Diatoms and Opal Production

Increased siliceous productivity during glacial Terminations (Ts) for the past 540 kyr off NW Africa was explained by the strong deglacial weakening of silica-poor North Atlantic intermediate water reaching the mid-latitude NE Atlantic (Meckler et al., 2013). This weakening led to the increase of the silica supply to Mauritanian surface waters via mixing with underlying silica-rich deep water. New XRF data between 770 and 540 ka (MIS 19 th MIS 14) at Site ODP 658 suggest that the siliceous maxima during Ts did not occur before 540 ka.

We intend to test Meckler’s hypothesis between 770 and 540 ka. IN addition to recently gained XRF data at ODO Site 658, we propose to measure micropaleontological, sedimentological, mineralogical, and geochemical proxies. In doing so, we will present a high-resolution reconstruction of glacial-interglacial variability and glacial T dynamics between MIS 19 and MIS 14 and will able to test the possible impact of millennial-scale variations in the North Atlantic (Hodell et al., 2008) on the siliceous productivity at mid-Atlantic latitudes (Romero et al., 2008). This research will also contribute to the preparation the IODP expedition off NW Africa (proposal 973), as currently proposed for the IODP period 2013-2023.

Hypothesis

To test the role played the advection of silicate into the Mauritanian upwelling system through subpolar water masses compared with silicate input via winds and/or rivers.

Main Scientific Questions

1. Quantification of siliceous bioproductivity and opal fluxes off NW Africa as related to the hydroclimatic forcing of upwelling intensity off NW Africa during the Plio-Pleistocene.
2. Impact of variations of land precipitation and nutrient input on terrestrial runoff: assessing links between global monsoon winds circulation, chemical weathering and transport into ocean waters.
3. Interaction between bioproductivity and hydrological changes during warm stadials: Effect of strengthening of global monsoon, increase of Antarctic sea ice cover and NHG.
4. Role of advection of silicate into the Mauritanian upwelling system through subpolar water masses compared with silicate input via winds and/or rivers.

Working Area

Off Mauritania, North-western Africa

The focus of this research is ODP Site 658 (20.7492 N, 18.58W; water depth: 2,274m; Tiedemann et al., 1994). The sediment sequence at this Site has a hiatus extending between ca. 1.7 and 0.75 Ma. After finishing the analysis of the 540-770 kyr interval, we will test the same hypothesis for older times (1.7 – 2.5 Ma). In a second stage, we might study ODP Site 659 (18.077N, 21.026W; water depth: 3,082m), which provides a continuous record for the past 5 Ma.

References:

Hodell, D. A., Channell, J.E.T., Curtis, J.H., Romero, O.E., Röhl, U. (2008). Onset of “Hudson Strait” Heinrich events in the eastern North Atlantic at the end of the middle Pleistocene transition (∼640 ka)? Paleoceanography 23(4).

Meckler, A. N., Sigman, D. M. , Gibson, K. A. , François, R., Martínez-García, A. ,Jaccard, S. L. , Röhl, U., Peterson, L. C., Tiedemann, R., Haug, G. H. (2013). Deglacial pulses of deep-ocean silicate into the subtropical North Atlantic Ocean. Nature495(7442): 495-498.

Romero, O. E., Kim, J.-H., and Donner, B. (2008). Submillennial-to-millennial variability of diatom production off Mauritania, NW Africa, during the last glacial cycle. Paleoceanography 23(3).

Tiedemann et al., 1994, Astronomic timescale for the Pliocene Atlantic d18O and dust flux records of Ocean Drilling Program site 659. Paleoceanography 9(4), 619-638, https://doi.org/10.1029/94PA00208