Evolution of marine sedimentation in the Bering Sea since the Pliocene

Abstract

Sediment of the Bering Sea, derived mainly from biogenic, glaciomarine, and, secondarily, riverine sources, refl ects the history of oceanographic changes within the basin and climatic changes on the adjacent continents. Integrated Ocean Drilling Program (IODP) Expedition 323 recovered cores that reveal the evolution of sedimentation in the Bering Sea over the past 5 m.y., a period that includes globally signifi cant events such as the early Pliocene warm period, the onset of extensive Northern Hemisphere glaciation, and the Pleistocene glacial-interglacial and millennial-scale climate cycles. To begin to understand the Bering Sea regional response to and role in these global climate change events, we examined the sedimentary constituents of Expedition 323 sites U1339, U1343, and U1344 on the Bering Slope, and U1340 and U1341 on Bowers Ridge. New particle size and petrographic analyses, combined with shipboard lithostratigraphic and physical property data, are used to characterize sediment types and texture and its distribution through space and time. The sediment comprises mainly two components, opaline diatom valves and siliciclastic grains (mainly clay and fi ne silt size). Approximately 40% of the variance in particle size can be explained by the abundance and preservation of diatom valves, a rough indicator of biogenic opal productivity. Particle size data indicate that productivity was generally higher during interglacials compared to glacials, and higher during the Pliocene warm period, decreasing as Northern Hemisphere glaciation intensifi ed ~3 m.y. ago. Although the abundance of diatoms in the sediment varied, diatom ooze and diatom mud are the dominant lithologies at Bowers Ridge, indicating that there was a persistent supply of diatoms to the sediment in the open Bering Sea during the past 5 m.y. This study provides a comprehensive view of sediment types and sedimentation processes; future work should be aimed at validating our interpretations of past changes in productivity and siliciclastic sedimentation mechanisms with multiple additional proxies.

Orbital-scale benthic foraminiferal oxygen isotope stratigraphy at the northern Bering Sea Slope Site U1343 (IODP Expedition 323) and its Pleistocene paleoceanographic significance

“…Grain size analysis on the sediments recovered during IODP Exp. 323 suggested that the clay-sized particles at the Bering Sea Slope were delivered mainly from melting sea-ice (Aiello and Ravelo, 2012). Aiello and Ravelo (2012) further argued that silt-and sand-sized siliciclastic grains, which are also the main sediment component at Site U1343, could have been delivered from resedimentation processes via iceberg rafting.…”

“…323 suggested that the clay-sized particles at the Bering Sea Slope were delivered mainly from melting sea-ice (Aiello and Ravelo, 2012). Aiello and Ravelo (2012) further argued that silt-and sand-sized siliciclastic grains, which are also the main sediment component at Site U1343, could have been delivered from resedimentation processes via iceberg rafting. Sedimentation rates at the Bering Sea Slope (Sites U1343, U1344, and U1345) are high compared to those at the Bowers Ridge (Sites U1340, U1341, and U1342), which was attributed to greater contribution of these silisiclastic components to the Bering Sea Slope (Takahashi et al, 2011).…”

“…Smaller mean grain size and higher NGR at Site U1343, compared to the Bowers Ridge Sites U1340, U1341, and U1342 ( Fig. 1), suggest a greater contribution of terrigenous clay within sediments at the Bering Sea Slope (Aiello and Ravelo, 2012). Grain size analysis on the sediments recovered during IODP Exp.…”

“…Takahashi et al, 2011). At Site U1343, the natural gamma radiation (NGR) largely reflects the grain size variability within a size fraction between 0.04 μm and 2.0 mm (Aiello and Ravelo, 2012). A general coincidence in the timing between the positive peaks in % biogenic opal (Kim et al, in press) and negative peaks of gamma ray attenuation (GRA) indicate that GRA partially reflects sediment characteristics from biogenics (negative peaks) to silisiclastics (positive peaks).…”

“…Sediments recovered at Site U1343 are classified mainly into two groups: (a) diatom-enriched mud and (b) pelagic mud (Aiello and Ravelo, 2012). Site U1343 lithology alternates between these two primary types of sediments, with only minor amounts of volcanic shards and authigenic carbonate.…”