Disrupted Coherence Between Upwelling Strength and Redox Conditions Reflects Source Water Change in Santa Barbara Basin During the 20th Century

Varved sediments from the center of Santa Barbara Basin (SBB) off southern California are a valuable archive for high-resolution climate reconstruction. Using mass spectrometry imaging lipid biomarkers, this study examines interactions perennial upwelling strength and oxygen-driven redox conditions at sediment-water interface 1900 CE to 2009. In SBB, variations in recorded by isoprenoidal tetraethers planktonic archaea, while redox-sensitive C29 stanol/stenol ratio reflects oxygen content bottom water surficial sediment. The changing coherence these two proxies allows investigation interplay between upwelling, bioproductivity conditions, their dependence on SBB source composition during 20th century. Prior large-scale oceanographic regime shift observed North Pacific 1970s, both positively correlated: periods enhanced promoted mixing, resulting increased availability interface; conversely reduced favored development oxygen-depleted depth. wake basin-wide shift, led reduction southward flowing Current stronger influence poleward Undercurrent, which stratification supply warm, oxygen-poor tropical subsurface. As result, waters was predominantly regulated upwelling-induced productivity subsequent oxygen-consuming remineralization organic matter.