USING FORAMINIFERA IN STEMSEAS SITE 1 SEDIMENTS TO UNDERSTAND THE RECENT PALEOCEANOGRAPHIC AND PALEOCLIMATIC HISTORY OF TANNER BASIN, CALIFORNIA BORDERLAND

In May of 2016, the STEMSEAS Educational Transit cruise OC1605-tranA collected the STEMSEAS Site 1 core from the Tanner Basin in the California Borderland. This research serves as the first formal survey of the foraminifera preserved within that core. The purpose of this research is to use planktic and benthic foraminifera preserved within that core to understand the recent depositional and paleoenvironmental conditions at Site 1, and to place that information into a regional paleoceanographic and paleoclimatic context. In pursuing this purpose, this research aims to answer three questions: 1) Can biostratigraphic markers in the planktic foraminiferal assemblages in STEMSEAS Site 1 core be used to test the hypothesis that a shift in elemental ratio concentrations at 120 cmbsf marks the Pleistocene/Holocene boundary? 2) Is there evidence of turbidity flow deposition at STEMSEAS Site 1? 3) Can the foraminiferal assemblages within STEMSEAS Site 1 core be used to study paleoenvironmental changes in the California Borderland through time? Thirty-four sediment samples of the >63 mm size fraction from the core were analyzed, and the data from those samples were compared with lithologic and elemental data collected by the STEMSEAS cruise shipboard party, and with published regional data. Additionally, radiocarbon dates were obtained to develop an age model for the core, which allowed cored data to be interpreted in a temporal context. In answering the proposed questions, the study found that: 1) The shift in elemental data at 120 cmbsf occurs very close to the Pleistocene/Holocene boundary (~11.7 ka), and the Pleistocene/Holocene transition represents a period of low dissolved oxygen supply within the Tanner Basin and low surface productivity. 2) A small percentage of benthic foraminifera present at Site 1 were displaced to Site 1 from a shallower depth, suggesting that turbidity flows did impact sedimentation at this location, but this was not the dominant sediment transport process. 3) The core records a paleoenvironmental history of semi-regular millennial scale variation in sea surface temperature, upwelling strength, and nutrient influx that may have been driven by an increasing frequency and strength of El Niño/Southern Oscillation events during the past 12 kyr.