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This dataset contains grain size records from three Integrated Ocean Drilling Program core sites (U1345, U1343, and U1339) in the Bering Sea. These records are used to determine the effectiveness of different grain size parameters as proxies for sediment transport, current strength, and primary productivity in the Bering Sea during a past warm interval (Marine Isotope Stage 11, 424-374 thousand years ago (ka)). Grain size is measured using a laser diffraction particle size analyzer (Malvern Mastersizer 3000), and is reported for bulk sediments, and for the terrigenous fraction only. The raw dataset provided by the Malvern software includes the volume % of grains in 109 bin sizes, as well as the 10th (Dx10), 50th (Dx50) and 90th (Dx90) percentiles. We also provide the volume distribution of grains in the following size fractions: clay (less than 2 micrometers (μm)); silt (2-63 μm); sand (63-2000 μm); gravel (greater than 2000 μm); ice-rafted debris (greater than 150 μm; greater than 250 μm), and sortable silt (10-63 μm). Additional grain size parameters, including mean size, sorting and skewness, are calculated in GRADISTAT.
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Examining ocean currents off West Antarctica through particle-size analyses of a sediment core
In this study, sediments from the Pliocene warm period (3-5 million years ago) from a sediment drift deposit in the Amundsen Sea in Antarctica (drillsite U1533) were treated and analyzed for particle size distribution and sortable silt percentage. These variables help explain how fast ocean currents were moving under warmer climate scenarios. The sediments from beneath the seafloor were treated using hydrogen peroxide to break down any organic matter, followed by boiling with hydrochloric acid to break down carbonate. To remove chemicals, the sediment samples were placed into a centrifuge with 50 mL of DI water for 30 minutes, decanted, then another 30 minutes with 50 mL of DI water. After the samples were treated, they were placed into the Malvern Mastersizer 2000 to measure particle size distributions by using a laser and the resulting scatter patterns of the sediment particles. The results were graphed with depth beneath the seafloor to show the differences in sortable silt percentage over time. The results showed that the sortable silt percentage was low around the onset of the warm period, concluding that the movement of ocean currents during this time period dropped. These results were not typical, as models had predicted that warm periods would have faster ocean currents, and opens up the possibility for future research.
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- Award ID(s):
- 2114839
- PAR ID:
- 10429196
- Date Published:
- Journal Name:
- 14th Annual GS-LSAMP/NNJ-B2B STEM Research Conference
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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The Eocene-Oligocene Transition (EOT) at ~34 Ma marked a climatic shift from greenhouse to icehouse conditions, towards long-lasting lower global temperatures and a continental ice sheet in the Antarctic. The relative importance of ocean gateways, pCO2, and ice growth as drivers of this transition are not fully understood. We report on sedimentological and inorganic geochemical results across the EOT at Ocean Drilling Program (ODP) Site 696 in the Weddell Sea, within the Antarctic limb of the Atlantic circulation. The geochemical composition of detrital, authigenic and biogenic marine sediment components, and sortable silt proxies demonstrate the impact of ice growth on high latitude water masses. Sortable silt grain size and Zr/Rb ratios attest to a period of vigorous circulation at ~36.2-35.8 Ma, coincident with a known warm interval in the Southern Ocean. Across the EOT, detrital provenance suggests that regional ice growth in the western Weddell Sea was stepwise, first expanding in the Antarctic Peninsula, followed by parts of West Antarctica. In conjunction with regional ice growth, high uranium enrichment factors (U EF) in sediments spanning the EOT interval indicate anoxic conditions in the sediment with evidence of carbonate dissolution. Following glacial expansion and sea-ice formation at ~33.6 Ma, a return to oxic conditions and carbonate preservation is observed with excess barium and phosphorous indicative of an increase in productivity, and potentially carbon export. Our results highlight the important connections between ice growth and the changing properties of high-latitude water masses at the EOT with impacts on the global ocean circulation.more » « less
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