دانلود رایگان مقاله شار در حال تکامل از گرد و غبار آسیایی در اقیانوس آرام شمالی

abstract

The aeolian deposits in the North Pacific Ocean (NPO) serve as important archives for the surface processes in the arid Asian interior. Aeolian flux, which is usually based on the ‘operationally defined aeolian dust’ (ODED) extracted from the pelagic sediments, is a widely used paleo-proxy that reflects aridity of the source regions. However, such reconstruction of aeolian flux is subject to large uncertainty associated with the age model due to the low sedimentation rate and lack of calcareous nannofossil of the pelagic sediments. Precipitation of authigenic minerals and contribution of volcanic ash also complicate interpretation of the reconstructed ODED flux. This work extracts ODED from the sediments recovered at Ocean Drilling Program (ODP) site 1208 on the Shatsky Rise in NPO. The high sedimentation rate at ODP site 1208 enables a high-resolution age model. The resulting ODED flux, which shows a progressive increasing trend over the past 25 Ma, is very different from the previous reconstructions. The study indicates that authigenic phillipsite contribute a significant portion to the sediment of 25–18 Ma, but the relative contribution of Asian dust to the ODED is roughly constant (60–80%) over the past 18 Ma. Thus, the progressive increasing trend of ODED flux at the ODP site 1208 is not contributed by authigenic phillipsite and volcanic ash but reflect the increasing flux of Asian dust. We propose that the increasing flux of Asian dust in NPO reflects the progressive aridification of Asian interior in response to global cooling and/or regional mountain building.

5. Conclusion

The expanded sedimentation and the well-constrained age model of the ODP 1208 core provide a rare opportunity to explore the flux of Asian dust in North Pacific Ocean. Progressive increasing flux of the ODED has been recorded since 25 Ma. Evidences from trace element and radiogenic Nd and Sr isotopes suggest that the increasing ODED flux is caused by increasing flux of Asian dust rather than the increasing contribution from volcanic ash and authigenic mineral. The increasing flux of Asian dust since 25 Ma reflect a progressive aridification of Asian interior that might be linked to global cooling or regional mountain building