[M-IS16] Paleoclimatology and paleoceanography

[MIS16-P10] Paleoceanographic changes in the western part of the Arctic Sea based on ostracods

*Katsura Yamada¹, Kosuke Yamaguchi¹, Masao Uchida², Takuya Itaki³, Kanako Mantoku² (1.Department of Geology, Faculty of Science, 2.National Institute for Environmental Studies, 3.National Institute of Advanced Industrial Science and Technology)

Keywords:Holocene, Paleoceanography, ostracod

Abrupt climate changes for a few thousand years are identified between Late Pleistocene and Holocene. Some of them are found in the Arctic Sea and northwestern Atlantic Ocean, suggesting that importance to understand paleoceanographic shifts accurately in the Arctic Ocean. However, oceanographic changes during the Holocene are ambiguous yet there. Thus, our aim is to clarify the Holocene oceanographic shifts in the area shallower than 200 m water depth in the western part of the Arctic Ocean. The study area is influenced by waters from the Pacific, Atlantic Oceans and river input. We used two cores; One was taken from the bottom at a water depth of 65 m in the Mackenzie trough located in river mouth of the Mackenzie river. Another was taken from the bottom in the northern part of the Chukchi shelf at a water depth of 197 m. This water depth is close to the depth bounding waters from the Atlantic and Pacific Oceans. Fossil ostracod assemblages and chemical compositions of the ostracod shells are investigated taken from the core sediments. Shallow marine ostracod taxa were dominated in the Mackenzie trough, and it is considered that the assemblage shifts related to water salinity changes. Conversely, samples from the Chukchi Sea contained ostracod taxa inhabiting in the Pacific and Atlantic Ocean waters. Mg/Ca of ostracod shells were measured by using ICP-AES. First, past water temperatures by using regression lines between Mg/Ca of the genus Krithe and water temperature in the previous study was calculated. Then, past water temperatures were reconstructed by relationships between Mg/Ca of Semicytherura complanate and the calculated water temperatures in both areas. The bottom water temperatures in the Chukchi shelf showed relative high values during 7000 and 2000 cal year BP. Dominance of ostracod taxa inhabiting in the Atlantic Ocean waters was identified in the two periods inferring intensification of the Atlantic Ocean water influence. Bottom water temperatures in the Mackenzie trough showed high value between 5500-4900 cal year BP and was stable after 4900 cal year BP. Salinity generally had increased from 7700 cal year BP to the present based on ostracod assemblage changes in the Mackenzie trough. Further, relative high salinity was recognized in 2600, 600, and 200 cal year BP. The long-term increase and temporal high values in salinity coincide with the timing of ice sheet expansions since the 5000 cal year BP in the Northern Hemisphere, implying that the salinity was affected by the glacier expansion in the trough.