U-Th chronology and paleoceanographic record in a Fe-Mn crust from the NE Atlantic over the last 700 ka

Details U-Th chronology and paleoceanographic record in a Fe-Mn crust from the NE Atlantic over the last 700 ka U-Th chronology and paleoceanographic record in a Fe-Mn crust from the NE Atlantic over the last 700 ka

Oct 2005

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2005gecoa..69.4845c&link_type=abstract

Geochimica et Cosmochimica Acta, Volume 69, Issue 20, p. 4845-4854.

Physics

Scientific paper

Hydrogenetic ferromanganese crusts (Fe-Mn crusts) provide a secular record of the variations of seawater composition responding to changes in ocean circulation and erosion processes. In this respect, the acquisition of an absolute and reliable chronology in Fe-Mn crusts is a prerequisite. Here we combine four different and complementary chronometers (10Be, 230Thex, 230Thex/232Th, 234U/238U) in a Fe-Mn crust dredged at ˜2000 m depth in the east Atlantic to first establish a reliable chronology over the Quaternary period. Then, we use EDS chemical analysis to look for correlation between major element chemistry and climate changes. (230Thex), (230Thex/232Th), and Be data give very consistent growth rates. In particular, the good match between (230Thex) and (230Thex/232Th) data indicates that at the location of crust 121DK, 230Th and 232Th fluxes in the water column change simultaneously and suggests that the normalization of 230Thex to 232Th makes (230Thex/232Th) a better chronometer. Our best-fit model suggests that crust 121DK experienced changes in growth rates at ˜122 and 312 ka and a growth with a constant 230Th initial flux. This chronology returns an age of 680 ka for the uppermost 1.5 mm. The (234U/238U) depth profile, however, was clearly affected by diffusion of 234U in the porous crust and can therefore not be used to derive a reliable chronology. One part of the crust seems isolated from pore water diffusion and can be physically recognized as a zone of very small porosity. On the basis of the (230Thex/232Th) chronology, major element chemistry is shown to be linked to climate change. Mn/Fe variations compare well with those in a Fe-Mn crust from the Pacific, showing systematic maxima during glacial stages 2 and 4. High Mn/Fe are tentatively interpreted to reflect expansion of the oxygen minimum zone during glacial periods, resulting from higher bioproductivity. In addition we note that the surface (230Th/232Th) activity ratio of crust 121DK is entirely consistent with advection of deep water from the western toward the eastern Atlantic basin.

Affiliated with

Also associated with

No associations

Rating

U-Th chronology and paleoceanographic record in a Fe-Mn crust from the NE Atlantic over the last 700 ka does not yet have a rating. At this time, there are no reviews or comments for this scientific paper.

If you have personal experience with U-Th chronology and paleoceanographic record in a Fe-Mn crust from the NE Atlantic over the last 700 ka, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and U-Th chronology and paleoceanographic record in a Fe-Mn crust from the NE Atlantic over the last 700 ka will most certainly appreciate the feedback.

Rate now

Comments { 0 }

Profile ID: LFWR-SCP-O-1625361