oxide grains of all sizes into iron sulfides. This is evidenced by the downhole decrease in the bulk susceptibility, particularly in the upper 100 m or so of the stratigraphic sections.  more » « less
Award ID(s):
1426132
NSF-PAR ID:
10047415
Author(s) / Creator(s):
; ; ;
Date Published:
Journal Name:
Abstracts - Geological Society of America
Volume:
49
Issue:
6
ISSN:
0435-3986
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
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The sediments along this transect were originally spot cored more than 50 y ago during Deep Sea Drilling Project Leg 3 (December 1968–January 1969) to help verify the theories of seafloor spreading and plate tectonics. The SAT expeditions targeted six primary sites on 7, 15, 31, 49, and 61 Ma ocean crust that fill critical gaps in our sampling of intact in situ ocean crust with regard to crustal age, spreading rate, and sediment thickness. Drilling these sites was required to investigate the history, duration, and intensity of the low-temperature hydrothermal interactions between the aging ocean crust and the evolving South Atlantic Ocean. This knowledge will improve the quantification of past hydrothermal contributions to global biogeochemical cycles and help develop a predictive understanding of the impacts of variable hydrothermal processes and exchanges. 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During engineering Expeditions 390C and 395E (5 October–5 December 2020 and 6 April–6 June 2021, respectively), a single hole was cored through the sediment cover and into the uppermost rocks of the ocean crust with the advanced piston corer and extended core barrel systems at five of the six primary proposed SAT sites. Reentry systems with casing were then installed either into basement or within 10 m of basement at each of those five sites. Expedition 390 (7 April–7 June 2022) conducted operations at three of the SAT sites, recovering 700 m of core (77% recovery) over 30.3 days of on-site operations. Sediment coring, basement coring, and wireline logging were conducted at two sites on ~61 Ma crust (Sites U1556 and U1557), and sediment coring was completed at the 7 Ma Site U1559. 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